design new load shedding scheme considering …

DESIGN NEW LOAD SHEDDING SCHEME

CONSIDERING POSSIBLE ISLANDING OPERATIONS

IN SRI LANKAN NETWORK

H.P.G.R.N.Chamikara

09/8653

Degree of Master of Science

Department of Electrical Engineering

University of Moratuwa

Sri Lanka

September 2012

DESIGN NEW LOAD SHEDDING SCHEME

CONSIDERING POSSIBLE ISLANDING OPERATIONS

IN SRI LANKAN NETWORK

Henpita Polwatthe Gamarallage Nadun Chamikara

09/8653

Dissertation submitted in partial fulfillment of the requirements for the

Degree Master of Science in Electrical Engineering

Supervised by: Dr.K.T.M.Udayanga Hemapala

Department of Electrical Engineering

University of Moratuwa

Sri Lanka

September 2012

i

DECLARATION

“I declare that this is my own work and this dissertation does not incorporate without

acknowledgement any material previously submitted for a Degree or Diploma in any other

University or institute of higher learning and to the best of my knowledge and belief it does

not contain any material previously published or written by another person except where

the acknowledgement is made in the text.

Also, I hereby grant to University of Moratuwa the non-exclusive right to reproduce and

distribute my dissertation, in whole or in part in print, electronic or other medium. I retain

the right to use this content in whole or part in future works (such as articles or books)”.

……………………….

Signature of the candidate Date:

(H.P.G.R.N.Chamikara)

The above candidate has carried out research for the Masters Dissertation under my

supervision.

…………………………….

Signature of the supervisor Date:

(Dr. K.T.M. Udayanga Hemapala)

ii

ABSTRACT

Under frequency load shedding has been widely used to restore the power system frequency

following a severe generation demand unbalance due to a disturbance. If system frequency is not

counteracted properly system will be led to major blackouts. This frequency decline may be

corrected by shedding certain amount of load so that system is back to stable state. This dissertation

discusses on designing of new under frequency load shedding scheme align with the development

of Sri Lankan power system. Further, due to present network configuration after certain power

System failures some part of the system isolates from the main system and operates in islanding

mode. This islanding operation fails at all the times due to unbalance of the generation and load.

This dissertation also discusses in what way to overcome above situation by rearranging 33 kV

Load Shedding Feeders in the Sri Lankan network.

Whole Sri Lankan power system has been modeled using the PSS®E (Power System Simulator for

Engineers) software. PSS®E dynamic model was validated considering an actual generator tripping

occurred in the system. The Existing Load Shedding scheme was simulated using this model and

identified its drawbacks. Proposed a new Load Shedding scheme and discussed the system

improvements with simulations. The observations and results obtained from the simulations

comprise frequency plots before and after applying the proposed new load shedding scheme.

Further, identified possible islanding operations and analyzed the stability of them with proposed

load shedding scheme. Finally rearrange the 33 kV load shedding feeders in the Sri Lankan

network to facilitate islanding operation by analyzing the stability of the islands using simulation.

This new load shedding schemes with rearranged 33 kV load shedding feeders will improve the

Power System reliability and have a definite positive effect on customers which in turn improve the

wellbeing of the people and economy of the country.

Key words: Load Shedding, Islanding Operations, Simulations, Scheme, Feeders.

iii

ACKNOWLEDGEMENT

First, I pay my sincere gratitude to Dr. K.T.M. Udayanga Hemapala who encouraged and

guided me to conduct this investigation and on preparation of final dissertation.

I extend my sincere gratitude to Prof. J.P. Karunadasa, Head of the Department of

Electrical Engineering and all the lectures and visiting lectures of the Department of

Electrical Engineering for the support extended during the study period.

I would like to thank Mr. N.S.Wettasinghe, Chief Engineer, Protection Development

Branch, Ceylon Electricity Board who gave me the initiative to do the Islanding Operation

study for the Sri Lankan Network.

I also thank to Eng. Eranga Kudahewa who gave me extreme support and valuable

instructions during the simulations and preparation of final dissertation.

I would like to take this opportunity to extend my sincere thanks to Mr.D.D.K.

Karunarathne, Deputy General Manager (TD & E), Mr.T.D.Handagama, Deputy General

Manager (System Control), Mr.D.S.R.Alahakoon, Chief Engineer (System Operations),

Mr. J.Nanthakumar Chief Engineer (Operation Planning), Mr. G.R.H.U.Somapriya,

Electrical Engineer (Protection Development Branch), Mr. R.G. Jayendra, Electrical

Engineer (AGSAREP Project), Mr. L.A.A.N.Perera, Electrical Engineer (Transmission

O&Ms Branch – Colombo Region) and all the Office Staff of Protection Development

Branch of Ceylon Electricity Board who gave their co-operation to conduct my

investigation work successfully.

It is a great pleasure to remember the kind co-operation extended by the colleagues in the

post graduate program, friends, my mother, father, sister Chathurika Ruchirani, brother-in

law Sameera Manusanka and specially my wife Nirmani Rajapakshe who helped me to

continue the studies from start to end.

iv

TABLE OF CONTENTS

Declaration of the candidate & Supervisor i

Abstract ii

Acknowledgements iii

Table of content iv

List of Figures vi

List of Tables vii

List of Appendices viii

1. Introduction 1

1.1 Background 1

1.2 Importance of the Load Shedding Scheme 1

1.3 Identification of the Problem 2

1.4 Motivation 3

1.5 Objective of the Study 3

1.6 Methodology 4

2. Existing Load Shedding Scheme 5

2.1 Load Shedding Scheme 5

2.2 Existing Load Shedding Scheme 7

2.3 System Response to the System Disturbances 8

2.3.1 Tripping of Norochcholai coal Power Plant 8

2.3.2 Tripping of Kerawalapitiya Power Plant 8

2.4 Analyze of Existing Load Shedding Scheme 9

3. Power System Simulation 10

3.1 The Power System Simulator, PSS®E 10

3.2 Planning Criteria 10

3.2.1 Voltage criteria 10

3.2.2 Thermal criteria 10

3.2.3 Security criteria 11

3.2.4 Stability criteria 11

3.3 Validation of PSS®E simulation with actual system disturbance 12

3.4 Selecting initial System condition for Load Shedding Studies 13

3.4.1 HMDP (Hydro Maximum Day Peak) 14

v

3.4.2 TMDP (Thermal Maximum Day Peak) 15

3.4.3 HMNP (Hydro Maximum Night Peak) 16

3.4.4 TMNP (Thermal Maximum Night Peak) 16

3.4.5 HMOP (Hydro Maximum Off Peak) 17

3.4.6 TMOP (Thermal Maximum Off Peak) 18

4. Proposed Load Shedding Scheme 19

4.1 Formulating a Load Shedding Scheme 19

4.2 Maximum anticipated overload 19

4.3 Number of load-shedding steps 20

4.4 Time Delay 20

4.4.1 Simulation 1 21



4.5 Size of the load shed at each step 26






4.6 Frequency settings 32

4.7 Proposed Load Shedding Scheme 32

5. Islanding Operation 34

5.1 Possible Islanding Operation 34

5.2 Tripping of 132 kV New Laxapana – Balangoda Line 1 and 2 34

5.3 Tripping of 132 kV Pannipitiya – Matugama Line and 45

Pannipitiya – Horana Line

6. Conclusion and Recommendation 52

Reference List 55

Appendix A: Load Flow Network Diagram of HMOP condition 57

Appendix B: Dispatch Scenario during HMOP Condition 58

Appendix C: Technical Details of Load Shedding relay 59

Appendix D: 33 kV Circuit Breaker Timing Test Results 60

vi

LIST OF FIGURES

Page

Figure 2.1 System Frequency variation with the Load Shedding operation 6

Figure 2.2 System Frequency variation on 07th of June 2011 at 12.17 PM 8

Figure 2.3 System Frequency variation on 27th of July 2011 at 09.17 AM 9

Figure 3.1 Simulated frequency response due to tripping of AES 163 MW 12

Figure 3.2 Actual frequency response due to tripping of AES 163 MW 12

Figure 3.3 Frequency response of the System at HMDP condition 15

Figure 3.4 Frequency response of the System at TMDP condition 15

Figure 3.5 Frequency response of the System at HMNP condition 16

Figure 3.6 Frequency response of the System at TMNP condition 17

Figure 3.7 Frequency response of the System at HMOP condition 17

Figure 3.8 Frequency response of the System at TMOP condition 18

Figure 4.1 Frequency response of the System for Simulation 1 21


Figure 4.3 Pickup and operated time of each stage of existing scheme 24

Figure 4.4 Pickup and operated time of each stage of new scheme 25







Figure 5.1 Network Configuration of the Island 34

Figure 5.2 Load Flow diagram of Balangoda 132 kV Busbar 40

Figure 5.3 Frequency response of the System 41

Figure 5.4 Frequency response of the System after modification of Load

Shedding Feeders. 43

Figure 5.5 Voltage response of the Busbars 43

Figure 5.6 Network Configuration of the Island 45

Figure 5.7 Frequency response of the System 49

Figure 5.8 Frequency response of the System after modification of Load

Shedding Feeders. 50

vii

LIST OF TABLES

Page

Table 2.1 Existing Load Shedding Scheme 7

Table 2.2 MW Rejection from Existing Load Shedding Scheme 7

Table 3.1 Allowable voltage variation in 220 kV and 132 kV systems 10

Table 3.2 Rate of Change of Frequency for different system conditions 18

Table 4.1 Proposed Load Shedding Scheme with new delay time settings. 26

Table 4.2 Proposed Load Shedding Scheme with new step size. 32

Table 4.3 Proposed New Load Shedding Scheme 33

Table 5.1 Night Peak load analysis of Balangoda GSS 35

Table 5.2 Night Peak load analysis of Deniyaya GSS 36

Table 5.3 Night Peak load analysis of Embilipitiya GSS 36

Table 5.4 Night Peak load analysis of Galle GSS 37

Table 5.5 Night Peak load analysis of Hambantota GSS 37

Table 5.6 Night Peak load analysis of Matara GSS 38

Table 5.7 Night Peak load analysis of Ratnapura GSS 38

Table 5.8 Generation Capacity of the Island 39

Table 5.9 Load Demand of the Island 39

Table 5.10 Load Shedded capacity of each GSS 40

Table 5.11 Under Frequency Trip Settings 41

Table 5.12 Load Shedded capacity of each GSS after modification 42

Table 5.13 Proposed Load Shedded capacity of each GSS in the island 44

Table 5.14 Night Peak load analysis of Ambalangoda GSS 46

Table 5.15 Night Peak load analysis of Horana GSS 47

Table 5.16 Night Peak load analysis of Mathugama GSS 47

Table 5.17 Generation Capacity of the Island 48

Table 5.18 Load Demand of the Island 48

Table 5.19 Load Shedded capacity of each GSS 48

Table 5.20 Load Shedded capacity of each GSS after modification 49

Table 5.21 Proposed Load Shedded capacity of each GSS in the island 51

Table 6.1 Proposed New Load Shedding Scheme 52

Table 6.2 Saved Load from Proposed New Load Shedding Scheme 53

Table 6.3 Saved Load from proposed feeder arrangement in each island 53

Table 6.4 Proposed Load Shedded capacity of each GSS in the islands 54

viii

LIST OF APPENDICIES

Page

Appendix A Load Flow Network Diagram of HMOP condition 57

Appendix B Dispatch Scenario during HMOP Condition 58

Appendix C Technical Details of Load Shedding relay 59

Appendix D 33 kV Circuit Breaker Timing Test Results 60

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Chapter 1

INTRODUCTION 1.1 Background

Power System reliability has gained utmost concern in modern era since it is one of the key

elements of modern development. Main parts of the Power System are Generation,

Transmission and Distribution. Each one of them has their own reliability improvement

methods such as Protection systems, Condition Monitoring Systems, etc. but when we

consider the system as a whole “Load shedding” is the main controlling method to keep up

the system alive when it goes to unstable state which National Control Center unable to

rectify. So having advanced Load shedding scheme is the prime importance in modern

days and these Load shedding schemes should also capable to facilitate Islanding operation

when system separates into regions due to limitations in the Network configuration during

system faults.

1.2 Importance of the Load Shedding Scheme

When a Power System is in stable operation at normal frequency, the total mechanical

power input from the prime movers to the generators is equal to the sum of all the

connected loads which also includes all real power losses in the system [1]. If any

significant unbalance occurs such as tripping of main generator in the system or tripping of

main transmission line in the system will causes a frequency variations. These frequency

variations occur due to slow down or speed up the rotors in the system. Normally rotors are

massive rotating masses which have immense kinetic energy. When one of the main

generators in the system trips, system will experience lack of generation than the loads so

rotors slow down and kinetic energy converted into electric energy and supply to the

system. As a result system frequency will drop. When main transmission line in the system

trips, system will experience excess of generation than load so rotors speed up to absorbing

energy. As a result system frequency will increase.

Governors in the generators sense small changes in speed resulting from gradual load

changes in the normal system. These governors adjust the mechanical input power to the

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generating units in order to maintain normal frequency operation [1]. But sudden losing of

large generator can produce a severe generation and load unbalance, resulting in a rapid

frequency decline. If the governors cannot respond quickly enough, the system may

collapse. So rapid and selective shedding of loads can make system recovery possible and

avoid prolonged system outage and restore customer service with minimum delay.

1.3 Identification of the Problem

Several procedures and criteria must be considered when designing load shedding scheme

for specific systems. These include [1]:

a) Maximum anticipated overload

b) Number of Load Shedding Steps

c) Size of the Load Shed at each Step

d) Frequency Setting

e) Time Delay

f) Location of the frequency relays

So detailed study of existing Load Shedding scheme of Sri Lankan Power System with

above settings is important.

When analyzing the historical data related to existing Load Shedding scheme; some of the

above settings were not updated according to the system expansion (as an example during

the period 2005 to 2012, Frequency setting and Time delay setting of Load Shedding

scheme is not changed but Sri Lankan transmission network significantly expanded,

generators such as Kerawalapitiya and Norochcholai connected to the system during the

same period), some were implemented by foreign consultants according to their own

standards without much concern about our network, some of the setting were implemented

purely to overcome the blackout situations and further some of the setting were

implemented case by case study with the similar system failures.

Due to above mentioned reasons and also analyzing the system behavior in last few years

during system disturbance, it can be identified that proper analysis and implementation of

new Load Shedding scheme is prime important in the present Power System point of view.

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Further, due to the present Network configuration after certain Power System failures some

part of the System isolates from the main system and operates in islanding Mode. This

Islanding operation fails at all the times due to unbalance of the Generation and Load. So

there is a necessity of rearrange the Load Shedding Feeders of each GSS to facilitate the

possible Islanding operations in Sri Lankan Network.

1.4 Motivation

The outcome of this project will be to develop a Load shedding scheme which facilitate

system recovery with minimum impact to the customers. Further, in the event of separation

of the system into regions it will facilitate Islanding operation which enables to supply

electricity to all the separated regions with minimum impact in their customers.

This Load shedding schemes will improve the Power System reliability and have a definite

positive effect on customers which in turn improve the wellbeing of the people and

economy of the country.

1.5 Objective of the Study

There are four objectives in this study,

1. Analyze Existing Load Shedding Setting such as,

• Maximum anticipated overload

• Number of Load Shedding Steps

• Size of the Load Shed at each Step

• Frequency Setting

• Time Delay

2. Propose suitable Load Shedding Setting for Sri Lankan Network.

3. Identify possible Islanding operations due to present Sri Lankan Network

configuration.

4. Rearrange the 33 kV Load Shedding Feeders in the Sri Lankan Network to

facilitate the possible Islanding operations in Sri Lankan Network.

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1.6 Methodology

1. Analyzing the Existing Load Shedding scheme using Power System simulator.

2. Propose suitable Load Shedding scheme using Power System simulator.

3. Identify possible Islanding operations due to present Sri Lankan Network

configuration.

4. Analyzing the stability of the above identified Islands using Power System

simulator (with the proposed Load Shedding scheme)

5. Rearrange the 33 kV Load Shedding Feeders in the Sri Lankan Network to

facilitate islanding operation by analyzing the stability of the islands using Power

System simulator (with the proposed Load Shedding scheme)

This study will help to find a feasible solution for the above section 1.3 mentioned

problems and the results obtained through this study could be used to improve the present

system reliability.

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Chapter 2

EXISTING LOAD SHEDDING SCHEME

2.1 Load Shedding Scheme

In the Power System, regular changes in the system load are handled by the frequency

controlling machine. In Sri Lankan network Victoria, Kotmale, New Laxapana and

Samanalawewa are the frequency controlling machines [2]. In generally frequency declines

due to generator deficiency is governed by the combined action of Spinning reserve and

frequency controlling machine. But in the event of rapid frequency decline, governor of the

frequency controlling machine has no time to response quickly. So it is necessary to

intentionally and automatically disconnect a portion of the load equal to or greater than the

overload. After the decline has been arrested and the frequency returns to normal, the load

may be restored in small increments, allowing the spinning reserve to become active and

any additional available generators to be brought on line.

Frequency is a reliable indicator of an overload condition (at a particular time, load on the

system is grater then the Generating capacity) [12]. Frequency sensitive relays which use

Voltage Transformer input to recognize the frequency can therefore be used to disconnect

load automatically. Such an arrangement is referred to as a load shedding scheme and is

designed to reserve system integrity and minimize outages. Although utilities generally

avoid intentionally interrupting service, it is sometimes necessary to do so in order to avoid

major system collapse. In general, noncritical loads, usually residential, can be interrupted

for short periods, minimizing the impact of the disturbance on service.

Automatic load shedding, based on under frequency is necessary since sudden, moderate to

severe overloads can drive a system into a hazardous state much faster than System

operator can react. Under frequency relays are usually installed at distribution substations,

where selected loads can be disconnected.

The object of load shedding is to balance load and generation. Since the amount of

overload is not readily measured at the instant of a disturbance, the load is shed a block at a

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time, each controlling its own block of load and each set to a successively lower

frequency. The first line of frequency relays is set just below the normal operating

frequency range. When the frequency drops below this level, these relays will drop a

significant percentage of system loads. It this load drop is sufficient, the frequency will

stabilize or actually increase again. If this first load drop is not sufficient, the frequency

will continue to drop, but at a slower rate, until the frequency range of the second line of

relays is reached. At this point, a second block of load is shed. This process will continue

until the overload is relieved or all the frequency relays have operated. An alternative

scheme is to set a number of relays at the same frequency or close frequencies and use

different tripping time delays [1].

Figure 2.1 – System Frequency variation with the Load Shedding operation.

Stage 2

Stage 1

Stage 4

Stage 3

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2.2 Existing Load Shedding Scheme

Table 2.1 – Existing Load Shedding Scheme

Stage Load to be

Remarks Tripping Criteria Tripped (%)

I 5 5% Load on only freq. based 48.75 Hz + t=100 ms

II 5 5% Load on only freq. based 48.50 Hz + t=500 ms

III 10

7% Load on only freq. based

48.25 Hz + t=1 s OR


49 Hz AND df/ft =

+ df/dt based 0.85 Hz/Sec

IV 10


48.00 Hz + t=1.5 s OR


49 Hz AND df/ft =


V 10


47.50 Hz + t=inst OR


49 Hz AND df/ft =


VI 10 10% Load on df/dt based 49 Hz AND df/ft =

0.85 Hz/Sec

The Existing Load Shedding Scheme is shown in Table 2.1, as per the scheme there are six

Load Shedding stages where first two stages reject 5% of the load each and other stages

reject 10% of the load each. So if all six stages operate 50% of the system load will be

rejected (Half of the system). It is like 30% of load base on Under Frequency which start

when frequency goes below 48.75 Hz and rest of the 20% of the load is based on the rate

of change of frequency. Load rejection amount during Off Peak, Day Peak and Night Peak

can be found in Table 2.2

Table 2.2 – MW Rejection from Existing Load Shedding Scheme

Off Peak Day Peak Night Peak

MW

% from

System Load MW

% from

System Load MW

% from

System Load

Stage 1 42.85 5.53 78.5 5.6 90.25 5.01

Stage 2 41.5 5.35 67.25 4.8 88.7 4.92

Stage 3 83.65 10.79 126.4 9.02 154.25 8.56

Stage 4 60.39 7.79 127.2 9.07 149.72 8.31

Stage 5 75.05 9.68 125.92 8.98 154.95 8.6

Stage 6 81.21 10.48 151.69 10.82 159.13 8.83

Total 384.7 49.62 676.96 48.29 797 44.23

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2.3 System Response to the System Disturbances.

Below shows the System Response to the system disturbance with existing load shedding

scheme.

2.3.1 Tripping of Norochcholai coal Power Plant

On 07th of June 2011 at 12.17 PM, Norochcholai coal Power Plant tripped [3]. Due to

tripping 240 MW rejected from the system and four stages of the Load Shedding Scheme

were operated rejecting 40% of the loads. Minimum frequency was 47.601 Hz and rate of

change of frequency (df/dt) is -0.743 Hz/Sec.

Figure 2.2 – System Frequency variation on 07th

of June 2011 at 12.17 PM.

2.3.2 Tripping of Kerawalapitiya Power Plant

On 27th

of July 2011 at 09.17 AM, Kerawalapitiya Power Plant tripped [3]. Due to tripping

137 MW rejected from the system and two stages of the Load Shedding Scheme were

operated rejecting 10% of the loads. Minimum frequency was 48.499 Hz and rate of

change of frequency (df/dt) is -0.046 Hz/Sec.

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Figure 2.3 – System Frequency variation on 27th

of July 2011 at 09.17 AM

2.4 Analyze of Existing Load Shedding Scheme

Existing Load Shedding Scheme is analyzed with the simulations and identified the best

settings for Load Shedding and hence proposes a new Load Shedding scheme for Sri

Lankan Network.

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Chapter 3

POWER SYSTEM SIMULATION

3.1 The Power System Simulator, PSS®E

The Siemens PTI Power System Simulator (PSS®E) is a package of programs for studies

of power system transmission network and generation performance in both steady-state

and dynamic conditions. PSS®E handles power flow, fault analysis (balanced and

unbalanced), network equivalent construction, and dynamic simulation [4].

3.2 Planning Criteria

The simulation studies are done according to the under mentioned planning criteria of the

Ceylon Electricity Board (CEB). The planning criteria are to ensure quality and reliable

supply under normal operating conditions as well as under contingencies [5].

3.2.1 Voltage criteria

The voltage criterion defines the permitted voltage deviation at any live bus bar of the

network under normal and contingency operating conditions as in Table 3.1 [7].

Table 3.1 – Allowable voltage variation in 220 kV and 132 kV systems

Bus bar voltage Allowable voltage variation (%)

Normal operating condition Single contingency condition

220 kV ±5% -10% to +5%

132kV ±10% ±10%

3.2.2 Thermal criteria

The design thermal criterion limits the loading of any transmission network element, in

order to avoid overheating due to overload.

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The loading of elements should not exceed their rated thermal loading values for steady

state conditions [5].

3.2.3 Security criteria

The performance of the transmission system under contingency situation is taken into

consideration in the security criteria. The adopted contingency level for the planning

purposes is N-1, i.e. outage of any one element of the transmission system at a time. After

outage of any one element (i.e. any one circuit of a transmission line or a transformer and

without any adjustment or corrective measure ), the system should be able to meet the

distribution demand while maintaining the bus bar voltage levels and loading of all the

remaining elements should not exceed their emergency ratings specified.

After system readjustment following a disturbance described above, the voltage and

loading of elements should return to their corresponding normal limits [5].

3.2.4 Stability criteria

Stability criteria should ensure the system stability during and after a system disturbance.

For all pertaining equipment in service, the system should remain stable in case of [5]:

• Three-phase fault at any one overhead line terminal, cleared by the primary

protection with successful and unsuccessful auto re-closing

• Loss of any one generation unit

• Load rejection by loss of any transformer

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3.3 Validation of PSS®E simulation with actual system disturbance.

On 24th

of December 2009 AES plant tripped rejecting 163MW (15.8 % of system

generation prior to generation loss)

Below figures illustrate simulated and actual frequency responses for the above incident.

Figure 3.1: Simulated frequency response due to tripping of AES 163 MW

Figure 3.2: Actual frequency response due to tripping of AES 163 MW

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In both cases frequency reached to below 48 Hz and thus under frequency load shedding

operated up to stage IV. Initial rate of change of frequency is in simulation and actual case

is 0.9 Hz/s and 0.65 Hz/s respectively. The time reached to minimum frequency is 4

seconds in the simulation and 5.5 seconds in the actual case after the disturbance. 166 MW

load rejection from all four stages at the simulation and 148 MW load rejection due to

under frequency load shedding in actual situation. Shape of the frequency variation is

almost similar in both cases.

Ultimately simulation results can be considered almost same as real system behavior.

3.4 Selecting initial System condition for Load Shedding studies

The basic characteristic of the frequency change of a power system is derived from the

following equation [9].

+ (1)

Where;

H - System inertia constant on system base (seconds)

df/dt - Rate of change of frequency, Hz/s

Pm(pu) - Remaining generation after generation loss in remaining system generation

base

Pe(pu) - System load prior to generation loss in remaining system generation base

f0 - Base frequency, 50 Hz

D - Power system load damping constant in pu/Hz

∆f - Change in frequency, Hz

Pm – Pe

Pm

- Amount of overload in remaining generation base

df

dt =

Pm(Pu) – Pe(pu)

2 x H

x f0

2H

D x ∆f

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Generally load damping (D) of a power system depends on the load mix and varying

around 1-2 %. An exact value of D can only be determined by observing the variation of

load with frequency on the system under consideration. For the illustration purpose let

consider the D as zero. So the equation will be simplify as follows,

(2)

From above equation, it can be identified that lower the System inertia, higher the rate of

change of frequency in the system and higher the possibility of collapsing the system.

Therefore to recognize the best initial System condition for Load Shedding studies, System

was simulated using PSS®E software under following six scenarios to identify the highest

Rate of change of frequency decline by tripping the 20% of the total demand of the system.

1. HMDP (Hydro Maximum Day Peak)

2. TMDP (Thermal Maximum Day Peak)

3. HMNP (Hydro Maximum Night Peak)

4. TMNP (Thermal Maximum Night Peak)

5. HMOP (Hydro Maximum Off Peak)

6. TMOP (Thermal Maximum Off Peak)

3.4.1 HMDP (Hydro Maximum Day Peak)

System was simulated with Load and Generation balance of 1525 MW and after 2 seconds

20% Generation (305 MW) was removed from the system. Three stages of the Load

Shedding Scheme were operated. Minimum frequency was 47.92 Hz and initial rate of

change of frequency is -0.734 Hz/Sec.

df

dt =

Pm(Pu) – Pe(pu)

2 x H

x f0

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Figure 3.3: Frequency response of the System at HMDP condition.

3.4.2 TMDP (Thermal Maximum Day Peak)


20% Generation (305 MW) was removed from the system. Three stages of the Load



Figure 3.4: Frequency response of the System at TMDP condition

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3.4.3 HMNP (Hydro Maximum Night Peak)


20% Generation (380 MW) was removed from the system. Two stages of the Load


change of frequency is -0.675 Hz/Sec

3.4.4 TMNP (Thermal Maximum Night Peak)





Figure 3.5: Frequency response of the System at HMNP condition

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Figure 3.6: Frequency response of the System at TMNP condition

3.4.5 HMOP (Hydro Maximum Off Peak)





Figure 3.7: Frequency response of the System at HMOP condition

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3.4.6 TMOP (Thermal Maximum Off Peak)





Summarizing the simulation results,

Table 3.2 – Rate of Change of Frequency for different system conditions

No. System Condition df/dt ( Hz/Sec)

1 HMDP -0.734

2 TMDP -0.676

3 HMNP -0.675

4 TMNP -0.802

5 HMOP -0.920

6 TMOP -0.820

After analyzing the simulation results, it was identified that HMOP scenario has the

highest Rate of change of frequency decline thus lowest system inertia. So HMOP is

selected as the best initial System condition for Load Shedding studies. Details of this

initial system conditions for the dynamic simulation are shown in the load flow diagram

attached in the appendix A and dispatch scenario is given in the appendix B.

Figure 3.8: Frequency response of the System at TMOP condition

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Chapter 4

PROPOSED LOAD SHEDDING SCHEME

4.1 Formulating a Load Shedding Scheme

Following factors are considered when analyzing existing load shedding schemes and

designing of the proposed load shedding schemes for the Sri Lankan network.

These include:

a) Maximum anticipated overload

b) Number of load-shedding steps

c) Time delay

d) Size of the load shed at each step

e) Frequency settings

4.2 Maximum anticipated overload

Load Shedding Scheme should be able to shed a load equal to the maximum anticipated

overload. Logically, there is no reason to limit load-shedding to any percentage of loads.

Indeed, it is desirable to shed 100% of load, preserving interconnections and keeping

generating units on line and synchronized, than to allow the system to collapse with

customers still connected. Even if 100% of the load is shed, service can be restored rapidly.

But if the system collapses, a prolonged outage would result. For this reason, it is

necessary to evaluate the cost of the load-shedding scheme in light of the probability that

an overload of a given severity can occur [1].

CEB Policy on Power System Operations, maximum loading on a generator is less than

20% of the total gross generation. CEB is following single outage criterion which is

mentioned in section 3.2.3.

In the existing scheme 50% of the load will reject after operation of all the stages, but due

to maximum loading on a generator is less than 20% of the total gross generation and

single outage criterion, Maximum anticipated overload will be 20% of the total load. But

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when consider n-2 outage criterion it is better to use value in-between 20% to 50%. This

value will be fine-tuned during identifying of step sizes of each load shedding stage.

4.3 Number of load-shedding steps

The basic and simplest load shedding scheme is one in which the predetermined

percentage of the load is shed at once when a group of relays senses a frequency drop.

Even though this scheme will arrest any anticipated frequency decline, it will often

disconnect far more customers than necessary. As per reliability concern it is not an

acceptable method. An improvement then would be to use two groups of relays, one

operating at a lower frequency than the other, and each shedding half the predetermined

load. The higher-set relays would trip first, halting the frequency decline as long as the

overload was half or less of the worst-case value. For more severe overload, the frequency

would continue to drop, although at a slower rate, until the second group of relays to shed

the other half of the expendable load.

The number of load shedding steps can be increased virtually without limit [13]. More the

number of steps, the system can shed load in small increments until the decline stops which

enable almost no excess load need be shed. But such a scheme may be difficult to

coordinate since there are so many steps.

Most utilities use between two and five load-shedding steps, with three being the most

common [1]. In existing Load Shedding scheme use six steps where the last step is purely

base on rate of change of frequency. So this scheme can be accepted since five steps Load

Shedding schemes are accepted universally.

4.4 Time Delay

Time delays of the existing Load Shedding Scheme are 0.1sec, 0.5sec, 1sec and 1.5

seconds respectively from Stage I to IV. Stage V is an instantaneous stage. The important

rule for Load Shedding Scheme is to use minimum possible time delays and lesser the

delay, the more easily the scheme can cope with severe system disturbance [1].

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So simulations were carried out using PSS®E software to improve the time delay settings.

For these simulations rate of change of frequency function is disabled since it is not

possible to obtain time delay values if load shed from this instantaneous function.

As per the section 3.4, CEB network is more viable to collapse during HMOP conditions

especially during 00:00 hrs to 05:00 hrs of the day due to low system inertia Constant. So

simulation was done with the similar load condition.

4.4.1 Simulation 1

Figure 4.1: Frequency response of the System for Simulation 1

Above simulation results were obtained with existing Frequency settings. System was

simulated with Load and Generation balance of 950 MW and after 2 seconds Norochcholai

Power Plant was removed from the system rejecting 190 MW, this is equal to the 20% of

the generation that time. Four stages of the Load Shedding Scheme were operated rejecting

251.12 MW of the loads. Minimum frequency was 47.90 Hz and Frequency stabilized at

50.59 Hz.

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4.4.2 Simulation 2


Above simulation results were obtained by changing the time delay to 0.5 sec for all the

stages except stage I (Time delay = 0.1 sec). System was simulated with Load and

Generation balance of 950 MW and after 2 seconds Norochcholai Power Plant was

removed from the system rejecting 190 MW, this is equal to the 20% of the generation that

time. Three stages of the Load Shedding Scheme were operated rejecting 201.2 MW of the

loads. Minimum frequency was 48.09 Hz.

When comparing Simulation 1 & 2, in Simulation 2 only three stages were operated which

reduced rejecting loads by 49.92 MW and also increased the system frequency by 0.19 Hz.

So from the above study it can be identified that reducing the time delay will make system

more reliable.

Before carryout the next Simulation, it should be identified the maximum time required to

trip a feeder from Load Shedding Scheme. Following factors should be consider when

selecting the maximum time value,

a) Operating time of the Load Shedding relay.

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b) Operating time of the Interposing auxiliary devises

c) Operating time 33 kV Circuit Breaker

a) Operating time of the Load Shedding relay.

Operating time of the Load Shedding relay can be estimated as 40 ms because most of the

frequency relays in CEB network are numerical type and these relays will operate below

20 ms. Please refer appendix C.

b) Operating time of the Interposing auxiliary devises

As per the below specifications CEB is recommending to use minimum interposing

auxiliary relays in-between relay and the circuit breaker trip coil, so 20 ms time delay is

sufficient for this factor.

“Relay contacts shall be suitable for making and breaking the maximum currents which

they may be required to control in normal service but where contacts of the protective

relays are unable to deal directly with the tripping currents, approved auxiliary contacts,

relays or auxiliary switches shall be provided. In such cases the number of auxiliary

contacts or tripping relays operating in tandem shall be kept to the minimum in order to

achieve fast fault clearance times. Separate contacts shall be provided for alarm and

tripping functions. Relay contacts shall make firmly without bounce and the whole of the

relay mechanisms shall be as far as possible unaffected by vibration, shock and bump or

external magnetic fields. [6]”

c) Operating time of the 33 kV Circuit Breaker

33 kV Circuit Breaker will trip within 3 cycle after trip signal received to the trip coil, so

operating time of the Circuit Breaker can be considered as 60 ms. Please refer appendix D.

Minimum Time delay = Operating time of the Load Shedding relay + Operating time of

the Interposing auxiliary devises + Operating time 33 kV Circuit Breaker

= 40 ms + 20 ms + 60 ms

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= 120 ms

Pickup (PU) and Operated (OP) frequency values of each stage of existing Load Shedding

Scheme with the above time value and rate of change of frequency of -0.85 Hz/sec can be

found in Figure 4.3.

Figure 4.3: Pickup and operated time of each stage of existing scheme

From Figure 4.3, it can be identified that Stage III & IV will pick up before operation of

Stage II, Stage V will pick up before operation of Stage III & IV and also Stage V will

operate before operation of stage IV. So to overcome above complications new time setting

is identified as 150 ms and this setting is proposed to Stage II to V. Stage I is not changed

since it is the initial stage of the Load Shedding Scheme.

Pickup (PU) and Operated (OP) frequency values of each stage of proposed Load

Shedding Scheme with the new time settings and rate of change of frequency of -0.85

Hz/sec can be found in Figure 4.4.

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Figure 4.4: Pickup and operated time of each stage of new scheme

With the use of new time delay to all the stages except stage I (Time delay = 0.1 sec)

4.4.3 Simulation 3



Norochcholai Power Plant was removed from the system rejecting 190 MW, this is equal

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to the 20% of the generation that time. Three stages of the Load Shedding Scheme were

operated rejecting 167.15 MW of the loads. Minimum frequency was 48.17 Hz.


reduced rejecting loads by 83.97 MW and also increased the system frequency by 0.27 Hz.

Frequency Stabilized at 49.75 Hz. So from the above study it can be found best time delay

value for proposed Load Shedding Scheme.

Table 4.1: Proposed Load Shedding Scheme with new delay time settings.

Stage Load to be




III 10


48.25 Hz + t=150 ms OR


49 Hz AND df/ft =


IV 10


48.00 Hz + t=150 ms OR


49 Hz AND df/ft =


V 10


47.50 Hz + t=150 ms OR


49 Hz AND df/ft =


VI 10 10% Load on df/dt based 49 Hz AND df/ft =

0.85 z/Sec

4.5 Size of the load shed at each step

The size of the load-shedding steps should be related to expect percentage overloads [14].

After the study of the system configuration reveals that there is relatively high probability

of losing certain generating units and transmission lines. So load shedding blocks should

be sized accordingly.

Since Sri Lankan network is large, there are many possible events causing only a small

percentage overload in itself. In this case, a number of overload situations may be lumped

together and handled in one step. On the other hand, it may be sufficient to shed a

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percentage of the overload in a few equal steps. In existing scheme 5% and 10% of step

sizes were used and by simulation using Power System Simulator (PSS®E) software

analyzed any future improvement is needed.

If we considered Simulation No. 3 with the proposed new time settings, System frequency

was stabled at 49.75 Hz even after operation of the load shedding stage three. This 49.75

Hz value is inside the system normal frequency range of 50.5 Hz to 49.5 Hz [2].

Stabilizing System frequency at 49.5 Hz will also accepted since it is in the normal

operating frequency range. So simulation done with reducing stage 3 step size from 10% to

5%. For these simulations also rate of change of frequency function is disabled and it will

be analyzed later.

4.5.1 Simulation 4



to the 20% of the generation that time. Three stages of the Load Shedding Scheme were

operated rejecting 121.14 MW of the loads. Minimum frequency was 48.17 Hz and rate of

change of frequency (df/dt) is -0.765 Hz/Sec. Frequency stabilized at 49.56 Hz.


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reduced rejecting loads by 129.98 MW and also increased the system frequency by 0.27

Hz. Frequency Stabilized at 49.56 Hz. So from the above study it can be found best step

size for Stage 3 of proposed Load Shedding Scheme.

When system disturbance occurs with n-1 stability criteria as per the proposed scheme only

up to stage 3 will operate. Next Simulation will be done when simultaneous two

disturbances occurred at same time in the system.

4.5.2 Simulation 5



Norochcholai Power Plant and Victoria Power Plant was removed from the system

rejecting 240 MW, this is equal to the 25% of the generation that time. Four stages of the

Load Shedding Scheme were operated rejecting 204.74 MW of the loads. Minimum

frequency was 47.95 Hz and Frequency Stabilized at 49.80 Hz.

System frequency was stabled at 49.80 Hz even after operation of the load shedding stage

four. This 49.80 Hz value is inside the system normal frequency range of 50.5 Hz to 49.5

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Hz [2]. Stabilizing System frequency at 49.5 Hz will also accepted since it is in the normal

operating frequency range. So simulation done with reducing stage 4 step size from 10% to

6%. For these simulations also rate of change of frequency function is disabled and it will

be analyzed later.

4.5.3 Simulation 6



Norochcholai Power Plant and Victoria Power Plant was removed from the system

rejecting 240 MW, this is equal to the 25% of the generation that time. Four stages of the

Load Shedding Scheme were operated rejecting 167.81 MW of the loads. Minimum

frequency was 47.97 Hz and Frequency Stabilized at 49.50 Hz.

When comparing Simulation 5 & 6, in Simulation 6 reduced rejecting loads by 36.93 MW

and Frequency Stabilized at 49.50 Hz. So from above study it can be found the best step

size for Stage 4 in the proposed Load Shedding Scheme.

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In the existing Load Shedding scheme 20% of the load will be rejected based on the rate of

change of frequency (dt/dt). So simulation was carried with dt/dt setting to identify system

response for this step size.

4.5.4. Simulation 7




to the 20% of the generation that time. df/dt Scheme was operated rejecting 181.81 MW of

the loads. Minimum frequency was 48.85 Hz and rate of change of frequency (df/dt) is -

0.92 Hz/Sec. Frequency stabilized at 49.85 Hz.

System frequency was stabled at 49.85 Hz even after operation of the df/dt stage. This

49.85 Hz value is inside the system normal frequency range of 50.5 Hz to 49.5 Hz [2].

Stabilizing System frequency at 49.5 Hz will also accepted since it is in the normal

operating frequency range. So simulation done with reducing df/dt stage step size from

20% to 12%.

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4.5.5. Simulation 8




to the 20% of the generation that time. Stage I of the Load Shedding Scheme and df/dt

stages were operated rejecting 139.52 MW of the loads (107.7 MW from df/dt stage and

31.82 MW from Stage I). Minimum frequency was 48.48 Hz and rate of change of

frequency (df/dt) is -0.92 Hz/Sec. Frequency stabilized at 49.6 Hz.

When comparing Simulation 7 & above simulation , 107.70 MW reject in above

simulation, so df/dt stage reduced rejecting loads by 74.11 MW and Frequency Stabilized

at 49.6 Hz. So from the above study it can be found best step size for df/dt step size for

proposed Load Shedding Scheme.

So maximum anticipated overload can be identified 41% of the total system load.

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4.6 Frequency settings

The determination of the frequency settings is depends on the system’s normal operating

frequency range. The frequency of the first step should be below the normal operating

frequency band of the system. Further first level should be set at below a certain value

which the system could be recovered by system operator or system could be operated

continuously for shorter period. Generally during very low off peak conditions system

experiences 2-3 % sudden generation loss mainly due to tripping of wind plants. System

frequency drops to around 49 Hz for the above said generation losses. By considering the

above facts it was decided to remain in the existing initial frequency setting of 48.75 Hz

[11]. Since existing frequency settings are in the steps of 0.25 Hz there is no point of

changing frequency settings.

4.7. Proposed Load Shedding Scheme

After analyzing the simulation results new load shedding scheme can be proposed as

shown in Table 4.2,

Table 4.2: Proposed Load Shedding Scheme with new step size.

Stage Load to be




III 5


48.25 Hz + t=150 ms OR


49 Hz AND df/ft =


IV 6


48.00 Hz + t=150 ms OR


49 Hz AND df/ft =


V 10


47.50 Hz + t=150 ms OR


49 Hz AND df/ft =


VI 10

10% Load on df/dt based

49 Hz AND df/ft =

0.85 Hz/Sec

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Table 4.2 can be future simplify as shown in Table 4.3,

Table 4.3: Proposed New Load Shedding Scheme

Stage Load to be




III 5 5% Load on only freq. based 48.25 Hz + t=150 ms

IV 6 6% Load on only freq. based 48.00 Hz + t=150 ms

V 10


47.50 Hz + t=150 ms OR


49 Hz AND df/ft =


VI 10


49 Hz AND df/ft =

0.85 Hz/Sec

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Chapter 5

ISLANDING OPERATION

5.1. Possible Islanding Operation

Due to limitations in Sri Lankan Network configuration following line tripping will

separate the system into two parts.

1. Tripping of 132 kV New Laxapana – Balangoda Line 1 and 2.

2. Tripping of 132 kV Pannipitiya – Matugama Line and Pannipitiya – Horana Line.

But even though there are capable Frequency controlling machines in these Islanded areas,

these systems always fails due to unbalance of Generation and Loads.

5.2. Tripping of 132 kV New Laxapana – Balangoda Line 1 and 2

Figure 5.1: Network Configuration of the Island

When this incident happens following Grid Substations are separated from the main

network.

I. Balangoda GSS

II. Deniyaya GSS

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1 2 3 4 5 6 7 8 Total Total

A A A A A A A A A MW

1-Mar Tuesday Night 19:30 130 102 177 157 20 40 20 -5 641 29.31045659

2-Mar Wednesday Night 19:30 127 95 176 150 18 28 20 -134 480 21.94854783

3-Mar Thursday Night 19:30 115 89 162 152 19 48 11 -38 558 25.51518686

4-Mar Friday Night 19:30 126 97 168 157 19 59 -39 -18 569 26.01817441

5-Mar Saturday Night 19:00 124 99 168 140 18 55 22 -90 536 24.50921175

6-Mar Sunday Night 19:30 129 94 175 152 17 65 20 -37 615 28.12157691

7-Mar Monday Night 19:30 126 102 172 32 18 91 17 -134 424 19.38788392




11-Mar Friday Night 19:00 110 102 171 159 17 85 -45 -8 591 27.02414952


13-Mar Sunday Night 19:30 102 96 140 149 15 63 -37 -8 520 23.77759349

14-Mar Monday Night 19:00 110 101 167 147 18 74 20 -5 632 28.89892131


16-Mar Wednesday Night 19:30 111 99 174 140 18 58 38 13 651 29.767718


18-Mar Friday Night 19:30 110 100 175 153 20 80 43 -12 669 30.59078854

19-Mar Saturday Night 19:30 95 94 169 144 17 75 -11 -28 555 25.37800843

20-Mar Sunday Night 19:30 95 92 150 138 17 32 -12 -22 490 22.40580925

21-Mar Monday Night 19:30 92 84 151 134 19 83 -10 -53 500 22.86307066

22-Mar Tuesday Night 19:30 107 86 190 149 22 60 -12 -20 582 26.61261425

23-Mar Wednesday Night 19:30 112 93 160 160 18 68 -50 -115 446 20.39385903


25-Mar Friday Night 19:30 110 98 138 148 16 72 10 -89 503 23.00024908


27-Mar Sunday Night 19:30 109 93 168 150 17 76 50 -110 553 25.28655615

28-Mar Monday Night 19:30 116 93 190 156 18 70 62 -95 610 27.89294621




Max. 33.56299 MW

TimeDate Day Zone

III. Embilipitiya GSS

IV. Galle GSS

V. Hambantota GSS

VI. Matara GSS

VII. Ratnapura GSS

Load Study had been carried out to find the total load of the above Grid Substations.

Off Peak, Day Peak and Night Peak data have been analyzed and find out that Night Peak

load is always higher than off peak and Day peak. So following tables will include Night

Peak load analysis only.

Balangoda GSS

Table 5.1: Night Peak load analysis of Balangoda GSS

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1G 1F 2G 2F 3 4 5 8 Total Total


1-Mar Tuesday Night 19:30 23 23 21 26 42 21 156 7.133278046

2-Mar Wednesday Night 19:30 39 79 48 64 75 36 341 15.59261419

3-Mar Thursday Night 19:30 41 70 48 73 69 38 339 15.50116191

4-Mar Friday Night 19:30 36 66 42 70 32 34 280 12.80331957

5-Mar Saturday Night 19:00 40 72 49 58 70 35 324 14.81526979

6-Mar Sunday Night 19:30 42 71 52 82 73 39 359 16.41568473

7-Mar Monday Night 19:30 38 70 50 73 70 39 340 15.54688805




11-Mar Friday Night 19:00 40 71 51 75 74 40 351 16.0498756


13-Mar Sunday Night 19:30 38 67 42 73 69 34 323 14.76954365

14-Mar Monday Night 19:00 40 61 50 83 75 38 347 15.86697104




18-Mar Friday Night 19:30 42 68 48 78 77 36 349 15.95842332


20-Mar Sunday Night 19:30 36 70 42 53 66 28 295 13.48921169

21-Mar Monday Night 19:30 42 69 54 66 81 31 343 15.68406647




25-Mar Friday Night 19:30 43 65 54 79 79 40 360 16.46141088


27-Mar Sunday Night 19:30 41 67 47 75 72 31 333 15.22680506

28-Mar Monday Night 19:30 40 66 48 75 76 37 342 15.63834033




Max. 17.51311 MW

TimeDate Day Zone

Deniyaya GSS

Embilipitiya GSS

1 2 3 4 5 6 7 8 Total Total


1-Mar Tuesday Night 19:30 55 66 65 44 102 332 15.18107892

2-Mar Wednesday Night 19:30 55 69 69 44 95 332 15.18107892

3-Mar Thursday Night 19:30 55 65 63 42 89 314 14.35800837

4-Mar Friday Night 19:30 57 69 67 41 97 331 15.13535278

5-Mar Saturday Night 19:00 55 66 65 45 99 330 15.08962664

6-Mar Sunday Night 19:30 60 70 65 92 94 381 17.42165984

7-Mar Monday Night 19:30 56 70 65 56 102 349 15.95842332




11-Mar Friday Night 19:00 56 65 119 48 102 390 17.83319511


13-Mar Sunday Night 19:30 56 69 120 42 96 383 17.51311213

14-Mar Monday Night 19:00 55 66 120 48 101 390 17.83319511




18-Mar Friday Night 19:30 75 70 124 54 100 423 19.34215778


20-Mar Sunday Night 19:30 89 60 121 43 92 405 18.51908723

21-Mar Monday Night 19:30 89 62 150 45 84 430 19.66224077

22-Mar Tuesday Night 19:30 10 60 145 86 301 13.76356854



25-Mar Friday Night 19:30 50 50 95 34 98 327 14.95244821


27-Mar Sunday Night 19:30 55 60 79 93 287 13.12340256

28-Mar Monday Night 19:30 40 55 117 41 93 346 15.8212449




Max. 21.03402501 MW

TimeDate Day Zone

Table 5.2: Night Peak load analysis of Deniyaya GSS

Table 5.3: Night Peak load analysis of Embilipitiya GSS

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Galle GSS

Hambantota GSS

1 2 3 4 5 6 7 8 Total Total


1-Mar Tuesday Night 19:30 177 21 10 138 346 15.8212449

2-Mar Wednesday Night 19:30 176 58 8 107 349 15.95842332

3-Mar Thursday Night 19:30 162 17 136 315 14.40373452

4-Mar Friday Night 19:30 168 56 104 328 14.99817435

5-Mar Saturday Night 19:00 168 54 103 325 14.86099593

6-Mar Sunday Night 19:30 175 58 104 337 15.40970962

7-Mar Monday Night 19:30 172 59 108 339 15.50116191

8-Mar Tuesday Night 19:00 170 18 144 332 15.18107892

9-Mar Wednesday Night 19:30 180 15 98 293 13.39775941


11-Mar Friday Night 19:00 171 15 90 276 12.620415


13-Mar Sunday Night 19:30 140 56 54 250 11.43153533

14-Mar Monday Night 19:00 167 52 54 273 12.48323658



17-Mar Thursday Night 19:00 164 12 10 70 256 11.70589218

18-Mar Friday Night 19:30 175 4 76 255 11.66016604


20-Mar Sunday Night 19:30 150 16 70 236 10.79136935

21-Mar Monday Night 19:30 151 13 77 241 11.02000006




25-Mar Friday Night 19:30 138 44 82 264 12.07170131


27-Mar Sunday Night 19:30 168 10 24 202 9.236680547

28-Mar Monday Night 19:30 190 63 41 294 13.44348555




Max. 15.95842332 MW

TimeDate Day Zone

1 2 3 4 5 6 7 8 Total Total


1-Mar Tuesday Night 19:30 65 75 85 285 105 110 220 75 1020 46.64066415


3-Mar Thursday Night 19:30 65 68 82 280 100 102 210 75 982 44.90307078

4-Mar Friday Night 19:30 65 72 85 285 100 102 225 78 1012 46.27485502

5-Mar Saturday Night 19:00 65 65 83 285 100 100 200 67 965 44.12572637

6-Mar Sunday Night 19:30 60 75 75 260 105 105 210 60 950 43.43983425

7-Mar Monday Night 19:30 60 65 85 285 90 100 200 65 950 43.43983425




11-Mar Friday Night 19:00 60 65 80 295 100 100 210 70 980 44.81161849


13-Mar Sunday Night 19:30 65 72 270 110 172 220 65 974 44.53726165

14-Mar Monday Night 19:00 70 70 85 295 100 105 220 78 1023 46.77784257




18-Mar Friday Night 19:30 70 82 78 290 105 108 220 78 1031 47.1436517


20-Mar Sunday Night 19:30 60 78 75 260 100 100 205 65 943 43.11975126

21-Mar Monday Night 19:30 65 82 88 290 100 112 220 82 1039 47.50946083


23-Mar Wednesday Off Peak 3:00 45 25 45 160 55 55 120 40 545 24.92074702

23-Mar Wednesday Day 11:30 55 25 45 290 60 65 180 55 775 35.43775952



25-Mar Friday Night 19:30 70 75 90 295 10 110 230 83 963 44.03427409


27-Mar Sunday Night 19:30 60 65 70 260 5 100 220 60 840 38.40995871

28-Mar Monday Night 19:30 65 75 88 390 5 110 220 81 1034 47.28083012




Max. 47.78382 MW

TimeDate Day Zone

Table 5.4: Night Peak load analysis of Galle GSS

Table 5.5: Night Peak load analysis of Hambantota GSS

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Matara GSS

Ratnapura GSS

1 2 3 4 5 6 7 8 Total Total





4-Mar Friday Night 19:30 420 280 102 185 128 205 225 104 1649 75.40240704


6-Mar Sunday Night 19:30 426 280 105 180 128 190 225 107 1641 75.03659791

7-Mar Monday Night 19:30 426 280 100 175 130 195 225 105 1636 74.8079672




11-Mar Friday Night 19:00 422 275 100 170 135 178 212 97 1589 72.65883856


13-Mar Sunday Night 19:30 422 275 172 175 125 190 25 105 1489 68.08622443

14-Mar Monday Night 19:00 423 280 105 170 140 185 230 104 1637 74.85369334




18-Mar Friday Night 19:30 419 285 108 180 135 188 237 105 1657 75.76821617


20-Mar Sunday Night 19:30 422 275 100 165 128 175 222 101 1588 72.61311242

21-Mar Monday Night 19:30 420 290 112 180 140 205 240 108 1695 77.50580954




25-Mar Friday Night 19:30 420 280 110 180 135 190 240 110 1665 76.1340253


27-Mar Sunday Night 19:30 422 270 100 175 130 170 226 102 1595 72.93319541

28-Mar Monday Night 19:30 418 255 110 175 132 215 221 101 1627 74.39643193




Max. 77.50581 MW

TimeDate Day Zone

1 2 3 4 5 6 7 8 Total Total


1-Mar Tuesday Night 19:30 153 51 -36 27 31 12 20 258 11.79734446

2-Mar Wednesday Night 19:30 158 50 -24 38 56 12 16 306 13.99219924

3-Mar Thursday Night 19:30 148 52 25 30 48 11 5 319 14.58663908

4-Mar Friday Night 19:30 140 49 -48 9 54 11 18 233 10.65419093

5-Mar Saturday Night 19:00 145 48 -38 24 48 12 -11 228 10.42556022

6-Mar Sunday Night 19:30 157 49 -27 28 55 12 12 286 13.07767642

7-Mar Monday Night 19:30 145 50 26 32 58 12 -8 315 14.40373452



10-Mar Thursday Night 19:30 164 55 -19 37 97 13 16 363 16.5985893

11-Mar Friday Night 19:00 159 54 -15 34 65 11 21 329 15.04390049

12-Mar Saturday Night 19:30 155 50 -49 31 -96 10 17 118 5.395684676

13-Mar Sunday Night 19:30 43 44 -52 10 36 10 8 99 4.526887991

14-Mar Monday Night 19:00 77 58 -43 22 89 12 9 224 10.24265566




18-Mar Friday Night 19:30 35 52 -19 77 98 12 17 272 12.43751044

19-Mar Saturday Night 19:30 33 45 -17 75 66 12 16 230 10.5170125

20-Mar Sunday Night 19:30 30 45 -61 73 36 10 -2 131 5.990124513

21-Mar Monday Night 19:30 31 69 -173 -45 67 11 -20 -60 -2.74356848

22-Mar Tuesday Night 19:30 72 53 -81 61 45 12 -27 135 6.173029078

23-Mar Wednesday Night 19:30 64 49 -173 -33 39 11 -73 -116 -5.30423239

24-Mar Thursday Night 19:30 68 54 -71 48 30 12 -16 125 5.715767665

25-Mar Friday Night 19:30 67 51 -199 -28 43 11 -73 -128 -5.85294609

26-Mar Saturday Night 19:00 69 52 -151 22 42 11 -73 -28 -1.28033196

27-Mar Sunday Night 19:30 65 52 -52 62 49 11 -62 125 5.715767665

28-Mar Monday Night 19:30 63 50 -30 -33 35 10 -73 22 1.005975109

29-Mar Tuesday Night 19:00 69 54 -206 -38 35 11 -74 -149 -6.81319506

30-Mar Wednesday Night 19:30 68 58 -75 69 45 12 -44 133 6.081576796


Max. 16.59859 MW

TimeDate Day Zone

Table 5.6: Night Peak load analysis of Matara GSS

Table 5.7: Night Peak load analysis of Ratnapura GSS

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There are three Generating Plants in this island.

I. Samanalawewa PS (Frequency Controlling Generator)

II. ACE Embilipitiya PS

III. ACE Matara PS

Table 5.8: Generation Capacity of the Island

Generation Plant Capacity / MW

Samanalawewa PS 2 x 60 120

ACE Embilipitiya PS 100 100

ACE Matara PS 4 x 5 20

Total Generation 240

Table 5.9: Load Demand of the Island

Grid Substation Demand / MW

Balangoda GSS 33.56

Deniyaya GSS 17.51

Embilipitiya GSS 21.03

Galle GSS 47.78

Hambantota GSS 15.96

Matara GSS 77.51

Ratnapura GSS 16.60

Total Demand 229.95

As per the analysis 10 MW generations is excess in this island, but analysis revealed that

islanding operation fails at all the time when New Laxapana – Balangoda Line 1 and 2

trips. When considering typical plant dispatch, ACE Embilipitiya plant is dispatching 97

MW, Samanalawewa Generator 1 and 2 is dispatching 20 MW and 40 MW or wise versa.

Then total generation in this island becomes 177 MW. So normal plant dispatch condition

there is a generation deficiency of 53 MW for this island and it receives via New Laxapana

– Balangoda Line 1 and 2.

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Figure 5.2: Load Flow diagram of Balangoda 132 kV Busbar.

So with the proposed load shedding scheme simulate the system with above estimated

Generation and load condition.

Table 5.10: Load Shedded capacity of each GSS

Grid Substation Load Shedded / MW

Balangoda GSS Not Assigned

Deniyaya GSS Not Assigned

Embilipitiya GSS Not Assigned

Galle GSS 7.5

Stage 1 4

Stage 4 3.5

Hambantota GSS Not Assigned

Matara GSS 23

Stage 1 14.5

Stage 4 8.5

Ratnapura GSS Not Assigned

Total Shedded Load 30.5

of 60

Deficit = (53 – 30.5) = 22.5 MW

Figure 5.3: Frequency response of the System

From above simulation results it can be identified that minimum frequency of the island

goes below 47 Hz for 2.5 seconds, where Generators will trip from Under Frequency Trip

Setting.

Table 5.11: Under Frequency Trip Settings

Generation Plant Under Frequency Trip Setting

Frequency Time Delay

Samanalawewa PS 47 Hz 0 Sec

ACE Embilipitiya PS 47 Hz 2.1 Sec

ACE Matara PS 47 Hz 0.24 Sec

So this Island operation is unstable even though simulation shows as stable since all the

above generators will trip from their Under Frequency Trip Setting. (There is no facility to

simulate the system with Under Frequency Trip Settings of the generators by using

available software license)

Finally, Simulate was carried out with more Loads added to the Load Shedding stages,

of 60

Table 5.12: Load Shedded capacity of each GSS after modification


Balangoda GSS 13.5

Stage 1 4.5

Stage 2 5

Stage 3 4

Deniyaya GSS 7.5

Stage 3 7.5

Embilipitiya GSS 8

Stage 1 1

Stage 2 7

Galle GSS 16.5

Stage 1 5

Stage 2 3

Stage 3 8.5

Hambantota GSS Not Assigned

Matara GSS 20.25

Stage 1 14.5

Stage 4 5.75

Ratnapura GSS Not Assigned

Total Shedded Load 65.75

Deficit = (53 – 65.75) = -12.75 MW

of 60

Figure 5.4: Frequency response of the System after modification of Load Shedding

Feeders.

Figure 5.5: Voltage response of the Busbars

Since the frequency stabilized at 49.25 Hz and bus voltages are within acceptable limits

(0.9 Pu – 1.1 Pu [2]) after Load Shedding operation, Samanalawewa Generator can keep

this system alive, which makes this Islanding Operation Successful.

of 60

Let’s also consider New Laxapana – Balangoda line loading when Load Shedding operates

up to stage 4 due to system disturbance outside the island. So under typical plant dispatch

condition 65.75 MW generation will be available more than loads in this island and will be

flow into the New Laxapana busbar via New Laxapana – Balangoda line. This is equal to

290 A. Since single line can carry 420 A hence both lines can carry 840 A, this island will

operate perfectly also in above stated condition.

Finally it can be identified that Islanding Operation is possible with Samanalawewa

Frequency controlling machine after the Load Shedding Feeders of the following Grid

Substation are arranged such a way that it will shed equal or more than below proposed

MW values in each Load Shedding stage.

Table 5.13: Proposed Load Shedded capacity of each GSS in the island

Grid Substation Existing Load Shedding

Amount / MW

Proposed Load Shedding

Amount / MW

Balangoda GSS - 13.5

Stage 1 - 4.5

Stage 2 - 5

Stage 3 - 4

Deniyaya GSS - 7.5

Stage 3 - 7.5

Embilipitiya GSS - 8

Stage 1 - 1

Stage 2 - 7

Galle GSS 7.5 16.5

Stage 1 4 5

Stage 2 - 3

Stage 3 3.5 8.5

Hambantota GSS - -

Matara GSS 23 20.25

Stage 1 14.5 14.5

Stage 4 8.5 5.75

Ratnapura GSS - -

Total Shedded Load 30.5 65.75

It is necessary to reduce above increased MW value (35.25 MW) from the rest of the

network to maintain the total load shedding step size of each stage equal.

of 60

5.3. Tripping of 132 kV Pannipitiya – Matugama Line and Pannipitiya – Horana

Line.

Figure 5.6: Network Configuration of the Island

When this incident happens following Grid Substations are separated from the main

network.

I. Ambalandoga GSS

II. Horana GSS

III. Matugama GSS

IV. Panadura GS

of 60

Load Study had been carried out to find the total load of the above Grid Substations.

Off Peak, Day Peak and Night Peak data have been analyzed and find out that Night Peak

load is always higher than off peak and Day peak. So following tables will include Night

Peak load analysis only.

Ambalangoda GSS

1 2 3 4 5 6 7 8 Total Total





4-Mar Friday Night 19:30 85 184 49 318 14.540913


6-Mar Sunday Night 19:30 87 187 52 326 14.906722

7-Mar Monday Night 19:30 82 174 47 303 13.855021




11-Mar Friday Night 19:00 85 185 51 321 14.678091

12-Mar Saturday Night 19:30 88 189 0 52 329 15.0439

13-Mar Sunday Night 19:30 87 191 51 329 15.0439

14-Mar Monday Night 19:00 110 189 15 314 14.358008




18-Mar Friday Night 19:30 86 198 49 333 15.226805


20-Mar Sunday Night 19:30 86 188 46 320 14.632365

21-Mar Monday Night 19:30 78 181 59 318 14.540913




25-Mar Friday Night 19:30 81 301 58 440 20.119502


27-Mar Sunday Night 19:30 78 285 132 495 22.63444

28-Mar Monday Night 19:30 78 299 132 509 23.274606




Max. 23.6861 MW

Date Day Zone Time

Table 5.14: Night Peak load analysis of Ambalangoda GSS

of 60

1 2 3 4 5 6 7 8 9 10 Total Total

A A A A A A A A A A A MW

1-Mar Tuesday Night 19:30 33 68 22 183 73 60 93 186 121 151 990 45.26888

2-Mar Wednesday Night 19:30 32 91 23 190 76 59 93 192 128 159 1043 47.69237

3-Mar Thursday Night 19:30 31 82 23 185 75 62 92 201 125 151 1027 46.96075

4-Mar Friday Night 19:30 6 78 32 174 64 57 84 178 112 145 930 42.52531

5-Mar Saturday Night 19:00 94 51 20 109 70 50 71 165 115 142 887 40.55909

6-Mar Sunday Night 19:30 95 73 23 119 75 55 87 188 123 153 991 45.31461

7-Mar Monday Night 19:30 93 70 21 108 71 48 72 173 111 140 907 41.47361




11-Mar Friday Night 19:00 94 92 21 111 72 52 90 186 119 151 988 45.17743


13-Mar Sunday Night 19:30 96 64 23 117 72 54 89 191 122 150 978 44.72017

14-Mar Monday Night 19:00 95 71 22 121 71 66 87 194 103 173 1003 45.86332




18-Mar Friday Night 19:30 99 82 25 120 76 56 95 195 123 153 1024 46.82357


20-Mar Sunday Night 19:30 93 55 24 112 67 47 80 169 118 149 914 41.79369

21-Mar Monday Night 19:30 90 66 22 111 76 55 94 200 125 156 995 45.49751




25-Mar Friday Night 19:30 103 90 23 121 76 56 97 205 129 158 1058 48.37826


27-Mar Sunday Night 19:30 96 84 23 43 77 58 92 181 125 151 930 42.52531

28-Mar Monday Night 19:30 93 37 22 36 75 61 96 194 119 159 892 40.78772




Max 48.3783 MW

Date Day Zone Time

Horana GSS

1 2 3 4 5 6 7 8 Total Total





4-Mar Friday Night 19:30 10 119 229 138 72 34 432 71 1105 50.52739


6-Mar Sunday Night 19:30 6 126 195 108 75 38 429 73 1050 48.01245

7-Mar Monday Night 19:30 10 130 223 108 69 19 420 68 1047 47.87527




11-Mar Friday Night 19:00 8 64 278 140 89 41 430 71 1121 51.25900


13-Mar Sunday Night 19:30 6 119 221 118 81 40 437 72 1094 50.02440

14-Mar Monday Night 19:00 9 123 270 146 93 43 424 71 1179 53.91112




18-Mar Friday Night 19:30 7 139 255 145 90 43 430 74 1183 54.09403


20-Mar Sunday Night 19:30 0 126 196 123 78 39 431 76 1069 48.88125

21-Mar Monday Night 19:30 6 136 274 148 91 40 437 78 1210 55.32863




25-Mar Friday Night 19:30 8 128 271 153 90 43 438 73 1204 55.05427


27-Mar Sunday Night 19:30 6 122 217 127 88 44 445 71 1120 51.21328

28-Mar Monday Night 19:30 9 126 269 162 92 44 316 70 1088 49.75004




Max 55.4658 MW

Date Day Zone Time

Mathugama

Table 5.15: Night Peak load analysis of Horana GSS

Table 5.16: Night Peak load analysis of Mathugama GSS

of 60

After this incident Panadura GSS has no feeding, so its load study is not done.

There are two Generating Plants in this island.

I. Kukule PS (Frequency Controlling Generator)

II. ACE Horana PS

Table 5.17: Generation Capacity of the Island

Generation Plant Capacity / MW

Kukule PS 2 x 35 70

ACE Horana PS 4 x 5 20

Total Generation 90

Table 5.18: Load Demand of the Island

Grid Substation Demand / MW

Ambalangoda GSS 23.69

Horana GSS 55.47

Mathugama GSS 47.38

Total Demand 126.54

As per the analysis 36 MW generations deficiency is in this island, so with proposed load

shedding scheme simulate the system for above Generation and load condition.

Table 5.19: Load Shedded capacity of each GSS


Ambalangoda GSS 3

Stage 1 3

Horana GSS 8

Stage 3 2

Stage 4 6

Mathugama GSS 15

Stage 1 4

Stage 2 4

Stage 3 7

Total Shedded Load 26

of 60

Deficit = (36 – 26) = 10 MW

Figure 5.7: Frequency response of the System

It can be identified that this System is unstable.

Then simulate with more Loads added to the Load Shedding stages and also priority given

to Stage 1 and 2.

Table 5.20: Load Shedded capacity of each GSS after modification


Ambalangoda GSS 4

Stage 1 4

Horana GSS 20

Stage 1 14

Stage 2 6

Mathugama GSS 26

Stage 1 14

Stage 2 4

Stage 3 8

Total Shedded Load 50

of 60

Deficit = (36 – 50) = -14 MW

Figure 5.8: Frequency response of the System after modification of Load Shedding

Feeders.

Since the frequency stabilized at 49.90 Hz and bus voltages are within acceptable limits

(0.9 Pu – 1.1 Pu [2]) after Load Shedding operation, Kukule Generator can keep this island

alive and which makes this Islanding Operation Successful.

Let’s also consider Pannipitiya – Matugama Line, Pannipitiya – Horana Line and Horana

- Matugama Line loading when Load Shedding operates up to stage 3 due to system

disturbance outside the island. So under typical plant dispatch condition 61 MW generation

will be available more than loads in this island and will be flow into the Pannipitiya busbar

via above mentioned lines (In Panadura GSS 11 MW rejects from Load Shedding). This is

equal to 267 A. Since single line can carry 630 A [10] and hence total of 1260 A, this

island will operate perfectly also in above stated condition.

Finally it can be identified that Islanding Operation is possible with Kukule Frequency

controlling after the Load Shedding Feeders of the following Grid Substation are

rearranged such a way that it will shed equal or more than below proposed MW values in

each Load Shedding stage.

of 60

Table 5.21: Proposed Load Shedded capacity of each GSS in the island

Grid Substation Existing Load Shedding

Amount / MW

Proposed Load Shedding

Amount / MW

Ambalangoda GSS 3 4

Stage 1 3 4

Horana GSS 8 20

Stage 1 - 14

Stage 2 - 6

Stage 3 2 -

Stage 4 6 -

Mathugama GSS 15 26

Stage 1 4 14

Stage 2 4 4

Stage 3 7 8

Total Shedded Load 26 50

It is necessary to reduce above increased MW value (24 MW) from the rest of the network

to maintain the total load shedding step size of each stage equal.

of 60

Chapter 6

CONCLUSION & RECOMMENDATION

Load shedding schemes have been deployed almost universally in the power systems to

provide the fastest possible remedial action in the event of severe generation – demand

mismatch. The under frequency load shedding scheme must be modified to adapt the

changes in the power system such as commissioning of large generators, increase in

demand and changing the operating conditions. This dissertation discussed about designing

of new under frequency load shedding scheme align with the development of Sri Lankan

power system.

In Chapter 4, whole Sri Lankan power system has been modeled using the PSS®E

software and Existing Load Shedding scheme was simulated using this model. Then

improve the Load shedding scheme settings step by step to reduce the rejecting loads from

the Load shedding scheme while maintaining the stability of the system. After analyzing

simulation 1 to 8, Proposed Load Shedding scheme is shown in Table 6.1.

Table 6.1: Proposed New Load Shedding Scheme

Stage Load to be




III 5 5% Load on only freq. based 48.25 Hz + t=150 ms

IV 6 6% Load on only freq. based 48.00 Hz + t=150 ms

V 10

8% Load on only freq. based 47.50 Hz + t=150 ms

OR

2% Load on only freq. based 49 Hz AND df/ft =


VI 10


49 Hz AND df/ft =

0.85 Hz/Sec

Load reduction from Load Shedding tripping after implementing the above scheme and be

found on Table 6.2.

of 60

Table 6.2: Saved Load from Proposed New Load Shedding Scheme

Further, due to present network configuration after certain power System failures some

part of the system isolates from the main system and operates in islanding mode. This

islanding operation fails at all the times due to unbalance of the generation and load. This

dissertation also discussed in what way to overcome above situation by rearranging 33 kV

Load Shedding Feeders in the Sri Lankan network.

In Chapter 5, it was identified possible islanding operations and analyzed the stability of

them with proposed load shedding scheme. Finally rearrange the 33 kV load shedding

feeders in the Sri Lankan network to facilitate islanding operation by analyzing the

stability of the islands using simulation.

Finally it can be identified that Islanding Operation is possible with Samanalawewa and

Kukule Frequency controlling machines after the Load Shedding Feeders of the following

Grid Substation are arranged such a way that it will shed equal or more than Table 6.4

proposed MW values in each Load Shedding stage.

Load reduction with proposed Load Shedding feeder arrangement of each island can be

found on Table 6.3.

Table 6.3: Saved Load from proposed feeder arrangement in each island

of 60

Table 6.4: Proposed Load Shedded capacity of each GSS in the islands

Grid Substation Proposed Load Shedding Amount / MW

Balangoda GSS 13.5

Stage 1 4.5

Stage 2 5

Stage 3 4

Deniyaya GSS 7.5

Stage 3 7.5

Embilipitiya GSS 8

Stage 1 1

Stage 2 7

Galle GSS 16.5

Stage 1 5

Stage 2 3

Stage 3 8.5

Matara GSS 20.25

Stage 1 14.5

Stage 4 5.75

Ambalangoda GSS 4

Stage 1 4

Horana GSS 20

Stage 1 14

Stage 2 6

Mathugama GSS 26

Stage 1 14

Stage 2 4

Stage 3 8

Finally it is recommended to analyze and revise the under frequency Load Shedding

scheme at least once in two years under consideration of continuous changes of the

characteristics of the Sri Lankan power system.

of 60

Reference list

[1] Walter A. Elmore, “Protective Relaying Theory and Applications”, Marcel Deckker Inc publications, New York, 10016, pp 345-355.

[2] Ceylon Electricity Board, “CEB Policy on Power System Operations”, July 2009.

[3] Failure Details, Ceylon Electricity Board, 2011.

[4] Siemens Energy Inc., “PSS®E 32.0 Program Operation Manual”, Siemens Power

Technologies International, New York, USA, 2009.

[5] Ceylon Electricity Board, “Coal Fired Thermal Development Project West Coast -

CEB Transmission Connection Power System Analysis Studies”, 2009.

[6] Ceylon Electricity Board, “Bidding Document, Part B-Technical Specification”,

vol. 5, pp. 12-62, 2011.

[7] PUCSL, “Findings of the committee appointed to investigate the power system failures on 9th October 2009”, 2009.

[8] Alstom Grid, “Network Protection & Automation Guide”, Alstom Grid Worldwide Contact Centre, France, 2011.

[9] P.Kundur, “Power System Stability and Control”, McGraw-Hill, New York, 1994.

[10] Ceylon Electricity Board, “Long Term Transmission Development Plan 2011-

2020”, July 2011.

[11] D.D.P. Yasarathna, “Review the Existing Load Shedding Scheme used in Sri Lanka

power system and Design a new Load Shedding Scheme”, University of Moratuwa,

Sri Lanka, 2002

[12] Alejandro P. Ojeda, “A Load Shedding Scheme for Inverter Based Microgrids”, Massachusetts Institute of Technology, USA, 2011

of 60

[13] R.L. Muttucumaru, “A new algorithm for load shedding in an industrial

cogeneration power plant”, Victoria University Of Technology, Australia, 1999.

[14] Poonam M. Joshi, “Load shedding algorithm using voltage and frequency data”,

The Graduate School of Clemson University, USA, 2007

[15] Yunfei Wang, “Advanced load shedding scheme for voltage collapse prevention”,

University of Alberta, Canada, 2011.

[16] Shahrzad Rostamirad, “Intelligent Load Shedding Scheme for Frequency Control

in Communities with Local Alternative Generation and Limited Main Grid

Support”, The University of British Columbia, 2009

[17] Haibo You, Vijay Vittal, Juhwan Jung, Chen-Ching Liu, Massoud Amin, Rambabu

Adapa,“An Intelligent Adaptive Load Shedding Scheme”,14th PSCC, June 2002

[18] Ding Xu, Adly A.Girgis, “Optimal Load Shedding Strategy in Power Systems with

Distributed Generation”, Clemson University, USA

[19] A.A. Mohd Zin, H.Mohd Hafiz, M.S Aziz, “A Review of Under Frequency Load Shedding Scheme on TNB System,” National Power & Energy Conference 2001

Proceedings), Malayia, pp 170-174, 2004.

[20] A. Gjukaj, G. Kabashi, G.Pula, N. Avdiu, B. Prebreza, “ Re-Design of Load

Shedding Schemes of the Kosovo Power System,” Worl Acadami of Science, Engineering and Technology 74, pp 262-266, 2011.

[21] Ceylon Electricity Board, “Statistical Digest 2011”.

of 60

Appendix A: Load Flow Network Diagram of HMOP condition

1130POLPI-1

132.2

1170SAMAN-1

129.3

1210BOWAT-1

132.2

1770KIRIB-1

2220KOTMA-2

222.3

2230VICTO-2

224.4

2240RANDE-2

225.4

2250RANTE-2

225.4

32.7

32.6

3620BADUL-3

32.8

12.6

4252RANTE-G2

1790RATMA-1

132.4

1300KELAN-1

132.7

132.6

4760COL_F-11

10.9

4750COL_E-11

131.1

3500KOSGA-3

33.1

33.1

3670MATARA-3

132.0

33.3

132.0

3520NUWAR-3

33.3

1520NUWAR-1

130.7

1620BADUL-1

130.5

131.2

3540ORUWA-3

33.0

1670MATARA-1

125.8

132.3

1660EMBIL-1

1100LAX-1

132.0

131.3

3200UKUWE-3

3530THULH-3

33.0

32.7

217.2

2300KELAN-2

216.2

1540ORUWA-1

132.1

1530THULH-1

131.2

132.3

218.4

33.1

3860MADAM-3

132.6

225.3

1705NEWANU-1

133.5

1700ANURA-1

1850PANAD-1

132.4

1800MATUG-1

132.6

132.6

1240VAVUN-1

3240VAVUN-33

32.9

32.8

32.7

127.4

3400HAMBA-33

33.0

3660EMBIL-3

32.9

32.7

33.4

1160INGIN-1

127.0

3160INGIN-3

125.7

33.3

3700ANURA-3A

216.2

32.9

33.0

1710TRINC-1

33.0

132.1

32.9

32.9

131.8

32.7

3690HABAR-3

33.0

1740RATNAP-1

129.633.2

1595KHD -1

132.2

133.3

1600BOLAW-1

131.032.6

132.2

32.6

1840JPURA_1

132.4

3840JPURA_3

131.9

132.0

132.3

10.9

4435COL_A_11

3890DEHIW_3

33.0

3800MATUG-3

33.0

1810PUTTA-1

135.1

33.7

2.8

0.92.8

0.9

3.8

9.6

3.8

9.6

5.2

9.9

5.2

9.9

23.0

3.823.0

3.8

25.5

5.1

25.3

3.9

40.2

1.1

40.2

1.1

0.6

9.230.8

14.3

5.6

3.0

18.4

9.4

5.4

24.0

14.6

17.3

7.2

21.8

9.8

3.9

12.0 6.6

8.1

5.6

8.2

17.3

28.6

5.5

28.3

4.6

9.6

7.1

5.1

10.4

1.2

10.4

1.2

14.6

3.0

14.4

5.0

23.1

3.1

23.1

15.1

9.0

3.6

3.6

2.222.9

2.1

0.0

0.0

0.0

6.7

11.4

13.9

4.5

10.0

4.7

0.0

1.9 0.0

1.9

0.0

0.0

0.0

0.0

104.2

34.6

103.5

42.8

104.2

34.6

103.5

42.8

2.8

0.2

2.8

0.2

2.6

1.4

0.1

16.7

3.4

64.5

46.1

64.5

46.1

0.0

43.9

43.9

6.1

3.1

3.3

17.3

10.9 17.3

10.9

34.6

21.8

7.8

2.6

1.2

0.4

0.0

0.0

21.5

3.621.5

3.6

0.0

0.5

0.0

0.0

40.6

40.1

0.0 0.0

0.0

0.4

1.8

11.1

6.9

0.4

1.8

23.0

12.6

5.4

7.6

19.5

75.9

27.7

76.1

75.9

27.7

76.1

27.1

22.3

1.9

9.6

9.6

0.7

13.3

1.2

13.2

2.3

1.3

0.2

1.3

0.2

2.5

4.5

48.0

44.2

48.1

48.0

44.2

48.1

43.0

20.6

0.0

0.0

23.4

18.9

30.0

5.430.0

5.4

27.3

17.8

0.2

89.2

6.1

89.1

6.689.2

6.1

89.1

6.6

77.1

13.777.1

13.7

9.5

54.9

28.9 54.9

28.9

6.8

0.0

12.0

20.0

26.2

14.8 46.9

19.4

67.0

12.8

20.6

11.3

11.3

6.7

6.2

3.6

1.2

6.3

6.3

2.8

12.6

4.6

19.0

8.4

16.7

19.5

6.7

19.0

2.3

19.2

0.3

18.4

10.7

9.2

5.3

9.2

5.3

1.0

000 30.8

14.8

8.1

8.1

8.2

0.0

16.4

1.6

16.4

1.6

8.3

7.3

0.2

7.3

0.2

23.0

53.8

23.0

51.8

23.0

53.8

23.0

51.8

22.2

30.5

30.5

4.9

4.1

2.9

8.4

1

23.1

8.2

L

37.0

17.0

H

1

1

2.2

1

2.9

1

20.6

10.0

1 25.0

7.0R

1

1 22.9

14.1

1 23.4

16.2

1

17.3

6.7

1

24.0

13.4

1

15.6

8.1

1

17.3

5.6

1

1 34.6

1 4.5

2.3

1 10.0

1 0.0

1

1 34.6

20.1

1

1

0.0

0.0

1

18.4

9.4

1

24.5

1

7.8

2.4

SW 0.0

1

1

1.2

1

0.0

1 12.6

4.3

23.2

8.2

L

2

37.3

17.0

H

2

25.0L

60.0

25.0L

2

24.0

3.0L

2 24.5

2.0L

1

1

2 40.0

26.0H

1

2

1

22.9

16.7

SW

19.7

1

23.0

11.5

1 22.9

11.0

1

7.5

4.5

SW

1

20.6

1

25.7

1

0.0

0.0

1

27.3

16.6

1

24.0

13.3

1

1

9.5

5.7

1 8.4

6.2

1

1

1 13.9

8.6

1 20.0

11.4

1

20.6

9.0

1 26.2

10.7

1

11.7

6.1

2

5.4R

1

1

30.0

5.4R

1

19.0

11.0SW

1

16.7

8.4

1

1

18.4

1

1 0.0

1 22.3

12.3

1

1.1

1 83.0

SW

10.4

0.033.0

4.5

33.0

6.7

5.6

0.0

3121WIMAL-3B

0.0

60.0

26.9

3780VALACH_3

33.0

131.4

1780VALACH_1

6.8

19.9

0.4

16.2

131.7

27.1

6.6

3.2

3560PANNI-3

30.0

1590SAPUGA-1

18.5

3830VEYAN-33

1250RANTE-1

26.5

75.3

26.5

26.0

11.6

26.0

11.4

18.9

15.7

4.5

26.0

11.6

26.0

15.7

3.3

0.3

2.2

22.9

1 1.6

1.0

25.9

11.7

14.1

25.9

13.2

8.6

3600BOLAW-3

1

1

10.0

1

SW 0.0

1.9

20.0

3.9

19.6

6.5

3.6

1.2

8.4

5.0L

16.0

25.7

18.8

9.3

1 10.0

0.0L

6.2

1

1

10.0

1

1

5.0

0.0R

1

14.5

10.1

4.1

1

129.7

132.5

3880AMBALA

32.8

9.6

6.0

4.8

3.0

4.8

1

9.6

5.8

1

15.6

15.0

7.5

1900PNNALA

11.2

0.9

1.6

14.7

9.1

1910ANIYA

3910ANIYA

15.6

10.0

16.2

1

16.2

10.0

131.7

32.9

1

19.5

10.0

SW

0.0

SW

0.0

20.6

6.7

6.1

6.7

1.6

0.0

11.1

7.9

6.5

3710TRINC-3

SW

1

2

0.0

0.0

0.0

0.0

0.7

3250RANTE-3

3630BALAN-3

0.0

L

0.0

33.3

23.8

10.4

2.3

9.1

3565PANNI-C

10.2

10.0

15.9

2.0

32.6133.3

7.3

2.5

1 7.3

2.3

32.8

1.1 1.1

0.6

13.0

131.4

14.1

5.014.1

5.0

3440KATUNA-3

32.7

1

12.7

9.7

0.0SW

0.0

1 0.0

0.0

3

3811CEMENT

32.8

16.2

131.1

11.2

6.8

6.8

86.5

30.7

86.5

30.7

87.2

14.5

87.2

14.5

8.2

1

1 10.0

0.0L

20.0

2580KOTUG-2

6.1

3.5

SW 0.0

1

219.2

32.6

18.9

216.1

32.9

11.4

4.5

14.1

1

1.3

13.9

7.8

1920SUB-C

132.7

4920SUB C-11

4.0

1

11.0

1760COL_F-1

8.0

33.2

8.0

4.4

11.0

1500KOSGA-1

15.1

22.2

13.7

3.5

13.6

5.0

10.4

8.2

23.0

3.9

22.7

2.0

23.0

3.9

19.8

1

190.0

1.0

000 174.3

29.1

4811PUTT COAL-2

19.8

1 0.0

0.0

43.0

1 15.6

11.2

52.9R

11.4

12.0

0.3

1651GALLE-2

10.9

43.5

0.0

0.0

0.0

0.0

16.7

29.3

32.8

1

5.7

3.2

3.3

1

1

1

1

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

4310SAPUG-P

11.0

1 48.0

32.0H

11.0

1

26.5

20.0H

2 35.5

20.0H 48.0

27.0 62.0

31.0

0.6

32.6

1

8.0

1.0

7.3

15.4

2.8

7.3

4.7

8.0

2560PANNI-2

132.2

2

60.0

19.4R

3

60.0

19.4R

2.8

1550KOLON-1 2

3.4

6.7

0.0

10.9

3302KELAN-3B

1650GALLE-1

2.4

9.2

20.6

4.6

20.6

4.6

1

2.5

3405HAMBA-33

1400HAMBA-1

127.6

4.0

3340BELIATT-3

126.7

1.1

1340BEATT-1

15.3

2.9

32.8

129.8

3.1

19.5

1150AMPA-1

3150AMPA-3

4251RANTE-G1

12.5

1120WIMAL-1

3120WIMAL-3

1110N-LAX-1

6.1

3.3

3650GALLE-3

129.5

3651GALLE-3B

6.7

129.3

1640DENIY-1

3640DENIY-3

3740RATNAP-3

1630BALAN-1

1140CANYO-1

132.0

1.4

1690HABAR-1

3245VAVUN-33

2.3

0.3

1200UKUWE-1

8.5

24.6

3770KIRIB-3

33.1

SW

130.6

0.0

5.6

132.8

131.1

22.7

2.0

2705NEWANU-2

3810PUTTA-3

0.0

4305KERAWALA-G

14.4

1680KURUN-1

3680KURUN-3

SW

75.3

32.8

1860MADAM-1

131.2

4810PUTT COAL-1

1580KOTUG-1

2830VEYAN-2

1830VEYAN-1

13.5

5.7

32.6

3701ANURA-3B

SW

2810PUTTALAM-PS

224.4

1.0

430

11.2

3581KOTU_NEW-3

3580KOTUG-3

32.6

3510SITHA-33

23.4

11.7

1440KATUNA-1

3900PANNAL

15.9

0.0

24.0

14.1

3590SAPUG-3A

33.0

4311SAPUG-P2

1310SAPUG-1P

1870K_NIYA-1

3870K-NIYA-3

SW 0

.0

3820ATURU-3

Present Transmission Network

0.9

1880AMBALA

10.8

1420HORANA_1

131.8

3420HORANA_3

132.2

1890DEHIW_1

20.6

1435COL_A_1

7.0

7.0

9.0

13.9

3301KELAN-3A

30.5

0.0

15.1

3850PANAD-3

12.3

3790RATMA-3A 1560

PANNI-1

10.9

0.0

0.2

1510SITHA-1

15.1

3550KOLON-3A

32.7

3551KOLON-3B

8.0

22.9

1750COL_E-1

2570BIYAG-2

2305KERAWALA_2

218.4

14.4

4306KERAWALA-S

0.9667

* 53.0

2.0

7.5

* 1

2.3

0.9667

1.0000 1.0166

* 53.0

2.0

40.7

7.5

* 1

2.3

6.3

6.3

40.7

1.0000

0.9833

3.2

17.3

4.1

* 2.8

0.7

1.0000

1.0000 0.9833

* 20.1

3.2

17.3

4.1

* 2.8

0.7

133.5

1.1000

1.0000 0.9833

* 54.6

21.5

34.3

35.1

* 2

0.4

1.0000 0.9833

* 54.6 21.5

34.3

35.1

* 2

0.4

10.6

1.0000

1.0000 1.083357.2

23.0

53.4

* 0.0

0.0

1.0000

1.0000 1.0833

* 23.0

57.2

23.0

53.4

* 0.0

0.0

* 23.0

4300GT 07

2222BARGE-2

3300KELANI-3

1.0000

1.0000 1.0493

* 48.0

44.2

48.0

41.7

* 0.0

0.0

1.0000

1.0000 1.0493

* 48.0

44.2

48.0

41.7

* 0

.0

0.0

4302KCCP ST

4301KCCP GT

4303AES GT

4304AES ST

1820ATURU-1

3570BIYAG-3

10.6

1.0000

* 20.1

3705NEWANU-3

1570BIYAG-1

1.1000

40.7

21.2

32.9

128.1

1.01661.0000

1.0

450

4430COL_I_11

19.3

1430COL_I_1

33.0

1410KUKULE-1

Bus - VOLTAGE (kV)Branch - MW/MvarEquipment - MW/Mvar

100.0%RATEA

1.050OV0.950UV

kV: <=60.000 <=120.000 <=200.000 >200.000

of 60

Appendix B: Dispatch Scenario during HMOP Condition

Machine ID MW

O/LAX-I 1 24 O/LAX-II 2 24.5 N-LAX-1 1 23.1432 N-LAX-1 2 23.2156 WIMAL-1 1 25 WIMAL-1 2 0 POLPI-1 1 37 POLPI-1 2 37.3 CANYO-1 1 30 CANYO-1 2 0 SAMAN-1 1 60 SAMAN-1 2 0 UKUWE-1 1 18 UKUWE-1 2 0 BOWAT-1 1 11 KELAN-1 1 0 KUKULE-1 1 30 KUKULE-1 2 30 KHD -1 1 46 EMBIL-1 1 40 PUTTA-1 1 83 KOTMA-2 1 0 KOTMA-2 2 60 KOTMA-2 3 60 BARGE-2 1 60.4 VICTO-2 1 0 VICTO-2 2 60 VICTO-2 3 60 RANDE-2 1 0 RANDE-2 2 40 RANTE-G1 1 25 RANTE-G2 1 0 GT 07 1 0 KCCP GT 1 0 KCCP ST 1 0 AES GT 1 0 AES ST 1 0 KERAWALA-G 1 81.3 KERAWALA-G 2 50 KERAWALA-S 3 90 SAPUG-P 1 48 SAPUG-P2 1 26.5 SAPUG-P2 2 35.5 PUTT COAL-1 1 190

Total 952.1588

of 60

Appendix C: Technical Details of Load Shedding relay

of 60

Appendix D: 33 kV Circuit Breaker Timing Test Results

design new load shedding scheme considering …

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