wind grid code for india draft

Draft Report

On

Indian Wind Grid Code

Submitted to

Centre for Wind Energy Technology

Velachery - Tambaram Main Road,

Pallikaranai, Chennai - 600 100, Tamil Nadu, INDIA

July 2009

Power Research and Development Consultants Private Limited

No 5, 11 th Cross, 2 nd Stage, West of Chord Road, Bangalore - 560086, Karnataka, INDIA. Ph: +91- 80-23192168 / 23192159, FAX: 23192210, E-mail – [email protected] Web site: www.prdcinfotech.com

Indian Wind Grid Code –Version 1.0 July 2009

Power Research and Development consultants (PRDC) Pvt. Ltd 1

Purchase Order No: C-WET/R&D/Grid Code/PR&DC/2008-09, Dated 03/03/2009

Document ref PRDC/2009-2010/C-WET/831 Signature Date

Mr. Sarasij Das

Prepared by Mr. Ramesh Pampana

Reviewed by Mr. V. Venkata Subba Rao

Approved by Dr. K. Balaraman



Preamble With due consideration of the fact of growing wind energy sector in India, a

Technical Working Group was formed by the Ministry of New and Renewable Energy

(MNRE), to formulate guidelines in addressing the technical issues/problems of

power evacuation and grid synchronization related to wind power projects.

The following are the members of the Technical Working Group:

i. Shri M.P. Ramesh, Ex-ED (C-WET) - Chairman

ii. K.P.Sukumaran, Advisor & Head, WE, MNRE - Member

iii. Shri P.S. Jagannatha Gupta, CE (Retd.), KPTCL - Member

iv. Shri R.N. Nayak, ED, PGCIL - Member

v. Chief Engineer (GM),CEA or his representative - Member

vi. Director (Transmission), Ministry of Power - Member

vii. Representative from TNEB - Member

viii. Representative from IWTMA - Member

ix. Shri S.K.Soonee, ED, PGCIL - Member

x. Director, MNRE - Member Secretary

The Technical Working Group met twice, first on19-01-2009, secondly on 17-04-2009

with regard to the requirement and development of grid code for wind power

generation in India. As a part of addressing the technical issues/problems of power

evacuation and grid synchronization related to wind power projects, the Technical

Working Group has awarded the task of “Developing of grid code for wind power

generation in India” to M/s Power Research and Development consultants (PRDC)

Pvt. Ltd, Bangalore. PRDC has formulated a draft report on the grid code for wind

power generation in India named as “Indian Wind Grid Code” which will be presented

before the committee.



Chapter 1 INTRODUCTION The Indian Electricity Grid Code (IEGC) provides the technical rules to facilitate the

operation, maintenance, development and planning of electricity grid. The objective of

IEGC is to maintain safe, reliable and disciplined operation of power system. The IEGC

guidelines and standards are to be followed by the various agencies and participants

of the power grid.

Indian power generation sector is changing its nature like elsewhere in the world with

focus on environmental impacts of conventional sources and need to encourage

renewable energy. More and more renewable energy sources, mainly wind energy, are

being integrated into the grid. Today, wind generation, whose penetration is increasing

have significant impact on Indian power grid. The IEGC as well as the state grid codes

were originally developed considering the synchronous generators generally used in

conventional power plants. Wind turbine generators (WTG) do not have the same

characteristics as synchronous generators and hence a modification or change in the

grid code is necessary. Indian Wind Grid Code (IWGC) has been developed for the

reliable and secure operation of the wind farms and their integration into the Indian

electrical system. This grid code can be used in tandem with the IEGC/State Grid code

or the IEGC and state grid codes can be amended with the provisions.

1.1 Objective

The primary objective of IWGC is to establish the technical rules which all wind

farms must comply with in relation to their planning, connection and operation on

the Indian grid.

1.2 Scope

All grid connected wind farms and those who operate the associated transmission

system are required to abide by the principles defined in the IWGC in so far as they

apply to them. The IWGC (except sections 4.6.6 and 5.10) shall come into effect

from dd/mm/yyyy. The timeline for implementing fault ride through capability

(section 4.6.6) and wind energy forecasting (section 5.10) shall be specified

separately by the concerned authority taking into account the penetration levels of

wind energy, cost of implementation and tariff structure and their usefulness in

terms of grid management strategies.



1.3 Structure of the IWGC

IWGC gives guidelines for transmission planning, grid connection and operation of

wind farms. The content of IWGC is as follows:

i) Role of various organizations and their linkages:

This chapter defines the functions of the various organizations as are relevant

to IWGC. The organizations and their linkages are defined to facilitate

development and smooth operation of regional grids.

ii) Planning code for transmission systems evacuating wind power:

This chapter provides the policy to be adopted in the planning transmission

system for wind power evacuation. The planning code stipulates the various

criteria to be adopted during the planning process.

iii) Connection code for wind farms:

This chapter specifies minimum technical and design criteria to be complied

with by wind farms connected to the system or seeking connection to the grid,

to maintain uniformity and quality across the power system.

iv) Operating code for wind farms:

This chapter describes the operational philosophy to maintain efficient, secure

and reliable grid operations of power grids having wind farms and conventional

power plants.

1.4 Non-compliance

In case of a persistent non-compliance of any of the stipulations of the IWGC by a

constituent or an agency (other than RPC, RLDC and SLDC), the matter shall be

reported by any agency/RLDC to the Member Secretary, RPC or the designated

agency. The Member Secretary, RPC or the designated agency, shall verify and

take up the matter with the defaulting agency for expeditious termination of the

noncompliance. In case of inadequate response to the efforts made by the Member

Secretary, RPC, the non-compliance shall be reported to CERC/SERC.

CERC/SERC, in turn after due process, may order the defaulting agency for

compliance, failing which; the CERC/SERC may take appropriate action. RPC or

the designated agency shall maintain appropriate records of such violations. In

case of a non-compliance of any of the stipulations of the IWGC by RLDC/SLDC or

RPC, the matter shall be reported to the CERC / SERC.

1.5 Exemptions

Any exemption from provisions of IWGC shall become effective only after approval

of the CERC/ SERC, for which the agencies will have to file a petition in advance.



1.6 Glossary and definitions

Item Definition

Act The Electricity Act, 2003

Available Active

Power

The amount of active power that the WTG could

produce based on current wind conditions.

BIS The Bureau of Indian Standards

Capacity factor The ratio of maximum generation in MW to sum of

installed capacity of individual WTGs in the Wind

Farm

CEA Central Electricity Authority of India

CERC The Central Electricity Regulatory Commission

referred to in sub-section (1) of Section 76 of the Act

CTU Central Transmission Utility means any Government

company, which the Central Government may notify

under sub-section (1) of Section 38 of the Act.

C-WET Centre for Wind Energy Technology

Dynamic VAr

compensation

An electrical facility designed for the purpose of

generating or absorbing reactive power.

Frequency

Response

The automatic adjustment of active power output

from a WTG in response to frequency changes

Grid connection

point

The point where all WTGs of a wind farm are

connected to the grid.

Point G in the following figure is referred as Grid

connection point.

Grid substation The substation to which the wind farm is connected.

Installed capacity The sum of rated generating capacity of each WTG in

a wind farm in MW

IEC The International Electro technical Commission.

IEGC Indian Electricity Grid Code



Inter State

Transmission

System (ISTS)

Inter-State Transmission System includes

i) any system for the conveyance of electricity by

means of a main transmission line from the territory of

one State to another State

ii) The conveyance of energy across the territory of an

intervening State as well as conveyance within the

State which is incidental to such inter-state

transmission of energy

iii) The transmission of electricity within the territory of

State on a system built, owned, operated, maintained

or controlled by CTU.

IWGC Indian Wind Grid Code

Plant Load Factor Plant load factor is the ratio of the energy actually

supplied by a plant (in a year) to the product of the

installed capacity and number of hours in a year.

Regional Load

Dispatch Center

(RLDC)

‘Regional Load Dispatch Centre’ means the Centre

established under sub-section (1) of Section 27 of the

Act.

Regional Power

Committee (RPC)

“Regional Power Committee” means a Committee

established by resolution by the Central Government

for a specific region for facilitating the integrated

operation of the power systems in that region.

SEB State Electricity Board including the State Electricity

Department.

SERC State Electricity Regulatory Commission.

State Load

Dispatch Centre

(SLDC)

‘State Load Dispatch Centre’ is the Centre establish-

ed under sub-section (1) of section 31 of the Act.

State Sub Load

Dispatch Centre

(SSLDC)

State's Sub Load Centre for local control at various

places in the state.

State Transmission

Utility (STU)

‘State Transmission Utility’ means the Board or the

Government Company specified as such by the State

Government under sub-section (1) of Section 39 of

the Act.

TSO Transmission System Operator



WTG Wind turbine Generator

Wind farm A wind farm is a collection of WTGs that are

connected to the grid at a common point

Wind farm operator The operator of the wind farm.

Wind farm owner Entity having legal right of the wind farm



Chapter 2

ROLE OF VARIOUS ORGANIZATIONS AND THEIR LINKAGES Chapter 2 of IEGC shall be followed.



Chapter 3

PLANNING CODE FOR TRANSMISSION SYSTEMS EVACUATING WIND POWER

This chapter comprises various aspects of transmission system planning for wind

power evacuation. Planning policy, planning criteria for transmission lines evacuating

wind power are discussed in this chapter.

3.1 Introduction

i) The planning code specifies the policy and procedures to be applied in planning

of transmission lines for evacuating wind power.

ii) Role of various organizations in wind farm planning procedure will be same as

planning procedure for conventional generators.

iii) The planning procedure shall be governed by IEGC and “Electricity Act, 2003”

3.2 Objective

The planning code for transmission systems for wind power evacuation shall be

part of bigger plan that encompasses overall grid planning.

The objectives of the planning code are:

i) To specify the principles, procedures and criteria which shall be used in the

planning and development of the transmission system evacuating wind power.

ii) To promote co-ordination between wind farm developers, system operators and

regional constituents in any proposed development of wind farms.

iii) To provide methodology and information exchange amongst regional

constituents and agencies in planning of transmission system for evacuation of

wind power.

3.3 Scope

The planning code applies to transmission licensees, wind farms, SEBs,

CTU/STUs and Distribution licensees involved in developing the transmission/

evacuation system for wind power evacuation.

3.4 Planning policy

CTU/STU/TSO may formulate perspective transmission plan for wind power

evacuation in a region. The transmission planning shall consider both short term

and long-term expected wind generation in the region. The planning shall fit into



National Electricity Plan formulated by Central Government, perspective

transmission plan developed by CEA, Electric Power Survey of India published by

CEA and policy guide lines (if any) issued by concerned ministry regarding

renewable energy development and shall be done taking into account the state

transmission plan.

3.5 Planning criterion

3.5.1 Study of transmission system for wind power evacuation

3.5.1.1 The transmission system shall be adequate for various wind generation and

load scenarios. The transmission system shall operate without violating any

system conditions during following scenarios:

i) System Peak Load with High Wind Generation

Explanation:-

During peak loading condition all the generating units in a region will be

running at or near to its maximum capacity. Power flow through the

transmission network will be at higher level. Evacuation planning of wind

farm shall ensure that power injected by wind farm shall not cause any

overloading/ congestion in the network during peak load condition.

ii) System Light Load with High Wind Generation

Explanation:-

Here, the aim is to ensure that during system light load condition, all the

available wind power is evacuated.

iii) Local Light Load with High Wind Generation

Explanation:-

Sometimes wind farms can have significant local load near the wind farms.

Here, the aim is to ensure that during local light load condition, all the

available wind power is evacuated to the system. It is to be noted that low

local load and low system load may not coincide in many parts of India due

to geographical diversity.



As the wind farms are distributed over large geographical area, the maximum

generation depends on geographical spread.

For scenarios mentioned in IWGC section-3.5.1, the “High Wind Generation”

shall correspond to:

i) 100% capacity factor for wind farms connected below 66kV.

ii) Minimum 90% capacity factor for wind farms connected at 66kV or 110 kV

or 132 kV.

iii) Minimum 80% capacity factor for wind farms connected above 132 kV.

Explanation:-

Normally in India, plant load factors of wind farms would lie in the range of 20-

30%.But, capacity factor may go up to 100% in a small wind farm. So, to have

economic viability, transmission planning of wind farms should consider

capacity factor as a parameter.

Wind turbines in a smaller wind farm face similar wind speeds as they are

spread over smaller geographical area. Output of these wind farms can reach

100% of installed capacity during high wind season. As the wind farm size

grows, capacity factor of wind farm decreases due to large geographical

spread.

Normally, higher capacity wind farms are connected at higher voltage levels.

Here, voltage level at the grid connection point is chosen as criteria because

power system behavior can be better categorized with voltage levels than

power.

100%, 90%, 80% values are based on consultation experience and also

available data from the literature.

3.5.1.2 Generally there shall be no restriction on the wind farm size and the voltage

level at which it shall be connected to the grid, provided all the requirements in

this IWGC are fulfilled.

Explanation:-

The relation between evacuating power and voltage level depends on many

parameters, such as:

- Local network and local load



- Transmission conductor characteristics

- Availability of substations

This relation can vary from one area to other. Providing a definite guideline on

evacuating power vs. voltage relationship can restrict setting up of new wind

farms in some areas where wind power can be evacuated reliably in spite of

violating the “evacuating power and voltage” guideline.

3.5.1.3 Lower ambient temperatures which are generally associated with higher wind

velocities may be considered for increasing the loadability of transmission

systems planned for evacuating wind power in cases where other alternatives

are prohibitively expensive affecting viability of the renewable energy project.

IEEE Std 738-1993 “IEEE Standard for Calculating the Current-Temperature

Relationship of Bare Overhead Conductors Contingency study " shall be

followed while calculating line loadability with respect to wind speed. A sample

calculation of transmission line loading with respect to wind speed is given in

Appendix B. In Appendix B transmission line loading limits with increasing wind

speeds are given for Zebra and Panther conductors.

3.5.2 Contingency study

Plant load factors of wind farms are significantly less than the conventional

generators. Hence, application of N-1 contingency criteria for planning of

transmission line(s) from wind farm to grid substation may not be economically

viable. Loss of generation from smaller wind farms may not have significant

impact on the grid operation.

3.5.2.1 Planning of transmission lines from wind farms connected at 220 kV voltage

level and above, to the grid substation shall be based on N-1 contingency

criteria. However, wind farms connected below 220 kV voltage level and below

100 MW installed capacity at 220 kV voltage level can be exempted from N-1

planning criteria.

3.5.2.2 The upstream network connected from grid substation shall be capable of

withstanding and be secured against the following contingency outages without

necessitating load shedding or rescheduling of generation during steady state

operation as defined in IEGC and State Grid codes

a) Outage of a 132 kV D/C line or,



b) Outage of a 220 kV D/C line or,

c) Outage of a 400 kV S/C line or,

d) Outage of single Interconnecting Transformer, or

e) Outage of one pole of HVDC bipolar line, or

f) Outage of 765 kV S/C line

The above contingencies shall be considered assuming a pre-contingency

system depletion (planned outage) of another 220 kV D/C line or 400 kV S/C

line in another corridor and not emanating from the same substation. All the

generating units may operate within their reactive capability curves and the

network voltage profile shall also be maintained within voltage limits specified.

3.5.3 Any one of the events mentioned in the adequacy and contingency study shall

not cause:

i) Unacceptable high or low voltage

ii) Prolonged operation of the system frequency below and above specified

limits.

iii) System instability

iv) Unacceptable overloading of transmission system elements.

3.5.4 Reactive power compensation

Reactive power compensation is important for wind farms to ensure reliable

and trouble free grid operation and stable voltage profile. Adequate planning of

reactive power compensation can minimize the reactive power loading on the

transmission line. Further, there is a close relation exists between voltage

instability and reactive power compensation. Hence, the reactive power

compensation is to be addressed in the planning exercise and a careful study is

required.

3.5.4.1 Reactive compensation of wind farms shall be able to maintain power factor

between 0.95 lagging and 0.95 leading at grid connection point.

Explanation: -

As per Indian state grid codes, power factor of conventional generators shall lie

between 0.95 leading to 0.85 lagging. Wind grid codes of UK, Germany ask for

0.95 leading to 0.95 lagging power factor. Canadian grid code asks for 0.95

leading to 0.90 lagging power factor.



So, it can be seen than grid codes mainly differ on the lagging power factor

limit. In India, reactive power injection from wind farms is least expected. So, in

IWGC the power factor range is limited between 0.95 leading to 0.95 lagging.

3.5.4.2 Planning studies for power evacuation from wind farms through long distance

transmission lines shall include voltage stability studies to investigate the

requirements of dynamic VAr compensation to prevent voltage collapse during

high wind generation. The modeling of WTG shall be based on the actual type

planned to be installed in the area by the developer of wind farm.

3.6 Planning data

3.6.1 Wind farm owner shall provide planning data to CTU/STU as mentioned in

Appendix A.

3.6.2 Wind power addition plan for every five years issued by the Ministry of New and

Renewable Energy shall be considered for the planning of transmission lines of

the CTU/STUs.



Chapter 4

CONNECTION CODE FOR WIND FARMS

This chapter comprises various technical requirements that wind farms have to satisfy

for grid connection. These provisions shall apply for wind farms that are connected to

the grid from dd/mm/yyyy.

4.1 Introduction

The connection code for wind farms specify the minimum technical and design

criteria which shall be satisfied by any wind farms seeking connection to

ISTSs/STSs/STUs. This shall be pre-requisite for the establishment of an

agreed connection.

4.2 Objective

The objective of the connection code is to ensure that any new or modified

wind farm connections, when established, shall neither suffer unacceptable

effects due to its connections to ISTS/STS nor impose unacceptable effects on

the system or the grid.

4.3 Scope

The connection code applies to all wind farms connected to the grid at any

voltage levels. The wind farms shall satisfy all requirements of connection code.

4.4 Procedure for connection

The connection procedure of wind farms connected to ISTS shall follow IEGC

section-4.4. Wind farms connected to intra state lines shall follow

corresponding state grid code for connection procedure.

4.5 Connection agreement

The connection agreement of wind farms connected to ISTS shall follow IEGC

section-4.5. Wind farms connected to intra state lines shall follow

corresponding state grid code for connection agreement.

4.6 Technical requirements to be met at grid connection point of wind farms

The entire grid connected wind farms shall satisfy technical requirements at the

grid connection point of the wind farm as mentioned in the following sub-

sections.



4.6.1 Transmission system voltage requirements

4.6.1.1 Transmission system voltage range The wind farms shall be able to deliver available or rated power when the

voltage at the grid connection point remains within following range:

Table 4.1: Voltage withstand limits for wind farms

Voltage (kV)

Nominal % Limit of

variation Maximum Minimum

400 +5% to -10% 420 360

220 +11% to -9% 245 200

132 +10% to -9% 145 120

110 +10% to -12.5% 121 96.25

66 +10% to -9% 72.5 60

33 +5% to -10% 34.65 29.7

Explanation: -

The minimum and maximum voltages for 400, 220 and 132 kV buses are taken

from IEGC. The minimum and maximum voltages for 110, 66 and 33 kV buses

are taken from the planning criteria of Revised TNEGC(page 24) “The

permissible voltage at the point of commencement of supply during the steady

state operation is +5% / -10% for system upto 33 kV voltage level…” .

4.6.1.2 Resonance

Wind farms shall avoid introducing undue resonance leading to over voltage at

grid connection point. Of particular concerns are torsional interaction, self

excitation of induction machines, transformer ferro-resonance, and the resonant

effects of capacitor additions. Wind farms connected to the grid through series

compensated transmission lines shall investigate the possibility of sub-

synchronous resonance due to torsional interactions.

4.6.1.3 Voltage unbalance

Voltage unbalance is defined as the deviation between the highest and lowest

line voltage divided by the average line voltage of three phases.



Connection of a WTG to an unbalanced system will cause negative phase

sequence current to flow in the rotor of the machine.

Wind farms shall be able to withstand voltage unbalance limits specified in

following Table 4.2:

Table 4.2: Voltage unbalance limits

Voltage level (kV) Unbalance (%)

400 1.5

220 2

<220 3

Explanation: -

CEA grid standard is followed

4.6.2 Reactive power capability of wind farms

The reactive compensation system of wind farms shall be able to attain

following characteristics:

i) Wind farms connected at 66 kV and below shall maintain power factor

between 0.95 lagging and 0.95 leading at grid connection point. A

generating unit operating at leading power factor absorbs reactive power

from the transmission system.

ii) Above 66 kV, wind farms shall be able to operate in voltage-power factor

operating region shown in Figure 4.1.



Figure 4.1: Voltage vs. power factor characteristics of wind farms connected

above 66 kV

Explanation: -

The voltage vs. power characteristic is based on the principle that wind farms

should not draw/inject large reactive power at lower/higher system voltages. In

general, the allowable power factor range of wind farms is 0.95 lagging to

leading. But, a comparatively higher leading power factor requirement is placed

when the system voltage is lower. Similarly, a lower lagging power factor is

required when the system voltage is higher. In other words, reactive power

drawl/injection shall be minimized at lower/higher voltages. This is depicted in

Figure 4.1. The Voltage vs. power factor characteristics in IWGC is derived

from German grid code of VE-T.

Voltage (kV) 420 245 145 121 410 238 141 117 400 220 132 110 380 215 128 105 360 200 120 96.25

Power Factor

0.95 0.98 1.0

leading lagging (absorption) (injection)



4.6.3 Frequency tolerance range

i) Wind farms shall be capable of operating continuously for system frequency

range of 47.5 to 51.5 Hz.

ii) Above 51.5 Hz and below 47.5 Hz, allowable frequency tolerance range

of wind farms will be according to wind turbine specifications.

iii) Wind farms shall remain connected to the grid when rate of change of

frequency is within 0.5 Hz/sec.

Explanation: -

The frequency range of 47.5 to 51.5 Hz is also proposed in the draft IS standard

on “Wind turbines - Design requirements”, which is under finalization by BIS -

Wind turbine Sectional Committee – ET 42. Hence it is suggested that the upper

limit may be restricted to 47.5 - 51.5 Hz.

4.6.4 Active power control

4.6.4.1Wind farms with connected at 66 kV and above shall have the ability to limit the

active power output at grid connection point as per system operator’s request.

The request from grid cooperator shall be under the conditions elaborated in

IWGC section 5.2.6 and 5.2.7.

Explanation: -

During system operations, grid operator in extreme conditions may ask the

wind farms to limit the power injection into the grid. The request from grid

cooperator shall be under the conditions elaborated in IWGC section 5.2.6. and

5.2.7. Wind farms connected at 66 kV and above shall be able to respond to

system operator’s request.

4.6.4.2 Active power output of wind farms shall vary with respect to frequency

as shown in Figure 4.2.



Figure 4.2: Variation of active power output of wind farms with respect to

frequency of wind farm

Explanation: -

The objective is to utilize wind power at its maximum. This characteristic is

derived from Irish grid code.

The upper limit of 50.3 is derived from recent amendment of IEGC in 2009.

4.6.5 Situations where wind turbines can be disconnected from grid

4.6.5.1 The wind farms shall be equipped with voltage and frequency relays for

disconnection of the wind farm at abnormal voltage and frequencies. The

relay settings shall be outside the operating range of voltage and frequency

mentioned in IWGC section 4.6.1 and section 4.6.3.

4.6.5.2 Wind farms connected below 66 kV can get disconnected from the grid during

system faults (fault ride through capability is not mandatory).

Per

cent

age

of A

vaila

ble

Pow

er

100% 50% 0%

47.5 50.3 51.5 Hz

Frequency



Explanation: -

Normally, wind farms connected below 66 kV are smaller in size. The

requirement of fault ride through can affect the economics of smaller wind

farms at present scenario.

4.6.6 Situations where wind turbines must remain connected to the grid

4.6.6.1 Wind farms shall remain connected to the grid during normal system

operation.

4.6.6.2 Wind farms connected at 66 kV and above shall remain connected to the grid

during system fault. Reactive power compensation equipment must also remain

connected during system fault.

4.6.6.3 Fault ride through requirements

Fault ride through requirements shall be applicable to all new wind farms

planned or commissioned after the date specified by concerned authority with

due consideration of penetration level, cost and tariff.

Wind farms connected at 66 kV and above shall have the operating region as

shown in Figure 4.3 during system faults. Wind farms can be disconnected if

the operating point falls below the line in Figure 4.3.

During fault ride through, the WTGs in the wind farm shall have the capability to

meet the following requirements:

a) Shall minimize the reactive power drawl from the grid.

b) The wind turbine generators shall provide active power in proportion to

retained grid voltage as soon as the fault is cleared.



Figure 4.3: Fault ride through characteristics

Where,

Vf = 15% of Nominal System voltage

Vpf = Minimum voltages mentioned in IWGC section 4.6.1.1

The fault clearing time for various system nominal voltage levels is given in the

following Table 4.3:

Table 4.3: Fault clearing time and voltage limits

Nominal system

voltage (kV)

Fault clearing

time, T(ms)

Vpf (kV) Vf (kV)

400 100 360 60.0

220 160 200 33.0

132 160 120 19.8

110 160 96.25 16.5

66 300 60 9.9

Higher fault clearance times for the wind farms may be agreed to with the

SEBs/STUs. In such case, the SEBs/STUs shall specify to the wind farm

operators the required opening times of circuit breakers at various locations.

V

olta

ge (

kV)

Vpf

Vf

Time (ms)

0 T 3000

Must not trip



Explanation: -

With increasing penetration, wind farms will have major impact in Indian power

system. So, the behavior of wind farms should tend to be same as conventional

power plants. Staying connected during system fault is a step towards that

direction. Today’s wind turbine technology has matured enough to provide this

requirement. All the international grid codes demand this criterion from wind

farms. The Fault ride through requirements in IWGC resembles to international

practice. The fault clearing time is taken from IEGC, state grid codes.

However, it may be advised that this facility may be provided for the future wind

farms development with due consideration of the cost impact.

4.6.7 Ability to withstand repetitive faults

Wind farms connected below 66 kV shall be capable of withstanding repetitive

faults in the grid as the fault occurrence in these systems is frequent.

Explanation: -

In India, the occurrence of faults in sub-transmission system is frequent. Hence,

the wind turbines may be thermally stressed. In such cases the machines shall

withstand the repetitive faults or shall disconnect from the grid. Similar

requirement is presented in Danish grid code.

4.6.8 Protection

All the grid connected wind farms must have protection systems to protect the

wind farm equipment as well as the grid, such that no part system shall remain

unprotected during faults.

4.6.8.1 The protection schemes for the wind farms shall be developed in coordination

with the grid protection schemes and this shall be carried out keeping in mind

the wind turbine manufacturing capabilities such as fault ride through capability,

voltage and frequency operational ranges etc.

4.6.8.2 The faults on the wind farm and/or its apparatus shall be cleared without any

time delay and in any event shall be cleared within in the fault clearing times

mentioned in IWGC section-4.6.6.3 with reliability, selectivity and sensitivity.



The protection co-ordination for the wind farms shall be monitored by the

SEBs/STUs/ISTSs.

4.6.8.3 The following are the minimum protection schemes that shall be installed for

wind farm protection:

i) under/over voltage protection

ii) under/over frequency protection

iii) over current and earth fault protection

iv) load unbalance (negative sequence) protection

v) differential protection for the grid connecting transformer

vi) capacitor bank protection

vii) tele-protection channels (for use with distance protection) between the grid

connection point circuit breaker and user connection point circuit

breaker

4.6.8.4 Back-up protection shall be provided for required isolation/protection in the

event of failure of the primary protection systems provided to meet the fault

clearance time requirements.

4.6.8.5 The protection requirements for the wind farm substation and for the

transmission system evacuating the wind power shall be as per the

specifications of STUs/SEBs/ISTSs.

4.6.9 Signals and data communication requirements

Wind farms connected at 66 kV and above shall have communication channel

which is continuously available to system operator. The communication facility

shall be provided at substation level of wind farms.

4.6.9.1 Signals from wind farm to system operator

Wind farm operator shall send following signals to the system operator:

i) Meteorological data

ii) Active/reactive power output

iii) On-off status

iv) Voltage regulation set point (if any)

4.6.9.2 Signals from system operator to wind farms

System operator shall send following signals to the wind farm operator:



i) Active power curtailment based on merit order

ii) Voltage regulation set point

iii) Start/stop instructions

4.6.9.3 Data to be submitted to system operator

The wind farm operator shall update the following information to the system

operator in case of any changes made:

i) Single line diagram of the wind farm

ii) Site common drawings

4.6.10 System recording instruments

A wind farm shall have data acquisition system/disturbance recorder/fault

locator for monitoring/ recording wind farm performance.

4.6.11 Wind farm equipment

This section discusses the standard requirements of wind farm equipments.

4.6.11.1 Lightning protection

Lightening protection of WTG system shall be according to IEC TR 61400-24

“Wind turbine generator systems – Part 24: Lightning protection.”

4.6.11.2 Earthing

Wind turbine grounding systems shall follow the recommendations of IEC TR

61400-24 (section 9).

4.6.11.3 Equipment standard

i) All sub-station equipments of wind farm shall comply with BIS/IEC or

prevailing code of practice.

ii) All equipment shall be designed, manufactured and tested and certified in

accordance with the quality assurance requirements as per IEC/BIS.

iii) Wind turbine shall have a valid type certificate issued by an accredited

certification body including CWET. If the type certificate is issued by an

agency other than CWET, it shall be on the quarterly list of models and

manufacturers issued by CWET/MNRE.



4.6.11.4 Ground clearance

Energized parts shall be maintained at safe vertical and horizontal clearances

as dictated by Indian Electricity Rules/Central Board of Irrigation and Power

standard adopted for conventional generators and its associated sub-stations.

4.6.11.5 Grid connecting transformer configuration for wind farms

The grid connecting transformer configuration shall be designed to provide:

i) A favorable circuit to block the transmission of harmonic currents.

ii) Isolation of transmission system side and wind farm side ground fault

current contributions

The preferred configuration of the grid connecting transformer is delta

connection on the wind farm side and grounded wye connection on the

transmission system (grid) side. Delta connection on the high voltage side of

the grid connecting transformer is not permitted.

Alternate transformer configuration including wye-wye or wye-wye with a

delta connected tertiary is also acceptable for the grid connecting

transformer.

If the wind farm is directly getting connected to the existing utility substation,

the standard practice of utility shall be followed.

Explanation: -

The purpose of prohibiting delta connection on the high voltage side of the grid

connecting transformer is to block the harmonics current and to detect the earth

faults on the grid side.

4.6.12 Auxiliary supply

Voltage and frequency excursions within the specified requirements in the

auxiliary power supply shall not trip the wind farm. The auxiliary supply of

reactive power compensating equipment shall be as per IEC-61400-1 “Wind

Turbine Safety and Design”.

4.6.13 Revenue metering

Revenue metering shall be in accordance with the “Central Electricity Authority

(Installation and Operation of Meters) Regulations”.



4.6.14 Procedure for site access, operational activities and maintenance

The connection agreement shall indicate procedures necessary for site access,

site operational activities and maintenance standard for equipment of the

CTU/STU at wind farm owner premises and vice-versa.

4.6.15 Responsibilities for operational safety

Wind farm operator shall be responsible for operational safety in the wind farm.

Wind farm owner shall be responsible for safeguarding all the equipments in

the wind farm against manufacturing defects, improper installation and due to

external impacts in connection with the following:

i) short circuit and earth currents

ii) recovery voltage during clearing of grid short circuits and earth faults

iii) rise in voltage on fault-free phases in the event of single phase earth faults

iv) phase failure

v) out-of-phase reclosing and other impacts that occur during abnormal

operating conditions



Chapter 5

OPERATING CODE FOR WIND FARMS

The operating code specifies the operating conditions that the wind farms shall comply

with for safety and reliable operation of the grid and shall be applicable to the wind

farms connected to the grid, and the SEBs/STUs/SSLDCs/SLDCs/RLDCs.

5.1 Operating policy i) The wind farms connected to the grid shall comply with this operating code

and shall operate as an integrated system with the grid.

ii) Control centers of the grid connected wind farms shall be manned round

the clock by qualified and adequately trained personnel.

5.2 Wind farm security and operating aspects

The operating margins for the wind farms during the normal and the

constrained operation shall be as below.

5.2.1 Operating margins

5.2.1.1 Voltage at the grid connection point

The wind farm operator shall operate the wind farm continuously for the voltage

ranges mentioned in following Table 5.1 during the steady state operation.

Table 5.1: Operating voltage limits for wind farms

Voltage (kV)

Nominal % Limit of

variation Maximum Minimum

400 +5% to -10% 420 360

220 +11% to -9% 245 200

132 +10% to -9% 145 120

110 +10% to -12.5% 121 96.25

66 +10% to -9% 72.5 60

33 +5% to -10% 34.65 29.7



5.2.1.2 Frequency of operation for wind farms

For the operating range of frequencies between 47.5 Hz to 51.5 Hz, the WTGs

shall operate according to the frequency response curve specified in IWGC

section-4.6.4.2. No WTGs shall be started if the frequency is above 51.5 Hz.

5.2.1.3 Active power and power factor

The grid connected wind farm shall be capable of supplying the active power

between the limits of 0.95 power factor lagging to 0.95 power factor leading at

the grid connection point.

5.2.2 Reactive power and voltage control

5.2.2.1 The wind farms shall have provision for VAr compensation/support such that

they do not draw reactive power from the grid. VAr exchanges with the grid

shall be priced as follows:

a) The wind farm owner pays for VAr drawl from grid when voltage at the grid

connection point is below 97%

b) The wind farm owner gets paid for VAr given to the grid when voltage is

below 97%

c) The wind farm owner gets paid for VAr drawl when voltage is above 103%

d) The wind farm owner pays for VAr given to the grid when voltage is above

103%

Explanation: -

This requirement is as mentioned in IEGC. This requirement can be met by all

the WTGs.

5.2.2.2 The wind farm operator shall endeavor to minimize the VAr drawl from the grid

when the voltage at the grid connection point is below 95% of rated, and shall

not supply to the grid VAr when the voltage is above 105%. As such to control

the VAr exchange, the wind farm operator shall provide the VAr compensation

or request SLDC/RLDC to change the taps of the grid connecting transformer.

Explanation: -

The WTG manufacture provides VAr compensation facility for each WTG

(switch able capacitor banks). So using this facility the wind farm operator can

control the VAr exchange depending on the grid connection point voltage.



Varying the grid connecting transformer taps also controls the VAr exchange

with the grid.

5.2.2.3 The charge/payment for VAr exchange from the grid shall be at nominal paise

per kVArh as specified by CERC/SERC and the transaction will be between the

wind farm owner and the state utility.

Explanation: -

Although not uniform, all the SERCs have fixed a nominal charge for the VAR

drawl by the WTG from the grid. For e.g., in Tamil Nadu, Rs 0.25/kVArh if the

ratio of kVArh drawn to KWh exported is upto 10%and Rs0.50/ kVArh for more

than 10%.

5.2.2.4 Not withstanding the above, SSLDC/SLDC/RLDC may direct a wind farm to

curtail its VAr drawl/injection in case the security of grid or safety of any

equipment is endangered.

5.2.3 Ramp rate limits

All the grid connected wind farms with installed capacity 50 MW and above

shall have the ramp up/down capability.

Explanation: -

Ramp control facility regulates the active power generated from the WTG and

also minimizes the variations in the generated power that may arise because of

wind variations. The performance is similar to that of governor control in case of

synchronous machines The system operator may ask the wind farm operator to

curtail the generated power due to increasing wind speed, turbines returning to

service after some outage or to increase the generated power due to increase

in system demand etc.

5.2.3.1 The WTGs shall have two ramp rates

a) 10 minute maximum ramp rate

b) 1 minute maximum ramp rate



5.2.3.2 The ramp rate limits shall be applicable for all ranges of operation including

start up, normal operation and shut down of the WTGs. An exception to this can

be situations where there is fall in wind speeds.

5.2.3.3 The wind farm operator shall inform SLDC/RLDC, the maximum and minimum

ramp rates of the WTGs at the time of commissioning. Any changes made to

the ramp rate limits shall be informed to the SLDC/RLDC and shall be done as

per their instructions.

5.2.3.4 Ramp limits for wind farms at the grid connection point shall be as given below

(Table 5.2) depending on the wind farm installed capacity.

Table 5.2: Ramp rate limits for wind farms

Explanation: -

This is in line with international practice. As per Irish wind grid code grid the

ramp rate averaged over 1 minute should not exceed 3 times the average ramp

rate over 10 minutes.

5.2.3.5 The ramping up/down of the wind power generation shall be done by the wind

farm operator as instructed by the system operator. On case to case basis, the

maximum ramp limits mentioned in IWGC section 5.2.3.4 may be changed on

the mutual consent between the system operator and the wind farm operator

provided the WTGs ramp limits are not exceeded.

5.2.4 Power quality

All the wind farms connected to the grid shall endeavour to maintain the voltage

wave-form quality at the grid connection point. The wind farms shall comply

with the “IEC 61400-21: Wind Turbine Generator Systems, Part 21:

Measurement and Assessment of Power Quality Characteristics of Grid

Connected Wind Turbines” standard.

Wind Farm Installed

Capacity (MW)

10 min Maximum

Ramp(MW)

1 min Maximum

Ramp(MW)

50-150 Installed Capacity/1.5 Installed Capacity/5

>150 100 30



Explanation: -

Power quality in relation to a wind turbine describes the influence of a wind

turbine on the power and voltage quality of the grid. The main influences of

wind turbines on the grid concerning power quality are the voltage flicker,

harmonics (for wind turbines with power electronic equipment), voltage

changes & fluctuations and the in-rush currents.

5.2.4.1Voltage flicker

The IEC 61000-4-15 (IEC, 1997) and IEC 61000-4-15 (IEC, 2003) standards

shall be followed with respect to voltage flicker limits and measurement

techniques.

Explanation: -

Flicker means the flickering of light caused by fluctuations of the mains voltage,

which can cause distortions or inconvenience to people as well as other

electrical consumers. The flicker measurement is based on measurements of

three instantaneous phase voltages and currents, which are followed by an

analytical determination of Pst (short-term flicker disturbance factor) for different

grid impedance angles.

5.2.4.2 Harmonics

Harmonics measurements shall be taken in accordance with methodologies of

IEC 61400-21 or IEEE STD 519-1992. The harmonic content at the grid

connection point shall be as follows:

Explanation: -

According to the guidelines (IEC 61400-21), harmonic measurements are not

required for fixed-speed wind turbines (Type A), where the induction generator

is directly connected to the grid. Harmonic measurements are required only for

variable-speed turbines with electronic power converters (Types C and D).

a) Harmonic content of the supply voltage is indicated by the following index:

Total harmonic distortion of voltage = VTHD (expressed as percentage)



240

22 1

100n

nTHD

n

VV

V

=

=

= ×∑

Where Vn: nth harmonic of voltage

V1: fundamental frequency (50 Hz) voltage

The maximum limits of VTHD shall be as per the following Table 5.3:

Table 5.3: Voltage harmonic limits

System Voltage

(kV)

Total Harmonic

Distortion (%)

Individual Harmonic of any

Particular frequency (%)

765 1.5 1.0

400 2.0 1.5

220 2.5 2.0

132 3.0 2.0

b) Harmonic content of the supply current is indicated by the following index:

Total Harmonic Distortion of current = ITHD (expressed as percentage)

2

21

100nTHD

II

I= ×∑

Where In: nth harmonic of current

I1: fundamental frequency (50 Hz) current

The maximum limits of ITHD shall be as per the following Table 5.4:

Table 5.4: Current harmonic limits

Explanation: -

The limits for VTHD are taken from CEA standards (Grid standards)

Regulations-2006 and the limits for ITHD are taken from IEEE STD-519,

1992.

Voltage level <69 kV >69 kV

ITHD 5.0 2.5



5.2.4.3 Voltage fluctuations

The wind farm operation shall comply with the following permissible voltage

fluctuation limits at the grid connection point.

a) Voltage fluctuation limit for step changes which may occur repetitively is

1%.

b) Voltage fluctuation limit for occasional fluctuations other than step changes

is 2%.

Explanation: -

The voltage fluctuations in a wind farm can occur because of the switching

operations (capacitor banks, WTG start/stop), inrush currents during WTG

starting etc. Such voltage fluctuations shall be limited to the values mentioned

in the above section.

5.2.5 Start and stop criteria

5.2.5.1 All the WTGs in a wind farm shall have the capability to receive the start/stop

signal from the wind farm operator and shall respond to the signal without any

time delay.

Explanation: -

This is to necessitate the wind farm owner’s control over the WTG operation.

The system operator may request the wind farm operator to start/stop the

WTGs as the situation demands. So, the WTGs shall respond to the start/stop

command send by wind farm operator without any time delay.

5.2.5.2 During the wind generator start-up, the wind farm operator shall ensure that the

reactive power drawl (inrush currents incase of induction generators) shall not

affect the grid performance.

Explanation: -

Fixed speed WTGs directly connected to the grid directly draws huge inrush

current during starting. This may cause voltage fluctuations and flickering at the

grid connection point.



5.2.5.3 The wind farm operator has to ensure that the start up and stopping of the

WTGs comply with the voltage quality requirements.

Explanation: -

Because, the switching operations and the inrush currents may cause

harmonics, voltage flicker and voltage fluctuations.

5.2.5.4 It is recommended that all WTGs in the wind farm shall not start and /or stop

simultaneously owing to high windy conditions.

Explanation: -

Simultaneous starting/stopping of the WTGs can cause power quality problems.

Also, it can cause large changes in the power injected into the grid.

5.2.6 Operation during transmission congestion

During network congestion the wind farm operator shall act according to the

instructions given by system operators. System operator (SSLDC/ SLDC/

RLDC) shall make reasonable effort to evacuate the available wind power.

System operator shall instruct wind farm operator to back down wind

generation only as a last resort, in view of the fact that the variable cost for wind

generation is all most equal to zero (just like overflowing reservoir mention in

Merit Order Dispatch).

Explanation: -

Taking into consideration the zero fuel costs and environmental issues, it is

recommended to evacuate all the available wind generated power to the grid.

During transmission congestion, the conventional generation shall be backed

down. Under extreme conditions, when the wind power generated exceeds the

system demand and when the local voltage limits are violated, it shall be the

responsibility of the wind farm operator to back down sufficient amount of the

wind generation, to maintain system security. This shall be done as per the

system operator’s instructions.



5.2.7 Operation in emergency condition

Under any emergency (faults in the vicinity of wind farms, loss of any of the

wind farm equipment, faults within the wind farms) the wind farm operator’s

prime priority shall be the grid security and shall act accordingly. Once the

emergency has subsided, the wind farm operator shall take all recovery

measures listed in IEGC section-5.8 to bring back the wind farm into normal

operation and shall report the events to SLDC/RLDC as mentioned in IEGC

section-5.9.

Explanation: -

The wind farms shall be operated as an integrated part of the grid. The wind

farm operator shall operate it deriving maximum benefits from the integrated

operation. System security shall not be endangered because of the

substandard/inefficient operational practices of the wind farms. The

contingencies (loss of any of the wind farm equipment, faults within the wind

farms) shall be attended by the wind farm operator, so that there is minimal

damage to the wind farm equipment as well as the grid. For contingencies in

the vicinity of the wind farm, the wind farm operator shall protect the wind farm

equipment from any imminent damage and shall take necessary measures to

mitigate the contingency. The measures can be riding through the fault or

ramping down the generation till the contingency has been remove, running in

island mode to meet the local demand etc.

5.3 Demand estimation for operational purposes

IEGC/ state grid codes describe the procedures/responsibilities of the SLDCs

for demand estimation of active and reactive power. Wind energy forecasting

described in IWGC section-5.10 shall be taken into consideration to meet the

estimated demand.

Explanation: -

The demand estimation for operational purposes is done on a

daily/weekly/monthly basis. The wind forecasting data obtained by the day

ahead forecasting can be useful in meeting the estimated demand. The hourly

forecast data can also be used as a part of the scheduling and dispatching.



5.4 Demand management

IEGC/ state grid codes describe the provisions to be made by SLDCs for

demand curtailment in the event of insufficient generating capacity or in the

event of breakdown or operating problems (such as frequency, voltage levels or

thermal overloads) on any part of the grid. The demand management

procedure of SLDC shall take into account variability of wind power generation.

Explanation: -

In a power system wind power generation profile and system demand may not

follow the same pattern. For e.g. system demand may be high when there is

least possible wind generation. So, the demand management procedure shall

consider the variations in the wind generation (can be known from the wind

forecast data) to maintain power balance in system operation.

5.5 Periodic reports

IEGC/ state grid codes discuss the periodic reports issued by RLDC/SLDC to

all constituents of the Region and RPC Secretariat requirements regarding grid

operation. The reports shall also cover the wind power generation profile and

injection to grid.

Explanation: -

Periodic reports issued by RLDC give the description of the grid performance

over a week/month. Wind generation in that region can also be included in the

periodic reports, because that gives a picture of wind energy profile, demand

met with wind generated power and also can be useful for evolving good

operational practices in the future.

5.6 Operational liaison

The Operational liaison function is a mandatory built-in hierarchical function of

the RLDC/SLDC and regional constituents, to facilitate quick transfer of

information to operational staff and is specified in the IEGC section-5.6. The

same shall be applicable to the grid connected wind farms.



Explanation: -

Wind farms are through their communication interface shall exchange the

information in relation to operations and/or events with SLDC/RLDC. It is the

mandatory built-in hierarchical function of the RLDC and Regional constituents

including the wind farms, to facilitate quick transfer of information to operational

staff for decision making and actions to be sought.

.

5.7 Outage planning

IEGC/ state grid codes set out the procedure for preparation of outage

schedules for the elements of the regional grid in a coordinated and optimal

manner keeping in view the regional system operating conditions and the

balance of generation and demand. The outage planning of wind farm and its

associated evacuation network shall be planned to extract maximum power

from the wind farm.

Explanation: -

The outage schedules prepared by the RPC Secretariat based on the inputs

from all the SEBs/STUs, CTU and ISGS. Wind farms shall also submit their

outage schedule(s), if any, to the concerned SEB/STU. The wind farm operator

shall also be aware of the planned/maintenance outages taking place around

the vicinity of the wind farm, so that these outages do not have any effect on

the wind power generation.

5.8 Recovery procedures

IEGC/ state grid codes specify the recovery procedures i.e., restoration of the

operation of the regional grid after severe disturbances, partial/total blackouts

that are developed by RLDC in consultation with all regional constituents/RPC

Secretariat. The grid connected wind farms shall comply with these recovery

procedures and shall abide by the guidelines of RLDC/SLDC during the

restoration process.

5.9 Event information

The entire grid connected wind farms shall follow the event reporting procedure

mentioned in IEGC section-5.9.



5.10 Scheduling process

As the penetration of wind power increases, the scheduling of other generating

plants would be have consider the availability of wind generation. Hence, it

would be necessary to carry out wind energy forecasting to know the predicted

wind power in next day on hourly basis so as to minimize the scheduling errors.

.

5.10.1 Forecasting

Wind being of intermittent nature, needs to be predicted with reasonable

accuracy for proper scheduling and dispatching generation in the

interconnected system. Hence wind forecasting is necessary for increased

penetration. Centralized wind forecasting facility shall be provided in an area

with aggregated capacity of 200 MW and above. The Centralized wind

forecasting system shall forecast the wind flow over a certain geographic area

(for a cluster of wind farms) and it shall be installed in consultation with

SSLDC/SLDC/RLDC. The centralized wind forecasting facility shall be built and

operated either by the system operator or wind developers in the area and

sharing of the cost shall be mutually discussed and agreed.

The wind energy forecasting system shall forecast power based on wind flow

data at the following time intervals:

i) Day ahead forecast: Wind power forecast with an interval of one hour for

the next 24 hours for the aggregate wind farms.

ii) Hourly forecast: Wind power forecast with a frequency of one hour and

interval of 30 minutes for the next 3 hours for the aggregate wind

farms.

The day ahead forecasting shall be done to assess the probable wind energy

that can be scheduled for the next day. The hourly forecast is necessary to

minimize the forecasting error that can occur in the day ahead forecasting of

wind power. The SSLDC/SLDC/RLDC shall receive the forecasted wind power

data which shall be used for scheduling.

Wind energy forecasting system shall be implemented within the time specified

by the concerned authority with due consideration of penetration level, cost and

tariff.



Explanation: -

Wind energy forecast corresponds to an estimate of the expected amount of

power production from wind farms over the forecast period. Evacuation of large

amounts of energy from intermittent sources like wind has considerable effect

on the generation-demand balance of a power system. So, for reliable system

operation wind energy forecasting is necessary for larger wind farms. As the

penetration level increases, it becomes difficult for the system operator to

maintain the correct generation mix. As the system operator is responsible for

maintaining balance between generation and demand, he should know in

advance the amount of wind generated power that can be scheduled and

dispatched from the wind farm, much like the conventional generation

scheduling and dispatching.

5.10.2 Scheduling

The scheduling of other generators by the SLDC/RLDC shall consider the

available wind generation for the duration. While scheduling generating stations

in a region, system operator shall aim at utilizing available wind energy fully and

the Merit Order dispatch shall not be applied for wind farms. The wind farms

shall be treated as over-flowing reservoir/run of the river hydro power plants as

defined in Tamil Nadu Electricity Grid Code.

5.11 Spinning reserve/ backup generation

The spinning reserve/ backup generation shall be necessary to account for the

wind power forecasting error and to meet the sudden loss of wind power

generation (due to contingency).The amount of the spinning reserve/ backup

generation that is to be maintained shall be decided by the SSLDC/SLDC/

RLDC based on the wind power forecast information.

Explanation: -

Keeping a certain amount of energy as spinning reserve/backup generation is

necessary to ensure that sufficient generation can maintained to meet the

demand incase of an unexpected loss of wind generation. Also to meet the

uncertainty in wind energy forecasting (forecasting error) the spinning reserve/

backup generation is necessary.



APPENDIX A

Planning Data (Wind farm)

The following data are to be made available to the planning wing of CTU/STU

by all the wind farms

A.1 Name of the Wind Farm

A.2 Wind Farms capacity

i) Total installed capacity

ii) Number of units and unit size

A.3 Site map

Provide the location map to scale showing roads, railway lines, transmission

lines, rivers, reservoirs.

A.4 Wind farm type

i) Type of wind turbines used in the wind farm Fixed Speed/Variable Speed.

ii) Type of wind farm operation- continuous or seasonal.

iii) Expected high wind and low wind seasons and MW generation output from

the wind farm during these periods.

A.5 Wind Turbine data

Data type Unit Value

Wind turbine manufacturer -

Wind turbine generator type -

Rated power of each wind turbine kW

Rated apparent power kVA

Rated frequency Hz

Frequency tolerance range Hz

Rated wind speed m/s

Cut-in wind speed m/s

Cut-out wind speed m/s

Rated voltage Volt

Rated current Ampere

Short circuit ratio

Synchronous speed RPM



Rated slip

Magnetizing reactance of generator p.u

Stator leakage reactance p.u

Stator reactance p.u

Rotor leakage reactance p.u

Rotor reactance p.u

Magnitude of inrush current Ampere

Time duration of inrush current s

In addition to the above mentioned data, the wind farm owner has to provide

dynamic model of wind farm. If all the WTGs in the wind farm are not identical,

the model shall incorporate separate modules to represent each type of WTG.

Appropriate data and parameter values must be provided for each model. The

dynamic model must represent the features and phenomena likely to be

relevant to angular and Voltage stability. These features include but may not be

limited to:

i) Generator model

ii) Blade pitch control

iii) Model of drive train

iv) Model of converter (if any)

A.6 Reactive compensation

Give detail of reactive compensation, operating power factor range.

A.7 Wind Turbine transformer data

i) Transformer voltage ratio

ii) Percentage impedance

iii) Winding connection

iv) Tap settings (if any)

A.8 Grid connecting transformer data

i) Transformer voltage ratio

ii) Percentage impedance

iii) Winding connection

iv) Tap settings (if any)



A.9 Power evacuation scheme

The following documents are to be furnished:

i) Single line diagram of power evacuation scheme.

ii) Details of conductor used for power evacuation



APPENDIX B

Conductor ampacity calculation and variation with w ind speed

In IEEE Std 738-1993[1], “IEEE Standard for Calculating the Current-Temperature

Relationship of Bare Overhead Conductors”, a simplified method of calculating the

current-temperature relationship of bare overhead lines, given the weather conditions,

is presented. This appendix gives an example for the steady-state thermal rating

(ampacity) calculation. It also gives loadability of Zebra and Panther conductors with

respect to varying wind speed.

B.1 Problem statement:

To find the steady-state thermal rating (ampacity) for a Drake conductor, 795 kcmil

26/7 ACSR, under the following conditions:

a) Wind velocity, V, is 2 ft/s at sea level perpendicular to the conductor.

b) Emissivity, ε is 0.5.

c) Solar absorptivity, α, is 0.5.

d) Ambient air temperature, Ta, is 40 °C.

e) Maximum allowable conductor temperature is 65 °C .

f) Conductor outside diameter, D, is 1.108 in.

g) Conductor ac resistance, R (Tc), is:

R (20 °C) = 2.177 x 10 -5 Ω /ft

R (75 °C) = 2.648 x 10 -5 Ω /ft

h) The line runs in an East-West direction.

i) Latitude is 30°N.

j) Atmosphere is clear.

k) Average sun altitude, Hc, between 10:00 am and 12:00 noon.

B.2 Calculation: -

The natural convection heat loss is calculated by means of equation (1):

Convected heat loss, 0.5 0.75 1.250.283 ( )c f c aq D T Tρ= − W/ft ---------------------------- (1)

Where,

Conductor diameter, D =1.108 in

Ambient temperature, Ta =40o C

Conductor temperature, Tc =65o C

Air film temperature (°C) T film = (Tc + Ta)/2 = 52.5 °C



Density of air, ρ f =0.06775 lb/ft3 (from Table1 of IEEE Std. 738 at 52.5 o C)

Therefore, substituting the above values in equation (1) gives, qc = 4.48 W/ft

Since the wind velocity is greater than 0 ft/s, the forced convection heat loss for

perpendicular wind is calculated according to both equations (2) and (3) corrected

for wind direction, and compared to the natural convection heat loss. The larger of

the heat losses due to both natural and forced convection is then used in

calculating the thermal rating:

( )0.52

1 1.01 0.371 f Wc f c a

f

D Vq k T T

ρµ

= + −

---------------------------- (2)

( )0.6

2 0.1695 f Wc f c a

f

D Vq k T T

ρµ

= −

----------------------------- (3)

Where,

D = 1.108 in

Velocity of air stream, VW = (2 ft/s) · 3600 (s/h)

Tc =65o C

Ta =40o C

Absolute viscosity of air,

µf = 0.04775 lb/h (ft) (Table1 of IEEE Std. 738 at 52.5 °C)

Density of air, ρ f =0.06775 lb/ft3 (from Table1 of IEEE Std. 738 at 52.5 o C)

Thermal conductivity of air at temperature,

kf = 0.00858 W/ft (°C) (from Table1 of IEEE Std. 738 a t 52.5 °C)

Therefore, substituting the above values in equation (2) and (3), gives

qc1 = 10.421 W/ft

qc2 = 9.837 W/ft

Therefore, qc= 10.421 W/ft of conductor

Since the wind is perpendicular to the axis of the conductor, the wind direction

multiplier, Kangle, is 1.0, and the forced convection heat loss is greater than the

natural convection heat loss. Therefore, the forced convection heat loss will be

used in the calculation of thermal rating.



B.3 Radiated heat loss (q r):

( ) ( )4 4273 273

0.138100 100

c ar

T Tq Dε

+ + = −

----------------------------- (4)

Where,

D = 1.108 in

∈= 0.5

Tc = 65 °C

Ta = 40 °C

Radiated heat loss, qr = 2.64 W/ft of conductor

Solar heat gain

( ) 'sin s sq Q Aα θ= ----------------------------- (5)

Effective angle of incidence of the sun's rays,

( ) ( )( )11cos cos . cos c cH Z Zθ − = − ----------------------------- (6)

Where,

Solar absorptivity, α = 0.5

Projected area of conductor, 'A =D/2= 0.092 ft

From Table 2 of IEEE Std. 738 at 30° North latitude :

Altitude of sun, Hc at 10:00 am = 62°

Hc at 12:00 noon = 83°

Hc at 11:00 am = (83°+62°)/2 = 72.5°

Azimuth of sun, Zc at 10:00 am = 98°

Zc at 12:00 noon = 180°

Zc at 11:00 am = (98°+180°)/2 = 139°

From Table 3 of IEEE Std. 738, Hc = 72.5° with a clear atmosphere:

By interpolation, Qs= 95.2 W/ft

Azimuth of line, Zl=90° or 270°

From equation (5), qs= 4.293 W/ft of conductor

From equation (6), θ =78.62°



B.4 Resistance at 65° C

( )R(75) R(20)R(65)=R(20)+ 65 20

75 20

− − −

= 2.313 x 10–5 Ω /ft

B.5 Steady-state thermal rating

The steady state thermal loading is given by, ( )I65

c r sq q q

R

+ −= ---------------------- (7)

qc = 10.421 W/ft of conductor

qr = 2.64 W/ft of conductor

qs= 4.293 W/ft of conductor

R (65) =2.313 x 10–5 Ω /ft

From equation (7), I = 615.7 A.

In general, the transmission line loading is a function of the following factors:

i) Conductor type

ii) Line length

iii) Weather conditions

The weather conditions that mainly impact the loading are the ambient temperature and

the wind velocities. Though, the ambient temperature is directly related to the wind flow

velocities, calculation have been made with varying wind velocity with constant ambient

temperature and are presented in Table B1 for Zebra and Panther conductors. It is

observed that with raise in wind speed, the ampacity of Zebra conductor would increase

by an average of 50A for 0.5m.sec increase in wind speed. Further, it is noted that wind

turbine would operate only with the wind speed above 4m/sec.



Table-B1: Conductor ampacity variation with wind velocity

Conductor age< 1yr;Ambient temp: 40oC;Final temp:65oC

Conductor ampacity (A)

Wind speed (m/s) ACSR Zebra conductor Panther conductor

0.5 687.43 439.91

1.0 793.69 509.64

1.5 876.81 557.75

2.0 945.79 601.88

2.5 1004.06 639.44

3.0 1054.96 672.23

3.5 1100.43 701.51

4.0 1141.71 728.08

Further, the relation between conductor ampacity and ambient temperature mentioned in

CBIP Technical Report 77 of May 1991 is furnished in Table B2 [2].

Table-B2: Conductor ampacity variation with ambient temperature

ACSR Zebra (54/3.18mm AL + 7/3.18 mm Steel); Region-Northern; Max design temperature -60,65,67 and 75 oC; conductor age : upto one year

Ambient Temperature(oC)

Ampacity(A) 60 oC

Ampacity(A) 65 oC

Ampacity(A) 67 oC

Ampacity(A) 75 oC

0.0 1090.3 1126.5 1140.5 1193.5 2.5 1067.8 1105.2 1119.5 1174.8 5.0 1044.9 1083.4 1098.4 1155.0 7.5 1021.4 1061.4 1076.8 1134.9 10.0 952.0 998.3 1013.1 1078.0 12.5 897.8 945.5 963.6 1030.5 15.0 839.4 891.2 910.5 982.4 17.5 784.9 840.7 861.8 963.1 20.0 766.2 823.4 844.8 947.8 22.5 708.9 771.3 794.4 903.6 25.0 658.3 724.1 749.1 864.1 27.5 604.0 701.2 728.0 826.6 30.0 541.7 647.5 677.2 783.2 32.5 503.8 596.1 628.7 742.6 35.0 495.0 588.9 622.0 737.3 37.5 378.6 495.6 535.1 667.4 40.0 352.2 477.6 518.6 654.3



ACSR Zebra (54/3.18mm AL + 7/3.18 mm Steel); Region-Northern; Max design temperature -60,65,67 and 75 oC; conductor age : one to ten years


Ampacity(A) 60 oC

Ampacity(A) 65 oC

Ampacity(A) 67 oC

Ampacity(A) 75 oC

0.0 1147.8 1187.4 1202.8 1261.2 2.5 1124.8 1165.5 1181.1 1241.5 5.0 1101.2 1143.1 1159.4 1221.4 7.5 1076.9 1120.4 1137.2 1200.7 10.0 1003.8 1051.8 1070.0 1138.9 12.5 948.8 998.5 1018.2 1091.3 15.0 885.4 941.4 962.5 1040.9 17.5 828.1 888.5 911.1 1018.2 20.0 809.0 870.8 894.0 1002.7 22.5 748.7 816.2 841.2 956.4 25.0 693.8 768.7 793.8 915.2 27.5 639.2 740.5 769.0 876.0 30.0 571.1 694.1 716.2 830.5 32.5 530.6 630.1 685.2 788.3 35.0 522.4 623.2 658.8 783.0 37.5 397.2 524.7 567.2 709.5 40.0 371.9 506.2 550.3 696.2

ACSR Zebra (54/3.18mm AL + 7/3.18 mm Steel); Region-Northern; Max design temperature -60,65,67 and 75 oC; conductor age : beyond ten years


Ampacity(A) 60 oC

Ampacity(A) 65 oC

Ampacity(A) 67 oC

Ampacity(A) 75 oC

0.0 1168.3 1207.0 1222.6 1282.8 2.5 1143.1 1184.9 1201.0 1263.0 5.0 1119.3 1162.3 1179.1 1242.8 7.5 1094.8 1139.4 1156.7 1221.9 10.0 1022.3 1071.4 1090.1 1160.6 12.5 965.7 1018.4 1038.5 1113.3 15.0 904.6 961.7 983.2 1063.3 17.5 847.7 909.1 932.2 1040.4 20.0 828.1 891.0 914.6 1024.5 22.5 768.3 836.7 862.2 978.4 25.0 713.5 787.5 814.9 937.3 27.5 659.5 760.9 790.7 898.2 30.0 594.2 704.9 737.3 853.0 32.5 551.9 651.3 686.6 810.8 35.0 542.1 643.2 679.9 804.6 37.5 420.5 546.63 589.0 732 40.0 394.3 527.1 571.1 717.9



ACSR Moose (54/3.53mm AL + 7/3.53 mm Steel); Region-Northern; Max design temperature -60,65,67 and 75 oC; conductor age : upto one year


Ampacity(A) 60 oC

Ampacity(A) 65 oC

Ampacity(A) 67 oC

Ampacity(A) 75 oC

0.0 1259.0 1301.8 1316.0 1379.8 2.5 1234.0 1277.2 1293.6 1357.6 5.0 1207.5 1252.1 1269.4 1335.1 7.5 1180.3 1226.7 1244.6 1311.8 10.0 1098.3 1149.7 1169.3 1242.3 12.5 1034.5 1089.9 1110.9 1188.7 15.0 965.5 1025.9 1048.3 1132.0 17.5 901.2 968.3 990.6 1080.2 20.0 880.0 948.7 971.6 1045.6 22.5 812.3 885.2 912.2 1011.0 25.0 750.3 829.7 858.9 964.4 27.5 689.2 775.9 807.4 920.3 30.0 914.6 711.7 746.4 868.8 32.5 541.1 650.4 688.5 821.1 35.0 534.5 645.0 683.6 817.1 37.5 384.9 530.1 577.3 732.6 40.0 358.4 511.7 560.5 719.5

ACSR Moose (54/3.53mm AL + 7/3.53 mm Steel); Region-Northern; Max design temperature -60,65,67 and 75 oC; conductor age : one to ten years


Ampacity(A) 60 oC

Ampacity(A) 65 oC

Ampacity(A) 67 oC

Ampacity(A) 75 oC

0.0 1328.6 1374.5 1392.2 1460.3 2.5 1302.0 1349.3 1367.5 1437.6 5.0 1274.7 1323.4 1342.4 1414.4 7.5 1246.8 1297.3 1316.8 1390.5 10.0 1160.3 1216.2 1237.5 1317.5 12.5 1093.2 1153.4 1176.3 1261.5 15.0 1020.7 1086.1 1110.6 1202.1 17.5 953.1 1023.7 1050.1 1148.0 20.0 931.4 1003.7 1030.7 1130.9 22.5 860.3 939.2 968.5 1076.1 25.0 795.3 881.1 912.7 1027.5 27.5 731.2 824.5 858.9 961.4 30.0 652.9 757.5 795.0 927.6 32.5 575.7 693.3 734.4 900.8 35.0 569.4 688.1 729.7 874.0 37.5 412.3 567.5 618.1 785.4 40.0 384.9 548.4 600.8 771.9



ACSR Moose (54/3.53mm AL + 7/3.53 mm Steel); Region-Northern; Max design temperature -60,65,67 and 75 oC; conductor age : beyond ten year


Ampacity(A) 60 oC

Ampacity(A) 65 oC

Ampacity(A) 67 oC

Ampacity(A) 75 oC

0.0 1350.7 1397.9 1418.1 1488.2 2.5 1323.9 1372.4 1391.1 1483.3 5.0 1296.4 1346.4 1365.8 1439.9 7.5 1268.1 1319.9 1340.0 1415.6 10.0 1182.4 1239.5 1261.4 1343.5 12.5 1115.7 1177.2 1200.6 1287.8 15.0 1043.8 1110.4 1135.4 1228.9 17.5 976.7 1048.5 1075.4 1175.2 20.0 954.4 1027.9 1055.4 1157.5 22.5 883.9 963.9 993.7 1103.1 25.0 819.3 906.1 938.1 1054.7 27.5 755.7 850.1 884.6 1008.8 30.0 678.5 783.5 821.2 955.3 32.5 602.5 719.6 761.2 905.8 35.0 594.3 613.6 754.9 900.7 37.5 443.2 595.4 645.8 813.5 40.0 414.6 575.0 627.1 798.9

ACSR Bersimis (42/4.57 mm AL + 7/2.54 mm Steel); Region-Northern; Max design temperature -60,65,67 and 75 oC; conductor age : upto one year


Ampacity(A) 60 oC

Ampacity(A) 65 oC

Ampacity(A) 67 oC

Ampacity(A) 75 oC

0.0 1498.6 1548.7 1568.0 1641.7 2.5 1467.9 1519.5 1539.3 1615.4 5.0 1436.5 1489.7 1510.4 1588.6 7.5 1404.2 1459.5 1480.8 1561.0 10.0 1304.6 1365.9 1389.3 1476.5 12.5 1227.1 1293.4 1318.6 1411.7 15.0 1143.4 1215.6 1242.6 1342.8 17.5 1065.3 1143.5 1172.7 1280.2 20.0 1040.6 1120.6 1150.5 1260.6 22.5 958.4 1046.1 1078.5 1197.1 25.0 883.2 978.8 1014.0 1140.9 27.5 809.0 913.7 951.7 1087.6 30.0 718.0 835.7 877.6 1025.3 32.5 627.9 761.1 807.4 967.7 35.0 622.1 756.4 803.1 964.2 37.5 434.8 614.6 672.3 860.9 40.0 404.2 593.9 653.5 846.3



ACSR Bersimis (42/4.57 mm AL + 7/2.54 mm Steel); Region-Northern; Max design temperature -60,65,67 and 75 oC; conductor age : one to ten year


Ampacity(A) 60 oC

Ampacity(A) 65 oC

Ampacity(A) 67 oC

Ampacity(A) 75 oC

0.0 1583.1 1638.0 1659.2 1740.6 2.5 1551.5 1608.0 1629.7 1713.6 5.0 1519.0 1577.2 1599.9 1686.0 7.5 1485.8 1546.1 1569.4 1657.6

10.0 1380.8 1447.6 1473.2 1569.0 12.5 1299.5 1371.6 1399.0 1501.2 15.0 1211.4 1289.9 1319.4 1429.2 17.5 1129.5 1214.3 1246.1 1363.7 20.0 1104.1 1190.9 1223.4 1343.7 22.5 1017.8 1112.8 1148.1 1277.4 25.0 938.9 1042.4 1060.5 1218.7 27.5 861.2 974.3 1015.5 1163.1 30.0 765.8 892.6 937.9 1098.1 32.5 671.5 814.6 864.5 1037.0 35.0 665.8 810.0 860.3 1034.5 37.5 470.1 661.7 723.4 926.5 40.0 438.3 640.7 703.9 911.4

ACSR Bersimis (42/4.57 mm AL + 7/2.54 mm Steel); Region-Northern; Max design temperature -60,65,67 and 75 oC; conductor age : beyond ten years


Ampacity(A) 60 oC

Ampacity(A) 65 oC

Ampacity(A) 67 oC

Ampacity(A) 75 oC

0.0 1610.2 1666.7 1688.5 1772.3 2.5 1578.3 1636.4 1658.5 1745.1 5.0 1545.6 1605.4 1628.7 1717.3 7.5 1512.0 1537.9 1597.9 1688.8 10.0 1407.9 1476.3 1502.5 1600.8 12.5 1327.1 1400.8 1428.9 1533.5 15.0 1239.8 1319.8 1349.9 1462.1 17.5 1158.5 1244.8 1277.2 1397.2 20.0 1132.4 1220.7 1253.8 1376.5 22.5 1046.9 1143.2 1179.0 1310.7 25.0 968.7 1073.3 1111.9 1252.2 27.5 891.6 1005.6 1047.2 1196.9 30.0 797.6 924.8 970.4 1132.3 32.5 705.0 847.6 897.7 1072.4 35.0 696.9 841.0 891.6 1067.3 37.5 509.5 696.6 757.9 961.3 40.0 476.3 693.3 736.7 944.8



References:

[1] IEEE Std 738-1993 “IEEE Standard for Calculating the Current-Temperature

Relationship of Bare Overhead Conductors”, by Transmission and Distribution

Committee of the IEEE Power Engineering Society.

[2] S.K.Sonee, “Assessment of Transfer Capability in the Indian Bulk Electric

Power System”, GSIOAR07, 8th – 9th August 2007, IT-BHU, Varanasi.

wind grid code for india draft

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