practical impact of very small power producers (vspp) on control and protection system ... · 2015....

Practical Impact of Very Small Power Producers

(VSPP) on Control and Protection System in

Distribution Networks

Noppatee Sabpayakom and Somporn Sirisumrannukul Department of Electrical and Computer Engineering, Faculty of Engineering, King Mongkut’s University of

Technology North Bangkok (KMUTNB), Bangkok, Thailand

Email: {noppatees, spss}@kmutnb.ac.th

Abstract—Due to incentive policies to promote renewable

energy and energy efficiency, high penetration levels of very

small power producers (VSPP) located in distribution

networks have imposed technical barriers and established

new requirements for protection and control of the

networks. Although VSPPs have economic and

environmental benefit, they may introduce negative effects

and cause several challenges on the issue of control and

protection system. This paper presents comprehensive

studies of possible impacts on control and protection system

based on real distribution systems located in a metropolitan

area. A number of scenarios were examined primarily

focusing on state of islanding, and undisconnected VSPP

during faults. It is shown that without proper measures to

address the issues, the system would be unable to maintain

its integrity of electricity power supply for disturbance

incidents.

Index Terms—control and protection system, distributed

generation, renewable energy, very small power producers

I. INTRODUCTION

Traditionally, much of the electricity generated has

been produced by large-scale, centralized power plants

using fossil fuels (e.g., coal, oil, and gas), hydropower, or

nuclear power. The electrical energy is transmitted over

long distances by high voltage (HV) or extra high voltage

(EHV) transmission lines and from there, the high voltage

levels are converted to medium voltage (MV) and low

voltage (LV) levels through distribution lines in the

distribution system to end-use customers.

Such a centralized generation pattern, however, suffers

a number of drawbacks, such as a high level of

dependence on imported fuels that are price-vulnerable,

transmission losses, the necessity for continuous

upgrading and replacement of the transmission and

distribution facilities and therefore high operating cost, as

well as environmental impact. In addition, as electric

demand is substantially increasing as a result of economic

and social growths, the construction of a large sized

power plant is running into financial and technical

difficulties because it is capital intensive and needs

considerable amount of time to complete.

Manuscript received June 10, 2015; revised August 25, 2015.

Alternatively, an ideal alternative on electric power

supply to electric users is the installation of a small sized

generator or commonly known as distributed generator

(DG). For the last decade, distribution systems have seen

a large number of small sized generators due to incentive

policies to promote renewable energy and energy

efficiency. DGs can be powered by conventional and

renewable energy resources and in Thailand, a DG with a

net injected capacity less than or equal to 10MW is

commonly known as very small power producer (VSPP).

VSPPs are different in types of generating plant ranging

from well established technology such as combined heat

and power (CHP) units to more recent types of generation

technology like photovoltaics.

Although VSPPs have gained many positive effects,

they still have some specific, technical issues that need to

be addressed before their applications in the distribution

system driven by two fundamental goals can be fully

realized: 1) delivering an acceptable quality of supply to

consumers under normal conditions and 2) protecting the

integrity of the system when disturbed by faults.

There have been a number of problems reported in

literature that create complexity in control and protection

system of existing distribution networks such as failed

reclosing due to temporary fault current, out of

synchronous, protection coordination, false tripping,

protection under reach, and islanding operation [1]-[3].

It is obviously seen that while many of the problems are

shared in common, some are system-dependent.

Consequently, system operators and planners have to

carefully review and probably revise, if necessary, their

existing protection schemes to accommodate high

penetration levels of distributed generation.

This paper presents comprehensive studies on

technical impacts of VSPP on distribution systems in

metropolitan area, where the power delivery

infrastructure to the consumers is covered in three

provinces: Bangkok, Samutprakarn, and Nontaburi. The

distribution electricity infrastructure is of the type of

overhead and underground systems with different voltage

levels of 400V, 12kV, 24kV, 69kV, 115kV, and 230kV

[4].

The technical impacts are emphasized on control and

protection system. The studies were carried out through

International Journal of Electrical Energy, Vol. 3, No. 3, September 2015

©2015 International Journal of Electrical Energy 162doi: 10.18178/ijoee.3.3.162-168

power system analysis and simulation using real, existing

systems connected with VSPPs in a metropolitan service

area. The VSPPs are connected to a MV distribution

system, the main equipment of which consists of power

transformer, MV busbar, circuit breakers, MV feeders,

fuses, and DGs.

II. CONTROL AND PROTECTION SYSTEM OF

DISTRIBUTION NETWORK

The details of protective devices, protection

coordination, and restoration functions for interruption

events in the distribution system are described as follows

[4].

A. Protective Devices

A circuit breaker (CB) installed at the beginning of an

outgoing 12 or 24kV feeder (i.e., at the MV busbar of a

substation) is used to protect the feeder. It is a common

practice to utilize a fuse to protect a lateral MV feeder or

a downstream LV feeder behind a distribution

transformer. Fuse Type K (fast clearing time) is widely

used with a rating of 200A or 400A.

RR

FuseOC EF

DS

Figure 1. Operation of OC EF relay, RR, and fuse.

B. Protection Coordination

The non-directional overcurrent (OC) relay is

coordinately functioned with fuses and a reclosing relay

(RR) based on the principle of “fuse saving scheme”

using a microprocessor-based OC relay. A typical

protection system configuration of feeder is shown in Fig.

1. The fuse saving scheme strategy temporarily interrupts

an entire feeder for all faults occurring on the feeder with

the main objective to save expensive fuse replacement

and to reduce outage time of customers. The operation of

an OC relay is of two types: fast and slow, with details as

follows:

Instantaneous operation: At a current of 1,200 A

(for 24 kV) or at 1,800 A (for 12 kV) when a fault

is detected, the associated relay will disconnect the

CB at once to avoid damage on the fuse. After the

CB has been opened, this disconnecting mode will

be blocked. Then, the first step of reclosing relay

(RR) will come to operation by closing the CB.

Therefore, if the fault is temporary, the system can

return to normal without realizing a sustained

interruption.

Inverse definite minimum time (IDMT) operation:

With a rating of 600 A, 0.05 TMS (Time

Multiplier Setting), if the fault still remains, the

relay will not open the CB immediately, waiting

for the fuse to blow and isolate the faulty part. If

this is the case, the relay will not trip the CB;

therefore the customers in the healthy areas can

still be electrically supplied. On the other hand, for

example, a fault on the main feeder, for a short

period of time, the OC relay will trip the CB and

then the second step of the RR will be activated

instead.

The earth fault (EF) relay will monitor and detect earth

fault, with a rating of 120A 0.5 TMS.

The under-frequency (UF) relay monitors the system

frequency at an MV busbar. For an under-frequency

event mainly because of demand greater than supply, the

UF relay will shed some loads to keep the system balance

and prevent wide area outage such as cascade tripping. At

the frequency lower than 49Hz with a duration longer

than 0.15 second, the UF relay will start to trip feeders’

CBs for 5 different levels of the system frequencies (49,

48.8, 48.6, 48.3 and 47.9Hz).

Note that transmission lines are protected by distance

relay, directional overcurrent earth fault (OCEF) relays,

and current differential relays.

C. Restoration Functions

Automatic reclosing relay (RR) is a mechanism that

can automatically close the breaker after it has been

opened due to a fault. Because most of the faults on

overhead feeders or overhead transmission lines are

temporary (70-80%), reclosing relays play an important

role to increase system availability of supply (i.e.,

reducing outage time from sustained interruption to

momentary interruption) in an overhead feeder or an

overhead transmission line.

The control system of a recloser allows a preselected

number of attempts for service restoration after adjustable

sequential time delays. For example, a recloser may have

2 or 3 “fast” reclose operations with a few short time

delays, then a longer delay and one reclose; if the last

attempt does not successfully re-energize the line, the

recloser will lock out (for permanent faults) and require

human intervention to reset. In metropolitan distribution

systems, two pre-programmed attempts to re-energize the

feeders: first at 3 seconds and the other at 1 minute and

only one attempt at 4 seconds for the transmission lines.

For power transformer failures, restoration is

succeeded by the bus throw over (BTO), which is an

automatic function installed in the MV levels as shown in

Fig. 2. For a substation, the MV buses are separated by a

CB and each of the buses receives power from different

power transformers. When a fault occurs on one of the

transformers and after the HV-side CB disconnects the

transformer, the function of BTO will disconnect the

MV-side CB of the transformer and close the bus coupler

CB so that the two busbars are able to receive power from

the same power transformer. The function of BTO is

completed within 4 seconds after power transformer

failures.

A similar automated mechanism can be found in

transmission systems (69 or 115kV) for the line throw

over (LTO) or the coupler throw over (CTO). The former

is an automated function for line switching operation and


©2015 International Journal of Electrical Energy 163

the other for bus switching. For transmission line failures,

with the function of a LTO or a CTO will switch

substation’s CBs to receive power from another

transmission line within 0.2 second. The LTO function is

normally used in H–scheme substations while the CTO

function in double-bus single-breaker substations. Note

that the distribution systems do not have a syncheck relay.

LTO

BTO

Auto

Auto

RR RR RR RR

Figure 2. Operation of LTO, BTO, and RR for different fault locations.

III. STATE OF ISLANDING

The existing grid code for VSPP connection in the

network indicates that a VSPP is obliged to detect a fault

and to be self-disconnected within 0.1 second for a

machine-based VSPP [5] and 0.3 second for an inverter-

based VSPP [6]. This requirement prevents any damage

that may occur on VSPPs and electrical appliances, as

well as for safety to personal staff working onsite. To be

specific, islanding operation is currently not allowed.

Note that the self-disconnecting time for the inverter-

based VSPP in the previous grid code was 0.1 second.

Islanding situation is formed when associated

protective devices isolate small part from the main grid.

Because this small part contains DGs, it is possible that

some loads in the part can be served, causing positive and

negative impacts on the system [3].

For positive point of view, the system sees higher

power system reliability and therefore reduced electricity

outage cost of customers because VSPPs can serve some

loads while being waiting for the faulty part to be

repaired. Such intentionally islanded operation is useful,

for example, during scheduled maintenance. However, it

should be bear in mind that doing so needs to make sure

that the total capacity of the VSPPs is large enough to

supply the remaining load; otherwise, disconnection of

nonpriority loads, switching operation, and special

protection setting are required. In addition, incidents

while in islanding operation (e.g., changing demand,

short circuit, and personal staff working onsite) and while

in the process of reconnection to the main system at the

end of operation have to be taken into consideration.

Negative effects could happen because the isolated

network becomes a weak grid compared with the original

strong network (i.e., infinite bus). Therefore, problems on

stability and power quality (e.g., voltage regulation and

harmonics) can be expected, as well as protection

problems (e.g., coordination) and cause damage to

equipment in the network. To guard against unintentional

islanding operation, small generators are obliged to detect

isolation events and to be self-disconnected from the

network within suitable time frame.

IV. SMALL GENERATION AND SYMMETRICAL FAULTS

Let us consider a balanced fault shown in Fig. 3,

assuming that no load current is present in the system.

The fault level can be calculated using an equivalent

network shown in Fig. 4, where the generator model is

represented by an ideal voltage source serried with an

internal impedance ZS and feeder impedance ZL [7].

GDistance to fault = d

Line length = l

Figure 3. Symmetrical fault.

ZS ZL

E

Figure 4. Network equivalent for symmetrical fault.

For a three phase fault occurring at the end of feeder as

shown in Fig. 3, the fault current is given by:

f

S L

EI

Z Z

(1)

When a three phase fault is away from the substation

with a distance of d, the fault current becomes:

f

S L

EI

dZ Z

l

(2)

We can conclude that the impedance between the fault

position and the source limits the magnitude of fault

current. Namely, the fault current at the end of feeder is

less than that near the substation.

For a distribution system with a VSPP, the magnitude

of fault contribution from the VSPP depends on a few

factors. The first factor is the rating of the machine; that

is, the greater MVA, the higher the fault current. The

second factor is type of machines. The directly coupled

VSPP such as a synchronous generator or an induction

generator tends to supply more fault current, compared

with the converter interfaced VSPP [1]. Therefore, the

impact of protection is primarily focused on directly

coupled VSPP. Last, the fault current is location-specific.

A VSPP located near the fault position has a greater

contribution to the fault current.



V. IMPACT OF CONTROL AND PROTECTION SYSTEM

FOR UNDISCONNECTED VSPP DURING FAULTS

When there is a small generator installed in a

distribution system, power flows on the feeder become

multidirectional and so are fault currents. Those fault

currents may affect detecting operation of protective

devices. When a fault occurs and a VSPP is not self-

disconnected, the fault contribution from the VSPP or

islanding operation of the VSPP may affect protection

system and protection coordination. The following

impacts are foreseen.

A. Impact of RR: VSPP Supplies Arc to Temporary

Fault

Let us consider Fig. 5, where there is a temporary fault

on an overhead feeder. The OC instantaneous relay sends

a command to trip the CB to stop supplying the arc to the

temporary fault. After the fault has been cleared, the CB

is reclosed. However, if the VSPP has been continuously

supplying the fault, the arc might not have been

distinguished and may cause a problem for the first

attempt of the CB reclose. The network is still supplying

the fault and therefore the CB will be tripped by the OC

IDMT relay; otherwise, the fuse will blow. Such a

situation degrades the efficiency of the operation of the

RR for temporary faults, resulting in unnecessary opening

of the CB and therefore degrading system reliability as a

whole.

Figure 5. Impact of OC EF relay, RR, and fuse in overhead feeder.

B. Impact of RR to VSPP for Islanding Operation

Let us revisit Fig. 5 for a temporary fault on a feeder.

After tripping the CB by the OC relay, the temporary

fault disappears from the system. While some of the

system demand is being covered by the VSPP through the

feeder, the VSPP is working islandingly. Afterwards, the

RR sends a command to reclose the CB without syncheck

relay (as in the case of metropolitan distribution systems).

This reconnection process would introduce voltage

difference between the grid and the VSPP. The worst

case magnitude voltage of ˆ2P

V would be seen across

equipment, causing damage the equipment and also the

VSPP.

C. Miscoordination between OC Relay and Fuse

As already detailed, in a distribution system with an

overhead feeder, the coordination between the OC relay

and the fuses follows the fuse saving scheme. That is,

each of the fuses will interrupt only sustained faults. In

Fig. 5 for a fault on a feeder, the OC (IDMT) relay will

trip the CB before the fuse operates (i.e., before minimum

melting time). As in the case of temporary fault, after the

CB is closed by RR, the feeder is able to continue to

supply the loads as normal.

However, a feeder with a VSPP connected, when there

is a temporary fault, the fault contribution from the VSPP

may be added to the fault current from the grid, resulting

significantly high fault current seen by the fuse compared

with the fault current seen by the current transformer (CT)

of the OC relay, which detects the fault current from the

grid only. This excessive high current condition may

result in the fuse to blow before the OC (IDMT) relay to

trip the CB. Therefore, the protection coordination

between the OC relay and the fuses no longer follows the

fuse saving scheme. The negative effect is that fuses are

forced to operate more often than necessary (interrupting

both temporary and sustained faults), which worsens

system reliability as well as increases maintenance cost.

This problem could be avoided if the microprocessor

based OC relays were able to be programmed in two

modes of operation: instantaneous and IDMT as in the

case of the protection scheme in the metropolitan

distribution systems.

D. False Tripping / Sympathetic Tripping

For the sake of discrimination, the protection scheme is

required to response to only faults within their clearly

designated zone for fault isolation. However, this may not

be always the case for the presence of VSPP. As an

example, let us see Fig. 6. The VSPP connected at feeder

2 supplies part of the fault current to the adjacent feeder

via the MV busbar, with the remaining fault current

coming from the grid (Igrid). As already detailed, the

contribution of fault current magnitude of a VSPP

generally depends on its type, rating, and connecting

location. The fault current from the VSPP may exceed the

pickup level of the OC relay of feeder 2. Therefore, it is

possible that CB2, which is located at the healthy feeder,

is forced to open before CB1 (disturbed feeder) will be

disconnected on time to clear the fault.

Figure 6. False tripping of protection system.

This case can happen particularly in the weak grid with

long feeders and with a definite-time OC relay because it

is to make sure that the relay can detect low short circuit

current and hence low pick up current is usually set. An

effective way to tackle this problem is to install a

directional OC relay. However, such events are unlikely

to happen in the system because



feeders are not too long (typically less than 10 km),

maximum penetration of VSPP is limited at

4MW/circuit (for 12kV) and 8MW/circuit (for

24kV),

in the event as shown in Fig. 6, CB1 will be

disconnected at once by Instantaneous OC relay at

1,200A (24kV) or 1,800A (12kV).

The false tripping described above can be simulated by

a CHP-based VSPP in a distribution network. The

cogeneration system for heat and electricity receives

natural gas from a pipeline network. The installed

electricity generation capacity is 9.6MW, 6.4 of which is

offered to sell under a contractual agreement with the

network operator. Note that under the regulation of

purchasing electric power from cogeneration, the

measured Primary Energy Saving (PES) has to be greater

than 10% a year for the minimum requirement in the

regulation. CHP-based VSPPs should regularly be

audited for PES measurement after be granted licenses

[8].

A single line diagram of the substation with the

connected DGs is shown in Fig. 7. Two DGs are

connected closed to the substation, to be specific, at the

beginning of two of 24 kV feeders: F415 and F426. The

maximum short circuit current and Thevenin impedance

of the substation is shown in Table I. From Table I, the

MVA short circuit of the substation is calculated by (3).

3 ×24kV ×6.6kA = 274.357MVA (3)

System parameters of the VSPP are given in Table II.

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Figure 7. Single line diagram of the substation with connected DGs.

Fig. 7 shows a simulated network and balanced fault at

the beginning of feeder F415 by DIgSILENT [9],

whereas Table III shows the simulation results of

balanced short circuit current.

Considering Table III, we can see that from the real

case of each DG with the rating of 6.75MVA, there will

be in total a fault current from the network and from both

DGs flow through feeder F415 at 6.533kA. Therefore, the

OC (instantaneous) relay, which operates at a pickup

current of 1.2kA, will trip the CB of feeder F415.

Because a short circuit current from the second DG flow

through the feeder F426 is only 0.703kA, the CB of

feeder F426 will be idle in this case. Another case study

of interest is with each of the DGs having a modified

capacity of 8MVA (maximum allowable capacity in one

feeder). The simulation result indicate that both DGs

generate fault current not significantly different from the

base case. Likewise, when a fault occurs on feeder F426

near the substation, the simulation gives a similar

tendency. This simulation of the worst case scenario

confirms that the system will not be affected by false

tripping.

TABLE I. MAXIMUM SHORT CIRCUIT CURRENT AND THEVENIN

IMPEDANCES OF SUBSTATION

Base

Voltage

(kV)

ISC,3Ph

(kA)

Thevenin Impedance (Ohms) X/R Ratio

R1 X1 R0 X0 X1/R1 X0/R0

24 6.60 0.249 1.989 0.208 1.846 7.993 8.874

1st DG

F415

F426

Balanced Fault

2nd DG



TABLE II. SYSTEM PARAMETERS OF VSPP

Parameter Unit

Type of machine Synchronous

Connection Star

Rated output 6750 kVA

Voltage 6600 V

Frequency 50 Hz

Power factor 0.8

Direct axis synchronous reactance 2.32 p.u.

Direct axis transient reactance 0.304 p.u.

Direct axis subtransient reactance 0.19 p.u.

Negative sequence reactance 0.214 p.u.

Zero sequence reactance 0.133 p.u.

TABLE III. SIMULATION RESULTS OF BALANCED FAULTS

Case CB ''

kS ( MVA) ''

kI (kA)

Base case

(VSPP 6.75 MVA)

F415 271.57 6.533

F426 29.21 0.703

Worst case

(VSPP 8 MVA)

F415 274.85 6.612

F426 33.26 0.800

E. Impact of UF Relay and Function of LTO/CTO for

Islanding Operation of DG

Let us revisit Fig. 2. The substation is supplied from

two transmission lines and has a LTO (or a CTO)

function. When one of the lines is faulted and causes the

entire substation without electricity, the LTO will

perform switching operation within 0.2 second to recover

power from the other transmission line. Therefore, the

customers connected to this substation will experience

momentary interruptions.

If there is a VSPP connected to a MV busbar (or a

feeder), when a fault occurs at one of the two

transmission lines, the VSPP, which is assumed to have

enough capacity to supply almost the customer demands,

is not disconnected. With such a weaker network than the

original grid, the system frequency may go so low that

the UF relay can detect the falling frequency and trip

some (or all) the CBs protecting the outgoing feeders at

0.15 second (after the first transmission line outage). At

0.2 second, the LTO will try to energize another

transmission line to the substation. However, because the

feeders’ CBs have been opened, the customers of those

feeders will experience sustained interruption instead of

momentary interruption. Eventually, the customers have

to wait until the system operators coordinate with the

owner’s VSPP and close the CBs of the feeders. It can be

seen from this case that the presence of undisconnected

VSPPs degrade the efficiency of the operation of LTO

and CTO.

F. Impact of Distance Relay with Fault Contribution

from VSPP

Let us consider Fig. 8. Without a VSPP connected in

the network, when a fault occurs, the distance relay can

see the impedance defined by (4), which is exactly the

same as the fault location. However, with the presence of

the VSPP, the fault impedance is changed to (5).

Comparing two equations, we observe that the value of

the second term of (5) is greater than that of (4) due to the

fault contribution from the VSPP (I2). Without the VSPP,

I2 is zero and (4) and (5) become equal. It can be

concluded that the distance relay will see the distance

longer than actual and the relay decides not to trip the CB

as the fault stays outside its protective zone. In fact, it

should have been operated and this situation is known as

“Protection Under Reach”. In the metropolitan

distribution systems, distance relays are commonly used

to protect the transmission lines. Therefore, with high

penetration levels of VSPPs connected to transmission

lines, accuracy of the distance relay becomes problematic.

1 2 1Relay, without DG 1 2

1

( )L LL L

Z + Z IZ = = Z + Z

I (4)

1 1 1 2 2 2Relay, with DG 1 2

1 1

( )+ (1 + )L L

L L

I Z + I + I Z IZ = = Z Z

I I (5)

DG

Distance Relay

ZL1 ZL2

I1

I2

I1+I2

Figure 8. Impact of VSPP on distance relay.

VI. SUMMARY OF POTENTIAL PROBLEMS ON CONTROL

AND PROTECTION SYSTEM FOR VSPP

CONNECTION

For the metropolitan distribution systems, when there

is a fault in its networks and VSPPs are obliged to be

self-disconnected with a specified time frame (namely

within 0.1 second), it will not pose any threat on the

associated control and protection system. However, going

beyond this time frame may affect control and protection

system in the following aspects summarized in Table IV.

TABLE IV. POSSIBLE NEGATIVE IMPACTS ON CONTROL AND

PROTECTION SYSTEM IN METROPOLITAN DISTRIBUTION NETWORKS

FOR LATE DISCONNECTION OF VSPP AFTER FAULT EVENT

Causes

Control &

Protection

System Affected

Possible Consequences

Contribution of

VSPP to temporary

fault current

RR Failed reclosing

(If temporary fault is not

cleared, the event will be changed from momentary to

sustained interruption)

Islanding operation of VSPP

RR Out of synchronous (Equipment and VSPP may be

damaged)

Islanding operation of VSPP

UF relay, LTO or CTO

function

Activation of UF relay (If LTO or CTO function

cannot be achieved, the event will changed from momentary

to sustained interruption)

Contribution of VSPP to fault

current

Distance relay Protection under reach

Note that for ungrounded or neutral grounded

impedance systems, when there is a fault, islanding

operation of VSPPs may affect the EF relays. However,

because the distribution systems are normally solidly



grounded, there is no problem attached to the EF relays

for this situation.

VII. CONCLUSION

Because different distribution systems have different

protection schemes and operating principles, impacts of

small DGs are, in fact, system-specific and therefore it is

difficult to generalize effective ways to solve all control

and protection related problems. A number of scenarios

for possible impacts of VSPPs on control and protection

system have been comprehensively investigated in this

paper based on the protection and control schemes of

metropolitan distribution systems. To accommodate the

government policies to promote VSPPs for renewable

energy and energy efficiency, the implementation of

adaptive protection system become challenging for the

system operators and planners to retain system reliability.

New functionalities and communication technologies

such as smart grid or substation automation would be

required to arrive at optimal solutions that are

compromised between government policies and technical

issues.

ACKNOWLEDGMENT

The authors would like to express their sincere

gratitude to Metropolitan Electricity Authority (MEA) for

the financial and technical support of this research work.

REFERENCES

[1] J. Coster, “Integration issues of distributed generation in

distribution grids,” Proc. of the IEEE, vol. 99, no. 1, pp. 28-39, Jan. 2011.

[2] A. Girgis and S. Brahma, “Effect of distributed generation on

protective device coordination in distribution system,” in Proc.

IEEE Large Engineering Systems Conf. in Distribution System, 2001.

[3] P. Fuangfoo, et al., “PEA guidelines of impact study and operation

of DG for islanding operation,” in Proc. IEEE Industrial & Commercial Power Systems Technical Conference, 2007, pp. 1-5.

[4] Metropolitan Electricity Authority. [Online]. Available: www.mea.or.th

[5] Grid Code, Metropolitan Electricity Authority, Thailand, 2008.

[6] Grid Code for Solar PV Rooftop, Metropolitan Electricity Authority, Thailand, 2008.

[7] N. Jenkins, R. Allan, P. Crossley, D. Kirschen, and G. Strbac, Embedded Generation, IET, 2008, pp. 65-67.

[8] Regulations for CHP-Based VSPP, Metropolitan Electricity

Authority, Thailand, 2008. [9] DIgSILENT PowerFactory - User Manual, DIgSILENT GmbH,

2013, ch. 22.

Noppatee Sabpayakom is a Ph.D. student at

the King Mongkut’s University of Technology North Bangkok (KMUTNB),

Bangkok, Thailand, Faculty of Engineering, Department of Electrical and Computer

Engineering. He holds a Bachelor of

Engineering Program in Electrical Engineering (KMUTNB, 2004) and a Master

of Science Program in Electrical Power Engineering (KMUTNB, 2008).

He is a lecturer at the Department of Electrical Engineering Technology,

College of Industrial Technology, KMUTNB. His main research interests are power system operation, power system reliability, and

distributed generation.

Somporn Sirisumrannukul is an associate

professor at the Department of Electrical and Computer Engineering, Faculty of

Engineering, King Mongkut’s University of Technology North Bangkok (KMUTNB),

Bangkok, Thailand. His main teaching

responsibility includes power system-related courses for undergraduate and graduate

programs. His research interests are power system operation and optimization, reliability,

and renewable energy.



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