Article title: ‘Protection coordination for distribution system in the presence of distributed
generation’
Author names:
1.
Muhammad YOUSAF (Corresponding Author): Full Time M.Sc. Research Scholar,
Electrical Engineering Department, University of Engineering and Technology Taxila, Pakistan.
Email: engryousaf47@yahoo.com , Phone # +923144412003.
2.
Tahir MAHMOOD: Associate Professor, Electrical Engineering Department, University of
Engineering and Technology Taxila, Pakistan.
Protection coordination for distribution system in the presence of distributed generation
Muhammad YOUSAF and Tahir MAHMOOD
Abstract: This paper proposes an effective strategy to overcome the impacts on coordination among
the protection devices due to distributed generators (DGs) integration. Increased fault current magnitude
and changes in power flow directions are the major impacts imposed by DGs on a typical distribution
system. The recloser-fuse coordination is much influenced upon the integration of DGs. The proposed
approach presents the rehabilitation of recloser-fuse coordination for post DG integration effects using
the directional properties of a recloser. The simulation results show that coordination among protection
devices can be regained using fast operation of the recloser to design a fuse saving scheme in the
scenario of temporary faults occurrence. The designed scheme also works satisfactorily for the isolation
of permanent faulted section of the feeder. This technique is verified by simulation results performed on
a real 11 KV radial distribution feeder for different faults location and DG sizes.
1
Keywords: Protection Coordination, Distribution Generation (DG), Directional Recloser, Relays, Fuses,
Distribution Systems.
1. Introduction
Typical distribution systems were designed to operate radial configuration in which power flows from
the source towards the customers connected. So the protection coordination of the radial system is very
simple in nature. The distribution system contains the protection devices e.g. fuse, recloser, relays and
circuit breaker. These protective devices are coordinated in such a way to interrupt the unidirectional
flow of the fault current from the source end towards the fault point [1, 2].
However keeping in view the global concerns of the environment and to meet the load growth, the
distribution power planners has paid a great attention toward the distributed generation [3, 4].
Upon integration the distributed generation with distribution system, the configuration for power flow
for a conventional network has been changed from unidirectional to multidirectional system. However,
However, it is very important to know the margin required for the preservation of the protection
coordination when a DG is being integrated to a power system. The distributed system protection is to
be reviewed after the integration of DGs [2], [5], [6, 7].
In [8], researchers tried to solve miscoordination problem caused by DGs integration by formulating it a
mixed integer programming problem for a directional overcurrent relays. A mathematical problem was
first developed and differential evolution algorithm was used to solve the mis-coordination problem. But
differential evolution method contains much complication to be used for a large distribution feeder. It
was also suggested by researcher that after integrating each distribution unit, the existing protection
coordination must be checked in order to identify the impacts of adding DGs to the power system.
In [9],the authors used the new relay setting technique for the changed power generation and distribution
in the power system to solve mis-coordination problem. In [10], mis-coordination problem was resolved
2
by dividing the whole power system into different zones and installing a circuit breaker for each zone.
But this approach faced the problems of limitation for the case when very large distribution feeder was
used as a test system.
In [11], researchers performed research on reducing the contribution of DGs to the short circuit current
level by using the concept of fault current limiter (FCL) but it resulted in some disadvantages such as the
power dissipation across the fault current limiter as it is continuously being connected to the power
system. This power loss was much reduced by using superconducting fault current limiter (SFCL) in by
the authors since SFCL has zero resistance during normal operation of the power system and its
resistance goes on increasing due to the increased fault current. The major disadvantage of using SFCL
is that they are very costly and are being used by some developed countries[12, 13].
Since in power distribution system, about 75-80 % faults are temporary in nature. These faults can be
categorized as self-clearing faults [14]. Directional recloser can be used for the clearance of upstream
and downstream momentary faults in coordination with other protective devices of a distribution system.
The proposed approach will considerably reduce the duration of sustained interruptions. The proposed
scheme is used to establish the proper coordination among fuses and recloser to eradicate the impacts of
DGs integration on protection coordination. The designed scheme considers all the parameters of real 11
KV distribution feeders.
2. Algorithm for the proposed approach
The proposed approach has been implemented on a particular radial distribution feeder having DGs and
different protection components. The procedural steps followed for the proposed algorithm are shown in
Figure 1.
When a DG is being installed at a distribution feeder, then after its integration the conventional
protection scheme of the hosting feeder is checked to assure that whether DG has changed the protection
3
coordination of the feeder. If there were no change in protection coordination there is no need of
reconstruction of the feeder protection coordination. But it may be a very rare case when the traditional
coordination is retained. Mostly, it is lost due to fault current contribution by DGs [15].
I.
Calculate the Ifmin and Ifmax for the hosted feeder. In order to calculate Ifmin, the impact of DGs is
neglected and calculations are performed without DG integration whereas Ifmax is calculated after
integration of DGs.
II.
The Ifmin and Ifmax will give an idea about the current variation for the penetration of DGs into
distribution system.
III.
The characteristics curves of all the coordinated protection devices are plotted.
IV.
When a DG is integrated downstream the recloser and there is fault downstream the recloser, the
Irecloser will be less as compared to the Ifuse on faulted section.
V.
The next step is to reexamine the fast operation of the recloser in order to ensure the operation of
the recloser before the melting of fuse for fuse saving scheme.
VI.
The recloser fast operation curve will be shifted downward by a factor of ratio of Irecloser and Ifuse.
It will ensure the proper coordination is being established between fuse and recloser. The new
setting obtained from the newly constructed characteristics curve is implemented on the recloser.
Figure 1: The flow diagram of the proposed approach.
VII.
VIII.
Size of the fuses can also be updated to establish proper coordination among protection devices.
Revise recloser and fuses Time-Current Curves (TCC) curves according to changed parameters
for coordination for different protection devices.
IX.
Then fuse-Relay coordination is checked for hosting and neighboring feeder and confirmation of
its preservation is to be ensured.
4
X.
The algorithm can be repeated to regain the proper coordination among the different protection
devices.
3. Case study
In order to perform a comprehensive case study on the effectiveness of designed scheme on the real
distribution system, data of a practical 11 KV distribution feeder was used. This distribution feeder
named as Panian radial distribution feeder has about 168 numbers of nodes starting from 132 KV
Haripur grid station.
It has a total length of about 98.9 km and a total load of 8425 KVA whereas 4625 KVA load is
connected upstream the recloser while the 3800 is downstream the recloser. All protection devices
setting for the pickup currents are usually taken as 1.25 the full load current.
In order to establish a proper coordination among the protection devices, the difference among the
primary and backup protection devices must always be greater than 200-300 ms. The one line diagram
constructed in MS VISIO is shown in Figure 2 while Figure 3 represents the one line diagram in
Electrical Transient Analysis Program (ETAP).
Figure 2: One line diagram of 11 KV distribution feeder (case study)
The recloser is located at the mid feeder because of the integration of two DGs will not cause the
momentary interruption for a temporary fault occurrence for the case when recloser is at the start of the
feeder.
Keeping in view the complexity of this lengthy distribution feeder, the feeder under case study has been
reduced from 168 nodes to only 38 nodes by summing the loads on respective laterals and associated
sub laterals to the corresponding node. Practically, it was found that reduction of case study feeder from
complex shape to a simple one did not affected the overall results of load flow and protection and
protection coordination [3, 16].
5
3.1. All possible zones of protection
A zone of power system protection is the part of the circuit that is disconnected only when an electrical
fault occurs in that part of the power system preserving the continuity of supply to the healthy sections.
The radial distribution feeder has been divided into 40 zone of protection as shown in table 1. Each zone
has a primary protection as well as backup protection device.
Each protection zone is named after the name of the protection device being installed. To make easy to
understand, each protection devices was named to its corresponding node number and each bus bar
name is also named after the node number.
In view of the fact that protection of 11 KV distribution feeder was designed to operate in conventional
protection coordination order during the faulty conditions. In the absence of DGs, the protection devices
have to control the flow of fault current from grid source point towards the fault point. So a very limited
number of protection devices have to operate for the fault isolation that may be fuse, reclosers and
feeder relay.
Since recloser is installed to clear the temporary fault. So it must be properly coordinated with fuses.
However in case of multiple numbers of DGs integration, each reclose and fuse will experience different
level of fault as compared to DGs less environment for which they are being installed and coordinated.
The cause for mis-coordination problem among protective devices is explained for mid feeder recloser
in which a DG1 is connected downstream and another DG2 is connected upstream the recloser.
In this distribution feeder, each zone contains a lateral fuse which is coordinated with recloser and can
be operate according to fuse saving scheme for temporary fault occurrence.
All the parameters data about the size of conductor (DOG conductor denoted by ‘D’ in Figure 2),
Transmission line parameters and DGs sizes and their location is given in [2].
Figure 3: One line diagram of the radial 11 KV feeder constructed in ETAP
6
Table 1: All possible protection zones with primary and backup protection devices
4. DGs and protection coordination
In order to reduce the real power loss and to make the nodes voltage within acceptable limit, two DGs
have been inserted at two different nodes. DG1 having the size of about 3.722 MVA was connected to
node number 30 while DG2 with size of 2.28 MVA was connected to node number 14 [3]. After the
integration of DGs with distribution feeder, the power loss was much reduced from 605.5KW to 39.7
KW. And at the same time, voltage profile was much improved with 16% reduction in total voltage
drop[3]. But DGs integration caused a very serious problem to protection coordination for the
distribution feeder. When DGs are placed to the circuit, the objective is to isolate the faulted point fed by
a number of sources
The simulation results conducted shows a miscoordination between the protection devices. The
sequence of operation of protection devices is listed below in table 2 in the presence of DGs for a few
zones of protection.
Table 2: Sequence of operation of the devices in the presence of DGs
Simulation results show that in some cases the fuse was blown out before the operation of recloser
which is false tripping sequence as recloser setting was designed to operate earlier than fuse (fuse saving
scheme) in order to remove the temporary faults with de-energizing the faulted section and again
energizing.
In case of a line to ground (L-G) fault in fuse 1 zone, fuse 1 was tripped before the recloser. The reason
behind this false tripping can be explained with characteristics equations and TCC of the protection
devices.
Now, the fault current for a fault in distribution system is contributed by three fault current sources that
are from main distribution feeder, DG1 and DG2. In order to interrupt the fault current from main
7
distribution feeder, the correct tripping device is the main feeder relay which initiates the operation of
the associated M.V circuit breaker. If the fault occurs in relay zone, the DG1 contribution toward the
fault current (If) can be terminated by DG1 protection system while DG2 contribution can be ended up
by recloser operation. If the fault is in the recloser zone, the main distribution station and DG1
contribution can be controlled by recloser tripping while that of DG2 with DG2 protection system.
5. Renovation of protection coordination
When the DGs are integrated, it starts to contribute toward fault current. So for the same fault at the
same location, fault current magnitude increases causing a mis-coordination among the traditional
protection coordination. The table 2 shows that in most of the cases, a miscoordination occurs among the
protection devices. The results indicate that the original system loses selectivity after the DGs insertion.
The reason behind this is explained in next sections.
5.1.Mathematical Modeling
The recloser fault current (Irecloser) is always less than the corresponding laterals fuse current (Ifuse)
because it follows the two cases:
a) If the fault is downstream the recloser , then
Ifuse = Irecloser+ IDG1
(1)
Where Irecloser= Igrid+IDG2
b) If the fault is upstream the recloser, then
Ifuse = Irecloser+ IDG2+Igrid
(2)
These equations show that fault current is always higher for a fuse in the presence of DGs so fuse is
operated before the recloser tripping causing a false tripping. Since recloser follows the following
equation [17, 18]:
𝑡𝑜𝑝 𝐼 = 𝑇𝐷𝑆
𝐴
𝑝
𝐼
−1
𝐼𝑝𝑖𝑐𝑘 −𝑢𝑝
+𝐵
(3)
8
When the
𝐼𝑟𝑒𝑐𝑙𝑜𝑠𝑒𝑟
𝐼𝑓𝑢𝑠𝑒 factor is multiplied with Time Dial Setting (TDS) in equation (3), the
characteristic curve of the recloser will shift down resulting in new coordination among fuse and
recloser.
5.2. Protection Coordination Constraints
For typical over-current protection coordination, the following constraints to be meet for proper
coordination [18-20].
i.
The first constraint to be met is the equipment overload constraint.
Ipickup ≤ Ispec
(4)
This constraint satisfies the condition for each protection device of not being overloaded under
any circumstances. So pickup value of each protection devices must be less than the maximum
value for which it is designed. In this way, it will be able to perform its function properly.
ii.
There should be difference between operating time of upstream and downstream protection
devices in order to satisfy specified time margin.
Tup (If) - Tdown (If) ≥ tmargin
(5)
Where Tup (If) shows the operating time of upstream devices under faulty condition and Tdown (If)
indicates the operating time of downstream devices under faulty condition and difference of
these time constrains should some tome margin which is usually greater than 100 ms.
iii.
The recloser operating time in the fast mode must always be less than the minimum melting time
(MMT) for the respective fuse in order to design fuse saving scheme.
TRf (IR)-MMTf (IFuse) ≤ 0
(6)
Whereas difference between recloser fast operating time TRf (IR) and minimum melting time of the fuse
must be negative. It will cause the de-energizing the fault by fast operation of recloser and try to selfclear it. This will save interruption caused by fuse melting in case of temporary fault occurrence.
9
5.3. Plotting of TCC curves
The Time Current Curve (TCC) represents the sequence and time of operation of the protection devices.
The fuse TCC curve consists of two curves. The lower curve is Minimum Melting Time (MMT) while
the upper is called Total Clearing Time (TCT). The TCC curve for the cases mentioned in table 2 is
shown below in Figure 4.
Figure 4: TCC curve of protection devices in the presence of DGs
For the perfect coordination among the fuse and recloser, the recloser fast operation TCC curve should
be lower than the respective fuse MMT curve while recloser delayed operation curve must be laid above
the fuse TCT curve. This will result in recloser tripping in the fast mode of operation before the fuse
start to melt giving momentary fault a possibility of self-clearing[15, 21].
However, in case of permanent fault occurrence, fuse melts to operate before the recloser trips in slow
mode of operation. The relays TCC curves of main feeder relay and DGs protection relays lies above the
all the fuses and reclosers curves giving a back-up protection if primary protection devices fail in
successful operation.
5.4. Designing of protection coordination scheme
Since after the addition of DGs, power flow is changed from unidirectional to multidirectional; the
requirement is to trip the flow of multidirectional fault current. In this scenario, directional protection
scheme become the suitable choice to resolve the selectivity problem of the distribution system. Since
the fuses are located at the beginning of each lateral in which the flow of fault current is unidirectional,
so fuse do not need any directional property. Since fuses do not posses directional nature, if fuse are to
be designed for directional protection, they are to be replaced by recloser.
The fault current through the feeder relay is still unidirectional, so there is no need of directional
property of this relay. Since recloser is subjected to multidirectional fault current, so it must possess the
10
directional nature. In order to possess the directional nature, recloser must have two setting. One setting
is to be designed for the downstream fault location and other is designed for upstream fault location.
In the above designed scenario, the total load connected downstream the recloser is 3800 KVA so the
pickup current for this downstream setting is 249 A while for upstream setting of recloser, the pickup
current setting is 303 A.
Since DG2 is located upstream the recloser at node 14, so its protection relay should have a setting
slower than the downstream setting of recloser. This will result in tripping of recloser for a fault at its
zone before DG2 protection operates. This will resolve the selectivity problem recloser and DG2
protection system.
For DG1 which is located at node 30, its protection setting should be slower than the upstream setting of
the recloser so that it results in recloser tripping for a fault in the feeder relay zone. In order to
coordinate fuses on upstream side of the recloser, they should operate faster than recloser delayed
operation in order to isolate the fault zone for in case of a permanent fault. The fuse on the lateral
downstream the recloser must operate before the operation of DG1 protection system.
If the generator is to be connected to the sub lateral of distribution feeder, then lateral fuse can be
replaced with a directional recloser that allows interruption of fault current in both cases when the fault
is located upstream and downstream of the lateral recloser. After isolation of the faulted section, recloser
initiates the reclosing process for restoration of supply to healthy section. Using the above mentioned
scheme, protection coordination was restored among the protection devices.
5.5. Implementation of the proposed scheme
If there is a fault at relay zone, the fault current contribution from the distribution system was interrupted
by the feeder relay. The fault current from DG1 will be interrupted by the recloser and DG1 protection
11
will be its backup protection. The fault current contribution from DG2 will be interrupted from by DG2
protection system. In these circumstances, all the tripping decisions are correct.
Now if the fault location is downstream the recloser (recloser zone), then fault current coming from
distribution system and DG2 is interrupted by recloser and feeder relay and DG2 protection system will
works on its backup. The contribution of DG1 towards fault current will be terminated by DG1
protection system. The Figure 5 shows the fault current level through recloser and fuse for a L-G fault
on each node.
Figure 5: Fault Current Calculation for Recloser and Fuse for an L-G Fault on each node
After the penetration of DGs in distribution feeder, the fault current level and direction of fault current
flow changes for both recloser and fuses. So the TCC curves of recloser and relays should be revised
and fuses size should be updated. The multiplication of lowest value of IR/IF with recloser curve will
lower down the whole curve and protection coordination will be checked again. If the fault location is in
fuse zone for example Fuse 20, then fault current contribution from all sources will be interrupted by
recloser opening and DG1 protection relay. If the fault was temporary, then de-energizing and the
energizing the fault will result in fault removal. However if the fault still persist after the recloser
opening in fast mode of operation, then this permanent fault can also be removed by the associated
fusing protection device i.e. fuse 20. If this operation becomes unsuccessful in removal of fault, then
recloser tripping in slow mode of operation will works as its backup protection. And protection system
of DG1 will also works as the backup protection device.
6. Impact of DGs size on protection coordination
To illustrate the effect of DG size on protection coordination, the above proposed approach has been
examined for different sizes of the DG connected to the distribution system. As the fault current
12
contribution increases with the increase in DG size, so the time of operation of different protection
devices decreases with increase in DG size [22, 23].
The simulation for fault current contribution of different sources and their effect on protection
coordination can be depicted from the table 3. The simulations are carried out for a line to ground fault
on the node 20 downstream the recloser. The fault current contribution of each source and operating
time of each protection device is listed in table 3.
Table 3: Fault current contribution and time of operation for a fault downstream the reclose
It is concluded from the results that as the rating of DGs increases, their contribution towards fault
current increases while that of distribution substation (DS) decreases at the same time. The simulation
results also depict that operating time of main feeder relay is always greater than recloser and DG2
relay. This will result in recloser lockout operation for a recloser downstream fault before tripping of
feeder relay’s circuit breaker CB1. DG1 relay is required to operate before recloser delayed operation so
that before locking out the recloser; fault is completely de-energized in order to give it a chance of selfclearing. These results prove that protection coordination among these devices is survived at the
increased DGs size and multiple DGs integration for a fault downstream the recloser.
The Figure 6 is the graphical representation of the fault current contribution by each source while Figure
7 presents the graphical picture of the time of operation of different protection devices with variation in
DGs size.
Figure 6: Fault current contribution for a L-G fault downstream the reclose at node 20
Figure 7: Time of operation for different Protection Devices with different DGs Sizes with an L-G fault
at node 20
The same analysis can be performed for a fault upstream the main recloser. Now an L-G fault is located
in feeder relay zone upstream the recloser at node 17. The results of fault current contribution from each
13
source and operating time of each device is shown in under given table 4 and results are graphically
represented in Figure 8 and Figure 9.
Table 4: Fault current contribution and time of operation for a fault upstream the reclose
Figure 8: Fault current contribution for a fault upstream the reclose at node 17
Figure 9: Time of operation for different Protection Devices with different DGs Sizes with an L-G fault
at node 17
These results depict that temporary fault eradication needs tripping of all the fault current sources so that
contribution towards the fault current is terminated. This will result in temporary fault removal. But a
permanent fault needs the lockout operation of recloser along with isolation of other fault current
sources. Simulation results for faults other than L-G shows that this approach works properly for any
type of fault occurrence.
However, the protection coordination is needed to be checked after each insertion of new DG or
changing in the size of any existing DG. The selectivity problem can be resolved using the above
proposed curve fitting approach.
7. Conclusion
The paper illustrates the impacts of distributed generation integration on the protection coordination for
radial distribution networks. The proposed approach for restoration of protection coordination mainly
focuses on temporary fault removal without melting the fuse. It has been observed from simulation
results that the selectivity problem of the protection devices can be addressed using the curve fitting
technique. The multiple DGs integration with distribution feeder needs the utilization of directional
property of the recloser along with updating the fuse sizes and relays setting. The methodology is
validated for a real radial distribution feeder. The simulation results verify the proper functioning of this
technique for different fault location and DGs sizes. Thus proper coordination among different
14
protection devices can be restored to eradicate the impacts of post DG integration on distribution
network protection.
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Tables:
Protection
Zone
Primary
Protection
Devices
Feeder Relay
Zone
Feeder Relay
Recloser Zone
Recloser
Fuse 1 Zone
Backup
Protection
Device
Incoming
Feeder
Protection
Protection
Zone
Primary
Protection
Device
Backup
Protection
Device
Fuse 19 Zone
Fuse 19
Feeder Relay
Feeder Relay
Fuse 20 Zone
Fuse 20
Recloser, Relay
Fuse 1
Feeder Relay
Fuse 21 Zone
Fuse 21
Recloser, Relay
Fuse 2 Zone
Fuse 2
Feeder Relay
Fuse 22 Zone
Fuse 22
Recloser, Relay
Fuse 3 Zone
Fuse 3
Feeder Relay
Fuse 23 Zone
Fuse 23
Recloser, Relay
Fuse 4 Zone
Fuse 4
Feeder Relay
Fuse 24 Zone
Fuse 24
Recloser, Relay
Fuse 5 Zone
Fuse 5
Feeder Relay
Fuse 25 Zone
Fuse 25
Recloser, Relay
Fuse 6 Zone
Fuse 6
Feeder Relay
Fuse 26 Zone
Fuse 26
Recloser, Relay
Fuse 7 Zone
Fuse 7
Feeder Relay
Fuse 27 Zone
Fuse 27
Recloser, Relay
Fuse 8 Zone
Fuse 8
Feeder Relay
Fuse 28 Zone
Fuse 28
Recloser, Relay
Fuse 9 Zone
Fuse 9
Feeder Relay
Fuse 29 Zone
Fuse 29
Recloser, Relay
Fuse 10 Zone
Fuse 10
Feeder Relay
Fuse 30 Zone
Fuse 30
Recloser, Relay
Fuse 11 Zone
Fuse 11
Feeder Relay
Fuse 31Zone
Fuse 31
Recloser, Relay
Fuse 12 Zone
Fuse 12
Feeder Relay
Fuse 32 Zone
Fuse 32
Recloser, Relay
Fuse 13 Zone
Fuse 13
Feeder Relay
Fuse 33 Zone
Fuse 33
Recloser, Relay
Fuse 14 Zone
Fuse 14
Feeder Relay
Fuse 34 Zone
Fuse 34
Recloser, Relay
Fuse 15 Zone
Fuse 15
Feeder Relay
Fuse 35 Zone
Fuse 35
Recloser, Relay
Fuse 16 Zone
Fuse 16
Feeder Relay
Fuse 36 Zone
Fuse 36
Recloser, Relay
Fuse 17 Zone
Fuse 17
Feeder Relay
Fuse 37 Zone
Fuse 37
Recloser, Relay
Fuse 18 Zone
Fuse 18
Feeder Relay
Fuse 38 Zone
Fuse 38
Recloser, Relay
Table 1: All possible protection zones with primary and backup protection devices
17
Faulted
Zone
Fault
Type
Fuse 1
Zone
Fuse 10
Zone
Fuse 20
Zone
Fuse 30
Zone
Fuse 38
Zone
Status of Power
Sources
Sequence of Operation of Protection Devices
Grid
DG1
DG2
1st
2nd
3rd
4th
5th
L-G
ON
ON
ON
Fuse 1
Recloser
Feeder
Relay
Relay DG2
Relay DG1
L-G
ON
ON
ON
Recloser
Fuse 1
Relay DG2
Feeder
Relay
Relay DG1
L-G
ON
ON
ON
Fuse 20
Recloser
Relay DG2
Relay DG1
L-G
ON
ON
ON
Fuse 30
Recloser
Relay DG1
Relay DG2
L-G
ON
ON
ON
Recloser
Fuse 38
Relay DG1
Relay DG2
Feeder
Relay
Feeder
Relay
Feeder
Relay
Table 2: Sequence of operation of the devices in the presence of DGs
DG Size
(MVA)
Fault Current
Contribution (A)
DG
1
DG
2
DS
DG1
DG2
2
3
4
5
6
1
2
3
4
5
270
201
167
145
133
871
896
983
1060
1114
603
899
1120
1301
1450
Operating Time of various protection devices
(Seconds)
Feede
r
Relay
1.691
1.745
1.830
1.925
2.024
Recloser
Fast
Delay
0.091
0.088
0.085
0.084
0.083
1.655
1.631
1.567
1.518
1.479
DG1
Relay
DG2
Relay
1.435
1.370
1.097
0.937
0.833
6.209
3.247
2.206
1.725
1.547
Table 3: Fault current contribution and time of operation for a fault downstream the recloser
DG Size
(MVA)
Fault Current
Contribution (A)
DG1
DG2
DS
DG1
DG2
2
3
4
5
6
1
2
3
4
5
337
261
222
197
178
710
746
791
836
880
751
1170
1490
1760
1990
Operating Time of various protection devices
(Seconds)
Feeder
Relay
0.836
0.851
0.882
0.919
0.957
Recloser
Fast Delay
0.091
0.073
0.067
0.064
0.062
3.143
2.087
1.713
1.522
1.407
DG1
Relay
DG2
Relay
3.207
2.278
1.821
1.654
1.481
2.587
1.175
0.797
0.618
0.514
Table 4: Fault current contribution and time of operation for a fault upstream the recloser
18
Start
Figures:
Sectionalize the whole distribution Feeder
Plot TCC Curves of Reclosers and Fuses and Relays
Determine Initial and changed Parameters due to DGs Integration
Is Recloser-Fuse Coordination is
lost due to DG integration?
NO
Analysis of the Coordination between Protection Devices
Use the Fast and delayed Characteristics Curve of Recloser
Determine Fuse (IF) and Recloser (IR) Fault Current
Determine the factor IR/IF
Modify the Recloser Fast and Delayed Curve by factor IR/IF
andrecloser Fault Current
Update Fuses Size
NO
Is Fuse-Relay
Coordination is
lost in the
Feeder?
YES
Capacity of DGs to Suitable
Value to meet all Constraints
Stop
Figure 1: shows the flow diagram of the proposed approach.
19
Figure 2: One line diagram of an 11 KV distribution feeder (case study)
Figure 3: One line diagram of the radial 11 KV feeder constructed in ETAP
20
Figure 4: TCC curve of protection devices in the presence of DGs
6
Recloser
5
Fuse
Current (KA)
4
IR/IF
3
Fault Current without DGs
2
1
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38
Node
Figure 5: Fault Current Calculation for Recloser and Fuse for an L-G Fault on each node
21
1600
Current Contribution by each Source (A)
1400
1200
1000
800
DS
DG1
600
DG2
400
200
0
1
2
3
4
5
DGs Size (MVA)
Figure 6: Fault current contribution for a L-G fault downstream the reclose at node 20
7
6
Feeder Relay
5
Time (Sec)
Recloser (Fast)
4
Recloser (Delay)
3
DG1 Relay
2
DG2 Relay
1
0
1
2
3
4
5
DG Size (MVA)
Figure 7: Time of operation for different Protection Devices with different DGs Sizes with an L-G fault
at node 20
22
Current Contribution by each Source (A)
2500
2000
1500
DS
DG1
1000
DG2
500
0
1
2
3
4
5
DGs Size (MVA)
Figure 8: Fault current contribution for a fault upstream the reclose at node 17
3.5
3
2.5
Time (Sec)
Feeder Relay
2
Recloser (Fast)
Recloser (Delayed)
1.5
DG1 Relay
1
DG2 Relay
0.5
0
1
2
3
4
5
DG Size (MVA)
Figure 9: Time of operation for different Protection Devices with different DGs Sizes with an L-G fault
at node 17
23