**8. Simulation results**

As it mentioned previous, proposed protective scheme is simulated for a sample distribution network. Short circuit analysis and adaptive protection algorithm must be examined simultaneously and online. PSCAD is used for adaptive algorithm and distribution system simulation and MATLAB is used for short circuit analysis and state estimation using simulated annealing method. After changes in system topology, short circuit analysis results vary. So the short circuit analysis must be shared to adaptive algorithm online and a data transfer link is needed between PSCAD and MATLAB software.

Figure 4 shows the system single line diagram, load specification, fuses and reclosers situation and distributed generations. Total load of system is 2.2 MVA and the system voltage is 20 kV. DG's characteristics are shown in table 3. DG's are modeled as a source and internal impedance and Transformers connection is D/YG 11.

For implementation of proposed method, the network is divided to four zones. Zone 1 clarifies with C.B zone1 circuit breaker and consists of main source and DG2. Zone 2 clarifies with C.B zone2 circuit breaker and consists of DG1. Zone 3 clarifies with C.B zone3 circuit breaker and consists of DG3. Finally Zone 4 clarifies with C.B zone4 circuit breaker and consists of DG4 and DG5.


Table 3. DG's and transformers characteristics

differ more than a certain threshold from 1 p.u. should be discarded. Similarly, ampere measurements at both line ends should be almost equal for lines with negligible shunt

In this paper the Simulated Annealing Method (SA) is used in optimization part. Simulated annealing is a method for solving unconstrained and bound-constrained optimization problems (Ingber, 1993). The method models the physical process of heating a material and then slowly lowering the temperature to decrease defects, thus minimizing the system energy. In iterations of simulated annealing algorithm, a new point is randomly generated. The distance of the new point from the current point, or the extent of the search, is based on a probability distribution with a scale proportional to the temperature. The algorithm accepts all new points that lower the objective, but also, with a certain probability, points that raise the objective. By accepting points that raise the objective, the algorithm avoids being trapped in local minima, and is able to explore globally for more possible solutions. An annealing schedule is selected to systematically decrease the temperature as the algorithm proceeds. As the temperature decreases, the algorithm reduces the extent of its search to converge to a minimum. Many standard optimization algorithms get stuck in local minima. Because the simulated annealing algorithm performs a wide random search, the

As it mentioned previous, proposed protective scheme is simulated for a sample distribution network. Short circuit analysis and adaptive protection algorithm must be examined simultaneously and online. PSCAD is used for adaptive algorithm and distribution system simulation and MATLAB is used for short circuit analysis and state estimation using simulated annealing method. After changes in system topology, short circuit analysis results vary. So the short circuit analysis must be shared to adaptive algorithm online and a data transfer link is needed between PSCAD and MATLAB

Figure 4 shows the system single line diagram, load specification, fuses and reclosers situation and distributed generations. Total load of system is 2.2 MVA and the system voltage is 20 kV. DG's characteristics are shown in table 3. DG's are modeled as a source and

For implementation of proposed method, the network is divided to four zones. Zone 1 clarifies with C.B zone1 circuit breaker and consists of main source and DG2. Zone 2 clarifies with C.B zone2 circuit breaker and consists of DG1. Zone 3 clarifies with C.B zone3 circuit breaker and consists of DG3. Finally Zone 4 clarifies with C.B zone4 circuit breaker and

DG DG1 DG2 DG3 DG4 DG5 S (kVA) 400 150 400 200 150 R (p.u.) 0.0476 0.0935 0.0714 0.0914 0.0429 X (p.u.) 0.4846 0.6120 0.5244 0.7608 0.5389

chance of being trapped in local minima is decreased.

internal impedance and Transformers connection is D/YG 11.

**8. Simulation results** 

consists of DG4 and DG5.

Table 3. DG's and transformers characteristics

software.

susceptance.

Fig. 4. Proposed adaptive protection scheme for distribution system

The adaptive algorithm is tested under different conditions and faults to ensure of proper performance. These conditions are fault in DG, permanent and transient fault in system buses. The performance of adaptive relay has been studied for some of these faults.

In case of fault occurred in DG, Adaptive relay waits until DG protection system operates and issues the trip command. As it seen in figure 5, while a fault occurs in DG1, current comparator in adaptive relay permits that DG over current relay operates. While a fault occurs in a DG, only the faulted DG must be disconnected from network and the other parts must continue their normal operations as it seen in figure 5.

In case of studying permanent faults in a system bus, it is assumed that a fault occurs in bus 41 in zone 4. This fault occurs at t=2 s and the fault duration is 3 s. Figures 6 shows that the adaptive relay sends a trip command to DG4, DG5 and zone 4 circuit breaker immediately. As the fault is permanent, adaptive relays doesn't allow DG's to connect on network, even after clearing the fault. After disconnecting DG4 and DG5, the adaptive relay does a reclosing operation on zone 4 circuit breaker. First reclosing is done on the circuit breaker at 0.4 s after fault occurrence. Second and third reclosing are done 1.2 s and 2.4 s after fault occurrence. This is shown in figure 6. Since the fault is permanent, in each reclosing stage, the adaptive relay senses the fault and sends trip command. After the third reclosing, trip command is sent to zone 4 circuit breaker and zone 4 is disconnected from network.

A New Adaptive Method for Distribution System Protection

other zones can continue their normal operation. C.B status for DG3

0.0 1.0 2.0 3.0 4.0 5.0 6.0 .

C.B status for DG3

0.0 1.0 2.0 3.0 4.0 5.0 6.0 .


status. (b) DG3 C.B status.

Status


status. (b) DG3 C.B status.

**9. Conclusion** 

Status

Considering Distributed Generation Units Using Simulated Annealing Method 63

current in the network and since a close command is sent to zone 3 circuit breaker. It is needed that DG be connected to network after fault clearing. So that synchronization operation must be done on DG3 circuit breaker. As it seen in figure 8, adaptive relay permits

It must be noticed that adaptive relay does reclosing operation only in faulted zone and

C.B status for Zone 3

0.0 1.0 2.0 3.0 4.0 5.0 6.0 .

C.B status for Zone 3

0.0 1.0 2.0 3.0 4.0 5.0 6.0 .

3.2

2.4

2.4

. .

> . .

. .

Fig. 8. Adaptive relay operation while clearing fault before first reclosing. (a) Zone 3 C.B

The fault location is in bus 34 in zone 3, fault duration is 0.6 s, time to apply fault is t=2 s.

. .

(b) (a)

Fig. 9. Adaptive relay operation while clearing fault before second reclosing. (a) Zone 3 C.B

Distributed generations have possible characteristics for system operation enhancement. Using DG's in distribution systems has many benefits such as system reliability improvement, power loss reduction, development costs decrease, power quality


Status

1.2 s 0.4 s 0.8 s

explained situation, other zones should operate normally in network.

2 s

In this case, after the fault is sensed with adaptive relay in network, the trip command is sent to DG3 and zone 3 circuit breakers immediately. As it seen in figure 9, does the first reclosing on zone 3 circuit breaker. According to the fault time that is more than 0.4 s, relay senses the fault in first reclosing and sends trip command to zone 3 circuit breaker instantaneously. Adaptive relay send a close command to zone 3 circuit breaker 0.8 s after the first reclosing. Since the fault time is 0.6 s, relay doesn't sense the fault in second reclosing and permits zone 3 circuit breaker to close. Moreover adaptive relay permits DG3 circuit breaker to close 2 s after second reclosing by the synchronization operation. In the

(b) (a)


Status

3 s 0.4 s

DG3 circuit breaker to close after 3 s, so that synchronization could be done.

Fig. 5. Fault occurs in DG1. (a) DG1 C.B status. (b) Other DG's and zones C.B status.

Fig. 6. Fault occurs in zone 4. (a) DG4 and DG5 C.B status. (b) Reclosing on zone4 C.B.

In the proposed method, only the faulted zone and DG's in that zone are disconnected from network and therefore the other zones can continue their normal operation. In order that the faulted zone returns to network as soon as possible, it must been detected precisely so that the fault could be cleared from the zone. Figure 7 shows the adaptive relay operation in precise fault location determination.

Finally, adaptive relay operation in case of transient fault in system has been investigated. The fault duration is considered in three cases so that we can study the adaptive relay operation at three stages of reclosing. In this simulation, first stage of reclosing is done 0.4 s after the fault occurrence, second stage of reclosing in done 0.8 s after the first reclosing and third stage of reclosing in done 1.2 s after the second reclosing.

Fig. 7. Fault location determination in case of permanent fault

The fault location is in bus 32 in zone 3, fault duration is 0.3 s, time to apply fault is t=2 s.

As it seen in figure 8, adaptive relay sends the trip command to zone 3 and DG3 circuit breakers. After 0.4 s, a reclosing operation is done on zone 3 circuit breaker. As the fault duration is 0.3 s, after the first reclosing, adaptive relay doesn't sense the short circuit current in the network and since a close command is sent to zone 3 circuit breaker. It is needed that DG be connected to network after fault clearing. So that synchronization operation must be done on DG3 circuit breaker. As it seen in figure 8, adaptive relay permits DG3 circuit breaker to close after 3 s, so that synchronization could be done.

It must be noticed that adaptive relay does reclosing operation only in faulted zone and other zones can continue their normal operation.

Fig. 8. Adaptive relay operation while clearing fault before first reclosing. (a) Zone 3 C.B status. (b) DG3 C.B status.

The fault location is in bus 34 in zone 3, fault duration is 0.6 s, time to apply fault is t=2 s.

In this case, after the fault is sensed with adaptive relay in network, the trip command is sent to DG3 and zone 3 circuit breakers immediately. As it seen in figure 9, does the first reclosing on zone 3 circuit breaker. According to the fault time that is more than 0.4 s, relay senses the fault in first reclosing and sends trip command to zone 3 circuit breaker instantaneously. Adaptive relay send a close command to zone 3 circuit breaker 0.8 s after the first reclosing. Since the fault time is 0.6 s, relay doesn't sense the fault in second reclosing and permits zone 3 circuit breaker to close. Moreover adaptive relay permits DG3 circuit breaker to close 2 s after second reclosing by the synchronization operation. In the explained situation, other zones should operate normally in network.

Fig. 9. Adaptive relay operation while clearing fault before second reclosing. (a) Zone 3 C.B status. (b) DG3 C.B status.
