Create a 66kV ring main system of 6 buses and add 2 Grids with short circuit cur
ID: 2082755 • Letter: C
Question
Create a 66kV ring main system of 6 buses and add 2 Grids with short circuit current rating 9kA and 5kA located at BUS1 and Bus4 respectively and take 4 lines of 15to20kms of line length and impedance as per 66kv system guide lines and place 12 Directional over current relays?
1) Find Relay setting For 6 forward and 6 backward relays and obtain coordination between them
2) Add one more variable source at week bus and obtain a algorithm for adaptive DOCR protection and coordination?
u can use matlab
Need Proper explaination in written and also explaination of algorithm for optimised solution
Explanation / Answer
As mentioned in section II, the first one has been made in the frame of GA. In this research, the optimal coordination is done in such a way that all above three cases are satisfied. For the third case it is assumed that the distance relay is the main relay and the overcurrent relay is the backup. This assumption is a routine protection scheme in power networks. In interconnected networks, an overcurrent relay can be the backup of some other distance relays. Therefore, TSMs of all overcurrent relays and the operating time of the second zone of all distance relays must be determined for critical conditions. The critical condition is defined and shown in Fig. 2. An overcurrent relay is located at B and a distance one at M. The overcurrent relay is the backup of distance relay. When a fault occurs at F, the discrimination time between the operating time of overcurrent relay and that of the distance one is minimum. Therefore, the expression below must be appointed at the critical fault location, F. tb (F) tZ 2 > CTI (1) Where tb (F)is the operating time of overcurrent relay at F, tZ 2 is the operating time of the second zone of the distance relay and CTI is the coordination time interval. As mentioned above, coordination between overcurrent and distance relays must be made by adding a new constraint to OF in GA. The details of this method are described in section IV. Fig. 2. Critical fault location in coordination between overcurrent and distance relays IV. PROPOSED COMPUTATIONAL ALGORITHM In the new method, the OF is formulated as: (2) Where 1 ,2 ,3 are the weighting factors, i is the number of overcurrent relays that changes from 1 to N, k1 is the number of main and backup overcurrent relays that changes from 1 to P1 , k2 is the number of mai distance and backup overcurrent relays changing from 1 to P2 , tmbk1 is the discrimination time between the main and backup overcurrent relays. t mbDISOC k2 is the discrimination time between the main distance and backup overcurrent relays which is obtained from the equation below: (3) Where, tbOC k2 is the operating time of backup overcurrent relay for the fault at the end of the first zone of main distance relay(critical fault locations), tmDIS k2 is the operating time of the second zone of main distance relay and CTI is the coordination time interval that is equal to 0.3(sec). Two first terms of (2) are the same as the OF in [7]. The third term is added to OF to fulfill the requirement of overcurrent and distance relays. To describe the role of this new term, assume that tmbDISOCk2 is positive (fully coordinated), then the relative term in (2) becomes zero and OF also has a small value. However if tmbDISOCk2 is negative (miscoordination) the mentioned term will be equal to 23 ×tmbDISOCk2 and obviously for positive values of 3 the new term will have large values. Then, based on the concept of the evaluation and selection, those values that have more optimal OF values (less value) in the chromosomes, are granted more opportunities to be selected for the next iteration. The flowchart of new method is shown in Fig. 3. At first, after entering the network data, the impedances of the first, second and the third zones of distance relays are calculated. The operating time of the second and third zones of distance relays are selected respectively 0.3(sec) and 0.6(sec). Then, the short circuit currents for the faults exactly close to the circuit breaker (CB) of the main overcurrent relays and for the faults at the end of the first zone of main distance relays(critical fault locations) are calculated. After that, GA will start. ti ,tmbk1 and tmbDISOCk2 are c