Consider the protection zones at Station 2 in Figure 1, and answer the following

Question

Consider the protection zones at Station 2 in Figure 1, and answer the following questions (12pts) 1. a) b) c) d) e) f) Breaker 938 is covered by which zone(s)? Breaker 214 is covered by which zone(s)? Breaker 964 is covered by which zone(s)? Breaker 954 is covered by which zone(s)? The 161/13kV transformer bank is covered by which zone(s)? Do the zones properly overlap for each element? If not, which ones do not and what (if anything) should be done? Station 2 Line 2-3 161kv relays Line 1-2 relays Station 3 964 Line 2-3 Station 1 61kV 13kv Line 1-2 224 61kV Line relays 234 Line relays 244 for 161-13kv xfmr bank (B-set) 161kV bus diff relays relays Diff relays for 161-13kV xfmr bank (A-set) 13kV bus diff relays Figure 1. Problem 1

Explanation / Answer

a. Breaker 938 covers

(i) 161/13 KV Transformer bank, as it is located at high voltage side of Transformer

(ii) 13KV bus side and 13KV feeders, if any fault on 13KV feeder not cleared by respective breaker and / or Transformer LV breaker (214) not acted

and (iii) for protection of 161KV Bus in case of Bus bar protection acted

b. Breaker 214 covers

(i) 13KV Bus and (ii) 13KV lines, in case any 13KV line breaker not cleared by the respective line breaker

(iii) as this breaker is located at Low voltage side of Transformer, it is used for protection of Transformer for internal faults

c. Breaker 964 is located for protection of

(i)161KV line between station 2 and station 3 (towards station 3) and (ii) for 161KV bus in case of bus bar protection scheme acted

d. Breaker 954 is located for protection of (i) 161KV line between station 2 and station 1( towards station 1) and (ii) for protection of 161KV Bus in case of bus bar protection scheme acted

e. 161/13KV Transformer bank covered by breaker 938 on HV side and breaker 214 on LV side for protection of internal faults and external faults

f. Yes, all the elements are properly covered with good zone overlap

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