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The over current relays for the line protection and loads connected at the buses are shown in the figure
The relays are IDMT in nature having t he characteristictop = 0.14 × Time Muiltplier Setting (Plug Setting Multipleir)0.02 - 1
The maximum and minimum fault currents at bus B are 2000 A and 500 A respectively. Assuming the time multipiler setting and plug setting for relay RB to be 0.1 and 5A respectively, the operating time of RB (in seconds) is __________.
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- 0.023
- 23
- 2.3
- 0.23
Correct Option: D
For Real B
T.M.S = 0.1
P. S. M = 5A
| top = | ||
| (P,S.M)0.02 - 1 |
Ifault(max) = 2000A
Ifault (min) = 500
A Maximum load current at C = 100A
For a setting current of 1A, plug setting is 100%
| PSM = | ||
| CT ratio × current setting |
| = | = 20 | |
| 100 × 1 |
| top = | ||
| (P,S.M)0.02 - 1 |
| = | = 0.227 ≈ 0.23 sec | |
| (20)0.02 - 1 |
