Page 262 - Practical Power System and Protective Relays Commissioning
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Protection Relays Chapter | 18 259
When there is an open circuit in CT1 then the current I 1 of CT1 will pass
through the magnetizing impedance Z M2 and Z M3 and the relay total
resistance (R relay 1 R st )
V supervision 5 I 1 ((R relay 1 R st )// Z M2 // Z M3 )
The action of this supervision relay after a time delay of about 3 seconds
is to give an alarm that the busbar protection is faulty and to short circuit
the buswires to prevent damage to the relay and stabilizing resistors due to
the open circuit condition on one of the busbar protection CTs.
18.9.4 TYPICAL BUSBAR PROTECTION OF HIGH-
IMPEDANCE TYPE
Refer to the AC and DC circuits of the two section single busbar scheme
with one relay per zone circuits in Figs. 18.9.12 and 18.9.13.
FIGURE 18.9.12 Simple example for a single line AC circuit of two section single busbar
scheme with one relay per zone circuit.
