Page 94 - Practical Power System and Protective Relays Commissioning

92 Practical Power System and Protective Relays Commissioning

FIGURE 7.8 Monograph for dew points and ppm as function of pressure.

7.5 CIRCUIT BREAKER CONTROLS
7.5.1 Electrical Control
Before the introduction to the trip and closing circuit of CB, some circuits
are described.
1. Cut-off circuit
The closing coil has a short-time rating of 15 seconds, so it is
necessary to disconnect the power on this closing coil after the closing
operation is completed; this is called the cut-off circuit.
2. Seal in “self-holding” circuit
When the closing operation is started a self-holding process is
initiated for the closing circuit, after the operator presses the closing
pushbutton a closing relay is energized and closes its self-holding contact
to ensure the power is continuing to the closing relay until the end of the
closing stroke of the CB and this power is cut only by an auxiliary
contact of the CB.
3. Antipumping circuit
When there is a fault in primary system occurs,the protective relays
will issue a trip signal for the breaker during this moment the operator