Basic Connection of Trip Circuit:
Fig. shows the simple arrangement of trip circuit. The connection of trip circuit is divided into three parts.
First part is the primary winding of a current transformer (C.T.), which is connected in series with the line to be protected.
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| Circuit Diagram Of Trip Circuit |
Second part consists of secondary winding of C.T. and the relay-operating coil
Finally the third part is the tripping circuit and it may be operated either on a.c. supply or d.c. supply. It consists of a source of supply, the trip coil of the circuit breaker and the relay stationary contacts.
Under normal operating condition the current flowing through the C.T.secondary and hence through relay coil is not sufficient to attract the plunger. Hence the trip circuit remains open.
As soon as fault (say short circuit) occurs at point f on the transmission line as shown in Fig. 2.3.1, the current flowing in the line increases to a high value.
This causes the flow of heavy current through the relay coil, and relay to operate by closing its contacts.
This in turn closes the trip circuit of the breaker, making the circuit breaker open. Thus it isolates the faulty section from the rest of the healthy system.
In this way relay ensures the safety of the circuit equipment from damage and avoids the disturbance to normal working of the healthy portion of the system.
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