Static AC Circuit Breaker
- The basic circuit for the DC time delay relay is shown in the
figure A.
- The DC supply VCC depends upon rating of SCR. The zener
diode provides constant voltage for UJT.
- The voltage across load becomes zero
when the SCR is in off condition.
- When
the supply voltage is given to the circuit, the charging of capacitor is done
through Z – R1 – R2 – C – Z path.
- The UJT is switched on when voltage across capacitor is equal to UJT
peak point voltage.
- As soon as the UJT switched on, the discharging of capacitor
is done through (+) C – UJT – R4 – C (–).
- The SCR is turned on because gate terminal receives gate pulse
through voltage across resistance R4. The voltage across load is equal to
supply voltage minus voltage across SCR.
- The time delay of the circuit depends upon time constant ( R1 +
R2 ) C and its value can be adjusted by resistance R2.
- The resistance R3 works
as temperature compensation in the circuit and the temperature co – efficient
of the circuit can be set by selecting proper value of resistance R3.
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