Transformer gas protection circuit

Oil-immersed transformer gas protection circuit . When a minor fault (light gas) occurs inside the transformer, the
upper contact KGl-2 of the gas relay KG is closed and acts as an alarm signal. When a serious fault (heavy gas) occurs inside the transformer . The lower contact KG3-4 of KG
is closed, usually acting on the tripping mechanism YR of the circuit breaker QF through the intermediate relay
KM, and at the same time sending out a trip signal through the signal relay KS. But when KG3-4 is closed, you can also use the switching piece XB to switch, so that the KS coil is connected in series with the current limiting resistor R and acts on the alarm signal.
    Since the lower contact KG3-4 of the gas relay may "jib" (poor contact) during a severe gas fault, therefore. In order to
connect the tripping circuit stably and the circuit breaker to trip reliably, the upper contact KMl-2 of the intermediate relay KM is used as a "self-holding" contact
. As soon as KG3-4 is closed due to heavy gas action, KM is activated, and the upper contact KM1-2 is closed to maintain the operating state.
At the same time, the lower contact KM3-4 is also closed, causing the circuit breaker QF to trip. After the circuit breaker trips, its auxiliary contact QFl-2 disconnects the tripping circuit to reduce
the work of the intermediate relay contact, while its other pair of auxiliary contacts QF3-4 cuts off the self-holding circuit of the intermediate relay KM, so that the intermediate relay KM Relay
returns.