126, For a DC system there occurs positive ground or negative ground What are the hazards of running them?
A: DC system has a positive ground fault protection caused by the possibility of malfunction. Because the electromagnetic drive mechanism of the trip coil is usually connected to the negative power supply, if these circuits occur over the poor insulation it will lead to protection of mis operation. DC system negative ground, if there is another point in the circuit ground, it may make tripping or closing circuit to a short circuit, resulting in protection or circuit breaker refusal to move, or burn the relay, or fuse.
127, Transformer gas protection light-up, What is the reason?
A: TTransformer gas protection light-up reasons are:
(1) due to oil, fuel or cooling system is not tight so that air gets into the transformer.
(2) due to temperature drop or oil leakage caused by oil surface gas relay light gas below the float.
(3) transformer failure to produce a small amount of gas.
(4) the short circuit.
(5) gas relay or secondary circuit failure.
128, For AC fuse loop , DC control loop and signal circuit fuse how to choose?
A: The choice of fuse should be:
(1) AC circuit fuse protection device rated current of 1.2 times the selection.
(2) DC control, signal loop fuse generally used 5 ~ 10A.
129, If the transformer appears false oil level, which may be caused by?
A: The transformer appears false oil level may be caused by the following reasons:
(1) oil standard pipe block.
(2) respirator plug.
(3) airway vent plug.
(4) film-protected oil pillow in the refueling air is not exhausted.
130, transformer winding insulation damage that is caused by what?
A: Transformer winding insulation damage reasons are:
(1) line short-circuit fault.
(2) long-term overload operation, a serious aging insulation.
(3) winding insulation damp.
(4) Winding joint or tap-changer connection is bad.
(5) lightning wave intrusion, so that winding over-voltage.
