Basic requirements for transformer faults and their protection functions

Transformer protection is the key to ensure the safe operation of the transformer. Simply speaking, when the transformer is short-circuited during operation, over-current, over-voltage and some related electrical or non-electrical faults, it can quickly remove the fault and ensure the safe operation of the transformer. Electrical equipment, referred to as transformer microcomputer protection device.

Basic requirements for transformer protection:

(1) When the transformer fails, it should be disconnected from all power sources.

(2) The busbar or other components connected to the transformer have failed, and the faulty component should be separated from the faulty part for some reason (protection or circuit breaker failure). .

(3) When the transformer is overloaded, the oil level is lowered, and the oil temperature is too high, an alarm signal should be issued.

Transformer fault and abnormal state:

(1) The phase-to-phase short circuit of the winding and its lead-out line and the single-phase grounding short-circuit at the neutral point of the neutral point;

(2) Short-circuit between turns of the winding;

(3) Overcurrent caused by external phase-to-phase short circuit;

(4) Overcurrent and neutral point overvoltage caused by external ground short circuit in the direct grounding power grid of the neutral point;

(5) overload;

(6) overexcitation;

(7) The oil level is lowered;

(8) Transformer temperature and tank pressure rise and cooling system failure.

Transformer protection classification

(1) Main protection of transformer: differential quick-break protection; proportional differential protection (with second harmonic braking, CT disconnection blocking);

(2) Backup protection of transformer: overcurrent I section (jump section); with low voltage blocking, negative sequence voltage blocking; overcurrent II section (hop main change all side switch); with low voltage blocking, negative sequence voltage blocking Over-current I and II sections can be selected: phase-to-phase direction selection; time-limited quick-break (limited-time quick-break, limited-time quick-disconnect direction, low-voltage lockout); overload warning; CT disconnection (alarm); zero-sequence overcurrent (zero sequence Flow, zero sequence voltage blocking, zero sequence trip, zero sequence direction selection); PT loss of voltage (alarm); PT disconnection (alarm); bus grounding (alarm); pressure abnormality (SF6 low air pressure alarm);

(3) Transformer non-electricity protection: body light gas-alarm; body weight gas-trip; loaded light gas-alarm; loaded gas-trip; pressure release (cast-trip; back-alarm); temperature rise-alarm ; temperature is too high - trip; oil level high - alarm; oil level low - alarm; oil temperature high - alarm; oil temperature low - alarm; air cooling fault (cast - trip; back - alarm); other required non-electricity, etc. .