Transformer protection configuration principle

Transformer protection configuration principle

(1) Gas protection

(2) Differential protection

(3) Overcurrent protection or composite voltage blocking overcurrent protection

(4) Zero sequence current protection

(5) Zero sequence overvoltage protection

(6) Overload protection

(1) Gas protection is the main protection of the internal fault of the transformer body. Reflects various forms of short circuit and oil level reduction inside the transformer. There are two kinds of gas protection: the internal gas vibration protection action occurs when the short-circuit fault occurs, and the short-circuit device on each side of the transformer is tripped; the oil level of the transformer is reduced and slight gas is generated inside, and the light gas protection acts on the warning signal. If the transformer is equipped with an on-load voltage regulator, it should also be equipped with light-loaded, heavy-duty gas protection.

(2) Differential protection is the main protection of the inside of the transformer body, the casing and the lead wire. Reflects the phase-to-phase short circuit between the transformer winding and the lead-out line, the single-phase ground short circuit on the direct ground side of the neutral point, and the short-circuit between the winding turns. When the single-phase grounding short-circuit sensitivity of each side of 110kV and 220kV does not meet the requirements, the zero-sequence differential protection is added. The zero sequence differential protection only reflects the single phase ground fault, and its action requirements are the same as the longitudinal differential protection.

(3) Overcurrent protection generally refers to composite voltage blocking overcurrent protection, which is the backup protection of the transformer. Reflects transformer overcurrent caused by external phase-to-phase short circuit. For three-winding transformers and autotransformers, the protection is installed on the power supply side and the main load side. When the sensitivity requirement cannot be met, an overcurrent protection device can be installed on each side. Each side protection can be fitted with directional elements depending on the selectivity requirements.

(4) Zero-sequence current protection is the backup protection of the transformer. Reflects the overcurrent caused by the single-phase ground fault of the transformer directly connected to the neutral point of the three-phase system. The zero-sequence current protection of the double-winding and three-winding transformers is connected to the neutral current transformer. The auto-transformer zero-sequence protection is installed on the zero-sequence loop of the high- and medium-voltage side current transformers. When the 2nd side is running and the ground fault occurs internally, if the zero sequence current protection sensitivity cannot meet the requirements, zero sequence current protection should be added at the neutral point.

(5) Zero-sequence over-voltage protection The transformer with power supply on the low-voltage side. If the neutral point may be grounded or not grounded, the over-current caused by the external single-phase grounding and the over-voltage caused by the loss of the grounding neutral point shall be set to zero. In addition to the current protection, zero-sequence voltage protection should be added. This protection action disconnects the circuit breakers on each side with a delay.

(6) The overload protection of the overload protection transformer should reflect the overload of the common winding and each side. Overload protection uses a single-term, time-limited action on the signal.