Principles for Transformer Protection Configuration:

1. Protection against short circuit faults
① Gas protection
② Differential protection
③ Overcurrent protection (110KV, 10KV side)
④ Zero sequence protection on the high voltage side of the transformer
⑤ Zero sequence protection on the medium voltage side (when directly grounded in the power grid)
2. Abnormal operation protection
① Symmetric overload protection (high, low)
② Temperature protection
③ Cooling system protection
3. Gas protection and on load pressure regulating gas protection that reflect various faults and oil level drops inside the transformer.
① Composition of protective device: gas relay
② The light gas acts on the signal, while the heavy gas instantaneously triggers the circuit breakers on both sides of the transformer.
4. Reflect the phase to phase short circuit of transformer coils and their leads, as well as the longitudinal differential protection of single-phase grounding on the neutral point directly grounded side.
For transformers of 2000KVA and above that do not meet the sensitivity requirements for current quick break protection, differential protection should be installed for transformers of 6300KVA and above.
Differential protection should be able to avoid unbalanced currents generated by excitation inrush currents and external short circuits. Differential protection operates instantaneously on the circuit breakers on both sides of the transformer.