High-voltage line relay protection for the three-stage:

For high-side side of the 6 ~ 10KV substation main transformer substation, usually equipped with time-limited over-current protection; such as over-current protection action time is greater than 0.5 ~ 0.7s, should also be installed current quick-break protection. amorphous transformer with capacities of 800 KV · A and above and oil-immersed transformers in workshops of 400 KV · A and above shall be equipped with gas protection (also called gas relay protection) according to regulations. Transformers with capacities of 400 KV · A and above shall be fitted with overload protection according to the possible overload conditions when several units are operated in parallel or in a single operation and as a standby power source for other loads. Overload Protection and Gas Protection In the event of a minor fault (known as "light gas"), the signal is acted on, while others, including gas protection, are normally tripped in the event of a serious failure (commonly known as "heavy gas").
For high voltage side of the plant 35KV and above the total transformer substation main on load tap changer transformer, it should be installed over-current protection, current quick-break protection and gas protection; in case of possible overload, also need to install overload protection. However, if a single transformer with a capacity of 10,000 KV · A or more and a transformer operating in parallel with each capacity of 6300 KV · A and above is installed, a pilot differential protection is required to replace the current quick-break protection.