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What are the function of the main transformer protection?

 What are the main transformer protection?
         We usually encounter some unprofessional users to ask for price,such as the following questions:I need a main transformer protection device. Could you give me a price?but the main transformer protection is the protection of large main transformer configuration,Generally are sets,And  very different  with the general distribution transformer protection ,Today we will talk how select the main transformer protection as well as the main transformer protection by detailed!
Classification and protection configuration standard of main transformer
        Conventional main transformer is divided into two winding main transformer and the three winding:Two winding main transformer is generally equipped with two turns main transformer differential protection,Main transformer backup protection,Main transformer low backup protection,Main transformer non electric quantity protection and Main transformer backup operation box and other main equipment,Sometimes equipped with the main configuration change control device according to the project.The three winding main transformer protection configuration relative to the two winding main transformer configuration should be more complex and have higher requirements.,General used standard three ring main transformer differential protection of main transformer, high back-up protection, main transformer backup protection, main transformer backup protection for transformer low, non electricity protection, high and low voltage side of main transformer backup operation box, main control device, main transformer thermometer and other equipment,At the same time, main transformer protection usually needs communication.
Main transformer protection function requirement
        Main protection, main transformer differential protection and main transformer non power protection are mainly used as main protection, backup protection compound voltage over-current, zero current, 18KV single-phase grounding, over excitation protection, light gas, pressure release valve, temperature protection, temperature protection, coil temperature protection, oil level protection cooler fault protection. 
The core role and principle of main transformer protection
     1、Gas protection: reaction tank internal fault. According to the severity of the fault are light gas and heavy gas action. Principle: slight internal fault light gas alarm action, internal fault of oil flow to serious heavy gas relay tripping.
     2、differential protection:The reaction between low voltage transformer high, the fault of CT in the two groups. Principle: normal operation or external fault from time to time, access the same phase differential protection of high and low voltage CT in the protection of internal circulation but not through the differential protection relay. But in the internal fault is high, two low side current differential relay is superimposed on each other action
     3、Zero sequence protection: zero voltage and high side pressure neutral zero sequence current protection, the main side reaction of 110Kv single-phase grounding protection. According to the principle: whether the neutral point grounding operation, when single-phase grounding fault occurs when the high side, 110Kv side bus 110Kv side neutral point will produce zero sequence voltage and current respectively.
     4、Double closed voltage over current: general low voltage overcurrent plus zero sequence or negative sequence voltage as internal and external fault backup protection. 
Action and signal protection:
     1、Light gas: reaction tank internal light fault.
     2、Over load:
     3、Oil surface temperature is too high, winding temperature is too high and cooler all stop protection.
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