It is determined according to the capacity of the secondary load of the current transformer. Accumulate according to the rated power consumption of each component in the actual application, and leave a certain margin (generally guaranteed to run at about 75%). For example: 0.2-level measuring coil, generally followed by the meter required by the power supply bureau, generally including active watt-hour meters, reactive watt-hour meters, loss-of-voltage counters, etc., for example: the current loop power consumption of ordinary watt-hour meters is about 4VA; Therefore, if these three meters are available, the capacity should be 15VA (electronically). Specific calculations can be made here. The 0.5-level measuring coil is generally used for loop current signal measurement, and the load may include: ammeter, watt-hour meter, power meter, microcomputer current loop, etc. The 10P10 protection level coil is used as a protection signal, and the load may include a microcomputer current loop, a current relay, etc.