The main interference source is spark plug, high-voltage ignition coil cap and the high-voltage coil.

Epoxy cast dry-type distribution transformer high-voltage coil sealed by epoxy resin casting, using epoxy resin performance, cracking, high temperature, high mechanical strength, long life.

The metering error considers the non linear effect of the voltage coil and current coil in watt hour meter under different order of harmonics and different distortion degree of input waveform.