What Is The Difference Between A Three-phase Four-wire Mutual Inductance Meter And A Direct Meter?

There is no difference. The three-phase four-wire "mutual inductance meter" is actually equivalent to a three-phase four-wire 5A (ampere) electric energy (kWh) meter, but the input voltage is different.

The working voltage of the straight-through electric energy meter must be consistent with the voltage represented by the current in the circuit, while the electric energy meter using a current transformer can have the same voltage as required (quite a straight-through meter), or a fixed voltage of 100 volts. The current flowing during the time should be unified with the secondary current of the current transformer to be 5A. This kind of ammeter is usually used for high-voltage electric energy measurement