Zero-current zero-voltage switching for on-load tap changers

We present a new on-load tap changer (OLTC) design that provides the traditional advantages of the semiconductor-assisted OLTC over the classic, mechanical OLTC. The design provides zero-current, zero-voltage operation of both diverter switches at all times, eliminating contact wear due to arcing. The design of the diverter sub-circuit is discussed, including the introduction of a voltage source and corresponding control loop that provides the necessary shunt current or voltage to create the desired zero conditions in the diverter switches. The design differs from existing semiconductor-assisted OLTC systems by the fact that the semiconductor portion of the system is connected in a purely shunt configuration to the main current path. Under normal conditions the load current flows only in the selector and diverter switches making the system very low loss.