Three-Winding Distribution Transformer

This example shows the use of the linear transformer to simulate a three-winding distribution transformer rated 75 kVA - 14400/120/120 V.

Description

The transformer primary is connected to a high voltage source (14,400 V rms). Two identical inductive loads (20 kW -10 kvar) are connected to the two secondaries. A third capacitive load (30 kW -20 kvar) is fed at 240 V.

Initially, the circuit breaker in series with Load 2 is closed, so that the system is balanced.

Simulation

Open the powergui block to obtain the initial voltage and current phasors in steady state. As loads are balanced the neutral current is practically zero.

Furthermore, as the inductive reactive power of Load 1 and Load 2 (2*10 kvar) is compensated by the capacitive reactive power of Load 3 (20 kvar), the primary current is almost in phase with voltage The small phase shift (-2.8deg.) is due to the reactive power associated with transformer reactive losses.

Open the two scopes and start the simulation. When the circuit breaker opens, a current starts to flow in the neutral as a result of the load unbalance. When the breaker opens, the active power decreases from 70 kW to 50 kW.