Transformer protection circuit and method

An electrical protection circuit for use in an alternating current system including a transformer, the system comprising:

• (a) a switch assembly connected between a transformer neutral of a transformer and a ground, the switch assembly having an open position and a closed position, the open position disrupting the path through the switch between the electrical connection and the ground connection, and the closed position establishing a path connecting the electrical connection to the ground connection through the switch assembly, wherein in normal operation the switch remains in a closed position;
• (b) a DC blocking component positioned in parallel with the switch assembly and connected between the transformer neutral and the ground;
• (c) a voltage probe connected between the transformer neutral and ground and configured to monitor an instantaneous voltage level at the transformer neutral;
• and
• (d) a control circuit configured to control the switch assembly, the control circuit including a sensor configured to actuate the switch assembly to an open position at least upon detection of a harmonic signal in at least one phase of the transformer or a predetermined threshold of DC or quasi DC current between the transformer neutral and the ground.