Protection of an electrical apparatus

A method comprising:

• accessing a plurality of input signals, each input signal representing a voltage at one input node of a three-phase electrical apparatus;
• analyzing the plurality of input signals to determine whether an unbalanced condition exists in the three-phase electrical apparatus;
• determining an unbalanced metric of the three-phase electrical apparatus;
• determining a balance property of the three-phase electrical apparatus based on the unbalanced metric, wherein the balance property indicates whether the three-phase electrical apparatus is operating in a balanced condition or unbalanced condition;
• and
• determining whether a performance condition exists in the three-phase electrical apparatus based on frequency content of one or more of the input signals and the balance property.

A system comprising:

• an electrical apparatus comprising:
• a plurality of input nodes, each input node configured to electrically connect to a phase of an alternating-current (AC) electrical power distribution network;
• and
• an electrical network electrically connected to the input nodes;
• and a control system configured to:
• receive a plurality of input signals, each input signal representing a voltage at one input node of the electrical apparatus;
• determine an unbalance metric by comparing the plurality of input signals to each other;
• determine a balance property of the electrical apparatus based on the unbalance metric, wherein the balance property indicates whether the electrical apparatus is operating in a balanced condition or an unbalanced condition;
• and
• determine whether a performance condition exists in the electrical apparatus based on frequency content of one or more of the plurality of input signals and the balance condition.