A protection circuit may be electrically connected to a transformer neutral of a power grid transformer. The protection circuit may include a direct current (DC) blocking component electrically connected between the transformer neutral and a ground connection, as well as a direct current switch assembly positioned in parallel with the direct current blocking component between the transformer neutral and the ground connection. The direct current switch assembly includes at least one direct current switch having a switching element that is electrically controllable between a closed position and an open position. In some examples, a conductive housing encloses one or more switching elements. The conductive housing is electrically isolated from the ground connection. In further examples, one or more direct current switches may be electrically connected in series to provide greater voltage withstand and safety due to operational redundancy.

A relay protection method against LC parallel circuit detuning faults comprises the steps of: a relay protection device samples a current of a parallel LC, that is, a reactor and a capacitor, and samples a total current flowing through the whole LC; convert the current of the reactor into a current of an equivalent capacitor; calculate amplitudes of the current of the equivalent capacitor and a current of a realistic capacitor and calculate an amplitude of the total current flowing through the LC; calculate a current amplitude ratio of the equivalent capacitor to the realistic capacitor; and when the amplitude of the total current flowing through the LC is large enough, send an alarm signal or a trip after a setting time delay if the current ratio exceeds a preset upper and lower limit range. Also provided is a corresponding relay protection device.

A method for detecting an open current transformer in an electrical power system includes measuring for a voltage value on a secondary side of a current transformer. The method continues with observing the voltage value for a predetermined waveform and initiating corrective action in the electrical power system upon detection of the predetermined waveform.

A method for detecting an open current transformer in an electrical power system includes measuring for a voltage value on a secondary side of a current transformer. The method continues with observing the voltage value for a predetermined waveform and initiating corrective action in the electrical power system upon detection of the predetermined waveform.

Systems and methods for protecting an electrical component in an alternating current system that includes a transformer are disclosed. In one aspect, a circuit includes a switch assembly connected between a transformer neutral of a transformer and a ground and having an open position and a closed position. In normal operation, the switch remains in a closed position. The circuit further includes a DC blocking component positioned in parallel with the switch assembly and connected between the transformer neutral and the ground, a voltage probe connected between the transformer neutral and ground and configured to monitor an instantaneous voltage level at the transformer neutral, and 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.