Reducing transformer inrush current

A controller comprising:

• processing circuitry;
• and
• data storage storing instructions executable by said processing circuitry whereby said controller is operative to perform a method for reducing inrush current to a transformer when closing a circuit breaker arranged between an AC voltage source and the transformer in an electrical three-phase system, the circuit breaker comprising only three single-pole operated current interrupting means, one per phase, the method including:
• between the circuit breaker and the voltage source, monitoring a voltage in one of the phases;
• for each of a sequence of iterations:
• at a same opening angle relative to a reference angle of the monitored voltage, starting an opening sequence of the circuit breaker, opening the circuit breaker;
• at a closing angle relative to the reference angle, which is shifted in relation to the closing angle of all other iterations in the sequence, starting a closing sequence of the circuit breaker, closing the circuit breaker;
• obtaining an indication of a peak value of an overall inrush current resulting from the closing of the circuit breaker;
• and
• selecting for future use with said same opening angle, the closing angle of one of the iterations in which the overall inrush current is relatively low when compared with the other iterations of the sequence.

A circuit breaker comprising:

• a controller having:
• processing circuitry;
• and
• data storage storing instructions executable by said processing circuitry whereby said controller is operative to perform a method for reducing inrush current to a transformer when closing the circuit breaker arranged between an AC voltage source and the transformer in an electrical three-phase system, the circuit breaker comprising only three single-pole operated current interrupting means, one per phase, the method including:
• between the circuit breaker and the voltage source, monitoring a voltage in one of the phases;
• for each of a sequence of iterations:
• at a same opening angle relative to a reference angle of the monitored voltage, starting an opening sequence of the circuit breaker, opening the circuit breaker;
• at a closing angle relative to the reference angle, which is shifted in relation to the closing angle of all other iterations in the sequence, starting a closing sequence of the circuit breaker, closing the circuit breaker;
• obtaining an indication of a peak value of an overall inrush current resulting from the closing of the circuit breaker;
• and
• selecting for future use with said same opening angle, the closing angle of one of the iterations in which the overall inrush current is relatively low when compared with the other iterations of the sequence,
• a voltage sensor for the monitoring of the voltage, and
• an inrush sensor for the obtaining of the indication of a peak value of the overall inrush current.

An electrical system comprising:

• a transformer;
• and
• a circuit breaker, which includes a controller having:
• processing circuitry;
• and
• data storage storing instructions executable by said processing circuitry whereby said controller is operative to perform a method for reducing inrush current to the transformer when closing the circuit breaker arranged between an AC voltage source and the transformer in the electrical system, the electrical system being an electrical three-phase system, the circuit breaker comprising only three single-pole operated current interrupting means, one per phase, the method including:
• between the circuit breaker and the voltage source, monitoring a voltage in one of the phases;
• for each of a sequence of iterations:
• at a same opening angle relative to a reference angle of the monitored voltage, starting an opening sequence of the circuit breaker, opening the circuit breaker;
• at a closing angle relative to the reference angle, which is shifted in relation to the closing angle of all other iterations in the sequence, starting a closing sequence of the circuit breaker, closing the circuit breaker;
• obtaining an indication of a peak value of an overall inrush current resulting from the closing of the circuit breaker;
• and
• selecting for future use with said same opening angle, the closing angle of one of the iterations in which the overall inrush current is relatively low when compared with the other iterations of the sequence,
• a voltage sensor for the monitoring of the voltage,
• an inrush sensor for the obtaining of the indication of a peak value of the overall inrush current.

A computer program product comprising computer-executable components, which when run on processing circuitry of a controller, causes the controller to perform a method for reducing inrush current to a transformer when closing a circuit breaker arranged between an AC voltage source and the transformer in an electrical three-phase system, the circuit breaker comprising only three single-pole operated current interrupting means, one per phase, the method including:

• between the circuit breaker and the voltage source, monitoring a voltage in one of the phases;
• for each of a sequence of iterations:
• at a same opening angle relative to a reference angle of the monitored voltage, starting an opening sequence of the circuit breaker, opening the circuit breaker;
• at a closing angle relative to the reference angle, which is shifted in relation to the closing angle of all other iterations in the sequence, starting a closing sequence of the circuit breaker, closing the circuit breaker;
• obtaining an indication of a peak value of an overall inrush current resulting from the closing of the circuit breaker;
• and
• selecting for future use with said same opening angle, the closing angle of one of the iterations in which the overall inrush current is relatively low when compared with the other iterations of the sequence.