ON THE ISSUE OF VOLTAGE REGULATION BY A POWER TRANSFORMER WITH AN ON-LOAD REGULATOR

Abstract

The requirements for high-quality electricity supply to consumers are constantly growing. One of the key indicators of high-quality electricity supply is voltage deviation, the value of which varies depending on the load. In distribution electrical networks, voltage regulation is carried out using power transformers with on-load tap changers (OLTC) equipped with automatic regulators. Depending on the load change, in order to maintain the voltage within acceptable limits, the on-load tap changer constantly switches the branches of the power transformer windings, which leads to the depletion of the latter's working resource, i.e. an increase in the number of on-load tap changer switching operations leads to an improvement in voltage quality and a decrease in the reliability of the on-load tap changer.

In order to find a compromise between the number of OLTC switching operations and the quality of the supply voltage to electricity consumers, a number of voltage regulation laws have been developed, the mathematical models of which take into account the voltage output outside the permissible ranges, the signal delay for switching the OLTC, the derivative of the regulated voltage envelope, the prediction of the time of voltage entry into the insensitivity zone, and others. In most cases, these conditions allow minimising the number of OLTC switching operations while maintaining acceptable power supply quality. However, when the load is highly variable, the number of OLTC switching operations increases to ensure an acceptable voltage value.

The paper proposes a mathematical model of the voltage regulation law, which involves determining the tangent of the envelope angle of the regulated voltage several times during the signal delay time for switching the automatic regulator, which allows assessing how much the regulated voltage exceeds its permissible limits. And when the voltage differs significantly from the permissible value, the signal for switching the OLTC device is sent immediately after the end of the signal delay time for switching. If the regulated voltage slightly exceeds the permissible limits, then, provided that the sign of the derivative of the regulated voltage envelope is determined, a switching signal is generated when the derivative of the envelope voltage is directed away from the insensitivity zone. Otherwise, the OLTC device does not switch. This approach improves voltage quality and slightly reduces the number of OLTC device switches, which increases its reliability.

A device has been developed that, in conjunction with an automatic voltage regulator, implements the proposed voltage regulation law.