Abstract
Overvoltage transients occur after any type of switching activity in a power network, such as breaker operation, fault occurrence/clearance and rapid load change. This distortion of voltage is transformed to the secondary circuit of a voltage transformer. The maximum values of such impulses may many times exceed the rated value of its secondary voltage. This can lead to malfunction of measuring or protection devices connected to the secondary circuit of a voltage transformer and even their damage. The paper presents the application of determined values of ratio error at harmonics of the inductive voltage of the transformer to predict the value of transformed slow-front transient overvoltage to their secondary circuits. This will help to prevent malfunction of measuring or protection devices connected to the secondary side of the voltage transformer and increase their safety of operation. The inductive voltage transformer equivalent circuit for transformation of higher frequency components of distorted voltage must be extended with internal capacitances of windings. This is caused by the fact that the resonance phenomenon of the slow-front transient overvoltage results from leakage inductance and capacitance of primary winding, not from the magnetic core. Therefore, this behaviour is independent from the value of the applied voltage.
Highlights
In accordance with the standard IEC 60071-1, transient overvoltages may be divided into three types: slow-front, fast-front and very fast-front [1,2]
In this paper the determined characteristic of voltage ratio error at harmonics with frequency for a given medium voltage inductive instrument transformer is used to predict the value of the slow-front overvoltage in its secondary circuit
Their properties are studied under switching overvoltages cause by failure in operation of the PulseWidth Modulation (PWM) based programmable AC source when used to generate a voltage dip
Summary
In accordance with the standard IEC 60071-1, transient overvoltages may be divided into three types: slow-front, fast-front and very fast-front [1,2] It applies to three-phase AC systems having a highest voltage for equipment above 1 kV. In this paper the determined characteristic of voltage ratio error at harmonics with frequency for a given medium voltage inductive instrument transformer is used to predict the value of the slow-front overvoltage in its secondary circuit. The resonance frequencies and the measured values of ratio error and phase displacement do not change with the value of the applied voltage This is due to the fact that the transformation accuracy of the slow-front transient overvoltages results from the leakage inductances and the capacitances of windings [14,15,16,19,20]. Their properties are studied under switching overvoltages caused by failure in operation of the PulseWidth Modulation (PWM) based programmable AC source when used to supply a step-up transformer [26]
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