Transient Analysis of Power Systems

5 Calculation of Power System Overvoltages

Juan A. Martinez-Velasco and Francisco González-Molina

5.1 Introduction

An overvoltage is a voltage – between one phase and ground or between two phases – having a crest value exceeding the corresponding crest of the maximum system voltage. Standards distinguish several classes and shapes of overvoltages [1–4]:

1. Temporary overvoltages: These are undamped or weakly damped oscillatory phase-to-ground or phase-to-phase overvoltages of relatively long duration (seconds, even minutes). Temporary overvoltages are originated by faults, load rejection, resonance and ferroresonance conditions or by a combination of these factors.
2. Slow-front overvoltages: These are unidirectional or oscillatory highly damped overvoltages, with a slow front and a short duration. They are caused by switching operations, fault initiation or remote lightning strokes.
3. Fast-front overvoltages: These are caused primarily by lightning strokes, although they can also be caused by some switching operations or fault initiation.
4. Very-fast-front overvoltages: In general, these are the result of switching operations or faults. They are usually associated with high-voltage disconnect switch operation in gas insulated substations (GISs), and with cable-connected motors.

Standards also include continuous power-frequency voltages, which are originated when the system is under normal operating conditions [1]. For systems whose maximum voltage exceeds that given in the standards, ...