Abnormal States in Power Systems and Criteria for Their Recognition - Digital Signal Processing in Power System Protection and Control - page 3

Chapter 2
Abnormal States in Power Systems
and Criteria for Their Recognition

2.1 Introduction

The protection equipment is applied with the aim of minimizing the effects of
faults and other abnormal phenomena on the operation of electrical power systems.
An electrical power system is considered as all the plants required to generate,
transmit and distribute electrical power, including generators, power transformers,
lines and cables, circuit-breakers, etc.
Faults in power systems can be a result of external or internal influences,
whereas the most common reasons of abnormal states are:

• overvoltage due to lightning,
• short-circuits due to mechanical destruction or bridging of isolation (e.g. during
road works, caused by falling trees, animals, birds, etc.),
• thermal overload (overcurrents),
• aging of isolation,
• maintenance/staff mistakes,
• climatic disasters (floods, earthquakes, heavy snowfalls, icing, strong wind,
etc.).

The consequences of a fault may be:

• damage to the plant due to dynamic and thermal effects of the fault current,
• loss of supply to loads,
• danger to human lives,
• loss of system stability,
• possibility of cascading events leading to blackouts.
The protection devices may react to the events with tripping, alarm or signaling,
depending on the expected consequences of the event, see Table 2.1 . As one can
notice, not always the protection devices are about tripping, sometimes an alarm or
signaling is enough, depending on the situation at hand. Nevertheless, the