Page 7 - Practical Power System and Protective Relays Commissioning

2 Practical Power System and Protective Relays Commissioning

1.2.4 Loads
Loads are defined as items that consume electricity, for example, homes and
factories.

1.3 SYSTEM VOLTAGES

Voltages differ from country to country, however, a general classification is:
Generation voltage levels range from 12 to 33 kV.
Transmission voltage levels range from 110 to 800 kV.
Distribution voltage levels range from 4 to 35 kV.

1.4 POWER SYSTEM COMPONENTS

A power system is made up of multiple components. These are:
Generators that generate electrical power.
Transformers that change voltage levels as per system requirements.
Circuit breakers that open and close the power circuits under normal and
abnormal conditions.
Shunt reactors and capacitors that are used for system compensation for
reactive power in transmission lines.
Surge arresters are used for protecting the primary system from
overvoltages.
Protective relays are used to detect any faults in the system and to trip
the circuit breakers to isolate the faulty part in the power system to keep
other parts of the system healthy and working in normal condition.
Substations are nodes of several transmission lines or distribution lines
with power transformers.
Buses are heavy conductors that collect power and distribute it to the dif-
ferent system components.
These are all shown in the simplified power system shown in Fig. 1.1.

1.5 IEEE DEVICE NUMBERS AND FUNCTIONS FOR
SWITCHGEAR APPARATUS
The devices in switching equipment are referred to by numbers, according to
the functions they perform. These numbers are based on a system which has
been adopted as standard for automatic switchgear by the Institute of
Electrical and Electronics Engineers (IEEE). This system is used on connec-
tion diagrams, in instruction books, and in specifications. The standard num-
bers referring to device functions in switchgear components are as follows.
32 Directional power relay
21 Distance relay
25 Synchronizing or synchrocheck device