
83
H
2. Selectivity Techniques
Discrimination can be described as below picture #2. When the accident happens at S
1
, only MCCB
2
will operate,
leaving MCCB
3
or upstream MCCB
1
at rest. Discrimination is a method of protective coordination which will
activate only the protective device that is directly related to the fault circuit, and leaving other normal circuits to be
supplied with electricity continuously. By implementing the discrimination, this distribution system allows to
minimizes areas of power failure. Thus it enhance reliability on power supply. To achieve discrimination
coordination, MCCB should satisfy following conditions.
�
Main breaker’s trip operation launch time should be longer than branch breaker’s total breaking time.
�
In relation to main breaker’s trip time rise, short time withstand current capacity and short time delay factor
should be added to endure conducting peak current Ip and conducting energy I
2
t.
In fully rated system, every breaker is arranged to operate independently on its own rating. Breaker possess
breaking capacity which can resolve maximum short current that can be happened near its installed spot in the
power supply. This system is highly reliable, but discrimination function is limited to a few circumstances. And the
drawback is expensive installment cost for branch breakers. Fully rated system is relatively inexpensive to
discrimination system, however it is more expensive comparing to cascading. Every breaker should be able to
handle the maximum short current that might arise in its applied area. Continuity of electricity supply is inferior to
the discrimination system.
There are three basic approach to build power protection system; fully rated, discrimination, and cascading (series
-combination rated). Common goal of different approach is to protect system and machineries, yet installment
expenses or continuity of power supply under accidents have discrepancies for each approach.
Discrimination Protection
Fully Rated Protection
Picture 2. Discrimination Coordination
ACB
Main Breake
ACB
Operation Characteristic
MCCB1
Operation
Characteristic
MCCB2
Operation
Characteristic
MCCB
Operation
Characteristic
S1
Fault
Current
Operation
Characteristic
Protective Coordination
Содержание Metasol Series
Страница 32: ...31 D Digital Trip Relay D 3 Internal Circuit Diagram Internal Circuit Diagram ...
Страница 38: ...37 D Digital Trip Relay D Ground Fault Protection 4 Relay Function ...
Страница 39: ...38 Technical catalog for Susol Metasol ACB Technical catalog for Susol Metasol ACB D D IDMTL ...
Страница 40: ...39 D Digital Trip Relay D PT A Curve 4 Relay Function ...
Страница 136: ...K 136 138 1 Control Circuit 2 External Dimension Control Circuit and Dimension 135 ...
Страница 153: ...152 Technical catalog for Susol Metasol ACB Technical catalog for Susol Metasol ACB Memo ...
Страница 154: ...153 Technical Materials Memo ...