Section 2. Circuit Breaker Selection; Circuit Breaker Ratings; Selection Considerations; Circuit Voltage - GE SecoGear Application Manual

SecoGear Medium-voltage Switchgear Application and Technical Guide
Circuit Breaker Selection

SECTION 2. CIRCUIT BREAKER SELECTION

ANSI-C37.100 defines a circuit breaker:
A mechanical switching device, capable of making,
carrying, and breaking currents under normal circuit
conditions and also, making, carrying for a specified time
and breaking currents under specified abnormal circuit
conditions such as those of short circuit.

Figure 2-1: SecoVac VB2+ Circuit Breaker

The function of a circuit breaker is to carry and switch load
current and to interrupt short-circuit current when
required. A circuit breaker can be used to operate
frequently or infrequently, depending on the type and
application. To properly select a circuit breaker, it is
important to consider that the rating of the circuit breaker
must equal or exceed each of the calculated duty
requirements of the circuit in which the breaker is applied.
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CIRCUIT BREAKER RATINGS

GE SecoVac VB2+ circuit breaker ratings are shown in
Table 2-1. Interrupting ratings are intended for 60 Hz and
50 Hz applications. Table 1-2 and Table 1-3 show more
information on service conditions, definitions, ratings, test
and other applicable terms listed in ANSI and NEMA
standards.

SELECTION CONSIDERATIONS

Circuit breaker selection is based on the duty requirements.
For your application, find the model SecoVac VB2+ circuit
breaker rated for those specifications (Table 2-1). It is
important to consult the ANSI Standard C37.010 for proper
guidance on duty requirements (see "Related Circuit
Breaker References," item 2).
When selecting a circuit breaker, you must consider
several characteristics such as circuit voltage, system
frequency, continuous current, short-circuit current and
closing and latching current.

Circuit Voltage

ANSI standards determine that the nominal voltage classes
for medium voltage metal-clad switchgear are 4.16 kV, 7.2
kV, and 13.8 kV; in accordance with ANSI, SecoGear
switchgear is designed to operate at a voltage range from
2,400 V through 15,000 V.

System Frequency

SecoGear Metal-clad switchgear is rated to 60 Hz as a
standard with the option to provide a 50 Hz solution as
required. When determining the system frequency of any
switchgear, remember that the frequency rating should be
the same as the nominal frequency of the power system.

Short-Circuit Current

One of the first things to consider when selecting a circuit
breaker is the interruption rating of short-circuit current, for
any SecoVac VB2+ circuit breaker, the interrupting rating is
stated in three-phase, symmetrical, rms AC amperes.
Start by calculating the short-circuit current duty, followed
by selecting the required voltage class, and finally
determine the short-circuit current capability of SecoVac
that equals or exceeds the expected duty.
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