SecoGear Medium-voltage Switchgear Application and Technical Guide
DET-882
Control Power Equipment
20
©2017 General Electric All Rights Reserved
next operation is stored in the springs as soon as the
breaker is closed.
To permit control switch or automatic initiation of closing,
the AC source must also be present at the time of breaker
closing to energize the spring-release solenoid (close coil).
The SecoVac breaker mechanism is also capable of manual
operation, if necessary, both for charging the springs and
for releasing them to close the breaker.
For any control power source used for breaker closing, the
maximum closing load should be calculated using
Table 3-1. Usually, only one breaker will be closed at a
time, but the possibility of simultaneous closing of two or
more breakers must be examined. This possibility will
depend on the type of application and any special control
requirements, such as load restoration. Simultaneous
closing of two breakers could occur with multiple-breaker,
motor starting equipment, or with automatic reclosing
breakers. Also, on large installations, with several different
control points, different operators could cause
simultaneous manual operations.
Indicating Lamps
Position indicating lamps are powered by the closing fuses
on the AC control, the battery specifically used for tripping
purposes, or the trip fuses on the DC control. Indicating
lamps, represent a small, but steady load in the used in the
calculation for DC battery applications. We assume for
burden calculations 0.035 A per lamp for not more than
eight hours. These lamps are used for supervision of the
fuses in lockout relays, indicating lamps per breaker or for
remote indication in parallel with switchgear lamps. Newer
control switches and lockout relays may use indicating
lights integral to the device, which must be considered in
load calculations.
RELAYING
When using DC control power, the number of breakers to
trip at one time must be considered in sizing calculations.
This becomes critical for certain relay applications such as
bus differential or load shedding. Table 3-3 provides a
guide on the maximum number of breakers that can you
can trip simultaneously.
Table 3-3: Simultaneous Breaker Tripping
Number. of
Breakers in
Lineup
Probable Max. Number of Breakers
Tripped Simultaneously, per Cause
Time Delay
Fault
Protection
Instantaneous
Fault
Protection
Undervoltage
or Bus
Differential
2
1
1
1
1
2
1
1
1
3 – 5
2
3
All
6 – 10
3
4
All
> 10
—
1
—
1
All
Notes:
1.
Depends upon operating conditions.
2.
Use of single undervoltage or bus differential relay for tripping all
breakers.
If lockout relays are used as in differential relay circuits, the
following actions should apply:
•
With AC operation, each lockout relay must be provided
with a capacitor trip device
•
With DC operation, the breaker coils have to be
energized in order for the relay to cut itself off in case of
simultaneous breaker demand (Table 3-4)
Table 3-4: GE Type HEA Lockout Relay Coil Current
Characteristics
Operating
Voltage
HEA Relay Coil
Current
HEA Relay Coil
Resistance (@25 °C)
48 V
10.7 A
4.5 Ohms
125 V
5.5 A
23 Ohms
250 V
2.4 A
103 Ohms
EXCITATION POWER
When synchronous motors with brushless field excitation
are controlled directly from the switchgear, power for the
exciter field source is sometimes required from the
switchgear control power source.
This excitation demand varies with the machine, from 1 A
to perhaps 8 A DC, usually at approximately 100 V. With
rectified AC supply to the field, the AC equivalent of the DC
field current must be included the total CPT loading. (As a
first approximation, multiply the DC amperes by 1.15 and
convert to VA by multiplying this product by 125 V.) When
the exciter field is fed directly from the battery, the field
demand, as a nominal 8-hour load, must be included in the
DC steady load total.
Generators with static regulators usually require a
separate transformer on the incoming leads of the
generator breaker. This transformer is of the same epoxy-
cast coil, dry type, as the switchgear CPT, but is located in
its own rollout tray. Such dedicated transformers are not
part of the regular control power loading.
OTHER LOADS
When using the charger for DC control, you can use the
switchgear AC control power transformer and include the
load in the total AC demand. Using charger DC ampere
rating as a base, some ratios of equivalent AC loads at
different supply voltage and battery voltages (consult
Table 3-5).
Table 3-5: AC Load Factor for Charger Battery Voltage
Supply
Voltage
Load Factor
for 48 Vdc Battery
Load Factor
for 125 Vdc Battery
115 Vac
75 %
230 %
230 Vac
38 %
115 %
