DET-882
SecoGear Medium-voltage Switchgear Application and Technical Guide
Control Power Equipment
©2017 General Electric All Rights Reserved
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The charger must be selected with an ampere rating
sufficient to satisfy the simultaneous demand of the
following three functions:
•
Self-discharge losses of the battery.
•
Steady load of the station: indicating lamps, relays, etc.
•
Equalizing charges, or other high-rate output
requirements. The self-discharge or “trickle” current of a
lead-acid battery starts at about 0.25 % of the eight-
hour rate, and increases with age to about 1.0 % of that
rate. Nickel-cadmium cells can be assigned a similar
trickle current. Steady load is made up of the long-time
loads mentioned earlier in this section.
Equalizing charge is a monthly requirement for lead-acid
batteries except for the lead-cadmium class. When the
charger is first switched to the higher equalizing voltage,
the battery demands current equal to about 20 % of its
eight-hour rate.
Nickel-cadmium batteries do not require equalizing, but it
is convenient to use the same numbers for lead-acid in
establishing the charger capacity to be used for
occasionally “boosting” the nickel-cadmium battery.
In sizing the charger, the first number considered should be
the steady load from the preceding battery calculations.
Add to this load the equalizing charge current. A quick way
to find equalizing amperes is to divide the battery ampere-
hour capacity (at the eight-hour rate) by 40. The sum of
steady load and equalizing amperes is then compared with
a list of battery charger ratings; select a charger with a
rating that equals or exceeds this sum. The trickle current,
unless known to be quite large, is usually covered by the
margin between the standard charge rating and the sum
of steady and equalizing loads.
Occasionally a battery is shipped “dry,” with electrolyte
added at its destination. Such batteries require a
“conditioning” charge after filling; the amperes needed for
this are 25 % of the eight-hour rate, but with no other load
connected.
AC CONTROL POWER EQUIPMENT
Control power equipment for SecoGear Switchgear,
operated through an AC source should be powered from a
separate transformer that will not be likely to be de-
energized, in order to minimize the possibility of
unexpected interruption of the control system.
Application
When energizing a switchgear from multiple sources, it’s
necessary to operate breakers with a control power
transformer depending on the source; when we are using
applications that are not associated exclusively with a
specific source like feeders or bus-tie breakers, we can use
the transformer connected to the switchgear bus as a
source or the control power transfer panel located in the
switchgear, connecting the AC control bus to the energized
transformer.
Selection
We can obtain the breaker tripping power from a
capacitor-trip device for AC control; this option requires a
relatively small demand for tripping and closing the
breaker, and may not need to be included in the control
power transformer section. However, conditions where two
or more spring-charging motors are energized at the same
time may require special caution.
NOTICE
When equipment is initially installed and control power is
first energized, all connected SecoVac VB2+ breakers will
immediately begin to charge their closing springs, which
may overload the otherwise properly sized AC source. It
is recommended to either connect the secondary plug of
the breakers in one at a time after control power is
established, or pull the close circuit fuse blocks or close
circuit disconnects prior to energizing the control power
circuit.
Let’s look at an example of a small indoor lineup. The
configuration consists of five breakers and one auxilliary
compartment in a four section lineup. Each breaker has a
control switch and two indicating lights. The lineup has
optional stack heaters and two convenience outlets. The
lineup also has a requirement of 400 VA for remote lights.
The load calculations are shown in Table 3-9.
Table 3-9: AC Load Estimating Example
Load Type
Load
Indicating lamps (0.035 A x 230 V x
5 breakers x 2 lights)
80 VA
Equipment heaters (300 W x 4)
1200 VA
Convenience outlets (500 W x 2)
1000 VA
Remote lights
400 VA
Total
2680 VA