Instrumentation, Current, And Voltage Transformers; Am And Vm Scales; Ct And Vt Ratios; Table 4-1: Remote Control Schemes - GE SecoGear Application Manual

DET-882

Table 4-1: Remote Control Schemes

Control Location
Breaker Operation Close
Breaker Position Conn Test Conn Test Conn Test Conn Test
A
Remote
Control B
Scheme
C*
Basic Control
X
Key:
X = This manually initiated operation is possible.
* = This scheme uses same devices as scheme B, but different wiring.

Instrumentation, Current, and Voltage Transformers

Basic current or voltage indication in SecoGear switchgear
can be via a switchboard type analog meter and transfer
switch, a digital meter, or can be a feature of a
multifunction protective relay. Most solid-state
multifunction relays today offer some type of metering
capabilities, including voltage, current, watts, vars,
frequency, and the demand functions.

AM and VM Scales

Ammeter scales are determined by the CT ratio. Current
transformer ratings are normally selected based on
approximately 125 % of the ampacity of the feeder circuit
conductors. Current transformer ratios selected in this
manner permit settings of circuit overcurrent-protective
relays to provide good selectivity and protection. For a
properly designed circuit, operating at full load, this means
a maximum scale reading of between half and three-
quarter scale.
For a circuit that provides for substantial future expansion,
lower scale readings will indicate initial-load conditions.
The voltmeter scale, determined by the voltage
transformer ratio, is 125 percent of the nominal line-to-line
VT rating. Optional wattmeters and varmeters, switchboard
type, are available for most equipment. Wattmeter and
varmeter scales are determined by the CT and VT ratios.

CT and VT Ratios

Standard window-type current transformers are available
in ratios ranging from 50:5 to 4000:5 amperes. The basic
ground-sensor window-type CT (GSCT) ratio is 50:5
amperes, with a 7.25 in window. Relay accuracy class is
per IEEE C37.20.2-2015, Table 4. Higher accuracy classes
may be available; however, space for mounting such CTs is
limited.
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SecoGear Medium-voltage Switchgear Application and Technical Guide
Local
Trip Close
X X X
X X X
X X X X
X
X X
Remote
Trip
Devices Required
(in addition to remote control switch)
Local permissive switch (69CS), plus breaker
X X X
position switch (52POS)
Local permissive switch (52CS), plus breaker
X
position switch (52POS)
Local permissive switch (52CS), plus breaker
X
position switch (52POS)
Control switch (52CS)

Table 4-2: Single Ratio CTs

CT Ratio
50:5 A
100:5 A
150:5 A
200:5 A
250:5 A
300:5 A
400:5 A
500:5 A
600:5 A
800:5 A
1000:5 A
1200:5 A
1500:5 A
2000:5 A
2500:5 A
3000:5 A
4000:5 A
5000:5 A
Note:
1. High accuracy requires twice the mounting space of a standard
accuracy CT.
System and Equipment Protection
Standard High Accuracy
Accuracy Class
C10
C20
C20
C20
C20
C50
C50
C100
C100
C100
C200
C200
C200
C200
C200
C200
C200
Class 1
C10
C20
C50
C50
C50
C100
C100
C100
C200
C200
C200
C400
C400
C400
C400
C400
C400
C400
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