Target And Seal-In Unit - GE STD15C Instructions Manual

GEK—45 307
TABLE II
TARGET AND SEAL-IN UNIT
2.0 Amp Tap
0.6 Amp Tap
0.2 Amp Tap
DC Resistance
0.13 Ohms
0.6 Ohms
7 ohms
Carry Continuously
0.5 Amps 1.5 Amps 0.25 Amps
Carry 30 Amps for Secs. 0.5 Secs.
Carry 10 Amps for
30 Secs
4
Secs. 0.2 Secs.
AUXILIARY RELAY CONTROL CIRCUIT
The STD15C and STD16C relays are availabl e for use with 4S, 125, and 250 DC or 48,
110 and 220 DC control voltage , depending upon the relay model.
A plate with small
links
located on the front of the relay enables
the selectio n of one of these
voltage s.
The
STD
relay
is
provided with two open
contacts connected to a common output
circuit. The current—closing rating of the contact
is 30 amps for voltage s not
exceeding 250 volts.
If more than one circuit breaker is to be tripped, or if the
tripping current exceeds 30 amperes, an auxiliar y relay must be used with the STD
relay. After the breaker trips, it is necessary that the tripping circuit of these
relays (STD and auxiliar y)
be de-energized by an auxiliar y switch on the circuit
breaker or by other automatic provisio ns.
A manual reset relay is recommended and
normally used.
CHARACTERISTI Cs
PICKUP AND OPERATING TIME
The operatin g characte ristic is shown in Figure 7.
The curve for various percentage
slopes shows the percent slope versus the through current flowing in the transfor mer.
The percentage
slope is a
figure
given
to a particul ar slope
tap setting,
and
indicate s
an approximate
slope characte ristic.
Pickup at zero restrain t
is
approximately
30% of tap value
(see Table III). The dropout
time, when the
operatin g current is reduced to zero from any value above pickup, is less than 25
millisec onds.
Curves of the operatin g time of the main unit and of the instanta neous unit are
shown in Figure 5, plotted against differen tial current.
The main unit operatin g
time include s auxiliar y unit operatin g time.
OVERCURRENT UNIT PICKUP
The overcur rent unit
is adjusted
to pick up when the differen tial
current
transfor mer ampere-turns are 8 times the ampere turns produced by rated tap current
flowing in that tap.
For example:
When only one CT supplies current, and the tap plug for the CT is in the 5
ampere tap, 40 amperes are required for pickup.
This pickup value is based on
the AC component of current transfor mer output only, since the differen tial
current transfor mer in the relay produces only a half cycle of any DC (offset)
component present.
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