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nigher
1%
where:
I
current amperes
t
time in seconds
Short Time (electrical)
to the relay from the several sets of current transformers should not exceed 150. These multiples should
be calculated on the basis of
of the rectifiers in the through current restraint
current can flow through circuit breakers
AUXILIARY RELAY CONTROL CIRCUIT
The
and
with small links located on the front of the relay enables the selection of one of these voltages.
The
relay is provided with two open contacts connected to a
closing rating of the contact is 30 amps for voltages not exceeding 250 volts. If more than one
break& is to be tripped or if the tripping current exceeds 30 amperes. an auxiliary relay must be used
with the
relay.
be de-energized by an auxiliary switch on the circuit breaker
reset relay is
PICKUP AN0 OPERATING TIME
The operating characteristic Is shown in Fig. 1.
percent slope versus the through current flowing in the
given to a particular slope tap setting and indicates an approximate
zero restraint is
operating current is reduced from any value above pickup to zero is less than 25
of the operating time of the main unit and of the instantaneous unit are shown in Fig.
plotted against differential current.
OVERCURRENT UNIT PICKUP
The
unit is adjusted to pickup when the differential
'8 times the ampere
only one
amperes are required for pickup.
only, since the differential current transformer in the relay
cycle of any d-c
Courtesy of NationalSwitchgear.com
amperes for
may be applied for shorter lengths of time in accordance
For
the
fault current.
D - C
R e s i s t a n c e
0.13
Carry Continuously
0.5 Amps
4
carry
for
Carry 10 Amps for
30
relays are available for use with 48. 125, and 250 d-c
the breaker trips. it is necessary that the tripping circuit of these
and normally used.
CHARACTERISTICS
30 percent of tap value (see Table III). The dropout time
The main
produced by rated tap current flowing in that
supplies current. and the tap plug for the CT is in the
This pickup value is
present.
second measured in the primary Of any
and
the
Of the multiples Of tap
This limitation is a result of the voltage
Note that in Fig. 9 external fault
and 52-2 without being limited by the
TABLE II
2.0
0.6
Tap
Tap
0.6 Ohm
1.5 Amps
0.5
4
by other
The curve for various percentage
The percentage slope is a figure
operating time includes auxiliary unit operating time.
on the A-C
0.2
,
Tap
7
0.25
----
0.2
voltage. A
output circuit. The current
pickup at
For example:
ampere tap, 40
Of current
the
fed
Impedance.
the
the
a half
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