4 RELAY TESTING
4.1
SECONDARY INJECTION TEST EQUIPMENT
Although it
is
pcssible to verify correct relay operation after installation without
any special equipment it may be desirable to check all relay functions before
commissioning.
Basic
operation
of
the
relay
can
be
checked
using
a
commercial
secondary injection set capable of supplying up to
15
amps. Since the relay
operates
on
average RMS current values, a single phase current source
is
adequate. Figure 4-1
is
the schematic
of
a simple test circuit that
can
be built
to perform all the tests described
in
the following sections.
4.2
COMMISSIONING
RELAY TESTS
Prior to applyi(lg power to a
new
installation, system operation can
be
verified
by
applying currents through the relay current transformers
using
a primary
(high current) injection test set. Alternately, operation of all system components
except the phase
CTs
can
be
checked by disconnecting the current transformer
secondaries
and
applying
an
input
signal
to
the
relay
using
a
secondary
injection
test set similar to that shown
in
Figure
4-1.
4.3 OVERLOADS
Determine from the yellow product specification card whether the relay is de-
signed for 1 amp
or
5 amps CTs. Set the maximum load control
to
50%
of
CT
amps. The overload light should come on when injecting equal currents in all
three phases
of
0.5
amps
(1
amp CT's)
or
2.5
amps
(5
amp CTs). Other points
across the scale can also
be
checked. Verification
of
the overload/time curve
(Figure
3-2)
is possible by setting a known amount
of
overload and deter-
mining the time
to
trip. For example, with a 5 amp CT relay and the maximum
load control set at 50%, injecting 5 amps in each phase will cause the relay
to
trip within
117
seconds
if
run curve number 4 has been selected.
To
get
ac-
curate measurements it
is
necessary to know which
run
curve has
been
selected (Section
3.8),
to ensure that the memory is fully discharged by using
the emergency restart feature (Section
3.7),
and
to
ensure that the relay does
not go into start mode by slowly increasing the current
to
the overload level.
Once the relay
has
tripped due to the overload test it should not
be
possible to
reset
it
if
the memory
is
being used. Connect a jumper across
emergency
restart terminals 3 and 4 for 5 seconds to discharge the memory.
The
relay can
now
be
reset for further
tests.
If the relay
is
programmed for mechanical jam rapid trip (Section 3.9) set the
maximum load control to
100%
and
inject 5 amps
(5
amp model) or 1 amp
(1
amp
model). Slowly dial back the maximum load control until the relay trips The
current injected should exceed the full load control setting by the jam level
selected. For example.
if
mechanical jam rapid trip was set for 2 times full load.
with 5 amps injected
(5
amp
CT
model) the relay would tnp at a maximum load
setting of 50% since 5 amps represents a current level of twice full load. Further-
more, unlike prolonged overloads which cause lockout
when
the memory
is
used
it should
be
possible to immediately reset the relay after mechanical jam.
30
Courtesy of NationalSwitchgear.com
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