ABB CIRCUIT SHIELD 49/50/51 Anleitung Handbuch - Seite 4
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IB 7.2.1.7-4
Page4
4. INDICATORS
TARGETS
Motor Overcurrent Relay
For the Type 49/50/51, operation targets are provided for the 49 and 50/51 functions. For the Type 49/50, targets are
provided for the 49 and 50 functions; and for the Type 49, a target is provided for the 49
function.
Control power must be
present to reset the targets, and the overload unit must be in a "thermally-reset" condition.
PICKUP INDICATOR
A light-emitting-diode is provided to indicate when the input current is above the pickup setting. The led will flash on and
off at a rate that is related to the current
value:
the higher above pickup, the faster the rate of flashing. With the OVERLOAD
dial set at 1 minute, approximately 40 flashes will occur prior to a trip operation (assuming the relay was fully reset when the
overload was applied). For a 5 minute setting approximately 200 flashes will occur.
IMPORT ANT: the pickup indicating led is not an operation target. Once a trip occurs the state of the indicating led is
indeterminate. It may go out or it may remain continuously lighted. The led will remain in that state until secondary current
is re-established into the input of the relay. The relay is "timing-out" only when the Jed is flashing.
APPLICATION DATA
The ABB Circuit-Shield™ Type 49/50/51 three-phase Overcurrent Relay provides three important functions for the protection
of motors: overload, locked rotor, and fault detection. Although packaged in one case, the three functions are individually
adjustable, allowing optimum protection without compromise among the
various
elements.
Settings
are easily
made with
all adjustments on the front panel of the
relay.
OVERLOAD PROTECTION (Function 49)
The overload function has time-current curves which match the allowable heating times of typical motors, thus allowing use of
the full capability of the machine, without the risk of damage due to continuous or repetitive overloads. The time-current
curves are given in
605838,
on page 9.
Unlike bi-metals or other thermal type relays, the Type 49 element has memory of previous overloads with long
reset time; long enough to ensure proper protection in applications involving repetitive overloads and hard
starts.
If
a second overload occurs before the full reset of the memory, the relay will trip in a time shorter
than shown by the current curves. This relationship may be expressed by the equation below, which is a rough
approximation.
T12
T1
=
l -T1
+
(Valid when
Ti
less than I)
where
TR
is the time in minutes required for a specific time dial setting:
Time Dial
1
2
3
4
5
2.4
4.8
7.2
9.6
12
T2 is the time required for the second overload to cause the relay to
trip,
as a fraction of the
value
read
from
the time current curve.
TI is the time for which the first overload
lasted,
expressed
as
a
fraction of the time allowed
by
the time-current
curve. For example, with the relay set on
time
dial #1, if the first overload was
2
times pickup
and
lasted 20 seconds:
20
l
T1
=
········
·
-
.......
(for
time
dial
#
1)
60
3
TI2
is
the time between removal of first overload
and application
of the
second,
in minutes.