Testing Limitrip Devices
26
It will be helpful to note certain differences between Limitrip
and Static Trip II devices: (1) In the Limitrip system, the power
supply and signal transformers are relocated to and com-
bined in the “Sensor Transformers” mounted on the rear of
the breaker. There are two cores in each Sensor Trans-
former. One core provides power to the trip device and the
other provides the input signal. The PTS-4 test set is arranged
to provide both an input signal and power signal for test
purposes. Static Trip II device contains both power signal
transformers. (2) All adjustments are made with switches in
place of potentiometer type controls. (3) Only six long time
pick-up settings are provided compared with seven settings
for Static Trip ll. (4) Only four long time delay bands are
included compared with six for Static Trip II the shortest and
the longest bands are omitted on Limitrip. (5) The ground fault
tripping option is not available. (6) Instantaneous and short
time pick-up settings are switch selectable at 3X, 6X, 8X, and
12X as compared to continuously adjustable settings with
calibrated points of 3X, 5X, 8X, and 12X for Static Trip II. (7)
Time current curves are in multiples of pick-up setting rather
than in multiples of pick-up current.
General
1.
The “Tripping XFMR Rating” values represent the pri-
mary value of the sensor transformer in amperes. The
secondary value is one ampere.
2.
The pick-up settings of the long time element are switch
selectable at calibrated points “A” through “F” as shown
in the rating table.
3.
The pick-up settings of the instantaneous and short time
delay elements are switch selectable at 3, 6, 8 and 12
multiples of the long time pick-up setting.
4.
The long time element has 4 bands that are switch
selectable. The time delay at 4 multiples of pick-up is as
follows:
Band 1—2.25 Seconds
Band 3—9 Seconds
Band 2—4.5 Seconds
Band 4—18 Seconds
5.
The short time element has 3 time delay bands which are
switch selectable (minimum, intermediate, and maxi-
mum).
6.
The maximum interrupting time is the maximum length
of time that fault current flows, including arcing time.
7.
Instantaneous maximum interrupting time may be greater
when breakers are closed in on a fault depending on
actual fault conditions. The maximum potential increase
for a 3 phase fault is 0.01 seconds and for a single phase
ground fault is 0.02 seconds.
Connections—
Use Cord Set 1 8-732-1 84-507
The connections for the Limitrip trip devices are made with an
integral wiring harness that terminates directly on the Sensor
transformers on the back of the circuit breaker: To gain
access to these terminals, it is necessary to remove the circuit
breaker from the cubicle.
The trip device output leads are connected to the tripping
actuator by quick disconnect “couplers.” To connect the test
set output leads, the couplers are disconnected and jack
assemblies 18-732-085-501 and 502 are inserted into each
of the lines to the actuator. The test set leads are then plugged
into the jack assemblies.
The trigger test points are not brought out on the Limitrip
device, so the pick-up cord set is provided with “Grabbers”
to connect directly to the circuit board inside the device. See
Figure 18 for the correct location of the test points. Connect
the red “Grabber” to the long time pick-up test point and the
black “Grabber” to the pick-up common test point. The red
banana plug of the cord set connects to the jack assembly
on the red leads of the trip device and the black banana plug
to the jack assembly on the black leads of the device.
The connections to the sensor terminals at the rear of the
circuit breaker are made as shown in Figure 19. To test A
phase, make the following cord set banana plug connections
at the terminals of the A phase Sensor Transformer: Blue
banana plug into terminal B (power lead), Green banana plug
into terminal G (power lead), Yellow banana plug into terminal
Y (signal lead), and the Orange banana plug into terminal O
(signal lead). To test the other phases, move all four banana
plugs to the Sensor terminals of the phase being tested.
Note, on Sensor transformers rated 2000 amperes and up,
it is necessary to disconnect either the blue or green the lead
from the transformer and connect the test set directly to the
Limitrip device because the low impedance of the power
winding may prevent tripping.
