GE AKR-30 Series Maintenance Manual page 72

13.1 SERIES OVERCURRENT TRIPPING
DEVICE EC-2A
The Type EC-2A overcurrent tripping device is available in
three forms:
1 . Dual overcurrent trip, with long-time delay and high-set in-
stantaneous tripping.
2. Low-set instantaneous tripping.
3. High-set instantaneous tripping.
The dual trip has adjustable long-time and instantaneous
pick-up settings and adjustable time settings. Both forms of in­
stantaneous trip have adjustable pick-up settings.
ADJUSTMENT NOTE
Before attempting any checks or adjustments on breaker with
EC trip devices, the breaker mechanism and trip latch should be
checked to assure their proper functioning so that the breaker
trip shaft is free of high friction loads. The trip latch of the
breaker should also be checked for proper trip latch engage­
ment. See Section 7.15
Refer to Fig. 99 for the discussions given below.
1 3. 1 . 1 LONG TIME·DELA
INSTANTANEOUS TRIPPING
By means of the adjustment knob (3), which can be manipu­
lated by hand, the current pick-up point can be varied from 80
to 1 60 percent of the series coil rating. The indicator and a cal­
ibration plate (2) on the front of the case provide a means of
indicating the pick-up point setting in terms of percentage of coil
rating. The calibration plate is indexed at percentage settings of
80, 1 00, 1 20. 1 40, and 1 60.
As in the case of the EC-1 over-current trip, the long-time de­
lay tripping feature can be supplied with any one of three
time-current characteristics which correspond to the NEMA
standards maximum, intermediate and minimum long-time delay
operating bands. These are identified as 1 A, 1 B and 1C char­
acteristics, respectively. Approximate tripping time for each of
these. in the same order are
cent of the pick-up value of current. (See time-current charac­
teristic curves).
The tripping time may be varied within the limits shown on the
characteristic curves by turning the time adjustment screw (4).
Turning in a clockwise direction increases the tripping time;
counterclockwise motion decreases it. The dashpot arm (8) is
indexed at four points, MIN-1 13-213-MAX, as indicated in Fig.
100. When the Index mark on the connecting link (9) lines up
with a mart( on the dashpot arm, the approximate tripping time
by the characteristic curve is indicated. The 1 A and
as shown
dev1ces are shipped with this setting at the
1 B charactenst1c
mart( and the 1 C characteristic at the 1 13 mark. The standard
charactenst1c curves are plotted at these same settings.
T1me are Inversely proportional to the effective length
values
the arm Therefore. the linkage setting that gives the
of dashpot
hme value IS the one at which dimension "A", Fig.
shortest
is greatest . The t1me adJUStment screw (4) may be turned by in­
sertmg a Ph1ll1ps head screwdriver through the hole in the front
the case. 1s des�red to relate the linkage setting to the
of I I it
on
index the hnkage
marks
be done
by removing the two mounting screws.
case. Th1s may
one on each s1de of the case. which may
disturbing the tnp unit itself.
72
Y
AND HIGH-SET
30, 600
1 5, and 5 seconds at
it be
wi l l
necessary to remove the
be
taken off without
1 3.1 .2 INSTANTANEOUS LOW-SET TRIPPING
The low-set instantaneous pick-up point may be varied by the
adjustment knob
(3).
from 80 percent to 250 percent of the series coil rating, with . .
calibration plate indexed at values of 80, 1 00, 1 50, 200, and 250
percent of the rating.
1 3.1 .3 I N STANTANEOUS HIGH-SET TRIPPING
The high-set instantaneous pick-up value may have one of
the following three ranges: 4 to 9 times coil rating; 6 to 1 2 times
coil rating or 9 to 1 5 time coil rating. The pick-up setting may be
varied by turning the instantaneous pick-up adjusting screw
(12).
Three calibration marks (1 5) will appear on the operating
(14) and the value of these calibration marks will be indicated
by stampings on the
or
9X - 1 2X) (9X - 1 2X - 1 5X).
At the factory, the pick-up point has been set at the name­
plate value of the instantaneous trip current. (Usually expressed
in times the ampere rating of the trip coil). The variation in pick­
up setting Is accomplished by varying the tensile force on the
instantaneous spring
the position of the movable nut (1 1 ) on the screw. The spring is
anchored to this movable nut so that when the position of the
nut is changed, there is a corresponding change in the spring
load. As the spring is tighten
The top edge of the movable nut (1 1 ) serves as an index
pointer and should be lined up with the center of the desired cal­
ibration mark (1 5) to obtain the proper instantaneous trip setting.
The trip screw (6) on the end of the armature (7) should �
set so that it does not contact the trip paddle on the trip st­
until the air gap between armature and pole piece is reduced
3/32 in. or less, measured at the rivet in the pole piece. Also,
the armature must have a minimum of 1 /32 in. of travel beyond
the point in its motion at which the breaker is tripped.
Replacement of the EC-2A device is accomplished by the
same procedure described for the EC-1 series trip device; how­
per­
ever, in some cases, when replacing an EC-1 device with an
be
it will necessary to replace the trip paddles on the trip
EC-2A
shaft with ones which are slightly longer. When required these
will be provided with the replacement trip units.
NOTE:
Pick-up settings on the calibration plate of the EC-2A
device are calibrated for the specific device. When replacing
covers, replace on associated device.
213
99,
FIG. 1 00 TIME-ADJUSTMENT INDEXING
The calibration in this case usually ranr
arm
as follows: (4X - 6.5X - 9X) or (6X -
Turning the adjustment screw changes
(5).
�
. the pick-up point is increased.
arm
._