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GEI-12083
Item (2) may be checked by noting that torque is available and in the correct direction upon removal
of two of the three currents.
Each of the three current combinations should be tested in turn.
When
making these tests, the phase angle of the currents should be considerably different from the angle of
zero torq ue.
CAUTION:
Every circuit in the drawout case has an auxiliary brush; this is the short one in the case
(not on the cradle) which the connection plug or test plug should engage first.
On every current
circuit or other circuit with a shorting bar, make sure these auxiliary brushes are bent high enough
to engage the connection plug or test before the main brushes in the case do, as otherwise the CT
secondary circuit may be opened (where one brush touches the shorting bar) before the circuit is com-
pleted from the plug to the other main brush.
See Figure 15.
OPERATION
In analyzing various connections to the Type CAP15A relay, it is convenient to consider the maonet
as a group of eight wattmeter type units acting upon a single rotor, a combination of each coil and an
adjacent coil being assumed to be one element.
Of course, extraneous torques are developed by combinations of coils which are not adjacent.
However,
the torque of an adjacent pair of poles is largely relative to that of any other pair.
For instance, the
torque produced by the interaction between coils Band H (part "a," figure
7)
is approximately 15 percent
of that produced by coil combinations A-H, while the torque produced by combination C-H is about two per-
cent, a negligible amount.
The torques of alternate poles (e.g., A-C or B-H) being appreciable, the con-
nections are arranged so that their torques balance out substantially to zero, a factory adjustment being
provided for more accurate balance of the current torques.
(See CURRENT BIAS ADJUSTMENT).
Referring to
the currents in part "a," Figure 7, it can be seen that the torque produced by the interaction between
coils A and G is balanced by the equal and opposite torque of combination E-G is balanced by that of com-
bination C-E.
Part "a" of Figure 7 shows schematically the currents and voltages applied to the eight coils with
connections as in Figure 9, connection A.
For clarity one current coil and its adjacent potential coils
are isolated in part "b," Figure 7.
It is observed that 13 acts with EI-2 and E2-3' the resulting torque
being equivalent to the reaction of 13 with the vector difference of EI-2 and E2-3 (difference because
the potential coils are on opposite sides of the current coil).
The vector relations are also shown in
part "b."
Part "c" and "d" show corresponding coil and vector relations for the other two currents, 12
and II.
It
is noted (part "e" of Figure
7)
that the two remaining coil combinations produce equal and
opposite torques.
Considering a potential coil and its adjacent current coil, this combination would have maximum
torque when the current leads the voltage by 20 degrees. Hith the connections of part "a" of figure 7,
it is seen that 13 will lead EI-2 - E2-3, by 20 degrees when 13 lags its phase-to-neutral voltage by 40
degrees.
Thus, with these connections, maximum torque (balanced three-phase conditions) is obtained
when a current lags itsphase-to-neutral voltage by 40 degrees.
ADJUSTMENTS
CUP AND STATOR
These relays are properly adjusted at the factory to obtain the desired characteristic and it is
advisable not to disturb these adjustments.
If for any reason it becomes necessary to remove the contact
plate and rotor, the following procedure must be followed:
l.
2.
3.
4.
Remove the cradle from the case.
Remove the two screws holding the top inner block to the cradle and tilt the block up and back
so that it ;s possible to work on the top of the relay.
~isconnect the four leads which go to the contact plate at the terminals in the upper and lower
lnner blocks and draw the loose ends out through the holes in the mounting plate.
Remove the two screws which secure the top bearing plate.
8
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