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For sectionalizing transmission systems the cur
rent and time setting m ust be determined by
calculation, due consideration being given to the
time required for circuit breakers to open so that
proper selective action can be obtained throughout
the system.
Current Setting
The connector screw on the terminal plate above
the time scale makes connections to various turns
on the operating coil. By placing this screw in the
various holes, the relay will j ust close contacts at
the corresponding current, 4-5-6-8- 10- 1 2 or 1 5
amperes, o r as marked o n the terminal plate.
- -
The tripping value of the relay on any tap may
be altered by changing the initial tension of the
spiral spring. This can be accomplished by turn
ing the spring adjuster by means of a screwdriver
inserted in one of the notches of the plate to which
the outside convolution of the spring is fastened.
An adjustment of tripping current approximately
15 percent above or below any tap value, can b,�
secured without materially affecting the operating
characteristics of the relay. For example, on the
4 to 15 amp. relay, by choosing the proper tap, a
continuous adj ustment of tripping current from
3.4 amperes to 17.5 amperes may be secured. The
characteristic time curve will be affected less for
any large adjustment if the next higher tap is
selected and the initial tension of the spiral spring
is decreased to secure the desired tripping value.
For example, the relay should be set on the 8
ampere tap with less initial tension in order to
secure a 7 ampere tripping value.
Caution
Be sure that the connector screw is turned u p
tight s o a s t o make a good contact, for the operat
ing current passes through it. Since the overload
element is connected directly in the current trans
former circuit, the latter should be short-circuited
before changing the connector screw. This can be
done conveniently by inserting the extra connector
screw, located on the right-hand mounting boss,
in the new tap and removing the old screw from its
original setting.
Time Lever Setting
The index or time lever limits the motion of the
disc and thus varies the time of operation . The
latter decreases with lower lever settings as shown
in the typical time curves of Figures 23 to 27.
ADJ USTMENTS AND MAINTENANCE
All relays should be inspected periodically and
the time of operation should be checked at least
once every six months. For this purpose, a cycle
counter should be employed, because of its con
venience and accuracy. Phantom loads should not
be used in testing induction-type relays because of
the re5ulting distorted current wave form which
produces an error in timing.
All contacts should be periodically cleaned with
a
fine file.
purpose. The use of abrasive material for cleaning
contacts is not recommended, because of the
danger of embedding small particles in the face of
the soft silver and thus impairing the contact.
Types CO and COH Overcurrent Relays
S *
1002 1 10 file is recommended for this
The proper adjustments to insure correct opera
tion of this relay have been made at the factory
and should not be disturbed after receipt by the
customer. If the adjustments have been changed
or the relay taken apart for re > airs, the following
instructions should be followed in reassembling
and setting it.
(Overcurrent Element Circuit-Closing Relays)
Shift the position of the contact stop on the
time lever and adj ust the contacts so that they
barely touch when the time lever is set on zero.
Adj ust the tension of the spiral spring so that
the relay will close its contacts at its rated current,
as shown by the position of the screw on the
tap block.
Shift the position of the damping
magnets so that the time characteristics of the
relay, as shown by test with a cycle counter, are
as shown on the typical time curves. In the factory
the relay is tested from the No. 10 lever position.
The calibration is intended to be on the basis of
the cool or normal operating condition inasmuch
as overloads are of short d uration. When checking
a n umber of points on the time curves, it will be
necessary to cool the relay coils between points
particularly after operating at high currents. An
air hose may be used for this purpose.
The position of the torque compensator on the
overload element is adjustable, influencing the
shape of the curve. This is a factory adjustment
and the location of the torque compensator should
not be changed in the field. If the relay has a metal
cover, this cover must be in place when making
tests.
The relays with torque control terminals will not
operate until these terminals are short-circuited
either by a j umper or by the external control
contacts.
Contactor Switch (Circuit-Closing Relays)
Adjust the stationary core of the switch for a
clearance between the stationary core and the
moving core when the switch is picked up. This
can be most conveniently done by disconnecting
the switch and turning it or the relay upside-down.
Screw up the core screw until the moving core
starts rotating. Now back off the core screw until
the moving core stops rotating. This indicates the
point where the play in the moving contact assem
bly is taken up, and where the moving core j ust
separates from the stationary core screw. Back off
the stationary core screw one turn beyond this point
and lock in place. This prevents the moving core
from striking and sticking to the stationary core be
cause of residual magnetism. Adjust the contact
clearance for 332 inch by means of the two small n uts
on either side of the M icarta disc. The switch should
pick up at 2 amperes d-e. Test for sticking after 30
amperes d-e. have been passed through the coil.
Operation Indicator (Circuit-Closing Relays)
Adjust the indicator to operate at 0.2 or 1 .0
ampere d-e. as supplied gradually applied by loosen
ing the two screws on the under side of the as
sembly, and moving the bracket forward or back
ward.
If the two helical springs which reset the
armature are replaced by new springs, they should
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