Through Current Restraint; Instantaneous Overcurrent Unit; Location; Mounting - GE STD15C Instructions Manual

If harmonic restraint is found to be
THROUGH CURRENT
The through current restraint. which gives the relay the percentage differential or percent slope
characteristics are
with closed to
the two through currents. In testing
in one position and then the other, thus checking all the restraint coils. Uith the current
ampere position and the percent slope tap plug in the
up for values of the I and 13 currents indicated in Table IV.
in the 25 percent and 5 percent position.
prescribed. the adjustment may be made by adjusting
the through current branch (13) is slightly influenced by the application of differential current (II) and
should be checked to insure that it
Any in
restraint. However! after the slope setting has once
the slope
accordance with Table III.
NOTE: These currents should be permitted to flow for only a few seconds at a time
between tests; otherwise. the coils will be overheated.
NOTE: The percent slope tolerance is 10 percent of nominal. all in the plus direction. This is to
the slope characteristic never falls below tap value.

INSTANTANEOUS OVERCURRENT UNIT

This unit is
a high current of rated
rating as described under CHARACTERISTICS.
the lock-nut at the top of the unit and turning the cap screw until the proper pickup is obtained. In
this adjustment. the current should not be allowed to flow for more than approximately one second
i i m e .
DROPOUT OF UNIT
After the other
TEST section.
The location should
facilitate inspection and testing.
The relay should be mounted on a vertical surface.
in Figure 5.
Courtesy of NationalSwitchgear.com
It may be checked and adjusted using the circuit illustrated in Fig.
in Fig. 1.
II reads the differential current and I3 reads the smaller of
relays, the setting should be checked with the switch
If any one of these Set points is found to be the other than as
maintained as its proper value.
to give the desired slope will have small effect
The slope set points must then be rechecked to insure that they are in
POSITION
PERCENT
ON RHEOSTAT
SLOPE TAP'
Middle
Left
at the upper right-hand
through
If the setting is incorrect. it may be adjusted by loosening
are complete, check the dropout of the main
tests
clean and dry. free
of adjustment. it be corrected by adjusting Rheostat
percent position, the relay should Just
Repeat with the percent slope tap plug
It should be noted that the current magnitude in
any adjustment of minimum pickup will change
TABLE IV
AMPERES TRUE SLOPE
II
of the relay.
The unit should pick up at
and 6.

LOCATION

dust and excessive

MOUNTING

The outline and panel drilling
minimum pickup and harmonic
Its setting may
times the tap
as described under ACCEPTANCE
and
first
cooling
by passing
to
are