GE STD15C Instructions Manual page 12

This curve represents the
which is 75: or less of the value given on the curve does not necessarily indicate that
operate at higher through current
cause CT saturation.
Small rectifier-type AC voltmeters are suitable for the measurement of unbalance.
should not be left permanently connected since the shunt current it draws reduces the
PERCENT SLOPE SETTING
Scribe marks for 15. 25 and 40 percent slope settings are provided In both the
It practice to use the 25 percent setting unless special connections make It advisable
relays.
to use one of the others.
T A R G E T S
Targets are provided for both the seal-in unit
event of an internal fault. one or both of these units will operate depending upon the fault magnitude.
This will produce a target
the target should be reset by the reset slide located at the lower left hand corner
DISABLING OF TYPE STD RELAY
When by-passing a breaker for maintenance,
If the disabling of the relay is done by a remote switch rather than by
tripping.
connection plug, the following precautions should be taken:
The relay may be disabled by short-circuitino studs 8 and 9 of the relay or by opening the
1.
circuit at stud 1.
2. If the CT secondaries are short-circuited as part of the disabling procedure, the trip circuit
should be opened at stud 1 and studs 8 and 9 should be short circuited first.
on short circuitingthe CT secondaries alone, because any difference in time of shorting them
false tripping.
CONTACT CLEANING
For contacts. a flexible burnishing tool should be used. This consists of a flexible
strip of metal with an etched roughened surface , resembling in effect a superfine file. The polishing
action is so delicate that no scratches are left. yet corroded material will be removed rapidly and thoroughly.
The flexibility of the tool insures the cleaning of the actual points of contact.
Contacts should not be cleaned with knives. files or abrasive paper or cloth. Knives or files
leave scratches which Increase arcing and deterioration of the contacts. Abrasive paper or cloth
leave minute particles of insulating abrasive material in the contacts and thus prevent closing.
The burnishing tool described
An operation test and Inspection of the relay and its connections should be made at
Tests may be performed as described under INSTALLATION TESTS
six months.
on the service taps as described in this section.
Inserting or withdrawing a test plug with U-shaped through jumpers to complete the trip circuit
through the test plug, similar through jumpers should also be used on studs 8 and 9 to maintain the
the relay to the case. If this is not done, there is a risk of false tripping upon in-
connections
serting or withdrawing the plug.
Courtesy of NationalSwitchgear.com
relay characteristic.
This is especially true where very high through
See the corresponding heading under CALCULATIONS for further details.
of the
in the standard relay tool kit obtainable
PERIODIC TESTS
of a voltage across studs 8 and 9
the
unit which operates. After a fault Is cleared.
will be necessary to disable the relay to prevent
may
voltmeter
and
unit. In
the
the relay
It is not to rely
the factory.
every
if desired. they MY be