Percent Slope Setting; Std Relay - GE STD15C Instructions Manual

This curve represents the
which or' less of the value given on the curve does not necessarily indicate that
operate at higher through current values.
cause CT saturation.
Small rectifier-type AC voltmeters are suitable for the measurement Of unbalance. The
should not be left permanently connected since the shunt current it draws reduces the relay

PERCENT SLOPE SETTING

Scribe marks for 15. 25 and 40 percent slope settings are provided in both the ST015 and STF16
It is
to use one of the others. See the corresponding heading under CALCULATIONS for further details.
TARGETS
Targets are provided for
event of an internal fault. one or both of these units will operate depending Won the fault magnitude.
This will produce a target indication of the
the target should be reset by the reset slide located at the lower left hand corner of the relay.
DISABLING OF TYPE STD RELAY
by-passing a breaker for maintenance. it will be necessary to
If the
tripping.
plug, the following precautions should be taken:
The relay may be disabled by short-circuiting studs 8 and g of the relay or by Opening the
1.
circuit at stud
2. If the CT secondaries are short-circuited as part of the disablfng procedure, the
should be opened at stud 1 and studs 8 and g should be short circuited first.
on short circuitingthe CT secondaries alone. because any difference in time of shorting them may cause
false tripping.
CONTACT CLEANING
For cleaning 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
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 may
leave scratches which increase arcing and deterioration of the contacts.
leave minute particles of insulating abrasive material in the contacts and thus prevent closing.
The burnishing tool described is'included in the standard relay tool kit obtainable
An operation test and inspection of the relay and its connections should be made at
six months. Tests may be performed as described under INSTALLATION TESTS or. if desired, they may be
made on the service taps as described in this section.
When or withdrawing a test plug with U-shaped through jumpers to
through the test plug, similar through jumpers should also be used on studs 8 and g to maintain the
connections the relay to the case.
serting or withdrawing the plug.
Courtesy of NationalSwitchgear.com
relay characteristic.
This is especially true where very high through faults My
practice to use the 25 percent setting unless special connections make it advisable
the seal-in unit
the relay is done by a remote switch rather than by removing the relay
If this is not done, there is a risk of false tripping upon
OPERATION
the instantaneous
unit which operates. After a fault is cleared.
MAINTENANCE
PERIODIC TESTS
of voltage across studs 8 and g
unit. In
the relay to prevent false
It is not
Abrasive paper or cloth may
the trip circuit
will
circuit
to rely
the
once every