Wiring And Setup; Application Considerations; Sensitivity And Ct Ratios; Tripping On Facility Energization - Eaton Cutler-Hammer Digitrip 3000 Instructions For Installation, Operation And Maintenance

Page B6
5.0

WIRING AND SETUP

ENSURE THAT THE INCOMING AC POWER
SOURCES ARE DISCONNECTED BEFORE PER-
FORMING ANY WORK ON THE DIGITRIP 3000
PROTECTIVE RELAY OR ITS ASSOCIATED EQUIP-
MENT. FAILURE TO OBSERVE THIS PRACTICE
COULD RESULT IN SERIOUS INJURY, DEATH AND/
OR EQUIPMENT DAMAGE.
NOTE: The following material replaces sections 5-4,
on page 35.
Refer to Figures B-3, B-4, B-5, and B-6 for the DT3010/
DT3020 typical wiring diagrams. Note the following:
4.1 Direct wire connections to the terminal blocks must
not be larger than No. 14 AWG wire. However, larger
size wires can be used for the CT connections, with
the appropriate ring terminal.
4.2 All contacts are shown in the de-energized position.
NOTE: The Protection Off Alarm Relay is energized
when ac control power is applied and the DT3000 is
operating properly. To obtain a contact that closes
when protection is lost, use terminals 9 & 11 of TB2.
For a contact that opens when protection is lost, use
terminals 9 & 10 of TB2.
3. The Digitrip 3000 comes with the zone interlocking
jumpers installed (TB1 terminals 11 to 12 and 13 to
14). Leave these jumpers installed if zone selective
interlocking is not used. See Section 4 for more infor-
mation on zone interlocking.
NOTE: All wiring must conform to applicable federal,
state, and local codes.
6.0

APPLICATION CONSIDERATIONS

NOTE: The following material is an addition to
Section 4, on page 31.
WARNING
6.1

SENSITIVITY AND CT RATIOS

For scenarios where the relay must trip with loss of ac
power, the main-ct secondary current must be greater
than 9 amperes for a single-phase-to-ground fault or 6
amperes for a three-phase fault.
For best coverage of faults, the ct ratio should be chosen
so that normal full loading of the protected feeder corre-
sponds to a secondary current of approximately one per
unit or 5A secondary.
BEWARE OF MISAPPLICATION OF MAIN-CT
RATIOS. CONSIDER A CIRCUIT WITH A 400A LOAD
THAT NORMALLY REQUIRES A 400:5 CT RATIO,
BUT THE CT IS CONNECTED FOR 1200:5. NORMAL
LOADS WILL APPEAR AS SMALL CURRENTS, AND
EVEN SOME FAULTS MAY HAVE SECONDARY CUR-
RENTS BELOW 1 PER UNIT. THE DSPS WILL NOT
BE ABLE TO POWER THE RELAY FOR THESE
FAULTS.
6.2

TRIPPING ON FACILITY ENERGIZATION

Normally, the Digitrip 3000 with DSPS will be powered
from the auxiliary ac voltage.
If no auxiliary ac control power is present when the
breaker closes into a fault or if power is restored to a facil-
ity and a fault is present, the relay will power-up and trip
provided the current levels are above the minimum oper-
ating level. In this case, trip times will be approximately
100 ms longer than the case of having normal ac control
voltage prior to the fault.
This will also be true if the ac auxiliary power transformer
fails or the supply fuses have blown at any time prior to
the fault.
Visible front-panel metering displays, and/or network
data communications of the relay, comprise a good check
on the integrity of the ac supply. In addition, the Protec-
tion Off alarm will provide alarm indication if the power is
lost or if the relay has failed.
I.B. 17555C
CAUTION
Effective November 1999