DT3000
Instruction Leaflet
I.B. 17555D
Effective: Date 07/02
Page 73
For more information visit:
www.cutler-hammer.eaton.com
Supersedes I.B. 17555C dated November 1999
B5.0 WIRING AND SETUP
ENSURE THAT THE INCOMING AC POWER
SOURCES ARE DISCONNECTED BEFORE
PERFORMING ANY WORK ON THE DIGITRIP 3000
PROTECTIVE RELAY OR ITS ASSOCIATED
EQUIPMENT. FAILURE TO OBSERVE THIS
PRACTICE COULD RESULT IN EQUIPMENT
DAMAGE, SERIOUS INJURY, AND/OR DEATH.
Refer to Figures 3-1, B-3, B-4, and B-5 for the
DT3010/DT3020 typical wiring diagrams. Note the
following:
•
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.
•
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.
•
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
information on zone interlocking.
NOTE: All wiring must conform to applicable federal,
state, and local codes.
B6.0 APPLICATION CONSIDERATIONS
B6.1 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 corresponds 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 CURRENTS BELOW 1 PER
UNIT. THE DSPS WILL NOT BE ABLE TO POWER
THE RELAY FOR THESE FAULTS.
B6.2 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 facility and a fault is present, the
relay will power-up and trip provided the current levels are
above the minimum operating 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 Protection Off
alarm will provide alarm indication if the power is lost or if
the relay has failed.
B6.3 CT SATURATION
The DSPS has been designed and extensively tested to
ensure continued relay powering when the main Cts
saturate. It powers the relay even for extreme cases in
which the Ct delivers only a succession of current spikes of
1 to 2 ms each half-cycle.
Pay attention to the standard measuring limitations of any
protective relay with saturated Cts.
The saturated Ct is
exhibiting serious ratio error, and any connected relay will
measure lower current than is actually flowing in the
primary circuit. Tripping times will be longer than planned.
In extreme cases, the relay may not trip at all.
WARNING
