User`s guide

Volume 3—Power Distribution and Control Assemblies CA08100004E—November 2013 www.eaton.com V3-T9-239
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9.4
Metering Devices, Protective Relays, Software and Connectivity
Protective Relays
Harmonic Restraints
There are certain conditions
like energizing one side of the
transformer with the other
side de-energized (inrush
currents) or the paralleling
of two transformers
(sympathetic currents) that
can create false differential
currents. These differential
currents if not recognized can
cause a false trip; in the case
of inrush conditions or
sympathetic currents the
differential current is
characterized by a heavy
content of 2nd and 4th
harmonic currents. The
percentage differential
element is desensitize either
permanently (stationary
conditions) or temporarily
(transient conditions),
whenever the 2nd or 4th
harmonic exceed the value
programmed into the relay.
Another condition that can
create a false differential
current is a sudden change of
voltage or frequency, that can
put the transformer in an
overexcitation state. In this
case there is high content of
5th harmonic currents. The
percentage differential
element is also desensitized
when the 5th harmonic
content exceeds a predefined
value.
Dynamic Rise of the Operating
Characteristic
Unrestrained Differential
An unrestrained differential
element is provided for fast
tripping on heavy internal
faults to limit catastrophic
damage to the transformer
and minimize risks to the
remainder of the power
system.
Restricted Ground Fault
Ground differential protection
is applied to transformers
having impedance grounded
wye windings. It is intended
to provide sensitive ground
fault detection for low
magnitude fault currents,
which would not be detected
by the main percent
differential element.
Restricted Ground Fault
Overcurrent Elements
The ETR-4000 can be used
to provide backup for
transformer and adjacent
power system equipment.
Instantaneous overcurrent
elements can be used for fast
clearing of severe internal or
external (through) faults.
Time overcurrent protection
elements per winding allow
coordinating with the
adjacent protection zones and
acting as a backup protection.
There are 11 user-selectable
inverse-time overcurrent
curve characteristics. The
user can select from the
ANSI, IEC or thermal curve
families and can select
instantaneous or time delay
reset characteristics.
Negative Sequence Overcurrent
Since this element does
not respond to balanced
load or three-phase faults,
the negative-sequence
overcurrent element may
provide the desired
overcurrent protection. This
is particularly applicable to
delta-wye grounded
transformers where only
58% of the secondary p.u.
phase-to-ground fault current
appears in any one primary
phase conductor. Backup
protection can be particularly
difficult when the wye is
impedance grounded. A
negative-sequence element
can be used in the primary
supply to the transformer and
set as sensitively as required
to protect for secondary
phase-to-ground or phase-to-
phase faults. This element
should be set to coordinate
with the low-side phase and
ground relays for phase-to-
ground and phase-to-phase
faults. The negative
sequence element must
also be set higher than the
negative-sequence current
due to unbalanced loads.
Breaker Failure
The ETR-4000 transformer
protection relay includes two
breaker failure (50BF, 62BF)
elements that can be initiated
from either an internal or
external trip signal. These are
independent elements that
can be used to operate a
lockout relay or trip an
upstream breaker. The timer
must be longer than the
breaker operating time and
the protective function
reset times.
Maintenance Mode
The Maintenance Mode can
improve safety by providing a
simple and reliable method to
reduce fault clearing time and
lower incident energy levels
at energized panels. The
Maintenance Mode allows
the user to switch to more
sensitive settings via a
password protected soft
key, communications or
via a digital input while
maintenance work is being
performed at an energized
panel or device. The more
sensitive settings provide
greater security for
maintenance personnel and
helps reduce the possibility
of injury.
Monitoring and Metering
Sequence of Events Records
The ETR-4000 protection
relay records a maximum
of 300 events associated with
the relay. An event is
classified as a change of state
as detected by the relay.
These include relay pickups,
dropouts, trips, contact
closure, alarms, setting
changes and self-diagnostic
failures. Each event is date
and time stamped to a 1 ms
resolution. The events are
stored in a FIFO in
chronological order.
Trip Log
The ETR-4000 protection
relay will store a maximum of
20 trip records in a FIFO trip
log. Each trip record will be
date and time stamped to a
1 ms resolution. The trip
lo
g re
cord will include
information on the type of
fault, protection elements
that operated, fault location
and currents at the time of
the fault.