Current
protection functions:
ANSI 50/51 –
PHASE OVERCURRENT
Three-phase protection
against overloads and phase-to-phase
short-circuits.
ANSI 50N/51N OR
50G/51G – EARTH FAULT
Earth fault protection
based on measured or
calculated residual current
values:
- ANSI 50N/51N:
residual current
calculated or measured
by 3 phase current
sensors
ANSI 50G/51G: residual
current measured directly by
a specific sensor ANSI
50BF – BREAKER FAILURE
If a breaker fails to be
triggered by a tripping
order, as detected by the
non-extinction of the fault
current, this backup
protection sends a tripping
order to the upstream or
adjacent breakers.
ANSI 46 –
NEGATIVE SEQUENCE /
UNBALANCE
Protection against phase
unbalance, detected by the
measurement of negative
sequence current:
- Sensitive protection
to detect 2-phase faults
at the ends of long
lines
Protection of equipment
against temperature build-up,
caused by an unbalanced
power
supply, phase inversion
or loss of phase, and
against phase current
unbalance
ANSI 49RMS –
THERMAL OVERLOAD
Protection against
thermal damage caused by
overloads on machines (transformers,
motors or generators). The
thermal capacity used is
calculated according to a
mathematical model which
takes into account:
- Current RMS values
- Ambient temperature
Negative sequence current,
a cause of motor rotor
temperature rise
Recloser
ANSI 79
Automation device used to
limit down time after
tripping due to transient or
semipermanent faults on
overhead lines. The recloser
orders automatic reclosing
of the breaking device after
the time delay required to
restore the insulation has
elapsed. Recloser operation
is easy to adapt for
different operating modes by
parameter setting.
Directional
current protection
ANSI 67 –
DIRECTIONAL PHASE
OVERCURRENT
Phase-to-phase short-circuit
protection, with selective
tripping according to fault
current direction. It
comprises a phase
overcurrent function
associated with direction
detection, and picks up if
the phase overcurrent
function in the chosen
direction (line or busbar)
is activated for at least
one of the 3 phases.
ANSI 67N/67NC –
DIRECTIONAL EARTH FAULT
Earth fault protection,
with selective tripping
according to fault current
direction. 3 types of
operation:
- type 1: the
protection function uses
the projection of the I0
vector
- type 2: the
protection function uses
the I0 vector magnitude
with half-plane tripping
zone
- type 3: the
protection function uses
the I0 vector magnitude
with angular sector
tripping zone
ANSI 67N/67NC
TYPE 1
Directional earth fault
protection for impedant,
isolated or compensated
neutralsystems, based on the
projection of measured
residual current.
ANSI 67N/67NC
TYPE 2
Directional overcurrent
protection for impedance and
solidly earthed systems,
based on measured or
calculated residual current.
It comprises an earth fault
function associated with
direction detection, and
picks up if the earth fault
function in the chosen
direction (line or busbar)
is activated.
ANSI 67N/67NC
TYPE 3
Directional overcurrent
protection for distribution
networks in which the
neutral earthing system
varies according to the
operating mode, based on
measured residual current.
It comprises an earth fault
function associated with
direction detection (angular
sector tripping zone defined
by 2 adjustable angles), and
picks up if the earth fault
function in the chosen
direction (line or busbar)
is activated.
Directional power
protection functions
ANSI 32P –
DIRECTIONAL ACTIVE OVERPOWER
Two-way protection based
on calculated active power,
for the following
applications:
- active overpower
protection to detect
overloads and allow load
shedding
- reverse active power
protection:
- against generators
running like motors when
the generators consume
active power
- against motors
running like generators
when the motors supply
active power
ANSI 32Q/40 –
DIRECTIONAL REACTIVE
OVERPOWER
Two-way protection based
on calculated reactive power
to detect field loss on
synchronous machines:
- reactive overpower
protection for motors
which consume more
reactive power with
field loss
- reverse reactive
overpower protection for
generators which consume
reactive power with
field loss
Machine
protection functions
ANSI 37 – PHASE
UNDERCURRENT
Protection of pumps
against the consequences of
a loss of priming by the
detection of motor no-load
operation. It is sensitive
to a minimum of current in
phase 1, remains stable
during breaker tripping and
may be inhibited by a logic
input.
ANSI 48/51LR/14 –
LOCKED ROTOR / EXCESSIVE
STARTING TIME
Protection of motors
against overheating caused
by:
- excessive motor
starting time due to
overloads (e.g. conveyor)
or insufficient supply
voltage. The
reacceleration of a
motor that is not shut
down, indicated by a
logic input, may be
considered as starting.
- locked rotor due to
motor load (e.g. crusher):
- in normal operation,
after a normal start
directly upon starting,
before the detection of
excessive starting time,
with detection
of locked rotor by a zero
speed detector connected to
a logic input, or by the
underspeed function.
ANSI 66 – STARTS
PER HOUR
Protection against motor
overheating caused by:
- Too frequent starts:
motor energizing is
inhibited when the
maximum allowable number
of starts is reached,
after counting of:
starts per hour (or
adjustable period)
- Consecutive motor
hot or cold starts (reacceleration
of a motor that is not
shut down, indicated by
a logic input, may be
counted as a start)
- Starts too close
together in time: motor
re-energizing after a
shutdown is only allowed
after an adjustable
waiting time.
ANSI 50V/51V –
VOLTAGE-RESTRAINED
OVERCURRENT
Phase-to-phase short-circuit
protection, for generators.
The current tripping set
point is voltage-adjusted in
order to be sensitive to
faults close to the
generator which cause
voltage drops and lowers the
short-circuit current.
ANSI 26/63 –
THERMOSTAT/BUCHHOLZ
Protection of
transformers against
temperature rise and
internal faults via logic
inputs linked to devices
integrated in the
transformer.
ANSI 38/49T –
TEMPERATURE MONITORING
Protection that detects
abnormal temperature build-up
by measuring the temperature
inside equipment fitted with
sensors:
- transformer:
protection of primary
and secondary windings
- motor and generator:
protection of stator
windings and bearings.
Voltage protection
functions
ANSI 27D –
POSITIVE SEQUENCE
UNDERVOLTAGE
Protection of motors
against faulty operation due
to insufficient or
unbalanced network voltage,
and detection of reverse
rotation direction.
ANSI 27R –
REMANENT UNDERVOLTAGE
Protection used to check
that remanent voltage
sustained by rotating
machines has been cleared
before allowing the busbar
supplying the machines to be
re-energized, to avoid
electrical and mechanical
transients.
ANSI 27 –
UNDERVOLTAGE
Protection of motors
against voltage sags or
detection of abnormally low
network voltage to trigger
automatic load shedding or
source transfer. Works with
phase-to-phase voltage.
ANSI 59 –
OVERVOLTAGE
Detection of abnormally
high network voltage or
checking for sufficient
voltage to enable source
transfer. Works with phase-to-phase
or phase-to-neutral voltage,
each voltage being monitored
separately.
ANSI 59N –
NEUTRAL VOLTAGE DISPLACEMENT
Detection of insulation
faults by measuring residual
voltage in isolated neutral
systems.
ANSI 47 –
NEGATIVE SEQUENCE
OVERVOLTAGE
Protection against phase
unbalance resulting from
phase inversion, unbalanced
supply or distant fault,
detected by the measurement
of negative sequence voltage.
Frequency protection
functions
ANSI 81H –
OVERFREQUENCY
Detection of abnormally
high frequency compared to
the rated frequency, to
monitor power supply quality.
ANSI 81L –
UNDERFREQUENCY
Detection of abnormally
low frequency compared to
the rated frequency, to
monitor power supply quality.
The protection may be used
for overall tripping or load
shedding. Protection
stability is ensured in the
event of the loss of the
main source and presence of
remanent voltage by a
restraint in the event of a
continuous decrease of the
frequency, which is
activated by parameter
setting.
ANSI 81R – RATE
OF CHANGE OF FREQUENCY
Protection function used
for fast disconnection of a
generator or load shedding
control. Based on the
calculation of the frequency
variation, it is insensitive
to transient voltage
disturbances and therefore
more stable than a phase-shift
protection function.
Disconnection In
installations with
autonomous production means
connected to a utility, the
“rate of change of frequency”
protection function is used
to detect loss of the main
system in view of opening
the incoming circuit breaker
to:
- protect the
generators from a
reconnection without
checking synchronization
avoid supplying
loads outside the
installation.
- Load shedding The
“rate of change of
frequency” protection
function is used for
load shedding in
combination with the
underfrequency
protection to: either
accelerate shedding in
the event of a large
overload
- or inhibit shedding
following a sudden drop
in frequency due to a
problem that should not
be solved by shedding.
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