Protection
Description
ANSI 78PS - Pole slip
Characteristics
bcircular characteristic centered at origin defined by adjustable set point Zs
Protection against loss of synchronism on synchronous
machines, based on calculated active power.
2 types of operation:
btripping according to the equal-area criterion,
time-delayed
btripping according to power swing (number of active
power swings):
vsuitable for generators capable of withstanding high
electrical and mechanical constraints
vto be set as a number of rotations.
The 2 types of operation may be used independently or
at the same time.
DE51844
Functions
Sepam series 80
ANSI 12 - Overspeed
3
Detection of machine overspeed, based on the speed
calculated by pulse-counting, to detect synchronous
generator racing due to loss of synchronism, or for
process monitoring, for example.
Circular tripping characteristic of ANSI 21B protection.
btime-delayed definite time (DT) tripping when one of the three apparent
impedances enters the circular tripping characteristic.
ANSI 14 - Underspeed
Machine speed monitoring based on the speed
calculated by pulse-counting:
bdetection of machine underspeed after starting, for
process monitoring, for example
bzero speed data for detection of locked rotor upon
starting.
ANSI 50/27 - Inadvertent energization
Checking of generator starting sequence to detect inadvertent energization of
generators that are shut down (a generator which is energized when shut down runs
like a motor).
Consists of an instantaneous phase overcurrent protection confirmed by a timedelayed undervoltage protection function.
ANSI 50V/51V - Voltage-restrained
overcurrent
ANSI 64G - 100 % stator earth fault
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 21B - Underimpedance
Phase-to-phase short-circuit protection, for generators,
based on the calculation of apparent phase-to-phase
impedance.
U21
Z 21 = ---------------I2 – I1
apparent impedance between phases 1 and 2.
DE50099
Characteristics
binstantaneous or time-delayed tripping
bdefinite time (DT), IDMT (choice of 16 standardized
IDMT curves) or customized curve
bwith or without timer hold.
Protection of generators with earthed neutral against phase-to-earth insulation faults
in stator windings. This function may be used to protect generators connected to
step-up transformers
100 % stator earth fault is a combination of two protection functions:
bANSI 59N/64G1: neutral voltage displacement, protection of 85 % to 90 % of the
stator winding, terminal end.
bANSI 27TN/64G2: thrid harmonic undervoltage, protection of 10 % to 20 % of the
stator winding, neutral point end.
Stator winding of a generator protected 100 % by the combination of ANSI 59N and ANSI 27TN
protection functions.
ANSI 27TN/64G2 - Third harmonic undervoltage
Protection of generators with earthed neutral against phase-to-earth insulation faults,
by the detection of a reduction of third harmonic residual voltage.
Protects the 10 to 20 % of the stator winding, neutral point end, not protected by the
ANSI 59N/64G1 function, neutral voltage displacement.
Characteristics
bchoice of 2 tripping principles, according to the sensors used:
vfixed third harmonic undervoltage set point
vadaptive neutral and terminal third harmonic voltage comparator set point
btime-delayed definite time (DT) tripping.
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:
btransformer: protection of primary and secondary windings
bmotor and generator: protection of stator windings and bearings.
Characteristics
b16 Pt100, NI100 or Ni120 type RTDs
b2 adjustable independent set points for each RTD (alarm and trip).
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