TRANSFORMER PROTECTION
AMIT LOHIYA
TRANSFORMER PROTECTION WITH RET670 RELAY
Internal electrical faults in transformers
cause immediate damage and can often
lead to production loss for long duration
which leads to revenue loss.
This Presentation describes the basic
principles & functions of RET670 relay used
for Transformer Protection.
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RET670 Relay Hardware
Transformer Module
Binary Input Module
Binary Output Module
Communication Module
Power Source Module
Analog to Digital Converter
Central Processing Unit
Protection Functions in RET670 Relay
FUNCTION DEVICE NO
Transformer Differential Protection 87T
Restricted Earth Fault Protection 64R
Over Current Protection 50/51
Earth Fault Protection 50N/51N
Thermal Overload Protection 49
Over Excitation Protection 24
Over Voltage Protection 59
Under Voltage Protection 27
Breaker Failure Protection 50BF
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Transformer Differential Protection 87T
The transformer differential protection is a
UNIT protection and also serves as the
MAIN protection of transformers in case of
winding failure.
The protective zone of a differential protection
is clearly demarcated by input CTs to relay.
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Transformer Differential Protection 87T
FEATURES
1. Magnitude Compensation
2. Vector Group Compensation
3. Zero Sequence Current Elimination
4. Inrush Stabilization
5. Over Excitation Stabilization
6. Internal/External Fault Discriminator
7. Restrained Tripping
8. Unrestrained Tripping
9. CT Polarity Inversion
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Transformer Differential Protection 87T
CHARACTERISTICS
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Transformer Differential Protection 87T
CHARACTERISTICS
Values of the matrix A & B coefficients
depend on:
1.Power transformer winding
connection type, such as star or delta
2.Transformer vector group such as
Yd1, Dy11 and so on.
3.Settings for elimination of zero
sequence currents for individual
windings.
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Restricted Earth Fault Protection 64R
Restricted Earth Fault means an earth
fault from a restricted or localized
zone of a circuit.
The term "REF protection method "
means not to sense any earth
faults outside this restricted zone.
Out Zone Fault
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Restricted Earth Fault Protection 64R
REF is very sensitive for internal earth
fault and hence requires a
STABILISING RESISTOR to reduce
its sensitivity.
During fault, the maximum internal
fault current developed can reach high
voltages that can damage the relay
insulation.
Hence, a NON-LINEAR RESISTOR
(Metrosil) is used to limit this voltage
to a safe level.
In Zone Fault
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Over Current/Earth Fault Protection 51/50/51N/50N
Used as a back-up short circuit protection of power transformers.
OC4PTOC/EF4PTOC Function has 4 different, individual settable steps.
Delay time characteristics
Definite time delay
Inverse time delay (IDMT)
PHPIOC/EFPIOC provides instantaneous phase/earth overcurrent protection
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Over Current/Earth Fault Characteristics
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Thermal Overload Protection 49
Thermal Overloads effect
Forced ageing of Insulation,
Degrade quality of transformer oil
This function estimates the
heat content of transformer
using Thermal model, which is
based on current measurement.
Function has two warning levels
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Over-Excitation Protection 24
The power transformers today operate most of the
time near their designated limits.
Overvoltage and/or under frequency will result in an
excessive flux density level leading to eddy currents
flow.
The capability of a transformer to withstand over-
excitation depends on its thermal capacity and is
illustrated in the form of a thermal capability curve.
OEXPVPH function has thermal memory to mimic
thermal content of transformer.
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Over Excitation Protection 24
Characteristics
TAILOR MADE LAW
Over-Excitation capability curve &
V/Hz protection setting
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Over Excitation Protection 24
Characteristics
IEEE Curve
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Under & Over Voltage Protection 27/59
Under voltage protection (UV2PTUV)
is used to detect low power system
Voltage which can occur during faults
or abnormal conditions.
Over voltage protection OV2PTOV is
used to detect high power system
voltage which may occur during
abnormal conditions, such as, sudden
load loss, open line ends on long
lines.
UV2PTUV & OV2PTOV are two step
functions which can be set
independently.
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Breaker Failure Protection 50BF
In the design of the fault clearance
system the N-1 criterion is often
used. This means that a fault needs to
be cleared even if any component in
the fault clearance system is faulty.
Breaker failure protection (CCRBRF)
ensures fast back-up tripping of
surrounding breakers in case of own
breaker failure to open.
CCRBRF can also give a re-trip
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QUESTIONS
CONTACT INFORMATION
AMIT LOHIYA
PROTECTION ENGINEER
IPM / MFCL PANAGARH / ELECTRICAL
Mobile 1: +91 83 72 80 88 39
E-mail: [email protected]
THANK YOU & HAVE A GREAT DAY
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