Current Protection - ABB Relion 650 Series Product Manual

Transformer protection RET650
Version 2.2
three-winding power
transformer with all
three windings
connected
xx05000052.vsd
IEC05000052 V1 EN-US
three-winding power
transformer with two
circuit breakers and
two CT-sets on one
side
xx05000053.vsd
IEC05000053 V1 EN-US
Autotransformer with
two circuit breakers
and two CT-sets on
two out of three sides
xx05000057.vsd
IEC05000057 V1 EN-US
Figure 3. CT group arrangement for
differential protection
Two-winding applications
two-winding power
transformer
xx05000048.vsd
IEC05000048 V1 EN-US
Three-winding applications
three-winding power
transformer with all
three windings
connected
xx05000052.vsd
IEC05000052 V1 EN-US
three-winding power
transformer with
unconnected delta
xx05000049.vsd
tertiary winding
IEC05000049 V1 EN-US
Figure 4. CT group arrangement for
differential protection and other
protections
The setting facilities cover the application of the differential
protection to all types of power transformers and auto-
transformers with or without load tap changer as well as
shunt reactors and local feeders within the station. An
adaptive stabilizing feature is included for heavy through-
fault currents.
Stabilization is included for inrush and overexcitation
currents respectively, cross-blocking is also available.
Adaptive stabilization is also included for system recovery
inrush and CT saturation during external faults. A high set
20
unrestrained differential current protection element is
included for a very high speed tripping at high internal fault
currents.
Included is an sensitive differential protection element
based on the theory of negative sequence current
component. This element offers the best possible coverage
of power transformer windings turn to turn faults.
High impedance differential protection, single phase
HZPDIF
High impedance differential protection, single phase
(HZPDIF) functions can be used when the involved CT
cores have the same turns ratio and similar magnetizing
characteristics. It utilizes an external CT secondary current
summation by wiring. Actually all CT secondary circuits
which are involved in the differential scheme are connected
in parallel. External series resistor, and a voltage dependent
resistor which are both mounted externally to the IED, are
also required.
The external resistor unit shall be ordered under IED
accessories in the Product Guide.
HZPDIF can be used to protect tee-feeders or busbars,
reactors, motors, auto-transformers, capacitor banks and so
on. One such function block is used for a high-impedance
restricted earth fault protection. Three such function blocks
are used to form three-phase, phase-segregated differential
protection.
HZPDIF can be used as high impedance REF protection.
Restricted earth-fault protection, low impedance
REFPDIF
Restricted earth-fault protection, low-impedance function
(REFPDIF) can be used on all directly or low-impedance
earthed windings. The REFPDIF function provides high
sensitivity and high speed tripping as it protects each
winding separately and thus does not need inrush
stabilization.
The REFPDIF function is a percentage biased function with
an additional zero sequence current directional comparison
criterion. This gives excellent sensitivity and stability during
through faults. The function allows the use of different CT
ratios and magnetizing characteristics on the phase and
neutral CT cores. Unlike high impedance restricted earth
fault it allows for mixing with other functions and protection
IEDs on the same CT cores.

5. Current protection

Instantaneous phase overcurrent protection, 3-phase
output PHPIOC
The instantaneous three phase overcurrent (PHPIOC)
function has a low transient overreach and short tripping
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