1Ph High Impedance Differential Protection Hzpdif; Restricted Earth-Fault Protection, Low Impedance Refpdif; Additional Security Logic For Differential Protection Ldrgfc - ABB RET670 Product Manual

Transformer protection RET670 2.0
Product version: 2.0
three-winding power
transformer with all
three windings
connected
xx05000052.vsd
IEC05000052 V1 EN
three-winding power
transformer with two
circuit breakers and
two CT-sets on one
side
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IEC05000053 V1 EN
Autotransformer with
two circuit breakers
and two CT-sets on
two out of three sides
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IEC05000057 V1 EN
Figure 7. CT group arrangement for
differential protection
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.By introducing the load tap changer position, the
differential protection pick-up can be set to optimum sensitivity
thus covering internal faults with low fault current level.
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 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.

1Ph High impedance differential protection HZPDIF

The 1Ph High impedance differential protection 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
24
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. Several function block instances (for example, six)
can be available in a single IED.

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.
REFPDIF can also protect autotransformers. Five currents are
measured at the most complicated configuration as shown in
Figure 8.
YNdx
CT
d
Y
CB CB
CT
IED
The most typical
application
IEC05000058-2 V1 EN
Figure 8. Examples of applications of the REFPDIF

Additional security logic for differential protection LDRGFC

Additional security logic for differential protection (LDRGFC)
can help the security of the protection especially when the
communication system is in abnormal status or for example
when there is unspecified asymmetry in the communication link.
It helps to reduce the probability for mal-operation of the
protection. LDRGFC is more sensitive than the main protection
logic to always release operation for all faults detected by the
differential function. LDRGFC consists of four sub functions:
1MRK 504 141-BEN C
CT CT
CB CB
Autotransformer
CB CT
CB
CT
The most complicated
application - autotransformer
IEC05000058-2-en.vsd
ABB