4. Differential protection
Transformer differential protection T2WPDIF/T3WPDIF
The Transformer differential protection, two-winding T2WPDIF
and Transformer differential protection, three-winding
T3WPDIF are provided with internal CT ratio matching and
vector group compensation and settable zero sequence
current elimination.
The function can be provided with two or three three-phase
sets of current inputs. All current inputs are provided with
percentage bias restraint features, making the IED suitable for
two- or three-winding transformer arrangements.
Two-winding applications
xx05000048.vsd
IEC05000048 V1 EN
two-winding power
transformer
Three-winding applications
xx05000052.vsd
IEC05000052 V1 EN
three-winding power
transformer with all
three windings
connected
xx05000049.vsd
IEC05000049 V1 EN
three-winding power
transformer with
unconnected delta
tertiary winding
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-faults.
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 a high internal fault currents.
Included is an innovative sensitive differential protection
element based on the theory of symmetrical components. This
element offers the best possible coverage of power transformer
windings turn to turn faults.
Restricted earth fault protection REFPDIF
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 low-impedance 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.
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. Each
utilizes an external summation of the currents in the
interconnected CTs, a series resistor, and a voltage dependent
resistor which are mounted externally connected to the IED.
The external resistor unit shall be ordered under accessories.
HZPDIF can be used as high impedance REF protection.
5. Impedance protection
Power swing detection ZMRPSB
Power swings may occur after disconnection of heavy loads or
trip of big generation plants.
Power swing detection function ZMRPSB is used to detect
power swings and initiate block of all distance protection zones.
Occurrence of earth-fault currents during a power swing
inhibits the ZMRPSB function to allow fault clearance.
Underimpedance protection for generators and transformers
ZGCPDIS
The underimpedance protection for generators and
transformers ZGCPDIS, has the offset mho characteristic as a
three zone back-up protection for detection of phase-to-phase
short circuits in transformers and generators. The full scheme
three zones have independent measuring phase-to-phase
loops and settings that gives high flexibility for all types of
applications.
All three zones can be individually definite time delayed.
A load encroachment characteristic is available for the third
zone as shown in figure
Transformer protection RET650
1MRK 504 137-BEN B
Product version: 1.3
14
ABB
