ABB RET670 Product Manual page 13

ABB
Transformer protection RET670
Pre-configured
Product version: 1.1
two-winding
power
transformer with
two circuit
breakers and two
CT-sets on both
xx05000051.vsd sides
IEC05000051 V1 EN
Three-winding applications
three-winding
power
transformer with
all three
windings
connected
xx05000052.vsd
IEC05000052 V1 EN
three-winding
power
transformer with
two circuit
breakers and two
xx05000053.vsd
CT-sets on one
side
IEC05000053 V1 EN
Autotransformer
with two circuit
breakers and two
CT-sets on two
out of three sides
xx05000057.vsd
IEC05000057 V1 EN
Figure 5. CT group arrangement for
differential protection and
other protections
The setting facilities cover for applications of
the differential protection to all types of
power transformers and autotransformers
with or without load tap changer as well as
for shunt reactors or and local feeders within
the station. An adaptive stabilizing feature is
included for heavy through-faults. 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 level.
1MRK 504 091-BEN B
Stabilization is included for inrush currents
respectively for overexcitation condition.
Adaptive stabilization is also included for
system recovery inrush and CT saturation for
external faults. A fast high set unrestrained
differential current protection is included for
very high speed tripping at high internal fault
currents.
Innovative sensitive differential protection
feature, based on the theory of symmetrical
components, offers best possible coverage for
power transformer windings turn-to-turn
faults.
1Ph High impedance differential
protection HZPDIF
The 1Ph High impedance differential
protection HZPDIF function can be used
when the involved CT cores have the same
turn ratio and similar magnetizing
characteristic. It utilizes an external
summation of the phases and neutral current
and a series resistor and a voltage dependent
resistor externally to the IED.
Restricted earth fault protection (PDIF,
87N)
Restricted earth-fault protection, low
impedance function (REFPDIF) can be used
on all directly or low impedance earthed
windings. REFPDIF function can provide
higher sensitivity (down to 5%) and higher
speed as it measures individually on each
winding and thus do not need inrush
stabilization.
The low impedance function is a percentage
biased function with an additional zero
sequence current directional comparison
criteria. This gives excellent sensitivity and
stability for through faults. The function
allows use of different CT ratios and
magnetizing characteristics on the phase and
neutral CT cores and mixing with other
functions and protection IEDs on the same
cores.
Issued: June 2010
13