4. Application
RET615 provides main protection for two-winding power
transformers and power generator-transformer blocks. The
eight standard configurations offer comprehensive protection
functions for detection and elimination of operational
disturbance conditions and power transformer faults.
The standard configurations A, C, E and G are intended for
power transformers with earthed HV side neutrals. The A and E
configuration features low-impedance REF protection while the
C and G configurations offer high-impedance REF protection.
The B, D, F and H configurations fit transformers with solidly-
earthed LV side neutral or the LV side with a neutral earthing
resistor. The B, D, F and H configurations also fit applications
including a separate earthing transformer located within the
area of protection. The A, B , E, and F configurations also suit
applications, where the turns ratio of the CT of the neutral
earthing circuit differs from the turns ratio of the line CTs. The C,
D, G and H configurations require that the turns ratios of the
CTs are equal.
Standard configurations E, F, G and H include phase-voltage
protection and measurement functions which provide two-
stage power transformer overvoltage and undervoltage
protection and/or supervision.
Two optional RTD/mA modules are available. The optional
RTD/mA module offered for the standard configurations A-D
allows
up to eight analog signals to be measured via the six RTD
inputs and the two mA inputs using transducers. The RTD and
mA inputs can be used for measuring the oil temperature at the
bottom and top of the transformer. Furthermore, the RTD/mA
inputs can be used for measuring the ambient air temperature.
The RTD inputs also offer thermal protection of dry-type power
transformers fitted with Pt-100 temperature sensors.
Temperature measurement over the RTD/mA inputs extends
the function of the three-phase thermal overload protection of
the relay. Further, one of the RTD inputs can also be used as a
direct resistance measuring input for position information of the
on-load tap changer. Alternatively, the tap changer position
indication can be obtained via a mA-transducer.
The optional RTD/mA module offered for the standard
configurations E-H allows up to three analog signals to be
measured via the two RTD inputs and the one mA input using
transducers. The RTD inputs can be used for measuring the oil
temperature and the ambient air temperature. Temperature
measurement over the RTD inputs extends the function of the
three-phase thermal overload protection of the relay. For on-
load tap changer, the tap changer position indication can be
obtained via a mA transducer. If required, the analog
temperature or tap changer position values can be sent to other
devices using analog horizontal GOOSE messaging. Analog
values can also be received from other devices over the station
bus, thus improving the extent of relevant information.
R
L
ClearESC
I
O
U12 0. 0 kV
P 0.00 kW
Q 0.00 kVAr
IL2 0 A
A
RET615
Std. conf.
ANSI IEC
49T
50L/50NL
50P/51P
51P/51N
87NL
87T
3Ith>T
ARC
3I>>>
3I/Io
dIoLo>
3dI>T
A
GUID-6657E450-7FB8-4154-954D-E896064D04A3 V1 EN
Figure 9. Protection of a two-winding power transformer with RET615 standard configuration A
Figure 9 illustrates the protection of a two-winding power
transformer with RET615 standard configuration A. The main
protection used in this application example is transformer
differential protection. Additionally, restricted earth-fault
protection with numerical low-impedance principle is applied
on the transformer's HV side.
Transformer Protection and Control
1MRS756891 M
Product version: 5.0 FP1
ABB 15
To Next Page
Loading...
