ABB RELION 670 Series Product Manual page 26

Transformer protection RET670 2.1 IEC
two-winding power
transformer with
two circuit breakers
and two CT-sets on
both sides
xx05000051.vsd
IEC05000051 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 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 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
26
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.
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-US
Figure 8. Examples of applications of the REFPDIF
1MRK 504 155-BEN F
M13071-3 v13
M13047-3 v18
CT CT
CB CB
Autotransformer
CB CT
CB
CT
The most complicated
application - autotransformer
IEC05000058-2-en.vsd
ABB