Differential Protection; Transformer Differential Protection T2Wpdif And T3Wpdif; Identification; Application - ABB RELION 670 Series Applications Manual

1MRK 504 152-UEN B
Section 6
6.1 Transformer differential protection T2WPDIF and
T3WPDIF
6.1.1

Identification

Function description
Transformer differential protection,
two-winding
Transformer differential protection,
three-winding
6.1.2

Application

The transformer differential protection is a unit protection. It serves as the main protection of
transformers in case of winding failure. The protective zone of a differential protection
includes the transformer itself, the bus-work or cables between the current transformers and
the power transformer. When bushing current transformers are used for the differential IED,
the protective zone does not include the bus-work or cables between the circuit breaker and
the power transformer.
In some substations there is a current differential protection relay for the busbar. Such a
busbar protection will include the bus-work or cables between the circuit breaker and the
power transformer. Internal electrical faults are very serious and will cause immediate damage.
Short circuits and earth faults in windings and terminals will normally be detected by the
differential protection. Interturn faults are flashovers between conductors within the same
physical winding. It is possible to detect interturn faults if sufficient number of turns are
short-circuited. Interturn faults are the most difficult transformer winding fault to detect with
electrical protections. A small interturn fault including just a few turns will result in an
undetectable amount of current until it develops into an earth or phase fault. For this reason it
is important that the differential protection has a high level of sensitivity and that it is
possible to use a sensitive setting without causing unwanted operations during external
faults.
It is important that the faulty transformer be disconnected as fast as possible. As the
differential protection is a unit protection it can be designed for fast tripping, thus providing
selective disconnection of the faulty transformer. The differential protection should never
operate on faults outside the protective zone.
A transformer differential protection compares the current flowing into the transformer with
the current leaving the transformer. A correct analysis of fault conditions by the differential
protection must take into consideration changes due to the voltage, current and phase angle
Application manual

Differential protection

IEC 61850
identification
T2WPDIF
T3WPDIF
IEC 60617 ANSI/IEEE C37.2
identification device number
87T
3Id/I
SYMBOL-BB V1 EN-US
87T
3Id/I
SYMBOL-BB V1 EN-US
Section 6
Differential protection
IP14639-1 v3
M15074-1 v5
M16722-3 v9
99