ABB REG670 - Transformer Differential Protection T2 WPDIF and T3 WPDIF

Section 7 Differential protection
7.1 Transformer differential protection T2WPDIF and
T3WPDIF
7.1.1 Identification
Function description IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Transformer differential protection, two-
winding
T2WPDIF
3Id/I
SYMBOL-BB V1 EN
87T
Transformer differential protection,
three-winding
T3WPDIF
3Id/I
SYMBOL-BB V1 EN
87T
7.1.2 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.
1MRK 502 071-UEN - Section 7
Differential protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 127
Application manual