Application - ABB RELION REX640 Technical Manual

Section 4
Protection functions
4.3.2.6
606
however, reset the counters holding the blockings, so the blocking signals may return
when these conditions are not valid anymore.
External blocking functionality
TR2PTDF has three inputs for blocking.
• When the BLOCK input is active ("TRUE"), the operation of the function is
blocked but measurement output signals are still updated.
• When the BLK_OPR_LS input is active ("TRUE"), TR2PTDF operates normally
except that the OPR_LS output is not active or activated in any circumstance.
Additionally, the OPERATE output can be activated only by the instantaneous
high stage (if not blocked as well).
• When the BLK_OPR_HS input is active ("TRUE"), TR2PTDF operates normally
except that the OPR_HS output is not active or activated in any circumstance.
Additionally, the OPERATE output can be activated only by the biased low stage
(if not blocked as well).

Application

TR2PTDF is a unit protection function serving as the main protection for transformers
in case of winding failure. The protective zone of a differential protection includes the
transformer, the bus-work or the cables between the current transformer and the power
transformer. When bushing current transformers are used for the differential
protection relay, 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 for the busbar. The
busbar protection includes bus work or cables between the circuit breaker and the
power transformer. Internal electrical faults are very serious and cause immediate
damage. Short circuits and earth faults in windings and terminals are normally
detected by the differential protection. If enough turns are short-circuited, the
interturn faults, which are flashovers between the conductors within the same physical
winding, are also detected. The interturn faults are the most difficult transformer-
winding faults to detect with electrical protections. A small interturn fault including a
few turns results in an undetectable amount of current until the fault develops into an
earth fault. Therefore, 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 for external faults.
It is important that the faulty transformer is disconnected as fast as possible. As
TR2PTDF is a unit protection function, it can be designed for fast tripping, thus
providing a selective disconnection of the faulty transformer. TR2PTDF should never
operate to faults outside the protective zone.
TR2PTDF compares the current flowing into the transformer to the current leaving the
transformer. A correct analysis of fault conditions by TR2PTDF must consider the
changes to voltages, currents and phase angles. The traditional transformer
differential protection functions required auxiliary transformers for the correction of
1MRS759142 C
REX640
Technical Manual