A fault in the voltage-measuring circuit is called a fuse failure. This term is
misleading since a blown fuse is just one of the many possible reasons for a broken
circuit. Since incorrectly measured voltage can result in a faulty operation of some
of the protection functions, it is important to detect the fuse failures. A fast fuse
failure detection is one of the means to block voltage-based functions before they
operate.
Three phase network
VT
Fault in a measuring
circuit between
voltage transformer
and protection relay
e.g. blown fuse
REF 615
Figure 759: Fault in a circuit from the voltage transformer to the protection relay
A fuse failure occurs due to blown fuses, broken wires or intended substation
operations. The negative sequence component-based function can be used to
detect different types of single-phase or two-phase fuse failures. However, at
least one of the three circuits from the voltage transformers must be intact. The
supporting delta-based function can also detect a fuse failure due to three-phase
interruptions.
In the negative sequence component-based part of the function, a fuse failure is
detected by comparing the calculated value of the negative sequence component
voltage to the negative sequence component current. The sequence entities are
calculated from the measured current and voltage data for all three phases. The
purpose of this function is to block voltage-dependent functions when a fuse
failure is detected. Since the voltage dependence differs between these functions,
SEQSPVC has two outputs for this purpose.
6.5.7 Signals
6.5.7.1 SEQSPVC Input signals
Table 1276: SEQSPVC Input signals
Name
Type Default Description
I3P SIGNAL - Three-phase currents
U3P SIGNAL - Three-phase voltages
BLOCK BOOLEAN 0=False Block of function
Table continues on the next page
Supervision functions 1MRS759142 F
1336 REX640
Technical Manual
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