6.3.5
Application
Some protection functions operate on the basis of the measured voltage value in the
protection relay point. These functions can fail if there is a fault in the measuring circuits
between the voltage transformer (or combi sensor or voltage sensor) and protection relay.
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 trip.
Three phase network
VT
Fault in a measuring circuit
between voltage transformer and
protection relay e.g. blown fuse
GUID-A7539C67-4EB8-4656-92EE-561BE0B4BB1C V1 EN
Figure 198:
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
1MRS240050-IB C
Section 6
Supervision functions
REF615R
375
Technical Manual
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