Application - ABB REF615 Applications Manual

Section 7
Supervision functions
7.3.3
200
A criterion based on the delta current and the delta voltage measurements can be
added to SEQRFUF to detect the three-phase fuse failures which, in practice, are more
associated with the voltage transformer switching during station operations.

Application

Some protection functions operate on the basis of the measured value of voltage in
the relay point, for example, the distance protection function, undervoltage measuring
function and the voltage check for the weak in-feed logic. These functions may fail
if there is a fault in the measuring circuits between the voltage instrument transformers
and the terminal. A fault in the voltage measuring circuit is referred to as the 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 voltages may result in faulty
operation of some of the protection functions, it is important to detect fuse failures.
The fast fuse failure detection is one of the means to block voltage based functions
before they fail.
GUID-FA649B6A-B51E-47E2-8E37-EBA9CDEB2BF5 V1 EN
Figure 102: Fault on the circuit from the voltage transformer to terminal
A fuse failure occurs due to blown fuses, broken wires or intended substation
operations. The negative sequence 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 not be broken. The supporting delta based
function may also detect the fuse failure due to three-phase interruptions.
In the sequence based part of the function, a fuse failure is detected by comparison
of the calculated value of the negative sequence voltage and negative sequence
current. The sequence entities are calculated from the measured current and the
voltage data for all the 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, SEQRFUF has two outputs for this purpose. Some
voltage-dependent functions should be blocked whenever a fuse failure occurs.
The FUSEF_U output is intended to block these functions
1MRS756378 D
REF615
Application Manual