Application - ABB Relion SMU615 Technical Manual

Section 5
Supervision functions
5.3.5
146

Application

Some protection functions operate on the basis of the measured voltage value in the
merging unit 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 merging unit.
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
GUID-07CE285A-F302-4764-B51E-51CAA6819C79 V2 EN
Figure 101: Fault in a circuit from the voltage transformer to the merging unit
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.
Fault in a measuring
circuit between
voltage transformer
merging unit
and
e.g. blown fuse
1MRS758407 B
SMU615
Technical Manual