Application - ABB RELION SMU615 Technical Manual

1MRS758407 C
The activation of the BLOCK input deactivates both FUSEF_U and FUSEF_3PH
outputs.
5.3.5

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.
Figure 103: 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.
SMU615
Technical Manual
Three phase network
VT
Fault in a measuring
circuit between
voltage transformer
merging unit
and
e.g. blown fuse
Supervision functions
157