Application - ABB RELION REX640 Technical Manual

1MRS759142 C
6.5.6
REX640
Technical Manual
It is recommended to always set Enable seal in to "True". This secures
that the blocked protection functions remain blocked until normal
voltage conditions are restored if the fuse failure has been active for 5
seconds, that is, the fuse failure outputs are deactivated when the
normal voltage conditions are restored.
The activation of the BLOCK input deactivates both FUSEF_U and FUSEF_3PH
outputs.

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 operate.
Three phase network
VT
GUID-A19DA741-17BE-4B90-B8F2-B067B6BC5B6C V1 EN
Figure 670: 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
Fault in a measuring
circuit between
voltage transformer
and protection relay
e.g. blown fuse
Section 6
Supervision functions
1231