ABB RER620 Technical Manual page 386

Section 6
Condition monitoring functions
380
Since incorrectly measured voltage can result in a mis-operation of some of the protection
functions, fast failure detection is one of the means to block voltage-based functions before
they operate.
Figure 206: Fault in a circuit from the voltage transformer to the 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 not be broken. 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, 60 has two outputs for this purpose.
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