ABB RELION REX640 Technical Manual page 1336

Protection and control

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Supervision functions

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

Figure 759: 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

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.

SEQSPVC Input signals

Table 1276: SEQSPVC Input signals

Table continues on the next page

Three phase network

Fault in a measuring

circuit between

voltage transformer

and protection relay

e.g. blown fuse

Three-phase currents

Three-phase voltages

Block of function

1MRS759142 F

Technical Manual