ABB RELION REX640 Technical Manual page 487

Protection and control

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1MRS759142 F

output" mode, the function operates normally but the OPERATE output is not

INTRPTEF is an earth-fault function dedicated to operate in intermittent and

permanent earth faults occurring in distribution and sub-transmission networks.

Fault detection is done from the residual current and residual voltage signals by

monitoring the transients with predefined criteria. As the function has a dedicated

purpose for the fault types, fast detection and clearance of the faults can be

Intermittent earth fault

Intermittent earth fault is a special type of fault that is encountered especially in

compensated networks with underground cables. A typical reason for this type of

fault is the deterioration of cable insulation either due to mechanical stress or due

to insulation material aging process where water or moisture gradually penetrates

the cable insulation. This eventually reduces the voltage withstand of the insulation,

leading to a series of cable insulation breakdowns. The fault is initiated as the

phase-to-earth voltage exceeds the reduced insulation level of the fault point and

mostly extinguishes itself as the fault current drops to zero for the first time, as

form of spikes in residual current (Io) and in residual voltage (Uo), can be repeatedly

measured. Typically, the fault resistance in case of an intermittent earth fault is only

Figure 276: Typical intermittent earth-fault characteristics

Earth-fault transients

In general, earth faults generate transients in currents and voltages. There are

several factors that affect the magnitude and frequency of these transients, such

as the fault moment on the voltage wave, fault location, fault resistance and the

parameters of the feeders and the supplying transformers. In the fault initiation,

Technical Manual

. As a result, very short transients, that is, rapid changes in the

Residual current Io and residual voltage Uo

Protection functions

Pulse interval

~0.1 ... 5 kA