ABB RELION REX640 Technical Manual page 918

Protection and control

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Protection functions

function is blocked and the timers are reset. In the "Block OPERATE output" mode,

the function operates normally but the OPERATE output is not activated.

Overvoltage in a network occurs either due to the transient surges on the network

or due to power frequency overvoltages. Surge arresters are used to protect

the network against the transient overvoltages; power frequency overvoltage

of magnitude greater than 15...20% of nominal voltage is normally handled by

traditional overvoltage protection. However, slow voltage variations are usually

quantified by calculating the RMS value of the voltage. To assess the RMS voltage,

measurements are taken over a relatively long period of time to avoid any

instantaneous effect caused by switching transients or faults.

It is important to monitor such slow voltage variation which can cause sub-optimal

operation of the equipment. EN 50160 quantifies slow voltage variation using 10

min mean RMS value. CEI EN 50160 standard indicates that the RMS value of the

voltage calculated over a period of 10 min should not exceed 110% of the nominal

voltage; if the voltage exceeds this level, the generator must be disconnected from

the network within 3 s. PHVPTOV provides overvoltage protection by calculating the

RMS value over a period of 10 min.

A sudden change in the magnitude of the supply voltage is not immediately

detected by the RMS calculation; hence this is mainly used as an indication of

voltage quality supplied by the utility.

PHVPTOV Input signals

Table 872: PHVPTOV Input signals

PHVPTOV Output signals

Table 873: PHVPTOV Output signals

1MRS759142 F

Three-phase voltages

Block signal for acti-

vating the blocking

Initialize the volt-

age average measure-

Reset the volt-

age average measure-

Technical Manual