ABB Relion® Protection and Control REX640 Power quality

Power quality

In the EN standards, power quality is defined through the

characteristics of the supply voltage. Transients, short-duration

and long-duration voltage variations and unbalance and

waveform distortions are the key characteristics describing

power quality. The distortion monitoring functions are used for

monitoring the current total demand distortion and the voltage

total harmonic distortion.

Power quality monitoring is an essential service that utilities can

provide for their industrial and key customers. A monitoring

system can provide information about system disturbances and

their possible causes. It can also detect problem conditions

throughout the system before they cause customer complaints,

equipment malfunctions and even equipment damage or

failure. Power quality problems are not limited to the utility side

of the system. In fact, the majority of power quality problems

are localized within customer facilities. Thus, power quality

monitoring is not only an effective customer service strategy but

also a way to protect a utility's reputation for quality power and

service.

The protection relay has the following power quality monitoring

functions.

• Voltage variation

• Voltage unbalance

• Current harmonics

• Voltage harmonics

The voltage unbalance and voltage variation functions are used

for measuring short-duration voltage variations and monitoring

voltage unbalance conditions in power transmission and

distribution networks.

The voltage and current harmonics functions provide a method

for monitoring the power quality by means of the current

waveform distortion and voltage waveform distortion. The

functions provide selectable short-term 3- or 60- or 300

second sliding average and a long-term demand for total

demand distortion (TDD) and total harmonic distortion (THD).

The phase-specific harmonic content is measured for voltages

and currents, as well as DC component and fundamental

content. The dedicated harmonics measurement page in the

LHMI presents the measurements in a user-friendly manner.

Fault locator

The relay features an optional impedance-measuring fault

location function suitable for locating short circuits in radial

distribution systems. Earth faults can be located in effectively

and low-resistance earthed networks, as well as in

compensated networks. When the fault current magnitude is at

least of the same order of magnitude or higher than the load

current, earth faults can also be located in isolated neutral

distribution networks. The fault location function identifies the

type of the fault and then calculates the distance to the fault

point. The calculations provide information on the fault

resistance value and accuracy of the estimated distance to the

fault point.

Disturbance recorder

The relay is provided with a disturbance recorder featuring up to

24 analog and 64 binary signal channels. The analog channels

can be set to record either the waveform or the trend of the

currents and voltages measured.

The analog channels can be set to trigger the recording function

when the measured value falls below or exceeds the set values.

The binary signal channels can be set to start a recording either

on the rising or the falling edge of the binary signal or on both.

The binary channels can be set to record external or internal

relay signals, for example, the start or trip signals of the relay

stages, or external blocking or control signals. The recorded

information is stored in a nonvolatile memory in COMTRADE

format and can be uploaded for subsequent fault analysis.