Measurements

Power quality measurements are often part of a package of measures to improve the power quality of the installation. To obtain a reliable basis for further analysis, system studies and design, the measurements described below must be carried out correctly. This places high demands on measurement engineers in terms of knowledge:

instrument knowledge
power system design and operation
measurement methods and techniques
theoretical knowledge of circuit and harmonic analysis

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Power and harmonic measurements

Power and harmonic measurements are usually performed as a first step in the design of harmonic filters. Harmonic measurements are carried out in connection with harmonic-related problems such as e.g.

overloading of transformers, cables, motors, etc.
condenser failures
unjustified protection triggers
malfunction of computer equipment, control and monitoring circuits

There are no clear guidelines for the measurement procedure. It is important to keep in mind that solving harmonic problems requires combining measurements with analysis and system calculations. Measurements are used to map harmonic generation.

It is usual to start measuring at the level where problems occur or where filters are to be installed. However, it is important to be aware that harmonics generated by rectifiers can be amplified due to the resonance between inductive and capacitive components in the network. In cases where shunt capacitors or filters are present, these should be taken into account when assessing harmonic generation in the network. In networks with single-phase loads, the current in the neutral conductor must be measured in addition to the phase currents.

Transients, voltage dips, high frequency disturbances

Measurements are carried out in connection with device failures e.g. insulation faults in transformers, capacitors, cables, motors, flashover in electronic circuits or in case of protective trips of e.g. frequency converters and converters.

The measurement procedure depends on the type of transients to be recorded. Measurements of switching transients arising from the connection of transformers, capacitors, large motors, etc. can usually be carried out efficiently in cooperation with operators by making a number of connections and recording the results.

It must be remembered that transients are not repetitive because their amplitude depends on the instantaneous value of the voltage or current at the moment of switching. A large number of measurements must therefore be carried out to increase the probability of capturing the worst case scenario.

HARMONIZER Power Quality Consulting AB has many years of experience in power quality measurements. We use modern measuring instruments and well-proven measuring methods that comply with current standards.

Here are some examples of measurements taken.

Harmonic measurement, comparison between actual harmonicdistortion (red) and the standard requirements (green). The measurement shows the presence of harmonics with frequencies > 550 Hz exceeding the standard requirements and requiring filtering.