Calibration of power quality instruments

Purpose

Power quality is a summary concept for assessing the quality of delivered electricity. Voltage level, distortion and transients are some of the parameters that determine the quality. The instruments used to measure power quality are therefore multi-function instruments which are usually called power quality instruments.

Non-sinusoidal signals

Power quality deficiencies are often due to loads on the network, but can also be due to natural phenomena such as lightning strikes or incorrect connection actions by grid owners. The proportion of "bad" and "sensitive" loads has increased over the years, while the deregulation of the electricity market has meant that more parties are involved in the supply of electricity today, compared to before. Today, it is no longer possible to assume that all the voltages and currents of the electric power grid are almost sinusoidal. An increasing proportion of the motor loads are inverter controlled and the offices are filled with computers, IT equipment and so on. Virtually all lighting in offices and business premises and industries consist of fluorescent tubes or LED lamps. These loads do not draw sinusoidal current and therefore produce large harmonic currents which in turn give rise to harmonic voltages. Although conditions are far from ideal, measuring instruments are often calibrated for ideal sinusoidal voltages and currents. This is partly due to tradition, partly since it is significantly more difficult to measure with non-sinusoidal signals.

The need for measuring instruments that measure correctly even under these conditions has increased greatly, both ordinary instruments and power quality instruments. In many measuring contexts, for example in quality assurance, contracts or disputes, it is necessary to have calibrated measuring instruments. Reference instruments are needed that cannot only verify instruments under ideal conditions. At RISE, we can therefore offer calibration for voltage, current and power for non-sinusoidal signals.

By calibrating your instruments and measurement systems with us, you get high quality measurements and minimize losses due to measurement errors. Regular calibration will give you information about how stable the instrument measures.

Method

The basic function of a power quality instrument is to measure voltage, current, power and power factor. These functions are calibrated in the same way as a standard wattmeter. An extension of the basic function is to measure and save temporary peaks and dips in the voltage. The most common extra function of a power quality instrument is harmonic measurement, either to measure the level of individual harmonics or to measure the overall distortion level. Another common feature of these instruments is transient and flicker measurements.

With digital sampling technology as a basis, we have constructed a reference instrument, a digital sampling wattmeter, which, in addition to calibrating the above-mentioned quantities, can also be used for calibrating reactive and apparent power, power factor and total harmonic distortion.

Our reference instrument has, partly through our own verifications, partly through international comparison measurements, been found to have a measurement uncertainty that is within ±150 ppm in most situations. Through extensive research and development work, we can now offer calibration of even the most accurate instruments on the market.

Deliveries

We issue calibration certificates in Swedish or English. On our customer website for calibration, you can directly download the calibration certificate and get all the other information you need about the measuring devices.