Netzqualität

The different Power Quality parameters describe the deviation of the voltage from its ideal sinusoidal waveform at a certain frequency. These deviations can lead to disturbances, outages or damages of electrical equipment connected to the grid. The main parameters that power quality focuses on are: harmonics, unbalance in electrical systems, flicker, Voltage changes, Voltage peaks, transient recording and  frequency behaviour.

The Dewesoft Power Quality Analyzer can measure all these parameters according to the IEC 61000-4-30 Class A Standard. In comparison to conventional Power Quality Analyzers it’s possible to do more detailed analyses (e.g. raw data storing, behavior at faults, calculation of additional parameters etc.).

Harmonics are integer multiples of the fundamental frequency (e.g. 50 Hz for the grid in Europe) and cause a distortion in voltage and current of the original sinusoidal waveform. Harmonic voltages and currents caused by non-sinusoidal loads can affect the operation and lifetime of electrical equipment and devices. Harmonic frequencies in motors and generators can increase heating (iron & copper losses), can affect torque (pulsating or reduced torque), can create mechanical oscillations, and higher audible noise, it also causes aging of the shaft, insulation and mechanical parts and reduce the efficiency of the motor.

The term THD stands for the ratio of the effective value of the sum of all harmonic components up to a specified order to the effective value of the fundamental component. In general, it is defined as the sum of all harmonics relative to the fundamental frequency. The Total Harmonic Distortion (THD) for voltage and current can be calculated up to the 3000th order. The most important origins of harmonics are loads that are controlled by converters (diodes, thyristors, transistors).

Total Harmonic Current (THC) is the accumulated currents of the orders 2 to 40 that contribute to the distortion of the current waveform, and the current Total Demand Distortion (TDD) is defined as the ratio of the root-sum-square values of the harmonic current to the maximum demand load current times 100 to get the result in a percentage.

Flicker is a term used to describe fluctuations (repetitive variations) of voltage. Flashing light bulbs are indicators of high flicker exposure. Flicker is especially present in grids with a low short-circuit resistance and is caused by the frequent connection and disconnection (e.g. heat pumps, rolling mills, etc.) of loads that affect the voltage. A high level of flicker is perceived as psychologically irritating and can be harmful to humans.

Rapid Voltage Changes are parameters which are added as a supplement to the flicker standard. Rapid Voltage Changes describe all voltage changes that change the voltage for more than 3% at a certain time interval. These voltage changes can afterward be analyzed with different parameters (depth of voltage change, duration, steady-state deviation, etc.).