What Is Power Quality? Why Do Harmonics, Power Factor and Phase Imbalance Matter?
Power quality refers to how suitable the characteristics of electrical energy, such as voltage, frequency and waveform, are for the reliable and efficient operation of electrical equipment.
In industrial plants and commercial buildings, the performance of electrical systems does not depend solely on the amount of energy consumed. Conditions such as voltage fluctuations, harmonic distortion, low power factor and phase imbalance can affect the operating conditions of equipment, energy losses and continuity of operations.
For this reason, when assessing electrical systems it is important to examine power quality and load characteristics in addition to energy consumption.
What Are Harmonics and Why Do They Occur?
In an ideal alternating current system, the voltage and current waveforms are sinusoidal. Harmonics are frequency components that occur at integer multiples of the fundamental frequency and cause the waveform to become distorted.
Frequency converters, rectifiers, uninterruptible power supplies (UPS), LED drivers and other power electronics equipment are among the principal sources of harmonic currents.
Depending on the characteristics of the system, high harmonic levels can lead to additional losses in transformers and cables, overheating of equipment, stress on power factor correction systems and malfunctions in certain devices.
Total harmonic distortion (THD) is used to assess harmonic distortion. THD values, calculated separately for voltage and current, should be evaluated with regard to the operating conditions of the system concerned and the applicable technical limits.
What Is Power Factor?
Power factor is the ratio of active power to apparent power, and is one of the key indicators used to assess how electrical energy is being used.
Inductive loads, motors and transformers in particular, create a demand for reactive power. If reactive power demand is not managed properly, the current carried in the system and electrical losses can increase. It may also give rise to reactive energy charges under the conditions set out in the legislation.
For this reason, businesses manage their reactive power balance by using power factor correction systems.
Power factor is not, however, affected by reactive power alone. Harmonic distortion can also reduce the total power factor. Seeking a solution simply by adding capacitors, without first establishing the causes of a low power factor, is therefore not always the right approach.
What Is Phase Imbalance?
In three-phase electrical systems, an unequal distribution of loads across the phases can create an imbalance in the phase currents. Depending on grid conditions and system impedances, voltage imbalance can also occur.
Phase imbalance can cause additional losses in cables and transformers, overloading of the neutral conductor in some systems and, in three-phase motors in particular, temperature rise and performance problems.
It is therefore important to examine phase currents and voltages together, assess the load distribution and make appropriate improvements where necessary.
How Is Power Quality Measured and Assessed?
Power quality and electrical load characteristics are assessed using energy analyzers and power quality measuring instruments.
The measurements examine parameters such as voltage, current, active and reactive power, power factor, harmonics and phase balance. Where required, voltage fluctuations, voltage sags and other power quality events can also be recorded.
It is not always sufficient for measurements to be based only on values at a given moment. Particularly in facilities operating with variable loads, measurement records that cover different operating conditions are important for assessing problems accurately.
The data obtained establishes the current condition of the electrical systems, so that improvements to power factor correction systems, harmonic filtering, load balancing or other technical measures for the electrical infrastructure can be evaluated.