AC Power Quality Issues

18th  February, 2025.

In this post, we will see the issues faced in AC power quality.

Whenever we consider electrical power, we think that the power we receive is free from any disturbances. Practically, it is not. Whether we deal with power distribution from major substations or work in a control panel of an industrial plant or even a small power outlet in our homes, power quality issues are faced many times in AC supply. If we are not familiar with these issues, then we will not be able to address them. And in today’s times of industrial automation where many devices are low in power and sensitive to voltage fluctuations, these issues matter a lot. A small tolerance is acceptable, but a large deviation in the AC voltage flowing in the circuit can hamper the overall performance. In this post, we will see the various AC power quality issues faced in the real time world.

1. Voltage transients:

A voltage transient is defined as a condition where the voltage will spike for a very few moment (in milliseconds) and then become normal. It will just appear and go away, as if nothing happened. They can be best described as bursts, where it will come as a spike for a minute and go away. This sudden spike is very dangerous for electrical equipment, because it will be very high in voltage, as seen in the image below, and damage the components. Transients can occur due to many reasons like capacitor switching, electrostatic discharge, arcing, operation of power semiconductor devices, lighting, sudden opening or closing of switchgear, loose connections, or bad weather. The image shown is impulsive transient, meaning spike happening in only one direction (positive or negative phase cycle). If the spike occurs in both the cycles, then it is an oscillatory transient.

2. Long duration voltage variation:

This condition is relatively easier to understand. If your voltage in the system, be it high (overvoltage) or low (under voltage), is abnormal for more than 1 or 2 minutes, then it is a long duration voltage variation. If it is for a longer time, then it means that either some equipment has failed, or there is some human error, or there is a natural condition like lighting or storm existing for a long duration, or some failure of protection devices. Due to this, the power in the circuit will completely shut down, as such long duration variations cannot be withstood by any equipment. Refer to the below image for more understanding, where the voltage variation exists for a longer duration.

3. Voltage sags:

A voltage sag is a condition where the voltage drops below the desired level (typically below 90% of rated value) and hampers the performance of electrical equipment. It is also simplified as a voltage dip. A low voltage can occur mostly for shorter durations, and will happen due to conditions like equipment startup, short circuit faults, badly regulated transformers, and connection of heavy loads in place of rated loads. Voltage sags are not suitable for electrical equipment, as they do not provide the rated operating voltage, and can damage them over a period of time. Refer to the below image for more understanding, where the voltage dips exist for a short duration. The major difference between voltage sag and under voltage is that sag exists for a few cycles or minutes, but under voltage exists for a sustained duration and long time.

4. Harmonics:

Harmonics are a major concern of power quality. Voltage is transferred to us at a certain frequency, for example 50 hertz. This standard frequency is called 1st harmonic. When the frequency is multiplied by nth integer value, it is called as nth harmonic. So, a factor of 2 for 50 hertz means a frequency of 100 hertz and so on. Such high frequencies occur for a short duration of time and damage the electrical equipment. Harmonics are caused by non-linear loads (like rectifiers, inverters, drives, SMPS or motor starters), or the ones which do not consume sinusoidal waves of current as input. So, harmonics are mostly caused by load devices, and not during the power distribution stage. They consume current sometimes in the form of non-sine wave form, as these devices mostly convert AC to DC or vice-versa. Converting supply requires the use of high speed semiconductor devices and they have a high switching speed, which tries to create distortion in the original waveform. Harmonics can cause overheating of cables, create EMI noise and disturb the actual outputs, cause errors in reading values, heating of devices and similar types of disruption.

5. Voltage imbalance:

As the term defines, a voltage imbalance is a situation where the phase angles between three phases are different or unbalanced, resulting in a different reading of three phase voltage. A three phase voltage comprises three voltage waveforms separated by the same amount of phase angles. Then only, we will get 440V AC at the output. But, when these phase angles are different or not balanced with each other, the voltage generated too will be different. Voltage imbalance occurs through faulty transformers, faulty wiring supplying different current to different phases, or uneven distribution of single phase loads over three phase power systems (means loads are not equally divided over each phase). Due to this, the electrical equipment will get damaged to overload on one phase, causing overheating and hindering the performance of the system.

Some other issues faced with power quality are electromagnetic noise interference (unwanted high frequency signal from nearby equipment) and resonance (natural frequency of system matching with frequency of disturbances).

I have covered some general causes of AC power quality. I have also not attempted to cover all the topics, as it can vary from case to case. Once you are familiar with this guide, you can easily tackle all types of problems in it.

Thank you for reading the post. I hope you liked it and will find a new way in this type of technology.