Power quality theory

June 22, 2024 Luciano Bertene

Power quality is simply the interaction between electricity and electrical devices. We would say that the power supply is OK if the electrical devices are working correctly and reliably and are not damaged or overloaded. On the other hand, if electrical devices malfunction, are unreliable, or are damaged during normal use, we would suspect that the power quality is poor.

Power quality and electrical system problems

In general, any deviation from the conventional power supply (direct or alternating current) is classified as a quality problem. Quality problems are extremely rapid events such as voltage pulses/transients, high frequency noise, waveform errors, voltage swells and sags, and total power failure. Any type of electrical instrument will be affected by quality problems in other ways. We can determine if there is a quality issue by analyzing performance and evaluating the instruments or cargo. Under “Quality Events” you will find many detailed descriptions of quality issues.

Causes and effects of overvoltage

Overvoltage occurs when the voltage in an electrical system exceeds its normal or nominal value. This can have a significant impact on design and connected devices.

Here are some common causes and consequences of overvoltage

Lightning strikes:

Lightning strikes near power lines or public facilities can cause sudden high voltage spikes, resulting in power surges.

Switching operations

Rapid switching of electrical loads, such as turning motors or transformers on and off, can cause voltage spikes and result in overvoltages.

Defective equipment

Malfunctioning devices or components of the electrical system, such as faulty voltage regulators or faulty protection devices, can cause overvoltages.

Reactive power imbalance

Imbalance between system reactive power supply and demand can lead to surges, especially during times of low load.

Network outages

Disturbances in the electrical network, such as short circuits or network malfunctions, can cause voltage fluctuations and result in overvoltages.

Effects of overvoltage

Device Damage Overvoltage can seriously damage sensitive electronic devices and systems. Excessive voltage can lead to component failure, insulation breakdown, or even complete equipment failure.

Reduced useful life

Continuous overvoltages can significantly reduce the life of electrical devices and systems. Increased loads on components and insulation can accelerate wear and lead to premature failure.

Fire risks

Overvoltage can generate excessive heat in electrical systems, increasing the risk of fire. Overheated wires, cables and components can compromise insulation and potentially cause electrical fires.

Data loss and corruption

Power spikes or surges can disrupt electronic devices and data storage systems and result in data loss or corruption. This can have serious consequences for critical applications or data-sensitive environments.

Security risks

Overvoltages can pose safety risks to personnel working with electrical equipment. It can cause electric shocks, electric arcs and other dangerous situations and endanger people's well-being.

Prevention and harm reduction

To prevent and mitigate the risks associated with overvoltage, several protective measures can be taken. This includes installing surge protectors, voltage regulators, and voltage monitoring systems. Proper grounding and regular maintenance of electrical systems are also essential to ensure voltage stability and minimize the occurrence of surges.

Voltage levels in the electrical network structure

An electrical grid consists of a power plant, a transmission network, a subtransmission network, and a distribution network. These subsystems are interconnected through transformers T1, T2 and T3. Let's think a little about the country and observe some typical voltage levels to understand how the electrical grid works. Electrical energy is generated in a thermoelectric plant with a typical voltage of 22 KV. To transmit electricity, it is increased to a level of about 400 KV by power transformer T1. The T2 power transformer converts this voltage to 66 KV to supply power through the subtransmission line to industrial loads that require more power at high voltage. Most major industrial loads have their own transformers to step down the 66KV supply to the desired level. The reason for these voltage changes is to reduce the value of the transmission line for a given power level. Distribution networks are designed for many lower power levels and are fed with mid-level voltages.

Power system voltage structure in electrical system 002-7919014

The power distribution system starts with T3 electrical device transformer to reduce the voltage level from 66 KV to 11 KV. The distribution network includes loads of all types (such as office buildings, large residential complexes, hotels, etc.) or private residences. Typically, business customers receive a voltage of 11 KV. In contrast, residential customers receive 400-440 V electricity. Note that the above value is assumed for line-to-line voltages. Since residential customers receive single-phase power, they generally receive 230-250V power at their points. While low-energy residential customers get single-phase power, industrial and commercial customers get three-phase power, not only because of their high consumption, but also because many of them receive single-phase power. use three-phase motors with them. For example, the use of induction motors is extremely common among industrial customers who operate compressors, pumps, rolling mills, etc.

Conclusion

Power quality theory plays a critical role in understanding and maintaining the reliability of electrical systems. Deviations from traditional power supply, whether in the form of direct or alternating current, can lead to power quality problems with varying effects. These problems include high-speed events such as voltage pulses, transients, high-frequency noise, waveform errors, voltage spikes, voltage sags, and complete power failure. Power quality issues can impact each electrical device or load differently, highlighting the importance of power analysis and instrumentation or equipment evaluation.