Electric power quality (PQ), or voltage quality, involves voltage, frequency, and waveform.
Referring to IEC & IEEE standards, power quality (PQ) is an electromagnetic compatibility (EMC) requirement i.e. the compatibility between what comes out of an electric source (substation etc.) and the load that is connected into it.
Electromagnetic compatibility (EMC) is the branch of electrical engineering concerned with the unintentional generation, propagation and reception of electromagnetic energy which may cause unwanted effects such as electromagnetic interference (EMI) or even physical damage in operational equipment. The goal of EMC is the correct operation of different equipment in a common electromagnetic environment.
For any query on EMC, please contact TNB.
TNB has a representative in both the IEC & Malaysia’s SIRIM Technical Committee on EMC/Power Quality.
IEEE is an international society of electrical and electronic engineers. The recommendations of the IEEE come from industry experts who manage and design facilities. The IEEE 1100-1999 & IEEE 1159 are the best sources for defining PQ problems, and also to offer solutions to issues regarding equipment and systems.
IEEE Std. 1100-1999, IEEE Recommended Practice for Powering and Grounding
IEEE Std. 1159-2009, IEEE Recommended Practice for Monitoring Electrical Power Quality.
“PQ is related to the powering and grounding of electronic equipment in a way that’s suitable for the operations of an equipment, and compatible with the property’s wiring system and other connected equipment.”
The International Electronic Commission (IEC), is the world’s leading organisation for the preparation and publication of International Standards for “electrotechnology” (electrical, electronic and related technologies). IEC provides a platform to companies, industries and governments to meet, discuss and develop the International Standards required.
IEC Std. 61000-2-1, Electromagnetic compatibility (EMC) – Part 2: Environment – Section 1: Description of the environment – Electromagnetic environment for low- frequency conducted disturbances and signaling in public power supply systems.
“PQ is defined as conducted electromagnetic disturbances present in AC electrical supply network in the frequency range from 0 to 9kHZ, with an extension up to 148.5khZ.”
The conducted electromagnetic disturbances are:
Voltage dips and short supply interruptions
Power frequency variation
In the IEC, the concept of Electromagnetic Compatibility (EMC) is important to ensure minimum equipment mal-operation due to conducted electromagnetic disturbances. The conducted electromagnetic disturbances make up the electromagnetic environment for electrical equipment.
Electromagnetic Compatibility (EMC) is the ability of equipment or systems to function satisfactorily in their electromagnetic environment without introducing other intolerable electromagnetic disturbances to the environment.
Categories of PQ disturbances
Short duration PQ disturbances or PQ events : voltage sags, voltage swells & voltage transients
Continuous & steady state PQ disturbances : harmonics, notches, flickers, imbalance etc.
Electromagnetic Interference (EMI) is a phenomenon (voltage disturbances etc), while Electromagnetic Compatibility (EMC) is the ability of devices and systems to function in their electromagnetic environment without faults.
Power quality disturbances are low frequency conducted voltage disturbances in the frequency range of 0 kHz – 9 kHz, and are a part of the EMI environment for electrical systems.
Quality of supply depends on many factors during the transfer of electricity from the power station to your substation. For example, cable quality, lightning strike, 3rd party interference, your internal system etc…can contribute to the quality of your electricy supply.
In an electrical power system, there are protection systems (relays, fuses, etc.) installed to prevent faults from spreading. The direct impact of this process is characterised by short duration changes in the rms (root mean square) voltage magnitude supplied.
This short duration voltage disturbance is called voltage sag or voltage dip. Voltage sags are the most common events that affect power quality. They are also the most costly. Equipment used in modern industrial plants, such as process controllers, PLCs, adjustable speed drives, and robots, becomes more sensitive to voltage sags as the complexity of the equipment increases. Relays and contactors in motor starters are sensitive to voltage sags, resulting in downtime when they drop out.
The impact of voltage sag on your equipment depends on the voltage magnitude during voltage disturbance, how long the disturbance lasts, and the sensitivity of your equipment
Apart from voltage sags (or voltage dip), you may also encounter problems related to voltage transient and harmonics.
If you experience overheating transformers, frequent circuit breaker tripping, neutral conductors overload, computer lockups, equipment damage or unexplained downtime, it is likely that you have power quality related problems.
Voltage sag is a natural and unavoidable part of electrical power systems. It is caused by abrupt increases in loads, or by loose connections. In the past, most equipment were not sensitive to minor voltage disturbances. But now, some modern electricity utilisation equipment, either because of its design or its control features, have become more sensitive to voltage sag. The sensitivity varies from one equipment to another, so what may be considered poor power quality to one equipment may be perfectly acceptable to another.
Adjustable-speed (ASD) controls, robotics, programmable logic controllers, and even contractors for control applications are affected by voltage sags. This can be costly as production is affected. But how bad it is depends on the severity and duration of the voltage sag.
This is a phenomenon among electricity suppliers, consumers and manufacturers of equipment. Which is why it’s important that we explain to you why your equipment is sensitive to voltage sags. However, the good news is that the trip threshold of sensitive equipment can be modified, either with available settings in the controls, or by manufacturer design changes.
Ideally, electrical power in our facilities should be 50-Hz, 3-phase sine wave. However, in reality, some voltage sine wave is at a greater or smaller magnitude than their previous counterparts. Nonlinear loads do not draw current for the complete cycle of the sine wave, resulting in distortion of the original or fundamental 50-Hz sine wave.
As equipment is switched on and off, transients (or ‘spikes’) may occur along the sine wave. Depending on the magnitude and duration of these ‘spikes’, some electrical equipment will be affected, but not all. Get an electrical professional to diagnose the problem and to come up with a solution.
According to the IEC 61000 series standards, Power Quality is a compatibility problem. Please check if your equipment connected to the grid is compatible with the electromagnetic environment of the grid, and if the power delivered by the grid, including electromagnetic disturbances, is compatible with the equipment.
Lack of compatibility can cause your equipment to malfunction or operate erratically or incorrectly, resulting in inefficiency or shorter life span of your equipment.
Many PQ issues are caused by the mis-operation of end-user equipment that is connected to the network. But there are always at least 2 solutions – clean up the power or make the equipment tougher. Incompatibility between power supply and the industrial equipment can cause malfunctioning of equipment or reduced quality of industrial products.
Power quality disturbances occur in every power system around the world.
International standard bodies and associations like IEE (US), IEC (Europe) and SEMI, have produced many documents on PQ guidelines and standards for power utilities, equipment manufacturers and users.
The IEC committee has published IEC 61000 standards for managing power quality disturbances, and has also published many standards on power quality solution & guidelines, while the semiconductor industries have also produced standards (SEMI F47 & SEMI F49) for testing and managing short duration voltage variations (sags) for their members.
A procurement of new equipment that meets or exceeds IEC & SEMI requirement.
The best way to avoid PQ problems is to ensure that all equipment installed are compatible with the electromagnetic environment of the respective power systems. Procure equipment with proper technical specifications that incorporate proper immunity and emission requirement for all critical electromagnetic disturbances.
Conduct a background PQ survey to obtain better information on the existing electromagnetic environment. You can also refer to TNB for background data on electromagnetic environments for selected sites.
The general data to be compiled for electromagnetic environment are:
Please contact TNB for more information on Power Quality.
Check when the problem normally occurs i.e. at certain times of a day or at random.
Identify equipment and the protection systems that are frequently affected.
Refer to TNB to identify the types / sources / causes of the supply disturbances. Provide voltage measurement (if available).
a. Verify with the nearby factories for possibility of internal flashover in other customers’ installations. These flashovers could be the causes of the PQ disturbances.
b. Install a PQ monitoring equipment. Diagnose the new data recorded. Discuss with TNB the results of the action plans.
If the types / sources / causes of the supply disturbances originated from the AC power systems, TNB will implement mitigation measures to improve reliability of the power systems.
To further assist you, TNB will provide a report on the types / sources / causes of the supply disturbances. In the same report, summary of the EMC evaluation of the PQ disturbances and action plans performed will also be reported.
If the types / sources / causes of the PQ disturbances / events are known, discuss with TNB, electrical consultants or equipment manufacturers on measures for improving the immunity of the critical equipment or measures to minimise the emission of the PQ events from the internal loads in the factories.
Implement mitigation measures.
It is recommended that new customers design all their critical equipment and processes to meet or exceed the requirement of the technical standards.
PQ is measured by the consistency of the voltage supplied at your meter. The voltage waveforms may reduce, increase, fluctuate or distort due to various circumstances, therefore, the amount of voltage availability may fluctuate.
Any type of electrical equipment can be affected. Standard systems like lighting, air-conditions, fans, and communications equipment are often affected. The most costly power quality problems often happen to sensitive high-tech equipment such as computer controlled equipment and data systems.
Do your adjusted speed drivers often trip into offline mode?
Does your computer tend to shut down for no apparent reason?
Does your computer screen tend to jitter?
Do you get equipment problems during or shortly after a lightning storm?
Do your circuit breakers trip when they’re not even overloaded?
Are your transformer cases extremely hot?
Does your power factor capacitor bank fail prematurely?
Do your equipment tend to malfunction at the same time every day?
Do your automated systems fail for no apparent reason?
If you answered ‘yes’ to any of these questions, you are likely to have a PQ problem.
The most common causes are lightning strikes, equipment failures, third party intrusion, weather conditions, and operating on non-linear and fluctuating loads.
External causes are not always from electrical lines. Any wire entering a building may cause problems, including communication and data lines, telephone and coaxial lines as well as satellite connections.
IEC 61000-2-1: Definition of Electromagnetic Compatibility (EMC) EMC is concerned with the possible degradation of the performance of electrical and electronic equipments due to the disturbances present in the electromagnetic environment, in which the equipment operates.
IEC 61000-2-4: Compatibility levels in industrial plants for low frequency conducted disturbance.
IEC 61000-2-8: Electromagnetic compatibility (EMC) - Part 2-8: Environment - Voltage dips and short interruptions on public electric power supply systems with statistical measurement results.
IEC 61000-2-12; Electromagnetic compatibility (EMC) - Part 2-12: Environment - Compatibility levels for low-frequency conducted disturbances and signalling in public medium-voltage power supply systems.
IEC 61000-3-6: Assessment of emission limits for distorting loads in MV and HV power systems.
IEC 61000-3-7: Assessment of emission limits for fluctuating loads in MV and HV power systems.
MS 1760:2004: Guide on voltage dips and short interruptions on Public Power Supply System.
IEC 61000-4-11: Immunity test for voltage dips, short interruptions and voltage variation for equipment less than 16 Amp.
IEC 61000-4-34: Immunity test for voltage dips, short interruptions and voltage variation for equipment more than 16 Amp.
IEEE Std.1100-1999, IEEE Recommended Practice for Powering and Grounding.
IEEE Std 1159-2009, IEEE Recommended Practice for Monitoring Electric Power Quality Engineering Recommendation P28: Planning limits for voltage fluctuations caused by industrial, commercial and residential equipment in the United Kingdom.
Engineering Recommendation G5/4: Planning levels for harmonic voltage distortion & connection of non-linear equipment to Transmission and Distribution Systems in the United Kingdom.
SEMI F47: Specification for semiconductor processing equipment voltage sag immunity.
SEMI F49: Guide for semiconductor factory system voltage sag immunity.
There are others technical standards not mentioned here.