Basic PQ

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1. What is power Quality?

Power Quality is the interaction of electronic equipments with its electrical environment, including generators,

transformers, breakers and electrical wiring and grounding.The term Power Quality broadly refers to

maintaining a near sinusoidal power distribution bus voltage at rated magnitude and frequency. In addition the

energy supplied to a customer must be uninterrupted from the reliability point of view.

2. How is Power Quality measured?

Power Quality is measured by the consistency of the voltage supplied at your meter. The amount of voltage

available may fluctuate or change due to controllable or uncontrollable circumstances. The measure of power

quality depends up on the needs of the equipments that are being supplied.

3. Why is power quality such a problem today?

In recent years there has been an increased use of non linear loads which has resulted in an increased fraction

of non sinusoidal voltages and currents in electrical network. Therefore power quality problems to day are more

frequent and costly than ever before, despite the overall improvements in electricity reliability.

4. What terms are commonly used in the measurements and descriptions of power quality?

• Voltage sags/swells

• Voltage dips

• Voltage distortion

• Voltage unbalance

• Voltage interruption

• Voltage flicker

• Impulse or surge

• Harmonics

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5. List out the power quality problems and causes?

Broad Categories Specific Categories Characterization Methods Typical Causes

Transients

Impulsive

Peak magnitude, rise time

and duration

Lighting strike, Transformer

energisation and capacitor

switching

Oscillatory

Peak magnitude, Frequency

components

Line or Capacitor or Load

Switching

Short duration voltagevariation

Sag

Magnitude durationFerro resonant transformers

Single line to ground fault

Swell

Magnitude durationFerro resonant transformers

Single line to ground fault

Interruption

Duration Temporary (self Clearing faults)

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Long durationvoltage variation

Under voltage

Magnitude durationSwitching on loads, Capacitor

de-energisation

Over voltage

Magnitude durationSwitching off loads, Capacitor

energisation

Voltage Unbalance Symmetrical componentsSingle-phase load, Single

phasing condition

Waveform distortion

Harmonics

THD, Harmonic spectrumAdjustable speed drives and

non linear loads

Notching

THD, Harmonic spectrum Power Electronics converter

Voltage Flicker Frequency of occurrences,

modulating frequencyArc furnace, Arc Lamps

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6. What kind of equipments can be affected by power quality problems?

Any type of electrical equipment can be affected by power quality problems. However the most

costly power quality problems involve more sensitive high tech equipments, such as computer and

data systems, which can be affected by their direct power supply or through interactions with other

electrical equipments.

7. Are power quality problems are always noticeable?

No – in many cases disturbances can cause damage to circuits and other components. Unfortunately

many power quality problems go unsolved until a significant monetary loss is actualized, and even

then masked problems like failed electrical or electronic equipments hide the underlying power

quality problems tat are the root cause of these failures.

8. What causes power quality problems?

Most power quality problem causes can be divided into two categories – internal and external.

Internal factors: faults o lightning strikes on transmission lines or distribution feeders, equipment failures etc

External factors: Transformer energisation. Capacitor or feeder switching, Power electronic loads, Arc furnace

and induction heating systems switching on or off of large loads etc.

9. What are the types of electronic irregularities that cause power quality problems?• Outage or Interruptions:

An outage is a complete loss of voltage; it usually lasts for a few cycles to several hours. Ice storms, lightening

or winds are some of the more typical causes of power failures. As different loads having different

requirements, there is no universal standard for power acceptability considering outages.• Voltage sags or under voltage

A drop is service voltage below the proper nominal operating low voltage limit for several seconds in duration is

an under voltage condition. Voltage sag may be caused by faults in the transmission system or by the switching

loads with the large amount of initial starting / inrush current.• Voltage swell or Over Voltage

It is a steady state voltage for several seconds or longer which is above the upper source voltage limit. Over


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voltage usually occurs due to improper adjustments of voltage regulators, capacitors etc. Line to ground fault in

a three phase system may cause voltage swell in the un faulted phases.• Surges or impulses:

Surge is a transient voltage or current that can have a high magnitude for extremely shot duration. Causes

include lightning, normal operation of utility protection devices, equipment start up and shut down, welding

equipments. While lightning generates most impressive transients, switching large motors and transformers or

capacitor creates transients sufficient o destroy today’s delicate microprocessor based equipments.• Harmonics

The periodic steady state distortions of the standard sine wave due to equipment generating a frequency other

than the standard 50 cycles per second. Causes include electronic ballasts, non linear loads like switch mode

power supplies used in computers, variable frequency drives. In general harmonics cause magnetic portions of

the electrical system to over heat. Such as transformers, line reactors, magnetic relays and power factor

capacitors• Flicker

Flicker can be defined as the perceptible change in lamp output produced by a sudden change in supply

voltage. Some of the loads like arc furnace load undergo rapid changes and generates variable voltage dip

along the distribution feeder. The disturbance may affect some of the loads like incandescent lighting.

10. How is power quality problems diagnosed?

Electrical engineers and technical team use sophisticated monitoring and testing to isolate the specific type of

disturbances and pinpoint the root cause.

Examples of the testing that can be used include harmonic studies, load studies, disturbance monitoring, wiring

and grounding studies and power factor measurements.

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11. How do I know a certain problem is caused by power quality issues?

Determining the exact problems related to power quality issues requires sophisticated electronic test

equipments. The following questions are general indicators of power quality problems.

• Are you experiencing premature failures of electronic equipments or motors or drives?

• Do you have adjustable speed drives that frequently trip off-line?

• Do your computers lock up inexplicably?

• Does your computer monitor screens jitter?

• Do you have equipments problems during or shortly after lightning storms?

• Is interruptible power supplies frequently go to battery?

• Are circuit breakers tripping without being overloaded?

• Are transformers caught extremely hot to the touch?

• Do equipments frequently malfunction at the same time of the day?

• Do automated systems fail for no apparent reason?

• Do certain electronic systems work in one location but not in another location?

• Do light dim or flicker?

12. How is power quality problems fixed?

The solution to a power quality issue depend on the nature of the problem, but may include the installation of

power conditioning devices such as uninterruptible power supplies, transient voltage surge suppressors or

isolation transformers. Other potential solutions include facility rewiring or replacement of damaged or

degraded equipment.

13. How do I perform a power quality audit of my business?

The objective of a power quality audit is to find a solution to a problem. This is accomplished by checking the

wiring and grounding, which causes a significant amount of most commercial and industrial problems, and

checking the quality of both the internal and external voltage. This data is then used to determine an

appropriate solution. In conducting an audit, the power quality professional must find answers to four questions

viz;

• Does the facilities wiring and grounding meet code and more importantly is it adequate to meet their power

needs from a power quality stand point?

• What is the quality of the ac voltage supplying the equipment?

• What is the impact of electric utilities power system?

• What solutions are indicated by the audit data?

The last question off course is the most important. The best out come of any power quality audit is whether the

problem was solved or not.

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14. Is there a solution to the power quality problem?

Yes. HYKON UPQC can solve all the power quality problems

Power Quality Issues Hykon Power

Quality Products Benefits

Power factor, voltage

sags/swells, voltage

interruptions, over voltage,

under voltage

UPQC - Unified

Power Quality

Conditioner

• Regulates load voltage against sag/ swell and

other voltage fluctuations.

• Individual phase compensation of the load

voltages to eliminate voltage unbalance


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• Reactive current filtering by STATCOM

• Maintains Grid Power Factor near to unity and

brings down Maximum Demand ( MD)

• Uninterrupted production and supply

15. What is UPQC?

UPQC stands for Unified Power Quality Conditioner. UPQC is an active series / shunt power line conditioner. It

is used to compensate power quality issues such as Voltage sags, swells, Voltage imbalance, flicker, harmonics

and reactive current. It is a combination of a STATCOM as well as a series compensating stage connected

before the load in series with the power network using a matching transformer.

16. What is the basic function of UPQC?

• Load voltage regulation be series voltage injection

• Dynamic current Injection for reactive power compensation

UPQC is used to compensate voltage sags and current harmonics, control input power factor near to unity as

well as to regulate the load voltage. It can be installed by the electric utilities to damp out harmonic propagation

caused by resonance with line impedance and passive shunt compensators.

17. What is the basic topology of UPQC?

UPQC consists of 1 x 3 phase and 3 x 1 phase Voltage source converters sharing the same capacitive DC link.

The 3 phase converter will act as an Active Filter while the other is a series filter (Dynamic Voltage Regulator)

The basic block diagram of a UPQC is shown below:

18. What is the role of Series Active Filter and Shunt Active Filter in UPQC?

The Shunt Active Filter is primarily a Voltage Source Converter connected to Point of Common Coupling (PCC)

through series inductors. The Series Filter (DVR) is primarily a Voltage Source Inverter connected to Power

network with LC filter and isolation transformer. The secondary of the transformer is connected in series with

Power Network.

19. Where UPQC can be installed?

• IT Parks

• Commercial Office Complexes

• Semiconductor industries

• Machine Tool plants

• Process Industries

20. Can I use a Power Conditioner instead of UPS?

Your question involves two different technologies used for differing reasons. 95% of all power quality problems

are caused by transient noise, voltage surges, harmonics or frequently changing voltage conditions. Unified

Power Quality Conditioner provides solution for most of the power quality problems.The primary function of any

uninterruptible power supply ( UPS) is to provide an alternate voltage source ( batteries) to a critical load for

some period of time should a complete power failure occur. Complete power failure accounts less than 5% of all

power quality problems. For the other 955 of all the power quality problems unless the UPS is the on-line

version is of no help.

21. Does the UPQC need much on going service and maintenance?

No. Depending up on the environment that the HYKON UPQC located only preventive maintenance would be

required and that involves ensuring that the door and internal fans are fully operational and that all filters are

free of dust and not blocked.

22. Is the technology is developed by HYKON?

The technology is transferred from CDAC – which is a project supported by Dept of IT, Ministry of

Communication and Information Technology, Govt. of India and manufactured at HYKON.

23. Whether the HYKON UPQC technology field proven?

Yes. The 250 KVA proto model of UPQC is working in the Power Electronics Lab of C DAC

Thiruvananthapuram with light and fan loads of the centre connected for the past one year.

24. My question is not on the list – how can I get an answer to my question?

Please go to our FAQ form. We will answer your questions directly as quickly as possible.


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Basic PQ