ch 1_introduction to pq_bef44803

8/19/2019 Ch 1_Introduction to PQ_BEF44803

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BEF 44803

POWER QUALITY

WITH WISDOM WE EXPLORE


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1.1 Review about sources of powerquality issues

1.2 Significance of studying power

quality1.3 Power quality terminology

WITH WISDOM WE EXPLORE

Chapter 1: Introduction to Power Quality


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1.1 Review about sources of PQ issues

What is Power Quality (PQ)?

PQ Theory

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1

Need for PQ


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Concerns: Both Electric Utilities and End

user of Electric Power - Since 1980s PQ is the buzz word in the power industry.

- PQ is the multitude of individual types of power system

(PS) disturbances.- Engineers are now attempting to deal with these issues

using a system approach rather than handling them as

individual problems.

Background/Theory


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Four major reasons for the increased concern:

1. Newer-generation load equipment, with microprocessor-

based controls and power electronic devices, is more

sensitive to PQ variations than was equipment used in

the past.

2. The increasing emphasis on overall PS efficiency hasresulted in continued growth in the application of devices

such as high-efficiency, adjustable-speed motor drives

(ASDs) and shunt capacitors for power factor (pf)

correction to reduce losses. This is resulting inincreasing harmonic levels on PSs and has many people

concerned about the future impact on system

capabilities.

Background/Theory


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Four major reasons for the increased concern (contd.):

3. End users have an increased awareness of PQ issues.

Utility customers are becoming better informed about

such issues as interruptions, sags, and switching

transients and are challenging the utilities to improve the

quality of power delivered.4. Many things are now interconnected in a network.

Integrated processes mean that the failure of any

component has much more important consequences.

Background/Theory


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- Manufacturers want faster, more productive, more

efficient machinery. Utilities encourage this effortbecause it helps their customers become more profitable

and also helps defer large investments in substations

and generation by using more efficient load equipment.

- Such equipment suffers most from common power interruptions.

Background/Theory


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• 1. Many governments have revised their laws

regulating electric utilities with the intent of achievingmore cost-competitive sources of electric energy.Deregulation of utilities has complicated the PQ problem.In many geographic areas there is no longer tightlycoordinated control of the power from generation through

end-use load. While regulatory agencies can change thelaws regarding the flow of money, the physical laws of power flow cannot be altered. In order to avoiddeterioration of the quality of power supplied tocustomers, regulators are going to have to expand their

thinking beyond traditional reliability indices and addressthe need for PQ reporting and incentives for thetransmission and distribution companies.

Background/Theory


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• 2. There has been a substantial increase of interest in

distributed generat ion (DG), that is, generation of power dispersed throughout the PS. There are a number

of important PQ issues that must be addressed as part

of the overall interconnection evaluation for DG.

• 3. The globalization of industry has heightenedawareness of deficiencies in PQ around the world.

Companies building factories in new areas are suddenly

faced with unanticipated problems with the electricity

supply due to weaker systems or a different climate.

There have been several efforts to benchmark PQ in one

part of the world against other areas.

Background/Theory


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• 4. Indices have been developed to help benchmark the

various aspects of PQ. Regulatory agencies havebecome involved in performance-based rate-making

(PBR), which addresses a particular aspect, reliability,

which is associated with interruptions. Some customers

have established contracts with utilities for meeting a

certain quality of power delivery.

Background/Theory


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• Utility perspective:

Reliability and statistics demonstrating that its system is99.98 percent reliable. Criteria established by regulatory

agencies are usually in this vein.

• Manufacturer of load perspective:

Those characteristics of the power supply that enablethe equipment to work properly. These characteristics

can be very different for different criteria

PQ is ultimately a consumer driven issue:

Any power problem manifested in V, I, or f deviations thatresults in failure or mis-operation of customer equipment.

What is PQ?


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Other definitions:

• Study of powering and grounding electronic systems so as to maintain theintegrity of the power supplied to the system. IEEE Standard 11598 defines

power quality as [1.23]:

“The concept of powering and grounding sensitive equipment in a manner that

is suitable for the operation of that equipment”

• Power quality is defined in the IEEE 100 Author itat ive Dict ionary of IEEE

Standard Terms as ([1.42], p. 855):“The concept of powering and grounding electronic equipment in a manner that

is suitable to the operation of that equipment and compatible with the premise

wiring system and other connected equipment”

• Equally authoritative, the qualification is made in the Standard Handbook of

Electrical Engineers, 14th edition, (2000) ([1.43] pp. 18–117):“Good power quality, however, is not easy to define because what is good PQ

to a refrigerator motor may not be good enough for today’s personal computers

and other sensitive loads. For example, a short (momentary) outage would not

noticeably affect motors, lights, etc. but could cause a major nuisance to digital

clocks, videocassette recorders (VCRs) etc”

What is PQ?


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Need for PQ

Survey conducted by the Georgia Power Company for What causes PQ Problem?


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Need for PQ


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• Both tend to blame about 2/3rd of the

events on natural phenomena (e.g.Lightning).

• Customers much more frequently than

utility personnel, think that the utility is atfault.

Need for PQ


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• There are many events resulting in end-user

problems such as; capacitor switching (quitecommon) which can cause transient

overvoltages that disrupt manufacturing

machinery, momentary fault elsewhere in the

system that causes the voltage to sag briefly at

the location of the customer. This might cause

an adjustable-speed drive (ASD) or a distributed

generator to trip off, but the utility will have noindication that anything was amiss on the feeder

unless it has a PQ monitor installed.

Need for PQ


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• In addition other PQ problems related to

hardware, software or control systemmalfunction.

• Electronic components can degrade over timedue to repeated transient voltages and fail.

• It is becoming more common that designers of control software for microprocessor-basedequipment have an incomplete knowledge of how PSs operate and do not anticipate all types

of malfunction events. Thus, a device canmisbehave because of a deficiency in theembedded software.

Need for PQ


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• In response to this growing concern for PQ,

electric utilities have programs that help themrespond to customer concerns. The philosophy

of these programs ranges from reactive, where

the utility responds to customer complaints, to

proactive, where the utility is involved in

educating the customer and promoting services

that can help develop solutions to PQ problems.

Need for PQ


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• The economics involved in solving a PQ problem

must also be included in the analysis i.e. toinclude PQ variations on the supply side. Inmany cases, the optimal solution to a problemmay involve making a particular piece of

sensitive equipment less sensitive to PQvariations.

• There are standards for voltage and other technical criteria that may be measured, but the

ultimate measure of PQ is determined by theperformance and productivity of end-user equipment.

Need for PQ


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• It is actually quality of the V that is being

addresses in most cases.• P=V.I

• The power supply system can only control the

quality of the V; it has no control over thecurrents (I) that particular loads might draw.

Therefore, the standards in the PQ area are

devoted to maintaining the supply V within

certain limits.

PQ = Voltage (V) Quality


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• Although the generators may provide a near-

perfect sine-wave V, the I passing through theimpedance (Z) of the system can cause a variety

of disturbances to the V. For example,

1. The I resulting from a short circuit causes the

V to sag or disappear completely, as the

case may be.

2. Is from lightning strokes passing through the

PS cause high-impulse Vs that frequentlyflash over insulation and lead to other

phenomena, such as short circuits.



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• 3. Distorted Is from harmonic-producing loads

also distort the V as they pass through thesystem Z. Thus a distorted V is presented to

other end users.



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• Economic value

• Automation and more modern equipments use(means electronically controlled, energy-efficient

equipment that is often much more sensitive to

deviations in the supply V than were its

electromechanical predecessors).

• Industrial customers are now more acutely

aware of minor disturbances in the PS.

• Momentary utility breaker operation can result inUSD thousands by shutting down the production

line which requires hours time to restart.

Why we concern about PQ?


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• In the semiconductor manufacturing industry, the

economic impacts associated with equipmentsensitivity to momentary V sags resulted in thedevelopment of a whole new standard for equipment ride-through (SEMI Standard F-47,

Specification for Semiconductor ProcessEquipment V Sag Immunity).

• Residential customers typically do not suffer direct financial loss or the inability to earn

income as a result of most PQ problems, butthey can be a potent force when they perceivethat the utility is providing poor service.



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• Home computer usage has increased

considerably in the last few years and moretransactions are being done over the Internet.

Users become more sensitive to interruptions

when they are reliant on this technology.



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• Examples of poor PQ

Examples of PQ

1 2 Si ifi f t d i PQ


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1.2 Significance of studying PQ• To know about:

• PQ problems and their respective effects

• Financial losses due to maintenance cost, reduced life of equipments, and mis operation of protective devices

• Additional cost for compensation devices to mitigate the

causes (PQ is Electrical Systems by A. Kusko pp.10)

• Impacts of advanced technology (just to save cost andimprove efficiency) at the risk of system malfunctioning

• Use of advanced technology with compensation devices

• Monitoring/observation/evaluation & analysis/economical

solution of PQ problems• To take care about the reliability, consistency, and quality

of power supply

• more sophisticated electronic controls which are sensitive

to voltage variations


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1.3 PQ Terminology

• PQ problems and mitigation techniques by Bhim

Singh pp.12• PQ by C Sankaran pp. 13-20

• Electrical PS Quality by Roger C Dugan pp. 31
http://../PQ_Bhim%20SIngh.pdfhttp://../PQ_Bhim%20SIngh.pdfhttp://pq_bef44803_20132014-2/PQ%20Books%20Pdf%20copy/PQ_C%20Sankaran.pdfhttp://pq_bef44803_20132014-2/PQ%20Books%20Pdf%20copy/Electrical%20PS%20Quality_Roger%20C%20Dugan_Highlighted.pdfhttp://pq_bef44803_20132014-2/PQ%20Books%20Pdf%20copy/PQ_C%20Sankaran.pdfhttp://pq_bef44803_20132014-2/PQ%20Books%20Pdf%20copy/Electrical%20PS%20Quality_Roger%20C%20Dugan_Highlighted.pdfhttp://pq_bef44803_20132014-2/PQ%20Books%20Pdf%20copy/PQ_C%20Sankaran.pdfhttp://../PQ_Bhim%20SIngh.pdfhttp://../PQ_Bhim%20SIngh.pdfhttp://../PQ_Bhim%20SIngh.pdf

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