Intro to Power Quality

Chapter 01 Intro to Power Quality GV Nguyễn Hữu Phúc PQ is a Business Problem Power Quality issues cause business problems such as • Lost productivity, idle people and equipment • Lost orders, good wi.

Chapter 01_

Intro to Power Quality

GV: Nguyễn Hữu Phúc

PQ is a Business Problem

Power Quality issues cause business problems

such as:

According to Electric Light and Power Magazine, 30 to 40 Percent

of All Business Downtime Is Related to Power Quality Problems

Is Power Quality Such a Big Problem?

Why PQ is such a Big Problem?

• The sensitivity of today’s electronic equipment makes it susceptible to power disturbances

• For some devices, a momentary disturbance can cause

PQ Problems are Expensive

• Berkeley Lab Study Estimates $80 Billion Annual

Cost of Power Interruptions … Research News,

Berkeley Lab, February 2, 2005

• $50 billon per year in the USA is lost as a results

of power quality breakdowns … Bank of America

Report

• A manufacturing company lost more than $3

million one day last summer in Silicon Valley

when the “lights went out.” … New York Times

January 2000

• “A voltage sag in a paper mill can waste a whole

day of production - $250,000 loss” … Business

Week, June 17,, 1996

• Half of all computer problems and one-third of all

data loss can be traced back to the power line …

Contingency Planning Research, LAN Times

Instantaneous Sag 0.5 – 30 cycles

Momentary Sag 30 cycles – 3

sec Temporary Sag 3 sec – 1 min

Instantaneous Sag 0.5 – 30 cycles

Momentary Sag 30 cycles – 3

sec

Temporary Sag 3 sec – 1 min

Instantaneous Swell 0.5 – 30 cycles

Momentary Swell 30 cycles – 3

sec

Temporary Swell 3 sec – 1 min

Instantaneous Sag 0.5 – 30 cycles

Momentary Sag 30 cycles – 3

sec

Temporary Sag 3 sec – 1 min

Instantaneous Swell 0.5 – 30 cycles

Momentary Swell 30 cycles – 3

sec

Temporary Swell 3 sec – 1 min

Momentary Interruptions 0.5 – 30 cycles

Temporary Interruptions 30 cycles – 3

sec

Sustained interruptions > 1 min

Under voltages > 1 min

Over voltages > 1 min

Sustained interruptions > 1 min

Under voltages > 1 min

Over voltages > 1 min

Voltage imbalance Steady state

Waveform Distortion

Sustained interruptions > 1 min

Under voltages > 1 min

Over voltages > 1 min

Voltage imbalance Steady state

Waveform Distortion

DC offset Steady state

Harmonics Steady state

Inter harmonics Steady state

For Electric Utilities Control of Voltage and Prevention of Outages is Power Quality

• Uninterruptible Power Supplies

• Variable Frequency Drives

• Battery Chargers

• Large Motors During Startup

• Electronic Dimming Systems

• Lighting Ballasts (esp Electronic)

• Arc Welders, and Other Arc Devices

• Medical Equipment, e.g MRIs and X-Ray Machines

• Office Equipment and Computers

• Wiring

PQ Problems and Possible Causes

Overheated neutral

Intermittent lock-ups

Frequency deviations

Steady-state Shared neutrals

Improper or inadequate wiring High source impedance

SCR/Rectifiers and notching Harmonics

PQ Problems and Possible Causes

Overheated neutral

Intermittent lock-ups

Frequency deviations

Steady-state Shared neutrals

Improper or inadequate wiring High source impedance

SCR/Rectifiers and notching Harmonics

Interruption

Garbled data

Random increase in harmonics levels

Utility faults Inrush currents Inadequate wiring

PQ Problems and Possible Causes

Overheated neutral

Intermittent lock-ups

Frequency deviations

Steady-state Shared neutrals

Improper or inadequate wiring High source impedance

SCR/Rectifiers and notching Harmonics

Interruption

Garbled data

Random increase in harmonics levels

Utility faults Inrush currents Inadequate wiring

PQ Problems and Possible Causes

Overheated neutral

Intermittent lock-ups

Frequency deviations

Steady-state Shared neutrals

Improper or inadequate wiring High source impedance

SCR/Rectifiers and notching Harmonics

Interruption

Garbled data

Random increase in harmonics levels

Utility faults Inrush currents Inadequate wiring Intermittent lock-ups

Lights flicker

Garbled data

Sags/Swell Source voltage variations

Inrush/surge currents Inadequate wiring

Lightning Load switching Capacitor switching Static discharge Hand-held radios Loose wiring/arcing

PQ Problems and Possible Causes

Overheated neutral

Intermittent lock-ups

Frequency deviations

Steady-state Shared neutrals

Improper or inadequate wiring High source impedance

SCR/Rectifiers and notching Harmonics

Interruption

Garbled data

Random increase in harmonics levels

Utility faults Inrush currents Inadequate wiring Intermittent lock-ups

Lights flicker

Garbled data

Sags/Swell Source voltage variations

Inrush/surge currents Inadequate wiring Component failure

Lightning Load switching Capacitor switching Static discharge Hand-held radios Loose wiring/arcing

Overheated transformers and motors

Voltage and current distortions

Garbled data

Lock-ups

Harmonics Electronic loads

SCR/rectifier

Swells, 31%

Sags (Dips)

Associated with system faults Switching of heavy loads Starting of large motors

Swells

System fault conditions

Switching on a large capacitor bank

Switching off a large load

Cost of Voltage Sags

Textile Industry Plastics Industry Glass Industry Process Industry

Semiconductors

Losses per Voltage Sag Event

Source: EPRI “The Economics of Custom Power”, IEEE T&D Show 2003

Cost of Momentary Outages

Momentary Outages

create problems when

computers and clocks

reset, equipment stalls,

and work stops

Category Minimum Maximum

Industrial

Semiconductor Manufacturing $20.0 $60.0 Electronics $8.0 $12.0 Automobile Manufacturing $5.0 $7.5 Pharmaceutical $5.0 $50.0 Glass $4.0 $6.0 Rubber and Plastics $3.0 $4.5 Petrochemical $3.0 $5.0 Food Processing $3.0 $5.0 Textile $2.0 $4.0 Metal Fabrication $2.0 $4.0 Mining $2.0 $4.0 Paper $1.5 $2.5 Printing(Newspapers) $1.0 $2.0

Commercial

Hospitals, banks, civil service $2.0 $3.0 Communications, information processing $1.0 $10.0 Resturants, bars, hotels $0.5 $1.0 Commercial shops $0.1 $0.5

Source: EPRI “The Economics of Custom Power”, IEEE T&D 2003

Cost of Momentary Interuption

($/ kW Demand)

High Speed Waveform Capture

High Speed Waveform Capture Is the Most Important PQ

Troubleshooting Tool

Benefits of Continuous PQ Monitoring

to the Prevention of PQ Problems

• Power Quality monitoring provides a continuous

“Health Check” of a facility’s power system … for

example:

o Harmonic interaction between loads and

power conditioning equipment spotted

o High Inrush currents from equipment

startup detected

o Transients from load switching are seen

• It provides data to see, diagnose and avert

looming problems – “like squeaky brakes on a

car”

o Trends can be detected

o JIT equipment maintenance programs

can be established

• It acts like a “Black Box” on an airplane to tell

you what, when, and where a Power Quality

event occurred … to prevent it from reoccurring

What is needed for PQ Monitoring?

PQ Monitors must detect and record

the 7 types of PQ problems

These include Flicker and

Compliance to ITI (CBEMA), IEEE

and ISO Standards

Plus they must …

• Have enough storage to save the waveforms you need

• Have PQ analysis tools that produce usable, actionable recommendations

ITI: Information Technology Industry Council (Computer & Business Equipment Manufacturer’s Association)

Real Time Field Recorded Events

Source: AGA Brazil

PQ Meter ITI Capture

Equipment Interrupting Voltage Sags as Recorded

Damage Inducing Voltage Surges as Recorded

ITI Acceptable Power Disturbance Envelope

ITI: Information Technology Industry Council (Computer & Business Equipment Manufacturer’s Association)

Instantaneous Sag Event

Instantaneous Swell Event

Harmonic & Interharmonic Spectrum

Flicker Recording

Chapter 01_Intro to Power Quality

•Both electric utilities and end users of electric

power are becoming increasingly concerned about the quality of electric power

•The term power quality has become one of the

most prolific buzzwords in the power industry since

the late 1980s

There are four major reasons for the increased concern:

1 Newer-generation load equipment, with microprocessor-based controls and

power electronic devices, is more sensitive to power quality variations than was equipment used in the past

2 The increasing emphasis on overall power system efficiency has resulted in

continued growth in the application of devices such as high-efficiency, speed motor drives and shunt capacitors for power factor correction to reduce losses This is resulting in increasing harmonic levels on power systems and has many people concerned about the future impact on system capabilities

adjustable-3 End users have an increased awareness of power quality issues Utility

customers are becoming better informed about such issues asinterruptions, 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

There have been some developments that have had an impact on power quality:

1 Throughout the world, many governments have revised

their laws regulating electric utilities with the intent of

achieving more cost-competitive sources of electric energy

2 There has been a substantial increase of interest in

distributed generation (DG), that is, generation of power dispersed throughout the power system

3 The globalization of industry has heightened awareness

of deficiencies in power quality around the world

4 Indices have been developed to help benchmark the

various aspects of power quality

What Is Power Quality?

Any power problem manifested in voltage, current, or frequency deviations that results in failure or misoperation

of customer equipment

Results of a survey on the causes of power quality problems (Courtesy of Georgia Power Co.)

Power Quality= Voltage Quality

The Power Quality Evaluation Procedure

Basic steps involved

in a power quality evaluation

Terms and Definitions

Need for a Consistent Vocabulary

•Many ambiguous words have been used that have multiple or

unclear meanings

•For example, surge is used to describe a wide variety of disturbances

that cause equipment failures or misoperation

•A surge suppressor can suppress some of these but will have

absolutely no effect on others

•Terms like glitch and blink that have no technical meaning at all have

crept into the vocabulary

General Classes of Power Quality Problems

The IEC classifies electromagnetic phenomena into the groups shown

in the following table

Categories and Characteristics of Power System Electromagnetic

Phenomena

Transients

• An event that is undesirable and momentary in nature

• Another word in common usage that is often considered

synonymous with transient is surge

• Broadly speaking, transients can be classified into two categories,

impulsive and oscillatory

•These terms reflect the waveshape of a current or voltage

transient

Impulsive transient

An impulsive transient is a sudden, non–power frequency change in the

steady-state condition of voltage, current, or both that is unidirectional

in polarity (primarily either positive or negative)

Impulsive transients are normally characterized by their rise and decay times, which can also be revealed by their spectral content

For example, a 1.2x 50- μs 2000-volt (V) impulsive transient nominally rises from zero to its peak value of 2000 V in 1.2 s and then decays to half its peak value in 50 s

Lightning stroke current impulsive transient

Oscillatory transient

•An oscillatory transient is a sudden, non–power frequency change in the

steady-state condition of voltage, current, or both, that includes both positive

and negative polarity values

Medium-frequency oscillatory transients caused

by back-to-back capacitor bank switching

Low-frequency oscillatory transients

caused by capacitor bank energization

onto 34.5 kV bus voltage

Low-frequency oscillatory transients

caused by ferroresonance of an

unloaded transformer

Long-Duration Voltage Variations

•Long-duration variations encompass root-mean-square (rms) deviations at

power frequencies for longer than 1 min

Long-duration variations can be either overvoltages or undervoltages

Overvoltages and undervoltages generally are not the result of

system faults, but are caused by load variations on the system and

systemswitching operations

•Overvoltage

•An overvoltage is an increase in the rms ac voltage greater than 110 percent

at the power frequency for a duration longer than 1 min

•Overvoltages are usually the result of load switching (e.g., switching off a

large load or energizing a capacitor bank)

•Undervoltage

An undervoltage is a decrease in the rms ac voltage to less than 90 percent at the

power frequency for a duration longer than 1 min

Undervoltages are the result of switching events that are the opposite of the

events that cause overvoltages A load switching on or a capacitor bank switching off can cause an undervoltage until voltage regulation equipment on the system can bring the voltage back to within tolerances Overloaded circuits can result in undervoltages

Sustained interruptions

•When the supply voltage has been zero for a period of time in excess of1 min,

the long-duration voltage variation is considered a sustained interruption

•Voltage interruptions longer than 1 min are often permanent and require human

intervention to repair the system for restoration

Short-Duration Voltage Variations

•This category encompasses the IEC category of voltage dips and

short interruptions Each type of variation can be designated as

instantaneous, momentary, or temporary, depending on its duration as defined in the following table

•Short-duration voltage variations are caused by fault conditions, the energization of large loads which require high starting currents, or

intermittent loose connections in power wiring

•Depending on the fault location and the system conditions, the fault

can cause either temporary voltage drops (sags), voltage rises

(swells), or a complete loss of voltage (interruptions)

Interruption

•An interruption occurs when the supply voltage or load current

decreases to less than 0.1 pu for a period of time not exceeding 1 min

Sags [US] (dips[IEC])

•A sag is a decrease to between 0.1 and 0.9 pu in rms voltage or

current at the power frequency for durations from 0.5 cycle to 1 min

•Three-phase rms voltages for

a momentary interruption due

to a fault and subsequent

recloser operation

Voltage sag caused by an SLG fault (a) RMS waveform for voltage sag event (b) Voltage sag waveform

Temporary voltage sag caused

by motor starting

Swells

A swell is defined as an increase to between 1.1 and 1.8 pu in rms voltage or

current at the power frequency for durations from 0.5 cycle to 1 min

Voltage Imbalance

Voltage imbalance (also called voltage

unbalance) is sometimes defined

as the maximum deviation from the average of

the three-phase voltages or currents, divided

by the average of the three-phase voltages or

currents, expressed in percent

Imbalance is more rigorously defined in the

standards using symmetrical components

The ratio of either the negative- or zero

sequence component to the positive-sequence

component can be used to specify the percent

unbalance

The most recent standards specify

that the negative-sequence method be used

Instantaneous voltage swell caused by an SLG fault

Voltage unbalance trend for

a residential feeder