POWER QUALITY

UNIT - I

INTRODUCTION TO POWER QUALITY

Terms and definitions – Overloading – Under

voltage – Sustained interruption-Sags and

Swells –Waveform distortion – Total Harmonic

Distortion (THD) – Computer Business

Equipment Manufacturers Associations

(CBEMA) curve.

ENERGY• ENERGY CAN NEITHER BE CREATED NOR BE

DESTROYED BUT IT CAN BE CONVERTED FROM ONE FORM TO ANOTHER FORM.

ELECTRICAL ENERGY

• GENERATION OF ELECTRICAL

ENERGY IS NOTHING BUT THE

CONVERSION OF VARIOUS OTHER

FORMS OF ENERGY INTO AN

ELECTRICAL ENERGY.

WIND POWER PLANT

HYDRO POWER PLANT

SOLAR POWER PLANT

THERMAL POWER PLANT

ELECTRICAL POWER SYSTEM

• FLOW OF ELECTRICAL POWER FROM THE GENERATING STATION TO THE CONSUMER

1. GENERATING STATION

2. TRANSMISSION

3. DISTRIBUTION

POWER QUALITY = VOLTAGE QUALITY

“ Any Power Problem manifested in Voltage,

Current, (or) frequency deviations that results

in failure (or) mis-operation of customer

equipment ”.

It is related to hardware, software (or) control

system malfunctions.

WHY WE ARE CONCERNED ABOUT POWER QUALITY ?

The Main reasons behind the growing concern about PQ are:

• North American industries lose Tens-of-Billions of Dollars

every year in downtime due to power quality problems.

(Electrical Business Magazine)

• Load non-linearities in rising and is expected to reach 50 to

70% in the year 2005 (Electric Power Research Institute)

[Computers, UPS, fax machines, printers, fluorescent lighting,

ASD, industrial rectifiers, DC drives, arc welders, etc).

WHY WE ARE CONCERNED ABOUT POWER QUALITY ?

• Economic impacts on utilities, their customers, and suppliers of load equipment.

• Meeting Customer Expectations

• Customers :

1. Industrial

2. Domestic

3. Commercial

POWER QUALITY ISSUE AND PROBLEMS

Power Quality issues can be roughly broken into a number of sub-categories:

Harmonics (sub, super and inter-harmonics); Voltage swells, sags, fluctuations, flicker, and

transients Voltage magnitude and frequency deviation,

voltage imbalance (3ph sys.) Hot grounding loops and ground potential rise

(GPR)–Safety & Fire Hazards Monitoring and measurement.

BLOCK DIAGRAM GENERATION

TRANSMISSION & DISTRIBUTION

CUSTOMERS

INDUSTRIAL CUSTOMERS

RESIDENTIAL CUSTOMERS

COMMERCIAL CUSTOMERS

TRANSIENTS

• Used in the analysis of power system variations to denote an event that is undesirable and momentary in nature.

• Classified in to 2 categories(i) Impulsive Transient(ii) Oscillatory Transient

TYPES OF TRANSIENTS

IMPULSIVE TRANSIENT• It is a sudden, non-power

frequency change in the steady state condition of voltage, current (or) both that is unidirectional in polarity.

• They are normally characterized by their rise and decay times, which can also be revealed by their spectral content.

OSCILLATORY TRANSIENT• It is a sudden, non-power

frequency change in the steady state condition of voltage, current or both, that includes both positive & negative polarity.

• Example :Capacitor Bank

Energization.

OVERVOLTAGE• An overvoltage is an increase in the r.m.s. ac

voltage greater than 110 % at the power frequency for a duration longer than 1 min.

• It is a result of load switching.Eg : Switching OFF a Large load

Energizing a capacitor bank

UNDERVOLTAGE

• An undervoltage is a decrease in the rms ac voltage to less than 90 % at the power frequency for a duration longer than 1 min.

Example : Load Switching Capacitor Bank Switching off

INTERRUPTIONS

An interruption occurs when the supply voltage or load current decreases to less than 1p.u for a period of time not exceeding 1 min.

It can be the result of power system faults, equipment failures and control malfunctions.

VOLTAGE SAG

• A sag is a decrease to between 0.1 and 0.9 p.u in r.m.s voltage or current at the power frequency for durations from 0.5 cycle to 1 min.

VOLTAGE SAG

VOLTAGE SWELL• A swell is defined as an increase 1.1 and 1.8

p.u in r.m.s voltage or current at the power frequency for durations from 0.5 cycle to 1 min.

VOLTAGE IMBALANCE

• Also called Voltage Unbalance• Maximum deviation from the average of the

three phase voltages (or) currents.

SYSTEM MODEL

Converter Type Arc Type Dynamic Cyclical Ripple Inrush Temporal Motorized on/off SMPS ASD Saturation Type

NonlinearLoad

NLL

R s L sV s V L

YF(s)

on/off orPWM

Load Bus

ElectricUtility

Transformer

System+Transformer+FeederElectric

Equivalent(Plant) Load

Switched/ModulatedPower Filter or Static

Capacitor Compensator

i s

ControlSignals

SmartController

*V s

Ps

SMPFDifferent

Topologies

Nonlinear Load (NLL)

* Smart-controllers arebased on specified control

objectives

eight designs(Dr. A.M. Sharaf) YF (TAF, C-Type, HPDF, Special Topology)

TOTAL HARMONIC DISTORTION

• The ratio of the root mean square of the harmonic content to the r.m.s value of the fundamental quantity expressed as a percent of the fundamental.

TOTAL HARMONIC DISTORTION

WAVEFORM DISTORTION

• Steady-state deviation from an ideal sine wave of power frequency principally characterized by the spectral content of the deviation.

• 5 types of waveform distortion1. DC offset2. Harmonics3. Inter-Harmonics4. Notching5. Noise

WAVEFORM DISTORTION TYPES

ITI CURVE• ITI Curve ---- Information Technology

Industry Council Curve

• A set of curves published by ITI representing the withstand capabilities of computers connected to power systems in terms of magnitude and duration of the voltage disturbance.

CBEMA CURVE

• CBEMA ---- Computer Business Equipment Manufacturers Association.

• A set of curves representing the withstand capabilities of computers in terms of the magnitude and duration of the voltage disturbance.

• Standard for measuring the performance of all types of equipment and power systems.

CBEMA CURVE