UNIT – 1: INTRODUCTION TO POWER QUALITY TWO MARKS

3.1     Syllabus

 

EE 1004   POWER QUALITY                                                                                                    3 0 0 100

1.                  INTRODUCTION TO POWER QUALITY                                                                   3

Terms and definitions: Overloading, under voltage, sustained interruption; sags and swells; waveform distortion, Total Harmonic Distortion (THD), Computer Business Equipment Manufacturers Associations (CBEMA) curve.

2.         VOLTAGE SAGS AND INTERRUPTIONS                                                                  7

Sources of sags and interruptions, estimating voltage sag performance, motor starting sags, estimating the sag severity, mitigation of voltage sags, active series compensators, static transfer switches and fast transfer switches.

3.         OVERVOLTAGES                                                                                                          10

Sources of over voltages: Capacitor switching, lightning,  ferro resonance; mitigation of voltage swells: Surge arresters, low pass filters, power conditioners – Lightning protection, shielding, line arresters, protection of transformers and cables, computer analysis tools for transients, PSCAD and EMTP.

4.         HARMONICS                                                                                                                  12

Harmonic distortion: Voltage and current distortion, harmonic indices, harmonic sources from commercial and industrial loads, locating harmonic sources; power system response characteristics, resonance, harmonic distortion evaluation, devices for controlling harmonic distortion, passive filters, active filters, IEEE and IEC standards.

5.         POWER QUALITY MONITORING                                                                            13

Monitoring considerations: Power line disturbance analyzer, per quality measurement equipment, harmonic / spectrum analyzer, flicker meters, disturbance analyzer, applications of expert system for power quality monitoring.

L = 45   Total = 45

REFERENCE BOOKS

1.                  Roger.C.Dugan, Mark.F.McGranagham, Surya Santoso, H.Wayne Beaty, ‘Electrical Power Systems Quality’ McGraw Hill, 2003.

2.                  PSCAD User Manual.

3.2       Part A Questions with Answers & Part B Questions

UNIT – 1: INTRODUCTION TO POWER QUALITY

TWO MARKS

1.      Define power quality .

            Power quality has been defined as the parameters of the voltage that affect the customers supersensitive equipment.

2.      What are the commonly used terms that describe the parameters of electrical power that describe or measure power quality.

                  Sag, swell, interruption, transients, harmonics, waveform distortion, over voltages, under voltages, voltage imbalance, power frequency variations, etc.

3.      What is the most common power quality problem.

                  Voltage sags are considered the most common power quality problem.. These can be caused by the utility or by customer loads. When sourced from the utility , they are most commonly caused by faults on the distribution system. These sags will be from 3 to 30 cycles and can be single or three phase. Depending on the design of the distribution system, a ground fault on 1 phase can cause a simultaneous swell on another phase.

4.      What is the second most common power quality problem.

Power quality problems are related to grounding , ground bonds and neutral to ground voltages, ground loops, ground current or ground associated issues.

5.      What type of equipment is affected by power quality issues.

                  All electrically operated or connected equipment is affected by power quality.

6.      What are the types of power quality solutions available on the market today.

  There are hundreds  of manufacturers making thousands of different power quality solutions today. The categories of these solutions are :

·               Utility based solutions for the substation level.

·               User based solution for whole facility protection.

·               User load level solutions for specific loads

7.      How can power quality problems be detected.

·               A  piece of equipment misoperates at the same time of day.

·               Circuit breakers trip without being overloaded.

·               Equipment fails during a thunderstorm.

·               Automated systems stop for no apparent reason.

8.      What are harmonics.

                  Harmonics are distortions in the AC waveform. These distortions are caused by loads on the electrical system that use the electrical power at a different frequency than the fundamental 50 or 60 Hz.

9.      How do harmonics affect the electrical system.

                  In general harmonics cause magnetic portions of the electrical system to overheat. Such as transformers, line reactors, magnetic relays and power factor capacitors.

10.  How do harmonics affect the load.

The affect of harmonics on loads varies a great deal and is dependent on the load

itself. Most loads are not affected by moderate levels of harmonics . Exceptions to this are loads that perform electrical measurements in the frequency domain of the harmonics.

11.  How do you measure power quality?

                  It requires power quality measurement equipment to measure , record and diagonos harmonic problems. Power quality instruments offer a service of characterizing all aspects of power quality and determining if it is acceptable to the load.

12.  Why is power conditioning needed?

Effective power conditioning will prevent the erosion of your equipment and by filtering out these harmful properties will substantially enhance its reliability.

13.  What types of equipment are affected by power line noise?

                  Any equipment based on semiconductor technology can be affected  which includes all computers , telecommunications PBXs and key systems, automated  manufacturing and design  systems, computerized medical equipment and point of sale terminals.

14.  Why are these transients or noise on the power line causing problems now?

                  Advances in digital logic technology have produced smaller and more sophisticated devices. This new generation of micro-circuitry is extremely dense and substantially more susceptible and transient damage.

15.  What represent quality of power?

                  This term covers technical aspects as well as non-technical aspects like the interaction between the customer and the network operator. Eg. The speed with which the network operator reacts to complaints, etc.

16.  What are the power quality issues?

                  Power frequency disturbances, power system transients, grounding and bonding, electromagnetic interference , power system harmonics, electrostatic discharge, power factor.

17.  Classify power quality events in short duration events.

·         Sag

·         Swell

·         Interruption.

18.  Mention the types of sag.

·         Instantaneous sag.

·         Momentary sag

·         Temporary sag.

19.  Mention the types of swell .

·            Instantaneous swell

·            Momentary swell

·            Temporary swell.

20.  List the types of interruption.

·               Sustained interruption

·               Momentary interruption

·               Temporary interruption.

PART – B

1.      What are the major power quality issues and explain them.

2.      Explain power quality and explain the reasons for increased concern in power quality.

3.      Explain the various types of power quality disturbances.

4.      Explain the impacts of power quality.

5.      Discuss in detail about sags and swells.

6.      Discuss in detail about transients.

7.      Define waveform distortion and explain the waveform distortion categories.

8.      Explain total harmonic distortion and total demand distortion.

9.      Discuss about the CBEMA curves and explain the events described in the curve.

10.  With a waveform sketch , explain the terms.

·         Voltage sag

·         Voltage interruption

·         Voltage swells

·         Sag with harmonics.