POWER QUALITY MODULE 5

1. WHAT IS POWER QUALITY

IT DETERMINES THE FITNESS OF A POWER SUPPLY SYSTEM

IT CAN BE A MEASURE OF RELIABILITY OF A SUPPY; or

IT CAN BE THOSE CHARACTERISTICS OF A SUPPLY THAT WILL ENABLE

A DEVICE TO WORK PROPERLY.

A POWER SUPPLY WHICH IS FREE FROM DISTURBANCES CAN BE

CONSIDERED AS A GOOD QUALITY POWER.

2.POWER QUALITY ISSUESTHOSE DISTURBANCES WHICH AFFECT THE POWER SUPPLY SYSTEM

“Any power problem manifested in voltage, current, or frequency

deviations that results in failure or misoperation of customer

equipment”.

2.POWER QUALITY ISSUES

3. CLASSIFICATION OF POWER QUALITY ISSUES1. Conducted low-frequency phenomena

a. Harmonics, interharmonics

b. Signalling voltages

c. Voltage fluctuations

d. Voltage dips and interruptions

e. Voltage unbalance

f. Power frequency variations

g. Induced low-frequency voltages

h. DC in AC networks

3. CLASSIFICATION OF POWER QUALITY ISSUES2. Radiated low-frequency phenomena

a. Magnetic fields

b. Electric field

3. Conducted high-frequency phenomena

A. Directly coupled or induced voltages or currents

B. Unidirectional transients

C. Oscillatory transients

3. CLASSIFICATION OF POWER QUALITY ISSUES4. Radiated high-frequency phenomena

a) Magnetic fields

b) Electric fields

c) Electromagnetic fields

5. Electrostatic discharge phenomena (ESD)

Sudden discharge between two electrically charged bodies

6. Nuclear electromagnetic pulse (NEMP)

The sudden burst of electro-magnetic radiation (EM Pulse) during nuclear

explosion will change the electric and magnetic field

4. TRANSIENTS“AN EVENT THAT IS UNDESIRABLE AND MOMENTARY IN NATURE”

2 TYPES : IMPULSIVE AND OSCILLATORY

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 (ositive or negative)

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

4. TRANSIENTSIMPULSIVE OSCILLATORY

4. TRANSIENTS

OSCILLATORY – 3 TYPES

High frequency transients (Frequency greater than 500 kHz).

Medium frequency transients (Frequency between 5-500 kHz).

Low frequency transients (Frequency less than 5 kHz)

CAUSE

Lightning

5. LONG-DURATION VOLTAGE VARIATIONS

•Variations in RMS value of voltages at power frequencies for

longer than 1 min.

LONG DURATION

VOLTAGE VARIATION

OVER VOLTAGE UNDER VOTAGE

5. LONG-DURATION VOLTAGE VARIATIONS

EFFECTS

• Hardware failures.

• Crashes in PLC and other

computerized equipment.

SOLUTION

• UPS.

• Power

Conditioners.

• Voltage

Regulators.

5.1 OVER VOLTAGE

“Increase in the RMS ac voltage greater than 110 percent at the

power frequency for a duration longer than 1min”

CAUSE

Switching off a large load

Energizing a capacitor bank

5.2 UNDER VOLTAGE

“Decrease in the RMS ac voltage less than 90 percent at the

power frequency for a duration longer than 1 min”

CAUSE

Switching ON a large load

De-energizing a capacitor bank

6. SUSTAINED INTERUPTIONS

Situation when the supply voltage is ZERO for more

than 1 min.

Requires human intervention to repair and restore the

system.> 1 min

7. SHORT DURATION VOLTAGE VARIATIONS

Def : • Short and temporary disturbances occurring in power system.

Cause:

• Switching on large loads

• Loose connections

• faults

Types:

• Voltage sag

• Voltage swell

• Interruptions

7. SHORT-DURATION VOLTAGE VARIATIONS

EFFECTS

• Hardware failures.

• Crashes in PLC and other

computerized equipment.

SOLUTION

• UPS.

• Power

Conditioners.

• Voltage

Regulators.

7.1 INTERRUPTIONS

“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”

CAUSE

Power system faults

Equipment failure

Control malfunctions

< 1 min

7.2 VOLTAGE SAG (DIP)

“A sag is a decrease in voltage to a value 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”

CAUSESingle line to ground fault

Switching ON heavy loads

Starting of large inductions motors

7.3 VOLTAGE 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”

CAUSE

Switching OFF heavy loads

Energizing capacitor banks

8. VOLTAGE FLUCTUATIONS

“Voltage fluctuations are systematic variations of the voltage to

a value between 0.9 to 1.1 pu”

CAUSE

Loads with continuous variation in current

SOLUTION

• Power

Conditioners.

• UPS

EFFECTS

• Hardware failures.

• Crashes in PLC &

computers

8. VOLTAGE FLUCTUATIONS

•Max Permissible Voltage Variation - 1.5%.

NOMINAL SYSTEM VOLTAGE (KV RMS)

MAXIMUM (KV RMS)

MINIMUM (KV RMS)

765 800 728

400 420 380

220 245 198

132 145 122

110 121 99

66 72 60

33 36 30

9. POWER FREQUENCY VARIATIONS

MAX PERMISSIBLE RANGE

49.2 to 50.3 Hz

“Deviation of the power system fundamental frequency from it

specified nominal value (e.g., 50 or 60 Hz)”

CAUSE

Poor speed regulation of alternator

EFFECTS

System crash

Speed variation in motors

SOLUTION

• Power

Conditioners.

• VDF, UPS

10. WAVEFORM DISTORTION

“Waveform distortion is defined as a steady-state deviation

from an ideal sine wave of power frequency principally

characterized by the spectral content of the deviation”

10. WAVEFORM DISTORTION

5 TYPES

HARMONICS

INTER HARMONICS

DC OFFSET

NOTCHING

NOISE

10.1 HARMONICS“Harmonics are sinusoidal voltages or currents having

frequencies that are integer multiples of the fundamental

frequency (usually 50 or 60 Hz)”

10.2 INTER HARMONICS

“Voltages or currents having frequency components that are not

integer multiples of the fundaments frequency are called inter

harmonics ”

10.2 INTER HARMONICS & HARMONICS

CAUSE

• Non-linear loads.

• SMPS used by personal

computers.

• VFD.

• Electronics devices.

SOLUTION

• Power

Conditioners.

• Harmonic filters.

EFFECTS

• Overheating

conductors and

transformers.

• Decreased efficiency.

• Increases losses

10.3 DC OFFSET

“The presence of a dc voltage or current in an ac power system

is termed dc offset”

10.3 DC OFFSET

CAUSE

• Fault in power

electronic devices.

SOLUTION

• DC Filters

EFFECTS

• Overheating of

transformers.

• Saturation of transformer

core

• Reduction in transformer

life.

• Corrosion of earth

10.4 NOTCHING

“Periodic voltage disturbance caused by the normal operation of

power electronic devices”

10.4 NOTCHING

CAUSE

• 3-phase power

electronic converter.

SOLUTION

• Isolation of

sensitive devices.

EFFECTS

• Injects harmonics to the

supply.

• Causes over heating

10.5 NOISE“Unwanted electrical signals with broadband spectral content

lower than 200 kHz superimposed upon the power system

voltage or current in phase conductors, or found on neutral

conductors or signal lines ”

10.5 NOISE

CAUSE

• Power electronic

devices.

• Control circuits

• Arcing equipments

• SMPS.

SOLUTION

• Isolation of

sensitive devices.

• Filters.

• Power

conditioners

EFFECTS

• Injects harmonics to the

supply.

• Disturbance in micro

controller, computers and

PLC.