other power quality issues- - copy

8/2/2019 Other Power Quality Issues- - Copy

1/16

Click to edit Master subtitle style

4/16/12

Other Power Quality Issues-

Voltage Variation,Voltage Steps,Voltage fluctuations andLoad currents

RAJ MOYAL

EE-084022


2/16

4/16/12

CONTENT

WHAT IS POWER QUALITY

PQ PROBLEM

WHY PQ IS SUCH A BIG PROBLEM

VOLTAGE VARIATIONS

VOLTAGE STEPS

VOLTAGE FLUCTUATIONS

LOAD CURRENTS


3/16

4/16/12

WHAT IS POWER QUALITY

The term Power quality is used

to describe the extent of

variation of the voltage, current

and frequency on the power

system. The variation of voltage


4/16

4/16/12

Power Quality problems

Definition.

P.Q. problems is any power problemmanifested in voltage , Current ,orfrequency deviation that result infailure or miss operation of Costumerequipment.e.g.

Surges and spikes (overpowering).

Harmonics ( current & voltage )

Voltage Fluctuations.

44


5/16

4/16/12

Why PQ is such a Big Problem?

The sensitivity of todays electronicequipment makes it susceptible to

power disturbances.

For some devices, a momentarydisturbance can cause

scrambled datainterrupted communications

system crashes and equipment failure


6/16

4/16/12

Voltage Variations

It is slow variation in rmsvoltage,mainly due to the daily loadvariations.

Types of voltage variations-

- - Sag

- - Interruption- - Overvoltage


7/16

4/16/12

Sag a decrease in RMS voltagelasting

from a half-cycle to a few seconds.


8/16

4/16/12

Interruption complete loss of

voltage.


9/16

4/16/12

Overvoltage an RMS increase involtage

lasting more than a few seconds.


10/16

4/16/12

Voltage Variation Sources

Supply side variations

Short circuits

Capacitor switching Load switching

Regulator malfunction

Load side variations

Motor starting


11/16

4/16/12

VOLTAGE EVENTS

DISTURBANCE EFFECT

Overvoltage Overstress insulation

Under voltage Excessive motor current

Unbalance Motor heatingInterruption Complete shut-down

Sag Variable speed drive & computertrip-out

Swell Overstress insulation

Fluctuations Light flicker


12/16

4/16/12

Voltage Steps

It is sudden change in rms voltagedue to transformer tap changeroperation,load switching

situation,and switching of shuntcapacitors and inductors.

Voltage steps exceeding a certainthreshold need to be considered inany performance criterion.


13/16

4/16/12

Voltage Fluctuations

It is change in rms voltage on a veryshort time scale(seconds or less) due tofast variations in the load current.

It will lead to variation in the intensityof lightning,a phenomena called lightflicker.

Light flickering exceeding certain level


14/16

4/16/12

Well defined standards have beendeveloped to determine whether acertain voltage fluctuation will leadto light flicker:the so called

flickermeter concept.

As voltage fluctuations are due toload variations,responsibility restswith customer behind the loadvariations.


15/16

4/16/12

Load Currents

Current disturbance,both variations andevents is a problem when they do notlead to any voltage

disturbance.e.g.reactive component ofthe current.

This will lead to an increase in losses in

the system,and(variation in rms)requires overratings of seriescomponents like cables and

transformers.


16/16

4/16/12

THANKS

other power quality issues- - copy

Documents