POWER QUALITY ISSUES 1.VARIOUS PROBLEMS 2. VOLTAGE SAG 3. MITIGATION USING AUTOTRANSFORMER

1. PRESENTED BY:
ROHIT VIJAY
M.TECH
PGICE1650127
POWER QUALITY ISSUES

2. CONTENTS
 INTRODUCTION
 DIFFERENT ISSUES
 VOLTAGE SAG ANALYSIS
 VOLTAGE SAG MITIGATION ANALYSIS
 REFERENCE

3. INTRODUCTION
 Modern society is heavily dependent on the electric
supply.
 Electric power delivered is characterized by two
factors namely- “continuity” of supply and the
“quality” of voltage.
 According to IEEE Standard 1100, power quality is
characterized as “The idea of controlling and
establishing the touchy supplies in a manner that is
suitable for the operation of the gear.”

4. DIFFERENT ISSUES
 Interruptions: It is the failure in the continuity of
supply for a period of time. This is defined by IEC
(International Electro technical Committee) as “lower
than 1% of the declared value” and by the IEEE as
“lower than 10%”.
 Short Interruption: of few mille seconds.
 Long Interruptions: few mille Seconds to several
seconds

5.  Waveform Distortion: sinusoidal nature is not maintained.
Example DC Offset and Harmonics
• Frequency Variations:. The frequency of the framework is
identified with the rotational rate of the generators in the
system. The frequency variations are caused if there is any
imbalance in the supply and demand.
• Voltage Sag: the voltage level by 10% to 90% for a period
of half cycle or more.
starting of an electric motor, which draws more current
Faults in the power system
Sudden increase in the load connected to the system

6.  According to standard IEEE 1346-1998, Voltage Sag is
defined as-A decrease in rms voltage or current at the
power frequency for durations of 0.5 cycle to1 min.
typical values are 0.1 to 0.9 pu.”

7.  Characteristics of Voltage Sag: magnitude, duration
and phase angle jump.
 The short circuits in power system not only cause a
dip in voltage, but also change the phase angle of the
system. The change of phase angle is called as “Phase-
Angle Jump”. It causes the shift in zero crossing of
the instantaneous voltage.

8. Voltage Swell:
The under voltage or voltage sag is the prominent one
as it occurs often and affects the power system
network largely.

9. VOLTAGE SAG MITIGATION ANALYSIS
 During the Production of Equipment: The device
manufacturers use a specific curve like ITIC
(Information Technology Industry Council) curve
during manufacturing.
 Power Conditioning Equipment: These devices may
be connected at the source side or in the transmission
network, or at the load end. In general, these devices
are connected at the point of common coupling (PCC)
where the load is connected to the supply. This is done
as the cost of the power conditioning device increases
from load end to source side.

10.  Line-voltage regulators: tap changing transformers,
CVT’s, buck-boost regulators etc.
 SVC (Static VAR Compensators)
 UPS (Uninterruptible Power Supplies)
 Custom Power Devices:- Dynamic Voltage Regulator
(DVR), D-STATCOM, autotransformer.

11.  Auto-Transformer:- The auto transformer is
controlled by a PWM operated power electronic
switch.

12.  An IGBT Switch
 Auto-Transformer
 Ripple Filter
 Bypass Switch

13.  Control Strategy:
 Advantages: • Less cost
• Less number of switches required
• Reduced gate driver circuit size
• No energy storage device

14. REFERENCE
 POWER QUALITY ISSUES AND THEIR MITIGATION
TECHNIQUES 1SUMAYYA SHAHEWAR, 2RAVI
MALOTH, 3S.SUSHMALATHA.
 MCGRANAGHAN, M.F.; MUELLER, D.R.; SAMOTYJ,
M.J., "VOLTAGE SAGS IN INDUSTRIAL
SYSTEMS," INDUSTRY APPLICATIONS, IEEE
TRANSACTIONS ON , VOL.29, NO.2, PP.397,403,
MAR/APR 1993.
 ELECTRICAL POWER SYSTEM SECOND EDITION
C.L.WADHWA

15. THANK YOU