P O W E R Q U A L I T Y I M P R O V E M E N T U S I N G D V R

P R E S E N T E D B Y

A . S . S A I S U M A N T H( 1 2 R 9 1 A 0 2 4 8 )

TEEGALA KRISHNA REDDY ENGINEERING COLLEGE

A TECHNICAL SEMINAR

ON

Technical seminar coordinatorsMr A. Naga Sridhar Asst. professor

Mr B. Ramesh Asst. professor

Head of the departmentProf P. Krishna

ABSTRACTPower quality is one of major problems in the today’s

scenario. It has become important with the introduction of complex devices, whose performance is very sensitive to the quality of power supply. Power quality problem is an occurrence developed as a nonstandard voltage, current or frequency that results in a failure of end use equipment. Some of the major problems dealt here is the power sag and swell. This paper describes the effectiveness of using dynamic voltage restorer (DVR) in order to mitigate voltage sags and swells in low voltage distribution systems. Dynamic Voltage Restorer can provide the most cost effective solution to mitigate voltage sags and swells that is required by customer. The Dynamic Voltage Restorer (DVR) is a rapid, flexible and resourceful solution to power quality problems.

INTRODUCTION• Power quality is of great importance in all

modern environments where electricity is involved • It has become important with the

introduction of complex devices, whose performance is very sensitive to the quality of power supply. • Power quality problem is an occurrence

developed as a nonstandard voltage, current or frequency that results in a failure of end use equipment. • These problems may cause the apparatus

tripping, shutdown commercial, domestic and industrial equipment, and miss process of drive system.

Extensive use of sensitive electronic equipment has increased power quality problems like 1.Transients

2.voltage sag

3.voltage swell

4.voltage interruption

DYNAMIC VOLTAGE RESTORERThe Dynamic Voltage Restorer (DVR), also referred to as the Series Voltage Booster (SVB) or the Static Series Compensator (SSC), is a device that utilizes solid state (or static) power electronic components, and is connected in series to the utility primary distribution circuit. • Dynamic Voltage Restorer is a power electronic device that can protect sensitive loads from various disturbances in the power supply.

• The basic principle of a DVR is simple, by supplying a voltage of desired magnitude and frequency, the DVR restores the load voltage to a desired pre-sag voltage quantity even when source voltage is not balanced.

• Circuit Diagram of DVR

• Equivalent circuit diagram of DVR

BASIC CONFIGURATIONS OF DVRDVR comprises of three main parts1. Voltage

injection transformer2.Energy storage unit3. Inverter4.Passive filters5.By-pass switch

• Description: A decrease of the normal voltage level between 10 and 90% of the nominal RMS voltage at the power frequency, for durations of 0.5 cycle to 1 minute.

Causes: • Faults on the transmission or distribution

network (most of the times on parallel feeders).

• Faults in consumer’s installation. • Connection of heavy loads and start-up of

large motors.Consequences: • Malfunction of microprocessor-based

control systems(PCs, PLCs, ASDs, etc.) • Tripping of contactors and relays • Disconnection and loss of efficiency in

rotating machines.

THREE-PHASE SAG VOLTAGES

VOLTAGE SWELL• Description: Momentary increase of the

voltage, at the power frequency, outside the normal tolerances, with duration of more than one cycle and typically less than a few seconds.

Causes: • Start/stop of heavy loads• badly dimensioned power sources• badly regulated transformers (mainly

during off-peak hours).Consequences: • Data loss, flickering of lighting and

screen• stoppage or damage of sensitive

equipment if the voltage values are too high.

THREE-PHASE SWELL VOLTAGES

ADVANTAGES• DVR is mostly preferred because it is less

expensive. If compared to DSTATCOM and UPS, DVR is a lot cheaper. • UPS requires a lot of maintenance which may

be due to problems of battery leakage and replacement. • DVR is small in size and is a better power

effective device as compared to others link UPS, SMES and DSTATCOM. • DVR also compensates line voltage harmonics

LIMITATIONS

to keep its cost low as well as to reduce the voltage drop across it in standby mode.• In order to reduce the cost of DVR, the energy

storage size of DVR is kept low. Due to voltage dips, the stored energy can deplete fast and therefore to avoid load tripping due to insufficient stored energy, an adequate control is required.

• DVR has a limited current conduction and voltage injection capability ,due to such design of DVR

CONCLUSION• Therefore, when applying DVRs, it is vital

to consider 1.Nature of the load 2.Voltage supply 3.Transmission system• This also explains various advantages and

limitations related to DVR