AALIM MUHAMMED SALEGH COLLEGE OF AALIM MUHAMMED SALEGH COLLEGE OF ENGINEERINGENGINEERING DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERINGDEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING

EE 1004 - POWER QUALITY

UNIT-I AN OVERVIEW

PREPARED BY A.MOHANASUNDARAM M.E., ASSISTANT PROFESSOR

What is power quality ?What is power quality ?

Any power problem manifested in voltage, current, or frequency deviations that results in failure or misoperation of customer equipment.What are the concerns for PQ?1.Newer generation load equipments2.Better efficiency3. Consumer awareness4.Interconnected system

Over voltageOver voltage

Daily Voltage Fluctuations

Voltage SagVoltage Sag

SwellSwell

HarmonicsHarmonics

TransientTransient

UnbalanceUnbalance

NotchingNotching

Power qualityEnd users industrial , commercial, and residential

The utilitiestransmission anddistribution suppliers

What is What is brownoutbrownout??A brownout is an intentional drop in voltage in an electrical power supply system used for load reduction in an emergency. This condition may be short term (minutes to hours) or long term (1/2 day or more). A power line voltage reduction of 8 - 12% is usually considered a brown-out. 

The term brownout comes from the dimming experienced by lighting when the voltage sags. A voltage reduction may be an effect of disruption of an electrical grid, or may occasionally be imposed in an effort to reduce load and prevent

a blackout

Distribution Voltage Regulation

Voltage Problem SummaryVoltage Problem Summary

Comparing Typical SolutionsComparing Typical Solutions

Power qualityPower quality

Power transformer have a magnetic circuit that is disrupted by the quasi-DC GIC: the field produced by the GIC offsets the operating point of the magnetic circuit and the transformer may go into half-cycle saturation.

This produces harmonics to the AC waveform, localised heating and leads to high reactive power demands, inefficient power transmission and possible mis-operation of protective measures. Balancing the network in such situations requires significant additional reactive power capacity.

The magnitude of GIC that will cause significant problems to transformers varies with transformer type. Modern industry practice is to specify GIC tolerance levels on new transformers.

On 13 March 1989, a severe geomagnetic storm caused the collapse of the Hydro-Québec power grid in a matter of seconds as equipment protective relays tripped in a cascading sequence of events. Six million people were left without power for nine hours, with significant economic loss. Since 1989, power companies in North America, the UK, Northern Europe, and elsewhere have invested in evaluating the GIC risk and in developing mitigation strategies.

A set of curves published by the Information Technology Industry Council (ITI) representing the withstand capabilities of computers connected to120-V power systems in terms of the magnitude and duration of the voltage disturbance.

The ITI curve replaces the curves originally developed by the ITI’s predecessor organization, the Computer Business Equipment ManufacturersAssociation (CBEMA).

Information Technology IndustryCouncil (ITIC)

Computer Business Equipment Computer Business Equipment Manufacturers Association (CBEMA) Manufacturers Association (CBEMA) curvecurve

Information Technology IndustryInformation Technology IndustryCouncil (ITIC)Council (ITIC)

Flicker has been described as"continuous and rapid variations in the load currentmagnitude which causes voltage variations." Theterm flicker is derived from the impact of the voltagefluctuation on lamps such that they are perceived toflicker by the human eye. This may be caused by anarc furnace, one of the most common causes of thevoltage fluctuations in utility transmission and distributionsystems.

STANDARDS AND GUIDELINES REFERRING TO POWER QUALITY

IEC 61000 Series of Standards for Power

Part 1 (General).

Part 2 (Environment).

Part 3 (Limits).

Part 4 (Testing and Measurement Techniques). Part 5 (Installation and Mitigation

Guidelines).

IEEE-519 Standard