power_quality_3 Seminar

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Detecting, Identifying, and Correcting Power Quality Problems


Abstract

In little more than ten years, electricity power quality has grown from obscurity to a major issue. Electronic converters and power electronics gave birth to numerous new applications, offering unmatched comfort, flexibility and efficiency to the customers. The technological advancement in electronic field resulted into sophisticated equipments. The use of such equipments is increasing day by day because of their advantages. These equipments are highly sensitive to poor power quality. These require reliable and good power quality free from all power quality issues.


However, their proliferation during the last decade is creating a growing concern and generates more and more problems: not only these electronic loads pollute the AC distribution system with harmonic currents, but they also appear to be very sensitive to the voltage distortion. Then, electricity power quality is becoming a major issue for utilities and for their customers, and both are quickly adopting the philosophy and the limits proposed by the new International Standards .
Today, recent advances in power electronic technology are providing an unprecedented capability for conditioning and compensating harmonic distortion generated by the non-linear loads. This new innovative active conditioner appears to be the easiest of use, the most flexible, the most efficient and cost effective one Power quality monitors assist the troubleshooter to identify and solve many power quality problems. Disturbance waveshapes from these monitors provide important clues toward locating the source of these problems. The paper presents examples showing how to analyze these clues, but also shows that similar disturbance waveshapes may still have radically different causes.



Introduction

The power quality problem is defined as any problem manifested in voltage, current or frequency deviations that results in mal-operation of customer equipment. The power quality problem causes the deterioration of performance of various sensitive electronic and electric equipments. The good quality of power can be specified as
The supply voltage should be within guaranteed tolerance of declared value.
The waveshape should be pure sine wave within allowable limits for distortion.
The voltage should be balanced in all three phases.
Supply should be reliable i.e continuous availability without interruption
Modern industrial machinery and commercial computer networks are prone to many different failure modes. When the assembly line stops, or the computer network crashes for no apparent reason, very often the electric power quality is suspected. It is a convenient culprit, as it is invisible and not easy to defend. Power quality problems may be very difficult to troubleshoot, and often the electric power may not have any relation to the actual problem. For example, in an industrial plant the faults of an automated assembly machine may ultimately be traced to fluctuations in the compressed air supply or a faulty hydraulic valve. Or in an office building, the problems on a local area network may be find their root cause with coaxial cable tee locations that are too close together, causing reflections and signal loss.




The role of monitors for troubleshooting power quality problems is undeniable. Industrial plant electricians will use disturbance analyzers to settle arguments about the quality of power, especially during the installation of new plant equipment when there are

inevitably a number of problems associated with the normal commissioning process. Disturbance analyzers, set to trigger on abnormal voltage conditions, allow the troubleshooter to determine if the electric power is to blame for the problem. Installing a power quality monitor after the event has already occurred does nothing to tell us about what had already happened. This is one of the chief frustrations of the power quality engineer.

Monitoring after the event has already happened tells us little about the past. So power quality disturbance analyzers are becoming a permanently installed feature of plant and substation equipment. This is done to respond to the important role power quality maintains in our increasingly automated society. It is done so that we have a record when things go wrong. Power quality monitoring can tell us a great deal about our power system health. We only need to be able to read and interpret the clues correctly. The paper provides examples of how do recognize these clues. It also gives guidelines for summarizing these results over a period of time.