Power Quality issues in electrical power distribution systems

Power Quality issues in India distribution system

Quality is a perception, and if consumers are happy with the things/service delivered to them, then one can say that things/service is of good quality. In respect of electric power, the consumers had less awareness and information 30 years ago. Now, as more and more people are using electrical gadgets, for various reasons, Power Quality is a major expectation from all section of people. Most of the consumers are worried about scheduled/unscheduled load 

shedding, low voltage, Flickering (Brownouts), High voltage and Transients. The interest in Power Quality (PQ) is related to all three parties concerned with the power i.e. utility companies, equipment manufacturers and electric power consumers, and involves huge loss to the utilities 

and consumers. Since, mitigation of PQ problems  requires huge investments in generation, transmission and distribution, the Government of India and the respective State Governments have already started investing in all 

these three sections in phased manner.

 What is Power Quality and Why Power Quality is 

important?

It is the devoir of the utilities to supply the power at specified voltage and frequency and if they fail to do so then it is termed as inferior power quality. It is important to note that the consumer appliances are to be operated as per specifications. If there is mismatch between the 

specified values and actual values beyond the tolerance limit then it will impair the functioning of the appliances leading to adverse effect to the extent of failure of the appliances. Hence, it is a must to maintain the voltage and frequency at specified values. The typical sources of power 

quality are:

1.The power utilities, which create PQ problems, are also affected by it, in terms of financial loss as well as losing the consumer confidence.

2. Increased consumer awareness in the recent years, viz., earlier it was only ‘Light On’, now it is more.

3. Increase in Industrial automation and importance of productivity in a competitive global market.

4. Health of equipment and appliances

Classification and impact of Power Quality 

problems:

To make the study of PQ problems useful, the various types 

of disturbances need to be classified by magnitude and 

duration.

1. Complete interruptions : This is the major problem in 

India and the reasons are many:

✓Mismatch between Generation and Load, leading to scheduled and unscheduled load shedding. Many times, this happens because of overloading of transmission/distribution lines or power/distribution transformer and lack of redundancy in the infrastructure. Unscheduled load shedding is resorted to sudden drop in generation or technical problems in the local network. Frequent Local interruptions, the duration of which may be a fraction of an hour to 5-6 hours, occur due to line clear taken by local staff for line/transformer maintenance, tree trimming, system improvement works, etc. In such cases, industries and commercial establishments will face lot of inconveniences and suffer financial losses. The utilities themselves incur losses as they miss the 

opportunity to sell power during such interruptions. In India, no mechanism has been established to inform all the consumers affected in such cases regarding the possible duration of outage. They keep calling whatever number they have, only to get vague/no answers.

✓ Since transmission lines and distribution lines are laid for long distances, environmental (like rain and wind) related damages can happen any time in the year. In villages, lines run for distances ranging from 5 KMs to 30 KMs in the fields, forests or hills, making it more prone to line faults and difficult to access for fast repairs. Few, semi-skilled staff,accompanied by no or infrequent conveyance facility add further delay. In the city, congested roads, traffic and trees are the major impediments.

2. Flickering (over voltage fluctuations), spikes and surges i.e., Brownouts: the main causes are loose connections in the transformer bushings or line jumpers. Poor workmanship, overload on staff(less staff, more work) or starting of a large inductive load (welding machine). Frequent tripping can also be included in this category.

Frequent tripping occur when line is faulty and, the Master Unit Sub Station(MUSS) staff informs the O&M staff keeps on isolating bit by bit and the line trips again. During the testing of last bit, either the line gets charged or declared as permanently faulty, wherein the consumer will experience full restoration of power or 

complete darkness, respectively.

✓ Low Voltage: This occurs during the overload of transmission line or distribution line. Most of the lamps and electrical gadgets do not operate during low voltage. Single Phasing also can be included in this category, which occurs when a line jumper is cut or a High Tension (HT) side fuse is blown in the transformer.

4. High Voltage: The consumer experiences high voltage when one phase in a 3 phase system fails , or when there is a loose connection in one bushing of the transformer, leading to severe unbalanced supply of 440 volts (instead of 230 volts) to few consumers. Many electrical gadgets will be damaged during such time.

✓Transformer Failure: Usually a minimum of 10% of the distribution transformers will fail every year in any utility. The number of consumers affected depends upon the capacity of transformer, viz., higher the capacity, more consumers are affected. The replacement may take 5 hours to 24 hours or more, depending upon the availability of staff/ crane, number of transformer failed on that day/ availability of good/ repaired good transformers, and time of transformer failure ( if it has failed in night time, the replacement initiation itself may start on the next day morning). 

Sometimes, power transformer may fail, which is rare compared to distribution transformer failure, leading to interruption to a larger area.