Power quality in industrial and commercial systems

Lecture in power quality

Nowadays, the quality of the power supply is very important consideration for both power utilities and consumers. Electrical engineers have always been concerned about power quality. They see it as anything that affects voltage, current, and frequency of power being supplied to end-users.

A power quality (PQ) problem is defined as any problem that causes voltage, current, or frequency deviations in the supply and may result in failure or mal-operation of end-user equipment.

It should be noted that in the majority of cases, power quality actually refers to the quality of the voltage.

Although such standards are often used as benchmarks, there is no agreed definition on how to accurately quantify power quality. The ultimate measure is determined by the performance and productivity of end-user equipment.

Historically, PQ and reliability were synonymous. In early days, the main concern was about “keeping the lights on”. Various measures were applied to protect power system: use of surge arresters and circuit breakers, redundancy, computers checking power flow and transient stability, etc.

Since the late 1980s, the emphasis has shifted from reliability concern at generation, transmission and distribution level to concern about PQ at the customer or end-user level.

There are four major factors that cause an increased need to solve and prevent power quality problems:

1. Increased use of power quality-sensitive equipment
2. Increased use of equipment that generates power quality problems
3. Increased inter-connectedness of power system
4. Deregulation of the power industry

Reliability measures for distribution systems

One reliability measure is the supply availability, defined as the time that supply is available to customers. Expressed as a percentage, with 100% indicating no supply interruption. In 2000/2001, average number of minutes EnergyAustralia’s 1.4 million electricity customers were without supply was 101 minutes.

This corresponds to a supply availability of 99.98%, i.e. supply availability is less than 4 nine’s.