12/05/2011 | Autor / Editor: Francis Phang Steve Verret / Dominik Stephan
Every F&B plant requires continuous and very high volume production to remain profitable. As the cost associated with missed production volume will be substantial, any possibility of shutdown because of voltage sag should be eliminated.
In most industrialized countries with vibrant automated manufacturing sector, the electrical utility grid supply has been vastly improved with advanced technologies. It is no longer a question if factories are having power supplied to them, but how good the quality of power supplied to them. This advancement and improvement in utility supply has; for the past decade, brought up the two separate issues of Power Reliability (PR) and Power Quality (PQ). Power Reliability deals with the availability of electrical power whenever the switch is turned on, regardless of the quality of the power supply. Utility companies in industrialized countries are selling electricity with reliability that is measured in the number of ‘nines’. When utility companies sell 99.999 per cent reliable power (five ‘nines‘), this translates to about five minutes of no power
in one year.
Power Quality; on the other hand, describes how ‘clean’ the power that has been supplied to the users. If the magnitude of power supplied is often short of the rated nominal voltage, or the waveforms are distorted, this can be described as having poor Power Quality. The advancement of electronics, IT and control technologies, has revolutionized the manufacturing processes with sophisticated automation systems. The manufacturing systems have evolved from mainly manual and mechanical based systems to highly efficient and automated systems that have high content of electronic controls and processes.
Mechanical based systems are often more tolerant of having not so perfect power supply, and that is the reason why the quality of power supply has not been looked into in the past. With the introduction of electronic automation system on the manufacturing floor, it has become more sensitive and demanding on the quality of the power supplied to the factory.
Extensive studies have been carried out by the utilities companies and the manufacturing companies on Power Quality issues. It was found that 98 per cent of all power quality problems are voltage sag that last not more than five seconds. It is defined as a reduction in voltage magnitude below a sag magnitude threshold with duration typically from several cycles to several seconds. There are several incidents that can cause voltage sag event. Stormy weather, utility switchgear failure, human handlings errors, hindrances caused by animals etc., are some of the most common causes of voltage sag.
These events are beyond control for both the plant operator and the utility company. There are steps that the utility companies can take to minimize the occurrence of voltage sag event, but total elimination is almost impossible. Plant operators will have to actively implement appropriate mitigation techniques to prevent their process from being impacted by voltage sag, instead of demanding the same from utility companies.
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