PFC boosts Perkins' efficiency

Edited by the Engineeringtalk editorial team Nov 7, 2002

Although the Perkins Engines plant at Peterborough has always had power factor correction equipment, a survey of its substations found that, typically, the power factor was 0.8.

The Perkins Engines plant at Peterborough employs 3000 people and makes about 1000 engines and engine kits a day.

The plant is a substantial user of high-voltage supply and consumes about 8MW of electricity, distributed via seven substations within the Peterborough site.

With a high inductive load, typical of a manufacturing facility of its type, power factor correction is a major consideration for the company.

The electricity company for the region, in keeping with most others in England, now imposes a reactive energy charge - reactive energy (sometimes referred to as "useless" energy) is effectively the power used to energise the magnetic circuits in, for instance, AC motors.

By having an efficient power factor, substantial savings are made on the system, stresses are reduced throughout the system and there are some financial savings through reduced transformer losses.

While Perkins has always had power factor correction equipment, the requirement to improve that equipment had been identified.

The company therefore commissioned a survey of its substations and it was found that, typically, the power factor was 0.8.

It was clear there was high inductive load and scope for power factor improvement.

For example, the load through the transformers, once power factor correction equipment was fitted, dropped by an average of 20% with a significant reduction in stress on the system.

Perkins called in PFC Engineering from the earliest stage, including the initial surveys.

Subsequently, PFC completed a more exhaustive survey of all seven substations.

During the surveys, PFC also considered the harmonics within the system; as otherwise, the indiscriminate deployment of power factor capacitors can create harmful amplification of harmonics on the system.

This, in turn, can lead to damaging resonance, which can affect the system and harm equipment connected to it.

It was important to understand all these factors in order to design a balanced system.

Perkins Engines, like just about every plant in Britain, has witnessed an increased use in inverters for variable speed AC motor drives.

This has significantly increased the harmonic content of the lines.

Some of the circuits at Perkins that power these inverters also feed the offices where there are computers and other equipment, so line cleaning (harmonic filtering) was essential.

PFC Engineering therefore fitted reactors to certain substations within the Perkins plant to cope with the harmonic distortion - the combination of the line reactor specification and the capacitor size is an important consideration.

One substation has a harmonic filter that removes 75-90% of the harmonic distortion, and others use partial filters to remove, say 40-50% of the harmonics while providing an effective power factor remedy.

There are a significant number of PFC Engineering's power factor correction panels installed in all seven substations in the Peterborough site and most of these enable a power factor of between 0.9 and 0.97 to be achieved.

The losses and the stresses on the system have been reduced dramatically and the Perkins plant runs more efficiently as a result.

Stuart Neal, Perkins' electrical engineer who has overseen the work points out that: "While industrial sites must believe they have effective power factor correction installed, many would be surprised at their true position if they properly surveyed their installations".

Neal continued: "We have been delighted and impressed with the way in which PFC Engineering approached our own requirement.

The survey was expertly conducted and the recommendations were technically sound and realistic.

The quality and effectiveness of PFC's products is excellent and the company's service has also been exemplary".