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Article Date: 4th November 2013

ABB enables Essex & Suffolk Water to make Savings by Improving Power Factor

Power Factor - Power Quality - Energy Management - Power Systems

ABB PFC Capacitors

ABB’s specialist power quality products have enabled Essex & Suffolk Water (ESW) to solve power factor issues affecting the power supply at a pumping station in Essex.

The pumping station is a major clean water pumping station built in the 1930s, which supplies ESW’s customers in south west Essex and the east London with water sourced from the River Stour near Colchester. The site is equipped with three pumps, each of which is powered by a 335 kW DC motor and variable speed drive system.

ESW called in its long-term contractor Mid Kent Electrical (MKE) to investigate some issues with the DC drive systems. MKE is an ABB Motor Service Partner and member of the ABB Drives Alliance.

During its investigations, MKE found that the Power Factor Correction (PFC) capacitors installed within each of the drive systems had failed, leading to poor power factor on site and a high demand for reactive power, which resulted in high charges for reactive power from the electricity supplier.

Power factor
Power factor is the ratio of “real” power that is used by the businesses to do actual work, in this case pumping water, compared to the “apparent” power that needs to be supplied by the electricity supplier. It is often seen as a measure of electrical efficiency, a power factor that is equal to one demonstrates that power is being consumed with 100% efficiency.

One way of thinking about it is that the power you buy comes in two distinct parts, just like a frothy latte. The coffee body is the ‘active power’ that you can use to do work, while the froth on top is what we call ‘reactive power’. Some is useful but too much reactive power is simply a waste, the same as the foam you leave behind in your glass.

What causes poor power factor?
Equipment such as AC motors, arc welders, furnaces, fluorescent lighting and air conditioning can cause a poor power factor. The more inductive loads like these that you have on your network, then the more likely it is that you will have a poor power factor.

This happens when the equipment being used on site causes the voltage and current waveforms to be out of phase with each other.

A low power factor leads to energy loss through heat, which shortens the life of equipment. It also reduces the capacity of cables and equipment such as supply transformers and switchgear.

All UK electricity suppliers impose penalty charges when power factor is lower than 0.9 because of the extra power they need to supply and most now impose them when it is lower than 0.95.

Correcting the site’s power factor
In the case of ESW’s pumping station, the PF had dropped to 0.78, leading to a demand for reactive power with a monthly cost greater than £200.

To correct the power factor, MKE installed a total of six new 92 KVAr capacitors, on the three DC drive systems. The capacitors are ABB’s CLMD type, which are designed for reliable power factor correction with low losses over a long life.

Installing the CLMD capacitors immediately improved the site power factor and reduced the monthly charge for reactive power to only a few pence.

Russel Kimpton, Drive Systems Engineer at MKE said: “Solving the power quality issues on any site is always the right thing to do. ABB’s PFC capacitors are reducing the site’s CO2 emissions by about 80 tonnes per year and enabling significant savings on the annual electricity bills.”

Having corrected the pumping station’s power factor, MKE also solved problems experienced at the site due to harmonics.

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