Mitigating harmonics caused by Variable-frequency drives (VFDs)

ABB reveals secrets of harmonic mitigation at CWIEME Chicago

Global leader in power and automation ABB will use its seminar at the upcoming CWIEME Chicago exhibition to raise awareness of the negative impacts of line current harmonics – and how to reduce them.

 

Variable-frequency drives (VFDs) are a regular companion to electric motors in fan, pump and conveyor applications, allowing precise control over the speed, torque and direction of rotation for improved performance and energy efficiency. But with their many benefits also come a number of issues relating to power quality.

ABB seminar at CWIEME Chicago exhibition “Whenever power is converted from AC to DC – be that in a drive, welding equipment, computer power supplies or copy machines – the smooth, sinusoidal waveform of the current is lost,” explains Rick Hoadley, principal consulting applications engineer at ABB. “Along with the fundamental frequency in the current you also get other higher frequencies – known as harmonics –which distort the voltage on the transformer secondary, where other equipment might also be connected.”

How these harmonics are created, the effects they have and how they can be minimized will be the subject of a seminar by Mr. Hoadley at CWIEME Chicago, the Americas’ largest electrical manufacturing exhibition, happening between September 30 and October 1 at the city’s DE Stephens Convention Center.

“A lot of the time people hear the term harmonics and don’t really understand what it means and if it is a problem or not. My seminar aims to help them understand those issues, how they differ when a drive is powered from a generator rather than the utility, and how the power factor is also affected,” Mr. Hoadley says.

Hoadley emphasizes that the topic is not only of interest to those using or looking to purchase VFDs but also the wider electrical industry, where power converters are used.

“Transformer manufacturers, for example, need to understand harmonics because they affect the way transformers are designed and sized. Meanwhile, the power industries need to understand how harmonics and harmonic filters affect the way currents are drawn from generators. The seminar will help to answer questions such as: Are the transformers or generators sized properly? Have they selected the best type of filter for optimal performance with the drive?” Mr. Hoadley adds.

Too much or too little

There are three main problems that harmonics can cause. The first is to decrease the peak of the voltage, with the result that equipment expecting a certain voltage will not operate at peak efficiency. This can be a concern for many customers, especially those that may need to use VFDs for pumping water. Harmonics can easily cause as much as 10% more current to be drawn than is needed, meaning that the transformers and wires that carry the power will see a 20% increase in their losses. This can decrease the service life of equipment and some devices used by the utility. The life of power factor correction capacitors, can also be dramatically affected.

“Even if customers aren’t experiencing specific problems related to increased current, minimizing harmonics can reduce operating costs,” Mr. Hoadley says. “For example, a drive is drawing 330 amps from a transformer. The 330 amps is made up of 300 amps of fundamental current, and an additional 150 amps of harmonic current. Reducing the harmonics will lower the losses, improve the power factor, and allow for greater utilization of the transformer. This way you have an additional 30 amps to power other pieces of equipment. The reduction in losses and the improvement in the power factor lead to lower electric bills.”

Time runs away

As well as affecting the power that is delivered to equipment, harmonics, especially notches, can wreak havoc with counting systems. Electrical clocks or timers typically measure time based on the number of times the waveform crosses zero volts. Some drives, however, can create extra zero-voltage crossings, causing clocks to speed up.

“At one site I visited recently the time clocks went faster every time a piece of equipment was turned on. After one hour of work, the clocks would show two hours had elapsed, much to the operators’ amusement!” Mr. Hoadley says.

In all seriousness, unreliable timing systems could negatively affect quality or performance or even give rise to a safety risk.

A large part of Mr. Hoadley’s seminar will be dedicated to determining how much harmonic distortion is too much and what limits are suggested for different applications. Some methods for limiting harmonics will also be suggested, including passive and active filters and special phase shifting transformers.

“I’ve been working with harmonics since 1996 and they remain a concern for many customers. I’m looking forward to sharing some of my knowledge with new audiences at CWIEME Chicago and helping them to improve the performance, efficiency and profitability of their products and operations.”

Mr. Hoadley will be presenting his seminar on ‘Mitigating harmonics caused by VFDs’ at the CWIEME Connect Theater on Tuesday, September 30 at 16:30-17:10 CDT.

CWIEME Chicago – The Americas’ biggest showcase for the coil winding and electro-magnetic industry

Dates: September 30 – October 1, 2014
Venue: DE Stephens Convention Center, Chicago
Opening times: 10:00 am to 5:00 pm
Admission: Free

For more information and to register for the event, please visit www.coilwindingexpo.com/chicago

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