Harmonic Series Michael

Awareness about harmonic distortion on electrical networks is growing, but there’s still a lot to be learned. In this article we take a look at how harmonic filters help to reduce this distortion, and when is best to apply them. 

Businesses of all types rely on clean electricity to power their operations. But it’s not about provenance, or its generation from a renewable source (not in this article, anyway). We’re talking about the quality of the electricity. 

Businesses rely on clean electricity that hasn’t been polluted by harmonics. 

The wrong kind of harmonics 

In music, harmonics can create a richer, fuller sound. These are the good kind of harmonics.  

On an electrical network, harmonics are a distortion of the electrical current that takes up capacity in cables and transformers. This can cause power quality problems that, over time, work together to damage a business’ profitability. Distortion in voltage, equipment and conductors overheating, misfiring in variable speed drives and torque pulsations in motors create multiple inefficiencies in the equipment on site. This compromises its ability to operate at optimum levels, creating more opportunity for failure. 

We’re discussing the bad kind. 

The main culprit behind harmonic distortion 

Variable speed drives (VSD) are one of the main culprits contributing to harmonic distortion. It occurs when a VSD converts AC to DC power using a diode rectifier, which draws harmonic current from the network. This current leads to distortion in the voltage and propagates through the network. 

While harmonic distortion from a single unit won’t necessarily be a problem, that’s not really what happens in practice. Plants and facilities usually have multiples VSDs, or larger units, which create larger and more complex harmonic problems for engineers to content with. 

How harmonic filters solve the problem 

As a manufacturer of VSDs, the team at Toshiba is well-placed to help businesses tackle their harmonic distortion issues head-on. With an in-depth understanding of the equipment, there are four key solutions they provide that will reduce, or eliminate, harmonics from a business’ electrical network: 

  • Toshiba manufacture VSDs with built-in harmonic filtering, utilising a DC choke that goes a long way to reduce harmonic current. Quite often, this is sufficient 
  • Adding to the built-in filter by installing an AC line reactor. Connected to the input of the VSD, this enhances the effects of the DC choke and further mitigating harmonics. No moving parts, no fancy electronics, just one simple component that does the job 
  • Instead of a standard drive with a diode rectifier, Toshiba provides VSDs with an active front end (AFE). Generally the simplest solution, this can virtually eliminate harmonics altogether 
  • Active harmonic filters. Also capable of virtually eliminating harmonics, typically one filter connects into the motor control centre and occupies a smaller footprint than a collection of AFE drives 

Or, alternatively, they do nothing. Because, sometimes, there are no appreciable harmonic effects caused by VSD.  

It’s all a matter of knowing why. 

While there’s a growing awareness about harmonic disturbance in the industry, there’s still a lot to be learned 

The biggest issue that is often seen is engineers simply throwing money at the problem by installing harmonic filters to make sure the problem doesn’t occur in the first place. And while this arguably does work, it also adds increasing complexity and cost.  

In a facility with hundreds of VSDs operating, installing equipment to filter out harmonics can add hundreds of thousands of dollars to the solution. It also reduces the overall reliability of the facility: you’ve added more parts to the equation, which means more opportunity for things to go wrong. 

It’s not simply a matter of injecting money into the problem. Harmonic distortion is best solved by keeping things simple.  

With their comprehensive understanding of VSD technology, the team at Toshiba take the time to undertake the right calculations first. They pay close attention to the drives they’re installing, understanding what the drives are generating and how much distortion they’re going to create. This allows them to identify which solution will work best, whether it’s a DC choke, an AC reactor solution or an active harmonic filter, and then including this at the right place in the design. 

With extra planning, based on their vast, real-world experience with their own VSD technology, this can save a business thousands of dollars. 

Managing harmonic distortion and fighting electrical pollution is a balancing act 

Toshiba’s harmonic filters are purpose-designed to complement their VSD technology. After all, in small numbers, VSDs don’t necessarily cause problems. But their popularity, and growing numbers and sizes of the componentry, means more harmonic distortion. 

Having the right harmonic filter technology is important; but having an engineering team who understand what’s going on, who can predict what the harmonic effects of componentry are going to be, and who can advise customers on the optimal solution that’s worth its weight in gold. 

This sponsored editorial is brought to you by Toshiba. For more information, visit toshiba.com.au

Featured image: Harmonic series amplitude over time. Courtesy of Toshiba. 

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