March 20, 2017

Don’t let harmonics get you down

In 1976, it was discovered that the bacteria causing Legionnaires disease, an atypical strain of pneumonia, had always been present in water, but it was the precise temperature of the water in heating, ventilation and air conditioning systems that facilitated the bacteria’s maximum reproduction levels. This is just one example of the unintended consequences of technology.

A similar and more recent story comes from the world of industry and features the growing problem of harmonic currents and utility level voltage distortion, as a result an increasing number of non-linear loads in industrial and commercial environments. Here, John Mitchell, global business development manager of CP Automation, shares his top tips for companies that want to commission or replace harmonic filters.

Active versus passive

The first thing you should decide is whether you need a passive or an active harmonic filter. The traditional option is an electro-mechanical or semiconductor controlled passive filter, used to minimise power quality problems in the network. These filters operate mainly on a fixed basis and are tuned to a harmonic order close to the order to be eliminated.

Often new equipment is specified to meet a THID%, but the problem for many plants is they do not know how bad their site is already. It’s almost like fixing a sticky plaster to a deep wound. Instead, companies should look at what is physically and commercially viable in the long term.

When making a decision, you can also consider a mixed solution. By fitting passive filters on many applications, you should be able to add a smaller active solution, which can save a lot of costs depending on the plant.

One drawback of passive filters is that they are most efficient when the load is operating above 80%.

On the other hand, active harmonic filters continuously monitor the network and inject exactly the right amount of compensation current when it is needed. The filter compensates the harmonic current or voltage drawn by each load. This allows current waveform to be restored instantaneously and lowers current consumption.

For installations in which current load changes constantly, active harmonic filters work best. They can filter harmonics over a wide range of frequencies and adapt to any type of load.

Regardless of what type of harmonic filter you decide to use, make sure it has the relevant UL certifications for the environment in which it's going to run. If unsure, you should always refer to an expert.

Holistic approach

Before commissioning a harmonic filter for your application, it’s important to assess the entire system, calculate the harmonics and size the right solution for your specific set up. It is not enough to look at one troublesome application individually; instead, you need to look at the plant or entire operation as a whole. Often what looks like the problem can actually be an effect rather than a cause.

Companies should identify and understand all the components installed on site when it comes to both linear and non-linear loads. They should also be aware of the transformer size and the rated short-circuit breaking current. Only after understanding the system in its entirety, can a company make an informed decision on what type of harmonic filter it needs, as well as what capacity and additional features the filter should have.

CP Automation recommends performing a survey of the plant and capturing as much information as possible over several days. After this initial analysis, we can recommend the most appropriate product and install it without significant disruptions.

After the harmonic filter has been live for a several days, another survey should be performed to check if all problems have been resolved. This ensures the product is appropriate and it gives companies real peace of mind.

The increasing levels of harmonic currents in industrial and commercial applications are certainly an unintended consequence of rapid technology uptake. Luckily, like the Legionnaires disease bacteria problem, the solution is simple, sustainable and inexpensive. Moreover, if you’re unsure of what harmonic filter your system needs, help is never too far away.

March 09, 2017

The road to energy efficiency starts here

Did you know the invention of robots dates back to XVth century? When Leonardo da Vinci explored the idea of the human body as a machine, he came up with a robotic knight - medieval armour designed with gears, wheels, pulleys and cables that allowed it to move its arms and legs. Premature inventions like this one populate the engineering landscape to this day, often when it comes to energy-saving technologies such as regenerative braking.

Here, Tony Young, owner director of CP Automation, explains how easy it can be to make industrial applications more energy efficient by using regenerative braking.

One solution suitable for many industrial applications, particularly in heavy engineering, transport, mining, the elevator market and other applications that involve a lot of braking and restarting is regenerative braking. When braking, an electric motor generates energy that can be used immediately in the local grid and thus reducing the draw from the mains supply.

In effect, this means turning your motor into a generator, converting mechanical energy into electrical energy, which can be fed back to the local network. The mechanism is extremely common in electric and hybrid vehicles where the energy is stored in the batteries and works particularly well in urban environments, where drivers tend to brake often enough to generate a lot of energy.

Lesser known applications of regenerative braking can also be found in industry. By using a regen unit like RevCon in engine test stands, transmission, escalators, power plants and many other applications that use continuous braking, you can regenerate the braking energy of the driven system, and feed it back into the network.

Regen power can be sized to the application; for a 90kW drive, for example, a 30kW regen unit could be suitable - because it rarely brakes at full capacity. The capacity range of regen can vary anywhere between 4kW and 300kW – the higher the capacity, the bigger the savings and the faster the payback. A good regen unit should work with any AC drive and should be easy to retrofit to any inverter, irrespective of design or manufacturer, due to its non-software driven installation protocol - plug and play so to speak.

RevCon can use a feed-in tariff similar to the ones found on domestic and semi-commercial wind turbines, to allow companies to charge the electricity supplier for the excess returned power, should the building not use the energy locally.

So why isn’t regen braking used in more industrial applications? Although the cost of regen units has gone down significantly over the last few years, they are still much more expensive than some of their alternatives. Like many other technologies that were ahead of their time, regenerative braking is likely to increase in popularity in the next few years. To stay ahead of the curve, companies should investigate the benefits of the technology sooner rather than later.