May 23, 2017

The brake chopper size conundrum

Many drives manufacturers design and build their products with a seventh Insulated-Gate Bipolar Transistor (IGBT), in the form of a brake chopper, incorporated into the device. Here, John Mitchell, global business development manager of CP Automation, looks at the dangers of taking your IGBT for granted.

Manufacturers often include a brake chopper up to a certain size of inverter, but beyond that size, they will expect customers to use an external unit. However, to reduce the cost of the drive to the end user, the seventh IGBT isn’t necessarily rated to the full power rating of the drive itself.

Most inverter manufactures will argue that the cost benefit of not rating the IGBT to the full capacity of the drive is more than worth the loss of braking capacity. Furthermore, there is an argument that this is a legitimate design decision - manufacturers will claim that a very high percentage of end user applications don’t actually the full braking capacity.

In very light duty applications, such as emergency stop applications for instance, underrating the built in brake chopper wouldn’t be a problem. In fact, anything that is up to ten per cent duty will be very unlikely to suffer any kind of issue at all.

In contrast, any kind of application where the drive system has to stop and start regularly, such as an elevator or conveyor, needs to pay more attention to the brake chopper.

The real problem is not the manufacturer’s decision to install a low capacity IGBT but the decision not to make this information very clear in the manual and the accompanying documentation.

The key point in any application is that the mechanical stopping of the load is just as important as selecting the drive system.

For instance, a fifty-metre crane that lowers at half a metre per second will clearly take 100 seconds to lower fully. It may only do that twice a day, but when it does, it is operating at full capacity - not 30 per cent or 50 per cent. From a chopper and resistor point of view, that is a continuous period that the drive's onboard brake chopper couldn’t cope with.

The drive manufacturer might argue this only represents 20 per cent duty, but that’s where the application knowledge of the integrator or maintenance team becomes crucial. During the 100 seconds of descent, the application is dumping more and more energy and the resistors are getting hotter and hotter. It could be quite dangerous to attempt this kind of application with an inadequately sized internal seventh IGBT.

The bottom line is that brake choppers should be sized for the worst case, not the cumulative case. If you're worried you might be ignoring your drive applications, get in touch with your friendly automation maintenance and repair specialist today.

April 21, 2017

Increased efficiency for uninterruptable power supply


CP Automation now distributes and fits the REVCON boost converter module RSU as part of its range. This unit enables highly efficient uninterruptable power supply (UPS) of variable frequency drives (VFD). This compact power unit has huge cost saving implications for anyone that uses power loss ride through in their processes.

UPS systems provide an electrical supply that is converted from batteries when the mains supply is lost in situations such as brown outs, unstable supplies or emergency lift evacuations. The REVCON boost converter module RSU is set to change the way factories maintain their power supply.

"Traditional UPS systems lead the power to the VFD through the complete UPS application, even when power supplies are operating normally," said John Mitchell, global business development manager at CP Automation. "This results in unnecessary power losses due to rectification and invertation of the voltage.

"By adding a REVCON boost converter to the system, the UPS remains inactive when power supplies are working normally. This means the VFD is supplied directly by the mains, rather than having the middle-man UPS system causing unnecessary power losses."

When the mains power supply is down, the REVCON boost converter is activated and sets the voltage value from the batteries to the required level of the VFD. This maintains the power supply in the DC bus to the VFD, without any interruption.

This simple principle enables a highly efficient, yet inexpensive option for uninterruptable power supply to VFD drives. While conventional UPS systems have an efficiency of 90 to 95 per cent, adding a REVCON boost converter means the UPS setup will have efficiency greater than 99.5 per cent. This has huge cost saving implications for a range of industries that use power loss ride through in their processes.

CP Automation is available to supply and install the REVCON boost converter module RSU. For more information about CP Automation's catalogue of REVCON products, go to www.cpaltd.net.

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April 03, 2017

Common causes of electric motor failure


Modern electric motors may be more efficient and reliable than their ancestors, but they can still fail sometimes. Here, Martin McGuffie, service manager of Euroserv, sister company of CP Automation, explains the three common causes of electric motor failure and how maintenance staff can reduce the impact equipment failure can have on business.

How long do electric motors actually last before they break down? The answer is often disputed, with some manufacturers stating 30,000 hours and others suggesting they can power through for up to 40,000 hours. However, most manufacturers are in agreement that electric motors last much longer when maintained properly.

Understanding the state of an electric motor’s health requires a range of tools and techniques, as well as thorough record keeping and regular maintenance. This allows the engineer to identify trends or weak points more easily.


Weakened insulation

Nearly half of electrical failures in motors begin with weakening of the insulation around individual wires in the motor coils. This is often caused by thermal stress, contamination and movement of the winding due to the magnetic forces during start-up and shut-down of the motor.

Overheating can also cause the winding insulation to deteriorate quickly — for every ten centigrade rise in temperature, the insulation life is cut in half. Overheating can occur when the power quality is poor or when an electric motor is forced to operate in a high-temperature environment.

Contamination

Contamination is another one of the leading causes of motor failure. Contaminants include airborne dust, dirt or any abrasive substance that finds its way into the motor. When they come into contact with the motor, foreign bodies can cause denting of the bearing raceways and balls resulting in high vibration and wear.

Luckily, preventing contamination is fairly easy. Main sources of contamination include dirty tools, work areas and hands. Motors can also be contaminated by foreign matter in lubricants and cleaning solutions.

Engineers should keep work areas, tools and fixtures clean to help reduce contamination failures. Also, when laying out the space, companies should try to keep motor assemblies and operation areas away from grinding machines to reduce the amount of foreign bodies that might contaminate the motors.

Lack of maintenance

A well-planned preventative maintenance programme is the key to dependable, long-life operation of motors and generators. It also helps reduce unscheduled production stoppages or long repair shutdowns.

The first step towards preventative maintenance is understanding how often tests need to be carried out on the motor. This varies, depending on the age, condition and quality of the machine, as well as the environment it operates in.

Static tests are an easy method of identifying weaknesses within the motor winding. The tests focus on winding and insulation resistance, as well as turn-to-turn and phase-to-phase insulation condition. With the right equipment, these tests can be performed without taking the motor off site, thus minimising downtime.

Motor testing and analysis equipment, such as Euroserv’s SKF Static Motor Analyzer Baker DX, can survey all insulation and windings in AC and DC motors, coils and generators. During a site visit, Euroserv attends with the all-in-one tester, providing customers’ maintenance staff an analysis of the condition of the impedance, capacitance, phase angle, resistance, insulation and step voltage.

Motor failure can cause downtime, meaning companies can lose thousands of pounds every minute when operations are stopped. Instead of exposing themselves to downtime, customers should request regular motor testing and analysis, ideally every six months, to ensure their electric motors are healthy, efficient and reliable.

To find out more information about the SKF Static Motor Analyzer Baker DX, get in touch with Euroserv here.

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.