Getting more from the motor

According to legend, the American industrialist Henry Ford once said: "If you need a machine and don't buy it, then you will ultimately find that you have paid for it, but don't have it".

As time passes, inefficient industrial machines consume more and more costly energy and begin eating away at budgets. In developed economies, it is estimated that electric motors account for about half of the total energy consumed.

Variable speed drives (VSDs) can reduce the energy bill on many motor-driven systems by more than their own capital cost in a relatively short period, often in less than a year. As energy prices continue to soar, the return on investment on a VSD application increases in proportion to the bill.

False economy

Failing to invest in VSDs, as part of any system that incorporates an electric motor, will cost money in the long term - far more money than simply paying for the VSD in the first instance. As Steve Brambley, deputy director of trade association GAMBICA, explains, 97 per cent of the lifetime costs of a motor come from the energy it consumes. "Running old or inefficient equipment is a false economy. The real barrier to investment is the understanding of the lifetime cost of a system at a corporate and financial level. In contrast, I think engineers readily accept the benefits of motor control."

VSDs are particularly beneficial in variable torque load applications, such as fans and pumps where the output is controlled by other means such as inlet or outlet throttling, or damper adjustment. For example, savings of up to 50 per cent of energy use are achievable by reducing the motor speed of a fan or pump by 20 per cent.

Surprisingly, it is still common to find industrial cooling systems using fans driven by motors that are started direct on-line, running at constant speed, with the output of the fan being controlled by a variable mechanical damper. The fans are often vastly over-specified and the damper needed to reduce the excessive output.

Despite the surprisingly low take-up in the intervening years, wind back a couple of decades and motor drives were all the rage. Seemingly every week, new technologies were coming on-stream, new variations on the electronic methods of controlling the output and efficiency of electric motors.

But as the drives market matured, technology advances gave way to commodity items. Differentiation between products became less to do with technical innovation and more about price and customer service - factors of great interest to purchasing managers and finance directors, but not likely to excite the engineer.

During that time, the SPS Drives Exhibition in Nuremberg Germany, last held in November 2014, has also evolved - from a table-top exhibition supporting a high-level technical conference into a nine-hall automation extravaganza. So amongst the grey suits of the marketing executives, how much genuine innovation is on show? Should engineers attend the show, or is it now the province of the buyers of commodity items?

In truth, of course, the answer lies somewhere in between, as exhibitors recognise. "Today's consumers expect their products, however sophisticated, to be intuitive, readily available, quick to set up and safe to use," says Nigel Dawson, product manager for electric drives at Festo. "Naturally, this expectation has spread into the world of industrial automation, but what does the future hold for electric drives? Currently, there are three trends that are dictating development: speed and ease of specification, simplified control and maintenance, and machinery safety."

Simpler and safer

How can vendors help to reduce the time taken for engineers and machine builders to dimension and select their products?

Festo's Optimised Motion Series of electric drives is based on the principles of being instantly accessible and easy to use. By using an intuitive online configuration tool, the specification and selection process can be made simple, and to help sizing selection a range of pre-defined and tested combinations with all of the necessary data is available. For simpler ordering, the complete drive package - comprising mechanical system, motor and motor controller - is available with just a single part number. And, for easier assembly, the motor and mechanical system are integrated.

The second trend is for simplified control and maintenance: via the web browser, engineers and machine builders can source electric drives that are easy to commission, program and maintain. The expectation is that the drives are easy to set up and control, without the need to purchase additional specialist programming cables and software.

A standard Ethernet CAT5 cable, which is relatively cheap and readily available, connects directly into the controller from a standard laptop and, using the controller's IP address, the user commissions it, just as one would do when setting up a home router. This web-based configuration makes control simple, as it uses the basic principles of solenoid valve technology. The diagnostic function, also accessed via a standard web browser, supports simplified maintenance.

The final trend which is influencing the sector is machinery safety. But the issue highlighted by Dawson is that the machinery safety industry is focused on electrically and electronically monitored systems that end at the motor. The question is who is monitoring the mechanics? Here, Festo has developed an overall safety concept integrating clamping modules and linear feedback systems onto its EGC axis range. These mechanical measures, combined with safety functions in the drives and motors and specific electric drive safety controllers, allow engineers and machine builders to create fully certified systems from a single supplier with full documentation and circuit diagrams.

Smart motors

Sometimes referred to as 'smart motors', integrated motor-drive units unify the functionality of a motor, VSD and control unit. They are usually available in sizes up to 11kW.

The integrated units can interface with transducers and analyse and react to different load conditions without needing to feed information back to a central control system. This can result in a faster response time, lower cabling losses and space savings.

The Lenze Smart Motor, which was on show at Nuremberg, is aimed at the materials handling and conveyor markets. By adding intelligence to asynchronous motors, the Smart Motor is designed to run at a fixed speed, but not necessarily at a single speed. Up to five speeds between 500 and 2600rpm can be programmed, and switching is by digital signal. Speed setting is by Android smartphone using contactless NFC (Near Field Communication), and can be done even before the motor is powered for the first time.

Immediately this can generate cost savings by reducing the number of variants of geared motors used on a machine. Instead of several drives with different gear ratios, a single model of Smart Motor can be used with different programmed speeds. Aside from the wide speed setting range, the electronics also achieve high starting torques, soft start and stop ramps, also saving energy. High starting torque is achieved by an exact match between the drive electronics and the motor. Typically for a pallet conveyor this can allow the use of a motor with a size 80 frame instead of a 90 frame. Once up to speed the smaller motor will run nearer to its rating and therefore with higher efficiency, saving energy.

In terms of purchase cost, the Lenze Smart Motor falls between that for a standard motor and one equipped with a variable speed inverter drive. A closer comparison for cost would be with a two-speed motor and here the Smart Motor scores, particularly with its adjustable soft start and stop ramps, and motor thermal protection.

The Smart Motor is available as a package with the new Lenze g500 range of gearboxes. There are three different configurations - helical, shaft-mounted helical and helical bevel - with outputs up to 600Nm. These gearboxes are smaller and lighter than previous models, but also offer high efficiency at around 96 per cent.

Soft starters

To help save energy, it is sensible to turn off a motor when it is not required. A soft starter is a convenient way to enable frequent stopping and starting. A motor will draw a high current from the supply as it starts up, but it is possible to fit a soft starter device that limits the start-up current and achieves a smoother acceleration profile. This extends the life of the motor by reducing wear on the mechanical parts and preventing electrical components from overheating. Consequently the maximum number of starts and stops per hour may be increased. Often the life of the driven machine will also be extended due to the reduced acceleration stresses at start-up.

On display at SPS was Eaton's new option for motor control, the PowerXL DE1 Variable Speed Starter (VSS). This combines the simplicity of a conventional fixed-speed starter with ability to vary the speed of the motor. VSS can be expected to be more in evidence in future, providing a reliable and cost-effective alternative for motor control that will be particularly useful for increasing energy efficiency in applications where fixed-speed starters were previously used.

"The Energy-related Products (ErP) Directive and the growing levels of machine automation are leading to the increased use of variable speed drives, even in comparatively simple applications," said Guido Kerzmann, product line manager at Eaton, Electrical Sector EMEA. "In many of these applications, however, particularly those involving pumps and fans, VSDs offer too much complexity and functionality, but ordinary motor starters provide no control over speed."

VSS is also a new approach to standards compliance in constant-speed applications where IE2 motors have to be used (as IE3 motors cannot be physically accommodated). Other applications where a VSS is beneficial include very high start frequencies or where there is a high thermal load on the motor.

Eaton is currently offering two sizes: the 45mm-wide slimline version is suitable for use with motors up to 1.5kW, while the 90mm model can be used with motors from 2.2kW to 7.5kW. Both models have internal motor protection functions as well as motor thermistor and short-circuit protection.

The PowerXL DE1 VSS offers trip-free operation that detects regenerative energy fed back from the motor and automatically allows for this. They also provide a DC braking function prior to start-up, which is particularly useful in fan applications. While the standard settings will be suitable in the majority of cases, for special applications there is a universal plug-in configuration tool that allows key parameters, including ramp time, motor protection and terminal arrangement, to be set by the user. Alternatively, the device can be configured using external keypads or via software.

Miniature EtherCAT Servo Drive

The Gold Twitter Nano Drive from Israeli company Elmo is worth considering for applications that require very high servo performance but are very limited with space. In addition, the device is rugged to meet the growing needs to mount the drives on the motor, next to the motor, or on the moving mechanical load, thus ensuring high servo performance and saving huge costs in hardware and cabling. The Gold Twitter runs optimally on any servo motor and operates in current, velocity, and advanced position modes. It supports any feedback sensor in single, dual and gantry loop configurations.

Weighing just 18g and less than 13cm³ in volume, the Gold Twitter delivers up to 4000W of qualitative power, ultra-high current (50A/100V). Advanced servo capabilities are backed up by support for EtherCAT and CANopen fieldbus communication standards, for deployment in a variety of application configurations, compliant with international safety, EMC standards and STO certification.

"At a record-setting power density while delivering ultra-high power of 4000W, we improved the efficiency by 200 per cent, reduced the volume by 75 per cent and increased the power density by more than 400 per cent," says Haim Monhait, Elmo CEO. "We're not aware of anything in the industry that approaches this power and size density. Based on the premise that the best way to dissipate heat is not to generate it in the first place, the Gold Twitter incorporates proprietary FASST (Fast and Soft Switching Technology), resulting in over 99 per cent efficiency with negligible EMI."

Easily set up and tuned using the Windows-based Elmo Application Studio II (EASII) software, the Gold Twitter servo drive can operate as a single-axis control or as part of a multi-axis control system in a distributed configuration real-time network. Expanded features include a powerful internal breaking shunt resistor and multi extended I/O interface.

Energy-efficient motors

Over and above deploying variable-speed drives, using high-efficiency motors can give additional significant cost savings if sized correctly and used in the right applications. Compared to a standard motor, a high-efficiency model can be up to three per cent more efficient. For example, a 90kW high-efficiency motor could cost £1,200 more to buy than the standard model, but will save £12,000 during a 10-year service life. Think of what a plant with hundreds or even thousands of motors could save.

WEG is a motor company, headquartered in southern Brazil, but which is active in Europe with its range of energy-efficient motors. It is a major supplier to the Middle East region, especially in the oil and gas sector. It is also a strong contender in the UK water treatment industry.

The UK Water Industry Mechanical and Electrical Specifications (WIMES) define the requirements for mechanical and electrical equipment. The guidelines enable the user to select motors now which not only comply with the second stage of the EU Regulations, but offer increased levels of efficiency, lower running costs and reduced CO2 emissions. The specification defines the requirements for the performance, design, construction and testing of three phase, low voltage, squirrel cage, totally enclosed, fan cooled, induction motors for use in the water industry. The standards are reviewed every three years, ensuring they are up to date.

WEG's WIMES-compliant W22 line is available in two versions, designed to meet the IE2 (High) and IE3 (Premium) efficiency classes. Importantly, the IE3 Premium Efficiency versions of the motors are available now, in standard IEC frame sizes, well in advance of the next phase of the EuP Motor Regulations, currently due for implementation in 2015/2017.

This year, WEG launched its W22Xd Super Premium Efficiency range of hazardous area motors, which are claimed to be the most energy-efficient flameproof motors on the market. "Energy efficiency is becoming an increasingly important topic in the Middle East," says Colin Cox, managing director WEG Middle East. "The region is incredibly proud of its development over the last 20 years and as it continues to look to move towards a more sustainable future, energy efficient motors will further establish the region as an efficient user of the world's resources as well as contributing to a company's bottom line."

The W22Xd hazardous area motors are designed for use in aggressive and explosive atmospheres, while exceeding IE4 energy efficiency levels with minimised noise, vibration, and low operating temperature for increased reliability and safety. They are available in sizes 3.0-1000kW for gas groups IIA, IIB and IIC.