Half the world's electrical energy goes through electric motors, so it is likely that a lot of energy used by your organisation is being consumed by a motor. Imagine if a car that cost $15 000 consumed $3000 worth of petrol per week. That's the capital-to-operating cost ratio for electric motors. The key to improving efficiency is to consider: the efficiency of the actual motor its suitability for a particular task. The best way to maximise energy savings is to work backwards from the task to be performed to the power input of the motor, because large savings are the aggregation of many small savings made. Due to energy losses from the power plant to end use, efficiency gains multiply back through the process. For example, in an average system in NSW, for every kilowatt of energy saved at a pipe (by reducing friction), 2.4 kilowatts are saved at the motor and 8 kilowatts at the power plant. Therefore it is important to take a systems approach when looking at motor efficiency.

Save up to 40% of your energy costs by improving your motor system.

Taking Action

Looking at the System

The table below shows how energy losses accrue throughout the entire system.

By increasing the efficiency of all components in the system, including the motor, drive control, fans and ducts, the efficiency of the overall system can be increased by 30%. The motor 1.Do you need it? The first thing to think about is whether you actually need the motor at all. Reassessing the motor's function sometimes means you can do without it. Often a smaller motor can provide the necessary power requirements. 2.Can motor use be reduced? Reduce operating hours by installing: a simple time-switch to restrict the time that the motor runs. a calendar time switch which prevents a motor (e.g. in an air conditioning system) from running on public holidays and weekends. These switches can be linked to a Building Management System.

Install a time switch to ensure motors are only running when needed. Establish a regular maintenance program, including checking for excess heat emitted from motors and recording motor details. Install a Variable Speed Drive which allows the motor size to be closely matched to the actual load by changing the speed of the motor.

3.Do you have the right motor for the job?

• Cost

Many companies buy the motor with the lowest initial capital cost, but ignore its operating costs and energy efficiency. It is important to look at the entire life costs of the motor - including purchase price, installation costs and operating costs. By investing in a more efficient motor, the reduced operating costs achieved will far exceed the additional capital cost needed to buy one.

• High efficiency motors

Many motor manufacturers have two lines of motors-standard efficiency and high (premium) efficiency. "High Efficiency Motors" (HEM) are about 2-4% more efficient and offer lower operating costs and reduced energy consumption when compared to standard motors. For example, a 10 kW HEM may have an efficiency of 93 per cent, compared with the standard electric motor's 88 per cent-a saving of 5 per cent in both energy and greenhouse gas emissions. The reduction in electricity costs will usually recoup the extra money paid for a HEM in about two years.

Other benefits from HEMs include a cooler running temperature, thus reducing space cooling costs, and increasing grease life. They also maintain high efficiency over a wider range of loads and have a greater thermal tolerance (i.e. don’t heat up so quickly when overloaded).

It is important to match the HEM to the application because it operates at a slightly higher full-load speed than standard motors. This means that centrifugal loads, such as pumps, fans and compressors, can be affected by this higher speed, delivering more fluid and consuming more energy.

To avoid negating your energy savings, be sure to match the motor’s operating speed with the load requirements. This may mean replacing an existing motor with a smaller one, trimming impellers on pumps or changing gear or pulley ratios.

• Size

It is common practice in Australia to oversize motors in an attempt to insure against unexpected peak loads or to allow for process expansion in the future. As a result, hundreds of motors used in industry are grossly oversized.

Motors are most efficient when operating at full load. By installing a smaller motor, which operates at full load, the operating effciency will be greatly improved.

4.How can the system be improved?

• Install a Variable Speed Drive (VSD)

A VSD is an electrical device which controls power to the motor and is suitable if the loads are not always constant. Instead of continuously running at full speed, regardless of the loads, the VSD varies the speed of the motor to accurately match the loads.

The following graph shows the difference in energy requirements between running a fan at reduced flow using a standard throttled system as opposed to using a VSD. With a VSD, the motor uses only half the energy that would be required by a throttled system.

VSDs can be 2-5 times the cost of the motor, but can achieve energy savings of up to 50% per year. Savings are most dramatic when a VSD is applied to a motor driving a centrifugal pump. Where VSDs are too expensive, cheaper alternatives include:

• Multi-speed motors
• Two or more motors running parallel systems, with one motor running for base load, and the second only used at times of peak load. For example, two chillers in a building air conditioning system, or two exhaust fans in a carpark. This approach also offers improved reliability, as a back up is available if one motor or component fails.

5.Maintain your system

• Check that drive belts, chains and coupling are in good condition and are adjusted in accordance with the equipment supplier’s recommendations.
• Check for motors which are running hot, as this is a sign that energy is being lost. Use an infrared non-contact thermometer in preference to touching the casing. A motor casing temperature of 60°C or higher should be investigated.
• Check your motor alignment. If your motor is misaligned, some parts will wear more quickly, reducing the motor’s service life.
• Record data for each motor used to determine if any are running unnecessarily. Record information such as the motor’s application, the nominal power (in kW) from the motor identification plate and how the motor is controlled (float switch, time switch, etc.)
• Replace rather than rewind. It is common practice to rewind an electric motor several times throughout its operational life. Each time a motor is rewound the efficiency is reduced by up to 3%. As a result, a large proportion of motors in Australia operate at a lower efficiency than their nameplate efficiency. For example, a 3% efficiency reduction in a 30kW motor would add $150 to the operating cost each year (based on an 80% load, 3,000 operating hours per year, 10 cents per kWh). The best solution if your motor burns out may be to look at your loading needs and the purchase of a new high efficiency motor to match that load.