Energy efficiency

Reference manual

  1. Introduction: setting the scene 
  2. Selecting the best motor and equipment 
  3. Commissioning 
  4. Motor and system maintenance and operation 
  5. Motor repair and replacement 
  6. Utility management 
  7. Maintenance management systems: plant inventory and records

Motor and system maintenance and operation

Improving the way you maintain your electric motor systems can be a risk free, easy and cost effective way of increasing your organisation's efficiency and lowering costs. According to the Electrical Power Research Institute in the United States, for example, many organisations can increase the operating efficiency of their equipment by 10 to 15 per cent, through proper maintenance alone.

Various international studies suggest that most organisations can also achieve large and cost-effective energy savings through best practice maintenance and operation, by developing a better understanding of their process requirements and by optimising controls and equipment to ensure these requirements are efficiently met.

There are many other benefits to best practice maintenance and operation, including:

This section discusses best practice operation and best practice maintenance.

Best practice operation

Best practice operation ensures that machines operate only when necessary, and efficiently deliver what is required.

There are many opportunities to improve operating efficiency. Some are simple, such as turning equipment off when it is not needed. Others require a better understanding of a technology or process, such as substituting inefficient control of flow from pumps and fans by throttling or damping with more efficient methods such as impellor trimming or inlet guide vane flow control.

A regular review of your process requirements and how these are being met will help you to discover savings opportunities. Often, the exact operating requirements of your plant were not known during its design, or your plant or operation has changed since installation, and although it appears to function well, significant inefficiencies may now exist. A review will most likely identify many and varied opportunities that can be carefully assessed to determine which ones offer the best return for the least risk.

Best practice maintenance

Best practice maintenance requires the right type of organisational culture and the willingness of well-trained staff to perform maintenance activities regularly, efficiently and effectively.

A best practice maintenance culture values the maintenance function, has qualified and experienced maintenance staff supported by systems, procedures and resources (including tools). This culture:

Many maintenance activities are simple and others more complex - they can all help you avoid the costly consequence of motor failure.

Best practice maintenance activities include:

Machine cleaning

You must regularly clean and protect your electric motors and equipment and ensure they are well ventilated. This makes it easier to inspect and detect problems. Also, cleaning reduces wear and tear - dirt can be highly abrasive to moving parts, contaminate bearings, coat windings and often combines with water to create a corrosive mixture.

Regular cleaning also guarantees adequate cooling. This is critical, since the life of an electric motor is halved for every 10oC rise above operating temperature.

Machine set up and alignment

Machine set-up is critical to alignment and reliable machine performance. You should ensure that all technicians involved in setting up machinery are trained in at least one advanced method of alignment. Of course, they should also follow machine manufacturers instructions and recommendations.

You should mount machines on a rigid base, and check that no distortion occurred after the machine was fixed to the floor or another structure. 

Use the reverse dial indicator or laser techniques to align your machines. Ensure your staff are trained and accredited by recognised experts, so they can deal skilfully with the many variables involved in alignment. You should engage the services of specialists, as needed, to assist with alignment.

Since V-belts often make up 25 per cent or more of the drives in an industrial plant, a belt tensioner is an essential item for every technician's toolbox. By ensuring your V-belt drives are set up properly, you can improve their operating efficiency by up to four per cent at very little cost. This can save many thousands of dollars for large motor users. It can also prolong the life of your belt drive since wasted energy is dissipated as heat and the life of a V-belt, like the life of the motor itself, is halved for every 10o Celsius rise above the operating temperature.

Most manufactures recommend a re-check on V-belts tension after they have been operating for 24 hours, and this is critical to ensure efficient operation and long life.

Bearing selection, fitting techniques and lubrication

Ensure that bearings on all critical and high-value machines:

Bearings are a fundamental part of all rotating machinery. They are generally reliable and, if selected, fitted and lubricated properly, they will provide five to 20 years of service. 

The most common causes of premature failure of bearings, in order of probability, are:

  1. poor fitting
  2. poor sealing
  3. inappropriate selection
  4. unsuitable lubrication
  5. outside factors that place great stress on bearings, such as misalignment or vibration.

Always examine failed bearings to determine the fundamental cause of failure and rectify the cause before you replace the bearing. This reduces the chance of the next bearing failing for the same reason. 

Machine condition assessment

Ongoing knowledge of machine condition is vital to reliable machine performance. Plan regular visual and operational checks on machinery and ensure your organisation's maintenance staff are well trained. Staff should use all of their senses - sight, smell, hearing, and touch - as well as basic monitoring equipment (for example, a hand-held vibration meter or thermometer) to monitor machine condition. All results should be recorded and made readily available to staff.

Conduct a regular vibration survey for high-value machines, and machines critical to process that operate above 600 rpm. Always conduct a vibration check after repair, cleaning, or alterations to speed of rotating components.

Use infrared condition monitoring of switchboards to help identify problems that may lead to switchboard failure or fires.

Electrical performance assessment

Poor power supply quality will have an adverse impact on both motor efficiency and reliability. Best practice organisations ensure that:

  1. The supply voltage at the motor terminal is within 90 to 110 per cent of nominal voltage marked on the motor nameplate. Voltage fluctuations can result from improperly adjusted transformers, undersized cables or poor power factor in the distribution network.
     
  2. Voltage imbalance - or the maximum difference of the voltages in relation to the average voltage - is under one per cent. Common causes for voltage imbalance are: non-symmetrical distribution of single-phase loads on the three-phase network; an open circuit in one of the phases; or unequal cable lengths and sizes causing voltage drop in one of the phases. Voltage imbalance leads to high current imbalance, which leads to high losses.
     
  3. Harmonic distortion producing devices (such as variable speed drives, other power electronic devices and arc furnaces) are isolated from other equipment by separate feeders, transformers or harmonic filters. In motors, harmonics can increase losses, reduce torque, cause torque pulsation and overheating.

Understanding the quality of a power supply and rectifying quality problems often requires specialist skills and equipment. Your organisation may need support from a qualified consultant or your electricity supplier.

Motor Solutions