Industry is flooded with advice on how to save energy with electric motors. Most of these items of advice only tackle one issue, or in even worse cases only provide a single and biased viewpoint. With over 30 years of experience in motor control, Fairford Electronics is uniquely positioned to provide honest, unbiased and reliable information. Here are 10 tips from them on saving energy and money.
The phrase, ‘If you can’t measure it, you can’t manage’ remains a true statement for electric motors. To make the biggest impact, you must have a clear understanding of which motors and processes are consuming the most energy in your plant. This will allow you to target your efforts, and gain the quickest Return on Investment.
2. Understand Energy Use
Electric motors are energy conversion devices, they convert electrical energy into rotational energy and some heat. It is important to understand the difference between motor speed (rotational speed) and motor load [opposing force (torque)]. The energy consumption of a motor is related to both speed and load. A slow motor with a full load will consume more energy than a fast motor with no load.
3. Fixed Speed v Variable Speed
Consider which applications are already variable speed, those that must remain fixed speed and those where the speed could be reduced. Be careful though, reducing speed on some applications will not reduce energy consumption. For example, halving the speed of a conveyor system will just mean the conveyor will take twice as long to move the same amount of material.
4. Turn it Off
It sounds simple, but the most effective way to save energy is to switch the motor off when it’s not needed. Often the reason for not doing this is the perceived risk of additional wear and tear at motor start up. This is especially true for motors started Direct On Line or with Star Delta starters.
5. Efficient System Design
There is a little point in installing the latest high efficiency motors and equipment, if the entire system is fundamentally inefficient.
Study how the system works and identify when and where the motor is doing work unnecessarily.
6. Slow Down
In the simplest terms, at the same load, a slow motor does less work than a fast motor. So you can only save energy in applications where you need less work done.
Variable Speed Drives save energy by allowing the motor to do less work. They are very effective in reducing speed and saving energy in applications where the main opposing force is drag, so this is especially true in HVAC, fan and centrifugal pump applications. Due to the physics of drag, a small reduction in motor speed will result in a larger reduction in the work done and the energy consumed.
7. Use Energy Saving Motor Controls
All motors, even IE3/NEMA Premium Efficiency Motors are most efficient at near full load, as motor load fall below 50%, efficiency begins to reduce. This effect exists because the motor will always use a certain amount of energy to create the magnetic fields needed to rotate the motor irrespective of load.
In applications where the motor load is variable or the motor runs at light loads for long periods, Intelligent Energy Saving Motor Controllers should be used.
8. Size Motors Correctly
At full load all motors, even old motors, are surprisingly efficient. But as the load reduces, motor efficiency quickly falls away – even on the latest high efficiency motors. Therefore, a high efficiency motor is only truly efficient when it is being used near full load conditions.
It is a good engineering practice to slightly oversize a motor for a particular application, this will extend motor life and provide some extra capacity – when it is required, and if a motor is oversized, larger than required, the motor should be re-examined.
9. Use High Efficiency Motors
The latest IE3/NEMA Premium Efficiency motors are more efficient, but the efficiency gains are marginal. Only in few cases where the motor is very old and running 24/7, it will make financial sense to replace a perfectly functioning motor with a new motor.
However, upgrading the motor as it reaches the end of its service life, or when the motor fails, should be considered as best practice. Motor rewinds should only be considered when the motor cannot be replaced due to specific technical reasons or lack of availability of suitable replacements.
10. Reduce Wear & Tear
After energy costs, down time is the next single biggest cost to any plant operator.
A large amount of wear occurs when an electric motor is started; the high initial currents and forces put great strain on the mechanical and electrical systems. To reduce the damaging effects, Soft Starters should be used in all fixed speed applications, and this then will extend motor life.