The first industrial electric motor was probably considered a breakthrough in this category even as there was plenty of room for improvement. As technology has advanced, electric motor manufacturers have successfully developed better motors that use less energy and lower costs.
While it’s only natural for motor manufacturers to employ the latest technology in creating industrial electric motors, the scope for further advancements in producing as well production methods has been widely instrumental in improving the efficiency of electric motors.
Here are a few interesting statistics for you to sample:
- The global electrical market was valued at over USD 70 billion in 2015 and is expected to grow at a CAGR of 4.2% from 2017 to 2025.
- World electricity usage is estimated to reach 35k trillion KWh by 2035 and about 28% from it will be used by electric motors.
- 50% of all electric motors are installed in EU, US and China.
- 90% of installed motors run continuously at full speed and use mechanical systems to regulate output.
The future definitely looks promising!
Before getting into the efficiency aspect, it is important to know more about the simple electric motor used in industries.
A simple DC motor converts direct current electrical energy into mechanical energy and typically comes equipped with a high number of coils, which make it efficient. However, it can still result in a lot of energy wastage due to:
- The friction between the commutator and brushes
- The loss of torque at certain angles
Further, if the motor gets stuck while trying to lift a heavy load, the rotor coils can easily overheat and melt. This is why a number of industrial and heavy home appliances use electric motors.
How Electric Motor Manufacturers Can Save Electricity with Electric Motors
The way the electric motor is designed and the way it is used are the two determinants that help save electricity with their use.
Let us have a look at the design aspect first.
Using Copper Windings in the Stator Coils
As far as the conductivity of the motor is concerned, it is always better to go for copper coils rather than outdated aluminum ones. This is because aluminum’s conductivity is lower than copper’s. To keep up with copper coils, aluminum magnet wires may need larger cross-sections so they can provide the same level of conductivity. Windings wound with an aluminum wire may have greater volume compared to a copper wire motor of the same size.
If you’re still using aluminum windings, it is important to ensure that the ends of the aluminum magnet wire are properly connected. This is because aluminum oxidizes much faster than other metals; and if powdered aluminum is exposed to air, it will oxidize fully in just a few days and leave behind a fine white powder.
In order to make a proper connection that ensures good conductivity, the oxide layer of the aluminum magnet wire must be pierced so as to prevent the aluminum from coming in further contact with air.
It is important to realize that achieving motor efficiency has more to it than just deciding between aluminum and copper windings. Several motor manufacturers have developed high-pressure piercing crimp connectors to enable better efficiency. This has been done in an effort to help aluminum windings keep up with their copper counterparts.
This means that even though copper has an upper hand, it is possible for motors with aluminum windings to match the power of copper ones. The latter takes time and money though.
Aluminum requires more turns and a larger diameter wire, which may not always be economically viable.
If the motor is required to work occasionally or for a short duration, and when efficiency and volume are not of the essence, using aluminum magnet wires can make sense. Otherwise, copper windings should always be preferred.
Using Copper Bars in the Rotor
When it comes to rotors, copper offers the advantage of efficiency here as well. Copper rotors are preferred in energy-conscious industries in developed countries and also in developing nations where electricity is often in short supply and costly.
Copper rotors are a better bet compared to aluminum ones in terms of motor quality, reliability, costs, efficiency, and lifespan.
Machining All Moving Parts to High Precision
Whether it is turning tasks or milling operations, machining entails removing material from a compartmental unit to a highly tolerable substance. Precision machinery is required to achieve the highest tolerance to the smallest measurable degree. It could be metal cutting or coal mining, precision machinery provides the required accuracy needed to produce the desired materials in the required quantities.
The moving parts of machines need timely maintenance to enable maximum output and efficiency. Maintenance should only be done by experts as the machines require inspection of all the parts to meet each requirement. The machines are designed and manufactured to handle meticulous tasks. Regular maintenance is crucial to ensure that the machine parts function optimally and produce the desired results according to task standard.
Using Special High-Quality Steel for Rotor and Stator
In modern times, high-tech electrical steels are essential in manufacturing economically-viable stators and rotors, which are used in an array of electric motor applications, generators and transformers. This works well because they ensure high magnetic permeability and low power losses to achieve top-notch performance.
However, power losses in electrical steel occur due to several reasons. Eddy currents (also called Foucault currents) come into play when a magnetic field is alternated. Rolling steel to a thinner gauge controls these eddy currents and reduces the classical eddy current losses. This is especially true of application frequencies beyond the standard 50 or 60 Hz.
Keeping the Rotor and Stator as Close as Possible without Touching
This can be achieved through precision manufacture. When the rotational speed goes into several thousands of rotations per minute (rpm), the electrical steel in the rotor can experience tremendous stress. High stress is especially felt in areas around the magnet slots, where narrow equipment holds the magnets in place.
When it comes to an induction motor, the transfer of energy takes place through the air gap between the stator and the motor. The air gap is necessary to minimize reluctance. A small air gap will lead to less energy loss and higher efficiency. Also, the total flux linkage between stator and rotor widens as the air gap decreases. Higher flux linkage results in lowered energy loss and heightened efficiency. A smaller gap also helps avoid noise.
More Coils Make Motor More Efficient
The wires in the phase coils in small-sized power motors are thinner. However, the number of coil turns needs to be high in order to increase the magnetomotive force (or current density).
The resistance of phase windings is higher than that found in high-power motors, and the power loss density is higher (and efficiency lower) than in high-power motors.
Low-power motor with high speeds will, therefore, need more magnetomotive force. This means it will need more coils with a higher number of turns with thin wire that produces higher current density compared to high-power motors.
Using Variable Speed Drives
Variable Speed Drives (VSDs) or adjustable speed drives are heavy industrial electric motors, the speed of which can be adjusted with the help of an external controller. These drives are used in process control as they help in conserving energy in plants that make use of numerous powerful electric motors.
VSDs are typically used as energy savers in pump and fan appliances, since they better process operations, especially where flow control is necessary. They also provide soft-start capabilities, which bring down electrical stresses and line voltage sags that are generally found in voltage motor start-ups, particularly when driving high-inertia loads.
How Electric Motor Users Can Ensure Better Efficiency
As mentioned, the way energy-saving electric motors are used by manufacturers, industries, and homeowners, also determines their efficiency. So here’s more on what the users can do to ensure efficiency and longevity of a motor:
Using Smart Motors with Appropriate Motor Starter/Controller
While smart motors are widely available and used today, it is crucial to choose the best fit to minimize downtime, improve efficiencies and lower costs.
Industrial engineers know of the burden that electrical consumption by motors (particularly those used in fans, pumps, and compressors) puts on their operating budgets. To mitigate this, they use efficient motor control technologies that use only the necessary amount of energy to start motors, reveal diagnostic data, and reduce downtime. With the increasing acceptance of motor starters, motor starter technology has also gained prominence.
Here are a few important questions to consider before deciding on potential applications for electric motors:
a. Will the application need speed control even when the motor is at a certain speed?
Speed control requirements need to be decided upon as early as possible. Some soft starters have limited slow-speed control between starting and stopping. The important thing to remember is that the operating speed of the motor cannot be changed because the soft starter regulates only the voltage of the motor and not the frequency.
b. Will the application need specific start and stop times?
Usually, start and stop times with soft starters are dependent on the load. Internal algorithms adjust the voltage based on pre-programmed times to increase the current and torque to start the motor and/or decrease them to stop it. If the load is light, the motor can take less time to start than the programmed value.
New-age soft starters have employed advanced algorithms, leading to more accurate and less load-dependent start and stop times.
c. Will the application need full torque at no speed?
A Variable-frequency Drive (VFD) may work best with applications that need full torque at zero speed. It can produce rated motor torque from zero to rated speed and even provide full torque at no speed.
Soft starters, on the other hand, typically operate between the frequency of 50 to 60 Hertz, and full torque can only be availed at full voltage. Initial torque (available at zero speed) usually ranges from zero to 75 percent and can be programmed.
d. Will the application need constant torque?
Soft starters alter the voltage to control current and torque. At the time of starting, the current varies according to the voltage, while the motor torque varies as the square of the applied voltage.
The torque may not remain constant at different applied voltages, a condition which may get more complex with varying loads.
Certain soft starters work on torque control algorithms, but this does not necessarily relate to constant torque. During acceleration, however, VFDs use different frequencies on the motor, while changing the voltage as per the frequency. The VFD control mode is referred to in terms of constant volts per hertz and produces a constant torque.
e. What are the cost, size and thermal concerns?
At amperage less than 40 amps (which is low), soft starters can provide a minor cost advantage over VFDs. As the amperage and the power increase, the cost of VFDs increases faster than the cost of soft starters and can reach tremendous levels at high amperages (100 amps).
When it comes to size, soft starters provide a better advantage over VFDs at all amperages, thanks to the construction of each device. As the current and the power increase, the difference can also become larger.
Moreover, when soft starters are teamed with an internal or external electromechanical bypass, they are more effective as compared to VDFs and can produce less heat. This is because the construction of the soft starters have comparatively less active components in the circuit during start, run and stop modes.
f. What are the installation and harmonics considerations?
Installation concerns can be categorized into cost, size, temperature, and power quality. Soft starter installations involve smaller sizes and lower costs, which is why they are not much of a concern.
Also, soft-starter harmonics are less than those compared to VFDs. Long cable runs for VFDs need to be considered with more attention than those of soft starters. Further, special wire types may not be needed for soft starters, and electromagnetic compatibility may not be considered either.
Discontinue Using Motors When Not Needed
As simple as it sounds, it still makes sense to reiterate that the most effective way to save energy is to turn the motor off when it is not in use. More often than not, users hesitate to switch the motor off because they believe that starting it up over and over again will lead to major wear and tear.
One way to mitigate this is by using soft starters as they reduce wear and tear at every start. A properly installed and specified soft starter reduces the pressure on mechanical and electrical systems to a great extent.
Reducing Wear and Tear
Reducing motor wear and tear is among the primary concerns of users. A great deal of wear and tear takes place when an electric motor is started as the high initial currents and forces pressurize the mechanical and electrical systems.
This can be detrimental, but the damaging effects can be brought under control with the help of soft starters. These can be used in all fixed speed applications as doing so will extend motor longevity. You can also employ VSDs, but these may be costly and less efficient.
Using High-Efficiency Motors
Motor efficiency can be derived from two factors: the size of the motor and its efficiency quality.
For smaller motors, in particular, size is an important factor that affects efficiency. For larger motors, it is the efficiency classes that matter more.
The great thing about using energy efficient motors is that they use less electricity, do not heat up easily, and last longer. Energy efficient electric motors are characterized by better motor design, which results in less heat loss and lower noise. The use of high-quality materials, tighter tolerances, and improved manufacturing techniques also help reduce losses and enhance efficiency.
To assess the benefits of high-efficiency electric motors, it is necessary to first define “efficiency” for an electric motor. It is the ratio of mechanical power delivered by the motor (output) to the electrical power supplied to the motor (input). Therefore,
Efficiency = (Mechanical Power Output/Electrical Power Input) x 100%
So, if a motor is said to be 80 percent efficient, it implies that it converts 80 percent of the electrical energy into mechanical energy. The remaining 20 percent of the electrical energy is lost in the form of heat (as the motor heats up).
Buying the Right-Sized Motors
Motors tend to be most efficient between 60 percent and 100 percent of their full-rated load, and most inefficient below 50 percent loading. This means that merely buying the correct-sized motor can increase efficiency to a great extent.
Most often, oversized motors do operate below 50 percent of their rated load, which means they are not only inefficient but also prove to be more expensive than motors of the right size. Moreover, they may also reduce the power supply to the machine, which increases the load on the electrical system.
With ‘energy efficiency’ becoming the buzzword in global sustainable industrial practices, it is important to integrate it into our daily household and industrial applications. Using energy efficient motors is a big step and with proper installation, they can run cooler, deliver higher service standards, last longer, provide better insulation, and emit less noise and vibrations.
With so many benefits to look forward to, electric motor manufacturers need to ensure that they produce and employ energy efficient motors, thereby increasing their efficiency, lowering costs, and helping the environment.