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Motors are applied where there is the need to move certain objects. The efficiency of the motor determines the cost-effectiveness of the movement thereof. A motor typically generates some rotational motion and transmits it to the end compartment where that motion is used. Some of the power generated by the motor is lost along the way due to factors such as friction or heat loss. Motor efficiency is thus the ratio of actual energy utilized to that fed into the mechanical system. Of course, the more efficient motors ensure a low cost of operation which is always desired by a motor user.
In this article, we will attempt to explain how you can make a more informed decision as to which motor may be better suited to your application.
Some Terms
Before delving deep into the explanation of motor efficiency and how it can be estimated, here are a few important terms:
Work
Work is the amount of energy involved in moving a certain mass through a distance with the use of force.
Power
Power is work done over time.
Efficiency
The ratio between the magnitude of the energy input that can be converted to useful output energy or work involving a system.
Rated load
The load a machine can deliver with sufficient efficiency.
Full load
The maximum load a machine can provide.
Power Factor
The ratio of real power to apparent power in a circuit.
Actual power is the electrical power used, apparent power is the total electrical power delivered to the circuit.
Rotor
The part of a motor that moves to rotate the shaft to provide mechanical energy.
Stator
The fixed part of the motor with some windings, or fixed magnets with cores of different metal sheets or of laminated materials.
This will give you a view of the structure of motors and the basic principles concerning their operation.
Motor efficiency formula
The efficiency of an electric motor is calculated by finding the input power and output power of the motor. Efficiency is the ratio of output power to input power, expressed in terms of percentage. The following are the steps:
Calculate the input power (Pin): which is the electrical power fed to the motor. The formula is Pin = V x I, where V is the voltage across the motor and I is the current through the motor. Make sure the units are consistent, such as volts times amps.
Measure or Calculate Power Output (Pout): the mechanical power of the motor. It could be determined by different approaches based on the specific application involved. For example
If the torque, T, and angular velocity, ω produced by a motor are known, this formula Pout = T x ω can be made.
An approximate value for power output, when the speed of the motor and the rated power consumption are known, is given by Pout = Prated x (N/Nrated), where Nrated is the rated speed.
Calculating Efficiency (η): This is obtained from η = (Pout / Pin) x 100%. This gives the percentage of efficiency.
For example, let the input power to the motor be 1000 watts Pin and the output power Pout be 800 watts. The calculation of the efficiency is shown below.
η = (800 / 1000) x 100% = 80%.
From this, it’s evident that the efficiency of the motor is 80% and hence 80 % of the input electrical energy is transformed into useful mechanical power.
Note that motor efficiency is dependent on the load conditions as well as temperature and design. It is, thus, always a good idea to make measurements or consult the motor specification to find what the actual efficiency for the practical application is.
Motor efficiency and its classes
Two types of tests are generally carried out for the measurement of a motor’s efficiency – a no-load test as well as a loaded one. A no-load test has no load on the motor. In contrast, a test that is run with an already known load is called the load test. During these tests, the input power and the output power of the motors are measured by specialized instruments, and the efficiency is calculated based on the formula previously illustrated. Note that the efficiency of motors changes under different load conditions, and therefore testing the motors at their usual operating condition gives correct measurements.
Several classes of motor efficiency have been assigned by the International Electrotechnical Commission and the National Electrical Manufacturers Association. Such ratings are based on a maximum allowable loss on a motor and are only limited by the design and/or size of the motor. The higher the rating on efficiency, the lower the losses allowed, thus a generally more efficient motor will come out.
The major classes of motor efficiencies:
Standard Efficiency (IE1, NEMA Design A): This is the lowest efficiency rating of motors and is generally applied to older or lower-cost motors. These motors range from 50 to 90% efficient, depending on their size and application.
High Efficiency (IE2, NEMA Design B): The minimum value of efficiency in this class is 3-6% higher than that for the standard efficiency class. These motors are relatively more efficient and are applied in applications where energy conservation becomes a priority.
Premium Efficiency (IE3, NEMA Design C): The minimum value of efficiency in this class is higher by 2-3% than in the high-efficiency class. These motors are the most efficient and are applied in high-performance applications where energy efficiency and reliability matter a lot.
Ultra High Efficiency (IE4, NEMA Design D): The minimum efficiency for this class is 1-2% higher than the High Efficiency class. These are the most developed and efficient motors, allowing the lowest losses and highest overall efficiency.
A higher efficiency-rated motor can be selected to help reduce energy consumption and operating costs while improving performance and reliability. Consult motor specifications and take measurements to get an accurate picture of motor efficiency in a real-world application.
Maintaining Motor Performance and Improving Motor Efficiency
In every system, some losses make the output lower than the input. That is why we have to consider the efficiency of the system, one of which is motor efficiency. There are some reasons for motor losses, which include friction, motor magnetic energy dissipation, and resistive losses. Reduction in motor losses increases motor efficiency.
One thing is constant monitoring of the motor. This also involves observing the age of the motor, the output power given, and the rating power of the motor to monitor the long-term efficiency of the motor. In addition, you want to monitor voltage unbalance, current unbalance, and power factor. You want a power factor close to 100 percent.
There are several ways of improving motor efficiency:
1. The main cause of losses in motors is the stator. Itt has been reported that the stator accounts for about 30% or more of the overall losses of the motor. The mass of the stator windings needs to be kept at a large value to reduce its corresponding resistive losses.
6, Motor lubrication is another important factor that can ensure the motor operation efficiently. Ensure that the different types of grease do not run at the same time and that lubrication intervals are based on the installed speed rating of the motor, bearing size, type of grease, and rise in temperature.
In sum, understanding motor efficiency can be critical to optimizing energy use and reducing operating costs. High-efficiency-rated motors can go a long way in the pursuit of sustainability and cost-effectiveness, whether for businesses or individual applications. From industrial to transport systems and appliances, no area can afford to slight the contribution of high-efficiency motors. So, strive together to develop better efficiency in motors for a greener and more efficient future. Let us power the world with the east energy wastage.
