- #1
srinaath
- 52
- 2
why there is a decrease in efficiency of induction motor when power rating is low? example 1 HP motor efficiency is say 85% then 1/4HP motor efficiency is less than 85%? please clear me this doubt?
Why efficiency of induction motor is low for low HP?
- Thread starter srinaath
- Start date
In summary, there is a decrease in efficiency of an induction motor when its power rating is low. This is because the slip increases and the weight per power unit also increases. This can be explained by the motor's dimensions, which are based on its rated torque. As the torque increases proportionally with the rated power, the stator inside diameter also increases. This results in a decrease in weight per horsepower, leading to lower mechanical and magnetic losses. Additionally, the slip decreases with an increase in power, resulting in lower electrical losses per horsepower.
- #2
gracy
- 2,486
- 83
This might help 
- #3
Babadag
- 590
- 156
Indeed, according to most of catalogues the efficiency and power factor decreases if the rated power decreases [and also if the rated velocity decrease].The slip increases. The weight per power unit increases.
In my opinion this could be the explanation:
The motor dimensions-the stator inside diameter at the air gap- is stated according to motor
rated torque.
D=K*T^(1/3)
For the same rated rpm the torque increases proportionally with the rated power.
T=K*P/rpm then:
Dint=K*P^(1/3)
Actually Weight1/Weight2~=(P1/P2)^(a/3) a=1 to 2.5
That means the weight/hp is less for high hp and then mechanical losses[friction, ventilation] and
magnetic losses are less for more power rated. Also the slip decreases if power increases, so the electrical losses Plosses=Pm*(1-s) will decrease.
In my opinion this could be the explanation:
The motor dimensions-the stator inside diameter at the air gap- is stated according to motor
rated torque.
D=K*T^(1/3)
For the same rated rpm the torque increases proportionally with the rated power.
T=K*P/rpm then:
Dint=K*P^(1/3)
Actually Weight1/Weight2~=(P1/P2)^(a/3) a=1 to 2.5
That means the weight/hp is less for high hp and then mechanical losses[friction, ventilation] and
magnetic losses are less for more power rated. Also the slip decreases if power increases, so the electrical losses Plosses=Pm*(1-s) will decrease.
- #4
Babadag
- 590
- 156
Correction:
electrical losses=~k*Pmec*s.Then electrical losses/HP=~s.Less slip less electrical losses per HP.
electrical losses=~k*Pmec*s.Then electrical losses/HP=~s.Less slip less electrical losses per HP.
Related to Why efficiency of induction motor is low for low HP?
1. Why is the efficiency of an induction motor lower for low horsepower?
The efficiency of an induction motor is determined by the power output divided by the power input. For low horsepower motors, the power output is lower, resulting in a lower efficiency. This is due to the fact that smaller motors have higher resistance and losses, which decrease their efficiency.
2. How does the size of an induction motor affect its efficiency?
The size of an induction motor has a direct impact on its efficiency. Smaller motors have higher resistance and losses, resulting in lower efficiency. Larger motors, on the other hand, have lower resistance and losses, leading to higher efficiency.
3. Can the efficiency of a low horsepower induction motor be improved?
Yes, the efficiency of a low horsepower induction motor can be improved through various methods. These include using higher quality materials, improving the design and construction, and reducing losses through proper maintenance and operating conditions.
4. Are there any benefits to using a low horsepower induction motor despite its lower efficiency?
Despite the lower efficiency, low horsepower induction motors have their advantages. They are generally more affordable and require less maintenance compared to larger motors. They are also more compact, making them suitable for smaller spaces.
5. How does the load on an induction motor affect its efficiency?
The efficiency of an induction motor is affected by the load it is operating under. Under light loads, the motor's efficiency decreases due to increased losses. On the other hand, operating the motor under its rated load can improve its efficiency and performance.
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