Induction motors
” Induction motors are single excited electrical machines which requires very less maintenance. Stator contains the winding fixed in a silicon steel stamping Which only need the rated power supply.While solid rotor made from silicon steel stamping rotates in between the stator without any winding. Rotor’s stamping contains the solid aluminum conductors in a skewed form. “
When a rated power supply is get connected across the stator’s winding, A rotating magnetic field develop across the rotor.
Due to Induction, current get induced on short circuited bars of the rotor. Rotor’s generated current interacts with magnetic field of stator. Due to magnetic field interaction & resultant torque; rotor starts rotating.
Majority of industrial motors are Induction motors That’s why It becomes crucial to study every aspect of it.
Similar to other machines, Induction motors also contains a name plate. Name plate is a type of metallic plate which is attached with motor which describes its important credentials. Whatever the step we are going to take whether we are going for motor connections or finding a motor fault. The first & most important step is reading a “Name plate”.
The list of parameters for Induction motor is very long. Its not possible to mention all the parameters so few of them which are most important, get highlighted on name plate. In this post, We are going to discuss the Name plate of Induction Motor.
Why is Name Plate Important?
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Helps in correct motor selection
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Prevents overloading and overheating
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Essential for starter and protection device selection
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Useful during maintenance and troubleshooting
NAME PLATE OF INDUCTION MOTOR
Before brief description about the specifications, Important terms which are normally printed on name plates are :
- Manufacturer name & Serial number
- Motor Rating (kW Or hp)
- Speed
- Voltage
- Frequency
- Rated current
- Duty cycle
- Motor Connections
- Efficiency
- Power factor
- Bearing size
- Ambient temperature
- Torque
- Manufacturing date
- Insulation class
- frame type
- Weight of Motor
- Cooling system
- Ingress protection
All the terms are briefly described next !
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MANUFACTURER NAME & LOGO
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A name plate of ‘Crompton greaves’ make; 0.75kW-3phase Induction motor is shown above !
When we see a motor’s name plate, Our first sight drop on Logo or Name of the Manufacturer.
Top companies are in every field. These companies set benchmark for other companies behind them. These following companies try to follow the benchmark set by the top companies.
Likewise In India, Electrical motor manufacturers Siemens, Kirloskar, ABB, Crompton Greaves etc. are at top in motor manufacturing. These companies spend lot of money & effort on research, quality & testing. The product of top companies are bit costly but it feel safe and reliable when a well known label of these companies is get seen.
2. Serial Number
Serial number of a motor is like a unique identification number(UIN) which makes the motor unique. It makes the motor; Only individual with that particular number from manufacturer side. With this serial number, Traceability become easy.
An image shown above contains the serial number; been circled red.
3. Frame Size
Motor’s frame size is a standard which tells about motor’s mounting type & its all around measurements like; Its shaft, mounting hole & distance in between them. Since it is not possible to mention all the measurements on single name plate that’s why a standard number is given to a particular motor frame.
Same frame size motors are identical in shape & size even if the manufacturer is different. It is very helpful, When there is need of motor replacement. We just only need to see the frame size rather than total measurement of feet & mounting position. These frame standard build by NEMA(National Electrical Manufacturers Association). Above shared motor’s frame size is GD80.
4. Motor Rating (KW OR HP)
Motor Rating implies motor’s rated power which is a very important parameter. It could be given in hp or in KW or in both.
A name plate of 0.75 KW induction motor is shown below :
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5. VOLTAGE
Motors are designed for particular voltage range at which motor operate at optimum efficiency & achieve its maximum useful life.
That voltage consideration should be according to rated supply voltage.
In an image below working voltage of 3 phase Induction motor is 415±10%. Which means working voltage shall be in between 373 to 456Volts.
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6. FREQUENCY
It is an important parameter Because speed is frequency dependent in Induction motors. Speed is directly proportional to frequency of power supply. As frequency increases speed increases. In India, frequency standard is 50hz±3%.
In an image below Supply frequency for 3 phase Induction motor is 50±5% which means frequency range must be in between 47.5Hz to 52.5Hz.
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7. SPEED
Speed of Induction motor is described in RPM (Rotation per minute). Generally, Induction motor are available in 2800,1440,960 & 750 RPM at 50hz frequency.
As explained above ” Speed is directly proportional power supply frequency, As frequency increases speed increases.”
Synchronous speed, Ns= [(120*frequency) / poles]
CASE1. Poles=4, frequency=50Hz, Ns=[(120*50)/4]=1500rpm
CASE2. Poles=4, frequency=60Hz, Ns=[(120*60)/4]=1800rpm
Which means speed increases as frequency increases.
CASE1. Poles=4, frequency=50Hz, Ns=[(120*50)/4]=1500rpm
CASE2. Poles=4, frequency=60Hz, Ns=[(120*60)/4]=1800rpm
Which means speed increases as frequency increases.
BUT Induction motor‘s speed is not Synchronous speed. In Induction motor, Magnetic field which is generated by stator actually rotates at synchronous speed & rotor tries to catch that magnetic field.
In Induction motor, Rotor speed is slower than synchronous speed. The difference in synchronous speed & rotor actual speed is known as slip(s) which in general explained in percentage. Slip=[(Ns-Nr)/Ns]*100
In an image below :
At rotor speed(Nr) is 1410 rpm
At rotor speed(Nr) is 1410 rpm
Synchronous speed(Ns) is 1500 rpm
Slip=[(1500-1410)/1500]*100=6%
Slip=[(1500-1410)/1500]*100=6%
Since Induction motor don’t rotates at synchronous speed that’s why Induction motor are known as ‘Asynchronous motors’. The impact of supply frequency remains the same on rotor speed as on synchronous speed.
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8. RATED CURRENT
Rated current shows final current limit up to which motor can work continuously in a safe limit. Under the rated current; motor’s noise, vibration & temperature remains in permissible range. Rated current of the motor depend upon the power rating, voltage & Type of power supply(No. of phases).
Load current more than rated current produces excess stress on the winding which deteriorate the useful life of the motor. In worst case, High current can damage the winding insulation permanently.
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9. DUTY CYCLE
Duty cycle defines the type of working periods at which Induction motor designed for !
Since it is not necessary that all the motors run continuously for long period of time. There is operation of starting, No load running, full load running, Breaking & Rest period of Induction motor. These operations are viewed by how these operations affect the motor temperature in order to determine if the selected motor is up-to the mark for the application.
According to application requirements,
- Some applications having long run time period such that motor reaches to its final temperature equilibrium state. Such duty known as ‘continuous duty(S1)’.
- Some applications have short run period than there is rest period, such that motor’s temperature reaches to ambient temperature after reaching its final equilibrium temperature. Such duty known as ‘short time duty (S2)’.
- Some application have cyclic continuous state such that motor runs & stops continuously. Its lowest temperature doesn’t reach to ambient temperature. Such duty known as ‘Intermittent periodic duty (S3)’.
- Some applications have continuous run period, break period & rest period such duty known as ‘continuous duty with breaking(S4)’.
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10. EFFICIENCY
“Efficiency which is expressed in percentage which explain how efficiently motor can consume Electrical power. Ultimately, It describe the final outcome; mechanical power; after excluding all the losses. Efficiency is the ratio of mechanical power output to electrical power input.”
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11. POWER FACTOR
- Power factor defines how efficiently Electrical power is being consumed. As a consumer, We have to pay for total power While power factor describes how much power is utilized in useful power.
- Power factor is percentage ratio of Ture power(KW to apparent power(KVAH).
- Maximum value of power factor is 1 While lowest value is 0. It fluctuates in between 0 & 1.
Induction motors are type of inductive loads. & In Inductive loads power factor lags behind the maximum value.
Induction motor‘s power factor normally lies in between 0.70-0.9(lagging).
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12. BEARING SIZE
A few motor manufacturers mentions bearing sizes on name plate. There is benefit of bearing size mentioning, if bearing got damaged; We can arrange the bearings by knowing the bearing numbers without opening the motor covers.
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13. INSULATION CLASS
Insulation class refers to maximum temperature which motor’s insulation can withstand.
There are different classes of insulation in which four classes are the major one Which are shown in a tabular form:
There are different classes of insulation in which four classes are the major one Which are shown in a tabular form:
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All the insulation classes are considered at ambient temperature of 40°C. It is very important to consider Insulation class in motor selection because wrong insulation selection leads to sudden deterioration of motor. The place where motor is going to be installed, ambient temperature & type of pollution around the motor, all the parameters are important to consider.
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14. TORQUE
Torque is the rotational force produced by the rotor. SI unit of torque is newton-meter. In some cases torque is mentioned in kg-m . Motor’s power rating is calculated after considering the rated ‘torque’ & ‘rpm’.
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15. COOLING SYSTEM
Normally we have seen, A cooling fan is mounted on the shaft at the back of motor. But there are many more different cooling methods. In big size motors, An auxiliary fans or water pumps are provide for motor cooling. To mention the cooling method, A number system is created Which describes the type of cooling.
For example
IC411 -(TEFC) Totally enclosed fan cooled
In this, motor is fully closed. A fan is mounted on shaft at non driving end which passes air from the motor surface.
IC411 -(TEFC) Totally enclosed fan cooled
In this, motor is fully closed. A fan is mounted on shaft at non driving end which passes air from the motor surface.
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16. INGRESS PROTECTION
Industrial environment is hard; In some cases it is very hard. Iron dust, moisture, vibrations, corrosive environment put bad impact on motor’s winding.
There is danger of ingress of Solid (dust) particle & liquid material. To protect the motor from both solid & liquid particles, motors are manufactured accordingly.
Motors IP rating should be considered according to the place.
The ingress protection of motor is denoted in a combination of numbers & alphabets.
For example
IP44- IP stands for ingress protection. Units digit is given for the protection from the liquid & Tens digit given for the protection from the solid particles.
Tens digit
If given tens digit is 1, It provides protection from object greater than 50 mm.
If given tens digit is 4, It provides protection from object greater than1mm. At 6, it is dirt proof.
Unit digit
if given unit digit is 1, It provides protection from water droplets falling downward for 10 Minutes.
if given unit digit is 8, It provides protection from water immersion for long period.
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17. MANUFACTURING DATE & WEIGHT
Manufacturing date & weight of the motor also mentioned on the name plate.
SUMMARY
- Induction motors are essential, low-maintenance electric motors widely used in industries.
- Understanding their specifications, primarily detailed on the nameplate, is crucial for proper installation and maintenance.
- Key information includes the manufacturer’s name, serial number, power rating (kW or hp), voltage, frequency, speed, rated current, and efficiency.
- The nameplate also clarifies the motor’s duty cycle, insulation class, torque, cooling method, and ingress protection. Additionally, It provides information about bearing sizes, manufacturing date, and weight.
- Familiarity with these nameplate details ensures optimal performance and longevity of Induction motors in various applications.
Hope this article will be helpful. If you have any query or suggestion please do comments!