Electric Motor and its types and working principle

about electric motor and its type

1. ELECTRIC MOTOR Electric motor, any of a class of devices that convert electrical energy to mechanical energy. Principle of electric motor: All electric motors are based on electromagnetism. In these motors, magnetic fields are formed in both the rotor and the stator. The product between these two fields gives rise to a force, and thus a torque on the motor shaft.

2. TYPES OF MOTOR Electric motors come in a variety of sizes and capacities and are produced for different applications. There are two main types of electric motor: 1. AC motor 2. DC motor.

3. DC MOTOR A DC motor is an electrical machine which converts electrical energy into mechanical energy. The basic working principle of the DC motor is that whenever a current carrying conductor places in the magnetic field, it experiences a mechanical force. Types of DC Motor: There are 4 major types of DC motor and they are, 1. Series DC Motor 2. Permanent Magnet DC Motor 3. Shunt/Parallel DC Motor 4. Compound DC Motors

4. AC MOTOR They only require a low power upon start-up, and they allow for controlled acceleration, which means that they can retain a constant speed and performance. There are two main types of AC motors: 1. Synchronous Motor 2. Induction Motor

5. Synchronous Motor: The synchronous motor changes the alternating current into mechanical power at the desired frequency.  The speed of the motor is synchronized with the AC frequency.  There is no air gap available in the speed of the stator current and rotor. So it provides more rotation accuracy. Induction Motor: working principle is that, the AC in the rotor of the motor is required to generate torque that is gained through electromagnetic induction which results from the stator winding’s rotary magnetic field.

6. Induction motors are classified into two types:  Single-phase Induction Motor: The single-phase induction motor is not self-starting. When the motor is connected to a single-phase power supply, the main winding carries an alternating current. Three-Phase Induction Motor: In three-phase induction motor there are two types: 1. Squirrel Cage Induction Motor 2. Wound Rotor or Slip Ring Induction Motor

7. Squirrel Cage Induction Motor: It typically consists of two main components: the stator and the rotor. When an alternating current is run through the stator windings, a rotating magnetic field is produced. This induces a current in the rotor winding, which produces its own magnetic field. The interaction of the magnetic fields produced by the stator and rotor windings produces a torque on the squirrel cage rotor. Wound Rotor or Slip Ring Induction Motor: The stator of the wound rotor induction motor is the same as a squirrel cage induction motor. The rotor of the motor is wound for the same number of poles as that of the stator. The rotor has three-phase insulated windings with each winding connected to slip rings via brushes. Here, the function of the brush is to collect current to and from the rotor winding.

8. Service factor (SF): Service factor -  SF  - is a measure of periodically overload capacity at which a motor can operate without beeing damaged. The NEMA (National Electrical Manufacturers Association) standard service factor for totally enclosed motors is  1.0 . This service factor can be used for the following: To lengthen insulation life by lowering the winding temperature at rated load. To handle intermittent or occasional overloads. To allow occasionally for ambient above 40°C. 5. To compensate for low or unbalanced supply voltages.

9. NEMA does add some cautions, however, when discussing the service factor: Operation at service factor load for extended periods will usually reduce the motor speed, life and efficiency. Motors may not provide adequate starting and pull-out torques, and incorrect starter/overload sizing is possible. This in turn affects the overall life span of the motor. Do not rely on the service factor capability to carry the load on a continuous basis. The service factor was established for operation at rated voltage, frequency, ambient and sea level conditions.

10. MOTOR SPECIFICATIONS

11. DUTY CYCLE The relative duty cycle is the percentage of the time with constant load with respect to the total duration of a duty cycle. The duty cycle of an electric motor is closely related to the electric motor is closely related to the duty type of the electric motor.

12. DUTY TYPES The duty type of an electric motor defines the load cycle of the electric motor and ranges from S1 to S9, where S1 is for continuous duty with the motor running 24/7, and S9 is for converter duty. S1-continuous duty:The first, and simplest, type of work cycle is continuous duty. This is also referred to by its abbreviated name, S1 duty. In this type of operation,  the motor runs with a constant load long enough to reach thermal equilibrium.

13. S2-short time duty:The short time duty (or short time operation)  indicates an operating mode of increased performance but for a shorter length of time . Commonly it is also referred to the maximum load (the performance) at which and the related maximum length of time a device can be operated without to failure.

14. S3-Intermitent duty :Intermittent periodic duty is the simplest type of variable duty. This sequence of identical cycles each contains a period of constant load and a period at rest. This is very similar to S2 duty but differs because it never reaches ambient temperature during its rest period. This duty cycle is abbreviated as S3 followed by the percentage of time under load (calculate S3 xx%, where the % = ∆Tc/T).

15. S7-Perpetual operation with electric breaking:The other periodic duty cycles S4-S6 and S8-S9 are similar to S3 and S7 but can be done with or without rest, starting, braking, and loading. Potential applications of sustained operation with electric braking could include rolling or blooming mills for steel manufacturing, supply chain machinery across material handling and even some medical technologies, including precision applications.

16. COOLING METHODS Several types of cooling systems are available for electric motors, including:  Air cooling Liquid cooling Heat pipes cooling Hybrid cooling with heat pipes and liquid

17. AIR COOLING(IC 01/IC 06): Air cooling is one of the most common cooling methods, where  cooling fins or external fans help dissipate heat from the motor's surface . Regular maintenance involves ensuring proper airflow, cleaning cooling fins, and inspecting fan functionality to prevent overheating WATER COOLING (IC 511/IC 516): Water cooling involves circulating cooling water through pipes around the motor's frame or within the motor housing. Maintenance requires monitoring water flow and pressure, checking for leaks, and ensuring that the water quality meets specifications. HEAT PIPE COOLING: heat pipes are incorporated into the stator slot to directly cool the windings . Most of the heat in an electric motor is generated in the motor winding. Thus, putting the heat pipe in close proximity to the copper winding will make the heat transfer most efficient there. HYBRID COOLING WITH HEAT PIPES AND LIQUIDS: hybrid cooling with heat pipes and liquid can maintain the motor's temperature as well as save energy when compared to the liquid cooling alone.

18. INTERNATIONAL MOUNTING CODE Type of construction and installation are identified with an inter-nationally standardized IM code in accordance with IEC 600 34-7 This code takes into account: The position of the motor shaft The type of bearing shield Fastening of the machine Method of installation Nature of the shaft end

19. TYPES OF CONSTRUCTION OF MOTORS Base foot-mounted motors secure to surfaces using a base with feet, common in industrial settings, providing stability through secure installation holes. Flange mounted motors have a designed flange for direct attachment to equipment, ensuring stability during operation. Configurations like C-flange and D-flange cater to specific applications. Foot and Flange mounted motors combines feet for surface attachment and a flange for direct equipment connection. This dual-mounting option offers versatility, emphasizing adherence to manufacturer guidelines for proper installation and performance.

20. READING OF IM CODE: Code example: IM B3  Code example: IM 1001  

21. Direct On-Line (D.O.L.) Starting : In this method, the motor draws a high starting current (about 4 to 7 times of the rated current) and at low power factor. Therefore, DOL starting is suitable for relatively small motors (up to 10 kW). Stator Resistance Starting : In this method, external resistance is connected in series with each phase of the stator winding during starting. The external resistance causes voltage to drop across it so that reduced voltage available across the motor terminals. Hence, the starting current is reduced. The starting external resistances are gradually cut out in steps from the stator circuit, as the motor accelerates. When the motor attains the rated speed, the starting resistances are completely cut out and full line voltage is applied across the motor terminals. Autotransformer Starting : Autotransformer starting is employed to reduce the starting voltage of induction motors, typically for motors over 25 hp. A change-over switch is used to initially connect the autotransformer, providing 60-80% of the line voltage during motor start. This minimizes starting current to a safe level. As the motor reaches about 80% of its rated speed, the switch is shifted to 'Run,' eliminating the autotransformer and applying full line voltage. This method offers advantages like low power loss and reduced starting current. Star-Delta Starting : In the star-delta starting method for squirrel cage induction motors, the stator windings initially operate in a star configuration during starting. The six leads of the stator winding are connected to a change-over switch. When the motor starts, the switch is set to 'Star,' connecting the windings in a star arrangement, allowing each phase to receive V/√3 volts, reducing the starting current. Once the motor reaches 80% of its rated speed, the switch is shifted to 'Delta,' changing the connection to a delta configuration. This provides full line voltage to each phase for efficient running of the motor. This method helps in limiting starting current and is commonly used in induction motors. Rotor Resistance Starting: In the rotor resistance starting method, a star-connected variable resistance is introduced into the rotor circuit of an induction motor through slip rings. Initially, during startup, the variable resistance handle is in the 'OFF' position, adding maximum resistance to each phase of the rotor circuit. This reduces the starting current and enhances starting torque due to the external rotor resistance. As the motor accelerates, the external resistance is progressively eliminated from the rotor circuit. Once the motor reaches its rated speed, the handle is switched to the 'ON' position, completely removing external resistance and allowing the motor to operate at full efficiency. This method optimizes starting conditions by controlling rotor resistance during the acceleration phase. THREE PHASE INDUCTION MOTOR STARTING METHODS

22. Direct On-Line (D.O.L.) Stator Resistance Autotransformer Star-Delta Rotor Resistance

23. MOTOR FRAME SIZE

24. An electric motor frame refers to the main structural components that provide support and housing for the internal parts of an electric motor. The key elements of an electric motor frame typically include: End Brackets/End Bells – These caps on each end of the motor house the bearings that support the motor shaft.

25. There are three types of frame Small Medium Large

26. MOTOR POWER RATING: This indicates how much power the motor can generate and consume. Similarly, the kVA and horsepower ratings are for the motors’ generators and alternators. While these numbers represent the motor’s output, they do not reflect the overall power factor. It relates to motor current and voltage suplly

27. Example

28. Horse power of a motor Horsepower (hp) is a  unit of measurement   of  power , or the rate at which  work  is done, usually in reference to the output of engines or motors. There are many different standards and types of horsepower. Two common definitions used today are the  mechanical horsepower  (or  imperial horsepower ), which is about 745.7  watts , and the  metric horsepower , which is approximately 735.5 watts.

29. Motor Horsepower Calculations (Mechanical Power Output) Mechanical power can also be defined in Horsepower (hp). For example, a mechanical power level of 1 hp is equivalent to 746 watts (W) or 0.746 kilowatts. Here is a formula for electric motor horsepower calculations: Where: P out =Output power (hp) t=Torque (lbf.ft) N=Rotational speed (rpm)

30. Types Of Insulation Class in Motors The insulation of the winding in your electric motor has a major impact on your life expectancy and reliability. Which means that using the wrong insulation class can be very expensive. The best way to avoid this error is to familiarize yourself with the basic concepts of insulation classes. The purpose of the motor insulation classes is to describe the insulation capacity of the motor winding to handle heat. There are currently four classes of electrical motor insulation in use: A, B, F and H (although there are also classes N, R and S). Of these four, B, F and H are the most commonly used. These classes specify the allowable temperature rise from an ambient temperature of 40 ° C.

31. Types Of Insulation Class in Motors Class A: Maximum temperature rise: 60 ° C Hot spot over-temperature allowance: 5 ° C Maximum winding temperature: 105 ° C Class B: Maximum temperature rise: 80 ° C Hot spot over-temperature allowance: 10 ° C Maximum winding temperature: 130 ° C

32. Types Of Insulation Class in Motors Class F: Maximum temperature rise: 105 ° C Hot spot over-temperature allowance: 10 ° C Maximum winding temperature: 155 ° C Class H: Maximum temperature rise: 125 ° C Hot spot over-temperature allowance: 15 ° C Maximum winding temperature: 180 ° C

33. Types Of Insulation Class in Motors The maximum winding temperature is the sum of the ambient temperature (40 ° C) and the permitted temperature rise. The permitted temperature rise is made up of two parts: the maximum temperature rise for the insulation class plus a hot spot on the temperature allowance.

34. Why winding temperature is important When your electric motor operates at a temperature above the allowable winding temperature, the service life will always be reduced.In fact, an increase of 10 ° C above the maximum allowed can halve the life of the motor insulation. If you have a Class A insulated motor, the maximum winding temperature will be 105 ° C. If you are operating at 105 ° C, this means 20 ° C above its limits and each increment of 10 ° above this limit reduces the life span in 1/2. This operating temperature will reduce the engine’s service life to just 1/4 of its original life expectancy!Remember that the engine’s surface temperature may appear high, but it is still within limits.Say you have a Class F insulated motor rated for a winding temperature of 155 ° C.

35. Why winding temperature is important You or one of your technicians inadvertently put your hand on the surface of the engine and notice that the engine is hot. Is the engine too hot? Maybe, but probably not. A rule of thumb is that the surface temperature is usually only 30 ° C lower than the winding temperature. So with all that said, an engine that is extremely hot to the touch is not necessarily operating beyond its rated temperature.