Electric Motor

 

TYPES OF MOTOR:

ELECTRIC MOTORS
DC MOTORS		AC MOTORS		OTHER MOTORS
DC Shunt Motor		Induction Motor		Stepper Motor
Separately Excited Motor		Synchronous Motor		Brush-less Motor
Series Motor				Hysteresis Motor
MPMDC Motor				Reluctance Motor
Compound Motor				Universal Motor

 

An induction motor or asynchronous motor is an AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stater winding. An induction motor can therefore be made without electrical connections to the rotor.

 An induction motor's rotor can be either wound type (Slip ring rotor) or squirrel-cage type.

A synchronous electric motor is an AC motor in which, at steady state, the rotation of the shaft is synchronized with the frequency of the supply current; the rotation period is exactly equal to an integral number of AC cycles. Synchronous motors contain multi phase AC electromagnets on the stator of the motor that create a magnetic field which rotates in time with the oscillations of the line current. The rotor with permanent magnets or electromagnets turns in step with the stator field at the same rate and as a result, provides the second synchronized rotating magnet field of any AC motor. A synchronous motor is termed doubly fed if it is supplied with independently excited multiphase AC electromagnets on both the rotor and stator.

The synchronous motor and induction motor are the most widely used types of AC motor. The difference between the two types is that the synchronous motor rotates at a rate locked to the line frequency since it does not rely on current induction to produce the rotor's magnetic field. By contrast, the induction motor requires slip: the rotor must rotate slightly slower than the AC alternations in order to induce current in the rotor winding. Small synchronous motors are used in timing applications such as in synchronous clocks, timers in appliances, tape recorders and precision servomechanisms in which the motor must operate at a precise speed; speed accuracy is that of the power line frequency, which is carefully controlled in large interconnected grid systems.

 

MOTOR NAME PLATE:

Make
Order No		Frame	324T
Type	SD 100	Service Factor	1.15
HP/KW	30	VOLTS	415
AMPS	40.8	Phase (Ø)	3
R.P.M. (n)	1485	Hz	50
Duty	S1	Power Factor (cosØ)	1.0
Ingress Protection	IP55	Weight	556 lbs
Class Insulation	F	Efficiency (ɳ)	93.0
Connection		Ambient	0-50 °C
NEMA Design	A	KVA Code
DE Bearing		Opp. DE Bearing

 

 

Name Plate Terms	Meaning
Volts	Rated terminal supply voltage.
Amps	Rated full-load supply current. Some motor name plate have FLA - Full load Current
H.P.	Rated motor output in Horse power
R.P.M	Rated full-load speed of the motor.
Hertz	Rated supply frequency.
Frame	External physical dimension of the motor based on the NEMA standards
Duty	Motor load condition, whether it is continuous load, short time, periodic, etc.
Date	Date of manufacturing.
Class Insulation	Insulation class used for the motor construction. This specifies max. limit of the motor winding temperature.
NEMA Design	This specifies to which NEMA design class the motor belongs to.
Service Factor	Factor by which the motor can be overloaded beyond the full load.
NEMA Nom. Efficiency	Motor operating efficiency at full load.
PH	Specifies number of stator phases of the motor.
Pole	Specifies number of poles of the motor.
Y	Specifies whether the motor winding are Star (Y) connected or Delta (Δ) connected.
Safety Standard Symbol	Specifies the motor safety standard.

 

MOTOR DUTY/ LOAD CYCLE:

The term duty defines the load cycle to which the machine is subjected, including, if applicable, starting, electric braking, no-load, and rest de-energized periods, and including their duration and sequence in time. Duty considered as a generic term, for example, can be classified as a continuous duty, short-time duty, or periodic duty.

Continuous running duty (type S1)

For a motor suitable to this duty type, the rating at which the machine may be operated for an unlimited period is specified. This class of rating corresponds to the duty type whose appropriate abbreviation is S1.

The duty type S1 can be defined as operation at a constant load maintained for sufficient time to allow the machine to reach thermal equilibrium.

 

Short-time duty (type S2)

For a motor suitable to this duty type, the rating at which the machine, starting at ambient temperature, may be operated for a limited period is specified. This class of rating corresponds to the duty type whose appropriate abbreviation is S2.

The duty type S2 can be defined as operation at constant load for a given time, less than that required to reach thermal equilibrium, followed by a time de-energized and at rest of sufficient duration to re-establish the equilibrium between the machine temperature and that of the coolant temperature.

A complete designation provides the abbreviation of the duty type followed by an indication of the duration of the duty (S2 40 minutes).

 

Periodic duty (type S3-S8)

For a motor suitable to this duty type, the rating at which the machine may be operated in a sequence of duty cycles is specified. With this type of duty, the loading cycle does not allow the machine to reach thermal equilibrium.

This set of ratings is linked to a defined duty type from S3 to S8 and the complete designation allows identification of the periodic duty.

If no otherwise specified, the duration of a duty cycle shall be 10 minutes and the cyclic duration factor shall have one of the following values: 15%, 25%, 40%, 60%.

The cyclic duration factor is defined as the ratio between the period of loading, including starting and electric braking, and the duration of the duty cycle, expressed as a percentage.

 Intermittent periodic duty (Duty type S3)

DEFINITION – The duty type S3 is defined as a sequence of identical duty cycles, each including a time of operation at constant load and a time de-energized and at rest. The contribution to the temperature-rise given by the starting phase is negligible.

A complete designation provides the abbreviation of the duty type followed by the indication of the cyclic duration factor (S3 30%).

 Intermittent periodic duty with starting (The duty type S4)

The duty type S4 is defined as a sequence of identical duty cycles, each cycle including a significant starting time, a time of operation at constant load and a time de-energized and at a rest.

A complete designation provides the abbreviation of the duty type followed by the indication of the cyclic duration factor, by the moment of inertia of the motor J_M and by the moment of inertia of the load J_L, both referred to the motor shaft (S4 20% J_M = 0.15 kg m² J_L = 0.7 kg m²).

Intermittent periodic duty with electric braking (The duty type S5)

The duty type S5 is defined as a sequence of identical duty cycles, each cycle consisting of a starting time, a time of operation at constant load, a time of electric braking and a time de-energized and at a rest.

A complete designation refers to the duty type and gives the same type of indication of the previous case.

 

Continuous-operation periodic duty (The duty type S6)

The duty type S6 is defined as a sequence of identical duty cycles, each cycle consisting of a time of operation at constant load and a time of operation at no-load. There is no time de-energized and at rest.

A complete designation provides the abbreviation of the duty type followed by the indication of the cyclic duration factor (S6 30%).

 

Continuous-operation periodic duty with electric braking (Duty type S7)

The duty type S7 is defined as a sequence of identical duty cycles, each cycle consisting of a starting time, time of operation at constant load and a time of electric braking. There is no time de-energized and at rest.

A complete designation provides the abbreviation of the duty type followed by the indication of both the moment of inertia of the motor J_M and the moment of inertia of the load J_L (S7 J_M = 0.4 kg m² J_L = 7.5 kg m²).

Continuous-operation periodic duty with related load / speed (Duty type S8)

The duty type S8 is defined as a sequence of identical duty cycles, each consisting of a

time of operation at constant load corresponding to a predetermined speed of rotation, followed by one or more times of operation at other constant loads corresponding to different speeds of rotation. There is no time de-energized and at rest.

A complete designation provides the abbreviation of the duty type followed by the indication of the moment of inertia of the motor J_M and by the moment of inertia of the load J_L, together with the load, speed and cyclic duration factor, for each speed condition (S8 J_M = 0.7 kg m² J_L = 8kgm² 25kW 800rpm 25% 40kW 1250rpm 20% 25 kW 1000 rpm 55%).

Non-periodic duty (type S9)

Duty with non-periodic load and speed variations

For a motor suitable to this duty type, the rating at which the machine may be operated non-periodically is specified. This class of rating corresponds to the duty type whose appropriate abbreviation is S9.

The duty type S9 is defined as a duty in which generally load and speed vary non-periodically within the permissible operating range. This duty includes frequently appplied overloads which may greatly exceed the reference load.

Duty with discrete constant loads and speeds (type S10)

For a motor suitable to this duty type, the rating at which the machine may be operated with a specific number of discrete loads for a sufficient time to allow the machine to reach thermal equilibrium is specified.
The maximum permissible load within one cycle shall take into consideration all parts of the machine (the insulation system, bearings or other parts with respect to thermal expansion).

The maximum load shall not exceed 1.15 times the value of the load based on duty type S1. Other limits as regards the maximum load may be given in terms of limits of temperature of the winding. The minimum load may have the value zero, when the machine operates at no-load or is de-energized and at rest.

This class of rating corresponds to the duty type whose appropriate abbreviation is S10.

The duty type S10 is defined as the operation characterized by a specific number of discrete values of load maintained for a sufficient time to allow the machine to reach thermal equilibrium. The minimum load during a duty cycle may have value zero and be relevant to a no- load or rest condition.

A complete designation provides the abbreviation of the duty type followed by the indication of the per unit quantities p/Δt for the partial load and its duration, and by the indication of the per unit quantity T_L which represents the thermal life expectancy of the insulation system related to the thermal life expectancy in case of duty type S1 with rated output, and by the quantity r which indicates the load for a time de-energized and at rest (S10 p/Δt = 1.1/0.4; 1/0.3; 0.9/0.2; r/0.1 T_L = 0.6).

INGRESS PROTECTION:

Ingress protection ratings or IP ratings refer to the level of protection offered by an electrical enclosure, against solids and liquids. In an environment where dust or water could damage electronic components, a sealed enclosure is used to prevent such ingress and safe house the electronics.

IP (INGRESS PROTECTION) RATING GUIDE
SOLID		LIQUID
Level of Ingress Protection		Level of Ingress Protection
1	Protected against a solid object greater than 50 mm (such as a hand)(50 N of force)	1	Protected against vertical falling drop of water for 10 minutes at rate of 1 mm/min.
2	Protected against a solid object greater than 12.5 mm (such as a finger)(10N of force)	2	Protected against diagonally falling (up to 15 Deg.) drop of water for 10 minutes at rate of 3 mm/min.
3	Protected against a solid object greater than 2.5 mm (such as a screwdriver)(3N of force)	3	Protected against diagonally falling (up to 60 Deg.) spray of water for 5 minutes at 0.7 LPM at 80-100 kPa.
4	Protected against a solid object greater than 1 mm (such as a wire)(3N of force)	4	Protected against water splashed from all direction for 5 minutes at 0.7 LPM at 80-100 kPa.
5	Dust protected. Limited ingress of dust permitted. Will not interfere with operation of equipment.	5	Protected against a 6.3mm water nozzle for 3 minutes at rate of 12.5 LPM at 30 kPa at a distance of 3 meter.
6	Dust tight. No ingress of dust.	6	Protected against a 12.5mm water nozzle for 3 minutes at rate of 100 LPM at 100 kPa at a distance of 3 meter.
		7	Protected against 30 minute submersion at a depth of 1 meter.
		8	Protected against continuous submersion for a long period at a depth of 3 meter.
		9K	Protected against powerful, high temperature water jets.

 

 

Insulation Classes for Electric Motors

NEMA (National Electrical Manufacturers Association) motor insulation classes describes the ability of motor insulation in the windings to handle heat. There are four insulation classes in use namely: A, B, F, and H. All four classes identify the allowable temperature rise from an ambient temperature of 40° C (104° F). Classes B and F are the most common in many applications.

Temperature rises in the motor windings as soon as the AC motor is started. As shown in the table below, the combination of ambient temperature and allowed temperature rise equals the maximum rated winding temperature. Allowable temperature rise is made up of the maximum temperature rise for each insulation class plus a hot-spot over-temperature allowance. If the motor is operated at a higher winding temperature, service life will be reduced. As a rule,
a 10° C increase in the operating temperature above the allowed maximum can cut the motor’s insulation life expectancy in half.

The table below shows the different insulation classes as defined by NEMA:

Class	Maximum Ambient Temperature (°C)	Maximum Temperature Rise (°C)	Hot-spot Over Temperature (°C)	Maximum Winding Temperature (Tmax)(°C)
A	40	60	5	105
B	40	80	10	130
F	40	105	10	155
H	40	125	15	180

 

Hot-spot Over Temperature Allowance

Each insulation class has a margin allowed to compensate for the motor’s hot spot. The hot-spot is a point at the center of the motor’s winding where the temperature is higher.

FRAME SIZE:

The two-digit frame number relates to the shaft height in sixteenths of an inch. You can figure that a 48-frame motor will have a shaft height of 48 divided by 16, or 3 in. Similarly, a 56-frame motor has a shaft height of 3.5 in.