1. ACTIVE LEARING ASSIGNMENT
ELECTRONIC &COMMUNICATION
SEM-3 YEAR-2014/15
Electrical Machine
( )

2. VENUS INTERNATIONAL COLLAGE OF TECHNOLOGY
PREPARED BY :-
Pooja Patel ( )
Varsha Shukla ( )
Akshay Parekh ( )
Rohit Sutariya ( )
Brinda Gandhi ( )
GUIDED BY : NIRAJ PANDEY
VENUS INTERNATIONAL COLLAGE OF TECHNOLOGY

3. Motors & Motor Starters

4. Motors AC-Motors Parts of an Electric Motor
A. Stator : Stationary Frame
B. Rotor : Revolving Part
The rotary motion in an ac-motor is caused by the fundamental law of magnetism.
This law states that like poles repel and unlike poles attract.

5. Diagram of an ac-motor This shows a three phase, two pole stator.
Where A, B, and C are the three phases

6. Synchronous Speed
Speed at which it takes the motor to go one cycle and one revolution. S=[120*frequency}] (# poles) Example: For a three-phase, 60 Hertz, 2 pole motor: S=[120*60]/2=3600 revolutions per minute

7. Example. A 2 pole, 60 Hz motor runs at a full-load speed of 1760 rpm
Example. A 2 pole, 60 Hz motor runs at a full-load speed of 1760 rpm. What is the slip?

8. Ans. %slip= * =51.1%

9. Single-Phase Motors Supplied by single source of ac voltage
Rotor must be spun by hand in either direction, does not have a starting mechanism
Has no starting torque
Three different types of single-phase motors: split-phase, capacitor start, permanent split-capacitor, and shaded- pole motors

10. Resistance Split-Phase Motors
Has a start winding and a main winding
Winding currents are out of phase by 30 degrees, this produces a flux field that starts the motor
Main winding current (IM) and start winding current (IS) lags supply voltage (VL)
Start (inrush) current is high
Needs centrifugal starting switch or relay to disconnect the start winding (protects it from over heating)
Efficiency is between %

11. DC Motors Consists of an armature winding and a stator winding
Armature windings act as the rotor
Has three different classifications: constant torque, constant horsepower, or a combination of the two
Standard industrial dc motors are shunt wounded
Modifications of the dc motor are: shunt wound, stabilized shunt exciting fields, compound wound motors, and series wound motors

12. Armature Voltage Control
Is used for motor speeds below base speed
Output torque= T=k*ø*IA
k is machine constant
ø is the main pole flux
IA is the armature current

13. Shunt Field Control Is used for motor speeds above base speed
Horsepower, (HP)= Torque*rpm
5252
Where torque is in lb-ft

14. Speed Regulation Speed Regulation (IR)= no load rpm- full load rpm

15. Brushless DC Motors
Three phase ac power is converted into dc by the input side of the motor to charge up a bank of storage capacitors
These capacitors are called the Buss
The purpose of the buss is to store energy and supply dc power to transistors in the output side as the motor requires the power to start up

16. Brushless DC Motors
This picture is a representation of the encoders (rotor part of the motor) telling the corresponding transistors (stator) to turn on in order to get maximum torque from the motor

17. Motor Control Starters
Motor will draw high inrush current while the starter will slow current down
Starter reduces the amount of torque needed to start the motor

18. Magnetic Motor Starter
Normally open contacts
Not always possible to control amount of work applied to the motor
Has overloads
Motor may be overloaded resulting in damage to the motor
Open due to excessive motor current, high temperature, or a combination of both

19. Reversing Motor Starter
Contains two starters of equal size
Two starters connect to the motor
Interlocks are used to prevent both starters from closing their line contacts at the same time
Figure 14-4A

20. Reduced-voltage Motor Starter
Applies a percentage of the total voltage to start (50% - 80%)
After motor rotates, switching is provided to apply full voltage
Torque will be reduced when starting
Four types:
1) Autotransformer
2) Primary Resistance
3) Wye – Delta
4) Part Winding

21. Autotransformer Starter
Two contactors are used:
1) Start contactor
- Closes first and connects motor to the line
through an autotransformer
- Deenergizes
2) Run contactor
- Motor switches to this contacter which has
full voltage

22. Primary Resistor Starter
Two contactor
1) Line contactor
- First to energize connecting motor to the
line voltage through a resistor
- After preset time, contactor opens
2) Accelerating contactor
- Energizes
- Causes smooth acceleration to full voltage

23. Wye – Delta Starter Three contactors are used
1) Line contactor and start contactor
- Energizes first and connects motor in wye
putting about 58% of line voltage across
each motor phase
- Contacts open after preset time
2) Run contactor
- Energizes connecting motor in delta and
putting full voltage on the motor

24. Part Winding Starter
Starter supplies about 48% of normal starting torque
Not truly a reduced-voltage means
Two Types
1) Two-Step - one winding connected to
full voltage line and, after a preset time,
the other connects
2) Three-Step – one winding is connected in series
with a resistor to the voltage line; after interval, resistor
is shorted out and then second line is connected to
full voltage line

25. Solid-State Motor Starter
For lower starting torque and smooth acceleration
Used on conveyors, pumps, compressors, etc.