Lab manual Synchronous motor: Plot the V and inverted V- curve

 Bundwan Polytechnic

Department of Electrical Engineering

Lab Manual 

By- Palash Das 

Lecturer in Electrical Engineering.

Subject : Synchronous, Induction and Special Electrical Mchines.

Topic: Synchronous Motor- to plot the V’ curve and inverted V – curve

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Experiment Name: Conduct the test on load and no- load to plot the  V’ curve and inverted V – curve (at no- load )  of a Synchronous Motor.

Experiment No:

Experiment Date:

Aim: ∆ To plot V-curve of the synchronous motor

           ∆ To plot inverted V-  curve of the synchronous motor .

Theory:  Synchronous Motor – A synchronous motor is a double excited AC motor. It runs at speed of synchronous speed which bears a specific relation with supply frequency and pole of the machine. The construction of a synchronous motor  similar as the construction of an alternator. Some important points regarding the synchronous motor are following…

✓✓ It runs as a speed of synchronous speed produced by the supply

✓✓  It runs as a constant speed motor.

✓✓It acts as power factor  improvement device when runs no load or light load and leading power factor

✓✓ It can run in various power factor of the load.

✓✓ It is double excited synchronous AC Motor. Stator is supplied by AC and rotor is supplied by DC.

V – curve: It is the relation between  excitation current(If) and armature current (Ia).

When field current or excitation current is low, armature current is high at a instant of start . Armature current decreases due to the increase of field current at lagging load. ** . At leading load Ia increases due to the increase of If (Field current).This  can be observed in the right half portion of the curve.

Inverted V – Curve : It is the relation between power factor and field current.

·        At lagging load,  p.f increases due to the increase of field current and reaches its maximum value that is unity power factor. Now if, field current increases slighty then armature current starts to decrease at leading load.

Circuit diagram.

 

 

Connection: Connect the circuit as directed by the guidance.

 

Precautions:

Ø  Connect the ammeters in series with load or supply .

Ø  Connect votmeter in parallel.

Ø  Don’t connect the field before start of the motor . After start, connect the field to the main circuit. Measure the speed of the motor after and before of the connection of field.

Specifications:

SL. No.	Equipment	Type	Range	Quantity
	Volt meter	MI
	Ammeter	MI MC
	Rheostat
	Tachometer	Digital
	Wattmeter
	Connection wires

 

Name plate:  3 Phase Synchronous Motor

Power Rating
Frequency
Speed
Power factor
Supply Voltage
Rated current
Field current
Field voltage

 

Data Table:

SL. No.	Field Current	Armature current	Power Factor

 

Calculations:

 

 

Graph:

Conclusions:

 

 

 

Viva Questions:

1.What is Synchronous Motor?

2.What is the effect of field current on power factor.

3. What do you mean by hunting?

4.Why synchronous motor is a double excited motor?

5.Write applications of synchronous motor ?