Experiment No. 4
Electrical Machines-II
Experiment No. 4
1.0
Title:To Synchronise the Three phase alternators by using Synchroscope / lamp method and study
load sharing.
2.0
Prior Concepts:•
•
3.0
EMF equation.
Alternator on load.
New Concepts:Proposition 1:- Effect of Speed on Frequency and Magnitude of Voltage:When speed of prime mover is increased then the frequency and magnitude of generated e.m.f.
increases.
Concept Structure 1:-
Proposition 2: Synchronising of Alternators:The process of connecting an alternator in parallel with another alternator or with common bus bars
is known as synchronizing. The conditions to be satisfied for synchronising are (i)
Terminal voltages should be equal.
(ii)
Frequency of EMF generated should be equal.
(iii)
Phase sequence of each alternator should be same.
Concept Structure 2:-
22 ♦
MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION
Electrical Machines-II
4.0
Learning Objectives:4.1
4.2
5.0
Experiment No. 4
Intellectual Skills:-
•
•
•
To understand and state the necessity of Synchronisation.
To understand effect of speed and field current on EMF.
To select proper instruments and loading arrangement.
Motor Skills:-
•
•
•
•
•
To make the connections as per circuit diagram.
To start the motor i.e. the prime mover of each alternator.
To adjust the terminal voltage to the rated value of each alternator.
To synchronise two alternators.
To observe and note the load shared by two alternators.
Equipments :–
A)
•
•
•
•
•
•
•
•
•
•
•
B)
•
For Synchronisation of two alternators
DC Motor coupled to alternator
DC Motor - —— HP, ——— V.,———— A, ——— rpm.
Alternator - ——— V, ——— kVA, ——A, 3 ph. ,50 Hz, ——— rpm.
Two similar sets.
Ammeters – (a.c.) ……….. A
- 06 No.
Ammeters – (d.c.) ……….. A -02 No. ; ………….. A
- 02 No.
Voltmeters –(a.c.) ………... volts
- 02 No.
Voltmeters –(d.c.) ………... volts
- 02 No.
Phase sequence indicator
Frequency meter
Synchroscope
Synchronising lamp set
Tachometer
Rheostats – (R1) ——— Ohm, —— A; (R2)——— Ohm, ——— A.
OR
Alternator Synchronising panel having similar setup
Load sharing by Two alternators :
In addition to instrument setup in part A,
Three phase suitable balanced load (Resistive , Inductive or Capacitive)
MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION
♦ 23
Experiment No. 4
6.0
Circuit Diagram :–
A)
24 ♦
Electrical Machines-II
Circuit Diagram for Synchronisation of two three phase alternators
MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION
Electrical Machines-II
B)
7.0
Experiment No. 4
Circuit Diagram for sharing of load by two alternators
Stepwise Procedure :A)
For synchronisation of alternators
1.
Switch ON Main supply.
2.
Switch ON both MCB ( if applicable).
3.
Adjust the DC voltage to rated value with dimmer of DC motor set 1.
4.
Start the DC Motor with three point starter.
5.
Adjust the speed of DC motor up to rated speed by field control.
6.
Give the excitation to set 1 and adjust the AC voltage of alternator 1 to rated value as
indicated on the digital voltmeter on the panel or analog voltmeter on work table.
7.
Adjust the speed and check the frequency as indicated by digital / analog frequency
meter on the panel or work table.
8.
Switch ON the contactor 1( if applicable).
9.
Adjust the DC voltage to rated value with dimmer of DC motor set 2.
10.
Start the DC Motor with three point starter.
11.
Adjust the speed of DC motor up to rated value by field control.
12.
Give the excitation to set 2 and adjust the AC voltage of alternator 2 to rated value as
indicated on the digital voltmeter on the panel or analog voltmeter on the work table.
13.
Adjust the speed and check the frequency as indicated by digital frequency meter on
the panel or analog meter on work table.
14.
Switch ON the contactor 3 (if applicable).
MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION
♦ 25
Experiment No. 4
15.
16.
17.
18.
19.
20.
21.
B)
8.0
Electrical Machines-II
Check the phase sequence of each alternator.
Check whether the incoming machine is slow or fast by synchroscope. Adjust the
speed and see that the speeds are equal.
Check whether the speeds are equal by lamp method.
Synchronise both alternators by synchroscope or lamp method.
Reduce the excitation of both alternator to zero.
Reduce the voltage across each of the DC motor to zero.
Switch OFF both the motors.
For load sharing by two alternators
1.
Follow the steps 1 to 18 as in part A.
2.
Switch ON the load by closing contactor 5 (if applicable).
3.
Gradually increase the load in steps and take reading of load shared by both the
alternators.
4.
Change the excitation and observe the load sharing between alternator 1 and 2.
5.
Switch OFF the load.
6.
Reduce the excitation of both alternators to zero.
7.
Reduce the voltage across the DC motor to zero.
8.
Switch OFF both the motors.
Observation Table:A)
B)
For Synchronisation of alternators:
As such there are no observations to be taken. Only Conditions for Synchronising have to be
satisfied prior to synchronisation.
For Load sharing between two alternators:
Dated signature of
subject teacher
9.0
Conclusion :1.
2.
3.
4.
Two alternators can be synchronized when the required conditions are satisfied.
Load sharing between two alternators is possible if they are operated in parallel.
If the excitation of alternator is increased then load shared is ———————
If the excitation of alternator is decreased then load shared is ———————
10.0 Questions:(Note :- Teacher shall distribute the following questions in Three different groups)
1.
State the conditions for synchronisation of two alternators.
2.
Whether the alternator can be synchronised with an existing bus?
3.
State the effect of wrong synchronisation.
4.
State why pair of lamps are required in lamp method of synchronisation?
26 ♦
MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION
Electrical Machines-II
5.
6.
7.
8.
9.
10.
Experiment No. 4
State the advantages of parallel operation of two alternators.
State the effect of change in excitation and input to prime mover on load sharing of alternator.
Explain the necessity of synchronisation of alternators.
State the advantages of using number of small generating units instead of single large unit
for supplying power.
Why the frequency of incoming alternator is kept slightly higher than bus-bar frequency?
State how the load division is carried out in case of d.c. generators and in case of alternators?
Space for answers
MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION
♦ 27
Experiment No. 4
Electrical Machines-II
Space for answers
Remark / Grade
Date :-
28 ♦
Checked by
MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION
0
