Lab Manual - Basic Electrical Engineering Electrical Engineering (EE) Notes | EduRev

Electrical Engineering (EE) : Lab Manual - Basic Electrical Engineering Electrical Engineering (EE) Notes | EduRev

 Page 1


                                                                                                                                JEE-Lab(EE-1202)/PBC/05 
DEPARTMENT OF ELECTRICAL ENGINEERING 
BENGAL ENGINEERING AND SCIENCE UNIVERSITY, SHIBPUR 
 
BASIC EE LABORATORY    First/ Second Semester  
Expt.No.1202-/1(a) 
 
FAMILIARISATION EXPERIMENT 
(VARIAC, POTENTIAL DIVIDER, MCV, MIV, MCA, MIA) 
 
Object : 1.  To become familiar with ‘POTENTIAL DIVIDER’ and ‘VARIAC’ 
 
  2.  To become familiar with Moving-coil and Moving-iron type ammeter and 
voltmeters and to understand the limitations of moving coil type 
instruments. 
 
THEORY: 1. POTENTIAL DIVIDER 
 
It is a device by which we can obtained a variable output d.c. voltage (whose magnitude 
can be varied from zero to the supply voltage) from a fixed d.c. supply. 
 
 
Fig. 1(a)     Fig. 1(b) 
 
 
With reference to Fig. 1(a), if 
 
R   = Resistance between moving contact points JJ 
R
1
 + R
2
 = resistance between the input terminals of the potential divider,  
when no current is flowing through the output circuit 
 
2 1
1
1
R R
V
I
+
= 
2 1
2
1 2 1 o
R R
R
V R . I V
+
= = = 
 
 1
Page 2


                                                                                                                                JEE-Lab(EE-1202)/PBC/05 
DEPARTMENT OF ELECTRICAL ENGINEERING 
BENGAL ENGINEERING AND SCIENCE UNIVERSITY, SHIBPUR 
 
BASIC EE LABORATORY    First/ Second Semester  
Expt.No.1202-/1(a) 
 
FAMILIARISATION EXPERIMENT 
(VARIAC, POTENTIAL DIVIDER, MCV, MIV, MCA, MIA) 
 
Object : 1.  To become familiar with ‘POTENTIAL DIVIDER’ and ‘VARIAC’ 
 
  2.  To become familiar with Moving-coil and Moving-iron type ammeter and 
voltmeters and to understand the limitations of moving coil type 
instruments. 
 
THEORY: 1. POTENTIAL DIVIDER 
 
It is a device by which we can obtained a variable output d.c. voltage (whose magnitude 
can be varied from zero to the supply voltage) from a fixed d.c. supply. 
 
 
Fig. 1(a)     Fig. 1(b) 
 
 
With reference to Fig. 1(a), if 
 
R   = Resistance between moving contact points JJ 
R
1
 + R
2
 = resistance between the input terminals of the potential divider,  
when no current is flowing through the output circuit 
 
2 1
1
1
R R
V
I
+
= 
2 1
2
1 2 1 o
R R
R
V R . I V
+
= = = 
 
 1
                                                                                                                                JEE-Lab(EE-1202)/PBC/05 
Procedure: 
 
i) Connect MCA and MIA in series and MCV and MIV in parallel as shown in 
Fig.1(b) 
ii) Note the positions of the moving contacts at which the output voltage is (a) 
approximately zero, (b) maximum and nearly equal to the supply voltage. 
iii) Keep the load resistance fixed. Vary the output voltage in 3 steps and record 
ammeter and voltmeter readings in Table I and of the data sheet. 
iv) Record what happens when terminal connections of MCA and MIA and also 
MCV and MIV are reversed, in Table II of the Data Sheet. 
 
THEORY : II – VARIAC 
 
Description: It is an a.c. device used to obtain variable output alternating voltages 
(magnitude can be varied from zero to a voltage even higher than the 
supply voltages). 
 
Procedure:  
1.  (i) Make connection as shown in Fig.2(a) below:  
 
 
    Fig. 2(a)     Fig. 2(b) 
  
 (ii) Vary the position of the moving contact and record ammeter and 
voltmeter readings in Table III of the Data Sheet. 
 
REPORT: 1(a) Moving coil instruments can measure only................................ 
  1(b) Moving iron instruments can measure ..................................... 
 
2. A moving-coil ammeter is giving deflections in the wrong direction. How 
can you make it to read in the proper direction? 
 
3. You are given a moving coil and a moving iron instrument. Can you 
recogrnise the meters from their scales? 
 
4. Can you use a potential divider for obtaining variable d.c. supply from a 
fixed a.c. supply? 
 
 2
Page 3


                                                                                                                                JEE-Lab(EE-1202)/PBC/05 
DEPARTMENT OF ELECTRICAL ENGINEERING 
BENGAL ENGINEERING AND SCIENCE UNIVERSITY, SHIBPUR 
 
BASIC EE LABORATORY    First/ Second Semester  
Expt.No.1202-/1(a) 
 
FAMILIARISATION EXPERIMENT 
(VARIAC, POTENTIAL DIVIDER, MCV, MIV, MCA, MIA) 
 
Object : 1.  To become familiar with ‘POTENTIAL DIVIDER’ and ‘VARIAC’ 
 
  2.  To become familiar with Moving-coil and Moving-iron type ammeter and 
voltmeters and to understand the limitations of moving coil type 
instruments. 
 
THEORY: 1. POTENTIAL DIVIDER 
 
It is a device by which we can obtained a variable output d.c. voltage (whose magnitude 
can be varied from zero to the supply voltage) from a fixed d.c. supply. 
 
 
Fig. 1(a)     Fig. 1(b) 
 
 
With reference to Fig. 1(a), if 
 
R   = Resistance between moving contact points JJ 
R
1
 + R
2
 = resistance between the input terminals of the potential divider,  
when no current is flowing through the output circuit 
 
2 1
1
1
R R
V
I
+
= 
2 1
2
1 2 1 o
R R
R
V R . I V
+
= = = 
 
 1
                                                                                                                                JEE-Lab(EE-1202)/PBC/05 
Procedure: 
 
i) Connect MCA and MIA in series and MCV and MIV in parallel as shown in 
Fig.1(b) 
ii) Note the positions of the moving contacts at which the output voltage is (a) 
approximately zero, (b) maximum and nearly equal to the supply voltage. 
iii) Keep the load resistance fixed. Vary the output voltage in 3 steps and record 
ammeter and voltmeter readings in Table I and of the data sheet. 
iv) Record what happens when terminal connections of MCA and MIA and also 
MCV and MIV are reversed, in Table II of the Data Sheet. 
 
THEORY : II – VARIAC 
 
Description: It is an a.c. device used to obtain variable output alternating voltages 
(magnitude can be varied from zero to a voltage even higher than the 
supply voltages). 
 
Procedure:  
1.  (i) Make connection as shown in Fig.2(a) below:  
 
 
    Fig. 2(a)     Fig. 2(b) 
  
 (ii) Vary the position of the moving contact and record ammeter and 
voltmeter readings in Table III of the Data Sheet. 
 
REPORT: 1(a) Moving coil instruments can measure only................................ 
  1(b) Moving iron instruments can measure ..................................... 
 
2. A moving-coil ammeter is giving deflections in the wrong direction. How 
can you make it to read in the proper direction? 
 
3. You are given a moving coil and a moving iron instrument. Can you 
recogrnise the meters from their scales? 
 
4. Can you use a potential divider for obtaining variable d.c. supply from a 
fixed a.c. supply? 
 
 2
                                                                                                                                JEE-Lab(EE-1202)/PBC/05 
 3
5. What are the differences between a variac and a potential divider? 
DATA SHEET 
 
TITLE OF THE EXPERIMENT:.................................................................................. 
 
PERFORMED BY:....................................................................... 
 
Date :...........................................    Roll No............................. 
 
Experiment No................... 
 
Apparatus used: 
 
No. Item Range Lab. No. 
    
    
    
    
    
    
    
    
 
A) EXPERIMENTAL DATA: 
 
TABLE – I 
 
Readings of No. of 
Obvs. MCA MIA MCV MIV 
Remarks 
      
      
      
      
      
 
TABLE – II 
 
METER Normal Connection Reversed Connections 
MCA   
MIA   
MCV   
MIV   
 
 
 
 
 
Page 4


                                                                                                                                JEE-Lab(EE-1202)/PBC/05 
DEPARTMENT OF ELECTRICAL ENGINEERING 
BENGAL ENGINEERING AND SCIENCE UNIVERSITY, SHIBPUR 
 
BASIC EE LABORATORY    First/ Second Semester  
Expt.No.1202-/1(a) 
 
FAMILIARISATION EXPERIMENT 
(VARIAC, POTENTIAL DIVIDER, MCV, MIV, MCA, MIA) 
 
Object : 1.  To become familiar with ‘POTENTIAL DIVIDER’ and ‘VARIAC’ 
 
  2.  To become familiar with Moving-coil and Moving-iron type ammeter and 
voltmeters and to understand the limitations of moving coil type 
instruments. 
 
THEORY: 1. POTENTIAL DIVIDER 
 
It is a device by which we can obtained a variable output d.c. voltage (whose magnitude 
can be varied from zero to the supply voltage) from a fixed d.c. supply. 
 
 
Fig. 1(a)     Fig. 1(b) 
 
 
With reference to Fig. 1(a), if 
 
R   = Resistance between moving contact points JJ 
R
1
 + R
2
 = resistance between the input terminals of the potential divider,  
when no current is flowing through the output circuit 
 
2 1
1
1
R R
V
I
+
= 
2 1
2
1 2 1 o
R R
R
V R . I V
+
= = = 
 
 1
                                                                                                                                JEE-Lab(EE-1202)/PBC/05 
Procedure: 
 
i) Connect MCA and MIA in series and MCV and MIV in parallel as shown in 
Fig.1(b) 
ii) Note the positions of the moving contacts at which the output voltage is (a) 
approximately zero, (b) maximum and nearly equal to the supply voltage. 
iii) Keep the load resistance fixed. Vary the output voltage in 3 steps and record 
ammeter and voltmeter readings in Table I and of the data sheet. 
iv) Record what happens when terminal connections of MCA and MIA and also 
MCV and MIV are reversed, in Table II of the Data Sheet. 
 
THEORY : II – VARIAC 
 
Description: It is an a.c. device used to obtain variable output alternating voltages 
(magnitude can be varied from zero to a voltage even higher than the 
supply voltages). 
 
Procedure:  
1.  (i) Make connection as shown in Fig.2(a) below:  
 
 
    Fig. 2(a)     Fig. 2(b) 
  
 (ii) Vary the position of the moving contact and record ammeter and 
voltmeter readings in Table III of the Data Sheet. 
 
REPORT: 1(a) Moving coil instruments can measure only................................ 
  1(b) Moving iron instruments can measure ..................................... 
 
2. A moving-coil ammeter is giving deflections in the wrong direction. How 
can you make it to read in the proper direction? 
 
3. You are given a moving coil and a moving iron instrument. Can you 
recogrnise the meters from their scales? 
 
4. Can you use a potential divider for obtaining variable d.c. supply from a 
fixed a.c. supply? 
 
 2
                                                                                                                                JEE-Lab(EE-1202)/PBC/05 
 3
5. What are the differences between a variac and a potential divider? 
DATA SHEET 
 
TITLE OF THE EXPERIMENT:.................................................................................. 
 
PERFORMED BY:....................................................................... 
 
Date :...........................................    Roll No............................. 
 
Experiment No................... 
 
Apparatus used: 
 
No. Item Range Lab. No. 
    
    
    
    
    
    
    
    
 
A) EXPERIMENTAL DATA: 
 
TABLE – I 
 
Readings of No. of 
Obvs. MCA MIA MCV MIV 
Remarks 
      
      
      
      
      
 
TABLE – II 
 
METER Normal Connection Reversed Connections 
MCA   
MIA   
MCV   
MIV   
 
 
 
 
 
                                                                                                                                JEE-Lab(EE-1202)/PBC/05 
 4
 
DEPARTMENT OF ELECTRICAL ENGINEERING 
BENGAL ENGINEERING & SCIENCE UNIVERSITY, SHIBPUR 
 
BASIC EE LABORATORY                      First/ Second Semester  
 
Expt.No. 1202-/1(b) 
 
TITLE OF THE EXPERIMENT: “FAMILIARIZATION  WITH THE WATTMETER” 
 
Object : To become familiar with wattmeter connections at different current and 
voltage ratings. 
 
Theory : A wattmeter is an instrument which measures electrical power. 
                Power = voltage X current. 
               Thus a wattmeter has a voltage or pressure coil which senses voltage 
across the circuit of which the power is to be measured and a current coil which 
senses the current in the circuit. Thus a wattmeter will read when its current and 
pressure coils are excited simultaneously. So a wattmeter must have at least four 
terminals. The symbolic representation is shown in FIGURE-1. 
                However in portable wattmeter, quite often many more terminals are 
provided for measuring power at different current and voltage ranges. 
 
Procedure :  
              (i) Make connections as shown in the FIGURE-1 with current range of 
2.5A and voltage range of 125V/150V. 
              (ii) Adjust the variac output voltage to 125V/150V allowing a current to 
flow through the load. Record the wattmeter reading in TABLE-1 of the data 
sheet. 
              (iii) Change the voltage range to 250V/300V and record the wattmeter 
reading in table-2 
              (iv) Change the current range to 5A and record the wattmeter reading in 
TABLE-1. 
(v) Change the voltage range to 125V/150V and record the wattmeter 
reading in TABLE-1. 
(vi) See what happens when, 
a) the current coil is reversed 
b) The pressure coil is reversed 
c) Both current and pressure coils are reversed and complete 
TABLE-1. 
            
 
 
 
 
Page 5


                                                                                                                                JEE-Lab(EE-1202)/PBC/05 
DEPARTMENT OF ELECTRICAL ENGINEERING 
BENGAL ENGINEERING AND SCIENCE UNIVERSITY, SHIBPUR 
 
BASIC EE LABORATORY    First/ Second Semester  
Expt.No.1202-/1(a) 
 
FAMILIARISATION EXPERIMENT 
(VARIAC, POTENTIAL DIVIDER, MCV, MIV, MCA, MIA) 
 
Object : 1.  To become familiar with ‘POTENTIAL DIVIDER’ and ‘VARIAC’ 
 
  2.  To become familiar with Moving-coil and Moving-iron type ammeter and 
voltmeters and to understand the limitations of moving coil type 
instruments. 
 
THEORY: 1. POTENTIAL DIVIDER 
 
It is a device by which we can obtained a variable output d.c. voltage (whose magnitude 
can be varied from zero to the supply voltage) from a fixed d.c. supply. 
 
 
Fig. 1(a)     Fig. 1(b) 
 
 
With reference to Fig. 1(a), if 
 
R   = Resistance between moving contact points JJ 
R
1
 + R
2
 = resistance between the input terminals of the potential divider,  
when no current is flowing through the output circuit 
 
2 1
1
1
R R
V
I
+
= 
2 1
2
1 2 1 o
R R
R
V R . I V
+
= = = 
 
 1
                                                                                                                                JEE-Lab(EE-1202)/PBC/05 
Procedure: 
 
i) Connect MCA and MIA in series and MCV and MIV in parallel as shown in 
Fig.1(b) 
ii) Note the positions of the moving contacts at which the output voltage is (a) 
approximately zero, (b) maximum and nearly equal to the supply voltage. 
iii) Keep the load resistance fixed. Vary the output voltage in 3 steps and record 
ammeter and voltmeter readings in Table I and of the data sheet. 
iv) Record what happens when terminal connections of MCA and MIA and also 
MCV and MIV are reversed, in Table II of the Data Sheet. 
 
THEORY : II – VARIAC 
 
Description: It is an a.c. device used to obtain variable output alternating voltages 
(magnitude can be varied from zero to a voltage even higher than the 
supply voltages). 
 
Procedure:  
1.  (i) Make connection as shown in Fig.2(a) below:  
 
 
    Fig. 2(a)     Fig. 2(b) 
  
 (ii) Vary the position of the moving contact and record ammeter and 
voltmeter readings in Table III of the Data Sheet. 
 
REPORT: 1(a) Moving coil instruments can measure only................................ 
  1(b) Moving iron instruments can measure ..................................... 
 
2. A moving-coil ammeter is giving deflections in the wrong direction. How 
can you make it to read in the proper direction? 
 
3. You are given a moving coil and a moving iron instrument. Can you 
recogrnise the meters from their scales? 
 
4. Can you use a potential divider for obtaining variable d.c. supply from a 
fixed a.c. supply? 
 
 2
                                                                                                                                JEE-Lab(EE-1202)/PBC/05 
 3
5. What are the differences between a variac and a potential divider? 
DATA SHEET 
 
TITLE OF THE EXPERIMENT:.................................................................................. 
 
PERFORMED BY:....................................................................... 
 
Date :...........................................    Roll No............................. 
 
Experiment No................... 
 
Apparatus used: 
 
No. Item Range Lab. No. 
    
    
    
    
    
    
    
    
 
A) EXPERIMENTAL DATA: 
 
TABLE – I 
 
Readings of No. of 
Obvs. MCA MIA MCV MIV 
Remarks 
      
      
      
      
      
 
TABLE – II 
 
METER Normal Connection Reversed Connections 
MCA   
MIA   
MCV   
MIV   
 
 
 
 
 
                                                                                                                                JEE-Lab(EE-1202)/PBC/05 
 4
 
DEPARTMENT OF ELECTRICAL ENGINEERING 
BENGAL ENGINEERING & SCIENCE UNIVERSITY, SHIBPUR 
 
BASIC EE LABORATORY                      First/ Second Semester  
 
Expt.No. 1202-/1(b) 
 
TITLE OF THE EXPERIMENT: “FAMILIARIZATION  WITH THE WATTMETER” 
 
Object : To become familiar with wattmeter connections at different current and 
voltage ratings. 
 
Theory : A wattmeter is an instrument which measures electrical power. 
                Power = voltage X current. 
               Thus a wattmeter has a voltage or pressure coil which senses voltage 
across the circuit of which the power is to be measured and a current coil which 
senses the current in the circuit. Thus a wattmeter will read when its current and 
pressure coils are excited simultaneously. So a wattmeter must have at least four 
terminals. The symbolic representation is shown in FIGURE-1. 
                However in portable wattmeter, quite often many more terminals are 
provided for measuring power at different current and voltage ranges. 
 
Procedure :  
              (i) Make connections as shown in the FIGURE-1 with current range of 
2.5A and voltage range of 125V/150V. 
              (ii) Adjust the variac output voltage to 125V/150V allowing a current to 
flow through the load. Record the wattmeter reading in TABLE-1 of the data 
sheet. 
              (iii) Change the voltage range to 250V/300V and record the wattmeter 
reading in table-2 
              (iv) Change the current range to 5A and record the wattmeter reading in 
TABLE-1. 
(v) Change the voltage range to 125V/150V and record the wattmeter 
reading in TABLE-1. 
(vi) See what happens when, 
a) the current coil is reversed 
b) The pressure coil is reversed 
c) Both current and pressure coils are reversed and complete 
TABLE-1. 
            
 
 
 
 
                                                                                                                                JEE-Lab(EE-1202)/PBC/05 
Report : 1) Calculate multiplying factors from the current and voltage ranges 
used. When power factor is unity, 
                          Voltage range used X Current range used X Power factor (Cosø)  
Multiplying Factor = ---------------------------------------------------------------------------------
------ 
                                                                  Full scale division 
2) A wattmeter is giving negative deflection. How can you give the deflection in 
the correct direction? 
3) How do you specify a wattmeter? 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 5
L
O
A
D
A
PRESSURE
COIL
CURRENT 
COIL 
VARIAC
1-PH., 230V, 50 Hz 
A.C.SUPPLY 
DOUBLE POLE REWIRABLE
SWITCH FUSE UNIT
CIRCUIT DIAGRAM 
FOR FAMILIARIZATION OF WATTMETER 
MIA 
A L
COM V
WATTMETER
FIGURE-1
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