bev 20501 electical engineering lab 1

BEV 20501

ELECTICAL ENGINEERING LAB 1

DEPARTMENT OF ELECTRICAL POWER

ENGINEERING

FACULTY OF ELECTRICAL AND

ELECTRONIC ENGINEERING

1

EXERCISE 1

ELECTRICAL WIRING INSTALLATION FOR LIGHTING CIRCUIT –

(1 NOS LAMP CONTROLLED BY 1 UNIT ONE-WAY SWITCH)

2

EXERCISE 1

ELECTRICAL WIRING INSTALLATION FOR LIGHTING CIRCUIT – (1 NOS LAMP CONTROLLED BY 1 UNIT ONE-WAY SWITCH)

LEARNING OUTCOME

1. To familiarize the students with wiring regulations.

2. To know the method of marking cables and colour codes.

3. To use proper tools according to desired application.

4. To determine suitable cable sizing and current rating.

5. To familiarize with installation accessories and fittings.

6. To Testing wiring installation.

CONTENT

1.1 THEORY

1.1.1 Definition of End Circuits

End circuit is defined as the circuit that link from distribution fuse box and terminates at load or outlet socket or electrical appliances within the corresponding wiring installation. In other words, end circuit involves final connection at consumer wiring installation up to distribution fuse box.

1.1.2 Types of End Circuit

There is two types of end circuit, which are:

(i) Lighting Circuit

(ii) Power Circuit

3

1.13 Lighting Circuit

This circuit involves the installation for lamps, ceiling fan, door bell, electric timer and etc. The maximum load that can be connected to one end circuit with 6A (MCB) rating is 10 points of lamp and fan. The rated power for each point of lamp or fan is assume to be 100W.

1.14 Switch

Switch is a mechanical device that can connect and cut off circuit manually or intermediately. Single phase supply typically utilize single pole switch, such as one-way switch, two-way switch and intermediate switch. There are various types and shape of switched available in the market.

1.15 One-Way Switch

One way switch is a device that can isolate and control end circuits. It is also known as a support switch and usually manufactured with two terminals. Normal current rating for this circuit is 6 A and for surface mounting, it employs the installation box.

Cable that is connected from LIVE point at distribution box up to switch terminal is known as LIFE wire while cable connection between switch terminals up to point lamp is known as SWITCH wire. NEUTRAL wire is connected from lamp point back to distribution box.

Figure 1.1: Diagram for simple application of one-way switch.

N Neutral Wire

L Life Wire

Lamp

Switch Wire

One-way switch

4

1.2 EQUIPMENTS / MATERIALS LIST

1.2.1 Wiring Hammer (cross pein)

1.2.2 Lead Strip Cutter / Scissor Cutter / Conduit Cutter

1.2.3 Combination Pliers

1.2.4 Side Cutter Pliers

1.2.5 Long Nose Pliers

1.2.6 Test – Pen

1.2.7 Screw Driver Set (Flat and Philip)

1.2.8 Measurement Tape / Ruler

1.2.9 Cordless Drill

1.2.10 Cables 1.5 mm2 pvc (3/0.737 mm2) – black, green, red, yellow, blue

1.2.11 PVC Casing @ PVC Pipe Conduit c/w accessories

1.2.12 PVC Round Block

1.2.13 PVC Switch Base

1.2.14 Ceiling Rose

1.2.15 Lamp Holder – Battent / Pandent

1.2.16 Bulbs / Lamps

1.2.17 One Way Switch – 1 Gang

1.2.18 Nails

1.2.19 Screws

1.2.20 Multimeter

5

ACTIVITIES

Activity 1

1. Estimate the actual measurement on the wiring board according to schematic diagram shown in Figure 1.2.

2. Estimate cables length appropriately.

3. Stack the base of PVC casing or PVC conduit on the wiring bay according to the circuit layout.

4. Lay cables along PVC casing or PVC conduit according to the wiring diagram.

5. Fitting the switch and lamp holder at the point of wiring.

6. Put the bulbs or lamps at the lamp holder.

7. Test the circuit using multimeter or others testing instrument based on Tables 1.1 and 1.2.

8. Connect the circuit to power supply and observe the circuit operation.

L1

S1

CEILING LEVEL

300 300

450

200

500

200

Figure 1.2 : Circuit Diagram (in mm scale)

6

L1

S1

LNE

CEILING LEVEL

L 1

L

N

E

Figure 1.3 : Wiring Diagram

7

Table 1.1: Continuity Test (Without Load)

S1 L-L N-N E-E

ON

OFF

Table 1.2: Short Circuit Test (With Load)

S1 L-N N-E L-E

ON

OFF

Activity 2 (Questions)

1. Define the term of electrical conductors.

2. Explain the electrical short circuit that occur in wiring.

3. Discuss the purpose of continuity and short circuit testing in wiring installation.

REFERENCE

1. Lab Sheet 1st Edition BEF 23401, Electrical Wiring Laboratory.

8

EXERCISE 2

ELECTRICAL WIRING INSTALLATION FOR POWER CIRCUIT –

(2 NOS SOCKET OUTLET 13A CONNECTED BY RADIAL CIRCUIT)

9

EXERCISE 2

ELECTRICAL WIRING INSTALLATION FOR POWER CIRCUIT – (2 NOS SOCKET OUTLET 13A CONNECTED BY RADIAL

CIRCUIT)

LEARNING OUTCOME

1. To familiarize the students with wiring regulations.

2. To know the method of marking cables and colour codes.

3. To use proper tools according to desired application.

4. To determine suitable cable sizing and current rating.

5. To familiarize with installation accessories and fittings.

6. To Testing wiring installation.

CONTENT

2.1 THEORY

2.1.1 Definition of End Circuits

End circuit is defined as the circuit that link from distribution fuse box and terminates at load or outlet socket or electrical appliances within the corresponding wiring installation. In other words, end circuit involves final connection at consumer wiring installation up to distribution fuse box.

2.1.2 Types of End Circuit

There is two types of end circuit, which are:

(i) Lighting Circuit

(ii) Power Circuit

10

2.1.3 Power Circuit

The wiring installation of power circuit can be divided into two types:

i) Radial Circuit

ii) Ring Circuit

2.1.4 Radial Circuit

A radial circuit is a mains power circuit found in some homes to feed sockets and lighting points. It is simply a length of appropriately rated cable feeding one power point then going on to the next. The circuit terminates with the last point on it. It does not return to the consumer unit or fuse box.

Radial circuits can therefore only serve a smaller area. Using 2.5mm2 PVC/PVC cable combined with a 20amp fuse/MCB an area less than 30 square meters is permissible. For 4mm2 cable, combined with a 32 A MCB or a 30 A cartridge fuse (a re-wirable fuse is not allowed) an area of 60 square meters is permissible.

Spurs can be added at points along the radial circuit if required. High powered appliances (cookers / showers) must have their own radial circuit.

Figure 2.1: Radial Circuit Diagram.

L

E N

Outlet Socket

11


2.2.1 Wiring Hammer (cross pein)

2.2.2 Lead Strip Cutter / Scissor Cutter / Conduit Cutter

2.2.3 Combination Pliers

2.2.4 Side Cutter Pliers

2.2.5 Long Nose Pliers

2.2.6 Test – Pen

2.2.7 Screw Driver Set (Flat and Philip)




2.2.11 PVC Casing @ PVC Pipe Conduit c/w accessories

2.2.12 PVC Socket Base

2.2.13 Socket Outlet 13A

2.2.14 Nails

2.2.15 Screws

2.2.16 Multimeter

2.2.17 Socket Tester

12

ACTIVITIES

Activity 1


2. Estimate cables length appropriately.

3. Stack the base of PVC casing or PVC conduit on the wiring bay according to the circuit layout.

4. Lay cables along PVC casing or PVC conduit according to the wiring diagram.

5. Fitting and install the socket outlet at the point of wiring.

6. Test the circuit using multimeter or others testing instrument based on Tables 2.1 to 2.4.


SO1SO2

CEILING LEVEL

300 300

500

200

450

Figure 2.2: Circuit Diagram (in mm scale)

13

CEILING LEVEL

SO1SO2

L N E

N L

E

LN

E

Figure 2.3: Wiring Diagram

Table 2.1: Continuity Test Between Input and SO1

S01 L-L N-N E-E

ON

OFF

14

Table 2.2: Continuity Test Between Input and SO2

S02 L-L N-N E-E

ON

OFF

Table 2.3: Continuity Test Between SO1 and SO2

SO1 SO2 L-L N-N E-E

ON ON

ON OFF

OFF ON

OFF OFF

Table 2.4: Short Circuit Test

L-N N-E E-L


1. Named two (2) types of PVC conduit that commonly used in electrical wiring.

2. Explain why the earth pin of a 13A plug top is longer than the line and neutral.

REFERENCE


15

EXERCISE 3

ELECTRICAL WIRING INSTALLATION FOR SUPPLY SYSTEM BELONG FROM KWH METER TO

CONSUMER CONTROL UNIT (DB)

16

EXERCISE 3

ELECTRICAL WIRING INSTALLATION FOR SUPPLY SYSTEM BELONG FROM KWH METER TO CONSUMER CONTROL UNIT (DB)

LEARNING OUTCOME

1.1 To familiarize the students with wiring regulations.

1.2 To know the method of marking cables and colour codes.

1.3 To use proper tools according to desired application.

1.4 To determine suitable cable sizing and current rating.

1.5 To familiarize with installation accessories and fittings.

1.6 To Testing wiring installation.

CONTENT

3.1 THEORY

3.1.1 Electrical Supply System

Electrical supply system is composed of two groups that belongs to:

i) Supplier

Is a cut out unit that consist of neutral link, service fuse and Kilowatt Hour Meter.

ii) Consumer

This system starts from distribution fuse box (DFB) that comprises main switch, earth life circuit breaker (ELCB), distribution fuse board and wiring installation system.

17

3.1.2 Consumer Control Unit

Below figure represent the general form of electrical supply system and end circuit.

Figure 3.1 : Electrical Supply System

3.1.3 Distribution Box

Distribution box is consist of:

a. Main Switch

b. Earth Life Circuit Breaker (ELCB)

c. Miniature Circuit Breaker (MCB)

1

2

3

4

5

6

2x20W Fluorescent lamp

1x65W Ceiling Fan

4x36W Down Light

3x40W Fluorescent lamp

2x65W CeilingFan

2x36W Bulp lamp

2x13A Outlet Socket

2x13A Outlet Socket

2x13A Spare

Cut Out Unit

And

Neutral Link

kWH 60A SPN

Main Switch

40A PLBB

ELCB

2x6mm2 PVC/PVC

2x1.5mm2 PVC

2x2.5mm2 PVC

PFA 6 ways

One pole

And Neutral

Belongs to Supplier Belongs to Consumer

Control Circuit End Circuit

18

3.1.3.1 Main Switch

Main Switch is a mechanical device that can open and connect circuit manually. Main switch can be used in the form of SPN (Single Pole and Neutral) or TPN (Triple Pole and Neutral). Main switch is very important as it protect circuit from excessive current or short circuit.

3.1.3.2 Earth Life Circuit Breaker (ELCB)

ELCB ensures the safety of electrical appliances user and electrical. It can be switch ON manually and TRIP automatically whenever earth leakage occurs.

3.1.3.3 Miniature Circuit Breaker (MCB)

MCB is a fuse-fuse or circuit breaker for electrical power distribution to end circuit or other sub circuit.


3.2.1 Toolbox c/w all handtools accessories




3.2.5 PVC Casing @ PVC Pipe Conduit cw accessories

3.2.6 Meter KwH

3.2.7 Cut-Out unit 60A

3.2.8 Neutral Link unit

3.2.9 PVC Meter Board

3.2.10 Distribution Box (DB)

3.2.11 Main Switch 32A

3.2.12 Earth Leakage Circuit Breaker (ELCB) 40A

19

3.2.13 Miniature Circuit Breaker (MCB)16A and 6A

3.2.14 Copper Busbar

3.2.15 PVC DB Board

3.2.16 Nails

3.2.17 Screws

3.2.18 Multimeter

3.2.19 Socket Tester

ACTIVITIES

Activity 1


2. Estimate the conduit or casing length and install it to the wiring bay area.

3. Install all accessories at the Distribution Box (Main Switch, ELCB and MCB) then, please make an installation to the PVC Distribution Board.

4. Install Cut-Out and Neutral Link unit and Meter KwH to the PVC Meter Board.

5. Install the complete (DB Board) and complete (Meter Board) on wiring bay and also lay cables along PVC casing or PVC condiut according to the wiring diagram.

6. Make the wiring fitting from Meter Board to Distribution Board (Please use the suitable size of the cables).

7. Test the circuit using multimeter or others testing instrument based on Tables 3.1 to 3.6.


20

CEILING LEVEL

200

200

450

DISTRIBUTION

BOARD

SET

METER

BOARD

SET

TO POWER CIRCUIT TO LIGHTING CIRCUIT

E

200

Figure 3.2: Circuit Diagram (in mm scale)

21

CEILING LEVEL

METER

BOARD

SET

DISTRIBUTION

BOARD

SET

LN

E

E N

TO END CIRCUITS

MAIN

SWITCHELCBMCB

METER

kWH

NEUTRAL

LINK

CUT-OUT

6A16A

Figure 3.3: Wiring Diagram

22

Table 3.1: Continuity Test Between Source and Output Meter

L-L N-N

Table 3.2: Continuity Test Between Output Meter and Output Main Switch

Main Switch L-L N-N

ON

OFF

Table 3.3: Continuity Test Between Output Main Switch and Output ELCB

ELCB L-L N-N

ON

OFF

Table 3.4: Continuity Test Between Output ELCB and Output MCB

MCB L-L

ON

OFF

Table 3.5: Continuity Test Between Output ELCB and Neutral Bar

N-N

Table 3.6: Continuity Test Between Earth Cable and Earth Bar

E-E

23


1. Explain the purpose of neutral cable in electrical wiring installation.

2. Discuss the purpose of grounding in electrical wiring installation.

3. Is there any difference between earthing and grounding? Please explain.

REFERENCE


24

EXERCISE 4

BASIC STATISTICAL SAMPLING

25

EXERCISE 4

BASIC STATISTICAL SAMPLING

LEARNING OUTCOME

1. To observe the value of statistical analysis as sampling technique.

2. To gain experience of analysis by analyzing experimental data.

3. To acquire the knowledge of sampling technique to be implemented in future undertakings/experiments.

CONTENT

4.1 THEORY

Statistical analysis is frequently performed on samples of very large quantities to determine the probable variation in values of the entire lot. The percentage of the entire lot which will fall within a specific range of values can be predicted quite accurately from the statistical analysis of the samples.

For example, a company may purchase a large quantity of some components such as resistors and decide to use the resistors in an application requiring a high degree of accuracy. If a statistical analysis on a sample of resistors shows that a very high percentage of the resistors are likely to fall within some predetermined range of values.

Under ideal conditions, a very large number of measurements will provide a distribution of readings, with the greatest number of readings approximately equal to the actual value. On either side of the actual value, the frequency of readings will decrease, producing an approximately normal distribution curve, as shown in Figure 4.1.

In this experiment students are given a task to perform a statistical analysis on three samples of different sizes. Using the data, students are advised to draw a plot and discuss it. The small size of the total lot and the samples may create a difficulty to conclude it completely in a valid way. However, this laboratory experience will still prove to be valuable to the students.

26

Equations:

Figure 4.1: Normal distribution curve.

4.2 EQUIPMENT LIST

4.2.1 Composition resistors of same color-coded value 60 units

4.2.2 Multimeter (preferably a digital multimeter) 1 unit

27

4.3 ACTIVITIES Activity 1

1. With the help of ohm meter measure and record the value of each resistor.

2. Select eight resistors at random from the total lot, measure and record their corresponding values in Table 4.1 (in column sample 1).

3. Mix all the resistors and select any 12 resistors randomly. The selection may or may not include resistors from the previous selection. Measure and record the values of the 12 resistors in Table 4.2 (in column sample 2).

4. Mix all the resistors together and select, at random, a sample of 16 resistors, measure and record their values in Table 4.1 (in column sample 3).

5. Plot (bar graph, or histogram, as shown in Figure 4.2) for each sample on a separate graph paper, in which each block represents a resistor having that value of resistance.

6. Divide it in three portions vertically. Plot a histogram for each of the three samples of resistors.

7. Connect maximum points of each histogram by making a smooth curve. If the numbers of resistors in the samples were much larger, then it would give an approximate normal distribution curve as shown in Figure 4.1. However, the curves may be skewed because samples are small.

8. Calculate average deviation “Dn” and standard deviation “Sn” of each sample and record their respective values in Table 4.1.

9. From Dn and Sn, choose the best, the second best and the worst sample and record their respective calculations in Table 4.2.

Figure 4.2: Distribution of resistance values around the expected value of 150 Ω.

28

Table 4.1: Sampling table.

Resistance value Sample 1 Sample 2

1 1 1

2 2 2

3 3 3

4 4 4

5 5 5

6 6 6

7 7 7

8 8 8

9 Average deviation for sample 1 D1=

9

10 10

11 11

12 12


Sample 3

14

15 1


2

17 3

18 4

19 5

20 Standard deviation for sample 1 S1=

6

21 7

22 8

23 9


10

25 11

26 12

27 13


14

29 15

30 16

Table 4.2: Best, second best and worst sample.

Best sample

Second best sample

Worst sample

29


1. Differentiate between “D” and “S”.

2. Discuss the results obtained for each “D” and “S”.

3. Give overview on the selection of the best sample, the second best sample and the worst sample.

REFERENCE

1. Lab Sheet 1st Edition BEF 23401, Electrical Power Measurement Laboratory.

30

EXERCISE 5

MEASUREMENT USING DC BRIDGES

31

EXERCISE 5

MEASUREMENT USING DC BRIDGES

LEARNING OUTCOME

1. To study the resistance measurement technique,by using Wheatstone bridge.

2. To study the resistance measurement technique, by using Kelvin Double bridge.

CONTENT

5.1 THEORY

5.1.1 Measurement of unknown resistance using DC Bridges

Accurate measurementsof resistances may be performed by using impedance-measuring bridges. There are a number of bridges, which are identified usually by their inventor's name to measure different type of resistances and impedances.A typical bridge circuit is given in Figure 5.1.

Figure 5.1: The basic impedance bridge.

32

When the equation (5.1) is satisfied, the voltages of nodes A and B are equal and the current of the detector, is zero.

Z1Z4 = Z2Z3.......(5.1)

The unknown impedance, Z4 is given by:

Z4 = (Z2/Z1) Z3.....(5.2)

For measuring real impedances, i.e., since all impedances are resistors therefore the bridge is known as Wheatstone bridge. For measuring capacitance, inductance or complex impedances at least one of the Z1, Z2, Z3 must becomplex in order to satisfy the balance equation.

5.1.2 Resistance Measurement using the Wheatstonebridges

The basic bridge circuit, that is the Wheatstone bridge, is suitable to measure medium range resistance. A DC voltage source and DC meter may be used in this case, since the impedances to be used are real.

Figure 5.2: Wheatstone bridge

For the resistive case the Equation 5.2 becomes:

Rx = (R2/R1) R3.....(5.3)

For the maximum sensitivity of the bridge all resistance values should be in the same range (as close to each other as possible) as a result of maximum power transfer theorem.

33

5.1.3 Resistance Measurement using the Kelvin Double bridges

Figure 5.3: The basic impedance bridge.

The Kelvin Double bridge is a modification of the Wheatstone bridge and provides greatly increased accuracy in the measurement of low-value resistances, generally below 1Ω. The term double bridge is used because the circuit contains a second set of ratio arms. The unknown resistance RX can be calculated as follows:

.....(5.4)

Where “Ry” is the yoke resistance which is measured between the node connecting “R3” and “b” and the node connecting “RX” and “a”. When the galvanometer registers a null point, R1/R2= a/b results as:

... (5.5)

34

5.2 EQUIPMENT LIST

5.2.1 Digital Multimeter 1 unit

5.2.2 DC power supply 1 unit

5.2.3 Galvanometer 1 unit

5.2.4 Variable Resistor 25K Ω 1 unit

5.2.5 Low value resistors as RX (unknown resistor) 2 unit

5.2.6 Connecting wires and wires with crocodile clips necessary

5.2.7 Portable Double bridge (Kelvin bridge)

Yokogawa 2769, 0.1 m Ω. to 110 Ω 1 unit

5.2.8 0.1 Ω,5 W wire wound resistor as standard resistor 1 unit

5.3 ACTIVITIES

5.3.1Activity 1

Determining an unknown resistor using Wheatstone bridge

1. Connect the Wheatstone bridge circuitas shown in Figure 5.2 with R1, R2 and R3 (Variable Resistor). Set R1=R2= 10kΩ. Use an unknown resistor with a relatively low resistance value, and 1V DC power supply for the voltage source. Connect a DCvoltmeter or multimeter between nodes V2-Vx as the initial detector.

2. By adjusting R3, obtain the balance of the bridge. (Note: Replace with a

galvanometer to achieve better accuracy once null point is reached by the multimeter/setDC voltmeter at low volt range).

3. Calculate the value of unknown resistance Rx using Equation 5.3.

4. Calculate the value of unknown resistance RX.

5. Record the values in Table 5.6 below:

Table 5.1: Adjusting arm resistance “R3” and unknown resistance “Rx”.

No. R1 R2 R3 RX

1. 10kΩ 10kΩ

35

5.3.2 Activity 2

Determining an unknown resistor by using Kelvin Bridge (Yokogawa 2769).

(Note: Before operating the portable Double bridge or Kelvin bridge please refer to the Laboratory Yokogawa folder to be familiar with the equipment first).

1. Make sure that the INT, BA as well as terminal are shorted securely.

Place the BA switch to OFF position, open the terminal .

2. Set the GA sensitivity dial to CH position. By doing this, check that the galvanometer driving battery is good. When the pointer of the galvanometer deflects to the blue zone on the scale, this shows that the battery is good.

Notes : Its take 1 to 2 second for stabilized indication.

3. Set the GA sensitivity dial to G2 and check that the galvanometer indication is in the zero position. If deviated, turn carefully the zero adjusting screw of the galvanometer to obtain a true zero point.

4. Connect the unknown resistor to the measuring terminals RX.

5. Select an appropriate multiplying constant plug position depending on an approximate value of the measured unknown resistor from Table 5.8, then firmly insert it into theposition.

6. Turn the BA switch ON.

7. Set the measuring dial to a position near the center, push the GA button switch momentarily and observe the galvanometer. If the deflection is on the (+) side,increase the dial value to obtain zero indication by repeating the above operation. When the indication comes near the zero position,push and turn the GA button switch either clockwise or counterclockwise to lock the switch. Then move the measuring dial to obtain zero indication on the galvanometer. If the indication is or the (-) side in the beginning of this adjustment, reduce the dial value and obtain zero indication in the same manner as above. If more sensitivity is required, select G1 position first and G0

8. When the galvanometer indication comes to zero through adjustment of the measuring dial, the resistance value of is calculated from the

following equation .

Hence Rx = (indication on the measuring dial) x (multiplying factor) Ω

= ………..Ω

9. When measurement is finished, first release the GA button switch, then turn off BA switch and set GA sensitivity dial to GA-OFF position.

36

Figure 5.4: Kelvin Bridge: Yokogawa 276910

1. Measuring dial - this dial is used to adjust the measuring arm.

2. Multiplying factor switching plug – the multiplying factor is selected by

this plug.

3. Battery switch – this switch turn on/off the power to the bridge.

4. Galvanometer button switch – the galvanometer is connected to the

bridge by depressing this switch. This switch is locked by turning it

clockwise or counterclockwise while keeping depressed.

5. Galvanometer sensitivity dial – the galvanometer sensitivity is selected

by this dial. G0 gives the highest sensitivity. G1 is medium and G2 is

lower than G1. With this switch, the galvanometer driving battery can be

checked through observing the meter. When the pointer is deflected to the

blue zone, this shows that the battery is good. Also this switch turns on/off

the galvanometer driving battery.

6. INT.BA –A- Terminal - when the self-contained battery is used to supply

power to the bridge, these terminals are short circuited by the short-bar.

1

10 9

2

8

6

7

3

4 5

Zero adjustor

37

7. EXT .BA –A- Terminal – when an external power supply is used ,these

terminal are short –circuited by the short bar.

8. Terminal – an unknown resistance is connected to these terminals.

The Rx terminals consist of current terminal C1,C2 and potential terminal

P1 and P2.

9. P2s Terminal – this is one of the potential terminals to switch the

standard F2771 is connected.

10. EXT. BA Terminal – an external battery is connected across these

terminals. The (-) side of the terminal is one of the current terminals to

which the external standard resistor is connected.

Table 5.2: Multiplying constant plug position.

Multiply Measuring range Standard Resistor

Resistance Accuracy Max. Current

0.0001 01mΩ to 1.1m Ω 0.01 Ω ±0.1% 10A

0.001 1mΩ to 11m Ω 0.1 Ω ±0.1% 3A

0.01 0.01 Ω to 0.11 Ω 1 Ω ±0.1% 1A

0.1 0.1 Ω to 1.1 Ω 10 Ω ±0.1% 0.3A

1 1 Ω to 11 Ω 100 Ω ±0.1% 0.1A

10 10 Ω to 110 Ω 0.01 Ω ±0.1% 0.01A

5.3.3 Activity 3 (Questions)

1. Differentiate between the accuracy of the Wheatstone bridge and Kelvin Double Bridge.

2. Signify the bridgeto be used for the measurement of a test resistor having a value around 50 kΩ?

3. Record experimentaldata.

Result from Wheatstone Bridge experiment

i. R3=………………………………..Ω

ii. Rx=……………Ω± ………………..%

38

4. Record experimental data.

Result from KelvinBridge experiment

i. Rx=…………… Ω± ………………..%

REFERENCE

1. Lab Sheet 1stEdition BEF 23401, Electrical Power Measurement Laboratory.

39

EXERCISE 6

POWER MEASUREMENT OF DC AND AC SINGLE

PHASE LOAD

40

EXERCISE 6

POWER MEASUREMENT OF DC AND AC SINGLE PHASE LOAD

LEARNING OUTCOME

1. To learn the method of measuring DC and AC single-phase power by using wattmeter.

2. To learn the technique of analysisto obtaining power factor through power measurement.

CONTENT

6.1 THEORY

6.1.1 ELECTRODYNAMOMETER WATTMETER

Figure 6.1(a) shows the internal connection of the current coil and the voltage coil of the wattmeter.

Figure 6.1(b) shows the schematic diagram used to represent wattmeter when connected to a load.

Figure 6.1: Alternating current-direct current wattmeter.

41

The electrodynamometer wattmeter employs a current circuit and a potential circuit. The current circuit consists of two fixed coils of heavy wire which are connected in series with the line.

The potential circuit consists of the two moving coils, usually wound with much smaller-diameter wire, connected in series with a high-value of non-inductive resistance, and whichis placed across the line.

Figure 6.1(b) also shows the simple connection of the wattmeter to measure power in a single phase circuit. The electrodynamometer wattmeter can be used to measure power in a dc as well as in ac circuit irrespective of the waveform.

6.1.2 WATTMETER SPECIFICATIONS

Normally inexpensive wattmeter’s have accuracies of +3%. There are more accurate instruments which have an accuracy of 0.25% of full scale deflection (fsd). Allwattmeters will measure dcas well as ac power, in some cases up to 2,500 Hz. Most are multi-range instruments with high and low range depending on the voltage range to be used.

6.1.3 GENERAL NOTES

When applying voltage larger than the wattmeter voltage range, connect a potential/voltage transformer (PT/VT) in the voltage circuit as shown in Figure 6.2. Connect the PT according to symbols shown in the diagram labeled on the PT. In this case power “P” consumed on the load becomes as follows:

P = Indication on wattmeter * Multiplying constant * Transformation ratio … (6.1)

Figure 6.2: When Voltage Exceeds Wattmeter Rating.

42

When current flowing is larger than the wattmeter current range,connect a current transformer (CT) in the current circuit as shown in Figure 6.3. When connecting the CT, pay attention not to making mistakefor the terminal symbols shown in the diagram. In this case, power “P” consumed on the load becomes as follows:

P = Indicated value on wattmeter * Multiplying constant *Ratio of current transformation… (6.2)

Figure 6.3: When Current Exceeds Wattmeter Rating.

When measuring power having voltage and current larger than the wattmeter voltage and current ranges, use a circuit as shown in Figure 6.4. In this case power “P” consumed on the load becomes as follows:

P = Indicated value on wattmeter * Multiplying constant * Transformation ratio *Ratio of current transformation … (6.3)

43

Figure 6.4: When Voltage and Current Exceeds Wattmeter Rating

(Note: For power measurement, use the wattmeter voltage terminal range close to the circuit voltage and use the maximum wattmeter current terminals if current flowing through the load is unknown. In addition, when measuring power by the use of a CT, pay attention that the CT secondary side does not open. If a shorting switch is provided on the CT secondary side, always short the secondary side before changing wiring on the current terminals).

When measuring power consumed on the load with the power factor approximately of 1 using a wattmeter for low power factor, pay attention to the voltage and current range selections, because the wattmeter for low power factor has high sensitivity about 5 times higher than that of normal wattmeters.

In addition, power measurement with the wattmeter for low power factor connected with PT and/or CT worsens accuracy due to bad influence of phase-angle errors of the PT and/or CT upon the wattmeter. Therefore it is recommended that the PT and/or CT be not used with the wattmeter for low power factor.

44

6.2 EQUIPMENT LIST

6.2.1 Portable Standard Wattmeter 120/240V, 1 unit

6.2.2 Portable Standard AC Voltmeter 1 unit

6.2.3 Portable Standard DC Voltmeter 1 unit

6.2.4 Portable AC ammeter 1 unit

6.2.5 Portable Standard DC Ammeter 1 unit

6.2.6 Bench-top DC Power Supply 1 unit

6.2.7 Bench-top AC Voltage supply: Single-phase 1 unit

6.2.8 Resistor load bank 1 unit

6.2.9 Capacitor load bank 1 unit

6.2.10 Inductor load bank 1 unit

6.2.11 Wires/Cables as necessary

6.3 ACTIVITIES

6.3.1 Activity 1

Measurement of power in a DC circuit

Figure 6.5: Connection of meters forthe measurement of power of a DC Load.

45

1. Connect the circuit as shown in Figure 6.5.

2. Use the master-slave DC supply unit to provide a maximum dc voltage of 60V.

3. Choose the resistive load of about 200 ohm and 300 ohm.

4. Switch on the supply.

5. Read the meters to obtain V,A and W.

6. Add in another load resistance and obtain another set of reading. Make sure that the current does not exceed the limit of the ammeter or the current rating of the wattmeter.

7. Tabulate the readings and check the results by completing the calculations as indicated in the Table 6.1.

Table 6.1: Measurement of DC Power consumed forthe ResistiveLoad.

Reading of

voltmeter

Reading of

ammeter Wattmeter

Product of voltage

and current

Difference between

P1 and P2: Remarks

V(V) I(A) Reading Multiplying constant

Power P1(W) P2=V x i P1-P2

200 ohm

300 ohm

6.3.2Activity 2

Measurement of power in an AC circuit-resistive load:

Figure 6.6: Connections and arrangement of meters in the measurement of power in an AC circuit with a resistive load

46


2. Use the bench AC supply of 150V AC

3. Choose the resistive load of about 200 ohm and 300 ohmfrom the resistor load bank.

4. Switch ON the supply.

5. Read the meters to obtain V, A andW.



Table 6.2: Measurement of AC Power consumed on Resistive Load.

Reading of

voltmeter

Reading of

ammeter Wattmeter

Product of voltage

and current

Difference between

P1 and P2: Remarks

V(V) I(A) Reading Multiplying constant

Power P1(W) P2=V x i P1-P2

200 ohm

300 ohm

6.3.3Activity 3

Measurement of power in an AC circuit-capacitive load:

Figure 6.7: Connections and arrangement of meters in the measurement of power in an AC circuit with a capacitive load.

47


2. Use the bench AC supply of 150V AC.

3. Choose the resistive load of about 200 ohm and 300 ohmfrom the resistor load bank and capacitor of 4 µF rating from the capacitor load bank.





Table 6.3: Measurement of AC Power consumed on Capacitive Load.

Reading of voltmeter

Reading

of ammeter Wattmeter

Apparent power (S)

Reactive Power (Q)

Power factor Remarks

V(V) i(A) Reading Multiplying constant

Power P1(W) V*i(VA)

Q=((V.i)²-P²)½

CosФ=

P/(V.i)

200 ohm

4 µF

300 ohm

4 µF

6.3.4Activity 4

Measurement of power in an AC circuit-inductive load:

Figure 6.8: Connections and arrangement in the measurement of power in an AC circuit with an inductive load

48


2. Use the bench AC supply of 25V AC only.

3. Choose the resistive load of about 200 ohm and 300 ohmfrom the resistor load bank and inductor of 50 mH rating from the inductor load bank.





Table 6.4: Measurement of AC Power consumed on inductive Load.

Reading of voltmeter

Reading

of ammeter Wattmeter

Apparent power (S)

Reactive Power (Q)

Power factor Remarks

V(V) i(A) Reading Multiplying constant

Power P1(W) V*i(VA)

Q=((V.i)²-P²)½

CosФ=

P/(V.i)

200 ohm

50mH

300 ohm

50mH

6.3.5 Activity 5 (Questions)

1. Argument thedifference between the powers indicated on the wattmeter and that obtained from the voltmeter and ammeter? (For all AC power measurements).

2. Compare DC power with AC power consumed for the same load under the same supply voltage. If there is any difference between them,debate on it.

REFERENCE

1. Lab Sheet 1stEdition BEF 23401, Electrical Power Measurement Laboratory.

49

EXERCISE 7

BASIC ELECTRICAL MEASUREMENT USING DC SOURCE

50

EXERCISE 7

BASIC ELECTRICAL MEASUREMENT USING DC SOURCE

LEARNING OUTCOME

1. Be able to read measured value of DC ammeter correctly.

2. Be able to connect DC ammeter correctly.

3. Be able to connect DC voltmeter correctly.

4. Be able to measure the resistance value of a given resistor effectively.

CONTENT

7.1 THEORY

DC ammeters are connected in series in the circuit for current measurement. Therefore, they should have a low electrical resistance. This is essential in order that they cause a small voltage drop and consequently absorbed small power.

Figure 7.1: Ammeter connection.

51

Figure 7.2: DC current measurement.

Voltmeters are connected in parallel with the circuit for voltage measurement. They should have a high electrical resistance. This is essential in order that the current drawn by them is small and consequently the power absorbed is small.

The main types of instruments used as ammeters and voltmeters are:

Permanent magnet moving coil (PMMC)

Moving iron

Electro-dynamometer

Hot wire

Thermocouple

Induction

Electrostatic

Rectifier

52

Figure 7.3: DC voltage measurement.

An ohmmeter is a convenient direct reading device for resistance measurement. These instruments have a low degree of accuracy. The statement regarding accuracy is not intended in an unfavorable sense there is a wide field of application for this instrument in determining the approximate value of resistance.

An ohmmeter is useful for getting the approximate resistance of circuit components such as heater elements or machine field coils, measuring and sorting resistors used in electronic circuits and for checking continuity of circuit.

Type of Ohmmeter (general):

Series type ohmmeter

Shunt type ohmmeter

Series-shunt type ohmmeter

Figure 7.4: Resistance measurement.

53

7.2 EQUIPMENT LIST

7.2.1 Digital Multimeter 2 units

7.2.2 Universal plug-in board - 0102-032 1 unit

4.2.3 7.2.3 Power supply console - 603 -041 1 unit

4.2.4 7.2.4 Electronics devices

7.2.4.1 R = 100 ohm 1 unit

7.2.4.2 R = 150 ohm 1 unit

7.2.4.3 R = 200 ohm 2 units

7.2.4.4 R = 300 ohm 1 unit

ACTIVITIES

Activity 1

Resistance Measurement

1. Read resistance value from color code as specified in the Table 7.1.

2. Measure resistance by using digital multimeter. Record them into the Table 7.1

Table 7.1: Resistance color code reading and measurement.

R(Ω) R from color code reading(Ω) R from measuring (Ω)

100

150

200

300

4.7k

54

Activity 2

Current Measurement

Figure 7.5: Current measurement.

1. Connect the circuit as shown in Figure 7.5, then read and record current value into the Table 7.2.

2. Connect ammeter after load, then read and record current value into the Table 7.2.

3. Change the value of load as in Table 7.2, measure and record the current value.

4. Calculate the current for each load and fill the Table 7.2.

Table 7.2: Measured and calculated current value.

LOAD

MEASURED VALUE (mA) Calculated Current (mA)

Before load connection

After load connection

150 Ω

200 Ω

300 Ω

Note: I calculation

55

Activity 3

Voltage Measurement

Figure 7.6: Voltage measurement.

1. Connect circuit as shown in figure 7.6.

2. Calculate U1 and U2 from the circuit. Record calculated value into the Table 7.3.

3. Measure voltage across R1 and R2. Record the results into Table 7.3

4. Repeat step 2 and 3 by using resistance as specified in Table 7.3.

Table 7.3: Measured and calculated voltage value.

Resistor Measured Value Calculated Value

R1(Ω) R2(Ω) U1(V) U2(V) U1(V) U2(V)

200 Ω 100 Ω

200 Ω 150 Ω

200 Ω 200 Ω

200 Ω 300 Ω

Note: Calculate value U1= U2 =

U1

U2

56

Activity 4

Voltage and Current Measurement

Figure 7.7: Voltage and current measurement.

1. Connect a circuit as shown in Figure 7.7.

2. Calculate and measure U1, U2, U3 and U4 from the circuit. Record the value into the Table 7.4.

3. Calculate and measure I1, I2 and I3 from the circuit. Record the value into the Table 7.5.

4. Compare the result with calculated value.

Table 7.4: Measured and calculated voltage value.

Voltage (V) Measured Value (V) Calculated Value (V)

U1

U2

U3

U4

Table 7.5: Measured and calculated current value.

Current (mA) Measured Value (mA) Calculated Value (mA)

I1

I2

I3

U1

U2

U3

U4

57


1. Show how this ammeter would be connected to the light bulb circuit to measure the circuit’s electric current.

2. Draw a schematic diagram of this same circuit (with the ammeter connected).

3. Determine the amount of voltage measured at points A and B with reference to ground, and also determine voltage VAB (defined here as the voltage indicated by a voltmeter with the red test lead touching point A and the black test lead touching point B):

i. VA =

ii. VB =

iii. VAB =

REFERENCE

1. Lab Sheet 2nd Edition BEF 23401, Electrical Principal Laboratory.

58

EXERCISE 8

BASIC ELECTRICAL MEASUREMENT USING AC SOURCE

59

EXERCISE 8

BASIC ELECTRICAL MEASUREMENT USING AC SOURCE

LEARNING OUTCOME

1. Be able to connect the AC circuit with RL, RC and RLC loads.

2. Be able to connect a series and parallel circuits.

3. Be able to read measured values of AC Ammeter and AC voltmeter correctly.

4. Be able to connect AC Ammeter correctly.

5. Be able to compare calculated value with measured value.

CONTENT

8.1 THEORY

Phasor Relationship for Circuit Elements

In order to analyze the phasor domain voltage-current relationship for circuit involving the passive elements resistor (R), inductor (L) and capacitor (C), we have to transform the voltage-current relationship of those elements in time domain into frequency domain.

Phasor Relationship for Resistor

If the current that flows through a resistor R is )cos()( tIti m , the

voltage across it is given by Ohms law as

)cos()()( tRItRitv m (1)

The phasor form of this voltage is

mRI V (2)

60

But, the phasor representation of the current is mII . Therefore

RI V (3)

In addition, from Equation (3), the voltage and current are proved to be in phase. The phasor diagram for this relation is as shown in Figure 8.1.

Figure 8.1: Phasor diagram for the resistor

RL Circuits

An RC circuit contains both resistance and inductance. It is one of the basic types of reactive circuits. This subtopic will cover a basic series and parallel RL circuits and their responses to sinusoidal voltages. Series parallel combinations are also examined. Power considerations in RL circuits are introduced and discussed.

Sinusoidal Response of RL Circuit

In an RL circuit, the resistor voltage and the current lag the source voltage. The inductor voltage leads the source voltage. Ideally, the phase angle between the current and inductor voltage is always 90°. These generalized phase relationships are indicated in Figure 8.2. The amplitudes and the phase relationships of the voltages and current depend on the values of the resistance and the inductive reactance.

When a circuit is purely inductive, the phase angle between the source voltage and the total current is 90°, with the current lagging the voltage. When there is a combination of both resistance and inductive reactance circuit, the phase angle is somewhere between zero and 90°, depending on the relative values of the resistance and the inductive reactance. Because all inductors have winding resistance, ideal conditions may be approached but never reached in practice.

61

Figure 8.2: Illustration of sinusoidal response for RL circuit.

Analysis of Series RL Circuits

Phase Relationships of the Current and Voltages

In a series RL circuit, the current is the same through both the resistor and the inductor. Thus, the resistor voltage is in phase with the current, and the inductor voltage leads the current by 90°. Therefore, there is a phase difference of 90° between the resistor voltage, VR, and the inductor voltage, VL. From Kirchhoff's voltage law, the sum of the voltage drops must equal the source voltage. However, since VR and VL are not in phase with each other, they must be added as phasor quantities with VL leading VR by 90°, as shown in Figure 8.3. Vs is the phasor sum of VR and VL. This equation can be expressed as

LR VVVs 22 (4)

The phase angle between the resistor voltage and the source voltage can be expressed as

R

X

V

V L

R

L 11 tantan (5)

Figure 8.4 shows a voltage and current phasor diagram that represents the waveform diagram of Figure 8.3.

62

Figure 8.3: Phase relation of current and voltages in a series RL circuit.

Figure 8.4: Voltage phasor diagram for waveform in Figure 8.3.

Figure 8.5: Voltage and current phasor diagram for waveform in Figure 8.4

63

Analysis of Parallel RL Circuits

Phase Relationships of the Currents and Voltages

Figure 8.6(a) shows all the currents and voltages in a basic parallel RL circuit. The source voltage, VS appears across both the resistive and the inductive branches, so VS, VR and VL are all in phase and of the same magnitude. The total current, Itot divides at the junction into the two branch currents, IR and IL. The current and voltage phasor diagram is shown in Figure 8.6(b). The current through the resistor is in phase with the voltage. The current through the inductor lags the voltage and the resistor current by 90°. By Kirchhoff’s current law, the total current is the phasor sum of the two branch currents. The total current is expressed as:

LRtot III 22 (6)

The phase angle between the resistor current and the total current is

R

L

I

I1tan (7)

Figure 8.5(a) & (b): Current in voltage in parallel RL circuit.

64

RLC Circuits

In this subtopic, we will learn about frequency response of circuits with combinations of resistance, capacitance, and inductance (RLC). Both series and parallel RLC circuits will be discussed.

Impedance and Phase Angle of Series RLC Circuits

A series RLC circuit is shown in Figure 8.7. It contains resistance, inductance and capacitance.

Figure 8.7: Series RLC Circuit.

Inductive reactance (XL) causes the total current to lag the source voltage. Capacitive reactance (XC) has the opposite effect: It causes the current to lead the voltage. Thus, XL and XC tend to offset each other. When they are equal, they cancel, and the total reactance is zero. In any case, the total reactance in a series circuit is

CLtot XXX (8)

The term XL - Xc means the absolute value of the difference of the two reactance. That is, the sign of the result is considered positive no matter which reactance is greater. For example, 3-7 = -4, but the absolute value

is 473 . When XL>Xc, the circuit is predominantly inductive; and when

XC > XL, the circuit predominantly capacitive. The total impedance for a series RLC circuit is given by

tottot XRZ 22 (9)

and the phase angle between Vs and I is

R

X tot1tan (10)

65

Analysis of Series RLC Circuits

Figure 8.8 shows that for a typical series RLC circuit the total reactance behaves as follows: Starting at a very low frequency, XC is high, XL is low, and the circuit is predominantly capacitive.

As the frequency is increased, XC decreases and XL increases until a value is reached where XC = XL and the two reactance cancel, making the circuit purely resistive. This condition is called the series resonance.

As the frequency is increased further, XL becomes greater than XC, and the circuit is predominantly inductive.

Figure 8.8: Variation of XC and XL with frequency.

The graph of XL is a straight line, and the graph of XC is curved, as shown in Figure 8.8. The general equation for a straight line is y = mx + b, where m is the slope of the line and b is the y-axis intercept point.

The formula XL = 2πfL fits this general straight-line formula. The XC curve is called a hyperbola, and the general equation of a hyperbola is xy = k, where k is a constant.

The equation for capacitive reactance Xc = l/2πfC, can be rearranged as XCf = 1/2πC which match with the hyperbolic general equation.

66

Parallel RLC Circuits

Impedance and Phase Angle

The circuit in Figure 8.9 consists of the parallel combination of R, L, and C. To find the admittance, add the conductance (G) and the total susceptance (Btot) as phasor quantities. Btot is the difference of the inductive susceptance and the capacitive susceptance.

cL

CLtotXX

BBB11

(11)

RG

1 (12)

Therefore, the formula for admittance is

22

totBGY (13)

The total impedance is the reciprocal of the admittance

YZ tot

1 (14)

The phase angle of the circuit is given by the following formula:

G

Btot1tan (15)

When the frequency is above its resonant value (Xc < XL), the impedance of the circuit in Figure 8.9 is predominantly capacitive because the capacitive current is greater, and the total current leads the source voltage.

When the frequency is below its resonant value (XL < XC), the impedance of the circuit is predominantly inductive, and the total current lag the source voltage.

Figure 8.9: Parallel RLC circuit.

67

Current relationship

In a parallel RLC circuit, the current in the capacitive branch and the current in the inductive branch are always 1800 out of phase with each other. For this reason, IC and IL subtract from each other, and thus the total current into the parallel branches of L and C is always less than the largest individual branch current, as illustrated in the waveform diagram of Figure 8.10(a). The current in the resistive branch is always 90° out of phase with both reactive currents, as shown in the current phasor diagram of Figure 8.10(b). The total current can be expressed as:

22

CLRtot III (16)

Where ICL is the absolute value of the difference of the two currents, |IC-IL|, and is the total current into the Land C branches. The phase angle can also be expressed in terms of the branch currents as:

R

CL

I

I1tan (17)

(a) (b)

Figure 8.10: (a) IC and IL effectively subtract.

Figure 8.10(b) Current phasor diagram for a parallel RLC circuit.

68

8.2 EQUIPMENT LIST

8.2.1 Resistive load panel 0102-014 1 unit

8.2.2 Inductive load panel 0102-015 1 unit

8.2.3 Capacitive load panel 0102-016 1 unit

8.2.4 Power supply console 0603-041 1 unit

8.2.5 Digital Multimeter 2 units

ACTIVITIES

Activity 1 (The Series Resistive-Inductive Load Circuits)

A

V

L

N

10 Vac,

50HzR

L

Figure 8.11: R-L series.

1. According to Figure 8.11 complete the experiment circuit using insulated connecting leads. Insert 210 Ω resistor and 0.4 H inductor in series as the load. The input supply is set to 10Vac, 50Hz.

2. Using AC ammeter and AC voltmeter, measure and record the values of current and voltage respectively in Table 8.1.

3. Change the value of load according to the values given in Table 8.1 and record the results.

4. Compare the measured value and calculated value.

69

Table 8.1: Series Resistive-Inductive load calculated and measured value.

Load(R + L) Calculation Value Measurement Value

Z V supply (Volt) I (mA) V load (Volt) I (mA)

210Ω + 0.4H 244.7 10 40.8 8.7 30

210Ω + 0.8H 327.5 10 30.5 9 20

210Ω + 1.0H 377.8 10 26.5 9.5 15

390 Ω + 0.4H 409.7 10 24.4 9.5 20

470Ω + 0.4H 486.4 10 20.5 9.0 18

860Ω + 0.4H 869.1 10 11.5 9.5 20

Activity 2 (The parallel Resistive-Inductive Load Circuits)

A

V

L

N

10 Vac,

50Hz

R L

Figure 8.12: R-L parallel.

1. According to Figure 8.12, complete the experiment circuit using insulated connecting leads. Insert 210 Ω resistor and 0.4 H inductor in parallel as the load. The input supply is set to 10Vac, 50Hz.

2. Using AC ammeter and AC voltmeter, measure and record the values respectively in Table 8.2.



70

Table 8.2: Parallel Resistive-Inductive load calculated and measured value.

Load

(R // L)

Calculation Value Measurement Value

Z V supply (Volt)

I (mA) V load (Volt) I tot (mA)

210Ω // 0.4H 10.77 10 92.78 8 68.7

210Ω // 0.8H 161.13 10 62.06 8 55.5

210Ω // 1.0H 174.59 10 57.20 8 50.2

390 Ω // 0.4H 119.56 10 83.64 10 54.4

470Ω // 0.4H 121.36 10 82.39 10 52.8

860Ω // 0.4H 124.28 10 80.46 10 48.6

Activity 3 (The Series Resistive – Capacitive Load Circuits)

A

V

L

N

10 Vac,

50HzR

C

Figure 8.13: R-C series.

1. According to Figure 8.13, complete the experiment circuit using insulated connecting leads. Insert 390 Ω resistor and 2 μF capacitor in series as the load. The input supply is set to 10Vac, 50Hz.

2. Using AC ammeter and AC voltmeter, measure and record the values of current and voltage respectively in Table 8.3.



71

Table 8.3: Series Resistive – Capacitive load calculated and measured value.

Load

(R + C)


XC Z V supply (Volt) I (mA) V load (Volt) I (mA)

390Ω + 2μF

390Ω + 4μF

390Ω + 8μF

210Ω + 4μF

470Ω + 4μF

860Ω + 4μF

Activity 4 (The Parallel Resistive – Capacitive Load Circuits)

A

V

L

N

10 Vac,

50Hz

R C

Figure 8.14: R-C parallel.

1. According to Figure 8.14, complete the experiment circuit using insulated connecting leads. The input supply is 10Vac, 50Hz. Insert 390 Ω resistor and 2 μF capacitor in parallel as the load.

2. Using AC ammeter and AC voltmeter, measure and record the values of current and voltage respectively in Table 8.4



72

Table 8.4: Parallel Resistive – Capacitive load calculated and measured value.

Activity 5 (The Series RLC Load Circuit)

A

V

L

N

50 Vac,

50Hz

R

C

L

Figure 8.15: RLC series.

1. According to Figure 8.15, complete the experiment circuit using insulated connecting leads. The input supply is 50Vac, 50Hz. Insert 390 Ω resistor, 0.4 H inductor and 2 μF capacitor in series as the load.

2. Using the AC ammeter and AC voltmeter, measure and record the values of current and voltage respectively in Table 8.5.



Load

(R // C)


Z V supply (Volt) I (mA) V load (Volt) I (mA)

390Ω // 2μF

390Ω // 4μF

390Ω // 8μF

210Ω // 4μF

470Ω // 4μF

860Ω // 4μF

73

Table 8.5: Series RLC Load calculated and measured value.

Load

(R + L + C)


Z tot V supply (Volt) I (mA) V load (Volt) I (mA)

390Ω + 0.4H+ 2μF

470Ω + 0.4H+ 2μF

860Ω + 0.4H+ 2μF

390Ω + 0.6H+ 2μF

390Ω + 1.0H+ 2μF

390Ω + 0.4H+ 4μF

390Ω + 0.4H+ 8μF

Activity 6 (The Parallel RLC Load Circuit)

A

V

L

N

50 Vac,

50Hz

R L C

Figure 8.16: RLC parallel.

1. According to Figure 8.16, complete the experiment circuit using insulated connecting leads. The input supply is 50Vac, 50Hz. Insert 390 Ω resistor, 0.4 H inductor and 2 μF capacitor in parallel as the load.

2. Using the AC ammeter and AC voltmeter, measure and record the values of current and voltage respectively in Table 8.6.



74

Table 8.6: Parallel RLC Load calculated and measured value.

Load

(R // L // C)


Z tot V(Volt) I tot(mA) V load (Volt) I tot (mA)

390Ω // 0.4H // 2μF

470Ω // 0.4H // 2μF

860Ω // 0.4H // 2μF

390Ω // 0.6H // 2μF

390Ω // 1.0H // 2μF

390Ω // 0.4H // 4μF

390Ω // 0.4H // 8μF


1. What is the applied voltage for a series RLC circuit when IT = 3 mA, VL = 30 V, VC = 18 V, and R = 1000 ohms?

2. How much current will flow in a series RLC circuit when VT = 100 V, XL = 160 Ω, XC = 80 Ω, and R = 60 Ω?

REFERENCE


75

EXERCISE 9

AC VOLTAGE MEASUREMENT USING

OSCILLOSCOPE

76

EXERCISE 9

AC VOLTAGE MEASUREMENT USING

OSCILLOSCOPE

LEARNING OUTCOME

1. To learn how to measure AC Voltages using Oscilloscope.

2. To give knowledge and understanding peak to peak voltage, rms value and period for 1 cycle.

3. To be familiar using Oscilloscope.

4. To measure the power dissipated in an ac circuit.

5. To study the characteristic of ac power.

CONTENT

9.1 THEORY

A sinusoidal voltage is given by v(t) = Vm cos(wt+Ɵ), where Vm is the peak value of the voltage, w is the angular frequency in radian per second and is the Ɵ phase angle.

Sinusoidal signals are periodic, repeating the same pattern of values in each period T. Because the cosine/sine function completes one cycles when the angle increases by 2 π radians, we get:

wt = 2π

The frequency of the periodic signal is the number of cycles completed in one second. Thus we obtain:

The units of frequency are hertz (Hz).

The angular frequency

Substitute for T, we find that W = 2πf

77

RMS Value of the Sinusoid

Consider a sinusoidal voltage given by

)cos()( tVtv m

To find the rms value, we substitute,

)1.1()(cos1

0

22 dttV

TV

T

mrms

Use the trigonometric identity

)2cos(2

1

2

1)(cos2 zz

To write Equation 1.1 as

)2.1()]22cos(1[2 0

2

dttT

VV

Tm

rms

Integrating, we get

T

rmsrms tT

T

VV

0

2

22sin(2

1

2

-----------------(`1.3)

Evaluating, we have

)2sin(

2

122sin(

2

1

2

2

tTT

VV rms

rms ---(1.4)

78

We know that 2t . Thus, we obtain

)2sin(2

1)24sin(

2

1)2sin(

2

1)22sin(

2

1

T

0

)2sin(2

1)2sin(

2

1

Therefore, Equation (1.4) reduces to

2

mrms

VV ---------------------------------------(1.5)

Electrical power in a dc circuit is calculated by P =VI. This is also true in an ac circuit with a pure resistor the instantaneous variations of current through the resistor follow exactly the instantaneous changes in voltage. This is called that the current is in phase with the voltage.

It is possible that the current is not in phase with the voltage when a load contains reactive elements such as an inductor or capacitor.

The load absorbs energy during the instantaneous power in positive direction and returns energy during the instantaneous power in negative direction.

The current I and voltage V appear a phase angle Ɵ and power P will be P = VI cos Ɵ, If the current is in phase with the voltage (Ɵ = 0), the power will be P = VI

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9.2 EQUIPMENT LIST

9.2.1 Linear Circuit Lab Main Module KL-21001

9.2.2 Basic Electricity Experiments Module Kl 13001

9.2.3 Digital Multimeter

9.2.4 Digital Oscilloscope

ACTIVITIES

Activity 1

1. Set the main unit KL-21001 and locate the block a.

2. Using the oscilloscope, measure and record the AC SOURCE output terminals 0-9V.

3. Draw the output in the graph.

Vpk-pk:________________ Vrms:_______________

Period:_________________ Frequency:___________

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Activity 2

1. Set the module kl-13003 and locate the block a.

2. According to Figure 9.1, complete the experiment circuit with short-circuit clips.

3. Using the multimeter adjust VR1 to 1kΩ.

4. Measure and record the voltages across VR1 and R1 by using the oscilloscope.

Figure 9.1: Series R1 and VR1.

VR1

Vpk-pk:________________ Vrms:_______________


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R1

Vpk-pk:________________ Vrms:_______________


Activity 3

1. Adjust VR1 to 200 Ω, measure and record the voltages across VR1 and R1 by using the oscilloscope.

VR1

Vpk-pk:________________ Vrms:_______________


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R1

Vpk-pk:________________ Vrms:_______________


Activity 4

1. Set the module KL-13001 on the main unit KL-21001 and locate the block a. Measure and record the resistance of R1.

R1 = ______________Ω

2. Measure AC source 0-9V using multimeter.

V = ______________V

3. According to Figure 9.2, complete the experiment circuit with short-circuit clips.

4. Measure and record the current value.

I = ____________mA

5. Using the equation P = VI cos Ɵ, calculate and record the power dissipated by the circuit.

P = __________W

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6. Using the equation P = , calculate and record the power dissipated by

resistor R1.

P = __________W

7. Using the equation P = I2R, calculate and record the power dissipated by the resistor R1.

P = __________W

8. Do all of the power values agree?

Yes / No

9. Turn off the power. Touch the body of R1 immediately to feel the temperature. What is the form that power converted to?

__________________________________________________________

___________________________________________________________

Figure 9.2: Resistive circuit.


1. Someone prepares to use an oscilloscope to display an AC voltage

signal. After turning the oscilloscope on and connecting the Y input

probe to the signal source test points, this display appears:

What display control(s) need to be adjusted on the oscilloscope in order

to show a normal-looking wave on the screen?

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2. Determine the frequency of this waveform, as displayed by an

oscilloscope with a vertical sensitivity of 2 volts per division and a time-

based of 0.5 milliseconds per division:

REFERENCE


bev 20501 electical engineering lab 1

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