Electric Engineering Fundamentals Lab ENG 207

Electric Engineering Fundamentals Lab ENG 207 Designed & Edited By Eng. Ahmed Shafik Eng. Mohamed Tawfik Supervised By Dr. Meshaal Al-Shaher Dr. Meshal Al-Gharaballi Fall 2017-2018

Lab Schedule From Date To Experiment Title Quiz Pre- Lab Report 24-Sep 28-Sep DC Spice 1-Oct 5-Oct Ex1. Ohm's Law Exp 1 8-Oct 12-Oct Ex2. KVL and KCL Quiz 1 Exp 2 Exp 1 15-Oct 19-Oct Ex3. Node, Mesh and Superposition Quiz 2 Exp 3 Exp 2 22-Oct 26-Oct Ex4. Thevenin Equivalent Theorem + Training Quiz 3 (spice) Exp 4 Exp 3 29-Oct 2-Nov DC Practical Exam + DC PSpice test Exp 4 5-Nov 9-Nov AC Spice 12-Nov 16-Nov Ex5. AC Measurements Exp 5 19-Nov 23-Nov Ex7. Phase shift Measurements Quiz 4 Exp 7 Exp 5 3-Dec 7-Dec Exp 8 : Steady-state power calculation Quiz 5 Exp 8 Exp 7 10-Dec 14-Dec Ex9. Electric Wiring + Training Quiz 6 (Spice) Exp 8 17-Dec 21-Dec AC Practical Exam + AC PSpice test Exp 9-27 Dec اخر تاريخ لمراجعة الدرجات Grading Policy Pre-Lab 10% Reports 10% 6 Quizzes 20% 2 Exams 40% 2 Spice tests 20% Total 100% Second Midterm is considered as Final Exam Absence of any practical exam = FA Absence انذار اول = absence o 1 st انذار ثاني = absence o 2 nd o 3 rd absence = FA. All reports and data sheets should be done by computer; no hand writing will be accepted. Pre-Lab = Data Sheet + Spice Simulation Data Sheet should be signed by the lab engineer at the end of the lab Mobiles and Calculators are not allowed in the practical exams. Any violation of this rule will be considered as cheating and will be dealt with accordingly. Report Grading Policy Cover Table of Contents Objective 1 Equipment Theory 1 Procedure + Circuit 1 Pspice simulation Data Sheet 1 Questions 4 Conclusion 1 References Report Format 1 Total 10

Lab Regulations 1) Performance & Pre Lab: (10 points) PSpice simulation report (student name and ID must be typed on the circuit simulation, otherwise the report will not be graded.) (5 pts) For the Data Sheet, Theoretical part should be filled in and printed by computer before the lab. (2 pts) Note: Lab engineer has to sign the pre lab note before students leave the lab. Performance: (3 pts) o o Student must attend all Lab sessions in time. Students must leave the bench clean and switch all the equipments off before leaving the lab. o o Food and drinks are not allowed in the labs. Cell phone use in the labs is prohibited. 2 grades of the per-lab grade will be deducted if the student violates any of the previous points. 2) Attendance Students should attend the lab in time. Late students will not be allowed to attend the lab and will get zero mark for (Pre Lab Note, Performance, Quiz and Report). Students can attend in their section only, for critical cases only, the student has to download and fill the form and sign it to attend in different section. Absent students for 3 out of 10 labs or more will get FA. Absence of any practical tests = FA

3) Report Layout: A typical lab report should contain the following sections (in order), you can download the report sample from the site: Cover Page Table of Contents Objective Theory Experimental Procedure + Exercise PSpice Simulation Data Sheet Conclusion References. Writing techniques: Report and Pre Lab note should be written by computer. The font and size of the normal text is TimesNewRoman 12. The font and size of the heading and subheading is TimesNewRoman 16/14. The report should contain page numbers. All figures and tables should have a title caption. The theory part should contain (figures, equations, description) for each part of the objective.

1 1 Familiarization, and Ohm's Law Objectives To be familiar with the laboratory equipment and components. Verification of Ohm s law. Series and parallel circuits. Theory Part I : Lab equipment and components: DC Power Supply: It is a multi-channels power source device to generate a variable DC voltage, Figure 1-1: DC power supply sample Function Generator (FG): It is a device to generate a variable AC signals with different wave forms (sine, square and triangle). Figure 1-2: Function Generator

2 Resistor: There are two types of resistors in the lab, resistor substitution box (from 0 to 9.999 M) and discrete resistors. See Figure 1-5 for the discrete resistor values reading table. Resistor Substitution Box Figure 1-3: Resistors Discrete Resistors 4-band Color Code Figure 1-4: 4-band color code table

3 5-band Color Code Figure 1-5: 5-band color code table

4 Example: (a) (b) Figure 1-6: Color code example a) For the resistor of figure 1-6-a, the value can be calculated as follows: R N 1N 2 N 3 N 4 Where: N i = band value. R = 02 x 10 5 + 10% = 200 K + 10% b) For the resistor of figure 1-6-b, the value can be calculated as follows: R N1N2 N3 N4 N5 Where: N i = band value. R = 330 x 10 1 + 0.1% = 3.3 K + 0.1%

5 Inductor: There is inductance substitution box in the lab (from 0 to 9.999 H). Figure 1-7: Inductance substitution box Capacitor: There is capacitance substitution box in the lab (from 0 to 99.999 uf). Figure 1-8: Capacitance substitution box Digital Multi-Meter (DMM): DMM is a measuring instrument to measure voltage, current, ohm, frequency. Figure 1-9: DMM sample

6 Digital Oscilloscope (CRO): CRO is a multi-channels measuring instrument to measure and display voltage wave forms with different measurements readings. Figure 1-10: CRO Sample Bread Board: It is a board to connect the circuits. Figure 1-11: Bread Board Sample Part II : Ohms's Law: Ohm's Law says: The current in a circuit is directly proportional to the applied voltage. V I R (1)

7 I I 1/R V Circuit Diagram Relationship Between V & I (slope=1/r) Figure 1-12: Ohm s Law Part III : Series & Parallel Circuits: Figure 1-13: Series and Parallel Connections

8 Connect the circuit as shown in Figure 1-14 by the following steps: OrCAD Simulation Part I: Figure 1-14: Circuit Diagram 1) Start OrCAD [Appendix A-1] 2) Add a Resistor [Appendix A-2] (R 1 =3 KΩ) 3) Add DC Voltage Source (Vs) [Appendix A-5] 4) Add Ground [Appendix A-11] 5) Connect the circuit by adding wires [Appendix A-10] 6) Add CRO current probe to measure I [Appendix A-12] 7) Select DC sweep analysis with the following parameters [Appendix A-14] Name = Vs Start Value = 0 End Value = 9 Increment = 1 8) Simulate the circuit [Appendix A-13] 9) The following wave form will be displayed in a new window. 2.8mA 2.4mA 2.0mA 1.6mA 1.2mA 0.8mA 0.4mA 0A 0V 0.5V 1.0V 1.5V 2.0V 2.5V 3.0V 3.5V 4.0V 4.5V 5.0V 5.5V 6.0V 6.5V 7.0V 7.5V 8.0V 8.5V 9.0V 9.5V 10.0V I(R1) V_Vs 10) Calculate the line slope = and compare it with the theoretical value.

9 Part II: A I B1 (a) V S I (b) Figure 1-15: Circuit Diagram 1) Start OrCAD [Appendix A-1] 2) Add Resistors [Appendix A-2] R 1 = R 2 =1KΩ, R 3 = R 4 = 2KΩ 3) Add DC Voltage Source (Vs) [Appendix A-5] Vs = ask your engineer 4) Add Ground [Appendix A-11] 5) Connect the circuit by adding wires [Appendix A-10] 6) Simulate the circuit [Appendix A-13] 7) Calculate the equivalent resistor. R AB1 = V s I = 1) Start OrCAD [Appendix A-1] 2) Add Resistors [Appendix A-2] R 1 = R 2 = R 3 =1KΩ 3) Add DC Voltage Source (Vs) [Appendix A-5] Vs = ask your engineer 4) Add Ground [Appendix A-11] 5) Connect the circuit by adding wires [Appendix A-10] 6) Simulate the circuit [Appendix A-13] 7) Calculate the equivalent resistor. R AB2 = V s I =

10 Experimental Work Equipments: 1) DC Voltage Source 2) Bread Board. 3) DMM 4) Discrete resistors I Procedure: Part I : Ohm s Law: Figure 1-16: Circuit Diagram 1) Select a discrete resistor R = 3 KΩ, measure the resistor value R = 2) Measure the resistance of the wires, make sure that its value not equal to OL 3) Connect the circuit as shown in Figure 1-16 with the shown values. 4) Vary the DC voltage source and measure I. Fill table 1-1. Table 1-1 V S 3 6 9 I (ma) Q1: Draw I versus V, find the slope of the curve and what does the slope represent?. Theoritical Measured Q2: Compare the slope of Q1 with the theoretical value. % error 100 Theoritical Q3: What are the error sources in Q2?

11 Part II: Parallel and Series Circuits: A B1 (a) A (b) B2 Figure 1-17: Circuit Diagram 1) Connect the circuit as shown in Figure 1-17-a, R 1 = R 2 =1KΩ, R 3 =R 4 = 2KΩ, Measure R AB1. R AB1 = 2) Connect the circuit as shown in Figure 1-17-b, R 1 = R 2 =R 3 =1KΩ. Measure R AB2. R AB2 = Q4: Calculate R AB1 and R AB2 theoretically. Q5: What is the relation between the circuit of Figure 1-17a and Figure 1-17b

12 2 KVL, KCL, and equivalent circuit resistance Objectives Verification of KVL and KCL. Simulating the DC circuits using OrCAD. Measuring and calculating the equivalent resistance of different circuits. Theory Kirchhoff s Voltage Law (KVL) KVL states that the algebraic sum of all voltages around a closed path (or loop) is zero. Figure 2-1 shows an example for closed loop circuit. For the circuit shown in Figure 2-1, applying KVL: Figure 2-1: KVL example Kirchhoff s Current Law (KCL) Kirchhoff s current law (KCL) states that the sum of the currents entering a node is equal to the sum of the currents leaving the node. For the circuit shown in Figure 2-2, applying KCL: Figure 2-2: KCL example

13 Parallel and Series Circuit Connections n n N N 1 1 1 1 1 R R R... R R... R R R R n 1 R ab 1 2 N n n 1 ab 1 2 N n Series Connection Parallel Connection Figure 2-3: Series-Parallel Connections Delta to Wye Conversion Delta to Why conversion (given R a, R b, R c ) Why to Delta conversion (given R 1, R 2, R 3 ) Figure 2-4: Delta Why conversions

14 Connect the circuit as shown in Figure 2-5 by the following steps: OrCAD Simulation I 3 V 1 A I 1 I2 + 1 L 1 L 2 L 3 4 3 6 + + + 2 5 + + V 2 Figure 2-5: Circuit Diagram 1) Start OrCAD [Appendix A-1] 2) Add a Resistor [Appendix A-2] (R 1 =R 4 =1 KΩ, R 2 =R 5 =2 KΩ, R 3 =R 6 =3.9 KΩ) 3) Add DC Voltage Source (Vdc) [Appendix A-5] (V 1 = ask your engineer Volt, V 2 = ask your engineer Volt) L 2 4) Add Ground [Appendix A-11] 5) Connect the circuit by adding wires [Appendix A-10] 6) Select the bias point simulation analysis [Appendix A-15] 7) Simulate the circuit [Appendix A-13] 8) Activate the voltage and current icons in the tool bar. 9) Fill Table 2-1. Table 2-1 I 1 I 2 I 3 Q1: Verify KCL at point A.

15 Delta to Wye Conversion A R 1 R 2 R 3 V S R 4 R 5 R 6 B Figure 2-6: Circuit Diagram 1) Start OrCAD [Appendix A-1] 2) Add a Resistor [Appendix A-2] R 1 = R 4 =1 KΩ, R 2 = R 3 =2 KΩ, R 5 = R 6 =3.9 KΩ 3) Add DC Voltage Source (Vdc) between the two nodes A and B = ask your engineer Volt[Appendix A-5] 4) Add Ground [Appendix A-11] 5) Connect the circuit by adding wires [Appendix A-10] 6) Select the bias point simulation analysis [Appendix A-15] 7) Simulate the circuit [Appendix A-13] 8) Activate the voltage and current icons in the tool bar. 9) Calculate the value of R AB R ab == V s I =

16 Experimental Work Equipment: a) DC Voltage Source b) Bread Board. c) DMM d) Discrete resistors. Part A KVL & KCL: 1) Select (using color table in Appendix B-1) and measure (using DMM) the resistors values. Fill the measured values of the resistors in Table 2-2. Table 2-2 R 1 R 2 R 3 R 4 R 5 R 6 2) Measure the resistance of the wires, make sure that its value not equal to OL 3) Connect the circuit shown in Figure 2-5, adjust V 1 = ask your engineer V and V 2 = ask your engineer V using DMM. 4) Fill table 2-3. Table 2-3 V R1 V R2 V R3 V R4 V R5 V R6 I 1 I 2 I 3 Q1: Using the measured values of table 2-2 and 2-3, verify KVL for closed loops L 1, L 2, and L 3. Loop L 1 : Loop L 2 : Loop L 3 : Q2: Using the measured values of tables 2-2 and 2-3, verify KCL at node A.

17 Q3: Repeat Q1 using results of OrCAD. Part B - Delta to Wye Conversion and equivalent resistance of different circuits: Figure 2-7: Circuit Diagram 1) Connect the circuit as shown in Figure 2-7. 2) Using DMM measure R ab. R ab = Q4: Find R ab theoretically in details (step by step with figures) and compare it with measured value in step 2 and the simulated value by OrCAD.

18 3 Nodal, Mesh and Superposition Analysis Objectives Verification of Nodal analysis method. Verification of Mesh analysis method. Verification of Superposition technique. DC circuits analysis using OrCAD. Theory Nodal Analysis Analysis Steps: 1. Select a node as the reference node. Assign voltages v 1, v 2,, v n-1 to the remaining n 1 nodes. The voltages are referenced with respect to the reference node. 2. Apply KCL to each of the n 1 non reference nodes. Use Ohm s law to express the branch currents in terms of node voltages. 3. Solve the resulting simultaneous equations to obtain the unknown node voltages. Example: Figure 3-1: Nodal Example Applying nodal equation for the circuit of Figure 3-1: V N 1 V 1 V N 1 V N 1 V N 2 0 R R R 1 3 2 V N 2 V 2 V N 2 V N 2 V N 1 0 R R R 5 4 2

19 Mesh Analysis A mesh is a loop which does not contain any other loops within it. Analysis steps: 1. Assign mesh currents i 1, i 2,..., in to the n meshes. 2. Apply KVL to each of the n meshes. Use Ohm s law to express the voltages in terms of the mesh currents. 3. Solve the resulting n simultaneous equations to get the mesh currents. Example: Figure 3-2: Mesh Loop Example Applying mesh loop equation for the circuit of Figure 3-2: Superposition technique: The superposition principle states that the voltage across (or current through) an element in a linear circuit is the algebraic sum of the voltages across (or currents through) that element due to each independent source acting alone. Superposition steps: 1. Turn off all independent sources except one source. Find the output (voltage or current) due to that active source using nodal or mesh analysis. 2. Repeat step 1 for each of the other independent sources. 3. Find the total contribution by adding algebraically all the contributions due to the independent sources. Example: For the circuit shown in Figure 3-1, to find I R1 using super position: Disconnect the voltage source V 2 and replace it with a wire (short circuit it) as shown in Figure 3-3-a.

20 Solve for I R1. Disconnect the voltage source V 1 and replace it with a wire (short circuit it) as shown in Figure 3-3-b. Solve for I R1. I R1 = I R1 + I R1 I R1 I R1 (a) Figure 3-3: Superposition Technique Example (b) OrCAD Simulation Connect the circuit as shown in Figure 3-4 by the following steps: C A L 3 B L 1 L 2 Figure 3-4: Circuit Diagram 1) Start OrCAD [Appendix A-1] 2) Add a Resistor [Appendix A-2], R 1 =2K, R 2 =2K, R 3 = 5.1K, R 4 = 1K, R 5 =1K. 3) Add DC Voltage Source (Vdc) [Appendix A-5], V 1 = ask your engineer V and V 2 = ask your engineer V. 4) Add Ground [Appendix A-11] 5) Connect the circuit by adding wires [Appendix A-10] 6) Select the bias point simulation analysis [Appendix A-15] 7) Simulate the circuit [Appendix A-13] 8) Activate the voltage and current icons in the tool bar.

21 9) Fill Table 3-1. Table 3-1 I R4 I R5 I R3 V A V B V C 10) Deactivate V 2 and simulate the circuit [Appendix A-13] 11) Fill table 3-2 V A Table 3-2 I R4 12) Deactivate V 1 and simulate the circuit [Appendix A-13] 13) Fill table 3-3. V A " Table 3-3 " I R4 Q1: Verify superposition technique for V A and I R3. Experimental Work Equipments: e) DC Voltage Source f) Bread Board. g) DMM h) Discrete resistors. Part A Nodal and Mesh Analysis a. Measure the resistance of the wires, make sure that its value not equal to OL b. For the circuit shown in Figure 3.4, select (using color table in appendix B-1) and measure (using DMM) the resistors. Fill the measured values of the resistors in table 3-4. Table 3-4 R 1 R 2 R 3 R 4 R 5

22 c. Connect the circuit shown in Figure 3-4, adjust V 1 = ask your engineer V and V 2 = ask your engineer V using DMM. d. Fill table 3-5. Table 3-5 I R4 I R5 I R3 V A V B V C Q1: Using the measured values of table 3-4 and 3-5, verify Nodal equations for A and B. Node A: Node B: Q2: Using the measured values of table 3-4 and 3-5, verify Mesh equations. Mesh L 1 : Mesh L 2 : Mesh L 3 : Part B Superposition technique: 1) Deactivate the voltage source V 2, measure and fill table 3-6 for V A and I R4 " " 2) Deactivate the voltage source V 1, measure and fill table 3-6 for V A and I R4 3) Verify superposition technique and fill table 3-6 for V A and I R4 Table 3-6 V A V A " V A I R4 " I R4 I R4

23 4 Thevenin s Equivalent Circuit & Max. Power Transfer Objectives Verification of Thevenin s Theory. Verification of maximum power condition. Determination of Thevenin s Eq. Circuit using OrCAD. Theory Thevenin s Theory Thevenin s theorem states that a linear two-terminal circuit can be replaced by an equivalent circuit consisting of a voltage source V Th in series with a resistor R Th, where V Th is the open-circuit voltage at the terminals and R Th is the input or equivalent resistance at the terminals when the independent sources are turned off. (a) Original Circuit Figure 4-1: Thevenin Theory (b) Thevenin Equivalent Circuit Maximum Power Transfer Maximum power is transferred to the load when the load resistance equals the Thevenin resistance as seen from the load (R L = R Th ). For Figure 4-2, maximum power equation is as follows: (1)

24 (a) The circuit used for maximum power transfer (b) Power delivered to the load as a function of R L Figure 4-2: Maximum Power Circuit OrCAD Simulation Connect the circuit as shown in Figure 4-3 by the following steps: X I Y 4 Figure 4-3: Circuit Diagram 1) Start OrCAD [Appendix A-1] 2) Add a Resistor [Appendix A-2] R 1 =2KΩ, R 2 =3.9KΩ, R 3 =1KΩ, R 4 =5.1KΩ, R L =1KΩ 3) Add DC Voltage Source (Vdc) [Appendix A-5] V S = ask your engineer 4) Add Ground [Appendix A-11] 5) Connect the circuit by adding wires [Appendix A-10] Part 1- Finding I through R L : 1) Select the bias point simulation analysis [Appendix A-15] 2) Simulate the circuit [Appendix A-13] 3) Activate the voltage and current icons in the tool bar.

25 I RL = ma Part 2: Calculating I using Thevenin s Circuit A) Finding V TH 1) Change the value of R L to be 1T (high value equivalent to open circuit). 2) Simulate the circuit [Appendix A-13] 3) Activate the voltage and current icons in the tool bar. Calculate V TH = V xy V TH = V B) Finding R TH 1) Change the value of R L to be 1f (very small value equivalent to short circuit). 2) Simulate the circuit [Appendix A-13] 3) Activate the voltage and current icons in the tool bar. I SC = ma 4) Calculate R TH V TH RTH = KΩ I SC Q1: Using Thevenin Equivalent Circuit, calculate I RL and compare it with the value in part 1. I RL = V TH R TH + R L = ma Experimental Work Equipments: i) DC Voltage Source j) Bread Board. k) DMM l) Discrete resistors and resistor box Part 1 Finding I RL 1) Measure the resistance of the wires, make sure that its value not equal to OL 2) Connect the circuit as shown in Figure 4-3 with the same values of resistors (using color resistor table in Appendix B-1). Fill the measured values of the resistors in table 4-1. Table 4-1 R 1 R 2 R 3 R 4 R L

26 3) Connect the circuit shown in Figure 4-3, adjust V S = ask your engineer using DMM. 4) Measure I. I RL = ma Part 2: Calculating I using Thevenin s Circuit A) Finding V TH Remove R L from the circuit and measure V TH = V xy V TH = V B) Finding RTH Remove R L and replace it with a short circuit wire. Measure I SC. I SC = ma Calculate R TH R TH = KΩ Q2: Using Thevenin Equivalent Circuit, calculate I RL and compare it with the value in part 1. I RL = ma Part 3: Maximum Power Transfer R TH V TH + R L - I Figure 4-5: Circuit Diagram Let V TH = 10 V and R TH = 2000. Connect the circuit as shown in Figure 4-5, where R L is a resistor box. Vary R L with the values of table 4-2. Fill table 4-2. Table 4-2

27 R L () I P RL = I 2 *R L 500 1500 2000 3000 4000 Q3: From table 4-2, plot P RL versus R L. What is the value of R L for maximum power. Comment? R L = KΩ P RL MAX = W

28 5 AC Fundamentals and Measurements Objectives To be familiar with the Digital Oscilloscope (CRO) and Function Generator (FG). Using P-Spice to simulate AC circuit analysis. AC measurements using CRO. Verifying the relation between Peak-Peak value and RMS values for AC circuits. Theory Alternating current (AC): the flow of charge is continually changing in magnitude (and direction) with time. Sample of AC supply waveforms: (a) sine wave (b) square wave (c) triangle wave Figure 5-1: AC waveforms samples AC Basics: V P V PP Figure 5-2: Sinusoidal Waveform

29 Frequency F: the number of cycles per second of a waveform in Hz. The period T: of a waveform is the duration of one cycle in seconds. T 1 F Peak Value: the peak value of a voltage or current is its maximum value with respect to zero. Peak-to-peak V PP : is the value between minimum and maximum peaks Root Mean Square (RMS) value: The effective value of a periodic current is the dc current that delivers the same average power to a resistor as the periodic current. Where: x is v(t) or i(t). (1) Table 5-1: RMS equations for different waveforms Wave Form RMS Sinusoidal wave V rms V PP 2 2 Triangle wave Square wave V V rms rms V PP 2 3 V 2 PP OrCAD Simulation Connect the circuit as shown in Figure 5-3 by the following steps: B Figure 5-3: Circuit Diagram 1) Start OrCAD [Appendix A-1]

30 2) Add 3 Resistors (R 1 =5.1KΩ - R 2 =2KΩ - R 3 =1KΩ - R 4 =5.1KΩ - R 5 =3.9KΩ- R 6 =2KΩ) [Appendix A-2] 3) Add V 1 = AC sine wave voltage source (Vsin pp ) = ask your engineer V [Appendix A-7] a. VOFF = 0 b. VAMPL = V 1 /2 c. FREQ = 2 KHz 4) Add Ground [Appendix A-11] 5) Connect the circuit by adding wires [Appendix A-10] 6) Add CRO probes to measure both V A and V B [Appendix A-12] 7) Adjust the transient simulation parameters [Appendix A-17] a. Max step size = 0 ns b. Run time = 1 ms c. Tick the skip initial transient bias point calculation. 8) Simulate the circuit [Appendix A-13] 9) To get the value of V A -V B, add trace [Appendix A-18] a. Trace expression = V(A)- V(B) 10) The following wave form will be displayed in a new window. 8.0V 4.0V 0V -4.0V -8.0V 0s 0.2ms 0.4ms 0.6ms 0.8ms 1.0ms V(R5:2) V(B) V(A) Time 11) Using the toggle cursor [Appendix A-19], fill table 5-2: Table 5-2 V A PP V B PP V AB PP Period T (msec) 12) Apply KVL for loop ABA to check your result.

31 13) Repeat the steps from 1 to 9, modify step 3 to be square wave (V PP = ask your engineer V, Freq. = 2 KHz) as follows: a. Add square wave voltage source (Vpulse) [Appendix A-8] i. DC=0 ii. AC=0 iii. V1= V 1 /2 iv. V2= -V 1 /2 v. TD= 0 vi. TR= 1f vii. TF= 1f viii. PW= 1 2 Freq. ix. PER= 1 Freq. = 0.25 msec = 0.5 msec 14) The following wave form will be displayed in a new window. 8.0V 4.0V 0V -4.0V -8.0V 0s 0.2ms 0.4ms 0.6ms 0.8ms 1.0ms V(R5:2) V(B) V(A) Time 15) Using the toggle cursor [Appendix A-19], fill table 5-3: Table 5-3 V A PP V B PP V AB PP Period T (msec) 16) Repeat the steps from 1 to 9, modify step 3 to be triangle wave (V PP = ask your engineer V, Freq. = 2 KHz) as follows: a. Add triangle wave voltage source (Vpulse) [Appendix A-9] i. DC=0 ii. AC=0 iii. V1= -V 1 /2 iv. V2= V 1 /2

32 v. TD= 0 vi. TR= 1 2 Freq. = 0.25 msec vii. TF= 1 = 0.25 msec 2 Freq. viii. PW= 1f 1 ix. PER= = 0.5 msec Freq. 17) The following wave form will be displayed in a new window. 8.0V 4.0V 0V -4.0V -8.0V 0s 0.2ms 0.4ms 0.6ms 0.8ms 1.0ms V(R5:2) V(B) V(A) Time 18) Using the toggle cursor [Appendix A-19], fill table 5-4: Table 5-4 V A PP V B PP V AB PP Period T (msec) Experimental Work Equipments: 1) Function Generator 2) Bread Board. 3) CRO, DMM 4) Discrete resistors. Procedure: Part 1: 1) Measure the resistance of the wires, make sure that its value not equal to OL 2) Connect the circuit as shown in Figure 5-3 with: (R 1 =5.1KΩ - R 2 =2KΩ - R 3 =1KΩ - R 4 =5.1KΩ - R 5 =3.9KΩ- R 6 =2KΩ) 3) Adjust the function generator to get sine wave with ask your engineer V PP and freq. = 2 KHz. 4) Fill table 5-5 by using CRO (use the math function to get V AB ). 5) Fill table 5-6 by using DMM.

33 Table 5-5 V A PP V B PP V AB PP Period T (msec) Table 6-6 I R1 RMS V B RMS 6) From table (5-5) calculate V B (RMS) = Part 2: 7) Adjust the function generator to get square wave with ask your engineer V PP and freq. = 2 KHz. 8) Fill table 5-7 by using CRO (use the math function to get V AB ). 9) Fill table 5-8 by using DMM. Table 5-7 V A PP V B PP V AB PP Period T (msec) Table 5-8 I R1 RMS V B RMS 10) From table 5-7, calculate V B (RMS) = Part 3: 11) Adjust the function generator to get triangle wave with ask your engineer V PP and freq. = 2 KHz. 12) Fill table 5-9 by using CRO (use the math function to get V AB ). 13) Fill table 5-10 by using DMM. Table 5-9 V A PP V B PP V AB PP Period T (msec) Table 5-10 I R1 RMS V B RMS 14) From table 5-9, calculate V B (RMS) =

34 Q1: Is the peak to peak values of the voltage or current changed by changing the wave form? Q2: Is the RMS values of the voltage or current changed by changing the wave form? Why? Q3: Find the RMS value for sine, square and triangle wave using general formula? Show your work in details ------------------------------------------------------------------------------------------------------------- -------------------------------------------------------------------------------------------------------------

35 6 Natural-Response of RL/RC circuits Objectives Study the natural response and step response of RL/RC circuits. Calculate the Time Constant. Theory When the dc source of an RC circuit is suddenly applied, the voltage or current source can be modeled as a step function, and the response is known as a step response. The natural response or transient response is the circuit s temporary response that will die out with time. The forced response or steady-state response is the behavior of the circuit a long time after an external excitation is applied. The complete response of the circuit is the sum of the natural response and the forced response. Natural Response + I o Vo - RL Circuit Figure 6-1 : RL & RC Circuit RC Circuit Where : t i ( t ) i e, t 0 (1) v ( t ) v e, t 0 (2) L L o eq (3) R eq is the time constant. I o is the initial conductor current at t=0. As shown in figure 6-2 and figure 6-4: Where: C o eq eq t R C (4) is the time constant. V o is the initial capacitor current at t=0. x ( t ) i ( t ) for RL circuit. (5) L

36 x ( t ) v ( t ) for RC circuit. (6) C Figure 6-2 : Natural Response Step Response i L + V c - Figure 6-3 : Step Response of RL & RC circuit V t s i L ( t ) (1 e ), t 0 (7) R t V ( t ) V (1 e ), t 0 (8) C s RL Circuit RC Circuit

37 Figure 6-4 : Step Response Time Constant : the time required for the natural response to decay by a factor of e-1 (36.8%) as shown in figure 6-2 or the time for the step response to be 63.3% of its final value as shown in figure 6-4. OrCAD Simulation Part A: RC Circuit s Figure 6-5: RC Circuit Connect the circuit as shown in figure 6-5 by the following steps: 19) Start OrCAD [Appendix A-1] 20) Add Resistor [Appendix A-2] R=500Ω 21) Add Capacitor [Appendix A-3] C=0.2uF 22) Add Vs = square wave voltage source (Vpulse) with amplitude V PP = ask your engineer and frequency =625 Hz [Appendix A-8] o DC=0

38 o AC=0 o V1= 0 o V2=V S o TD= 1f o TR= 1f o TF1f 1 o PW= 2 Freq. = 0.8m 1 o PER= Freq. =1.6m 23) Add Ground [Appendix A-11] 24) Connect the circuit by adding wires [Appendix A-10] 25) Add CRO probes to measure both Vs and Vc [Appendix A-12] 26) Adjust the transient simulation parameters [Appendix A-17] a. Print step = 0.000001 m, Final time = 2ms. 27) Simulate the circuit [Appendix A-13] 28) The output will be displayed in a new window as shown. 11. Trace the simulation [Appendix A-18] to get the time constant : Trace expression = 6.32 which represents 63.2% of the final value to get the time constant from the intersection of the 6.32 trace with the charging voltage. = 10 5 0 0s 0.2ms 0.4ms 0.6ms 0.8ms 1.0ms 1.2ms 1.4ms 1.6ms 1.8ms 2.0ms V(C1:2) 3.62 V(V1:+) 6.32 Time 12. Measure the value of V C at t = 0.2 msec, then verify this value theoretically by using equation (8). Calculate the %error. V C = (simulation)

39 V C = %error= (theoretical) Part B: RL Circuit Figure 6-6: RL Circuit 1) Repeat the steps of part A, connect the circuit as shown in figure 6-6 by changing the capacitor with an inductor=20mh and the value of R to be 2 KΩ [Appendix A-4]. 2) Trace the simulation [Appendix A-18] to get the time constant : Trace expression = 6.32 which represents 63.2% of the final value to get the time constant from the intersection of the 6.32 trace with the increasing V R response. = 3) Measure the value of V R at t = 0.3 msec, then verify this value theoretically by using equation (8). Calculate the %error. V R = V R = %error = (simulation) (theoretical) V (Note: i () t R L R, so the response of I L (t) is the same response of V R (t) divided by constant) Experimental work Equipments: 1) Resistor, capacitor, and inductor substitution box. 2) Function Generator. 3) Digital Multi-Meter DMM 4) CRO.

40 Procedure: Part A: RL Circuit 10 1.6m time Figure 6-7: Circuit Diagram Figure 6-8: Pulse Voltage 1) Measure the resistance of the wires, make sure that its value not equal to OL 2) Connect the circuit as shown in figure 6-7, 3) Adjust the function Generator to generate square wave with maximum amplitude= ask your engineer V and minimum amplitude=0 V, Frequency=625 Hz, as shown in figure 6-8 (by adjusting the amplitude value and the DC offset). 4) From the CRO screen, measure the value of. = 5) Calculate the % error between (Practical) and (OrCAD). (OrCAD) = %error = 6) Calculate the % error between (Practical) and (Theoretical). (theoretical) = %error =

41 Part B: RC Circuit 10 1.6m time Figure 6-9: Circuit Diagram Figure 6-10: Pulse Voltage 1) Connect the circuit as shown in figure 6-9, 2) Adjust the function Generator to generate square wave with maximum amplitude= ask your engineer V and minimum amplitude=0 V, Frequency=625 Hz, as shown in figure 6-10 (by adjusting the amplitude value and the DC offset). 3) From the CRO screen, measure the value of. = 4) Calculate the % error between (Practical) and (OrCAD). (OrCAD) = %error = 5) Calculate the % error between (Practical) and (Theoretical). (theoretical) = %error = Q1: Define time constant? τ =RC (for RC circuit) τ = R L (for RL circuit)

42 7 Sinusoidal AC Voltage & Current for RL & RC Circuits Objectives Study the sine wave of AC voltage and current. Measure Phase Shift between voltage and current. Theory Phase Shift Phase shift is the angle between voltage and current. Passive Circuit Elements A) Resistor Figure 7-1: Resistor Passive Element Figure 7-2: Time Domain Response (Voltage and Current are in phase)

43 I V Figure 7-3: Phasor Form Figure 7-4: Phaseor Diagram ( = 0o ) B) Inductor Figure 7-5: Inductor Passive Element Figure 7-6: Time Domain Response (Current lags the Voltage by angle = 90o) V V jli (1) Figure 7-7: Phasor Form Figure 7-8: Phasor Diagram ( = 90o ) I

C) Capacitor Figure 7-9: Capacitor Passive Element 90 o Figure 7-10: Time Domain Response (Current leads Voltage by angle = 90o) I V V 1 jc I (2) Figure 7-11: Phasor Form Figure 7-12: Phasor Diagram ( = 90o ) 44

45 D) R-L series AC circuit V Figure 7-13: RL Circuit i Figure 7-14: Time Domain Response (Current lags Voltage by angle ) I V j V ( jl R ) I (3) Figure 7-15: Phasor Form V I 1 L tan R V L V R (4) Figure 7-16: Phasor Diagram 0 90

46 E) R-C series AC circuit V Figure 7-17: RC Circuit Figure 7-18: Time Domain Response (Current leads Voltage by angel ) I I V R V V V C 1 V R I jwc Figure 7-19 : Phasor Form (5) tan CR 1 1 (6) Figure 7-20 : Phasor Diagram 0 90

47 OrCAD Simulation Part A: RL Circuit s Figure 7-21: RL Circuit Connect the circuit as shown in figure 7-21 by the following steps: 1) Start OrCAD [Appendix A-1] 2) Add Resistor (R= 1.200KΩ) [Appendix A-2] 3) Add Inductor (L=108 mh) [Appendix A-4] 4) Add V s = AC sine wave voltage source (Vsin pp ) = ask your engineer V [Appendix A-7] a. VOFF = 0 b. VAMPL = V s /2 c. FREQ = 1800 Hz 5) Add Ground [Appendix A-11] 6) Connect the circuit by adding wires [Appendix A-10] 7) Add CRO probes to measure both Vs and V R [Appendix A-12] 8) Adjust the transient simulation parameters [Appendix A-17] d. Max step size = 1000us e. Run time = 2ms f. Start saving data after = 0.1 ms g. Tick the skip initial transient bias point calculation. 9) Simulate the circuit [Appendix A-13] 10) The output will be displayed in a new window as shown.

48 4.0V 3.0V 2.0V 1.0V 0.0V -1.0V -2.0V -3.0V -4.0V 0.1ms 0.2ms 0.3ms 0.4ms 0.5ms 0.6ms 0.7ms 0.8ms 0.9ms 1.0ms 1.1ms 1.2ms 1.3ms 1.4ms 1.5ms 1.6ms 1.7ms 1.8ms 1.9ms 2.0ms V(R4:2) V(V2:+) Time 11. Measure X (the time shift between Vs and Vr). 12. Calculate (phase shift between Vs and Vr), using the following equation: X 360 T Where T (time period) = 1/Freq. X = T = = V R Leads or Lags Vs?. (9) Part B: RC Circuit s Figure 7-22: RC Circuit Connect the circuit as shown in figure 7-22 by the following steps: 1) Repeat the steps of part (A) except: a. Step 2 = R = 1900 Ω [Appendix A-2]

49 b. Step 3 = Capacitor (0.075 uf) [Appendix A-3] c. Step 4 = Freq = 1100 Hz d. Step 8: Adjust the transient simulation parameters [Appendix A-17] i. Max step size = 1ns ii. Run time = 4ms iii. Start saving data after = 2 ms iv. Tick the skip initial transient bias point calculation. The output will be displayed in a new window as shown 4.0V 3.0V 2.0V 1.0V 0.0V -1.0V -2.0V -3.0V -4.0V 2.0ms 2.1ms 2.2ms 2.3ms 2.4ms 2.5ms 2.6ms 2.7ms 2.8ms 2.9ms 3.0ms 3.1ms 3.2ms 3.3ms 3.4ms 3.5ms 3.6ms 3.7ms 3.8ms 3.9ms 4.0ms V(V2:+) V(R4:2) Time 2. Measure X (the time shift between Vs and Vr). 3. Calculate (phase shift between Vs and Vr), using the following equation: X 360 T Where T (time period) = 1/Freq. X = T = = V R Leads or Lags Vs?. (10) (Note : V R represents the response of I in the circuit for both RL and RC Circuit)

50 Part C: RLC Circuit A B C s Figure 7-23: RL Circuit Connect the circuit as shown in figure 7-23 by the following steps: 11) Start OrCAD [Appendix A-1] 12) Add Resistor (R= 1.200KΩ) [Appendix A-2] 13) Add Inductor (L=168 mh) [Appendix A-4] 14) Add Capacitor (C=0.132 uf) [Appendix A-3] 15) Add V s = AC sine wave voltage source (Vsin pp ) = ask your engineer V[Appendix A-7] h. VOFF = 0 i. VAMPL = V s /2 j. FREQ = 1320 Hz 16) Add Ground [Appendix A-11] 17) Connect the circuit by adding wires [Appendix A-10] 18) Add CRO probes to measure both Vs and V R [Appendix A-12] 19) Adjust the transient simulation parameters [Appendix A-17] a. Max step size = 1000us b. Run time = 2ms c. Start saving data after = 0.1ms d. Tick the skip initial transient bias point calculation. 20) Simulate the circuit [Appendix A-13] 21) The output will be displayed in a new window as shown.

51 4.0V 3.0V 2.0V 1.0V 0.0V -1.0V -2.0V -3.0V -4.0V 0.1ms 0.2ms 0.3ms 0.4ms 0.5ms 0.6ms 0.7ms 0.8ms 0.9ms 1.0ms 1.1ms 1.2ms 1.3ms 1.4ms 1.5ms 1.6ms 1.7ms 1.8ms 1.9ms 2.0ms V(R4:2) V(V2:+) Time 13. Measure X (the time shift between Vs and Vr). 14. Calculate (phase shift between Vs and Vr), using the following equation: X 360 T Where T (time period) = 1/Freq. X = T = = V R Leads or Lags Vs?. (9)

52 Experimental work Equipments: Resistor, capacitor, and inductor substitution boxes. Function Generator. Digital Multi-Meter DMM CRO. Procedure: Part A: RL Circuit Vpp/2 s T Figure 7-24: Circuit Diagram Figure 7-25: Sine Wave Voltage Source 1) Measure the resistance of the wires, make sure that its value not equal to OL 2) Connect the circuit as shown in figure 7-23. (R= 1.2KΩ) (L=108 mh) 3) Adjust the function Generator to generate sine wave with V PP = ask your engineer V, Frequency= 1800 Hz, (Note: be sure that the function generator is adjusted to high output impedance) 4) Measure and fill table 7-1. (V L will be measured by using the math function of the CRO) Table 7-1 Adjust Measure Calculate V S V R V L X (ms) T (ms) o 5) Compare calculated with the obtained from OrCAD. (OrCAD) = %error = (%error= calculated spice % ) calculated 6) Compare calculated with the theoretical obtained from eq. (4). calculated theoretical ) theoretical (theoretical) = %error = (%error= %

53 Note: = 2 Freq. Part B: RC Circuit Vpp/2 s T Figure 7-26: Circuit Diagram Figure 7-27: Sine Wave Voltage Source 1) Connect the circuit as shown in figure 7-24. R= 1900 Ω, C = 0.075 uf, Freq = 1100 Hz 2) Repeat the steps of part A and fill table 7-2. Table 7-2 Adjust Measure Calculate V S V R V C X (ms) T (ms) o 3) Compare calculated with the obtained from OrCAD. (OrCAD) = %error = (%error= calculated spice % ) calculated 4) Compare calculated with the theoretical obtained from eq. (6). calculated theoretical ) theoretical (theoretical) = %error = (%error= % Note: = 2 Freq.

54 Part C: RLC Circuit A B D Vpp/2 s T Figure 7-28: Circuit Diagram Figure 7-29: Sine Wave Voltage Source 1) Connect the circuit as shown in figure 7-28. R= 1.2KΩ, C = 0.132 uf, L=168mH, F=1320Hz 2) Connect CRO ch1 to point A and ch2 to point B to measure Vs PP and V L PP = V ch1-ch2. 3) Connect CRO ch1 to point B and ch2 to point D to measure V R PP and V C PP =V ch1-ch2. 4) Connect CRO ch1 to point A and ch2 to point D to measure o between Vs and V R PP. 5) Fill table 7-3. Table 7-3 Adjust Measure Calculate V S V L PP V C PP V R PP X (ms) T (ms) o Pf Q1: From table 7-3, verify KVL Σ V = 0.

55 Q2: V V in V o Pt3 0 Pt1 Pt2 NOTE: Both signals have same frequency 1. Complete the following table. Pt # X-axis value Y-axis value 1 0.05 ms 0 2 0.55 ms 0 3 0 2. Determine the frequency of the input voltage and the output current? 3. Determine the phase shift between V in and V o in seconds and degrees. 4. Is the current lag or lead the input voltage? State whether the circuitis RL or RC circuit

56 8 Sinusoidal steady-state power calculations Objectives Phase shift measuring between voltage and current. Calculation of average active, reactive, and apparent powers. Verification of power balance in the circuit. Improvement of power factor. Theory Power definitions P: Average active power in watts. Q: Reactive power in vars. S : Apparent power in VA. S: Complex power = P + j Q in VA. Power factor V V, I I For max v max phase shift v PF = power factor = cos() We have three cases as shown in Table 8-1. Table 8-1 Case Power Factor Phasor Diagram = 0 Unity power factor (V & I are in phase) I V = +ve Lagging power factor (I lags V) V I I I = -ve Leading power factor (I leads V) I V

57 Power triangle S P j Q (1) Pf = cos() (2) P, Q, S calculations S Q P Figure 8-1: Power Triangle Table 8-2 Voltage Source Case I max Equations V V, I I v max I V 1 1 sin (3) 2 2 * S V I V max I max cos jv max I max Resistor 2 2 V max I maxr P 2R 2 Inductor P = 0 Capacitor P = 0 j c Q Q = 0, S = P (4) 2 V max 1 2 Q I maxl 2L 2 S = j Q (5) 2 Vmax c 1 I 2 2 c 2 max S = j Q (6) Note: for any electric circuit, S 0, P 0, Q 0 Power factor improvement In a typical electric circuit, the current lags the voltage as shown in Figure 8-2. By adding a capacitor or (adjusting the existing capacitor in the circuit) will be decreased and pf will be improved. The best value of pf is unity where = 0. V I Figure 8-2: Lagging pf

58 OrCAD Simulation S Figure 8-3: OrCAD Circuit Diagram Connect the circuit as shown in Figure 8-3 by the following steps: 1) Start OrCAD [Appendix A-1] 2) Add 2 Resistors R 1 = 1KΩ, R 3 = 2KΩ [Appendix A-2] 3) Add Inductor L 1 =100 mh[appendix A-4] 4) Add capacitor C=0.1 uf[appendix A-3] 5) Add V s = AC sine wave voltage source (Vsin pp ) = ask your engineer V [Appendix A-7] VOFF = 0 VAMPL = Vs/2 FREQ = 1000 6) Add Ground [Appendix A-11] 7) Connect the circuit by adding wires [Appendix A-10] 8) Add CRO probes to measure both Vs and V R [Appendix A-12] 9) Adjust the transient simulation parameters [Appendix A-17] Max step size = 0ns Run time = 8ms Start saving data after = 6ms Tick the skip initial transient bias point calculation. 10) Simulate the circuit [Appendix A-13] 11) The following wave form will be displayed in a new window.

59 12) Using the toggle cursor [Appendix A-19], fill Table 8-3: Table 8-3 VPP (R1) Difference in time (X) Phase Shift pf (lead/lag/unity) 5.0V 13) Change the value of capacitor to 0.25 uf and repeat the step 10. 14) The following wave form will be displayed in a new window: 0V -5.0V 6.0ms 6.2ms 6.4ms 6.6ms 6.8ms 7.0ms 7.2ms 7.4ms 7.6ms 7.8ms 8.0ms V(L1:1) V(V1:+) Time 15) Using the toggle cursor [Appendix A-19], fill Table 8-4: Table 8-4 VPP (R1) Difference in time (X) Phase Shift pf (lead/lag/unity) 16) Comment on the obtained power factor.

60 Experimental Work Equipments: 1) Function Generator 2) CRO, DMM 3) Electronic Bread Board 4) Resistor, capacitor and inductance substitution boxes. 5) Discrete resistors. Procedure: Part A Power Calculations: Figure 8-4: Circuit Diagram 1) Measure the resistance of the wires, make sure that its value not equal to OL 2) Connect the circuit as shown in Figure 8-4 with the shown values. 3) Adjust the function generator to get sine wave with ask your engineer V PP and freq. = 1 KHz. (Note: be sure that the function generator is adjusted to high output impedance) 4) Connect the CRO channels to measure V S PP and V R1 PP as shown in Figure 8-4. 5) Measure V PP (R 2 //L 1 //C 1 ) = Ch 1 Ch 2 6) Fill Table 8-5. 7) Using equations 1 to 6, fill Table 8-6. Table 8-5 V S PP V R1 PP T between V S & V R1 V PP (R 2 //L 1 //C 1 )

61 Table 8-6 T 360 T pf (lead/lag) P VS Q VS P R1 P R2 Q L1 Q C1 Q 1 : Verify average active and reactive power balance. Part B Power factor improvement: 1) Change the capacitor value to 0.25 uf. 2) Fill Table 8-7. Table 8-7 Measure V S PP V R1 PP T between V S & V R1 Calculate pf (lead/lag/unity) Q 2 : explain the effect of capacitor on the pf.

62 9 Electric Wiring & Energy Objectives To be familiar with the protective devices for electric wiring. To study the final circuit diagram To study the calculation of customer electric energy cost. Theory The very nature of the grid system is such that power has to be transmitted over large distances. This immediately creates a problem of voltage drop. To overcome this problem, a high voltage is used for transmission (275 or 132 kv), the 275 kv system being known as the Super Grid. We cannot, however, generate at such high voltages (the maximum in modern generators is 25 kv) and transformers are used to step up the generated voltage to the transmission voltage. At the end of a transmission line is a grid substation, where the requirements of the grid system in that area can be controlled and where the transmission voltage is stepped down via a transformer to 132 kv. The system voltage is then further reduced at substations to 33 000, 11 000 and 415/240 V. 415/240 V 275 KV 11000/415 V 275/132 KV Figure 9-1: Kuwait Electric Energy System

63 Distribution Board (DB): A distribution board (or panel board) is a component of an electricity supply system which divides an electrical power feed into subsidiary circuits, while providing a protective fuse or circuit breaker for each circuit, and safety protective devices, (RCD), in a common enclosure. Figure 9-2: Distribution Board

64 Figure 9-3: DB 8-ways double busbar Electric Fuse: In electronics and electrical engineering a fuse (from the Latin "fusus" meaning to melt) is a type of sacrificial over-current protection device. Its essential component is a metal wire or strip that melts when too much current flows, which interrupts the circuit in which it is connected. A fuse interrupts excessive current (blows) so that further damage by overheating or fire is prevented. Wiring regulations often define a maximum fuse current rating for particular circuits.

65 Figure 9-4: Electric Fuses Low Voltage Circuit Breaker (LVCB) A circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city. Figure 9-4: Low Voltage CB

66 Fuses compared with circuit breakers Fuses have the advantages of often being less costly and simpler than a circuit breaker for similar ratings. The blown fuse must be replaced with a new device which is less convenient than simply resetting a breaker. Some types of circuit breakers must be maintained on a regular basis to ensure their mechanical operation during an interruption. This is not the case with fuses, which rely on melting processes where no mechanical operation is required for the fuse to operate under fault conditions. Earth Leakage CB and Residual Current Devices (RCD) In non-technical terms if a person touches something, typically a metal part on faulty electrical equipment, which is at a significant voltage relative to the earth, electrical current will flow through him/her to the earth. The current that flows is too small to trip an electrical fuse which could disconnect the electricity supply, but can be enough to kill. An ELCB detects even a small current to earth (Earth Leakage) and disconnects the equipment (Circuit Breaker). Earth Leakage Circuit Breakers and Residual Current Devices are safety devices that offer that additional protection. These two types of safety devices are used in areas that have high levels of earth impedance. These devices have the primary purpose of reducing the risk of shock in the event of a current flow to the earth. Principle of operation of an RCD Figure 8-5 illustrates the construction of an RCD. In a healthy circuit, the same current passes through the line coil and the load, and then back through the neutral coil. Hence, the magnetic effects of line and neutral currents cancel out. In a faulty circuit, either line-to-earth or neutral-to-earth, these currents are no longer equal. Therefore, the out-of-balance current produces some residual magnetism in the core. As this magnetism is alternating, it links with the turns of the search coil, inducing an electro-motive force (EMF) in it. This EMF in turn drives a current through the trip coil, causing operation of the tripping mechanism. Figure 9-5: RCD Circuit

67 Lighting circuits The loop-in system, this is the most common of all lighting circuitry and, as the name suggests, circuit cables simply loop in and out of each lighting point figure 9-6. Figure 9-6: Lighting Circuit Radial socket-outlet circuits Most domestic installations use ring final circuits to supply socket outlets, radial circuits are quite acceptable. The recommendations for such circuits are given in table 9-1. These radial circuits are shown in figure 9-7. Table 9-1: Conventional Circuit Arrangements for Radial Socket outlet Circuits. Protective Protective Maximum Cable Size Number of Device Size Device Type Floor Area Served Socket Outlets 30 A or 32 A any 75 m 2 4.0 m 2 unlimited 20 A any 50 m 2 2.5 m 2 unlimited

68 Ring Final outlet circuits Figure 9-7: Radial Socket Outlet Circuit In electricity supply, a ring final circuit or ring circuit (informally also ring main or just ring) is an electrical wiring technique developed that provides two independent conductors for live, neutral and protective earth (ground) within a building for each connected load or socket as shown in figures 8-8- a & 8-8-b. The ring acts like two radial circuits proceeding in opposite directions around the ring. If the load is evenly split across the two directions, the current in each direction is half of the total, allowing the use of wire with half the current-carrying capacity. In practice, the load does not always split evenly, so thicker wire is used.

69 Figure 9-8-a: Ring Final Circuit Figure 9-8-b: Ring Final Circuit

70 Power Consumption Consumers pay for the electrical energy they consume and NOT for the power. As before, the energy is related to the power by: Energy = Power x Time (1) Example 1: Consider a 1200 W hairdryer. How much does it cost per month if you use it every day for 15 minutes? The KWh in Kuwait costs 2 fils to the consumer and approximately 20 fils to the government. Solution: We want the number of KW times the number of hours to find the energy in KWh. The total time per month is about 15 min/day x 30 days/month = 450 min/month. = 450/60 = 7.5 h/month. So the energy used is 1.2 KW x 7.5 h = 9 KWh. Then, the cost is 180 fils. Example 2: A refrigerator rated at 1000 W operates one third of time. What does it cost per month? Assume 2 fils/kwh. Solution: 1000 W = 1 KW. The number of hours that the fridge is running is 1/3 x 24 h/day x 30 days= 240 h. So. Cost = 1 KW x 240 h x 2 fils/kwh = 480 fils. Sample of Warning Labels

71 Questions: Q1: What is the function of electric fuse? Q2: What is the function of circuit breaker? Q3: What is the function of earth leakage circuit breaker? Q4: A typical house contains air condition, clothes dryer, range, refrigerator, lighting and other appliances. Complete table 9-1, given that cost for KWh is 3 fils. Calculate the bill of the house for July. Table 9-1 House Consumption in July Item Consumption (KW) Consumption Duration (h) Air Condition 12 24 Clothes Dryer 3 2 Range 0.8 6 Refrigerator 0.4 24 Lighting 0.8 12 Total Total Consumption/Month Cost