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Laboratory Manual TPCT’S College of Engineering, Osmanabad Laboratory Manual Power Electronics For Third Year Students Manual Prepared by Prof. S. G. Shinde Author COE, Osmanabad TPCT’s College of Engineering Solapur Road, Osmanabad Department of Electronics &Telecommunication Vision of the Department: To be recognized by the society at large as an excellent department offering quality higher educationin the Electronics & Telecommunication Engineering field with research focus catering to the needs of the public ind being in tune with the advancing technological revolution. Mission of the Department: To achieve the vision the department will Establish a unique learning environment to enable the student’s face the challenges of the Electronics & Telecommunication Engineering field. Promote the establishment of centers of excellence in technology areas to nurture the spirit of innovation and creativity among the faculty & students. Provide ethical & value based education by promoting activities addressing the needs of the society. Enable the students to develop skill to solve complete technological problems of current times and also to provide a framework for promoting collaborative and multidisciplinary activities. College of Engineering Technical Document This technical document is a series of Laboratory manuals of Electronics and Telecommunication Department and is a certified document of College of engineering, Osmanabad. The care has been taken to make the document error- free. But still if any error is found, kindly bring it to the notice of subject teacher and HOD. Recommended by, HOD Approved by, Principal FORWORD It is my great pleasure to present this laboratory manual for third year engineering students for the subject of Power Electronics to understand and visualize the basic concepts of various circuits using electronic components. Power Electronics cover basic concepts of electronics. This being a core subject, it becomes very essential to have clear theoretical and designing aspects. This lab manual provides a platform to the students for understanding the basic concepts of Power Electronics. This practical background will help students to gain confidence in qualitative and quantitative approach to electronic circuits. H.O.D ECT Dept LABORATORY MANUAL CONTENTS This manual is intended for the Third Year students of ECT branches in the subject of Power Electronics. This manual typically contains practical/ Lab Sessions related to Power Electronics covering various aspects related to the subject for enhanced understanding. Students are advised to thoroughly go through this manual rather than only topics mentioned in the syllabus as practical aspects are the key to understanding and conceptual visualization of theoretical aspects covered in the books. SUBJECT INDEX: 1. Do’s & Don’ts in Laboratory. 2. Lab Exercises 1. To plot static characteristics of a SCR. 2. To plot V-I characteristics of Diac. 3. To study half controlled full wave bridge (semiconverter) rectifier. 4. To study V-I characteristic of TRIAC. 5. To perform of SCR commutation circuits. 6. To study fan control using SCR, and lamp dimmer using TRIAC. 7. To study the operation of series inverter and to obtain variable AC from DC input. 8. To study the operation of resistance triggering circuits of SCR. 9. To study the operation of resistance capacitance triggering circuits of SCR. 3. Quiz 4. Conduction of viva voce examination 5. Evaluation & marking scheme Dos and Don’ts in Laboratory :- 1. Do not handle any equipment before reading the instructions /Instruction manuals. 2. Read carefully the power ratings of the equipment before it is switched ON, whether ratings 230 V/50 Hz or 115V/60 Hz. For Indian equipment, the power ratings are normally 230V/50Hz. If you have equipment with 115/60 Hz ratings, do not insert power plug, as our normal supply is 230V/50Hz., which will damage the equipment. 3. Observe type of sockets of equipment power to avoid mechanical damage. 4. Do not forcefully place connectors to avoid the damage. 5. Strictly observe the instructions given by the Teacher/ Lab Instructor. Instruction for Laboratory Teachers:- 1. Submission related to whatever lab work has been completed should be done during the next lab session. 2. Students should be instructed to switch on the power supply after getting the checked by the lab assistant / teacher. After the experiment is over, the students must hand over the circuit board, wires, CRO probe to the lab assistant/teacher. 3. The promptness of submission should be encouraged by way of marking and evaluation patterns that will benefit the sincere students. Experiment No.1 Experiment Title: CHARACTERISTICS OF A SCR Aim:- To plot static characteristics of a SCR. Objective: To plot static characteristics of a SCR Apparatus:- Circuit board 0-300V high voltage supply,0-300V low voltage supply, milli-ammeter0-100mA and 0-10mA. Voltmeter 1-100V, multi meter, connecting wires etc. Circuit Diagram:- Theory: SCR Modes of operation: There are three modes of operation for an SCR depending upon the biasing given to it: 1. Forward blocking mode (off state) 2. Forward conduction mode (on state) 3. Reverse blocking mode (off state) Forward blocking mode In this mode of operation, the anode is given a positive voltage while the cathode is given a negative voltage, keeping the gate at zero potential i.e. disconnected. In this case junction J1 and J3 are forward-biased, while J2 is reverse-biased, due to which only a small leakage current exists from the anode to the cathode until the applied voltage reaches its break over value, at which J2 undergoes avalanche breakdown, and at this break over voltage it starts conducting, but below break over voltage it offers very high resistance to the current and is said to be in the off state. Forward conduction mode SCR can be brought from blocking mode to conduction mode in two ways: either by increasing the voltage across anode to cathode beyond break over voltage or by applying positive pulse at gate. Once SCR starts conducting, no more gate voltage is required to maintain it in the on state. There are two ways to turn it off: 1. Reduce the current through it below a minimal value called the holding current and 2. With the gate turned off, short out the anode and cathode momentarily with a push-button switch or transistor across the junction. Reverse blocking mode SCRs are available with reverse blocking capability, which adds to the forward voltage drop because of the need to have a long, low-doped P1 region. (If one cannot determine which region is P1, a labeled diagram of layers and junctions can help). Usually, the reverse blocking voltage rating and forward blocking voltage rating are the same. The typical application for reverse blocking SCR is in current-source inverters. SCRs incapable of blocking reverse voltage are known as asymmetrical SCR, abbreviated ASCR. They typically have a reverse breakdown rating in the tens of volts. ASCRs are used where either a reverse conducting diode is applied in parallel (for example, in voltage-source inverters) or where reverse voltage would never occur (for example, in switching power supplies or DC traction choppers). Procedure:- 1. For forward characteristics - Connect the circuit as per the circuit diagram. - Adjust the value of gate current at 4.5mA &keep it constant. - Slowly increase the value of anode voltage till firing takes place. - Note down the readings and plot the graph. 2. For reverse characteristics - Reverse the high voltage power supply polarities and also the voltmeter, ammeter polarities on the HV side. - Note the anode current for changing voltage of Vak taking care that Vak does not exceed the reverse break over voltage Vboof SCR. - Remove all connection after switching off the power supply. Observations:- a. Forward characteristics Ig=3.5mA Ig=4mA Vak Ig Vak Ig b. Reverse characteristics Ig=3.5mA Ig=4mA Vak Ig Vak Ig Graphs/Formula (if any) Result: - The graph plotted as per the observations is theoretically matched Conclusion: The SCR is unidirectional device which conduct in forward bias & does not in reverse bias. The forward break over voltage can be reduced by increasing the value of gate current. Experiment No.2 Experiment Title: CHARACTERISTICS OF DIAC Aim:- To plot V-I characteristics of Diac. Objective: To plot V-I characteristics of Diac. Apparatus:- Circuit board,0-300V high voltage supply,0-30V Voltage supply,Voltmeter (0- 100V),Millimeter (0-100mA and 0-10mA), Multimeter, Connecting wires. Circuit Diagram:- Theory: The DIAC is a diode that conducts electrical current only after its break over voltage, VBO, has been reached momentarily. The term is an acronym of diode for alternating current.When breakdown occurs, the diode enters a region of negative dynamic resistance, leading to a decrease in the voltage drop across the diode and, usually, a sharp increase in current through the diode. The diode remains in conduction until the current through it drops below a value characteristic for the device, called the holding current, IH. Below this value, the diode switches back to its high-resistance, non-conducting state. This behavior is bidirectional, meaning typically the same for both directions of current. Most DIACs have a three-layer structure with breakover voltage of approximately 30 V. Their behavior is similar to that of a neon lamp, but it can be more precisely controlled and takes place at a lower voltage. DIACs have no gate electrode, unlike some other thyristors that they are commonly used to trigger, such as TRIACs. Some TRIACs, like Quadrac, contain a built-in DIAC in series with the TRIAC's gate terminal for this purpose. DIACs are also called symmetrical trigger diodes due to the symmetry of their characteristic curve. Because DIACs are bidirectional devices, their terminals are not labeled as anode and cathode but as A1 and A2 or main teminal MT1 and MT2.
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