The main advantage of this system lies in the smallest time interval during which motor can be brought to rest. The voltage Vz is applied to the charging circuit RC. Disadvantages, To study SCR/TRIC/ DIAC/ MOSFET/IGBT Characteristics. 4. APPARATUS REQUIRED: Trainer kit, Patch cards, Multimeters. Fig.2 shows the characteristics of TRIAC. To determine holding, latching current and break over voltage of given SCR. The firing angle can be controlled up to above 150o. The bridge circuit has two halves, the positive half consisting of the SCRs T1, T3 and T5 and the negative half consisting of the SCRs T2, T4 and T6. For firing angle less than 30°, the output terminal voltage of the converter is always positive, and the freewheeling diode does not come into operation. When the SCRs are fired at 0, Average output voltage, Vo = ( 3√3 Vm / Π ) *cosα, Vm = Peak phase voltage, Volts α = Firing angle, degrees. Name the three regions of operation in a MOSFET. Write down the expression for average output voltage of three phase full converter. A V-I Characteristic of SCR (Silicon Controlled Rectifier) is the Why i-mode is more sensitive among all modes? Fig. TP3:- Output for single lamp load connection (no waveform). Explain the working operation of V-I characteristics of S.C.R. A.C. Distribution Radial System 4. For large power dc loads, 3-phase ac to dc converters are commonly used. To study about single phase dual converter, 2. 1. It exhibits negative resistance characteristics. 2. To see the phase controlled converter output waveform, use a 230 / 12 V transformer for isolation purpose. In this mode the device is normally in off condition and a sufficiently large positive voltage on the gate terminal can turn on the device. Now gradually load the motor and take ,speed, current voltage readings. The force acting tangentially on the pulley is equal to the difference between two spring balance readings. It houses transformers for control circuit & 1 no of power transformer (0-130 v AC secondary o/p, 2 Amps), for energizing the power circuit. For reverse characteristics, change the connection to make M. 2. The switch SW3 is required to be kept in downward position for normal-dual converter operation. 2 - SCR Gate Characteristics. Why? 1. 1) Select Triac as the device under test by referring to the top RHS diagram. What is a three phase controlled rectifier? Define Holding current, Latching current on state resistance, Break down voltage, 3. The field supply during this process remains connected. VL = 81 volts (RMS), (i.e. You may observe o/p waveform across the attenuated test point for o/p. 6-12(b) is the symbol for triac. 2. This method of controlling the output power by varying the charging resistor ‘r’ is called ramp control, open loop control (or) manual control. Sheet Report 1 Object Power System Components Objectives To study- 1. 3. a) Reduce the gate voltage supply to zero. The V-I characteristics of a TRIAC is based on the terminal MT1 as the reference point. i.e. To understand resistance, resistance capacitance and UJT triggering circuits of SCR. Three phase half controlled bridge rectifier circuit consists of three SCRs in three arms and three diodes in the other three arms. As the current ‘i2’ is in the form of pulse, windings of the pulse transformer have pulse voltages at their secondary terminals. Circuit Diagram : Theory: An TRIAC is a device which can be turned on through the gate pulse for both positive and negative values of V AK and turned off using power circuit i.e., turn on is controlled … What are the different types of Power MOSFET? Objective A. Observe the ammeter reading by reducing the anode-cathode supply voltage V, 9. Objective B. As a result of their performance, trials tend to be used for low to medium power applicati… Yes. This is the break over voltage of CR1. Demonstrate bi-directional conduction of a gated TRIAC. The various types of three-phase phase-controlled converters are 3 phase half-wave converter, 3-phase semi converter, 3-phase full controlled and 3-phase dual converter. Explain the different working modes of operations of a TRIAC? ü Power Source 6.3 Vac, 500mA, ü Power Source 6 Vdc, 500mA, ü C1 0.1μF, electrolytic, ü DS1 Miniature lamp, ü Q1 DIAC, ST2, ü R1 47Ω, 1W, ü R2 10KΩ, 1W, ü S1 PBNO, ü S2 SPST. What are the two modes of operation present in the three phase half controlled rectifiers? It is a three terminal switching device similar to SCR (Thyristor) but it can conduct in both the directional since it construct by combining two SCR in anti-parallel state. MT 2 is positive with respect to MT X in the first quadrant and it is negative in the third quad rant. 6-12TRIAC During the positive half cycle of the input voltage, C begins to charge through R. When the capacitor voltage reaches the minimum gate trigger voltage SCR will turn on. You can observe various test points as described. When the other switch (SW2 marked power ON circuit) is switched on power transformer is brought into action & the system starts to work as dual converter. 6. Objective C. Demonstrate bi-directional operation of a DIAC. Electrical power is produced at the power stations which are located at favorable places, generally quite away from the consumers. For lamp load a separate load bank is provided. Operating characteristics of triac in the 1st and 3rd quadrants are similar but for the direction of flow of current and applied voltage. The Fig-3, shows the current and voltage waveforms for this circuit. What is commutation angle of a rectifier? b) Reverse the polarity of the gate voltage supply by reversing the power supply leads connected to your circuit. Three-phase half-wave converter is rarely used in industry because it introduces dc component in the supply current. When the dimmer voltage is around 32 volts the DIAC starts conducting as indicated by M3 meter. As compared with the anti-parallel thyristor configuration which requires two heat sinks of slightly smaller size, a triac needs a single heat sink of slightly larger size. 4. 7. These disadvantages are overcome by insulating the gate terminals from the channel with a thin layer of silicon dioxide (Metallic oxide). 3. In the middle (marked zero position) none of the pulses for triggering the thyristors are generated. i) Is the break over voltage approximately the same value in both directions? The characteristics of a TRIAC are similar to those of an SCR, both in blocking and conducting states, except for the fact that SCR conducts only in the forward direction, whereas the TRIAC conducts in both the directions. It is used extensively for control of power in AC circuit. Fig shows single phase fully controlled rectifier with resistive load. Positive or negative potential across the terminals can be triggered by reaching +/- breakover voltage. Fig. Ensure pot P1 in zero position & SW3 is in downward (NORMAL) position. C. Demonstrate bi-directional operation of DIAC. The circuit symbol and schematic construction of one such device are shown in fig.1. It is composed by joining p type and n type semiconductors in 5 layers as in fig. When ‘Vc’ reaches the unijunction threshold voltage Vz, the t-B1 junction of UJT breaks down and the capacitor ‘c’ discharges through the primary of pulse transformer sending a current ‘C2’ as shown. However a large input signal may momentarily overcome the reverse bias and turn on gate diodes drawing appreciable current from the source. The armature will be disconnected from power circuit & connected to lamp load which is located on the right hand side socket. Results are accurate. When the anode is more positive with respect to the cathode. What are the different families of thyristor devices? A TRIAC is a bidirectional thyristor (it can conduct in both directions) with three terminals. Characteristics of a Triac First Quadrant Operation of Triac. To obtain V-I characteristics and to find on-state forward resistance of given SCR. There is however; a major difference in the substrate. 7. ☞Set both voltages to minimum position, and then switch on SPDT. Thereby facilitating conversion of DC power onto AC. Now throw the switch SW3 in downward (NORMAL) position. Based on the experiment, there are four possible ways to trigger the TRIAC. Switch on power supply to the SCR trainer. To understand performance of SCR/TRIAC/DIAC/MOSFETS and IGBT. For each firing angle observe the output waveform through CRO. 2. Select proper desired mode of operation under closed loop/ open loop system. Hence the effect of the freewheeling diode is to cause a reduction of ripple voltage of the output terminals and at the same time to divert the load current away from the input lines. Maximum triac current, voltage across the triac and gate current limit is 600mA, 30V and 20mA respectively. … Current ‘I’, charges capacitor ‘c’ at a rate determined by ‘R’ voltage across capacitor is marked by ‘Vc’ as shown. R2 is the variable resistance. Diodes ‘D1’ to ‘D4’ rectify ac to dc. An electron movement in the n-channel, in turn causes substantial hole injection from p+ substrate layer into epitaxial n- layer. Set the gate current at a fixed value by varying RPS on the gate-cathode side. Vary the firing angle step by step in the range 180° – 0°. the power station, the transmission lines, and the distribution system. The two modes of its operation are non-circulating current mode and the circulating current mode. SCR Characteristics 3 2. thanks. D.C .Radial Distribution System 3. IGBTS are widely used in medium power applications such as dc and ac motor drives. Explain how synchronization of the triggering circuit with the supply voltage across SCR is achieved? 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