lab 1b practical

7/30/2019 LAB 1b Practical

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DEPARTMENT OF ELECTRICAL ENGINEERING

LAB WORK ET502 POWER ELECTRONICS

EXPERIMENT : 1b

TITLE : TURN ON AND TURN OFF THYRISTOR CHARACTERISTIC (PRACTICAL)

OUTCOME :

Upon completion of this unit, student should be able to:

i. Handle the practical work on the power electronics converters using appropriate equipment.[CLO3](PLO2,LD2,P3)

OBJECTIVES :

1. Describe the turn-on and turn-off characteristics of a thyristor2. Describe the turn-on and turn-off process of a thyristor3. Find the turn-on time and turn-off time of a thyristor by hardware construction

COMPONENTS/EQUIPMENTS:

1. SCR 2N15952. Resistor 100ohm (x2)3. Function generator (x2)4. DC Power Supply

BRIEF THEORY :

Silicon controlled rectifiers (SCRs), are one of the most popular and useful device among thyristors. It is

the most popular electrical power controller due to its fast switching action, small size and high current

and high voltage ratings. It has three terminals: the anode (A) and the cathode (K) are the power

terminals, and the gate (G) is the control terminal. When the SCR is forward-biased, that is when the

anode is made positive with respect to the cathode, a positive voltage on the gate with respect to turns

on (trigger) the SCR. However, the current through the SCR cannot be turned off using the gate. It is

turned off by interrupting the anode current. A pulse signal must be applied to the gate in order for the

SCR to conduct. If there is no pulse current at the gate, then the SCR will act as an open switch.


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PART 1:

Thyristor Turn-on Characteristics

PROCEDURE :

1. Construct your circuit based on Figure 1.2. Set the Function Generator (FG) as shown in Figure 1.3. Measure the delay time and the rise time to calculate the turn-on time. Note: Take these

readings from the anode current graph (-I(R1)).

PART 2:

Thyristor Turn-off Characteristics

PROCEDURE :

1. Construct your circuit based on Figure 2.2. Set the VSIN as shown in Figure 2.3. Set the Vgate as shown in Figure 2.4. Change the frequency (FREQ) from 20kHz to 25kHz and 40kHz and measure the gating

period, Delay time (Td), Reverse recovery time (Trr), rising time (Tr) and the Turn-off-time (Toff)

for frequency values of 20kHz, 25kHz and 40kHz.

Results:

As your result:

1. Sketch the respective graphs complete with their labels indicating gating period, Delay time(Td), Reverse recovery time (Trr), rising time (Tr) and the Turn-off-time (Toff).

2. Complete the chart below.3. Discuss the results by comparing the simulation results and the practical results.


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Part 1:

Figure 1: SCR turn on characteristics circuit

Part 2:

Figure 2: SCR turn off characteristics circuit

V1 = 0

V2 = 4V

PW = 1.2us

PER = 5.2us

V1 = 0

V2 = 4V

PW = 10us

PER = 50us

VAMPL = 10V

FREQ = 20k

20V

lab 1b practical

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