Page 296 - Electronic Mechanic - TP - Volume - 2

ELECTRONICS MECHANIC - CITS

EXERCISE 204: Test three phase, controlled rectifier for

half wave and full wave using SCRs

Objectives

At the end of this exercise you shall be able to:
• to demonstrate three phase, controlled rectifier half wave using SCRs.
• to demonstrate three phase, controlled rectifier Full wave using SCRs.
• to draw the characteristics from observations.

Requirements

Tools/ Equipments/ Instruments
• Combination Plier 250mm - 1 No. • Ammeter/Voltmeter - 1 No.
• Screwdriver Set 150mm - 1 No. • 3-phase Variac - 1 No.
• Wire Stripper - 1 No. • Multi-meter - 1 No.
• Type of Loads (R/R-L load) - 1 No.
Materials/ Components
• Patch Chord/ Connecting leads - 1 No.
• 3-phase Power modulator Kit - 1 No.
• DSO - 6 Nos.

Note:
Three phase converters are extensively used in industrial application up to 120kw level.
A full converters circuit, the thyristor is fired at an interval of π/3. The frequency of output ripple
voltage is 6fs and the filtering requirement is less than that of three phase semi and half wave
converters.
At ωt=π/6+α, thyristor T4 is already conducting and thyristor T1 is turned on during the interval
(π/6+α) ≤ ωt ≤ (π/2+α), thyristor T1 is turned on and the line-to-line voltage, Vab=(Van-Vbn) appears
across the load.

At ωt=T4 is turned off due to natural commutation. During the internal (π/2+α) ≤ ωt ≤ (π/2+α),
thyristor T1and T6 conduct and the line-to-line voltage Vac appears the load. If the thyristor is
numbered as shown in firing sequence is (1,6), (6,3), (3,2), (2,5), (5,4), and (4,1).
Formula Used
Semi-controlled Converter

Fully Controlled Converter

Procedure

1 Connect the circuit as per circuit diagram.
2 Vary the firing angle of the Thyristor Pairs to obtain different values of Voltage & current.

3 Record the output voltage & current.

279