# Thyristor Switch Application

Topics: Alternating current, Power supply, Voltage Pages: 12 (2496 words) Published: November 18, 2013
EE3092 – Laboratory Practice V

Thyristor Switch Application

Instructed by:

Name

: K.P.A.I.Perera

Index No.

: 100385H

Course

: BSc. Engineering

Group

: Group 09

Date of Per

: 26/06/2013

Date of Sub : 17/07/2013

OBSERVATION SHEET
Name

: K.P.A.I.Perera

Index No.

: 100385H

Course

: BSc. Engineering

Group

: Group 09

Date of Per

: 26/06/2013

Date of Sub : 17/07/2013
Instructed By :

a) DC switch opening and closing by means of a push button.

Fig 1: Commutation of Thyristor: A-K voltage

Time taken from stopping SR4 to stopping SR3 = 6.2 × 1ms
= 6.2ms

b) DC switch opening with an over current.

Fig 2: Gate voltage of Thyristor

c) C switching opening and closing by means of miniature switch.

Fig 3: Voltage waveform between R5 and R6

Calculation of gate current of SR1 and SR2
Resistance of R5 and R6 = 100 Ω
Peak value of voltage waveform = 50 × 3
=150V
Gate current of SR1 and SR3

= 150/100
= 1.5A

d) AC switch opening and closing with lights.

Fig 4: Waveform across R5 and R6

Calculation of gate current peak in SR1 and SR2
Peak value of voltage waveform = 50 × 3
= 150V
Gate current peak in SR1 and SR2 = 150/100
=1.5A

e) Mechanical switch opening and closing with a magnetic relay.

Fig 5: Voltage oscillogram of coil RL1

Switch on time = 1 × 10 ms
=10ms

DISCUSSION
i.

What are the advantages of using a thyristor switch in place of a mechanical switch. 

Fast Operation. usually less than 10μs. Fast turn-on time allows the thyristor to be easily synchronized with line zero-crossing. This also minimizes EMI and can greatly increase the lifetime of tungsten lamps, of considerable value in applications such as traffic signals. Lower (if any) minimum output current (latching current) required. Increased lifetime, particularly if activated many times, as there are no moving parts to wear.

Very Low Coupling Capacitance between Input and Output. This is a characteristic inherent in the optoelectronic-coupler used in the thyristor, and can be useful in areas such as medical electronics where the reduction of stray leakage paths is important. Output resistance remains constant regardless of amount of use. Clean, bounce less operation.

Decreased electrical noise when switching.
No sparking, allowing use in explosive environments where it is critical that no spark is generated during switching.
Totally silent operation.
Inherently smaller than a mechanical relay of similar specification (if desired may have the same "casing" form factor for interchangeability).
Much less sensitive to storage and operating environment factors such as mechanical shock, vibration, humidity, and external magnetic fields.
Cost is less than mechanical switches.
Thyristor is reliable than a mechanical switch.
Thyristors have almost zero maintenance cost whereas mechanical switches need to maintain well such as cleaning and lubricating.
Thyristors can handle more power than mechanical switches.
Thyristors do not need additional power for switching and also in thyristors power consumption is very low.
The ability of a thyristor to withstand peak currents many times the size of its average rating is high rather than a mechanical switch.
Operating voltage range is higher than mechanical switch.
Thyristors do not contain moving parts like mechanical switches. So thyristors response time is less than a mechanical switch
In thyristors we don’t get any current losses whereas mechanical switches consume more power due to internal coils
There are no arcs when we use thyristors.
The datasheet and the characteristics of a thyristor is available. But mechanical switches do not have such operating data tables.
Mechanical switches cannot use in high frequency applications, but thyristors can handle high frequencies.

ii.

For what type of application is the...

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