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MOHD ZUBAIRY AZWAN BIN SHUKRY2009680176

SHAZARIN BIN KHALID2009818516



SPARK GAP



SPARK GAP A spark gap consists of an arrangement of two conducting electrodes

separated by a gap usually filled with a gas such as air, designed to allowan electric spark to pass between the conductors. When the voltagedifference between the conductors exceeds the gap's breakdown

voltage, a spark forms, ionizing the gas and drastically reducing itselectrical resistance.



Recap

The breakdown voltage of an insulator is the minimum voltage that causes a portion of an insulator to becomeelectrically conductive.

Ionization is the process of converting an atom ormolecule into an ion by adding or removing chargedparticles such as electrons or ions.



History

David Hughes, a British scientist was discovered partially by accident the spark gap transmitter when he made severalimprovements to the wired telegraph but he never publishedhis findings.

Heinrich Hertz to produce his own spark gap transmitter andreceiver in 1886. Hertz also verified that the spark gap producedelectromagnetic waves.

Nikola Tesla further improved the technology by devising atransmission and receiving system that could be roughly tuned.

By 1895, Guglielmo Marconi was able to transmit a signal andreceive it almost a mile away. Marconi was able to establish asuccessful wireless telegraph company, and wireless telegraphy took off from there, with constantly improving technologiesand distance.





How spark gap works : Tesla coil





mailto:Tesla%20Orchestra%20@%20Ars%20Electronica%202011%20Linz.mp4



Applications

Ignition devices

Radio transmitters

Spark gaps as protective devices Sphere gap for voltage measurement

Power-switching devices

Visual entertainment



THYRATRONS



Introduction

What is thyratrons?

A gas filled tube used as a switch for high

electrical energy and controlled rectifier.Typically – ‘controlled gas rectifier’

What type of gas were filled in?

Mercury vapor, xenon, neon andhydrogen



Construction



Operation

Divided into three phases:

Triggering and commutation (closure)

Steady-state conduction Recovery (opening)



Triggering & Commutation

Suitable +ve triggering

pulse of energy is applied

to the grid, electrons plasma

forms in the grid cathode

region and cause breakdown

in high voltage region

between the grid and anode.



This begin the thyratrons

switching process.

The plasma formed in grid And anode diffuses back

through the grid into the

grid-cathode space– avalanche theory

Anode delay time : 100 -200ns



Steady State Condition

A typical hydrogen thyratron will conduct with nearly constant voltage drop on the order of 100V regardlessof the current through the tube



Recovery (Opening)

The gap ‘reopen’ via the ion diffusion to the tube inner walls and electrode surface.

Ion will recombine with electrons. Time taken : 30-150µs

Factors affecting time :

Tube type, gas filled, fill pressure





Variations Old technology:

Krytron

Sprytron Ignitron

Modern technology

Thyristor Triac



IGNITRON



Ignitrons Ignitrons are ignitor-fired mercury pool rectifiers with

very high peak and average current handling capability. electron tube functioning as a rectifier to convert

alternating current (AC) to direct current (DC)

a mercury arc rectifier controlled by a subsidiar electrode,the igniter, partially immersed in a mercury cathode.

A current passed between igniter and cathode forms a hotspot sufficient to strike an arc between cathode and anode

used in a wide variety of pulse powerapplications, such as capacitor discharge,

laser switching, magneforming,magnetizing and crowbar circuits.

They are used in switching service forcurrents ranging to 700,000 Amps with

voltages ranging to 50 kV.



Triggering ignitron

There are two main ways by which the triggercan be biased:

Anode excitation: common in resistance welding applications here the anode bias is

connected to the ignitor by means of a switch(thyristor, thyratron etc.) and a resistor/fusenetwork. The ignitor current drops rapidly onignition as the anode-cathode voltage drops very low during conduction.

Separate excitation: as the name suggests, herethe ignitor circuit is largely independent of themain circuit.

Op ti



Operation

(1) Anode, (2) Cathode, (3) Ignitor, (4)Mercury, (5) Ceramic insulators, (6)Cooling fluid

• A large steel container with a pool of mercury in the bottom thatacts as a cathode during operation

•

A large graphite or refractory metal cylinder, held above the poolby an insulated electrical connection, serves as the anode

• An igniting electrode (called the "ignitor"), made of a refractory semiconductor material such as silicon carbide,is briefly pulsed

with a high current to create a puff of electrically conductive

mercury plasma .• The plasma rapidly bridges the space between the

mercury pool and the anode, permitting heavy conduction between the main electrodes.

• At the surface of the mercury, heating by the resulting

arc liberates large numbers of electrons which help tomaintain the mercury arc.

• The mercury surface thus serves as the cathode,and current is normally only in one direction. Onceignited, and ignitron will continue to pa ss current until

either the current is externally interrupted or the voltageapplied between cathode and anode is reversed.



Iwasaki Ignitron It uses "Ferro-Electric Capacitor", a disc of barium

titanate material invented by Iwasakiengineer Takenobu Iida - the firstcapacitor capable of enduring thetemperatures in a lamp outer bulb. By combining this with a ceramic resistor

and a "sidac" semiconductor, a high voltageelectronic ignitor is created inside thelamp. Because there are no moving parts,its reliability is unsurpassed. This advanced

development makes lamp ignition far morereliable and the removal of the ignitor from theexternal circuit offers numerous advantages such aslower system cost, smaller luminaires, reducedelectrode wear, and no restriction on distancebetween lamp and gear.



Iwasaki Ignitron



THANK YOU

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