tripping and control of impulse generators
DESCRIPTION
Tripping and Control of Impulse Generators -High voltage engineeringTRANSCRIPT
04/20/23
UNIT 3
Tripping and Control of Impulse Generators
BY
HIGH VOLTAGE ENGINEERINGHIGH VOLTAGE ENGINEERING
04/20/23
Tripping and Control of Impulse Generators
In a multistage impulse generator; it is desired that triggering or flashover takes place first at the stage No. 1 and then in sequence at the higher number stages. Hence, the gap distance setting requirement is such that the gap distance set at stage one is smallest and the gap distances in higher stages are in increasing order by a small difference.
04/20/23
Tripping and Control of Impulse Generators
04/20/23
Tripping and Control of Impulse Generators
Impulse generator waveforms for uncontrolled operation
04/20/23
Tripping and Control of Impulse Generators
Controlled operation
04/20/23
Tripping and Control of Impulse Generators
Impulse generator waveforms for controlled operation
04/20/23
Tripping and Control of Impulse Generators
Three Ways of Triggering an Impulse Generator
• Fix the gap distance between the spheres and increase the stage applied dc voltage till the flashover occurs.
• Set the gap distance between the spheres large enough, apply a desired voltage across them and then reduce the gap distance till flashover takes place.
• Fix both, the desired stage voltage and corresponding gap distance within prescribed limits.Then apply the trigger pulse to the trigatron on the first stage.
• The third method is widely practiced since this is the only method to get impulses of exact desired magnitude repeatedly.
04/20/23
Tripping and Control of Impulse Generators
CONVENTIONAL TYPE :
• Impulse generators are generally have sphere gaps formed by hemispherical electrodes.
• The gaps are arranged such that sparking of one gap results in automatic sparkling of other gaps as the over voltage impressed on the other.
• Consistency in sparking will be achieved by irradiation of gap using ultra violet lamp provided from the bottom to all the gaps.
• To trip the generator at a predetermined time, the spark gaps may be mounted on a movable frame, and the gap distance is reduced by moving the movable electrodes closer.
• Disadvantage : difficult, not consistent & control tripping.
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Tripping and Control of Impulse Generators
Controlled Tripping : Three Electrode Gap
• First gap as a three electrode gap and firing it from a controlled source.• Central electrode is maintained at a potential in between the top and
bottom electrodes.• Since the impulse waves are shorter duration, synchronization should be
accurate between impulse generator and CRO.• S- closed, initiates the sweep circuit & grid of thyratron tube.• Time delay to thyratron ensures the sweep circuit begin to operate.
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Tripping and Control of Impulse Generators
Tripping of an impulse generator with a three electrode gap
04/20/23
Tripping and Control of Impulse Generators
Drawbacks in three electrode gap.• Larger space and elaborate construction.• Not very sensitive.
TRIGATRON GAP
• A device, known as "Trigatron", is used to control the flash over at the spark gaps in order to get a desired magnitude of the output voltage
repeatedly.
04/20/23
Tripping and Control of Impulse Generators
Trigatron gap
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Tripping and Control of Impulse Generators
04/20/23
Tripping and Control of Impulse Generators
• Trigatron", consists essentially of three-electrodes.
• The main electrode - indicated as HV and the earthed electrode are equal size spherical electrodes in the first stage of the generator.
• A small hole, drilled in the earthed electrode, holds a metal rod through it inside with the help of a bushing. The annular gap formed between the rod and the surrounding sphere is typically about 1 mm.
• The metal rod, or the trigger electrode forms third electrode, is essentially at the same potential as the sphere since it is connected to it over a high resistance R. The control or trigger pulse is applied between these two electrodes on the rod.
• The trigger electrode (pin) has an auxiliary circuit which can supply high voltage of about 10 kV to it. Since the pin is sharp, corona is produced at a relatively low voltage causing it to spark over to the earthed electrode.
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Tripping and Control of Impulse Generators
• The surface discharge or corona causes photo ionization in the pilot gap on applying an impulse voltage to the rod. Due to photo ionization enough initiatory electrons are made available in the annular gap which breaks down without appreciable time delay consistently at a given voltage across the gap 'd'. Thus a surface discharge is caused by the triggering pulse.
• When the generator needs to be energized, a pulse is applied to the pin. Breakdown of the pin gap simultaneously causes the main gap and hence the impulse generator to operate.
• A delay is usually provided between the auxiliary d.c. source and the pin so that the oscilloscope time base can be started just prior to the impulse being initiated.
04/20/23
Tripping and Control of Impulse Generators