Loading presentation...

Present Remotely

Send the link below via email or IM

Copy

Present to your audience

Start remote presentation

  • Invited audience members will follow you as you navigate and present
  • People invited to a presentation do not need a Prezi account
  • This link expires 10 minutes after you close the presentation
  • A maximum of 30 users can follow your presentation
  • Learn more about this feature in our knowledge base article

Do you really want to delete this prezi?

Neither you, nor the coeditors you shared it with will be able to recover it again.

DeleteCancel

GENERATION OF HIGH VOLTAGES AND CURRENTS

No description
by

Ainul Shazwanie

on 29 June 2015

Comments (0)

Please log in to add your comment.

Report abuse

Transcript of GENERATION OF HIGH VOLTAGES AND CURRENTS

GENERATION OF HIGH DC VOLTAGES
Needed in insulation tests on capacitors and cable.

Impulse generator charging units require high dc voltages about 100-200kV.
>> electronic valve rectifiers used
>> output current : 100mA
RECTIFIERS
OVERVIEW
Electrical eng. and applied physics required high voltages in several applications

Voltage :

Current :
GENERATION OF HIGH VOLTAGES AND CURRENTS
High impulse voltage are required for testing purpose
> to simulate overvoltages that occurs in power systems due to lightning or switching action

Insulting testing
+ power frequency AC
+ high frequency
+ switching/lightning impulses
High generation of amperes
> needed for short circuit testing of switchgear and surge diverters testing
VOLTAGE
CURRENT
HALF WAVE
FULL WAVE
VOLTAGE DOUBLER RECTIFIER
simple voltage doubler
cascaded voltage doubler
GENERATION OF HIGH AC VOLTAGES
Cascaded Transformer
-Normally, transformer is used for test purposes. Only test voltage of <200kw is suitable.
-If only a single unit of transformer is used, it will be
complicated in construction
and
not cost effective
due to
insulation problem
.
-Mechanism:-
Series and Parallel Resonant Set
-Harmonic distortion can be produced in the transformer and it must be filtered before supplying it to the test circuit.

>>> Therefore,
series resonant set
can be used to achieve
a pure 50Hz waveform
.
-
Parallel resonant set

can be used to minimize the max. power requirement of the low voltage winding of the test supply by
improving the power factor
.
GENERATION OF IMPULSE VOLTAGES
Standard Impulse Waveshape
-Lightning and switching surges cause a steep build up of voltage on transmission lines and other electrical apparatus called
transient overvoltages
.

-Normally, it has a rise time of 0.5μs to 10μs and decay time to 50% of the peak value of 30μs to 200μs.
-Example:-
1.2/50μs, 1000kV wave
Impulse Voltage Generator
-It provides impulse voltage waveshapes into the test object.

-The load in the cicuit may consist of R, L and C i.e. Transformer.

-The peak voltage output of the generator must be variable and changes with the impedance of the test object and the required waveshape.

>>>It has a charging component, producing the wavefront of the waveshape.
>>>It has a discharging component, producing the wavetail of the waveshape.
Wavefront Circuit
Wavetail Circuit
Multistage Impulse Generator
-It is used to obtain large impulse voltage. Therefore, a relative size of High Voltage transformer can be kept small and costs less.
-It charges a number of capacitor in parallel through a rectifier and discharges them in series. This results in:-
nominal output voltage
=
charging voltage x
the no. of stages
Marx Impulse Generator Circuit:-
GENERATION OF IMPULSE CURRENTS
Typical Impulse Current Wave
Lightning discharge involve both high voltage impulses and high current impulse.
Protective gear like surge diverters/collectors have to discharge the lightning currents without damage.
Thus the generation of impulse current waveforms of high magnitude (>100kA peak) is necessary.
Circuit For Producing Impulse Current Wave
A bank of capacitors connected in parallel are charged to a specific value and are dischagre through a series R-L circuit.
C represents a bank of capacitors connected in parallel which are charged from a d.c. source to a voltage up to 200kV.
R represents the dynamic resistance of the test object and the resistance of the circuit and shunt.
L is an air cored high current inductor.
Example:-
An impulse current generator has a total capactance of 8 μF. The charging voltage is 25kV. If the generator to give an output current of 10kA with 8/20μs waveform, calculate:
a) The circuit inductance.
b) The dynamic resistance in the circuit.
Solutions:-
Full transcript