Ee 2353 High Voltage Engineering Faculty Name:A.JAIBUNISHA Faculty Code: EE 58 Designation: LECTURER Department: EEE
Ee 2353 High Voltage Engineering Faculty Name:A.JAIBUNISHA Faculty Code: EE 58 Designation: LECTURER Department: EEE
Ee 2353 High Voltage Engineering Faculty Name:A.JAIBUNISHA Faculty Code: EE 58 Designation: LECTURER Department: EEE
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VOLTAGE DOUBLER CIRCUIT
In this method, during –ve half cycle, the Capacitor C1is charged
through rectifier R to a voltage +Vmax. During next cycle. C1rises to
+2Vmax .
C2.is charged to 2Vmax.
Cascaded voltage doublers can be used for producing larger output
voltage
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CASCADED VOLTAGE
DOUBLERS
Cascaded voltage doublers can be used for producing larger
output voltage
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VOLTAGE MULTIPLIER CIRCUITS
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VAN DE GRAFF GENERATOR
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Electrostatic generator
It consists of a stator with interleaved rotor vanes forming a
variable capacitor and operates in vacuum
The power input into the circuit P=VI=CVdV/dt+V 2dC/dt
The rotor is insulated from the ground,maintained at a potential
of +V.
The rotor to stator capacitance varies from C 0 to Cm
Stator is connected to a common point between two rectifiers
across –E volts.
As the rotor rotates, the capacitance decreases and the voltage
across C increases.
Output voltage of 1MV can be generated.
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GENERATION OF HIGH
ALTERNETING VOLTAGES
When test voltage requirements are less than about 300
kV,a single transformer can be used.
Each transformer unit consists of low,high and meter
winding.
Series connection of the several units of transformers used
to produce very high voltage.
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CASCADE TRANSFORMERS
First transformer is at ground potential along with its tank.The 2nd
transformer is kept on insulators and maintained at a potential of V 2.
The high voltage winding of the 1st unit is connected to the tank of the
2nd unit,the low voltage winging of this unit is supplied from the
excitation winding of the 1st transformer,which is in series with the
high voltage winding of the 1st transformer at its high voltage end.
The rating of the excitation winding is same as that of low voltage
winding.3rd transformer is kept on insulator above the ground at a
potential of 2V2.output of 3 stage is 3V2.
The rating of the low voltage winding of 230 or 400 Vcan be used to
produce 3.3 kV,6.6 kV or 11 kV.\
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GENERATION OF HIGH AC
VOLTAGE
CASCADE TRANSFORMER
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GENERATION OF HIGH AC
VOLTAGE
Cascade transformer with isolating transformer
for excitation
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GENERATION OF HIGH FREQUENCY
A.C HIGH VOLTAGES
High frequency high voltage damped oscillations are needed
which need high voltage high frequency transformer which
is a Tesla coil.
Tesla coil is a doubly tuned resonant circuit,primary voltage
rating is 10 kV and secondary voltage rated from 500 to
1000 kV.
The primary is fed from DC or AC supply through C1.A
spark gap G connected across the primary is triggered at V1
which induces a high self excitation in the secondary.The
windings are tuned to a frequency of 10 to 100 kHz.
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GENERATION OF IMPULSE VOLTAGES
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MARX CIRCUIT
Charging resistance Rs is liming the charging current from 50 to
100 mA. CRs is about 10s to 1 min.
The gap spacing G is grater than the charging voltage V.All the
capacitance s are charged to the voltage V in 1 min.
The spark gap G is made spark over, then all the capacitor C get
connected in series and discharge into the load load
In modified Marx circuit,R1is divided into n parts equal to R1/n
and put in series with the gap G, R2is divided into n parts equal
to R2/n and connected across each capacitor unit after the gap G.
The nominal output is the number of stages multiplied by the
charging voltage.
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MULTISTAGE IMPULSE GENERATOR
MARX CIRCUIT
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MULTI STAGE IMPULSE
GENERATORS
Modified Marx Circuit
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COMPONENTS OF A MULTISTAGE
IMPULSE GENERATOR
DC Charging set
Charging resistors
Generator capacitors and spark gaps
Wave shaping resistors and capacitors
Triggering system
Voltage dividers
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GENERATION OF SWITCHING SURGES
A switching surge is a short duration transient voltage produced in the
system due to a sudden opening or closing of a switch or c.b or due to an
arcing at a fault in the system.
Impulse generator circuit is modified to give longer duration wave
shape,100/1000 μs,R1 is increased to very high value and it is parallel to
R2 in the discharge circuit.
Power transformer excited by DC voltages giving oscillatory waves
which produces unidirectional damped oscillations.Frequency of 1to 10
kHz
Switching surges of very high peaks and long duration can be obtained
by one circuit,In this circuit C1 charged to a low voltage d.c(20 to 25
kV) is discharged into the low voltage winding of a power
transformer.The high voltage winding is connected inparallel to a load
capacitance C2,potential divider R2,gap S and test object.
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GENERATION OF IMPULSE CURRENTS
For producing impulse currents of large value,a bank of
capacitors connected in parallel are charged to a specified
value and are discharged through a series R-Lcircuit.
Im=V(exp(-αt))sin(ωt)/ωL
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GENERATION OF HIGH IMPULSE
CURRENTS
For producing large values of impulse,a no.of capacitors are
charged in parallel and discharged in parallel into the circuit.
The essential parts of an impulse current generator are:
(i) a.d.c. charging unit
(ii) capacitors of high value (0.5 to 5 μF)
(iii) an additional air cored inductor
(iv) proper shunts and oscillograph for measurement
purposes, and
(v) a triggering unit and spark gap for the initiation of the
current generator.
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TRIPPING AND CONTROL OF IMPULSE
GENERATORS
In large impulse generators, the spark gaps are
generally sphere gaps or gaps formed by
hemispherical electrodes.
The gaps are arranged such that sparking of one
gap results in automatic sparking of other gaps as
overvoltage is impressed on the other.
A simple method of controlled tripping consists of
making the first gap a three electrode gap and
firing it from a controlled source.
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TRIPPING AND CONTROL OF IMPULSE
GENERATORS
The first stage of the impulse generator is fitted with a three
electrode gap, and the central electrode is maintained at a
potential in between that of the top and the bottom electrodes
with the resistors R1 and RL.
The tripping is initiated by applying a pulse to the thyration G
by closing the switch S.
C produces an exponentially decaying pulse of positive polarity.
The Thyraton conducts on receiving the pulse from the switch S
and produces a negative pulse through the capacitance C1 at
central electrode.
Voltage between central electrode and the top electrode those
above sparking potential and gap contacts.
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TRIPPING CIRCUIT USING A TRIGATRON
This requires much smaller voltage for operation compared
to the three electrode gap.
A trigatron gap consists of a high voltage spherical
electrode, an earthed main electrode of spherical shape,
and a trigger electrode through the main electrode.
Tripping of the impulse generator is effected by a trip
pulse which produces a spark between the trigger
electrode and the earthed sphere.
Due to space charge effects and distortion of the field in
the main gap, spark over of the main gap occurs and it is
polarity sensitive.
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