HIGH VOLTAGE ENGINEERING

1. HIGH VOLTAGE ENGINEERING
Prof.P.Swaminathan
Asst.Prof.[SG]/EEE
KARUNYA UNIVERSITY
Overvoltage Phenomenon and
Insulation Coordination

2. NATURAL CAUSES FOR
OVERVOLTAGES —LIGHTNING
PHENOMENON

3. Charge Formation in the
Clouds

4. Cioud model according to
Simpson's theory

5. Mechanism of Lightning
Strokes

7. Travelling Waves on
Transmission Lines

8. Classification of Transmission
Lines
 Transmission lines are usually classified as
 (a) lines with no loss or ideal lines,
 (b) lines without distortion or
distortion less lines,
 (c) lines with small losses, and
 (d) lines with infinite and finite length defined by
all the four parameters.

9. Reflection and Transmission of
Waves at Transition Points

10. Successive reflections and
lattice diagrams
 (/) all waves travel downhill, i.e. into the positive time
 (M) the position of the wave at any instant is given by means
of the time scale at the left of the lattice diagram
 (//O the total potential at any instant of time is the
superposition of all the waves which arrive at that point until
that instant of time, displaced in position from each other by
time intervals equal to the time differences of their arrival
 (/v) attenuation is included so that the amount by which a
wave is reduced is taken care of and
 (v) the previous history of the wave, if desired can be easily
traced. If the computation is to be carried out at a point where
the operations cannot be directly placed on the lattice
diagram, the arms can be numbered and the quantity can be
tabulated and computed.

11. Reflection lattice of a travelling wave

12. Behaviour of Rectangular Travelling Wave
[Unit Step Function]
at Transition Points—Typical Cases
 Case (i): Open ended transmission line of surge
impedance Z:
 Case (Ii): Short circuited line:
 Case (Hi): Line terminated with a resistance equal
to the surge impedance of the line
 Case (Iv): Line terminated with a capacitor:
 Case (v): Transmission terminated by an
inductance L:
 Case (yi): Line having a series inductor:
 Case (ViI): Line terminated with a transformer
 (taken as an L-C parallel combination):

13. OVERVOLTAGE DUE TO SWITCHING
SURGES, SYSTEM FAULTS AND
OTHER ABNORMAL CONDITIONS
 Origin of Switching Surges
 The making and breaking of electric circuits with
switchgear may result in abnormal overvoltages in power
systems having large inductances and capacitances.
 The over voltages may go as high as six times the
normal power frequency voltage. In circuit breaking
operation, switching surges with a high rate of rise of
voltage may cause repeated restriking of the arc between
the contacts of a circuit breaker, thereby causing
destruction of the circuit breaker contacts.
 The switching surges may include high natural
frequencies of the system, a damped normal frequency
voltage component, or the restriking and recovery voltage
of the system with successive reflected waves from

14. Characteristics of Switching
Surges
 (i) De-energizing of transmission lines, cables,
shunt capacitor, banks, etc.
 (ii) Disconnection of unloaded transformers,
reactors, etc.
 (Uf) Energization or reclosing of lines and reactive
loads,
 (i v) Sudden switching off of loads.
 (v) Short circuits and fault clearances.
 (w) Resonance phenomenon like ferro-
resonance, arcing grounds, etc

15. Switching Overvoltages
In EHV and UHV Systems
 Interruption of low inductive currents (current
chopping) by high speed circuit breakers. This
occurs when the transformers or reactors are
switched off
 Interruption of small capacitive currents, such as
switching off of unloaded lines etc.
 ferro-resonance condition
 This may occur when poles of a circuit breaker do
not close simultaneously
 Energization of long EHV or UHV lines.

16. Energization of long EHV or UHV
lines
 (a) single pole closing of circuit breaker
 (b) interruption of fault current when the L-G or L-
L fault is cleared
 (c) resistance switching used in circuit breakers
 (d) switching lines terminated by transformers
 (e) series capacitor compensated lines
 (O sparking of the surge diverter located at the
receiving end of the line to limit the lightning over
voltages

17. Power Frequency Over voltages
in Power Systems
 The power frequency over voltages occur in
large power systems and they are of much
concern in EHV systems, i.e. systems of 400
kV and above. The main causes for power
frequency and its harmonic over voltages are
 (a) sudden loss of loads,
 (b) disconnection of inductive loads or
connection of capacitive loads,
 (c) Ferranti effect, unsymmetrical faults, and
 (d) saturation in transformers, etc.

18. Control of Over voltages
Due to Switching
 The overvoltages due to switching and
power frequency may be controlled by
 (d) energization of transmission lines in
one or more steps by inserting
resistances
 and withdrawing them afterwards,
 (b) phase controlled closing of circuit
breakers,
 (c) drainage of trapped charges before
reclosing,

19. Protection of Transmission Lines
against Over voltages
 Protection against Lightning Overvoltages
and Switching Surges of short Duration
 Overvoltages due to lightning strokes can be
avoided or minimized in practice by
 (d) shielding the overhead lines by using ground
wires above the phase wires,
 (b) using ground rods and counter-poise wires,
and
 (c) including protective devices like expulsion
gaps, protector tubes on the lines, and surge
diverters at the line terminations and substations.

20. Lightning Protection Using
Shielded Wires or Ground Wires

21. Protective Devices
 (i) Expulsion gaps
 (H) Protector tubes
 (Hi) Rod gaps
 (iv) Surge diverters or lightning arresters

22. Expulsion gaps
1. External series gap
2. Upper electrode
3. Ground electrode
4. Fibre tube
5. Hollow space

23. Protector tube mounting
 1 Line conductor on string insulator
 2. Series gap
 3. Protector tube
 4. Ground connection
 5. Cross arm
 6. Tower body

24. Surge diverters or lightning arresters

25. Valve Type Lightning Arrestor

26. PRINCIPLES OF INSULATION COORDINATION ON
HIGH VOLTAGE AND EXTRA HIGH VOLTAGE
POWER SYSTEMS

29. Basic Impulse Insulation Levels

30. Surge Protection of Rotating
Machine