This document provides an overview of high voltage techniques. It defines key concepts like voltage, potential, alternating voltage, and direct voltage. It explains why high voltages over 1000V are needed, such as to transmit more power over long distances with lower losses. The document also discusses high voltage levels used in Turkey and Northern Cyprus. It covers insulation, withstand voltages, overvoltages, and the importance of insulation coordination in electrical networks.

1. ADVANCED HIGH VOLTAGE TECHNIQUE
Assistant Professor Suna BOLAT
Office: ee 106
Phone: 366 2197

2. REVIEW
What is high voltage?
What is voltage for that matter?

3. Voltage
• Potential, V:
Electrical location of a point according to a reference.
unit: volt
• Voltage, U:
unit: volt
2
1
V2
V1
U = V2 - V1
referenceVr

4. Potential, V:
Electrical location of a point according to a reference.
unit: volt
Voltage
2
1
+V2
+ V1
- V3
referenceVr
3

5. Voltage
Voltage, U: potential difference
unit: volt
Reference, Vr
V1
V2
U = V2 - V1

6. Alternating voltage
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
-1.5
-1
-0.5
0
0.5
1
1.5
Umax
Voltage, U(t)
Time, t
Period, T = 1/f
Ue = effective value = Umax/2

7. Direct voltage constant
DIRECT VOLTAGE
IMPULSE VOLTAGE

8. High voltage
U > 1000 Volt = 1 kiloVolt
High voltage (HV)
U ≤ 1000 Volt = 1 kiloVolt
Low voltage (LV)

9. High voltage levels in Turkey
Nominal
voltage, Un
kV
Permissible
maximum
operating voltage,
Umax [kV]
Medium
voltage
3 3.6
6 7.2
10 12
15 17.5
20 24
30 (34.5) 36
High
voltage
66 72
154 170
Extra high
voltage
380 420 (400)

10. High voltage levels in TRNC
Nominal
voltage, Un
kV
Permissible
maximum
operating voltage,
Umax [kV]
Medium
voltage
11 12
22 24
High
voltage
66 72
132 145

11. High DC voltage
± 100 kV
± 200 kV
± 300 kV
± 400 kV
± 800 kV

12. Why do we need high voltage
1. MORE POWER
• Electrical power: P = V*I I = V/Z P = V2/ Z
• Electrical energy: W = P*t

13. Why do we need high voltage
2. DISTANCE BETWEEN ENERGY SOURCE AND THE CONSUMER
In order to cover voltage drops in long distances. As the line is
resistive, a voltage drop will occur along the line. The voltage at
the generator, UG, is higher than the voltage at the load, UL.

14. Why do we need high voltage
3. REDUCING LOSSES (1)
• If R is the overall line resistance, the following power transmission
losses, PΩ, occur:
• Relating the power losses to the transmitted power, we obtain the
relative power losses:
• Equation illustrates the inversely proportional relationship of the
transmission losses to the square of the line voltage.
• To keep losses low, power transmission lines are operated at
voltages which should, theoretically, be as high as possible.

15. Why do we need high voltage
3. REDUCING LOSSES (2)
coronaconsumption
generation
-P
P
P-P
heat
Leakage current

16. Why do we need high voltage
4. REDUCING DIMENSIONS & COST
Increasing the line voltage also implies an increase of the
insulation costs associated with components such as
transformers.
Decreasing losses imply increasing equipment costs.

17. REVIEW
Basic concepts and terminology

18. Electric network

19. Operating equipment
All the components that are connected to the electric power
system and carry high voltage and currents.
• Generator (supply)
• Transformer (conversion)
• Lines, cables, conductors, switchgears
• Measurement transformers, devices

20. Electrical network
Electrical installations with the same operating voltage

21. Insulation
Precaution against network faults between phases or phase to
neutral

22. Insulator
Material used for precaution in the insulation system
• Gas
• Liquid
• Solid
• Vacuum

23. Nominal system voltage, Un
The RMS phase to phase voltage by which an operating
equipment is designated and named.
Nominal voltage should be compatible with the operating
voltage

24. Operating voltage, Uop
It is the voltage by which an operating equipment is operated or
used.

25. Maximum system voltage, Um
It is the maximum voltage by which a system can be operated
Um = 15-20% Un+Un

26. Nominal withstand voltage
It is the voltage without resulting in short-circuit
• Nominal alternating-current withstand voltage
• Nominal impulse withstand voltage

27. Nominal a.c. withstand voltage
Short-duration&low frequency
• Raise the test voltage of each sample to a specific voltage
level with network frequency (50 Hz) in not more than 30
seconds
• Hold for 1 minute
• Does the insulator withstand to that voltage level?
Un Um Uw,ac Uw,impulse
30 kV 36 kV 70 kV 170 kV

28. Nominal impulse withstand voltage
This is the peak value of the switching or lightning impulse test voltage
at which an insulation shall not show any disruptive discharge when
subjected to a specified number of applications of this impulse under
specified conditions
• Apply 10 (or 15) positive and 10 (or 15) negative consecutive
impulses
• The wave should be 1.2 / 50 µs and conform to the requirements in
IEEE Std 4-1978
• If one flashover occurs, 10 (or 15) additional impulses shall be
applied
• Does the insulator withstand?

29. REVIEW
What does withstand mean?
What is withstanding to what?

30. Electrical discharges
• U Ub : Breakdown voltage 𝐸 =
𝑈
𝑑
•  𝐸 𝑏 =
𝑈 𝑏
𝑑
: Breakdown electric field, breakdown strength
U
DISCHARGE
Discharge can be in a form of
- Breakdown
- Flashover
- Partial discharge

31. Insulation ability
The behavior of an inlator against applied voltage type
Impulse characteristic

32. Insulation level
The threshold voltage for an insulator without any discharges

33. Insulation level
• Every electrical equipment has to undergo different abnormal transient
over voltage situation in different times during its total service life period.
• lightning impulses, switching impulses and/or short duration power
frequency over voltages.
• Depending upon the maximum level of impulse voltages and short
duration power frequency over voltages that one power system
component can withstand, the insulation level of high voltage power
system is determined.
• For the system rated less than 300 kV, the lightning impulse withstand
voltage and short duration power frequency withstand voltage are
considered.
• For equipment rated more or equal 300 kV, switching impulse withstand
voltage and short duration power frequency withstand voltage are
considered

34. Protection level
These are the highest peak voltage value which should not be
exceeded at the terminals of a protective device when switching
impulses and lightning impulses of standard shape and rate
values are applied under specific conditions.
Circuit, device,
system, ...
To be protected

35. Protection level

36. Insulation co-ordination
The selection of the electric strength of equipment in relation to the
voltages which can appear on the system for which the equipment is
intended.
The overall aim is to reduce to
• an economically and operationally acceptable level the cost and
disturbance caused by insulation failure and resulting system
outages.
• To keep interruptions to a minimum, the insulation of the various
parts of the system must be so graded that flashovers only occur at
intended points.
• With increasing system voltage, the need to reduce the amount of
insulation in the system, by proper co-ordination of the insulating
levels become more critical

37. Insulation co-ordination
Insulation
coordination
Insulation
Over
voltage
Protection

38. Grounded (earthed)&insulated networks
Z=0
directly grounded
network
Z=∞ insulated
network
Circuit, device,
system, ...
To be protected
Z = 0

39. Factor of earthing
• This is the ratio of the highest r.m.s. phase-to-earth power
frequency voltage on a sound phase during an earth fault to
the r.m.s. phase-to-phase power frequency voltage which
would be obtained at the selected location without the fault.
• This ratio characterizes, in general terms, the earthing
conditions of a system as viewed from the selected fault
location.
𝑚 =
𝑈 𝑝ℎ𝑎𝑠𝑒−𝑡𝑜−𝑝ℎ𝑎𝑠𝑒
𝑈𝑡𝑜−𝑒𝑎𝑟𝑡ℎ

40. Factor of earthing
𝑚 =
𝑈 𝑝ℎ𝑎𝑠𝑒−𝑡𝑜−𝑝ℎ𝑎𝑠𝑒
𝑈𝑡𝑜−𝑒𝑎𝑟𝑡ℎ
𝑈 𝑝ℎ𝑎𝑠𝑒−𝑡𝑜−𝑝ℎ𝑎𝑠𝑒: voltage between two phases
𝑈𝑡𝑜−𝑒𝑎𝑟𝑡ℎ: voltage of the phase without short circuit according
to the earth

41. Network
Grounded (earthed)&insulated networks
Up-p
Ue
Short circuit

42. Factor of earthing
• Neutral point directly grounded:
m ≤ 0.8
• Neutral point is insulated
m < 0.8

43. Neutral point is grounded
𝑚 =
𝑈 𝑝−𝑝
𝑈 𝑒
≤ 0.8
𝑈𝑒 ≤ 0.8 × 𝑈 𝑝−𝑝, 𝑈𝑒 ≤ 0.8 × 𝑈 𝑛
Un -> 3, 10, 15, 20, 30, 154, 380, ... kV
For Un=10 kV (phase to phase)
𝑈𝑒 ≤ 0.8 × 10 = 8 𝑘𝑉
It means: during a short circuit in one phase, 8 kV on each line!

45. OVERVOLTAGES

46. 1. Voltage rise
Incidents which result in a voltage rise:
• Ferranti effect
• Load rejection
• Capacitance switching
• Shortcircuit and fault clearances
• Ferroresonance

47. 2. Internal overvoltages
• Switching overvoltages
• Shortcircuit
• Resonance phenomena

48. 3. External overvoltages
• Overvoltages as a consequence of direct lightning strokes.