About HV Transmission, distribution, Voltage level classification, Insulation testing. Part 1 What is High Voltage?  Why Needed Levels of Voltages  Application of High Voltage Electrical Insulation and Dielectrics Part 2  Design & Test Issues for High Voltage Aircraft Electric Power System Introduction to the importance of HV in electric actuator systems Basic review of HV design Discussion of test methods Summary Part 3 Voltage Testing & Partial Discharge Measurement For Power Cable Accessories Introduction Ac Test After Installation Acrf Test System Schematic Diagram Of Test System Arallel Operation Mode Of Test System Artial Discharge Methods & Principle. Iscussion & Conclusion.

1. Introduction to High Voltage TechnologyIntroduction to High Voltage Technology
& insulation testing& insulation testing
Presented by: Zeeshan AkhtarPresented by: Zeeshan Akhtar
ID # : 6118000011ID # : 6118000011
Presented to:Presented to:
Prof.Du Bo XueProf.Du Bo Xue
Course: Introduction to high voltage and Advance technologiesCourse: Introduction to high voltage and Advance technologies

2. Contents:
Part 1
What is High Voltage?
 Why Needed
Levels of Voltages
 Application of High Voltage
Electrical Insulation and Dielectrics
Part 2
 Design & Test Issues for High Voltage
Aircraft Electric Power System
Introduction to the importance of HV in electric actuator systems
Basic review of HV design
Discussion of test methods
Summary
Part 3
Voltage Testing & Partial Discharge Measurement For Power Cable Accessories
Introduction
Ac Test After Installation
Acrf Test System
Schematic Diagram Of Test System
Arallel Operation Mode Of Test System
Artial Discharge Methods & Principle.
Iscussion & Conclusion.

3. What is high voltageWhat is high voltage
A mobile phone is operated from a 4VA mobile phone is operated from a 4V
battery. It may be destroyed if anyonebattery. It may be destroyed if anyone
attempts to operate it from a 12V carattempts to operate it from a 12V car
battery.battery.
Therefore 12V is quite a high voltage for aTherefore 12V is quite a high voltage for a
mobile phone.mobile phone.

4. What is high voltageWhat is high voltage
High voltage is specially referred toHigh voltage is specially referred to
electrical power system.electrical power system.
At Kaptai we
generate at 11kV
or 21kV
Step up
transformer is used
to rise the voltage
to 132kV or 230kV
Long transmission line used to
carry the power to Dhaka
Step down
transformer is
used to reduce
the voltage to
33kV
Step down
transformer is used
to reduce the voltage
to 11kV
Another Step down transformer
is used to reduce the voltage
further to 400V suitable for end
user.
Domestic users get electricity at
230Volt.
11kV
230~750kV33kV
11kV
400V
230V
230~750kV

5. What is high voltageWhat is high voltage
Below 11kV : Low voltageBelow 11kV : Low voltage
1000V – 57.5kV : MV (Medium Voltage)1000V – 57.5kV : MV (Medium Voltage)
57.5KV – 230kV : VHV (high voltage)57.5KV – 230kV : VHV (high voltage)
230~500KV : EHV ( Extra high voltage)230~500KV : EHV ( Extra high voltage)
500KV and above UHV : Ultra high voltage500KV and above UHV : Ultra high voltage

6. Levels of high voltage:
World over the levels are classified as:
LOW VOLTAGE
 MEDIUM VOLTAGE
HIGH VOLTAGE
 VERY HIGH VOLTAGE
EXTRA VOLTAGE
ULTRA HIGH Voltages
•However , the exact magnitude of these levels vary from country
to country. Hence this system of technical terms for the voltage
levels is inappropriate .
•In most part of the world even 440 V is considered to be high
voltage since it is dangerous for the living being.
•Hence it would be more appropriate to always mention the level
of voltage being referred without any set nomenclature .

7. Why high voltage
Basically it is required for transmission lines to be
able to transmit more power.
Equation for power is
P= V I Cos θ
Tarbela Karachi
I
Loss in
transmission line =
I2
R,
R is the resistance
of the line.
Therefore we conclude that it is not wise to increase the line
current to transmit more power over a line, keeping the voltage
same.
500 kV

8. Why high voltage
Basically it is required for transmission lines to be
able to transmit more power over the same line.
Equation for power is
P= V I Cos θ
Tarbela Karachi
I
I
Loss in transmission
line = I2
R,
R is the resistance of
the line.
I
Generator
I
Transformer
V
2V
Therefore we see that if the transmission line
voltage is increased it is capable of transmitting
more power without increasing the power loss in
the line.

9. Trends in voltage growth
Ac voltage
In our country the highest
operating voltage is
500kV.
We may realize our
position related to the
global trend.

10. Trends in voltage growth
DC voltage
Due to modern
Power electronics ..
HVDC becoming
superior on HVAC
over long
transmission >
500KM
Unfortunately
Pakistan have
no HDC
transmission

11. Fields of applications of HV
• Power system engineering
• Research laboratories
• Industries
• Nuclear research, particle
accelerators
• Electrostatic precipitators
• Automobile ignition coils
• Medical applications like X-ray
machine Interested
students may
find new areas of
application of HV

12. Insulation Testing:
• Insulation Testing of HV
equipment's like power
transformers, bushings, CB,
insulators, cables etc.
• Usually tests are done at a
voltage much higher than the
operating voltage.
• Generation, measurement and
control of different types of HV.

13. What we learn in
High Voltage
Engineering
• Failure mechanism of HV equipment's
caused by HV stress.
• Breakdown mechanism of different types
of insulating materials ( solid, liquid, gas,
vacuum) under different types of voltages
(ac, dc, li, si).

14. Few future prospects
of HV
• For cosmopolitan cities overhead
distribution lines are not allowed any
more. HV underground cables of
compact size is the solution.
• Compact all-in-one fix-and-forget type
GIS substations are required in near
future.
• HV has some residential and industrial
applications like water treatment plant,
insect killer/repeller, exhaust air
purifier etc. Interested students may add new
names to this list.

15. AC High Voltage
Time In ms
Voltage
In
kV
100kV
power frequency
ac voltage
?
10
ms
? Suppose it is said that the voltage is
100kV.
Then this peak value is = 100 X 103
X √2 volt
≅ 140kV
In high voltage engineering, we should
always be careful about the peak value
of the ac voltage, because this is the
maximum voltage in the system and
may be responsible for initiating
breakdown or failure.

16. DC High Voltage
Time In ms
Voltage
In
kV
?
100kV

17. Lightning Impulse
Time
In
μs
Voltage In kV
?
500kV
Wave front
=1.25(t2-t1)
10%
t1
90%
t2
50%
t3
t0
Wave tail
=t3-t0

18. VOLTAGE LEVELS
Consumer
ac power frequency :
110 V, 220 V- single phase
440 V, 3.3 kV ,6.6 kV, 11 kV-three phase (3.3 & 6.6 kV are being phased out)
Besides these levels ,the Railway Traction at 25 kV , single phase is one of the
biggest consumer of power spread at any particular stretch to 40 km of track length
Generation : Three phase synchronous generators
440 V, 3.3 kV, 6.6 kV (small generators) , 11 kV (110 & 220 MW)
21.5 kV ( 500 MW), 33 kV (1000 MW)
[limitation due to machine insulation requirement]
Distribution :
Three phase
440 V, 3.3 kV, 6.6 kV, 11 kV, 33 kV, 66 kV
With the increase in power consumption density, the power distribution voltage
levels are at rise because the power handling capacity is proportional to the square
of the voltage level.
(In Germany 440 V , 3.0 kV 6.0 kV, 10 kV, 30 kV, 60 kV)

19. AC Transmission :
110 kV, 132 kV, 220 kV, 380 - 400 kV, 500 kV, 765 - 800 kV, 1000 kV and 1150
kV exist.
Work on 1500 kV is complete.
In three phase power system, the rated voltage is always given as line to line,
rms voltage .
DC. Transmission :
dc single pole and bipolar lines : ± 100 kV to ± 800 kV

20. Advance countries like US, Canada and Japan have their single phase
ac power consumption level at 110 V .Rest of the whole world
consumes single phase ac power at 220 V .
The only advantage of 110 V single phase consumer voltage is that it is
safer over 220 V. However, the disadvantages are many.
Disadvantages :
It requires double the magnitude of current to deliver the same amount of
power as at 220 V
Hence for the same magnitude of I2R losses to limit the conductor or the
insulation temperature to 70° C (for PVC) , the resistance of the distribution
cable should be 4 times lower. Therefore, the cable cross-section area has to
be increased four folds.
Four times more copper requirement, dumped in the building walls is an
expensive venture.
Due to higher magnitude of current, higher magnetic field in the
buildings . Not good for health.
With the installation of modern inexpensive protective devices (earth
fault relays), 220 V is equally safe as 110 V

21. Rated maximum temperature of cables:
 It is important to understand the current and voltage carrying
capacities of a conductor separately. While the current carrying
capability is determined by the conductivity of the conductors, directly
proportional to the area of conductor cross-section, the voltage
bearing capacity depends upon the level of insulation provided to the
conductor .
The current carrying capability in turn is determined by maximum
permissible temperature of the insulation or that of the conductor.
 The real power loss, I2R and the rate of cooling determine the
temperature rise of the conductor which should not be more than the
maximum permissible temperature of the type of insulation provided
on the conductor .
Hence, not only electrical but thermal and mechanical properties of
insulation are important in power system .

22. Electrical Insulation and Dielectrics
Gaseous Dielectrics:
Atmospheric air is the cheapest and most widely used dielectric .
Other gaseous dielectrics, used as compressed gas at higher pressures
than atmospheric in power system, are Nitrogen ,
Sulphurhexafluoride SF6(an electro-negative gas) and it's mixtures
with CO2 and N2 . SF6 is very widely applied for Gas Insulated Systems
(GIS), Circuit Breakers and gas filled installations i.e. sub-stations and
cables. It is being now applied for power transformers also.
Vacuum as Dielectric :
Vacuum of the order of 10-5 Torr and lower provides an excellent
electrical insulation. Vacuum technology developed and applied for
circuit breakers in the last three decades is phenomenon .

23. Liquid Dielectrics:
Organic liquids, the mineral insulating oils and
impregnating compounds, natural and synthetic, of
required physical, chemical and electrical properties are
used very widely in transformers, capacitors, cables and
circuit breakers.
Ex: Polychlorinated biphenyls (PCBs)
Solid Dielectrics:
Very large in number .
Most widely used are : XLPE, PVC, ceramics, glass,
rubber, resins, reinforced plastics, polypropylene,
impregnated paper, wood, cotton, mica, pressboards,
Bakelite, Perspex, Ebonite, Teflon, etc.
 Introduction of nano materials are in offing.

24. Part 2
Design & Test Issues for High Voltage Design of
Electric Flight Control Actuation & Power
Electronics

25. HV Electric Actuation & Challenges in Design
• Previous generation electric drives mostly operated with line voltage operated at a
constant frequency unlike todays PWM driven motor/drives driven by high dV/dT PWM
drives and operated near or higher than Partial Discharge Inception Voltages (PDIV)
• Limited separation between high voltage signals and electrodes for (i) motor winding, i.e.
turn to turn (inter-turn) wire separation of copper enameled wires and, (ii) interconnects
signals for power drive reduces electric discharge voltage.
• Todays adjustable motor drives use inverter driven high current PWM signals resulting in
significantly higher electric stresses than previously experienced
• Limited volume/space limits the separation and spacing of high voltage signals/power
lines in electric machine windings as well as cabling and power electronics combined with
low pressure with high temperature often results in the operation near or, higher than
PDIV/CIV for electric discharge

26. Hi Voltage Electric Actuator: What is Hi Voltage?
• Paschen’s curve describes electric discharge voltage as a function of atmospheric pressure
and wiring/electrode separation defining the minimum voltage for breakdown in air to be
327V. Voltages, steady state or repeated transients higher than 327V are referred as high
voltages
• 270VDC input voltage based systems, and motor windings may experience repeated
applications of even higher than dc link/inverter voltage. It may increase electric motor
drive voltages further during 4 quadrant operation in high PWM/dV/dT driven electric
drives with added regenerative voltages.
• Apart from input electric power/voltages i.e., 270VDC or, 115VAC or, 230VAC, the
internally generated DC Link Voltage to drive motor inverter and installation dependent
motor winding voltages need considerations as it may be higher than PDIV or, CIV even
though input power voltages may be lower
• Imperfections in the insulation system and/or, lack of due consideration for Hi Voltage
design and results in partial discharge resulting in accelerated aging of insulation and its
dielectric strength and wiring that had been a subject of intense study after the loss of
TWA Flight 800 in 1996

27. High Voltage Design & Testing Guidelines For
Electric Actuators
• The high voltage (~327V) operation of electric actuators at extended
temperature ranges, humid conditions and at altitude affects the safety as
well as reliability of the electric drive including its power electronics, electric
motor etc.
• The current generation Hi Voltage PWM (pulse width modulated) drives
operating at high altitude have higher levels of electrical and mechanical
stress compared with those encountered in the past.
• Aircraft electric actuation systems have to meet certification requirements
including safety per FAR Pt 25 as well as operational reliability, availability,
continuity of service and life cycle data as per FAR Pt 90/91 & 121. This must
be done with no historical data, making them a ‘novel’ design.
• In general, aircraft electric power system are designed to operate below high
voltage or, corona inception voltages to avoid high voltage issues.

28. High Voltage (HV) Related Definitions
• Tracking
– Progressive formation of conducting paths, which are produced on the surface and/or
within a solid insulating material, due to the combined effects of electric stress and
electrolytic contamination
– Can occur at any voltage as long as conducting paths can be formed
– Very dependent on pollution layer
• Partial Discharges
– Electrical discharges which do not completely bridge gap
– Different forms – corona, surface, cavity, electrical trees, floating parts
– Substantially reduce the life of insulation
– EMC Issues (?) - fast current pulses, rise times in order of nanoseconds
– Very dependent on voltage type (i.e. AC/DC)
– The spacing between the conductors, their geometry, and the ‘imperfections’ in the
insulation materials, such as the presence of small/microscopic ‘voids’ in the insulation and
motor winding enamel such as polymides, contribute to the partial discharge
• Disruptive Discharges or, Arcing
– Electrical discharges which do completely bridge gap
– Flow of fault current follows discharge
– Can permanently damage insulation

29. Definitions
• Clearance is the shortest distance through air between two conductors
and is the path where damage is caused by short duration maximum peak
voltage
• Creepage is defined as the shortest distance between two conductive
parts along the surface of any insulating material common to both parts
and the breakdown of the creepage distance is a slow phenomenon based
upon dc or, rms voltage
• Clearance relates to flashover – creepage relates to tracking
Mammano B, ‘Safety Considerations in Power Supply Design, Underwriters Laboratory / TI

31. Partial Discharge Types

32. Partial Discharge Types

34. Paschen's Curve
100
1000
10000
100000
0.01 0.1 1 10 100 1000
p.d (Pa.m)
Vbk(Volts)
Small distance (high field)
Low pressure (high mean free path)

35. Electric Actuators & High Voltage
• Electric Actuators include Electronic Motor Control Unit (EMCU), Electric Drive/Motor
coupled to Mechanical Transmission for Electromechanical Actuators (EMA) or, to Hydraulic
Transmission for Electrohydrostatic Actuators (EHA).
• High Voltage (>327V) can be generated within the EMCU or at the Electric Motor / Drive
• Paschen’s Curve defines the relationship between voltage breakdown voltage as a function
of pressure (altitude) and airgap and below 327V there is no discharge and so no need for
concern.
• Previous generation electric drives mostly operated with line voltages lowered than
Paschen’s minimum operated at a constant frequency. Modern motor/drives driven by high
dV/dT PWM drives and operated near or higher than Paschen’s minimum.

36. HV Design for Electric Motor & Electronics
• HI VOLTAGE ELECTRONICS CIRCUITS ASSY. SHOULD BE DESIGNED TO HAVE ENOUGH INSULATION
BY SEPERATION/AIR GAPS & INSULATING COATINGS TO AVOID ANY ELECTRIC DISCHARGE
INCLUDING PARTIAL DISCHARGE/CORONA: MARGINS ON IPC-2221A?
• PRINTED WIRING BOARD/BOX LEVEL CONFORMAL COATING IS GENERALLY NOT CONSIDERED
ACCEPTABLE DUE TO ITS AGING/DEGRADATION
• ELECTRIC CABLING/WIRING & POWER ELECTRONICS MODULES/ASSY. SUBJECT TO HI VOLTAGES
SHOULD BE DESIGNED AND INDIVIDUALLY TESTED FOR PARTIAL DISCHARGE TO ENSURE ANY
MICROSCOPIC VOIDS/IMPERFECTIONS IN INSULATION
• ELECTRIC MOTOR WINDINGS THAT ARE SUBJECT TO HI VOLTAGES WHERE THE SEPERATION
BETWEEN WINDINGS IS POLYMIDE ENAMEL WITH LIMITED SEPERATION SHOULD BE TESTED &
EVALUATED FOR PARTIAL DISCHARGE OVER ITS LIFE AS THE INSULATION MAY DEGRADE WITH
CONTINUOUS USE
• PARTIAL DISCHARGE IS DEPENDENT UPON DRIVE VOLTAGE WAVEFORM: PEAK MAGNITUDE FOR
PARTIAL DISCHARGE IS LOWEST FOR SINUSOIDAL WAVEFORM, INCREASES FOR BIPLOAR-
SQUARE/RECTANGULAR WAVEFORM i.e., +/- 270VDC AND HIGHEST FOR UNIPOLAR
SQUARE/RECTANGULAR WAVEFORM i.e., 0-560VDC

37. Electric Motor Stator Winding & Electric Stress
Motor Windings,
Voltage Stress &
Partial Discharge
Inception Voltage
(PDIV), its Variation
with Freq & Temp.
Courtsey: Kaufhold et al.:Failure
Mechanism of Low Voltage, IEEE
Electrical Insulation Mag. March 1996

38. Effect of Cable Length Connecting Electronic Converter
with Motor Windings
Wiring distance between PWM/Square Wave based Power Drive/IGBTs and
Motor Winding results in higher voltages due to reflected waveforms:
700VDC Link Voltage may create 1.2-1.4kV at motor windings
270VDC Link Voltage may create 350-420V at motor windings
Courstey: Wheeler, IEEE Insulation Magazine March/April 2005

39. Overvoltage & Effects on Motor Windings
• Electric Motor Windings may see significantly higher voltages than input
power/voltages for PWM driven motors due to transient voltages /
overshoot at inverter and reflected voltages
• The close spacing of winding coils don’t allow traditional methods of
separation/clearances to be maintained for enhancing insulation strength
Melfi, ‘Low Voltage PWM Inverter Fed Insulation Issues, IEEE Trans IA, Jan 2006

40. The Role Of Insulation
• Insulation provides protection against voltage hazards, prevents leakage
current, electric discharge and short circuit current
• The operation of electric drives at high altitude/low pressure coupled with high
temperature, humidity, and with high current/frequency pulse width
modulated (PWM) drive signals lowers the strength of insulation .
• The limited space & separation distances between power signals, motor
wirings windings may result in designs operating in close proximity to the
voltage at which discharge will take place
• Any imperfection in an insulation system may result in partial discharge (PD)
which may reduce the life, reliability and integrity of the insulation and
eventually result in a full disruptive discharge such as arcing destroying the
insulation altogether.

41. Required Insulation Thicknesses
• Insulation thicknesses must more than
double to prevent PD when voltage is
doubled
400
600
800
1000
1200
1400
1600
1800
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Cable Insulation Thickness / mm
PartialDischargeInceptionVoltage/V
Relative Permittivity=3 Relative Permittivity=8

42. Electric Motor Winding Insulation Material Considerations
• Use of such higher grade PWM/corona resistant (CR) materials developed for industrial applications
or multiple coatings insulation over the copper enameled wire extends the endurance of the dielectric
strength under PD should be analyzed for aircraft applications
• These insulation material may become brittle and develop cracks when subjected to extreme
temperature variations in presence of other mechanical and vibration stresses over the life of the
equipment.
• The use of such materials or coatings for flight critical systems in aircraft requires their
characterization under altitude/low pressure, humidity etc. as well as aircraft containments such as
fuel, hydraulic fluids, lubricants etc for operation in presence of mechanical stress experienced by the
motor windings.
• Manufacturing of such materials per aircraft approved quality process i.e., bonded stores with
traceability should also be ensured.
• It will be ideal to avoid corona by design instead of trying to contain it for life time of the equipment

43. Insulation Material Selection
• The use of higher grade PWM/corona resistant (CR) materials developed for
industrial applications or multiple coating of insulation over the copper enameled
wire can extend the endurance of the dielectric strength when PD takes place
• However, these insulation material may become brittle and develop cracks when
subjected to extreme temperature variations in presence of other mechanical and
vibration stresses over the life of the equipment.
• The use of such materials or coatings for flight critical systems in aircraft requires
their characterization (electrical & mechanical) at altitude/low pressure, in the
presence of humidity etc. as well as when subject to aircraft containments such as
fuel, hydraulic fluids, lubricants etc
• Manufacturing of such materials per aircraft approved quality process, i.e. bonded
stores with traceability should also be ensured.
• It will always be ideal to avoid discharge by design instead of trying to contain it for
life time of the equipment

44. Avoidance Of Partial Discharge
• Can be achieved through very careful dielectric design
– Can reduce fields to a point below which void discharge cannot occur etc.
– Careful control of manufacturing process very important (e.g. in machine
windings – vacuum application to remove voids from encapsulation)
– Prevention of sharp edges to minimise field enhancement
• As with flashover, ultimately a test is required to prove absence of PD
• PD dependent on local pressure, temperature but a weak dependence on
frequency

45. Can We Tolerate Electrical Discharges?
• Tracking
– Cannot be allowed as it will cause carbonisation of insulation surfaces and
could cause fire
• Disruptive Discharges
– Cannot be allowed to occur as a disruptive discharge will normally require
the operation of circuit protection to clear
• Partial Discharges
– Can be allowed as long as a number of questions can be answered
• Does equipment remain safe, functional and reliable over the aircraft
lifetime?
• Is any interference caused to other systems?
– In reality, answering these questions is very difficult so PD must be
designed out
– Electrical utilities do not tend to allow partial discharge

46. Clearances To Avoid Flashover In Air
• Clearances between two conductive parts (e.g. connector pins) easily defined using
Paschen’s law
• Simple to make adjustments for temperature, pressure and frequency
– Breakdown voltage very approximately proportional to pressure
– Inversely proportional to temperature
– Can reduce by approximately 20% with use of high frequencies / PWM
• 1cm gap – 30kV DC @ sea level, 1.2kV @ 47000ft and 327V @ 150000ft
100
1000
10000
100000
0.0001 0.001 0.01 0.1 1 10 100 1000
Distance ( mm)
Vbk(Volts)
100,000ft 50,000ft 10,000ft Sea level
Higher Altitude

47. Creepage Distance Requirements
• Little known (or at least published) regarding creepage distance dimensioning (at
least in scientific literature)
• Important in determining safe distances over insulation surfaces
• While pollution is dominant in determining performance of surfaces, impact of
pressure on pollution (e.g. boiling point) is significant
• Measurements have shown observing IPC requirements can still lead to tracking
• Conformal coating can help eliminate tracking damage but is generally not
considered in terms of long term performance due to its aging/degradation

48. Particular Actuator / Power Electronic Issues
• Degradation from PD possible within winding structure
• Testing of multi-phase systems / ones operating with PWM difficult (although much can be
transferred from extensive work on higher voltage machines)
• Much work done on power electronic switches
– Particularly vulnerable to impact of humidity
– Difficult to test owing to presence of semiconductor element
– PD leads to degradation in very short timescale
• Industrial grade Power Electronics Modules with IGBTs or other power switching elements may be
a source of partial discharge (PD) due to stacking of different dielectric materials within the
module as many of the power electronics package designs use silicone gel during packaging of
electronics- presence of air molecules/voids in the gel make it susceptible to partial discharge

49. High Voltage (HV) Test Techniques
• HI-Pot Testing: A DC technique that will (usually) pick up gross
defects in an insulation system
– Many insulation systems have a frequency dependent insulation
strength (in terms of breakdown)
– Partial discharge not frequency dependent but a HI-Pot test will
not detect PD
– Won’t detect turn to turn insulation defects in a machine /
actuator
– There is therefore a place for HI-Pot testing but this is certainly
not the total solution
• Insulation Resistance/Simple AC Testing (i.e. raise the voltage
and measure corresponding leakage current)
– Improves matters, particularly if appropriate frequency is used,
but still cannot detect all partial discharge or turn to turn defects
(severe PD may be detected as leakage current flow)
• Surge testing
– This test detects ‘turn to turn’ or, ‘coil to coil’ or, ‘phase to phase’
insulation defects by comparing the transient response

50. HV Testing – Complete Systems
• Electrical Methods as defined in IEC60270/EN60270 require application of overvoltage and can be used for
passive elements inclnding wiring/cabling, PWBs, Motor/Stator Windings etc
• Overall assy can be tested using a non-intrusive i.e., calibrated RF Detection method operating in
altitude/thermal chamber. LRU/Box level testing is some times challenging with RF detection as the
box/enclosure provides shielding for Electro-Magnetic Emissions and may be masked.
• Significant difficulty in testing complete systems using standard lab testing techniques
• Entire systems must generally be energised with multi-phase / DC / PWM voltages
• Need non-contact testing to verify if PD is present
• When do we test? Type test or routine test?
Electrical Optical RF / EMI Acoustic
Description Electrical circuit that picks
up current pulse produced
by charge transfer during
partial discharge
Measures light
emission from partial
discharges
Measures radio
frequency interference
generated by the
discharge
Measures the acoustic
emissions produced
by a partial discharge.
Advantage A good sensitivity and
standard for all HV
equipment during
manufacture
Non-contact, applicable
for all voltage types.
Allows testing of
equipment in real
conditions
Non-contact,
applicable for all
voltage types. Allows
testing of equipment in
real conditions
Non-contact,
applicable for all
voltage types. Allows
testing of equipment
of real conditions
Disadvantage Sensitive to electrical noise.
Cannot test circuit in
operating condition in most
cases. Most commercial
equipment can only test at
Insensitive to any form
of internal partial
discharge. Sensitive to
light and highly
directional.
Depending on
equipment being
tested, EM emissions
can prevent detection
of PD
Sensitive to other
acoustic emissions.
Signals cannot always
propagate through
insulation / casings

51. Test Conditions
• It is essential that qualification and life cycle HV
testing (Hi-Pot, AC, PD etc) be carried out in an
appropriate test environment
• Electronic units and electric actuators should be
tested at the appropriate altitude, with vibration
and temperature cycling.
• The mechanical load will also need to be
incorporated into a test as this will affect the
circuit voltages

52. PWM & Impact of High Voltage on Insulation & Bearings
• Hi Voltage increases dV/dT affecting the life of
insulation and bearings current; limiting high
voltage to lower value will reduce
• Bearing current & insulation affect life/reliability
and equipment usually passes qualification test-
need to address mitigation
Courtesy: Muetze & Binder, IEEE Insulation 2006 Courtsey: Lipo,IEEE Ind Appl. Mag Jan/Feb 1998

53. Safety & Reliability Over The Equipment Lifetime
• Any design – electrical or mechanical operating at maximum possible design
stress can fail at any time. Reliability is built in the design by ensuring that the
operating stress is a fraction of maximum design stress
• The life of insulation under constant electric stress varies inversely to its applied
voltage and so it is important to ensure voltage gradients.
• Electronics elements should be designed to ensure that the minimum spacing
between conductors is maintained with added safety margins over the industrial
standards. Electric motor windings need careful attention to ensure that voltage
stresses remain within acceptable limits
• The design should be based on any steady state or repeated transient voltages
that occur with added safety margins to ensure safety.

54. Summary
• Voltages higher than the nominal input voltage can be present in an electric
actuation system
• These voltages can lead to tracking, partial discharge or breakdown
resulting in continual insulation degradation or arcing
• Designs must be analysed to determine maximum peak/transient voltages
and insulation materials / clearances / geometries selected accordingly
• Should always try and prevent partial discharge occurring and not control it
using materials
• Testing of equipment is essential – however it is difficult to
comprehensively test a complete system – need to consider the testing of
components / sub-assemblies
• There is a need for expanding on-line monitoring and PHM/Condition Based
Monitoring to ensure integrity of the insulation over the life of the
equipment for operation over minimum Paschen’s Curve

55. Part 3
•Voltage Testing & Partial Discharge
Measurement For Power Cable Accessories

56. PRESENTATION
SEQUENCE OBECTIVE
 INTRODUCTION
 AC TEST AFTER INSTALLATION
 ACRF TEST SYSTEM
 SCHEMATIC DIAGRAM OF TEST SYSTEM
 PARALLEL OPERATION MODE OF TEST
SYSTEM
 PARTIAL DISCHARGE METHODS &
PRINCIPLE.
 DISCUSSION & CONCLUSION.
OBJECTIVE :
 To compare best practices for cable testing.
 Predictive diagnostic programs to aging cable.


57. INTRODUCTION
 Using Frequency tuned
resonance
• Test system (20-300 Hz) to
calculate PD measurement.
 PD measurement method are
necessary to trace defect and
insulation of cable.
 Voltage testing provide
information about defect in the
insulation is dangerous or not
for later operation.
 Calibration is done through PD
calibrator on the cable
termination.
 Power Cables importance in
Transmission &
Distributionon system
 Consist of :
Cable
Joint
Termination
•  Identification &
Localization of partial
discharge.

58. AC TEST AFTER
INSTALLATION
 Follow the international standards IEC 60840
and IEC 62067 for testing of Power cable
insulation and their accessories.
 Apply : sinusoidal waveform, frequency: 20 and
300 Hz, voltage applied for 1.7 U0 /1 hour

59. Methods of Voltage Generated
 By a reactor with variable inductance and fixed
excitation frequency 50 or 60 Hz (ACRL) test
system.
 By a reactor with fixed inductance and frequency
tuned voltage excitation (ACRF) test systems.

60. ACRF TEST SYSTEM
 HV Reactor
 Exciter Transformer
 Control Unit
 Feeding Unit
 Blocking Impedance
 Voltage Divider & Software
 Frequency Convertor + Protection
Impedance.

61. SCHEMATIC DIAGRAM OF
TEST SYSTEM

62. PARALLEL OPERATION MODE OF
TEST SYSTEM

63. OPERATING RANGE OF THE RESONANT
TEST SYSTEM (ACRF)

64. PARTIAL DISCHARGE
Partial discharges are a sensitive
measure of local electrical stress and
the measurement is often used as a
quality check of the insulation.
Cable has small voids, cavities,
insulating contaminant conductive
protrusions in different interfaces or
mechanical cuts.
Erosion by ion bombardment and
chemical effects gradually change
small defects to electrical trees with

65. METHODS OF PD MEASUREMENTS
 HIGH FREQUENCY CURRENT TRANSFORMER
HFCT method at cross bonding box for 220 kV or earth wire of 66 kV for XLPE
cable systems Showed high sensitivity and calibration is possible using PD
calibrator on the cable terminations.
 COUPLING CAPACITOR
PD detection of high frequency signal generated from PD activities.
Measurement by use of a coupling capacitor is physically limited to a
maximum detectable cable length of approximately 2 km, depending on cable
parameters and PD background noise.

66. WORKING PRINCIPLE
 The sensitivity of the partial discharge detector has to be modified until
the
detector shows the calibration charge.
 For 220 kV, PD measurements carried out during HV tests, using a test
sequence providing several increase the voltage in steps of 127 Kv
(U0) and take a PD-measurement recording during 1 minute and
afterwards increase the voltage in further steps until 216 kV
 At each step note the measured PD value.
 Once reaching 216 kV leave this voltage applied for 1 hour and
observes if there is a change in the recorded PD pattern and value.
 While ramp the test voltage down, take another PD measurement for 1
minute
at 127 kV.

67. Time characteristic of
the 216 kV
Voltage test

68. PARTIAL DISCHARGE
MEASUREMENT
 Internal sensors integrated in each accessory or
external sensors HFCT placed inside bonding link
boxes.
 The PD sensitivity using HFCT the central
measuring frequency is recommended is to lie
between 2 MHz and 10 MHz in a flat zone of the
frequency spectrum.

69. CROSS BONDING LINKS WITH MOUNTED
THREE HFCT SENSORS FOR PD

70.  Test carried out on two cables having specification
1x3x1600 mm2,CU /XLPE/LEAD/HDPE ,220 kV with approximately 13 km
long,19 joints/phase, 3 straight joint box and 16 insulated joint box which are
divided into two sections by means of joints and it is terminated by composite
three outdoor and three GIS sealing ends per circuit.
 The result was a resonant frequency of 35.53 Hz for test voltage 216 kV.
 Inject a calibration pulse with known quantity of charge at the outdoor system
termination (i.e., between HV and ground terminals), the sensitivity of the PD
detector has to be modified until the detector shows the calibration charge.
 PD pulses occur in very short time, the width and rise time of the pulses are in
the nanosecond region. Consequently, PD pulses with energy frequency up to
hundred MHZ are generated these PD pulses will travel through the cable
earth conductor and finally can be recorded by the sensors
TEST RESULT &
DISCUSSION

71. PARTIAL DISCHARGE
RESULTS FOR
CIRCUIT 1 & 2

72. variation OF PC pattern
during
PD measurement
PD measurement OF
pattern
with some noise

73. EXAMPLE OF JOINT FAILURE
DURING WITH STAND TEST BY USING
RESONANT TEST
SYSTEM

74. CONCLUSION
 After installation of cable , test for HV/EHV XLPE
cables system by using resonant test system of (20
Hz -300 Hz) combined with PD detection is
performed by using HFCT sensors at each cross
bonding (CB) link boxes reduces the risk from the
service.
 After detecting the location of fault and repair the
cables and their accessories was done exactly in the
same place given good results.
 The experiences also show that the test voltage with
U0 for 24 h is not feasible for incidence of failure
after the test could be occurred.

75. Reference's!!!
• https://www.slideshare.net/
• https://www.google.com/photos/about/
• https://en.wikipedia.org/wiki/Main_Page