GENERATION OF HV IMPULSE AND TESTING ON INSULATOR
FAIZAL BIN HAMZAH
This Report Is submitted In Partial Fulfillment Of Requirement For The Degree of
Bachelor In Electrical Engineering (Industrial Power)
Fakulti Kejuruteraan Elektrik
Universiti Teknikal Malaysia Melaka
May 2008
ABSTRACT
The high voltage test configuration for impulse voltage up to 400 kv with
different output power. The major factor of constructing the impulse high
voltage kits is to simulate the stresses due to external and internal over voltage
and also for fundamental investigation of breakdown mechanism. This project is
using insulator (Rubber) as a test object to find the breakdown voltage and do
analysis of their breakdown characteristic. This application range for high
voltage kit covers not only in high voltage laboratories, but also as an industrial
test system for routine and type test on Electrical equipment or insulator
(Rubber).
Konfigurasi dalam ujian voltan tinggi untuk voltan dedenyut (Impulse)
menghasilkan voltan sehingga 400 kv dengan kuasa keluaran berbeza. Faktor
yang utarna dalam membina voltan tinggi adalah dengan menjalankan simulasi
desakan disebabkan oleh kegagalan luaran dan dalaman, ia juga untuk megkaji
asas mekanisme kegagalan. Projek ini dikaji dengan menggunakan penebat
(Getah) sebagai satu ujian bagi mencari voltan runtuh dan untuk menganalisis
ciri-ciri kegagalan itu sendiri. Julat aplikasi ini merangkumi peralatan voltan
tinggi bukan sahaja dalam makmal-makmal voltan tinggi, malah juga untuk satu
sistem ujian industri rutin dan jenis ujian yang dijalankan untuk peralatan
elektrik clan juga penebat (Getah).
CHAPTER 1
INTRODUCTION
1.1 High Voltage Definition
The definition of high voltage depends on the context of the discussion. Two
factors considered in the classification of a "high voltage" are the possibility of
causing a spark in air, and the danger of electric shock by contact or proximity.
In electric power transmission engineering, high voltage is usually
considered any voltage over approximately 35,000 volts. This is a classification
based on the design of apparatus and insulation.
The International Electro technical Commission and its national counterparts
(IET, IEEE, VDE, etc.) define high voltage circuits as those with more than 1000 V
for alternating current and at least 1500 V for direct current, and distinguish it from
low voltage (50-1000 V AC or 120-1500 V DC) and extra low voltage (<50 V AC
or 4 2 0 V DC) circuits [3]. This is in the context of the safety of electrical
apparatus.
In the United States 2005 National Electrical Code (NEC), high voltage is
any voltage over 600 V (article 490.2). Laypersons may consider household mains
circuits (1 00-250 V AC), which carry the highest and most dangerous voltages they
normally encounter, to be high voltage. For example, an installer of heating,
ventilation and air conditioning equipment may be licensed to install 24 Volt control
circuits, but may not be permitted to connect the 240volt power circuits of the
equipment.
Voltages over approximately 50 volts can usually cause dangerous amounts
of current to flow through a human being touching two points of a circuit, so safety
standards generally are more restrictive where the chance of contact with such high
voltage circuits exists.
1.2 Problem Statement
Each of the projects has their own problem to be discussing before starting
the project. By stating the problem statement it easy to know the purpose of doing
this project and what are the problem to be solved. Below are the problem
statements for this project.
To analyze the breakdown voltage of insulator (Rubber).
Procedure of testing must follow standard.
New lab still low of safety.
1.3 Experiment Objective
Before conducting or doing the project, the objectives of the project are the
main focus in this project. At the last of this report from the conclusion the objective
are stated where it succeed or not. Below are the objectives of this project.
To understand the characteristic of lighting impulse voltage (LI).
To generate a high voltage impulse using high voltage construction kit.
Do comparison between practical, experiment and simulation.
Do procedure and safety of using equipment in the lab.
Do a testing on insulator (Rubber) to analyze their breakdown voltage.
1.4 Scope of Project
This project report consists of five chapters, chapter one is introduction,
chapter two literature review, chapter three methodology, chapter four result and
discussion and chapter five is the conclusion. Chapter one will be explain about the
high voltage definition, history and standard. This chapter also states the problem for
the project, objective and scope of the project report.
Chapter two will discuss about the theory of impulse voltage, there are five
parts in this chapter to be discuss. First part about the theory of impulse voltage,
second part types of impulse testing, third part impulse voltage circuit, fourth and
five are about equipment and component that are use in this project.
Chapter three is the methodologies for the whole processes of project from
PSM I until PSM 11. In project methodology will explain the whole project
procedure from starting finding and research the topic until choose the best circuit.
For simulation method will explain the step of simulation project circuit. Lastly
experiment methods are explaining the step in the experiment project.
In chapter four is discussing about the project result, this chapter consist of
simulation and experimental result. In simulation part will discuss the result of
output waveform and experiment part will discuss the output waveform from the
oscilloscope. Finally the last chapter five is the conclusion of the whole project
report and suggestions.
CHAPTER 2
LITERATURE REVIEW
2.1 Impulse Voltage
Impulse voltages are frequently caused by two kinds of transient voltage
whose amplitudes may greatly exceed the peak values of the normal ac operating
voltage. The first kinds are lighting over voltages, an average bolt of negative
lightning carries a current of 30-to-50 kilo amperes, transfers a charge of 5
coulombs, and dissipates 500 megajoules of energy (enough to light a 100 watt light
bulb for 2 months). However, an average bolt of positive lightning (from the top of a
thunderstorm) may carry a current of 300-to-500 kilo amperes, transfer a charge of
up to 300 coulombs, have a potential difference up to 1 Giga volt (a billion volts),
and may dissipate enough energy to light a 100 watt light bulb for up to 95 years. A
negative lightning stroke typically lasts for only tens of microseconds, but multiple
strikes are common. A positive lightning stroke is typically a single event. However,
the larger peak current may flow for hundreds of milliseconds, making it
considerably hotter and more dangerous than negative lightning [2].
The second kind is caused by switching phenomena. Their amplitudes are
always related to the operating voltage and the shape is influenced by the impedance
of the system as well as by the switching conditions. The rate of voltage rise is
usually slower, but it is well known that the wave shape can also be very dangerous
to different insulation system, especially to atmospheric air insulation in
transmission system with voltage level higher than 245kV. Although the actual
shape of both kinds of over voltages varies strongly, it became necessary to simulate
these transient voltages by relatively simple means for testing purposes.
2.2 Types Of Impulse Testing
The IEEE-4 and IEC-60 Standard Techniques for HV Testing define various
wave shapes to be used in HV testing. Various ANSI, IEC, AEIC, and other
standards for T&D apparatus and other components define specific test requirements
and test voltage levels for particular products. Per the appropriate standard, impulse
testing is done as a design test, a production test, or both.
2.2.1 Lighting Impulse
Lighting impulse wave shape is defined with a front time of 1 . 2 ~ and
s a tail
time of 50ps, within tolerances. The front time Ts of a lighting impulse is a virtual
parameter defined as the 1.67 times the interval between the instants when the
impulse is 30% and 90% of the peak value (Figure 2.1).
The virtual origin 0 of a lighting impulse is the instants preceding that
corresponding to 30% by a time 0.3Ts. The time to half-value Tr (or tail time) of a
lighting impulse is a virtual parameter defined as the time interval between the
virtual origin 0 and the instant when the voltage has decreased to the half peak value
[]I.
The curves of lighting impulse often have high-frequency oscillations
superimposed, due to the pararistic inductances of the impulse circuit, the amplitude
should not exceed 5% of the test voltage.
Standard Lightning Impulse:
Front time Ts:
1.2ps (tolerance: f30%)
Time to half-value Tr:
50ps (tolerance: f20%)
Figure 2.1 : Lightning impulse
2.2.2 Switching Impulse
Switching impulse wave shapes is defined with a front time of 250ps and a
tail time of 2500ps, within tolerances. The time to peak C1 of a switching impulse is
the time interval between the actual origin and the instant when the voltage has
reached its peak value (Figure 2.2).
The time to half-value Th for switching impulse is the time interval between
the actual and the instant when the voltage has first decreased to half peak value.
The time above 90% is the time interval during which the impulse voltage exceeds
90% of its peak value [l].
Standard Switching Impulse:
Time to peak C 1:
250ps
(tolerance: f20%)
Time to half-value Th:
2500~s
(tolerance: f60%)
Figure 2.2: Switching impulse
2.3 Impulse Withstand Testing Characteristic
Figure 2.3 below are show the characteristic of impulse testing on insulator
to see whether there is any damage.
Figure 2.3: Observe Impulse Waveforms
In the event of complete damage, breakdown of the insulator due to the
application of the impulse voltage will be indicated as in (i). If the insulator has
suffered only a minor damage the waveform would show no distortion, but would
show as in (ii). If there is no damage caused due to the impulse, the waveform will
be complete and undistorted as in (iii). In testing high voltage insulator whose actual
breakdown is in air (i.e flashover take place before breakdown of insulator) figure
2.4 show the flashover impulse waveform.
Impulse
voltage
time
Figure 2.4: Chopped Impulse Waveform
2.4 Impulse Voltage Generator Circuit
Impulse generators for high voltage testing have been built up to now almost
exclusively in the well-known Marx circuit. The basic principle of this circuit is the
rapid series connection of charged capacitors whereby spark gaps are used to make
the series switching.
2.4.1 Single-Stages Generator Circuits
Figure 2.5: Impulse stage 1 circuit
Refer to figure 2.5 the capacitor C1 is slowly charge from a dc source until
the spark gap S break down. This spark gap acts as a voltage-limiting and voltagesensitive switch, whose ignition time (time to voltage break down) is very short in
comparison to Ts. As such single-stage generator may be used for charging voltages
from some kV up to about lMV, the sphere gap will offer proper operating
conditions. The resistor R1 and R2 and the capacitance C2 from wave shaping
network RI will primarily damp the circuit and control the front time Ts. R2 will
discharge the capacitor and therefore essentially control the wave tail. The
capacitance C2 represents the full load, example the object test as well as all other
capacitive elements, which are in parallel to the test object. From this circuit front
time and tail time can be calculated by using the equation below.
Front time, t, = 3(R,)
[2+c;2
Tail time, t, = 0.7(R, + R,)(C,
)
+ C,)
2.5 Insulator (Rubber)
Rubber is a natural or synthetic vulcanized high polymer having high elastic
properties. Electrical properties of rubber depend on the degree of compounding and
vulcanizing. General impurities, chemical changes due to ageing, moisture content
and variations in temperature and frequency have substantial effects on the electrical
properties of rubber. Some important electrical properties and application of
different types of rubber are given in figure 2.6.
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Figure 2.6: Properties and Application of Rubber
Figure below are the insulator to be use in the experiment, material are
rubber, dimension 0.5 x0.5m and thickness 3mm.
Figure 2.7: Rubber
2.6 Main Equipment
The high voltage KIT is supplied with two separate instrument, the control
unit OT276 and the AC, DC and impulse measurement unit DM551 [I].
2.6.1 Operating Terminal OT 276
OT276 controls the regulating transformer. It has based on conventional
relay technology and is built into a 19" standard housing of 3 unit's height.
Operation is by means of push buttons. The state of contactors as well as the current
and voltage on the secondary side of the regulating transformer are clearly indicated
on the fiont plate by means of LED display.
Figure 2.8 shows a picture of the 03276
Figure 2.8: Operating terminal OT276
2.6.2 M e a s u ~ Instrument
g
DM1551
The DM1551 is a microprocessor-mntrolled instrument. Input is via the
numeric keypad. A LCD-Display indicates measured values and function options.
With its optional triggering firnction, firing of the impulse configuration or a
chopping gap is possible. An interface is also available for connection to a host
computer. The DM551 is design in accordance with the international standard IEC
60060. Figure 2.9 shows a picture of DM551.
Figure 2.9: DM155 1
2.63 Oscilloscope Tektronix DPO 4034
The DP04000 Series digital phosphor oscilloscopes (DPO) deliver the
performance you need to visualize even your most demanding signals. Bandwidths
range h m 350 MHz to 1 GHz, and with all models offering a minimum of 5x
oversampling on all channels and sin(x)/x interpolation standard, you can be
confident that even the fastest transient events will be captured and displayed
accurately. Figure 2.10 show a picture of DPO 4034.
Figure 2.10: DPO 4034
2.7 Main Components
The components that use in the experiment are.
2.7.1 PZT 100-0.1: Single Phase AC Voltage Test Transformer
Test transformer which can be used for AC, DC and impulse voltage
generation. The output power can be extended by cascading the transformers.
Rated voltage :2x220V 1 1OOkV / 220V
Rated power : SkVA, continuous
1OkVA, 1 hour
Figure 2.1 1: PZT 100-0.1
2.7.2 STL 5 (STL7.5, STL 10): Regulating transformer
Figure 2.12: Regulating transformer
Power supply
: 230 V / 22 A (33,43 A)
Secondary voltage
: 0 ...230 V
Rated power
: 5 kVA (7.5,lO kVA) cont.
Frequency
: 50160 Hz
Weight
: 80 kg (255 kg, 260 kg)
2.73 GS HV Diode
Figure 2.13: HV diode
Diode can be used for impulse and DC voltage configurations. The diode
consists of a protecting resistor and a high voltage diode.
Protective resistor
: 100 WZ
Inverse peak voltage : 140 kV
Rated current
: 20 mA
2.7.4 RE Parallel (wave tail) resistor
Figure 2.14: RE
Resistor, which can be used as discharge resistor for DC and impulse voltage
configurations and as parallel resistor in impulse voltage configurations, determining
the duration.
Resistance
:Different values (2.4,2.5,120 WZ)
Max. DC and IMP voltage
: 140 kV
2.7.5 CS Smoothing and Energy Storage Capacitor
Figure 2.1 5: CS capacitor
Capacitor, which can be used as energy storage capacitor for generation of
impulse voltages or as smoothing capacitor for DC generation.
Capacitance
:25 nF
Max. DC and IMP voltage
: 140 kV
2.7.6 CB Load Capacitor
Figure 2.1 6: Load capacitor
Capacitor, which can be used as HV unit for measuring of impulse voltages
and as load capacitance.
Capacitance
: 1200 pF
Max. DC and IMP voltage
: 140 kV
2.7.7 RD: Series (wave front) resistor
Figure 2.1 7: Series resistor
Resistor, which can be used as charging resistor for multistage impulse
configurations, as current limiting resistor in DC configurations and as damping
resistor in connection with the grounding switch.
Resistance
: 10 Mi2 or 2.5 MR
Max. DC and IMP voltage
: 140 k V
2.7.8 ES: Grounding Switch
Figure 2.18: Grounding switch
Remote controlled switch, which can be used to ground the high voltage
construction KIT.
Max. DC and IMPvoltage
: 140 k V
Service voltage
:24 V, 50160 Hz
2.7.9 EST: Discharge and Grounding Rod
Figure 2.19: Discharge and grounding rod
Rod, for manual discharge of HV KIT components.
:2.5 m
Length
Discharge resistance : 100 W
2.7.10 EL: Electrode
Figure 2.20: Electrode
Electrodes, used together with grounding switch ES and for termination top
elements when test set should be corona-fiee.
Diameter
: 300 mm
Weight
:2kg
2.7.1 1 KF Sphere Gap
Figure 2.21 : Sphere gap
Sphere gap, for impulse voltage configuration.
Max. IMP voltage
: 140 kV
Sphere diameter
: 100 rnm
Max. gap setting
: 80 mm
2.7.12 AKF: Drive for Sphere Gap
Figure 2.22: Drive for sphere gap
Remote controlled drive for sphere gap KF and MF100. Drive shaft ASA
(short) for 1st Stage and ASB (long) for 2nd and 3rd Stage needed. The AKF is
clamped to a spacer bar D.
With capacitor motor :230 V
Frequency
: 50160 Hz
2.7.13 NTZ: Secondary Part For CB (Impulse)
Figure 2.23: NTZ
Low voltage divider for impulse measurements, which incorporates the LV
capacitors and a 75 R matching resistor. Connected between the HF-socket of the
load capacitor CB and the DM1 551 by means of a coaxial cable (MK BNC).
2.8 Summary
In this literature review part not all the theory and configuration will be used
because some of the data are not necessary for using in the project. The equipment
and component are explained about their function for guidance in proceeding to the
next chapter.
CHAPTER 3
METHODOLOGY
3.1 Project Methodology
Start
4
Study and research title of the
proiect
i
Study and analysis the circuit
using PSPICE software
simulation
t
Do the procedure and
experiment by construct the
High Voltage circuit
1
I
I
YES
Choose the best one of the
analysis circuit
(
End
]
Figure 3.1 : Project flow chart
I
I
By following the step in methodology before starting the project, first study
and research title of the project to find the basic theory, history and also know the
field that want to be research in the project. After that doing analysis of the circuit
project by using PSPICE software. By doing this the circuit are tested by simulating
its to get the proper result before using it in the experiment.
Then when the simulation had been test, do the experiment by constructing
the circuit project. The circuit is using component and equipment from Haefely.
During the constructing, follow the procedure because this circuit is high voltage
that can cause danger to life. If the experiment does not exceed the equivalent result
as in simulation, repeat the test or if the result still not exceed do the simulation
again to find the error. After the experiment exceed to the result choose the best one
of the analysis circuit.
3.2 Simulation Method
Choose the circuit for simulation
I
Construct the circuit in the
PSPICE
.c
Simulate the output voltage of
I
the experiment
I
Compare the result with
the result of the test
certificate and theory
m
Capture the waveform of the output
Figure 3.2: Simulation flow chart
Starting of the simulation fist choose which one of the circuit that want to be
simulate, there are four type of circuit in single stage impulse. But for this
simulation the circuits that want to best test in the experiment later are state by
Haefely. Then construct the circuit in the PSPICE software, to get high voltage
impulse characteristic first generate DC voltage source by constructing a rectifier
circuit. Rectifier circuit functions as to convert AC source to DC source using a
couple of diode and after that simulates the circuit to see the output result.
Compare the result with the result in the theory and test certificate, if the
result did not match with other result repeat the step by constructing again the circuit
until the result match. Finally capture the result of output waveform.
3.3 Experiment Method
*
Install the circuit as the diagram
I
I
Double-check the connection of the
circuit
-
1
Close the gate
+
Turn on the key, release the emergency
I
push stop button
Raise the voltage and adjust the
distance of sphere gab
Capture using the digital camera
Figure 3.3: Experiment flow chart
I