High Voltage Experiments

High Voltage Experiments
Introduction to
High Voltage
Experiments
About this manual
This manual has been developed as an orientation aid for those wishing to carry out high
voltage experiments with the Terco High Voltage Laboratory. It is intended as a companion
and preparatory manual to the Terco High Voltage Experiments manual.
Target Group
The target group of this manual is principally one or more of the following groups:



Those not familiar with the Terco HV Lab, components, controls or routines
Those who find themselves at a beginner’s level with respect to high voltage
experimentation
A combination of the above
Focus
Setup procedure for the three fundamental circuits for AC, DC and Impulse high voltages are
the main focal point of this manual reinforced by clear identification of each component with
photos and diagrams.
Each setup builds on that preceding, which in turn forms a base for more advanced
experiments.
It is intended that by following these procedural guidelines, participants will learn about each
part of the HV laboratory as well as develop safe routines in the HV laboratory environment.
Content and Structure
The first section of this manual highlights Safety Regulations for High Voltage Experiments.
This is very important information and participants are strongly urged to read this section
thoroughly before starting the experiments.
Following this are experiments on AC Voltage, DC Voltage and Impulse Voltage Generation
and Measurement.
Stockholm/Sweden
January 2011
January 2012 (rev)
Stuart Sunkel
Contents
About this manual
Contents
Safety Regulations for High Voltage Experiments
Introduction
Fencing
Safety locking
Earthing
Circuit and test setup
Conducting the experiments
Explosion and fire risk, radiation protection
Accident insurance
Conduct during accidents
Experiment 1.
Generation and measurement of AC voltage
Experiment 2.
Generation and measurement of AC voltage - Sphere Gap.
Experiment 3.
Generation and measurement of direct voltage
Experiment 4.
Generation and measurement of impulse voltage
Experiment 5.
Impulse voltage with the HV 9132 Trigger Sphere
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Safety Regulations for High Voltage Experiments
Introduction
Experiments with high-voltages could become particularly hazardous for the participants
should safety precautions be inadequate. To give an idea of the required safety measures,
an example the safety regulations followed in several High Voltage Laboratories attached to
the Technical University of Braunschweig shall be described below. These supplement the
appropriate safety regulations and as far as possible prevent risks to persons. Strict
observance is therefore the duty of everyone working in the laboratory. Here, any voltage
greater than 250 V to earth potential is understood to be a high voltage (VDE 0100).
Fundamental Rule:
Before entering a high-voltage setup area, participants must first ensure that all conductors
which can assume high potential and lye in the contact zone are earthed and that all main
leads are interrupted.
Fencing
All high-voltage setups must be protected against unintentional entry to the danger zone.
This is appropriately done with the aid of metallic fences. When setting up the fences for
voltages up to 1 MV the following minimum clearances to the components at high voltage
should not be exceeded:
Alternating and direct voltages
Impulse voltages
50 cm for every 100 kV
20 cm for every 100 kV
A minimum clearance of 50 cm shall always be observed, independent of the value and type
of voltage. For voltages over 1 MV, in particular for switching impulse voltages, the values
quoted could be inadequate; special protective measures must then be introduced.
The fences should be reliably connected conductively, earthed and provided with warning
boards inscribed: “High Voltage! Caution! Highly Dangerous!”. It is forbidden to introduce
conductive objects through the fence while the setup is in use.
Safety locking
In high-voltage setups each door must be provided with safety switches; these allow the door
to be opened only when all main leads to the setup are interrupted. Instead of direct
interruption, the safety switches may also operate the no-voltage relay of a power circuit
breaker, which on opening the door, interrupts all the main leads to the setup.
7
These power circuit breakers may also be switched on again when the door is closed. For
direct supply from a high-voltage network (e.g. 10 kV city network), the main leads must be
interrupted visibly before entry to the setup by an additional open isolating switch. The
switched condition of a setup must be indicated by a red lamp “Setup switched on” and by a
green lamp “Setup switched off”.
If the fence is interrupted for assembly and dismantling operations on the setup, or during
large-scale modifications, all the prescribed precautions for entry to the setup shall be
observed. Here, particular attention must be paid to the reliable interruption of the main
leads. On isolating switches or other disconnecting points and on the control desk of the
setup concerned, warning boards inscribed “Do not switch on! Danger!” must be displayed.
Earthing
A high-voltage setup may be entered only when all the parts which can assume high-voltage
in the contact zone are earthed. Earthing may only be effected by a conductor earthed inside
the fence. Fixing the earthing leads onto the parts to be earthed should be done with the aid
of insulating rods. Earthing switches with a clearly visible operating position are also
permissible. In high-power setups with direct supply from the high-voltage network, earthing
is achieved by earthing isolators. Earthing may only follow after switching the current source
off and may be removed only when there is no longer anyone present within the fence or if
the setup is vacated after removal of the earth. All metallic parts of the setup which do not
carry potential during normal service must be earthed reliably and with adequate crosssection of at least 1.5 mn2 Cu. In test setups with direct supply from the high-voltage network,
the earth connections must be made with particular considerations of the dynamic forces
which can arise.
Circuit and test setup
In the case that the setup is not supplied from ready wired desks, clearly marked isolating
switches must be provided in all leads to the low-voltage circuits of high-voltage transformers
and arranged at an easily identifiable position outside the fence. These must be opened
before earthing and before entering the setup.
All leads must be laid so that there are no loosely hanging ends. Low-voltage leads which
can assume high potentials during breakdown or flashovers and lead out of the fenced area,
e.g. measuring cables, control cables and/or supply cables must be laid inside the setup in
earthed sleeves. All components of the setup must be either rigidly fixed or suspended so
that they cannot topple during operation or be pulled down by the leads. For all setups
intended for research purposes, a circuit diagram shall be fixed outside the fence in a clearly
visible position. A test setup may be put into operation only after the circuit has been
checked and permission to begin work given by an authorized person.
8
Conducting the experiments
Everyone carrying out experiments in the laboratory is personally responsible for the setup
placed at his disposal and for the experiments performed with it. For experiments during
working hours one should try, in the interest of personal safety, to make sure that a second
person is present in the testing room. If this is not possible, then at least the times of the
beginning and ending of an experiment should be communicated to a second person. When
working with high-voltages beyond working hours, a second person familiar with the
experimental setups must be present in the same room.
If several persons are working with the same setup, they must all know who is to perform the
switching operations for a particular experiment. Before switching on high-voltage setups,
warning should be given either by short horn signals or by the call “Attention! Switching-on!”.
This is especially important during loud experiments, so that people standing by may cover
their ears. If necessary, the completion of the experiment can be announced when the
equipment is de-energized either by a single long tone or by the call “Switched off”.
Explosion and fire risk, radiation protection
In experiments with oil and other highly flammable materials, special care is necessary owing
to the danger of explosion and fire. In each room where work is carried out with these
materials, suitable fire extinguishers must be close to hand and ready for use. Highly
flammable waste products, e.g. paper or used cotton waste, should always be disposed of
immediately in metal bins.
Accident insurance
Everyone working in the Institute must be insured against accidents.
Conduct during accidents
Mode of action in case of an electrical accident:
1. Switch off the setup on all poles. So long as this has not been done, the victim of the
accident should not be touched under any circumstances.
2. If the victim is unconscious, notify the emergency service at once.
Telephone Number: ………..........................................................
3. Make immediate attempts to restore respiration by artificial respiration or chest
massage!
4. These measures must be continued, if necessary, up to the beginning of an
operation. (Only 6 to 8 minutes time before direct heart massage!).
5. Even during accidents with no unconsciousness, it is recommended that the victim
lies quietly and a doctor’s advice is sought.
9
10
Experiment 1.
Generation and measurement of AC voltage
SAFETY PRECAUTIONS!!!
It is important and essential that all participants familiarize themselves and strictly
follow all safety precautions described in the Safety Regulations for High Voltage
Experiments section before commencing experiments
1.1. Objective
Alternating voltages are required for most high-voltage tests. The investigations are
performed either directly with this type of voltage, or used in circuits for the generation of high
DC voltage and impulse voltages. This experiment examines the generation of High AC
Voltage using a Terco test transformer.
1.2. Reference
Terco HV 9150 Digital AC Voltmeter Manual
Terco HV 9103 Control Desk Manual
1.3. Equipment to be used
HV Test Transformer
Control Desk
Measuring Capacitor
AC Peak Voltmeter
Connecting Rod
Connecting Cup
Floor pedestal
Earthing Rod
HV9105
HV9103
HV9141
HV9150
HV9108
HV9109
HV9110
HV9107
1
1
1
1
1
1
1
1
1.4. Test setup
The test setup consists of the transformer, a measuring capacitor, a connecting cup and a
floor pedestal, the electrical relationship of which is presented below:
HV 9105
HV 9108
HV 9109
HV 9141
From Control Desk
Regulated Voltage Output
HV 9110
To Control Desk
AC measurement Input
Fig. 1.1 Circuit for AC Voltage Measurement via Control Desk Instrumentation
11
1.5. Introduction
1.5.1. Setting up the HV experiment
High Voltage AC is generated in the Laboratory using the 220V/100kV Test Transformer
(HV9105). This is fed and controlled from the Control Desk. The high voltage experiments
must be carried out in dedicated HV experimental areas enclosed with metal barriers. Control
desks with power supply installations, safety circuits and the measuring instruments
constitute the standard equipment. For voltage measurement, one instrument for measuring
the primary voltage of the transformer and one AC peak voltmeter (HV9150) are provided at
each desk. Participants should study the circuit of the Control Desk (HV9103) and familiarize
themselves with its operation before commencing the experiment.
This experiment assumes that power is supplied to the control desk and the door contact has
been connected.
1.5.2. Methods of Measuring High Alternating Voltages
High AC Voltages can be measured by different methods:
 Measurement of Urms using primary input voltage and Transformer Ratio
 Measurement of Û with the peak voltmeter (HV9150) via an AC Measuring Capacitor
(HV9141)
 Determination by using the breakdown voltage Ûd of a sphere gap
 Determination of Û using a circuit after Chubb and Fortescue. (Not covered here)
This experiment focuses on the first two methods of measurements, the results of which are
then used for comparison.
Transformer Ratio
To calculate Urms from the transformer primary input voltage and the transformer ratio, these
values must first be established.
The HV 9103 Control Desk provides a user-regulated output voltage of 0 - 220/230 VAC.
This is fed to the primary side of the HV 9105 transformer.
HV 9105 Transformer
Control
Desk
0V
Primary
Side
Uin
Secondary
Side
Transformer
Ratio = 450
Fig. 1.2 Simplified Transformer Circuit
Uout is found by simply multiplying Uin by the transformer ratio:
Uout = 450 x Uin
12
Uout
Measuring Capacitor
The simplest and most common way of finding the AC voltage value in the Terco HV setup is
by way of a measuring capacitor.
High-voltage capacitors are well-suited for the reduction of high alternating voltages to values
easily measurable with instruments.
Loading
To keep loading on the voltage source as low as possible, the HV capacitor C1 should be
kept as small as possible. (In our case, 100pF for the HV 9141)
Accuracy
Accuracy of high-voltage measurement with capacitors is then limited only by the
environment that can affect the capacitor, C1. This is represented by the earth capacitance
depicted as CE in circuit (a) below.
2C1
C
2C1
u(t)
CE
u(t)
Measuring
Circuit
Measuring
Circuit
(b)
(a)
Fig 1.3 (a) with Earth Capacitance (b) Equivalent capacitance, C
The measuring circuit is connected at the low-voltage output terminal.
For the current flowing through the measuring circuit, which is determined by the primary
capacitance C1, the earth capacitance reduces the effective primary capacitance to:
Under the assumption of homogenous distribution of earth capacitance, it can be shown the
CE is equal to 2/3 of the total earth capacitance Ce acting at C1.
For cylindrical dividers, Ce can be calculated at a value of 12 - 20 pF/m in height.
The effect of change of capacitance must remain small to ensure adequate measuring
accuracy. This can be achieved in practice by making the high voltage capacitors static
(always the same Ce).
13
1.6. Experiment and procedure
1.6.1. Checking the Experimental Setup
The complete circuit diagram of the control desk and the current paths of the safety circuits
should be discussed and wherever possible, the actual wiring of the experimental setup
traced.
A series of measures which guarantee protection against electrical accidents can be
identified in the circuit and the fulfillment of the safety regulations of Appendix-A should be
determined using the following methods.
1.6.2. Procedure
1. Ensure access to the specific manuals for the HV 9103 Control Desk and HV 9150 AC
voltmeter.
2. Check earth points. Always make sure there is a good quality earth connection, to which
all of the components can be connected. This should be a high quality busbar, situated
inside the cage, such as the one shown below.
Fig 1.4 Earthing Busbar
If earthing plates are present, check all connections between them and connect directly to
the busbar.
3. Make the transformer connections. Check that the 2 jumpers are present and connected
as indicated in the picture below.
Jumpers
To Earth Busbar
To Control desk
To Ground Plates
Fog 1.5 HV 9105 Transformer Connections
4. With the relevant connection cable, connect earth then the phases. The earthing
connector should be of an o-ring type to prevent accidental disconnections.
14
5. Connect the transformer to the Control Desk. Insert the cable connector through the cable
opening and into the Regulated Voltage output at the rear of the Control Desk.
Note that this is a twist connector. The plug is inserted at the 10 o’clock position and
twisted clockwise to the 12 o’clock position to secure.
Fig 1.6 Control Desk Regulated Voltage Output
Fig 1.7 Regulated Voltage Connector
6. Position the Measuring Capacitor. First, a HV 9110 Floor Pedestal will be required. The
measuring capacitor will stand upright on this. Position the floor pedestal about 60cm from
the transformer where it will not cause an obstruction.
Note! The measuring capacitor should be positioned so that the signal output connector is
at the bottom (indicated by the blue ring, below).
HV 9108
Connecting Rod
HV 9109
Connecting Cup
HV 9105
High Voltage
Transformer
HV 9141
Measuring
Capacitor
Transformer
Connection
Cable
HV 9108
Floor Pedestal
Earthing
Plates
Fig 1.8 AC Voltage Measurement Component Placement
15
7. Connect the capacitor to the transformer. Place a Connecting Cup on top of the upright
Measuring Capacitor, adjust the distance to the transformer and connect with a
Connecting Rod.
Note! If no Earthing Plates are used, connect the measuring capacitor to the earth
busbar.
8. Connect the Measuring Capacitor output to the Control Desk input. Connect the
appropriate coaxial cable from the Measuring Capacitor to the HV 9150 input, situated on
the rear panel of the Control desk.
Fig 1.9 HV 9150 AC Voltmeter Input
Fig 1.10 AC Measuring Capacitor Output
Note how the excess cable has been hung up on the cage with quick-ties to help protect
the cable and to prevent accidents inside the HV area.
9.
Make sure the Control Desk has an earth connection to the busbar.
10. After double-checking all connections and ensuring good earthing for all relevant
components, the Control Desk can be connected to the power supply.
11. The rear of the Control desk should resemble the picture below, except for the cable
hanging to the left, which is the connection cable for the DC voltmeter. This is covered in
future experiments. Note the Door Contact connection at the bottom left (white cable).
Fig 1.11Control Desk connected and ready for AC voltage measurement
16
Note! On leaving the HV cage, place the HV 9107 earthing-rod across the door opening in
a way that anyone entering must first pick it up. This is good practice and very important
for the continued safety of participants as it serves as a reminder to discharge any
components which may hold a charge on entering the HV area.
12. Perform an Analysis. With the equipment ready to start, calculate the following expected
AC values using the transformer ratio method and enter the results in the results table.
13. Prepare for measurement. With the key, unlock the Control Desk and turn it on by the
mains switch. Fig 1.12. (A.)
HV 9150
AC Peak voltmeter
Regulated Voltage Display
(Transformer primary)
A.
C.
B.
Fig 1.12 Control Desk
14. At this point, make sure the AC voltmeter is set to the desired measurement position.
Reset using the reset button if required.
(For more information, please see the dedicated HV 9150 AC voltmeter manual.)
15. Begin measurement. Switch on the primary side by pressing the corresponding button (B).
Next, do the same for the secondary side (B).
16. Gradually increase the voltage using the controllers (C).
At each primary voltage level in the results table, record the displayed value.
17. Decrease the voltage back to zero.
18. Switch off the Control Desk.
Note! On entering the cage, always use the earthing rod to discharge any potential live
power sources.
17
1.7. Results
Results Table
Primary (regulated)
Voltage
50 V
100 V
125 V
150 V
175 V
200 V
Calculated Secondary
Voltage
22.50
45.00
56.25
76.50
78.75
90.00
Indicated Secondary
Voltage
22.50
45.00
56.17
66.90
76.64
88.32
1.8. Evaluation
1. Did the values displayed on the HV 9150 AC voltmeter reflect the theoretical values
calculated using the transformer ratio?
2. If the values did not correspond, what could be some possible reasons for this?
1.9. Answers/Comments
1. It is unlikely / improbable that the displayed values will correspond exactly with the
theoretical values.
2. The measuring capacitor, however well designed, causes a voltage drop.
Capacitive losses to earth and other surrounding objects are high at high voltages.
None of the components can be considered to be ideal.
18
Experiment 2.
Generation and measurement of AC voltage - Sphere Gap.
SAFETY PRECAUTIONS!!!
It is important and essential that all participants familiarize themselves and strictly
follow all safety precautions described in Preface before commencing experiments
2.1. Objective
To further investigate the generation of High AC Voltage using a Terco test transformer and
measurement of such by way of a Measuring Sphere Gap.
2.2. Reference
Terco HV 9150 Digital AC Voltmeter Manual
Terco HV 9103 Control Desk Manual
Terco HV 9133 Measuring Sphere Gap Manual
2.3. Equipment to be used
HV Test Transformer
Control Desk
Measuring Capacitor
AC Peak Voltmeter
Measuring Sphere Gap
Connecting Rod
Charging Resistor
Connecting Cup
Floor pedestal
Earthing Rod
HV9105
HV9103
HV9141
HV9150
HV9133
HV9108
HV9121
HV9109
HV9110
HV9107
1
1
1
1
1
2
1
2
1
1
2.4. Test setup
The test setup builds on the previous setup with the addition of the HV 9121 Charging
Resistor and the HV 9133 Measuring Sphere Gap. Two connecting cups are required.
HV 9105
HV 9121
HV 9108
HV 9133
HV 9141
To Control
Desk
Regulated
Voltage
Output
M
To Control Desk HV 9150
AC measurement Input
To Control Desk HV 9133
Sphere Gap Control Output
Fig. 2.1 Circuit for Sphere Gap AC Voltage Measurement via Control Desk Instrumentation
19
2.5. Introduction
2.5.1. Setting up the HV experiment
The high-voltage experiments must be carried out in dedicated HV experimental areas,
enclosed with metal barriers.
2.5.2. Methods of Measuring High Alternating Voltages
High Alternating Voltages can be measured by different methods:
 Measurement of Urms using primary input voltage and Transformer Ratio
 Measurement of Û with the peak voltmeter (HV9150) in conjunction with AC Measuring
Capacitor (HV9141)
 Determination by using the breakdown voltage Ûd of a sphere gap;
 Determination of Û using a circuit after Chubb and Fortescue.
This experiment utilizes the Terco HV 9133 Measuring Sphere Gap to determine the
breakdown voltage.
Breakdown Voltage Ûd of a Sphere Gap
At high voltage, almost anything can become a conductor of electricity - even air. Proof of
this is seen in an everyday lightning strike. The point at which a gas or material stops being
as insulator and becomes conductive is known as its ‘Dielectric Breakdown’ point.
The voltage which must be applied for dielectric breakdown to occur is referred to as
‘Breakdown Voltage’.
Paschen’s Law
Paschen's law describes how the breakdown voltage of a spark gap depends on electrode
separation and the pressure of the surrounding gas.
It states that the voltage required to spark a specific gas is constant, if the same is true for
the product of pressure and separation.
Breakdown voltage in a gas:



V is the breakdown voltage in volts
p is the pressure in atmospheres
d is the gap distance in meters
The constants a and b depend upon the composition of the gas. For air at standard
atmospheric pressure, a = 43600000 and b = 12.8.
In reality, this relationship breaks down completely at low pressures and very short distances
(less than 5.7mm).
20
2.6. Procedure
2.6.1. Procedure
This experiment assumes the transformer and control desk have been connected and tested
in accordance with the previous experiment.
1. Ensure access to the specific manuals for the HV 9103 Control Desk, HV 9150 AC
voltmeter and HV 9133 Measuring spark Gap for reference.
2. Check earth points. Always make sure there is a good quality earth connection, to which
all of the components can be connected. This should be a high quality busbar, situated
inside the cage, such as the one shown below.
Fig 2.2 Earthing Busbar
If earthing plates are present, check all connections between them and connect directly to
the busbar.
3. Ensure the transformer is connected correctly to the control desk. For instructions on how
to do this, see previous experiment.
4. Stand the HV 9141 Measuring Capacitor on a Floor Pedestal and position a Connecting
Cup on top as in Experiment 1A.
Fig 2.3 Setup Step 1
5. Connect the Measuring Capacitor to the Control desk. (See preceding experiment)
21
6. Place the HV 9121 Charging Resistor between the transformer and the Measuring
Capacitor.
Fig 2.4 Setup Step 2
7. Now position the Measuring Sphere Gap. This will be connected via the Connecting Cup
on top of the Measuring Capacitor by a HV 9108 Connecting Rod so the distance should
reflect this. (For more information on the Measuring Sphere gap, please see the dedicated
manual).
Connecting
Cup here.
Fig 2.5 Setup step 3
8. Place a Connecting Cup on the top of the Measuring Sphere Gap and connect to the
Measuring Capacitor with a HV 9108 Connecting Rod.
Note! The Measuring Sphere Gap requires individual earthing.
9. Connect a suitable earth cable, with o-ring type connector, to the Earth Point near the
base of the HV 9133. Fasten the other end securely to the Earthing Busbar.
Earth Connection
Fig 2.9 Sphere Gap Earth Connection Point to Busbar
22
10. With the cable provided, connect the HV 9133 Measuring Sphere Gap to the HV 9133
Motor Control Input at the rear of the Control desk.
Fig 2.8 HV 9133 Sphere Gap Motor Control Input
11. After double-checking all connections and earthing, ensure that everybody has exited the
HV cage. On exiting, the last person should position the HV 9107 Earthing Rod across the
entrance before closing and locking the gate.
12. Switch on the Control Desk. Note the status of the warning lights above the gate.
Answer questions 1, 2 and 3 in the Questions section.
13. Adjust the sphere gap to the desired distance using the controller switches indicated by
the red ring, Fig 2.9 below.
Fig 2.9 Sphere Gap Adjustment Switches
14. Make sure the AC voltmeter is set to measure peak voltage, reset if necessary.
15. Sound the horn to warn others that loud noises may occur. (Blue ring, Fig 2.9)
16. Increase the voltage slowly and record the breakdown voltage indicated on the AC peak
voltmeter for each distance in the results table. Repeat each distance a few times for
improved accuracy.
17. Once the breakdown occurs, decrease the voltage until the spark is extinguished.
23
18. Cause a breakdown once again but this time, instead of decreasing the voltage, increase
the gap. Answer question 5 in the Questions section.
2.7. Results
Results table
Sphere Gap
Distance (m)
0.01
0.02
0.03
0.04
0.05
0.06
Theoretical
Breakdown Voltage (kV)
31.7
59.00
84.00
105.00
123.00
No breakdown
2.8. Evaluation
1. Which warning light is active?
2. What needs to occur for the other light to become active?
3. Failing to connect the door contact will result in what?
4. What is the function of the Charging Resistor in this circuit?
5. Was the breakdown voltage level consistent?
6. Why did the arc continue, even at larger distances?
24
Observed
Breakdown Voltage (kV)
18-50
25-70
50-100
70-120
75-???
-
2.9. Answers/Comments
1. The green light should be lit.
2. The HV transformer must be connected via the Control Desk buttons.
3. An inability to connect the HV transformer.
4. The main function is to slow any back-current from tripping the internal control desk
circuit breakers when the breakdown occurs. If the charging resistor is left out of the
circuit, the CB’s will have to be reset and the experiment restarted after each breakdown.
5. Possibly within +/- 5kV
6. Once the path has been created, it takes less energy to sustain. Therefore, the gap can
be made larger but still require the same level of energy.
Notes
25
26
Experiment 3.
Generation and measurement of direct voltage
SAFETY PRECAUTIONS !!!
It is important and essential that all participants familiarize themselves and strictly
follow all safety precautions described in the Safety Regulations for High Voltage
Experiments section before commencing experiments
3.1. Objective
The objective of this experiment is to investigate high direct voltage generation and
measurement using Terco HV equipment. The knowledge gained is a prerequisite for
performing following experiments.
Note: Extra care is essential in direct voltage experiments, since the high-voltage
capacitors in many circuits retain their full voltage, for a long time even after
disconnection. Earthing regulations are to be strictly observed. Even unused
capacitors can acquire dangerous charges!
3.2. Reference
Terco HV 9103 Control Desk Manual
Terco HV 9150 Digital AC Voltmeter Manual
Terco HV 9151 Digital DC Voltmeter Manual
3.3. Equipment to be used
COMPONENT DESCRIPTION
HV Test Transformer
Control Desk
Measuring Capacitor
Rectifier
Smoothing capacitor
Measuring Resistor
Insulating Rod
Connecting cup
Floor Pedestal
Connecting Rod
Spacer Bar
Electrode
Earthing Switch
Earthing Rod
AC peak voltmeter
DC Voltmeter
Resistor
Load Capacitor
TERCO TYPE
No.
HV9105
HV9103
HV9141
HV9111
HV9112
HV9113
HV9124
HV9109
HV9110
HV9108
HV9119
HV9138
HV9114
HV9107
HV9150
HV9151
HV9121
HV9120
27
QUANTITY
1
1
1
2
1
1
1
5
5
3
4
1
1
1
1
1
1
1
3.4. Test setup
HV 9111
HV 9111
HV 9108
HV 9108
HV 9138
HV 9141
HV 9124
HV 9112
HV 9113
Control
Desk Rear
Contacts:
HV 9114
HV9150 AC.
Regulated V.
Regulated V.
HV9114 Ctrl.
HV9151 DC.
AC Meas.
HV Transform
Rectification
DC Meas.
Fig. 3.1 Direct Voltage Measurement Setup Diagram
3.5. Recommended external equipment
None
3.6. Introduction
3.6.1. Generation of High Direct Voltages
High direct voltages required for testing purposes are mostly produced from high alternating
voltages by rectification and wherever necessary, subsequent multiplication.
Multiplication can be performed by way of a Greinacher Doubler Circuit which is outside the
scope of this Beginners Experiments manual but discussed further in the High Voltage
Experiments manual.
In this setup, the alternating high voltage is rectified with 2 HV 9111 rectifiers, placed in
series. The HV 9112 capacitor then smoothes the half-wave rectified voltage.
Atop the smoothing capacitor, an electrode is placed to provide a good contact surface for
the HV 9114 Grounding Switch.
The Grounding Switch makes contact with the electrode on loss of supply current to the
transformer, subsequently discharging the capacitor. This can occur when the transformer
supply current is switched off via the control panel or if the HV cage door is opened while an
experiment is in progress.
Note! Because of the potentially lethal voltages involved, the HV 9107 earthing rod should
always be used when entering the HV area.
The smoothed direct voltage is measured by voltage division in the HV9113 measuring
resistor and the value displayed on the HV9151 DC voltmeter, situated on the front panel of
the HV 9103 control desk.
28
3.7. Procedure
To use space more efficiently, the setup can be built in an ‘L’ shape as seen below. The
alternating voltage measurement setup in the left of the picture is positioned at a 90 degree
angle to the rectification step, which is built to the right.
HV 9111
Rectifiers
HV 9138
Electrode
HV 9124
Isolator
HV 9112
Smoothing Capacitor
HV 9114
Grounding
Switch
HV 9113
Measuring Resistor
HV 9107
Earthing Rod
Fig. 3.1 Direct Voltage Measurement Setup
Note! If earth-plates such as those above are not present, make sure each component is
sufficiently grounded by a suitable cable with o-ring connectors to prevent accidental
disconnection.
1. Start by building the alternating current setup from Experiment 1.
Fig. 3.2 AC Voltage Measurement Setup
2. Next position 3 floor pedestals in a line as seen in Fig 3.2, above.
3. Place the Positioning Ring of the HV 9114 Earthing Switch over the second floor
pedestal. The Smoothing Capacitor will then hold this in place when mounted.
4. Erect the HV 9124 Isolator first and place a Connecting Cup on top.
5. Secure the first section in place by adding the first HV 9111 Rectifier. It is good practice
to continue constructing each section until it is secure before moving on to the next. This
prevents any components being damaged from being accidentally knocked over.
29
Fig. 3.3 Rectifier and Isolator Secured
Note! Do not pick up the capacitor by the ends as a substantial charge may have
accumulated while at rest. It is good practice to always discharge a capacitor before handling
it. This is done easily by short-circuiting the ends with any electrical laboratory cable.
6. Resist picking the HV 9112 smoothing capacitor up by the ends, maneuver the bottom
connector through the Earthing-Switch Positioning-Ring and into the Floor Pedestal.
7. Place the HV 9138 Electrode atop the capacitor, making sure not to trap the Earthing
Switch Rod underneath (the rod should be able to drop away without hindrance).
Fig. 3.4 Rectifier and Smoothing Capacitor Section
8. Add the Connecting Cup and position the second rectifier to secure the section.
9. Construct the next section including the HV 9113 Measuring Resistor, a Connecting Rod,
Floor Pedestal and Connecting Cup.
Note! Ensure the signal output connector is closest to the floor as indicated below. Failure to
do so will result in high voltage being sent directly into the Control Panel.
30
Output Signal
Contact. (Low End)
Fig. 3.5 Measuring Resistor Orientation
10. Double-check all connections and exit the cage, leaving the Earthing Rod positioned
across the doorway, as usual.
11. Switch on the Control Desk. Make sure the regulated voltage is at minimum before
applying any power to the transformer.
12. Reset the AC voltmeter if desired; check that the correct stage level is set on both
instruments.
Note! Before starting the experiment, sound the warning horn to inform people close by that
an experiment is in progress and sudden loud noises can occur.
13. Answer questions 1 and 2 in the Questions section.
14. After sounding the horn, power may be provided to the transformer primary and
secondary sides.
15. At several levels, note the measured AC voltage levels and calculate the expected DC
voltage level. Compare with the rectified DC voltage level displayed.
Note! Before switching off the transformer from the Control Desk, remember to decrease the
regulated voltage down to zero.
Note! On entering the HV cage be sure to use the earthing rod to discharge any possible
sources of remaining voltage.
31
3.8. Results
Results Table
Alternating Voltage
Peak (kV)
15
25
50
75
100
140
Theoretical
Direct Voltage (kV)
10-15
18-25
28-35
55-70
75-90
110-125
Displayed
Direct Voltage (kV)
14.86
24.91
33.52
67.83
79.02
115.19
3.9. Evaluation
3.9.1. Questions
1. This experiment does not include a spark gap. In that case, what is a possible source of
sudden loud noise which is warned for?
2. What is the expected relationship between the AC voltage level and the rectified voltage
level?
3. What is ‘Ripple?
3.9.2. Explanations/Answers
1. On loss of power to the transformer, the earthing rod will make contact with the electrode
atop the HV 9141 Smoothing Capacitor. If this capacitor is currently holding a charge it
will be discharged in a matter of milliseconds or less. This quick transferral of energy
emits a loud ‘crack’ sound.
2. The measured DC voltage level should be close to that of the peak AC voltage level,
allowing for the ripple factor and minus the voltage drop across components together with
various capacitive losses suffered at high voltage.
3. Ripple is the small residual periodic variation of the direct current (dc) output of a power
supply which has been derived from an alternating current (ac) source.
Notes
32
Experiment 4.
Generation and measurement of impulse voltage
SAFETY PRECAUTIONS !!!
It is important and essential that all participants familiarize themselves and strictly
follow all safety precautions described in the Safety Regulations for High Voltage
Experiments section before commencing experiments
4.1. Objective
The objective of this experiment is to investigate impulse voltage generation and
measurement using Terco HV equipment. The knowledge gained is a prerequisite for
following the High Voltage Experiments manual.
Note: Extra care is essential in direct voltage experiments, since the high-voltage
capacitors in many circuits retain their full voltage, for a long time even after
disconnection. Earthing regulations are to be strictly observed. Even unused
capacitors can acquire dangerous charges!
4.2. Reference
Preceding manuals plus:
Terco HV 9152 Digital Impulse Voltmeter Manual
4.3. Equipment to be used
COMPONENT DESCRIPTION
HV Test Transformer
Control Desk
Smoothing Capacitor
Load Capacitor
Silicon Rectifier
Measuring Resistor
Charging Resistor
Wavefront Resistor
Wavetail Resistor
Sphere Gap
Drive for sphere gap
Insulating Rod
Connecting Rod
Connecting cup
Floor Pedestal
Spacer Bar
Electrode
Earthing Switch
Earthing Rod
DC Voltmeter
Impulse Peak voltmeter
Low Voltage Divider
TERCO TYPE
HV9105
HV9103
HV9112
HV9120
HV9111
HV9113
HV9121
HV9122
HV9123
HV9125
HV9126
HV9124
HV9108
HV9109
HV9110
HV9119
HV9138
HV9114
HV9107
HV9151
HV9152
HV9130
33
QUANTITY
1
1
1
1
2
1
1
1
1
1
1
2
2
7
6
4
1
1
1
1
1
1
4.4. Test setup
The test setup is based on the DC measurement setup from the preceding experiment with
the addition of a HV 9121 Resistor. To accommodate the extra space needed for the
extended setup, the HV 9113 DC Measuring Resistor is positioned at a 90° angle from the
line of the rectifiers. It is still connected to the HV 9112 Smoothing Capacitor.
The HV 9114 Earthing Switch has been moved to the left of the Smoothing Capacitor to
make room for the extra components to be added.
HV 9108
HV 9111
HV 9111
HV 9121
A
HV 9108
HV 9141
HV 9124
HV 9124
HV 9113
HV 9112
Control
Desk Rear
Contacts:
B
HV 9114
HV9150 AC.
Regulated V.
Regulated V.
HV9114 Ctrl.
HV9151 DC.
AC Meas.
HV Transform
Rectification
DC Meas.
Fig. 4.1 Impulse Voltage Measurement Setup Diagram Part 1
The figure below shows the continuation from points A and B in the slightly adjusted DC
measurement setup above. The components below complete the Impulse measuring setup.
HV 9125
HV 9122
A
Control Desk
Rear Contacts:
HV 9123
HV9125 Control
HV 9120
HV 9130
HV9125 Control
HV 9126
M
B
HV 9119
HV 9119
HV9152 Impulse
Fig. 4.2 Impulse Voltage Measurement Setup Diagram Continued
34
4.5. Introduction
4.5.1. Generation of Impulse Voltages
The identifying time characteristics of impulse voltages are given in Fig. 4.2. In this
experiment lightning impulse voltages with a front time T1 = 1.2 μs and a time to half value T2
= 50 μs are mostly used. This 1.2/50 μs form is the one commonly chosen for impulse testing
purposes.
As a rule, impulse voltages are generated in either of the two basic circuits shown in Fig. 4.3.
The relationships between the values of the circuit elements and the characteristic quantities
describing the time-dependent curve are given by the time constants:
τ1 ≈ Re(Cs+Cb)
τ2 ≈ Rd{CsCb)/(Cs+Cb)}
where Cs – Impulse capacitor, Cb- Load Capacitor, Rd- Front Resistor and Re - tail resistor.
For lightning impulse voltages of the standard form 1.2/50 the time constants are
τ1 = 68.22 μs
τ2 = 0.405 μs
When designing impulse voltage circuits, one should bear in mind that the capacitance of the
test object is connected parallel to Cb, hence the front time and the efficiency η in particular
can be affected. This has been allowed for in the standards by way of comparatively large
tolerances on T1.
Fig. 4.2 Characteristic parameters of standard test impulse voltages
a) lightning impulse voltage b)switching impulse voltage
Fig. 4.3 Basic Impulse voltage circuits
35
4.5.2. Breakdown Time-Lag
The breakdown in gases occurs as a consequence of an avalanche-like growth of the
number of gas molecules ionized by collision. In the case of gaps in air, initiation of the
discharge is effected by charge carriers which happen to be in a favorable position in the
field. If, at the instant when the voltage exceeds the required ionization onset voltage Ue, a
charge carrier is not available at the appropriate place, the discharge initiation is delayed by
a time referred to as the statistical time-lag ts.
Even after initiation of the first electron-avalanche a certain time elapses, necessary for the
development of the discharge channel which is known as the formative time-lag ta. The total
breakdown time-lag, between over-stepping the value of Ue at time t1 and the beginning of the
voltage collapse at breakdown, compromises these two components:
t1 = ts + ta.
These relationships are shown in Fig. 4.4.
Fig. 4.4 Determination of breakdown time-lag during an impulse voltage breakdown
36
4.6. Experiment and procedure
4.6.1. Investigation of a single-stage Impulse Generator
To ascertain the correct measurement of Impulses, the value displayed on the HV 9152
Impulse Voltmeter is compared with the level of DC voltage required to cause the
breakdown. in order to create sustained flashovers in a more controlled fashion, the HV 9121
Charging Resistor has been added. This will lengthen the charging time, creating a delay
between flashovers, thus, allowing for more accurate observations.
4.7. Procedure
1. Construct the AC and DC voltage measurement setup as below, note the position of the
additional HV 9121 Charging Resistor, the HV 9114 Grounding Switch and the HV 9113
DC Measuring Resistor.
HV 9124
Isolators
HV 9121
Charging Resistor
HV 9114
Grounding Switch
HV 9113
Measuring Resistor
Fig. 4.5 Impulse Voltage Measurement Setup Step 1
2. Building to the right of the HV 9112 Smoothing Capacitor, Insert a HV 9119 spacer bar
into the Floor Pedestal. At the other end of the Spacer Bar, add another Floor Pedestal.
The HV 9126 Sphere Gap Drive Unit will be mounted to this Spacer Bar.
37
3. Position the Sphere Gap Drive box near the right side Floor Pedestal. The connector for
the Drive Shaft should also be to the right as shown below. Fasten the Drive to the
Spacer bar using the Mounting Bracket Screws (this may need to be adjusted later).
HV 9126
Sphere Gap
Drive Shaft
HV 9126
Sphere Gap
Drive
HV 9119
Spacer Bar
HV 9125
Signal Input
Mounting
Brackets
Fig. 4.6 HV 9126 Sphere Gap Drive Placement
4. Stand the HV 9123 Wavetail Resistor upright on the free Floor Pedestal and add a
Connecting Cup.
5. The HV 9125 Spark Gap can now be mounted on the Connection Cups between the
Smoothing Capacitor and the Wavetail Resistor. The Sphere gap Drive Shaft Needs to
be positioned while the Spark gap is lowered into place. Loosen the Drive if required to
allow for better maneuverability. Tighten when finished. The Drive Shaft should rotate
freely and the closest sphere should move to the left or right when doing so.
Fig 4.7 HV 9125 Sphere Gap and Drive
6. Connect the HV 9126 Drive Signal cable to the HV 9125 Input at the rear of the Control
Desk.
38
7. Erect the HV 9120 Load capacitor on the last Floor pedestal. This can be done at a rightangle to save space if required. Place a Connecting Cup on top.
HV 9120
Load Capacitor
HV 9130
Low VoltageDivider
Note! Position the contact for the Low Voltage Divider nearest the floor.
8. Screw the HV 9130 Low Voltage Divider into place on the HV 9120 Load capacitor.
9. If more than one HV 9130 Low Voltage Divider is available, check that the divider and
capacitor have corresponding numbers.
10. Secure the last section in place by adding the HV 9122 Wavefront Resistor.
Fig 4.9 Impulse Setup almost complete - Cables to be organized
11. The setup should now resemble the picture above. It is important for safety and for the
lifetime of the equipment to ensure all cables are neatly organized and if possible, any
excess cableage hung out of the way.
Fig 4.10 Control Desk Cables
39
12. Double-check all connections and exit the cage, leaving the Earthing Rod positioned
across the doorway, as usual.
13. Switch on the Control Desk. Make sure the regulated voltage is at minimum before
applying any power to the transformer.
14. Test the Sphere gap Drive Control switches to ensure operation.
Fig 4.11 Sphere Gap Control Switches
15. Reset the voltmeters if desired; check that the correct stage level is set on all
instruments.
Note! Before starting the experiment, sound the warning horn to inform people close by that
an experiment is in progress and sudden loud noises can occur.
16. After sounding the horn, power may be provided to the transformer primary and
secondary sides.
17. At several Sphere Gap distances, note the DC voltage levels at which breakdown occurs
and observe and compare the resulting Impulse peak levels. Use the results table to
record this information if desired.
Note! Before switching off the transformer from the Control Desk, remember to decrease the
regulated voltage down to zero.
Note! On entering the HV cage be sure to use the earthing rod to discharge any possible
sources of remaining voltage.
4.8. Results
Results Table
Sphere Gap
Distance (mm)
-----20 10
-----30 20
-----40 30
50 40
-----60 50
-----70 60
------
Direct Voltage
Breakdown (kV)
28.02
53.21
78.96
105.16
122.75
No breakdown
40
Displayed Peak
Impulse Voltage (kV)
26.15
49.86
72.84
96.70
108.45
-
4.9. Evaluation
4.9.1. Questions
1. What time characteristics are desirable for Impulse Voltage creation?
2. Why are these time characteristics relevant?
3. What percentage of the DC voltage generated, transferred to Impulse voltage?
4.9.2. Explanations/Answers
1. Front time 1.2 μs front and 50 μs time to half.
2. This simulates real-life conditions during, for example, a lightning strike.
3. User observation.
Notes
41
42
Experiment 5.
Impulse voltage with the HV 9132 Trigger Sphere
SAFETY PRECAUTIONS !!!
It is important and essential that all participants familiarize themselves and strictly
follow all safety precautions described in the Safety Regulations for High Voltage
Experiments section before commencing experiments
5.1. Objective
The objective of this experiment is to investigate the operation of the HV 9132 trigger
Sphere.
5.2. Reference
Preceding manuals only
5.3. Equipment to be used
As for Experiment 4, with the addition of the HV 9132 Trigger Sphere and HV 9131 Optical
Trigger cable.
5.4. Test setup
The test setup is the same as the previous experiment. The HV 9132 Trigger Sphere
replaces the passive sphere nearest the transformer in the HV 9125.
HV 9132
Trigger Sphere
HV 9131
Optical Trigger
Cable
Fig. 5.1 Trigger Sphere and Cable Placement
5.5. Introduction
5.5.1. Triggering of Impulse Voltages
In order to study Impulse more closely, it is beneficial to have greater control over the
breakdown timing.
Because of the extremely short times involved, it may be hard to capture the desired
information. The trigger sphere not only provides a means of knowing when the breakdown
will occur but highlights one of the key characteristics of the breakdown.
43
5.6. Experiment and procedure
5.6.1. Investigation of a single-stage Impulse Generator
The Control Desk front panel houses the trigger button for the Trigger Sphere. Pressing this
button sends a light pulse along the fiber-optic cable to the Trigger Sphere where the inbuilt
electronics provide current to a sparkplug. The sparkplug ignites, providing the extra voltage
needed to initiate a breakdown in the air gap.
5.7. Procedure
1. Starting with the setup for Experiment 4, unscrew and remove the sphere. Every care
should be taken so that no marks are made on the sphere. Store this in a safe place.
2. Locate the trigger button on the trigger unit, on the front panel of the Control Desk. Push
the button (with the Control Desk switched on) and check that a light pulse can be seen
in the HV 9131 rear connector.
Fig. 5.2 Trigger Sphere trigger Button
3. Connect fibre optic cable to control desk and check that the pulse can now be seen at the
other end of the cable.
4. Open trigger sphere and connect 2 x 9V batteries. Close again by twisting into place.
5. Connect the fibre optic cable to the trigger sphere.
6. Test the Trigger Sphere, a spark should be seen and heard from the spark plug on
pressing the trigger button. Note! Do not hold the trigger sphere near or on the spark
plug!
7. If the test is successful the Trigger Sphere is OK for use. Remove the cable. Switch off
the Control Desk.
Note! On entering the HV cage be sure to use the earthing rod to discharge any possible
sources of remaining voltage.
8. Mount the Trigger Sphere in the HV 9125 Sphere gap by screwing into place, position the
optic cable input in the opening.
44
9. Insert and fasten the fibre optic cable in the trigger sphere.
10. On leaving the HV area, leave the Discharge Rod across the doorway and lock the door.
Note! Before starting the experiment, sound the warning horn to inform people close by that
an experiment is in progress and sudden loud noises can occur.
11. Try triggering a flashover at different distances and voltages. Note how much less voltage
is required to create a standing arc than to spontaneously jump the air gap.
Notes
45
The High Voltage Experiments manual series
Introduction to High Voltage Experiments manual
The Introduction to High Voltage Experiments manual includes procedural instructions for
building the fundamental single-stage HV circuits and controlling experiments via the
HV9103 Control Desk. These circuits include:



HVAC generation and measurement
HVDC generation and measurement
HV Impulse generation and measurement
After working through this manual, the user should feel confident working with the equipment
and have an understanding of the HV generation and measurement methods incorporated in
the Terco HV Laboratory as well as safety features and routines.
HV Lab Supplementary Connections manual
This manual includes information for the construction of advanced HV circuits. These circuits
are an extension of those investigated in this manual and require additional components.
Setups covered in the Supplementary Connections manual include:





Multiple stage AC (cascaded transformers)
2 stage DC setup
3 Stage DC setup
2 stage Impulse setup
3 stage Impulse setup
It is highly recommended that the user should work through the Introduction to High Voltage
Experiments manual before attempting any of these setups. Failure to do so could result in
damage to the equipment.
High Voltage Experiments manual.
The High Voltage Experiments manual introduces some common high voltage experiments
which can be performed with the help of the Terco HV Laboratory.
Note: Some experiments may require external equipment such as measuring circuits,
instruments, test objects and connectors not supplied with the Terco HV Laboratory.
In order to fully understand the concepts introduced in this manual, it is highly recommended
that the user has a good understanding of the fundamentals of HV. The user should also be
familiar with all components and correct experimentation techniques before working through
this manual.
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