High Voltage Test Techniques (eBook)

Kurt Feser, Dieter Kind (Autoren)

eBook Download: PDF | EPUB

2001 | 2. Auflage
320 Seiten
Elsevier Science (Verlag)
978-0-08-050810-8 (ISBN)

Infos

The second edition of High Voltage Test Techniques has been completely revised. The present revision takes into account the latest international developments in High Voltage and Measurement technology, making it an essential reference for engineers in the testing field.
High Voltage Technology belongs to the traditional area of Electrical Engineering. However, this is not to say that the area has stood still. New insulating materials, computing methods and voltage levels repeatedly pose new problems or open up methods of solution; electromagnetic compatibility (EMC) or components and systems also demand increased attention. The authors hope that their experience will be of use to students of Electrical Engineering confronted with High Voltage problems in their studies, in research and development and also in the testing field.
Benefit from a completely revised edition
Brings you up-to-date with th latest international developments in High Voltage and Measurement technology
An essential reference for engineers in the testing field

Inhalt

Front Cover 1
High-Voltage Test Techniques 2
Copyright Page 3
From the Preface to the 1st English Edition (in 1978) 4
Foreword to the 2nd English Edition 6
Table of Contents 8
Chapter 1. FUNDAMENTAL PRINCIPLES OF HIGH-VOLTAGE TEST TECHNIQUES 14
1.1 Generation and Measurement of High Alternating Voltages 14
1.2 Generation and Measurement of High Direct Voltages 36
1.3 Generation and Measurement of Impulse Voltages 55
1.4 Generation and Measurement of Impulse Currents 93
1.5 Non-Destructive High-Voltage Tests 105
Chapter 2. LAYOUT AND OPERATION OF HIGH-VOLTAGE TEST SETUPS 123
2.1 Dimensions and Technical Equipment of the Test Setups 123
2.2 Fencing, Earthing and Shielding of Test Setups 132
2.3 Circuits for High-Voltage Experiments 138
2.4 Construction Elements for High-Voltage Circuits 144
Chapter 3. HIGH-VOLTAGE PRACTICALS 161
3.1 Experiment "Alternating Voltages" 162
3.2 Experiment "Direct Voltages" 167
3.3 Experiment "Impulse Voltages" 175
3.4 Experiment "Electric Field" 182
3.5 Experiment "Liquid and Solid Insulating Materials" 195
3.6 Experiment "Partial Discharges" 206
3.7 Experiment "Breakdown of Gases" 218
3.8 Experiment "Impulse Voltage Measuring Technique" 228
3.9 Experiment "Trunsfurmer Test" 237
3.10 Experiment "Internal Overvoltages" 247
3.11 Experiment "Travelling Waves" 260
3.12 Experiment "Impulse Currents and Arcs" 274
Chapter 4. APPENDIX 286
4.1 Safety Regulations for High-Voltage Experiments 286
4.2 Calculation of the Short-Circuit Impedance of Transformers in Cascade Connection 289
4.3 Calculation of Single-Stage Impulse Voltage Circuits 291
4.4 Calculation of Impulse Current Circuits 293
4.5 Calculation of the Impedance of Plane Conductors 294
4.6 Statistical Evaluation of Measured Results 300
4.7 Specifications for High-Voltage Test Techniques 307
REFERENCES 309
SUBJECT INDEX 319

Textauszug

2

Layout and Operation of High-Voltage Test Setups

2.1 Dimensions and Technical Equipment of the Test Setups

The dimensions and equipment of a high-voltage laboratory1 are primarily determined by the magnitude of the voltage to be generated. A second important feature is the intended application e.g., for teaching purposes, as a testing or research laboratory.

2.1.1 Stands for High-Voltage Practicáls

Practicals are laboratory exercises which give the students an opportunity to conduct set experiments under supervision. The experiments would generally be performed in small groups of three up to a maximum of six participants. The experimental stands described below are designed for this kind of practicals.

In order to accommodate a large number of students, more stands must be available in which experiments can be conducted simultaneously. A useful guide for the setup of a practical laboratory would be approximately 1 experimental stand for every 20 students. The number of stands so derived imposes a certain restriction upon the voltage amplitude for economic reasons, which is also expedient with regard to clearer arrangement, and with that safety, of smaller setups.

If the maximum alternating voltage is restricted to 100 kV and the power ratings to between 5 and 10 kVA, the experimental stands could be set up in rooms with a normal height of 2.5 m. Moreover, the weight of the required construction elements, with the exception of the testing transformer, would be low enough to allow transport without crane facilities. Since most of the basic physical phenomena can already be observed within a voltage range of about 100 kV a.c, the restriction on this value does not impose any appreciable limit on the choice of experiments to be carried out. If necessary, the scope of the practicals could be widened by some demonstration experiments at a very high voltage.

As a proven example, one of the five identically set up experimental stands for high-voltage practicals at the High-Voltage Institute of the Technical University, Braunschweig will be described on the basis of Fig. 2.1. The protective barrier 1, consisting of wire mesh fixed to a metallic frame, is provided with a lockable door, near which work table 3 and control desk 4 are arranged. Inside the barrier is a working platform of two welded steel frames 5 with a covering of four hardwood panels. The steel frames serve as earthing points.

Table 2.3

Examples for the design data of impulse voltage generators

Figure 2.1 Dimensions of experimental stands for high-voltage practicals (in m)

1. Protective barrier,

2. Door,

3. Working table

4. Control desk,

5. Working platform

The high-voltage circuits are set up on the working platform; construction elements and accessories which are not required may be stored in trolley-drawers underneath. Further details may be taken from Fig. 2.2. For example, flexible cables for control and measuring purposes are already laid between the control desk and the working platform and need only be connected to the construction elements.

Figure 2.2 Experimental stand for a high-voltage practical (Dimensions according to Fig. 2.1, Photo: E. Sitte, Braunschweig)

A commonly adopted construction dispenses with the working platform. The high-voltage circuits would be set up directly on the ground, which is provided with an earthing sheet of aluminium or copper. Heavier circuit elements (e.g. transformers) or some parts of circuits could be mounted on trolleys.

2.1.2 High-Voltage Testing Bays

In planning these, it should be considered that they are often responsible for an appreciable portion of the total investment and personnel costs. The introduction of partially automated measuring and protocolling devices permits considerable saving of costs. Testing bays where routine and type tests on manufactured high-voltage equipment are to be carried out, are usually adapted to a particular kind of test. They should constitute an integral part of the production line.

In practice, the operating voltage of the equipment to be tested influences the spatial arrangement of the testing bay. This is because, with respect to the minimum clearances to be maintained in a test setup, the clearance of the test room must, for high voltages, be considerably greater than the height of the production rooms. In consequence, a test object with an operating voltage over 245 kV would, for constructional reasons alone, require its own testing hall. In this case, electromagnetic screening and darkening facilities for the room could also be easily introduced. Fig. 2.3 shows, as an example the possible layout of the testing hall for a factory in which transformers up to 400 kV are produced.

Figure 2.3 Testing bay tbr 400 kV power transformers (dimensions in m)

1. Screened high-voltage hail : a testing transformer (800 kV),

b capacitor (800 kV), c impulse generator (3 MV),

d impulse voltage divider (3 MV), e test object

2. Adjacent testing rooms

3. Control desk

Numerous technical disadvantages prevail when carrying out high-voltage tests in open air. In addition, there is uncertainty in planning the test schedule due to weather conditions, which is generally intolerable, particularly in factory testing bays. As a rule therefore, one prefers an indoor solution.

The high-voltage installations for testing bays conform to the maximum test voltage required, as well as the load represented by the test object. The guiding values listed in Table 2.1 are intended to give an idea of the magnitude of the test voltages for 3-phase high-voltage equipment with a given operating voltage. In any specific case, the exact values have to be taken from the appropriate test specifications valid at the time.

Table 2.1

Guiding values for test voltages and minimum clearances for test setups

When selecting the voltage generators using Table 2.1, one should observe that the rated voltage of the generator must be chosen to be higher than the test voltage given in the table. For a.c. testing transformers, an increase of about 10 % of the required test voltage is sufficient. For impulse voltage generators it is usual to specify the total charging voltage, which must be multiplied by the utilization factor to derive the peak value of the impulse voltage. The utilization factor is, however, influenced by the test object and, above all for the generation of switching impulse voltages, it can even assume values below 0.5. The following guiding values may be given for the factor by which the highest required withstand voltage should be multiplied in order to derive the required rated voltage of the test voltage generator:

Alternating voltage

1.1

Lightning impulse voltage

1.8

Switching impulse voltage

2.0

Direct voltage

1.2

The minimum clearances listed in the last column of Table 2.1 are guiding values for the lowest required air spacings between the parts of the test setup at high-voltage potential and those points in the surroundings at earth potential. At very high operating voltages the minimum clearances are determined by the magnitude of the positive switching impulse voltage to be generated, since a given electrode configuration can have a particularly low breakdown voltage for this type of voltage.

The majority of high-voltage test objects represent capacitive loading of the test voltage source. The following guiding values may be given for the capacitances [Siemens1960]:

Supports, insulators

20 pF

Bushings, inductive instrument

transformers

200-400 pF

Power transformers

(high-voltage winding against

up to 1 MVA

3000 pF

all other parts)

up to 100 MVA

25000 pF

Cable sample upto 10 m long

3000 pF

Experimental setup, measuring capacitor.

Leads for a.c. test voltage

up to 100 kV

100 pF

up to 1000 kV

1000 pF

The more common features of testing transformers are compiled in Table 2.2. Testing transformers are designed in most cases for short-time service of 15 min to 1 h; continuous operation is necessary only for temperature-rise tests or for an investigation of dielectric stability (cables, bushings).

Table 2.2

Examples for the design...

Produkt-Details

• Erscheint lt. Verlag: 24.1.2001
• Sprache: englisch
• Themenwelt: Technik ► Elektrotechnik / Energietechnik
• Themenwelt: Technik ► Maschinenbau
• ISBN-10: 0-08-050810-3 / 0080508103
• ISBN-13: 978-0-08-050810-8 / 9780080508108