Field strength in insulation

8/11/2019 Field strength in insulation

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SOFTWARE FOR CALCULATION

OF SAFETY FACTORS OF STRENGTHOF INSULATION BETWEEN THE WINDINGSAT THE EDGE OF THE WINDINGS

ENDINS

Version 01

USERS MANUAL

ENDINS_UM.00

2005


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Copyright 2002 OSC VITAlteration, duplication and distribution are prohibited.All rights reserved.

The data comprised in the document can be altered by the authors withoutpreliminary notice.

OPEN STOCK COMPANY

UKRAINIAN RESEARCH, DESIGN AND TECHNOLOGICAL TRANSFORMER INSTITUTE

OSC VIT

11 Dnepropetrovskoye shosse69069, Zaporozhye, Ukraine

Telephone: (0612) 52-64-91, 52-75-80Fax: (0612) 52-74-21, 52-81-26E-mail: [email protected]

WWW: http://www.vit.zp.ua/

DXF is trademark of Autodesk, Inc.Microsoft and Windows are registered trademarks of Microsoft Corporation

All the other names mentioned in the manual, are trademarks or registered trademarks of appropriatemanufacturers.


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CONTENTS

1 Field of the software application 42 Character and scope of calculations... 42.1 Characteristics of the transformer being calculated...42.2 Values to be calculated . . 42.3 Preparation of input data 52.4 Calculation results..52.5 List of diagnostic messages .. .53 Description of the software interface. ..64 Requirements to computer and operating system . ..6


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1 FIELD OF THE SOFTWARE APPLICATION

ENDINS software is used for execution of a calculation part for designing general-purpose transformers for voltage classes of 110 1150 kV, operating at a frequency of

50(60) Hz.Application of the software in calculation of insulation of 750-1150kV transformers

requires additional knowledge of know-how in design of insulation, characteristic fea-tures of technology of manufacture, treatment and checking of insulation quality.

The software is intended for calculation of safety factors of strength along the speci-fied field lines in oil ducts of oil-barrier insulation and estimation of the highest maximumelectric field intensity in the point (in oil) and the highest tangential component of electricfield along interfaces of dielectrics in the specified zone.

Safety factors of strength of oil ducts shall be calculated under the action of thespecified test voltages (lightning and switching impulses, one-minute and one-hour powerfrequency voltages). Estimation of the maximum intensity being the highest in the point

(in oil) and tangential component along the interfaces of dielectrics in the specified zoneis carried out under the action of one-minute voltage and full-wave lightning impulse, re-spectively.

2 CHARACTER AND SCOPE OF CALCULATIONS

2.1 Characteristics of the transformer being calculated2.1.1 Design models can be made for axially symmetric and plane fields with a sys-

tem of electrodes being asymmetric or symmetric relative to the plane of symmetry orsymmetry of the bodies arranged near to the earthed plane.

2.1.2 Calculations of safety factors of strength shall be made for insulation of trans-formers and autotransformers, having the following design features:

- Concentric round windings (interleaved, continuous, continuous with contrashields, helical, cylindrical multi-layer).

- Oil-barrier insulation with an employment of concentric cylinders, washers and an-gle washers.

- Insulated shielding rings at the edges and inside the windings.- Rectangular (ordinary, subdivided, transposed) or round insulated wires.2.1.3 For calculation of safety factors and estimation of the maximum and tangential

component the software obtains average intensities along the field lines in oil ducts,lengths of field lines and other parameters of electric field from ELAX-2D program.

2.2 Values to be calculated2.2.1 The software calculates safety factors of strength for all specified field lines atfull-wave lightning and switching impulses, one-minute and one-hour power frequencyvoltages. For insulation between the edges of the windings safety factors are calculated:in oil ducts at the surfaces of the windings (along insulation of shielding ring, along sur-faces of insulation of the outer coils), in oil ducts between angle washers, between anglewashers and cylinders or washers, depending on electric field configuration.

2.2.2 There is also estimated an acceptability in the specified insulation design of thecalculated highest maximum intensity in a point (in oil) and the highest tangential compo-nent of intensity along interfaces of dielectrics in a specified zone.

2.2.3 Execution of a series of calculations allows to obtain not only calculated safety

factors of strength of the insulation between the windings at the edge of the windings, butalso to improve insulation design as applied to materials and technology used by theCUSTOMER in manufacture and treatment of insulation.


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2.3 Preparation of input data.2.3.1 It is recommended to start calculation of the insulation between the ends of the

windings if a sketch is available, comprising the insulated shealding ring (if any), the first3-4 insulated coils of the windings, the most important insulating cylinders, angle washersand other insulating barriers.

For correct forming of electric field in a design zone it is necessary to simulate theremaining part(s) of the winding(s).

There should be calculated safety factors of oil ducts near shielding rings, at theouter coils and between the most important parts of insulation.

2.3.2 Instructions on calculation of electric field are given in the Users manual ofELAX-2D program. Usually calculation of insulation at the edge of the winding is made inthe mode of axially symmetric electrostatic field.

Calculation of the field is made for the models comprising: conductors in a form ofsolid bodies and thin shells with the specified potentials, dielectrics in a form of solid bod-ies and external dielectric in which all the remaining bodies and shells are arranged.

Simultaneous calculation for several distributions of potentials and (or) charges of thebodies is possible.2.4 Calculation results2.4.1 Calculation results of insulation electric strength are produced in a tabular form

with the indication of coordinates of origin of calculated field line, length of field line, op-erating intensity and calculated safety factors under the action of test voltages: long-duration elevated (one-hour) power frequency voltage, one-minute power frequency volt-age, switching impulse voltage and full-wave lightning impulse voltage. Minimum safetyfactors of the insulation design being calculated are also produced.

2.4.2There is produced information on estimation of permissibility of the highestmaximum intensity in the point in oil and the highest tangential intensity along interfaces

of dielectrics in a specified zone.2.4.3 Arrangement of field lines with minimum calculated safety factors in oil ducts

and of points of the maximum intensity in oil and the highest tangential intensity are pro-duced graphically by ELAX2D program.

2.4.4 If minimum calculated safety factors of strength of correctly formed model areequal to or exceed 1.15, and the maximum intensity in any point of the design zone doesnot exceed 10kVeff/mm (at one-minute voltage), as well as the highest intensity along thesurface of insulating parts at the effect of full-wave lightning impulse does not exceed 15kVm/mm, electric strength of the calculated part of insulation structure is considered tobe sufficient. Therewith it is expedient to analyze distribution of all calculated safety fac-tors with the aim of determining a possibility of simplification of the structure in places

with calculated safety factors being higher than, for example, 1.5.2.4.5 An example of calculation results is given in Table 1 and in Figure 1.2.5 List of diagnostic messages.List of diagnostic messages is given in users manual of ELAX2D program.


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3 DESCRIPTION OF THE SOFTWARE INTERFACE

The software is executed in a form of Dynamically linked library - DLL files forWINDOWS operating system. Interface of the software is in English.

4 REQUIREMENTS TO COMPUTER AND OPERATING SYSTEM

The software shall be executed on computers: Pentium-4 1500MHz, RAM 1024 Mb,HDD (400Mb of the disk free space shall be used for storage of temporary files whileexecuting calculations under the software). Operating system is WINDOWS NT, 2000Pro, XP Pro.


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Figure 1 Fragment of electric field at the lower edge of 500/230 kV

autotransformer windings


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Table 1 Minimum calculated safety factors of strength in oil ducts at the loweredge of the windings

+------------+------+------+------+------+------+------+--------------------+------+| | | | | | | Safety factor | |

| Nt_Nrt | R | Z | E | Ki | L +------+------+------+------+ Zone || | | | | | | LDPF | 1MPF | SI | FLI | |

+------------+------+------+------+------+------+------+------+------+------+------+

| Field lines with minimum safety factors |+------------+------+------+------+------+------+------+------+------+------+------+

|1(0)_912 | 687.5| 172.7| 1.72| 0.96| 4.79| - | 1.30| - | - | 3 |

|1(0)_913 | 689.2| 170.4| 1.73| 0.96| 4.81| - | 1.29| - | - | 3 ||1(0)_914 | 691.2| 168.2| 1.72| 0.96| 4.90| - | 1.29| - | - | 3 |

|1(0)_915 | 693.4| 166.2| 1.69| 0.96| 5.05| - | 1.30| - | - | 3 |

+------------+------+------+------+------+------+------+------+------+------+------+| Field line with the lowest safety factor |

+------------+------+------+------+------+------+------+------+------+------+------+

|1(0)_914 | 691.2| 168.2| 1.72| 0.96| 4.90| - | 1.29| - | - | 3 |

+------------+------+------+------+------+------+------+------+------+------+------+

Field strength in insulation

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