INTERRUPTORES DE SF6 WIKA JAR

Gas density monitors

Gas density switches

Gas density trans-

mitters

SF6 Gas Density Monitoring

Julio

Stamp

Contents

We wish to acknowledge our thanks to the following companies for

the provision of photographs: ABB, Alstom, Felten & Guilleaume,

Passoni & Villa, Solvay Fluor und Derivate, Trench

WIKA in the T & D industry 2

SF6 gas density monitoring

Introduction 3

Gas density indicators 4

Gas density monitors with localindicator and alarm contacts 4

Gas density monitors with localindicator, alarm contactsand external temperature sensor 4

Gas density switches(bimetal compensated) 5

Gas density switches(reference chamber compensated) 5

Gas density transmitters 5

Accuracy, calibration pressure 6

Deviation from the reference isochore 7

Calibration curves 7

Hermetically sealed cases 8

Gas compounds SF6 / N2 8

Computer aided calibration 8

Alarm contacts 9

Materials 9

Definition of essential terms 10

Design and calculation 10

Review of product information 11

Medium-voltage level 12

High-voltage level 16

Medium- and high-voltage level 24

References 25

2

WIKA in the T & D industry

Our knowledge for your success

In the course of the last five decades the name WIKA has

become a symbol for sophisticated solutions in the field of

pressure and temperature measurement. Our ever

increasing ability is the basis for implementation of innova-

tive technologies in the form of reliable products and

efficient system solutions.

Our top ranking in the world market today is thanks to the

consequent devotion to ensure first class quality backed

by more than 3,700 employees in the WIKA group of

companies. More than 500 experienced distribution

companies alone, ensure that our customers are serviced

individually and competently advised right from the outset.

Everywhere and at any time.

Made by WIKA

Apart from the headquarters in Klingenberg, there are

modern production facilities in Brazil, China, India,

Switzerland, South Africa and America. Here high quality

pressure gauges, thermometers and pressure or

temperature control instruments are developed and

produced. Altogether over 30 million instruments per

annum are despatched to customers in more than 100

countries. Some 300 million WIKA-instruments are in

service worldwide. For applications in SF6 gas-insulated

switching systems, some 400,000 instruments were

supplied.

A technical staff of more than 200 engineers and designers

are in continuous search to provide solutions for innovative

products, improved material and profitable production

methods. Close cooperation with universities and research

institutions together with extensive field experience ensure

the development of application-specific solutions.

The layout fundamentals concerning the compensation of

SF6 gas density monitors, gas density switches and gas

density transmitters are being prepared in our laboratories.

WIKA has been an acknowledged contact for questions

relating to gas density measurement in the T & D industry

for decades. Our products are used anywhere in the T & D

sector where safety-relevant process parameters have to

be monitored.

Alexander Wiegand, Chairman and CEO, WIKA

3

Introduction

Safe and reliable

Special solutions to meet the highest demands for

operational safety and reliability have been developed by

WIKA for the power generation, transmission and

distribution sector. WIKA has specifically developed

temperature-compensated pressure gauges for use in

switchgear that ensure safe operation of SF6 gas-insulated

equipment. Because of its exceptional properties, sulphur

hexafluoride (SF6) is used as an insulating, quenching and

cooling gas in manifold applications. Main areas of

application for SF6 gas in electrical engineering are:

� high-voltage air-insulated substations (AIS)

- life tank breakers

- dead tank breakers

� high-voltage gas-insulated substations (GIS)

� gas-insulated high-voltage cables

� instrument transformers

� transformers

Switchgear is hermetically sealed and filled with SF6 gas.

The material properties of SF6 gas which are essential for

such applications, such as the electrical disruptive strength

or the electric light arc quenching capability, are dependent

on the density of the SF6 gas. The required SF

6 gas density

depends on the respective application. This means that the

functional safety of the entire system is strongly dependent

on the density of SF6 gas which is why it must be

monitored.

Normal pressure gauges are not suitable for this monitoring

operation because, with the same gas density, the gas

pressure is dependent on the gas temperature in closed

gas systems. This dependency is specific to the used gas

and is shown in a vapour pressure diagram with lines of

identical density, the so-called isochores. Therefore the

temperature must also be

registered by suitable

monitoring systems

working on the pressure

measuring principle. This

enables the monitoring unit

to correct the measured

pressure value according to

the isochores. Such special

pressure gauges /

transmitters are the gas

density monitors as

described herein.

The right solution for every application

WIKA produces mechanical and electronic SF6 gas density

monitors in a variety of versions. It goes without saying that

it is also possible to produce customer-specific versions

apart from the standard models introduced in this

brochure. This ensures that the user can select the most

suitable instrument for his specific monitoring operation.

4


Gas density indicators

These instruments indicate the temperature-compensated

SF6 gas pressure. They are adjusted individually to their

calibration pressure. The accuracy is ± 2.5% within the

temperature range -20 ... 60°C. These figures refer to the

calibration pressure. For further details as to the selection

of the calibration pressure, please refer to the chapter

accuracy and calibration pressure.

Gas density monitors with local indicatorand alarm contacts

Gas density monitors with local indicator and alarm

contacts combine the indicator and switching function.

Each gas density monitor is adjusted individually to its

calibration pressure. In order to define the bimetal

compensation exactly, WIKA uses a computer-controlled

adjustment machine. Apart from considering the calibration

pressure this machine also takes into account the different

factors influencing the instrument, for example, the

bourdon tube and the characteristic data of the bimetal

used for temperature compensation. The class accuracy is

±2.5% within the temperature range -20°C ... 60°C. The

switching accuracy is ±2.5%. The information concerning

the switching accuracy refers to the calibration pressure.

For further explanations, please refer to the

chapter accuracy and calibration pressure.

Gas density monitors with local indicator,alarm contacts and external temperaturesensors

The temperature of the SF6 gas is measured by the external

temperature sensor. Therefore this monitor type is

particularly suitable for such applications where due to the

installation conditions it cannot be assured that the SF6 gas

temperature corresponds as closely as possible to the

ambient temperature of the gas density monitor.

Compensated pressure course Temperature-dependent pressure courseSF6 gas pressure in thecompartment

bar

Pfilling

5


Gas density switches(bimetal compensated)

Each instrument is adjusted individually to its calibration

pressure. As in the case of the gas density monitors with

local indicator and alarm contacts, the adjustment takes

into consideration the individual influencing factors of the

instrument. In addition the pressure of the reference

chamber is compensated.

The gas density switches use one suitable bimetal for

temperature compensation for each contact. This means

that each contact has its own calibration pressure which is

the same as the contact switching point. Therefore no

additional deviations in switching accuracy occur between

the different contacts as is the case of the previously

described gas density monitors with local indicator and

alarm contacts. There is no need for the user to specify the

calibration pressure.

Noteworthy is also the patent-protected

concept of these gas density switches. This

special concept makes these instruments

particularly suitable for outdoor installation.

The case of the gas density switch is

hermetically sealed.

Gas density switches(reference chamber compensated)

The working method of the gas density switch 851.52.063

follows the reference chamber principle. The reduction of

the dimensions has been a special target during the

development of this instrument. This switch can be used

for applications in the high-voltage level.

Moreover, this gas density switch may be

used in gas-insulated switchgear and life

tank breakers.

Gas density transmitters

The compensation of the temperature-dependent isochore

pressure change is done electronically. This procedure

ensures that the specified accuracy within the density

range of the application is kept. There is no need for the

user to specify a calibration pressure.

The measuring system of the gas density transmitter does

not need a reference chamber and works

in the pressure datum absolute pressure.

The measuring system of the gas density

transmitter is a modified piezoresistive

pressure sensor element and an electronic

temperature sensor. Compatibility to aggressive

media is ensured by an inline stainless steel

diaphragm. Silicon oil filling under a high vacuum

process transmits the SF6 gas pressure from the

stainless steel diaphragm to the silicon diaphragm

of the pressure sensor element. This so-called

internal chemical seal is a completely welded unit

to exclude possible conflict of soft sealing material

with the measured medium. This means no soft

sealing elements are used. This excludes also

leakages caused by the transmitter itself.

The integrated electronic amplifier is completely embedded

and provides a 2-wire signal output of 4 ... 20 mA as is

usual in measuring technology. Particular importance has

been attached to high quality electromagnetic compatibility

(EMC) of the gas density transmitter. This ensures

protection against interference and also

fulfills the high demands which occur

when operating high-voltage and medi-

um-voltage switchgear / systems.

6


Indication accuracy of the calibration pressure

Accuracy, calibration pressure

The reference isochore is defined by the calibration

pressure. Accuracy statements refer to the calibration

pressure. In the case of gas density indicators the filling

pressure of the switchgear is used as calibration pressure.

The calibration pressure has to be determined for gas

density monitors with local indication and alarm contacts.

The user has to select an optimal calibration pressure in

accordance with his particular application.

The importance of the function is determined when

selecting the calibration pressure. Usually more importance

is attached to the switching function than to the indicator.

The SF6 gas pressure is at 20°C and corresponds with the

calibration pressure when one single switch point is to be

controlled. Where two switching points are concerned

maximum accuracy can be achieved when the calibration

pressure is in the middle of the two switching points. If the

contacts have different significance in their controlling task

a calibration pressure has to be determined that

corresponds with the SF6 gas pressure of the most

important switching point.

The reference isochore is defined when the calibration

pressure is determined. However, since the isochores for

different SF6 gas pressures have different gradients,

deviations will be given in addition to the accuracy related

to the calibration pressure. The magnitude of the deviation

depends upon the SF6 gas temperature, calibration

pressure and switching point pressure. This deviation

decreases the closer the calibration pressure gets to the

switching point pressure. The magnitude of the switching

error can be reduced by selecting a suitable calibration

pressure (illustration: deviation from reference isochore).

Applicable for gas density monitors and gas density

indicators for 20°C is:

Indicating error: ±1%

Switching error: ±1%

Applicable for gas density monitors and gas density

indicators in the temperature-compensated range

from -20 to +60°C is:

Indicating error: ±2.5%

Switching error: ±2.5%

Density Pressure

temperaturecompensated

Density

calibration

tolerance band indicating accuracy

tolerance band higher switching

accuracy (upon request)

calibration

7


Deviation from the reference isochore;representation with a small difference between P

S1 and P

S2

Deviation from the reference isochore;representation with a large difference between P

S1 and P

S2

Deviation from the reference isochore

As explained in the chapter accuracy and calibration

pressure, all accuracy details refer to the reference isocho-

re for bimetal-compensated gas density controllers. The

SF6 gas temperature characteristic reveals there are

correspondingly different gradients at various pressures.

Due to this fact there is a reference isochore error as well

as the deviation from the reference isochore. The

magnitude depends on the different gradients of the

pressure characteristic.

Calibration curves

The basics for determining the compensation are as laid

down in our laboratory. We can calculate any given

magnitude status required for determining the SF6 with the

help of our own software for calculating the interrelations-

hip betweeen pressure and temperature. To be able to

consider non-linear SF6 behaviour we use our electronic

gas density transmitter to determine the design for virile

applications. p-t diagrams are measured in our laboratory

to validate the calculations.

Pdeviation

Pfilling

PS1

PS2

reference =

Pdeviation

Pfilling

PS1

PS2

reference =

8


Atmospheric pressure fluctuations

Hermetically sealed cases

By using chromium nickel steel cases, which are welded to

the measuring element, we can offer completely

encapsulated systems. The gas density of 1·10-5 [mbar l/s]

is determined by WIKA in individual tests with the helium

testing systems, thus ensuring:

� No influence through fluctuations in daily ambient air

pressure

� No influence through installation altitude

� Alarm contacts and measuring mechanism protection

against moisture, H2S etc.

Gas mixtures SF6 / N

2

Gas density monitors can be designed for gas mixtures for

use in cold climatic regions. These can also be designed

and built for special mixtures used in

gas-insulated lines.

Computer aided calibration

Computer aided calibration is the key to the optimal design

of density monitors. WIKA offers high precision in meeting

maximum demands in switchgear reliability. WIKA provides

the concept to achieve measuring accuracy in individual

measuring systems.

The tube behaviour is measured in each measuring system.

The kinematics can be designed optimally with exact

knowledge of the measuring element characteristics. In

addition to this the different assemblies are then carefully

tested. Switching accuracies up to 2.5% are possible by

combining computer aided calibration

with intensive testing and

the use of high quality

materials.

Gas density monitors may also be used incold climatic regions

9


Chromium nickel steelmeasuring systems Switchgear

Alarm contacts

Threshold values are usually controlled with magnetic snap

action contacts or microswitches. Density monitors with

supplementary electrical equipment are subject to individu-

al testing.

Density limits below the filling pressure (e.g. alarm,

emergency off) are controlled by contacts designed make

on declining density. In the case of increasing density the

threshold value (e.g. filling pressure reached signal) takes

the form of a contact which makes when filling pressure is

exceeded. These contacts are adjusted and fixed at the

factory to meet customer requirements.

Material

Used are high quality chromium nickel steel measuring

systems by which means we can achieve a measuring

system seal from 1·10-8 [mbar l/s] in the long term.

Definition of essential terms

Filling pressure

Nominal system pressure of the monitored SF6 gas tank at

+20°C. This information is required to dimension the

pressure measuring element where mechanical gas density

monitors are concerned (overload limit).

Calibration pressure

The calibration pressure defines the reference isochore for

temperature compensation.

Temperature compensation

The temperature compensation of the gas density monitor

effectively corresponds with its isochore when SF6 pressure

is at 20°C.

Switching point

The switching point defines the adjusted switching

pressure of the contact at SF6 gas

temperature +20°C.

10


Design and calculation

Using the WIKA software SF6 gas engineers and design

companies can calculate the relevant data for dimensioning

SF6 tanks. This software simulates the phase diagram in

accordance with Prof. Dr.-Ing. R. Döring to ensure highest

accuracy.

The WIKA SF6 software may be ordered using the fax form

on the back of this brochure.

11

Contents: range of products

Range of productsMedium-voltage level

233.52.063 Gas density monitor 12

233.52.063 Gas density indicator 13

851.52.063 MV Gas density switch(reference chambercompensated) 14


High-voltage level


233.52.100 Gas density indicator 17

233.58.100 Gas density monitor,EdF design 18

233.52.100 Gas density monitorwith externaltemperature sensor 19

851.52.063 HV Gas density switch(reference chambercompensated) 20

851.51.080 Gas density switch 21

851.51.100 Gas density switch 22

851.13.900 Gas densitytransmitter 23

Medium and hig-voltage level

851.15.505 Gas densitytransmitter 24

Connections / references 25

12

Medium-voltage

� local indicator with alarm contact

With the design of model 233.52.063, WIKA now offers the

world's smallest gas density monitor. The indication and

switching functions are integrated in this compact & high

precision measuring instrument. WIKA can now offer all the

advantages of its market proven system of bimetal-

compensated measurement, with space saving in mind.

Gas density monitorGas density monitor

Case

� fully welded stainless steel, leakage rate 1·10-5 mbar·l/s

(Helium leak test)

� hermetically sealed design

Measuring element

� welded stainless steel, leakage rate 1·10-8 mbar·l/s

(Helium leak test)

� long-term stability ensuring little need for re-calibration

233.52.063

13

Medium-voltage

� local indicator

With the design of model 233.52.063, WIKA offer the

world's smallest gas density indicator. The instrument

features local indication of the gas density.


Case


(Helium leak test)


Measuring element


(Helium leak test)


233.52.063

14

Medium-voltage

� reference chamber compensated

For the use in ring-main units, WIKA has designed a gas

density switch using the reference chamber principle. The

hermetically sealed gas density switch features up to 2

microswitches. All internal electrical connections offer

protection to IP68.

Gas density switchGas density switch

Case


(Helium leak test)

� hermetically sealed design (IP 68)

Measuring element


(Helium leak test)

851.52.063 MV

15

Medium-voltage

� for indoor installation


This gas density monitor is designed for indoor installation

and features protection to IP54.


Case

� stainless steel

Mechanical connection

� sealing surfaces microfinished (Rz = 10 µm)

� elongated sealing pin

212.22.100

16

High-voltage

� for outdoor installation


This gas density monitor is an instrument for universal use

in any SF6 gas application. Suitable for use in high-voltage

switches, gas-insulated switching units and transformers,

especially for use in medium-voltage switchgear, which

work under adverse climatic conditions.


Case


(Helium leak test)


Measuring element


(Helium leak test)


233.52.100

17

High-voltage

� for indoor installation

� local indicator

This instrument is designed for use in applications in which

the indicator is to function with an accuracy of ±2.5% of

the full scale value. It is often used in combination with

density switches. End users thus obviate the need for

conversion or graphic evaluation of the correlation between

pressure and density.

Gas density indicatorGas density indicator

Case


(Helium leak test)


Measuring element


(Helium leak test)


233.52.100

18

High-voltage


� EdF design terminal case

Based on the sturdy design of the cable box, the gas

density monitor 233.58.100 has approval for mains

operation of EdF. The cable connections of these

instruments utilise glass insulation.This design is used in

high-voltage switches in outdoor switching fields and gas-

insulated switching units.


Case


(Helium leak test)


� stainless steel cable gland (EdF)

Measuring element


(Helium leak test)


233.58.100

19

High-voltage



� external temperature sensor

Gas density monitors with external temperature sensor

measure the temperature at any location even when it is

located up to 6 m apart from the instrument. It is

particularly suited for such applications where due to the

installation conditions it cannot be assured that the relevant

gas temperature corresponds as closely as possible to the

ambient temperature of the gas density monitor.

Noteworthy is also the short response time of the

compensating system.

Case


(Helium leak test)


External temperature sensor

� maximum length 6 m

233.52.100


20

High-voltage

� reference chamber compensated

The working method of the gas density switch 851.52.063

follows the reference chamber principle. Size reduction has

been a specific task during the development of this

instrument. This product can be used in all high-voltage

level applications. Specifically, this gas density switch may

be used in gas-insulated switchgear and life tank breakers.


Case


(Helium leak test)


Measuring element


(Helium leak test)


851.52.063 HV

21

High-voltage

� bimetal compensated

Model 851.51.080 is a bimetal-compensated gas density

switch. Each contact is compensated by its own bimetal

strip, providing all switching contacts with an individual

reference isochore, which is determined by the switching

pressure. The different gradients of the SF6 gas curves do

not cause additional deviations from the switching points.

Case


(Helium leak test)


Measuring element


(Helium leak test)


851.51.080


22

High-voltage

� bimetal compensated

� increased switching capacity

Model 851.51.100 is a bimetal-compensated gas density

switch. Each contact is compensated by its own bimetal

strip, providing all switching contacts with an individual

reference isochore, which is determined by the switching

pressure. The different gradients of the SF6 gas curves do

not cause additional deviations from the switching points.


Case


(Helium leak test)


Switching contacts

� increased switching capacity

851.51.100

23

High-voltage


� density-proportional output signal4...20 mA

Gas density transmitters are electronically compensated.

The compensation follows the non-linear behaviour of SF6

gas, which is based on volatile applications. All density

transmitters work in the absolute pressure datum. The

piezoresistive sensor is insulated from the measuring

chamber by a chemical seal. All wetted parts are made of

stainless steel and welded. WIKA gas density transmitters

are suitable for gas-insulated switchgear. The field case

provides adequate access for cable terminations and

meets highest EMC standards.

Case

� fully welded stainless steel

� un-affected by atmospheric pressure fluctuations

� un-affected by installation altitude

� protection to IP 67

� field case design meets high EMC standards

851.13.900

Gas density transmitterGas density transmitter

24

Medium and high-voltage

� density-proportional output signal4...20 mA

Gas density transmitters are electronically compensated.

The compensation follows the non-linear behaviour of SF6

gas, which is based on volatile applications. All density

transmitters work in the absolute pressure datum. The

piezoresistive sensor is insulated from the measuring

chamber by a chemical seal. All wetted parts are made of

stainless steel and welded. Model 851.13.505 is suitable

for indoor installation of gas-insulated switchgear.

Gas density transmitterGas density transmitter

Case

� fully welded stainless steel

� un-affected by atmospheric pressure fluctuations

� un-affected by installation altitude

� protection to IP 54 up to IP 67

851.13.505

Connections / references

Choice of electrical andmechanical connections

Choice of electrical andmechanical connections

mechanicalconnections

electricalconnections

ReferencesReferences

ABB

Alstom

Badenwerk AG

Bayernwerk AG

Berliner Kraft- und Licht AG

China Light and Power

DILO

EdF

Elin Holec High Voltage

ENEL

Energie-Versorgungs

Schwaben AG

Felten & Guilleaume

Fuji

Hamburgische Elektrizitäts-

werke

Hitachi

Hongkong Electric

Hyosung Industries

Hyundai

KEPCO

Manufacturas Electricas

Meidensha

Merlin Gerin

Mitsubishi

National Grid

Nissin

Nouvo Magrini Galileo

Ontario Hydro

Ormazabal

Passoni & Villa

Powergrid

Preussen Elektra AG

VA Tech Reyrolle

Ritz Meßwandlerbau

RWE

Schneider Electric

Siemens

Takaoka

TEPCO

TNB

Toshiba

Trench

UNESA

TPC

VEAG

VEW

W. Lucy

25

WIKA Alexander Wiegand GmbH & Co. KG

Alexander-Wiegand-Straße 30

63911 Klingenberg • Germany

Telefon 0 93 72 / 132-8970

Fax 0 93 72 / 132-8966

E-Mail [email protected]

www.wika.de

Fax+49/93 72/132-8966

Sender’s comments

9018255 D 3 WEI 1001

Please send us the WIKA SF6 software

for €180,-

Please send us your overview brochure for gas

density measurement

Please send us the WIKA catalog on CD-Rom for

pressure and temperature measurement

Please give us a call

Field of action

High voltage switchgear

Medium voltage switchgear

Gas insulated high voltage cables

Instrument transformers

Transformers

Firstname, Name

Company

Street/Number

Postal Code/City

Country

Phone

E-Mail

Department

Fax

Julio

Stamp

INTERRUPTORES DE SF6 WIKA JAR

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