2770 501-6 en, Rev. 4

Gas insulated wall bushing, type GGFLInstallation and maintenance guide

This document must not be copied without our written permission, and the contents thereof must not be imparted to a third party nor be used for any

unauthorized purpose. Contravention will be prosecuted.

Safety informationKeep this instruction available to those responsible for the installation, maintenance, and operation of the bushing.

The installation, operation, and maintenance of a bushing present numerous potential unsafe conditions, including, but not limited to, the following:

High pressures

Lethal voltages

Moving machinery

Heavy components

Slip, stumble or fall

Specialized procedures and instructions are required and must be adhered to when working on such apparatus. Failure to follow the instructions could result in severe personal injury, death, and/or product or property damage.

Additionally, all applicable safety procedures such as regional or local safety rules and regu-lations, safe working practices, and good judgement must be used by the personnel when installing, operating, maintaining and/or disposing such equipment.

Safety, as defined in this instruction, involves two conditions:

1. Personal injury or death.

2. Product or property damage (includes damage to the bushing or other property, and reduced bushing life).

Safety notations are intended to alert personnel of possible personal injury, death or prop-erty damage. They have been inserted in the instructional text prior to the step in which the condition is cited.

The safety conditions are headed by one of the three hazard intensity levels which are de-fined as follows:

DANGERImmediate hazard which will result in severe personal injury, death, or property damage.

WARNINGHazard or unsafe practice which could result in severe personal injury, death, or property damage.

CAUTIONHazard or unsafe practice which could result in minor personal injury, or property damage.

DANGERThe bushing should always be earthed and de-energized when being worked on.

WARNINGIn view of the risks involved in lifting pressurised items, no lifting should take place at more than transport pressure.

The bushing is provided with a bursting disc as protection against overpressure. Do not in any circumstances exceed 700 kPa (7.0 bar) gauge pressure.

The test tap should never be open during operation. It should always be connected to earth directly or via an external impedance. The protective cover earths the test tap automatically when it is screwed on. Note that this does not apply when the tap box terminal is attached to the test tap.

Prior to shipping from the manufacturer, the bushing is filled with pure nitrogen at transport pressure 125 kPa (1.25 bar) absolute at 20°C. If the bushing is delivered with supports for the conductor tube during transport, the bush-ing is filled with nitrogen at transport pressure 125 kPa (1.25 bar) absolute at 20°C. See chapter 1.4 Mechanical data for information.

Table of contents

1. Description ________________________________________________________71.1 Design _______________________________________________________71.2 Operating conditions ___________________________________________81.3 Spare parts ___________________________________________________81.4 Electrical data _________________________________________________81.5 Mechanical data _______________________________________________81.6 Gas density ___________________________________________________81.7 Earthing ______________________________________________________10

2. Installation ________________________________________________________112.1 Recommended fitting sequence, alternative 1 ______________________112.2 Recommended fitting sequence, alternative 2 ______________________112.3 Special tools and material required ________________________________122.4 Transport, unpacking and lifting __________________________________12

2.4.1 Transport _________________________________________________122.4.2 Unpacking ________________________________________________122.4.3 Lifting ____________________________________________________132.4.4 Shipping supports _________________________________________14

2.5 Check before installation ________________________________________152.5.1 Insulation _________________________________________________152.5.2 Through-resistance ________________________________________152.5.3 Density monitor ___________________________________________152.5.4 Pressure gauge ___________________________________________15

2.6 Pressure gauge and density monitor ______________________________162.7 Gas filling and emptying _________________________________________16

2.7.1 Bushings with shipping supports _____________________________162.7.2 Bushings without shipping supports __________________________16

2.8 Test tap _______________________________________________________182.9 End shield ____________________________________________________192.10 Outer terminal ________________________________________________19

3. Maintenance and supervision ________________________________________203.1 Gas __________________________________________________________203.2 Electrical conduction ___________________________________________203.3 Hydrophobicity check ___________________________________________20

4. Disposal after end of service life ______________________________________20

5. References ________________________________________________________20

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1. Description

1.1 Design

This wall bushing is a gas-insulated bushing intended for use in HVDC valve halls. The main insulation consists of compressed SF6 gas (sulphur hexafluoride). The bushing consists of a cast aluminium intermediate flange fitted with two insulators, one of them for indoor use and the other for outdoor use.

The insulators consists of a glass fibre reinforced epoxy tube fitted with silicone rubber sheds. The respective connections to the intermediate flange and the cover are of cast alu-minium and are fastened with screws and nuts and provided with O-ring seals. All enclosing parts are designed to Swedish pressure vessel standards (TKN 1987). Current passes from the outdoor end connection through the cover to a tubular aluminium conductor. There is a corresponding arrangement at the indoor end to carry the current to the indoor end con-nection. The current passes either via firmly screwed multiple contacts or threaded connec-tions of the conductor to the covers. The thermal movement is compensated by one of the multiple contacts allowing the conductor to move in axial direction. When the conductor is threaded to the covers the thermal movement is compensated by a flexible bellow. During transport, the conductor can be supported by a number of solid nylon bars. These have to be removed before the bushing is put in service. See chapter 2.4.4 and Fig. 5.

Both ends of the bushing normally have shields to minimise corona. See chapter 2.8 Outer shields.

The test tap is on the intermediate flange, which is also fitted with gas connections and a bursting disc and, if ordered, a voltage limiting device.

Cover

Silicone rubber sheds

Upper insulating fitting

Lower insulating fittingIntermediate flange

Conductor tube

M12 for earthing

Outdoor insulator

Fastening plane

Indoor insulatorRating plate

Test tap

Density guard

Bursting disc

Voltage limiting device

Shield

Shield

Shield

Cover

Flexible bellow

Fig. 1. Design.

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1.2 Operating conditions

The table below shows the standard technical specifications for the GGFL wall bushing. For condition exceeding the below values, please contact the manufacturer.

Common specifications

Application HVDC valve halls

Classification SF6 gas insulated bushing

Ambient temperature +60 to –20°C for use in valve halls or equivalent environments

Altitude of site < 1000 m

Type of immersion media SF6 gas at 5.7 bar absolute at 20°C

Markings Conforming to IEC/IEEE

1.3 Spare parts

In the event of major damage to the bushing, we recommend sending it back to the manu-facturer for repair and electrical testing. For certain parts that can be damaged or lost during transportation, spare parts can be ordered from ABB.

1.4 Electrical data

The capacitance between conductor and earth, C1, and the capacitance of the test tap, C2, is stated for each bushing in its test certificate. The data plate and dimensional drawing of the bushing give the test voltages, operating voltage and operating current.

Table 1.

Bushing Article No. Calculated C1 (pF) Calculated C2 (pF)

GGFL 1175 2773 015-B 140 ± 15 230 ± 25

GGFL 1300 LF 152 001-C 140 ± 15 230 ± 25

GGFL 1300 LF 152 001-D 140 ± 15 230 ± 25

GGFL 1300 LF 150 001-S 150 ± 15 230 ± 25

GGFL 1300 LF 152 001-L 155 ± 15 230 ± 25

GGFL 1425 LF 150 001-P 155 ± 15 230 ± 25

GGFL 1460 LF 152 001-E 140 ± 15 230 ± 25

1.5 Mechanical data

Table 2.

Bushing Article No. Mass (kg) with SF6 gas

Bending test load x 1 minute (N)

Shipping supports

GGFL 1175 2773 015-B 1260 10 600 No

GGFL 1300 LF 152 001-C 1410 6 000 Yes

GGFL 1300 LF 152 001-D 1500 4 000 Yes

GGFL 1300 LF 152 001-S 1300 4 000 Yes

GGFL 1300 LF 152 001-L 1500 4000 Yes

GGFL 1425 LF 152 001-P 1650 4000 Yes

GGFL 1460 LF 152 001-E 1600 4 000 Yes

1.6 Gas density

WARNINGIf the bushing is equipped with supports for the conductor tube during transport, these must first be removed. See Fig. 5. A vacuum/gas filling process must then be done. See chapter 2.7.

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The two purposes of the compressed SF6 gas are to cool the tubular conductor and insulate it from earth. Its capacity for doing so depends on the density of the gas. The bushing is filled for operation with gas at a pressure of 570 kPa (5.7 bar) abs. at 20°C. The gas density is monitored by a density monitor equipped with three switches, one for each alarm level. The first is activated at a pressure of 530 kPa (5.3 bar) abs. at 20°C to indicate a low gas density. The second signal level is activated at 520 kPa (5.2 bar) abs. at 20°C to indicate a very low gas density. The third level gives an alarm at 500 kPa (5 bar) abs. at 20°C, which is the dimensioning density for the bushing. In order to increase the redundancies, an extra density monitor may be installed in an existing gas valve. Fig. 3 shows an example of a cir-cuit diagram for connections to the density monitor. Terminals 13 and 23 are not shown.

At gas densities below 500 kPa the type test levels for dielectric strength do not apply. The ability of the bushing to conduct current declines progressively with falling gas density.

Fig. 2. Density guard.

Fig. 3. Circuit diagram example.

Alarm level 1 (530 kPa): Switch number D1 is activated, circuit 11-13 is opened and 11-12 is closed.

Alarm level 2 (520 kPa): Switch number D2 is activated, circuit 21-23 is opened and 21-22 is closed.

Alarm level 3 (500 kPa): Switch number D3 is activated, circuit 31-33 is opened and 31-32 is closed. At gas densities below 500 kPa the type test levels for dielectric strength do not apply.

Switch number D3 D2 D1

Ground

Terminal block number

P/T = nominal

33 31 32 23 21 22 13 11 12

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1.7 Earthing

DANGERThe bushing should always be earthed and de-energized when being worked on.

The bushing flange should be earthed in order to prevent electrical discharges between the bushing flange and the wall to which the bushing is installed. Applying a flexible cable between one of the M12 threaded holes in the flange and the mounting plate in the wall may do this.

112770 501-6 en, Rev. 4

2. Installation

2.1 Recommended fitting sequence, alternative 1

1. Check that all necessary tools, accessories and equipment are at hand. See chapter 2.3.

2. Check the packaging for damages. See chapter 2.4.

3. Unpack. See chapter 2.4.

4. Lift the bushing out and place it on ground. Use the supports that come with the box. Carry out visual inspection of the bushing. See chapter 2.4.2.

5. Lift and screw firmly into wall. See chapter 2.4.3.

6. Fit the shields. See chapter 2.9.

7. Preferable, after the end shields have been fitted, connect the bushing to the main circuit via the end connections. See chapter 2.10.

8. Remove the supports used during transport and mount the gas valve and rupture disc unit. See chapter 2.4.4.

9. Vacuum and gas filling process. See chapter 2.7.

10. Check the insulation and the through resistance. See chapter 2.5.1 and 2.5.2.

11. Mount the density guards on the bushing. See chapter 2.6.

12. Connect the signal cables to the density guards. See chapters 2.6 and 2.8.

13. Check the density guards. See chapter 2.8.

14. Earth the bushing.

Tightening torques according to Table 3.

Table 3. Tightening torques for screw joints.

For metallic screw joints (Nm)

M6 10 ±10%

M8 24.5 ±10%

M10 49 ±10%

M12 84 ±10%

M16 203 ±10%

M20 396 ±10%

M24 685 ±10%

2.2 Recommended fitting sequence, alternative 2

1. Check that all necessary tools, accessories and equipment are at hand. See chapter 2.3.

2. Check the packaging for damages. See chapter 2.4.

3. Unpack. See chapter 2.4.

4. Lift the bushing out and place it on supports on the ground, high enough for removing the transport supports. Secure the bushing, so that it can not fall down from the sup-ports. Carry out visual inspection on the bushing. See chapter 2.4.2.

5. Remove the supports used during transport and mount the gas valve and rupture disc unit. See chapter 2.4.4.

6. Vacuum and gas filling process. See chapter 2.7. Fill SF6 gas to transport pressure, 125 kPa (1.25 bar) abs. at 20°C.

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7. Lift and screw firmly into the wall. See chapter 2.4.3.

8. Fit the shields. See chapter 2.9.

9. Preferably, after the end shields have been fitted, connect the bushing to the main cir-cuit via the end-connections. See chapter 2.10.

10. Fill the rest of the SF6 gas, see chapter 2.7.

11. Check the insulation and the through resistance. See chapter 2.5.1 and 2.5.2.

12. Mount the density guards on the bushing. See chapter 2.6.

13. Connect the signal cables to the density guards. See chapters 2.6 and 2.8.

14. Check the density guards. See chapter 2.7.

15. Earth the bushing.

2.3 Special tools and material required

An optional lifting device and crane for sufficient lifting height and weight.

Working platform for sufficient height and weight.

Gas of correct kind in sufficient quantity.

Thermometer to measure ambient temperature, filling device appropriate to bushing fill-ing valve, and precision manometer with range covering at least 100 - 600 kPa abs.

Torque wrench with grip 13, 16 and 18 mm and torque 19.6 - 68 Nm.

Gas filling equipment.

Vacuum pump for emptying.

Fomblin or vasline.

2.4 Transport, unpacking and lifting

2.4.1 Transport

The bushing should be transported horizontally in its box with the support and cover in-tended for the purpose.

2.4.2 Unpacking

Before unpacking, inspect the packaging for transport damage. After unpacking, check the bushing and its accessories for transport damage, with particular attention to the following: end connections, all joints between flanges and their screw connections, gas valves, density monitor, pressure gauge, bursting disc, and end shields.

The internal pressure of the bushing may be measured by precision manometer covering at least 0 – 50 kPa ( 0 – 0.5 bar) gauge pressure to see if it is still transport pressure. The ambi-ent temperature should be taken into account in interpreting the resulting measurement.

WARNINGDamaging the silicone insulator may lead to partial discharge during operation.

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2.4.3 Lifting

During manufacture at ABB, the bushing is filled with pure SF6 gas for testing. For ship-ping, supports for the conductor are mounted and the bushing is filled with nitrogen gas to a transport pressure of 125 kPa (1.25 bar) abs. at 20°C. The bushing should be lifted and handled at transport pressure.

Use clean, soft slings around the intermediate flange and the outdoor top end. Secure that the silver plating or paint does not get damaged during lifting.

To achieve the correct mounting angle, an optional lifting tool and a counter weight can be applied to compensate the different centers of gravity. Adjust the counter weight so the bushing is horizontal, before inserting it into the wall, see Fig. 8. The maximum load on the counter weight is 250 kg.

Mount the bushing in the wall, see Fig. 9.

CAUTIONBe careful not to damage the silver plated contact surface when attaching the slings.

Bushing Article No. Mass for counterweight

GGFL 1175 2773 015-B 160 kg

GGFL 1300 LF 152 001-C 80 kg

GGFL 1300 LF 152 001-D 125 kg

GGFL 1300 LF 152 001-S 60 kg

GGFL 1300 LF 152 001-L 145 kg

GGFL 1425 LF 152 001-P 165 kg

GGFL 1460 LF 152 001-E 75 kg

Fig. 4. Lifting tool.

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2.4.4 Shipping supports

Three or four solid bars of nylon internally secure the conductor during transport. The bars are threaded and attached in the gas-tight covers, which are placed on the indoor side of the intermediate flange. Such bars are mounted as standard on some bushings, see chapter 1.5 Mechanical data. When solid bars are mounted, the bushing is filled with nitrogen to transport pressure 125 kPa (1.25 bar) absolute at 20°C. The solid bars shall be removed and the bushing filled with SF6 gas according to the following sequence:

- Clean the intermediate flange properly from dust and dirt. This is to make sure no par-ticles can fall down into the opened holes during assembly.

- Reduce the pressure of nitrogen through the gas valve on the intermediate flange

- Dismount the gas-tight covers and remove the nylon bars

- Slightly moisten the O-rings with fomblin or vaseline

- Put the gas-tight covers back on the intermediate flange and tighten the screws with 20 Nm

CAUTIONMake sure that both sealing O-rings are undamaged and correctly positioned in their re-specitve grooves.

- Evacuate the bushing down to 1 mbar and re-fill with pure SF6 gas. See chapter 2.6 Gas filling.

Fig. 5. Support for conductor during transport.

Density monitor

Test tap

Solid bars of nylon during transport

Gas-tight covers

152770 501-6 en, Rev. 4

2.5 Check before installation

The bushing may be checked on a number of points before being put into operation or fitted in the wall. The most important characteristics that may be checked are insulation, through resistance, density monitor and pressure monitor.

2.5.1 Insulation

The resistance is measured between end connection and test tap. The value should exceed 1000 MΩ. This may be checked before filling with gas. It may also be checked by a Doble-test of capacitance and loss factor. Maximum voltages:

- 10 kV between end connection and test tap plug at transport pressure.

- 2 kV between measuring tap plug and flange at transport pressure.

These measurements should be done before connection to the main circuit, otherwise the results may be highly misleading.

WARNINGThe test tap should never be open during operation. It should always be connected to earth either directly or via an external impedance. The protective cap automatically earths the test tap when it is screwed on. Note that if the tap box terminal is used, the test tap is not automatically earthed.

2.5.2 Through-resistance

Measurement of resistance between the bushing end connections. The normal value is in the region of 50 - 500 mΩ depending on rated current and bushing length. If such a mea-surement has been performed during the routine test, the value can be compared to the test record. The ambient temperature at the time should be taken into account in interpreting measurement results.

2.5.3 Density monitor

The switching density of the density monitor may be checked by a precision manometer. The ambient temperature at the time should be taken into account in interpreting measure-ment results.

All switches of the density monitor may also be checked by removing the monitor from the bushing. All three levels should then indicate low pressure. When re-installing the switch, all levels should indicate proper gas pressure.

2.5.4 Pressure gauge

The reading on the pressure gauge may be checked by a precision manometer.

WARNINGThe bushing is provided with a bursting disc as protection against overpressure. Do not in any circumstances exceed 700 kPa (7.0 bar) gauge pressure.

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2.6 Pressure gauge and density monitor

The pressure gauge is, if supplied, delivered separately from the bushing and is installed as follows: Unscrew the protective cap from the valve. Check that the valve and the pressure gauge orifice are clean. Insert the pressure gauge orifice into the valve and screw down the clamping nut. Torque at 20 Nm.

The fitting sequence for the density monitor is the same as for the pressure gauge, but add the following: Connect signal cables.

2.7 Gas filling and emptying

2.7.1 Bushings with shipping supports

For these bushings a special gas filling equipment with a vacuum pump is required. The bushing should be evacuated down to 1 mbar before SF6 gas is filled up to the specified pressure. If there are any questions about this, please contact the manufacturer.

2.7.2 Bushings without shipping supports

Pure SF6 is normally used as insulating gas. An N2 + SF6 mixture is used in extremely cold climates (below -30°C) and filling instructions for this is given in a separate documents.

The gas used should meet the requirements of IEC 60376 ”Specification of new SF6”.

The gas quantity required appears in the dimensional drawing. The bushing is filled with ni-trogen at 125 kPa (1.25 bar) abs. at 20°C at the time of delivery. Filling is carried out via the gas valve on the intermediate flange. See Fig. 6.

For environmental reasons, avoid letting gas escape when filling or emptying SF6. Try to keep the gas in a closed system at all times.

Apply the cap to the gas valve after filling, otherwise corrosive substances from the environ-ment may disrupt the sealing function.

M30 x 2

Fig. 6. Gas filling equipment and gas valve.

Gas valve on the bushing flange.

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Filling pressure in MPa (abs) shown on data plate

Ambient temperature in °CFilling pressure in MPa (gauge pressure) read on pressure gauge

0.57 -30°C -20°C -10°C 0°C +10°C +20°C +30°C +40°C

0.36 0.38 0.40 0.43 0.45 0.47 0.50 0.52

When correct gas pressure has been set, remove the filling hose and fit the airtight bonnet to the check valve.

Fig. 7. Nozzle for connection to gas valve.

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2.8 Test tap

The test tap is designed as directed in ANSI/IEEE C57.19.01-1991 Type A Normally Grounded Tap and may be supplemented by a voltage limiting device according to Fig. 8, alternative 1. Connection to control cubicle is then done via tap box 2769 522-D.

WARNINGThe test tap should never be open during operation. It should always be connected to earth directly or via an external impedance. The protective cover earths the test tap automatically when it is screwed on. Note that this does not apply when the tap box terminal is attached to the test tap.

Earthing is not made automatically on test taps equipped with the tap box.

Tap box 2769 522-D

For connection to control cubicle (Pr 22.5)

Test tap 2769 523-F

Alternative 1 when voltage limiting device and tap box are included in delivery.

Test tap 2769 523-F

Alternative 2 when voltage limiting device is not included in delivery.

Fig. 8. Test tap.

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2.9 End shield

End shields are attached to existing screws at both ends of the bushing. The fitting of end shields should be carried out with the bushing filled to no more than transport pressure.

2.10 Outer terminal

CAUTIONBefore connection of untreated aluminium clamps, the outer terminals should always be cleaned with Scotch-Brite or similar product and lubricated with a suitable contact paste or a suitable grease before connection to the main circuit.

The outer terminals are normally supplied already mounted on the bushing. If they are not, or if they have to be replaced, the following applies: The contact surfaces on the bushing cap and the internal contact surface of the terminal have been surface-treated and should not be brushed before mounting, but they should be cleaned. Contact paste or grease should not be used between the terminal and the cap.

The compression ring, the O-ring and the terminal should be assembled according to Fig. 10.

Tighten first the screws that press the connection against the cap (M10), then the screws that compress the O-ring via the compression ring (M8). It is extremely important that tight-ening is done in stages or alternately so that the end connection and sealing ring are not tightened obliquely.

Fig. 9. End shield.

6 brackets, attached to existing screws

End connection, outer terminal

Outdoor side shield. Indoor side shield is not part of delivery from ABB Components.

Drain hole

Fig. 10. Fitting of end connection.

Outer terminal

Torque 20 Nm

Hex head screw M8 x 40

Spring washer 8,4 x 18,1

O-ring 99,1 x 5,7O-ring compression ring

Torque 40 Nm

Hex head screw M10 x 60

Washer 10,5 x 22 x 2

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3. Maintenance and supervisionGGFL bushings normally require no maintenance. The suggestions given below cover aspects of bushing supervision to be carried out, for example, on the occasion of station overhauls or normal scheduled maintenance.

3.1 Gas

The gas density should not be allowed to fall below the nominal insulating density. Checking that the density monitor and any pressure gauge are operating as intended may be carried out according to 1.6. Gas moisture content may be checked according to IEC 60376 B ”Specification of Dew Point Measuring”. Checking of gas characteristics may be carried out according to IEC 60480 ”Guide for checking SF6 taken from electrical equipment”.

3.2 Electrical conduction

The temperature in the bushing may be checked using Termovision infrared-sensitive equip-ment during operation. The normal temperature rise at rated current is 20 - 30 K above ambient.

3.3 Hydrophobicity check

The hydrophobicity of the silicone rubber may be checked as directed in product information 2750 515-53 ”Determination of the Hydrophobic Characteristics of a Surface”.

4. Disposal after end of service lifeThe aluminium parts of the bushing conform to Swedish Standard SS14. Cast parts are made of 4245 (ISO Al-Si7Mg). The tubular conductor is made of 4102 (~AA 6101).

The shielding parts are made of 4107 (ISO Al-SiMg, AA 6005). The epoxy tube and the silicone rubber contain no poisons or heavy metals and may be burned or deposited without harmful environmental effects.

The approximate material composition of GGFL is as follows:

- 40 % aluminium of various compositions

- 25 % glass fibre reinforced epoxy

- 35 % silicone rubber.

SF6 gas is handled according to chapter 2.7.

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5. ReferencesTest certificate

Dimensional drawing

IEC 60375 ”Specification of new SF6”

ANSI/IEEE C57.19.01-1991

IEC 60376 B ”Specification of Dew Point Measuring”

IEC 60480 ”Guide for checking SF6 taken from electrical equipment”

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ABB AB ComponentsVisiting address: Lyviksvägen 10Postal address: SE-771 80 Ludvika, SWEDENTel.+46 240 78 20 00Fax +46 240 121 57E-mail: sales@se.abb.comwww.abb.com/electricalcomponents

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