is 5596 (1970): method of test for determining deleterious ... · 2.1 deleterious substance -any...

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IS 5596 (1970): Method of test for determining deleterioussubstances in fibrous insulating materials [ETD 2: SolidElectrical Insulating Materials and Insulation Systems]

IS:5596-1970

Indian Standard

METHODS OF TEST FOR DETERMINING DELETERIOUS SUBSTANCES IN

FIBROUS INSULATING MATERIALS

( First Reprint OCTOBER 1997 )

UDC 621.315.614 : 620.193.4

0 Copyright 1970

BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

Gr 5 August 1970

IS : 5596 - 1970

Indian Standard

METHOD OF TEST FOR

DETERMINING DELETERIOUS SUBSTANCES IN FIBROUS INSULATING MATERIALS

Insulating Materials Sectional Committee, ETDC 18

Chairman

SnRI A. P. SEETKAPaTIIY

Members

Representing

Central Water & Power Commission ( Power Wing )

SHRI S. N. VIXZE ( Alternate to Shrr A. P. Seethapathy )

SRRI V. BALASUBRAnIANIAN Hindustan Brown Boveri Ltd, Bombay SHRI V. D. ERANDE ( Alternate )

SHRI C. E. BHASKAR RAO Bharat Bijlee Ltd. Bombay SHRI S. G. DESHXUKH ( Alternate )

SHRI D. P. BRATIA Directorate General of Supplies & Disposals ( Ministry of Foreign Trade & Supply )

SHRI S. G. PARANGE ( Alternate ) STIRI K. DO n hISWAMY Dr Beck & Co ( India) Ltd, Poona

SHRI S. B. RAPAT ( Ahnate ) SHRI S. N. GANDHI Permali Wallace Ltd, Bhopal

SHRI C. C. S~KARDA ( Alternate ) DR H. V. GOPALARRISHNA Indian Institute of Science, Bangalore SHRI S. J. HASAN Bakelite ( India ) Pvt Ltd, Bombay

SHRI Y. V. CHITTAL ( Alternate ) SHRI P. N. HIRIYANNAI~H Indian Electrical Manufacturers’ Association,

Calcutta; and Kirloskar Electric Co Ltd. Bangalore SHRI B. G. BHAKAY ( Ahrnate) Indian Electrical Manufacturers’ Association,

Calcutta Dn B. N. JAYARAM ( A&male ) Kirloskar Electric Co Ltd, Bangalore

SHRI A. S. LAKSHMANAN Senapathy Whiteley Pvt Ltd, Bangalore SHRI B. A. GOVINDARA~ ( Alternntr)

SHRI M. S. MAHADEVAPP.~ NGEF Ltd, Bangalore SHRI T. APPASWAXY ( Alternate )

SHRI R/I. K. MAJU~XDAR Heavy Electricals ( India ) Ltd, Bhopal SHRI M. V. DALAL ( Alternate )

SHRI S. N. MUKHERJI National Test House, Calcutta SHRI S. K. MURHERJEE (Alternate)

SHRI A. N. NIMKAR Jyoti Ltd, Baroda SHRI P. L. PRAoIrAN ( Alternate )

SHIZI S. R. RAiXAcHANDRaN Power Cables Private Ltd, Bombay SHRI S. K. GANDHI ( Alternate )

( Continued on page 2 )

BIJREAIJ OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARC

NEW DELHI 110002

IS:5596-1970

( ContinuedJrom page 1 )

Members Representin,n

SI-IRI V. S. Rho Directorate of Standardization, Department of Defwcr Production, Ministry of Defence

SHRI D. c. VATS.4 ( Ahnote )

SHRI S. SENQUPTA Formica India Ltd, Poona SHRI R. B. F. ROSARIO ( Alternate )

SHRI R. K. TANDAN National Physical Laboratory ( CSIR ), New Delhi SHRI Y. S. VEXKATEBWARAN, Director General, BIS ( Ex-o&i0 Member )

Dirrctor ( Elec tech ) ( Secretor_lf )

2

IS : 5596 - 1970

Indian Standard

METHOD OF TEST FOR DETERMINING DELETERIOUS SUBSTANCES IN

FIBROUS INSULATING MATERIALS

0. FOREWORD

0.1 This Indian Standard was adopted by the Indian Standards Institution on 6 March 1970, after the draft finalized by the Insulating Materials Sectional Committee had been approved by the Electrotechnical Division Council.

0.2 This standard describes reference test methods for the determination of certain substances or groups of substances which may be present in some fibrous materials used for electrical insulation. Such substances, if present in more than small quantities; may have a deleterious effect on the fibrous material or on other materials with which they are associated in use, and may, therefore, affect their performance in service.

0.3 Where the test method given in a standard for a particular insulating material differs from that described in this standard, the test method specified in the standard for the particular material should be used.

0.4 In preparing this standard, assistance has been derived from ERA Report No. 5234: Proposals for the Revision of B.S. 2689 : 1956 ‘Methods of test for deter’mining deleterious substances in fibrous electrical insulating materials ’ issued by the Electrical Research Association, Surrey, England.

0.5 For the purpose of deciding whether a particular requirement of this standard is complied with, the final value, observed or calculated, expres- sing the result of a test, shall be rounded off in accordance with IS : 2- 1960*. The number of significant places retained in the rounded off value should be the same as that of the specified value in this standard.

1. SCOPE

1.1 This standard describes reference methods of test for determining deleterious substances or groups of substances in the following fibrous

Rules for rounding off numerical values ( revised).

3

IS I SS96 - 1976

electrical insulating materials:

a) cotton, g) regenerated cellulose,

b) acetylated cotton, h) cellulose acetate,

c) wool, j) synthetic polymers,

d) silk, k) paper, e) jute, m) asbestos, and

f) flax, n) glass.

1.2 This standard does not apply to materials which have been given a finishing treatment, such as coating, waxing or polishing.

2. TERMINOLOGY

2.0 For the purpose of this standard, the following definitions shall apply.

2.1 Deleterious Substance -Any substance in a fibrous insulating material which may have an adverse effect upon the electrical or mecha- nical properties of the material; the term also includes a substance which may have an injurious effect on any material in contact with or adjacent to it.

2.2 Blank Test-A test carried out in conformity with the relevant test procedure but omitting the specimens.

3. GENERAL REQUIREMENTS

3.1 Conditioning -The tests shall be carried out on samples of fibrous insulating material which have been conditioned as described in Appendix A.

3.2 Precautions Against Contamination of Samples of Material - Every precaution shall be taken to avoid contamination of the fibrous insulating material during transport, storage, sampling, preparation of specimens and testing. In selecting samples of material in roll form, the outer damaged layers and three undamaged layers of the roll shall be discarded. Care shall be taken to ensure that samples are not contaminated by the atmosphere, particularly by the atmosphere of a chemical laboratory. The implements used for cutting or handling the material shall be chemi- cally clean.

3.3 Reagents - Unless specified otherwise, pure chemicals and distilled water ( see IS : 1070 - 1960* ) shall be employed in tests.

NOTE - !Pure chemicals shall mean chemicals that do not contain impurities which affect the test rrsults.

*Specification for water, distilled quality ( revised ).

4

IS : 5596 - la70

3.4 Laboratory Glassware - All laboratory glassware used for these tests shall preferably be of Type 1 or Type 2 glass conforming to IS : 230% 1963* and shall be thoroughly cleaned before use.

3.5 Heating - When heating is required, care shall be taken to avoid a method which is capable of producing uneven heating of the material under test.

3.6 Extraction - Where a water extraction is required use 10~ conductivity water having a conductivity not greater than 2 microsiemens/cm. In most tests, it is stipulated that the time of boiling shall be one hour. For most materials this is perfectly satisfactory, but for some synthetic materials hydrolysis may occur if the extract is boiled for this time and for such materials the time should be reduced to 10 minutes.

4. ACIDITY OF AQUEOUS EXTRACT

4.1 Number of Tests - Make three separate tests.

4.2 Test Sample - Cut the material into small pieces approximately 25 ~3 mm. Take care to avoid handling the material and the pieces. Weigh 3 g of the pieces to constitute the test sample.

4.3 Preparation of Water Extract - Use low conductivity water having a conductivity not greater than 2 microsiemens/cm.

Place the 3 g test sample in a glass flask ( see IS : 1381-1959t) fitted with a reflux condenser and add 150 ml of the distilled water. Boil gently for one hour. Decant the liquid and wash the pieces once by decantation with 50 ml of hot distilled water, adding this to the liquid used for

j extraction.

4.4 Method-Titrate the combined extract and washing with 0.05 N potassium hydroxide solution using one of the methods given in 4.4.1 or 4.4.2 for determining the end point.

NOTE - In cases of dispute use the electrometric method, which is to be regarded as the standard.

4.4.1 Indicator Method - Titrate the extracts at a temperature above 8O’C and use phenolphthalein as the indicator, the end-point being when the pink colour persists for three seconds. Correct each result by subtracting from it the amount of potassium hydroxide required to neutralize a blank from which the test pieces only are omitted. __ ..~~_ _ I

*Method of grading glass for alkalinity. tspecification for boiling flasks ( narrow-necked ).

5

IS : 5596 - 1970

4.42 Electrometric Method - Cool the combined extract and washings to a temperature of 27”f 2°C and titrate at this temperature using a PH meter and saturated calomel and glass electrodes. Stir the liquid constantly and from a 10 ml burette run in aliquots of 0.05 ml potassium hydroxide. Allow sufficient time after each addition to ensure stability, then obtain balance on the meter.

From a graph of volume in millilitres of potassium hydroxide plotted against change of PH per unit of titrant determine the end-point which corresponds to the peak of the curve. Correct the volume of titrant at the end-point by subtracting from it the amount of potassium hydroxide required to neutralise to the same PH value a blank from which the test pieces only are omitted.

4.4.3 Results - Calculate the results of each determination to the near- est O-1 mg of potassium hydroxide per gram ( mg KOH/g ) of test piece. Take the mean of the three separate results so obtained as the acidity.

5. WATER SOLUBLE MATTER

5.1 Apparatus - For extraction of the water soluble matter, a Soxhlet apparatus of suitable size is used. The whole apparatus, flask, Soxhlet extractor and reflux water condenser, is constructed with ground-glass joints ( see IS : 5165-1969* ).

5.2 Method - Approximately 5 g of the material is weighed accurately and placed in the Soxhlet extractor ( in a manner which permits free passage of liquid to all parts of the material ) and extracted with distilled water for four hours.

The frequency of siphoning should be as high as is consistent with complete retention of the solvent by the condenser and, in any case, not less than six changes per hour, care being taken to ensure the free passage of the solvent into the siphon tube.

The extract, filtered only if necessary, is transferred in suitable por- tions to a small tared silica or porcelain dish and evaporated to dryness on a steam bath. The dish and its contents are then heated at 1 lO”C, cooled in a desiccator and weighed, this process being repeated till a constant weight is attained. If the residue is hygroscopic the dish and contents are weighed in a closed weighing container.

5.3 Result material.

-The result is expressed as a percentage by weight of the

6. CHLORIDE CONTENT

6.1 Extraction - Use low conductivity water having a conductivity not greater than 2 microsiemens/cm. Carry out a blank test before each extrac-

‘Specification for interchangeable conical ground-glass joints.

6

1s : 5596 - 1990

tion and if the result exceeds 2 microsiemens/cm, repeat the test wit1 +he same extraction vessel. If the second result also exceeds 2 microsiemensjcm, discard the vessel.

Prepare the extract by cutting the material into pieces not greater than 20 x 3 mm and put 6 g of the pieces to 100 ml of water into a 250 ml glass flask (dee IS : 1381-1959* ) fitted with a reflux condenser of either the same quality of glass or quartz. Use apparatus having interchangeable conical ground-glass joints conforming-to IS : 5165 - 1969t. Boil the water gently for 10 minutes, care being taken not to char the material.

6.2 Method - Two methods have been prescribed, namely, electrometric method and turbidometric method. In case of quantities of chlorides being small, the latter may be used.

6.2.1 Electrometric Method - Place 20 ml of the extract in a small glass vessel and slowly evaporate to approximately 2 ml, avoiding bumping and splashing. Allow to cool and then transfer the concentrated solution and washing water ( total volume 5 ml) to a small glass vessel containing 25 ml of acetone and five drops of 0.1 N nitric acid. The electrode system consisting of a silver/silver chloride electrode and a mercurous sulphate electrode is then placed in the liquid which is kept constantly agitated by a glass covered magnet activated by a magnetic stirrer under the glass vessel. The electrodes are then connected in series with a sensitive galvanometer, a suitable current limiting resistance and a tapping key. When a galvanometer of sensitivity 1 x 10VgA per mm at one metre scale distance is used, a suitable series resistance is 3 megohms.

To determine the chloride content the solution is titrated with 0.002 N silver nitrate solution from a microburette and after each small addition a reading is taken on the galvanometer by depressing the key. The galvanometer deflections are then plotted against the volumes of silver nitrate added and the end-point of the reaction is indicated by the point of maximum slope of the curve.

The weight of chloride ion in grams is O*OOO 07 x volume in ml of 0.002 N silver nitrate solution.

6.2.1.1 Result - Express the weight of the chloride ion as parts per million of the weight of material.

6.2.2 Turbidometric Method

6.2.2.x Standard chloride solution - Dissolve 1.000 g of sodium chloride it1 water and make up the volume to 1 000 ml. Pipette out 10 ml from this solution and dilute with water to 1000 ml. One millilitre of the solution is equivalent to 0.0 1 mg of chlorides ( as NaCl ).

‘Specification for boiling flasks ( narrow-necked ). tSpecification for interchangeable conical ground-glass joints.

7

IS : 5596 - 1970

6.2.2.2 Procedure - Take 20 ml of the extract and add slight excess of concentrated nit, ic acid ( see IS : 264-1968* ). Add 1 ml of silver nitrate solution ( approximately 4 percent ). Transfer into a Nessler tube (capacity 100 ml ) and make up the volume to the mark with water. Carry out a control test using the same quantities of the reagents in the same total volume of the reaction mixture and adding standard chloride solution drop by drop till the turbidity produced matches with the sample solution.

7. SULPHATE CONTENT

7.1 Preparation of Aqueous Extract - The material shall be cut into pieces not exceeding 25 mm in length and 3 mm in width. Twenty grams of the pieces shall be boiled in 300 ml of distilled water for one hour. The extract shall be filtered, the filtering medium washed and the washings added to the filtrate. Excess of precipitated chalk to neutralize the solution shall be added.

The neutralized solution shall then be boiled for 10 minutes and filtered, the filtering medium washed and the washings added to the filtrate. Transfer the washings and filtrate in a loo-ml volumetric flask and make up the volume to the mark with distilled water. If necessary the filtering and washing process shall be repeated and the volume redetermined.

7.2 Method - Two methods have been prescribed, namely, the gravimetric method and turbidometric method. In case of quantities of sulphate being small, the latter may be used.

7.2.1 Gravimetric Method - Place 50 ml of the extract in a clean boiled- out glass beaker, and add 1 to 2 ml of 10 percent dilute hydrochloric acid. The solution shall be brought to boiling and 1 to 2 ml of 5 percent barium chloride solution added. Boiling shall be continued for 5 minutes, and the solution left to cool, and stand over-night. Any precipitate of barium sulphate which forms shall be filtered, washed free from chlorides, dried and ignited. It shall then be moistened with concentrated sulphuric acid, re-ignited and weighed.

The weight of BaSOI x O-412 = weight of SO,.

7.2.1.1 Result -Express the weight of sulphate ion as parts per million of the weight of material.

7.2.2 Turbidometric Method

7.2.2.1 Standard subhate solution - Dissolve 0.123 g of sodium sulphate in water and make up the volume to 1 000 ml. One millilitre of this solution is equivalent to 0.1 mg of sulphate ( as Na,SO& ).

*Specification for nitric acid (jird reuision ).

8

IS : 5596 - 1970

7.2.2.2 Procedure - Take 50 ml of the extract, add 5 ml concentrated hydrochloric acid ( see IS : 265- 1962* ) and evaporate to dryness on a water- bath. Dissolve the residue in 20 ml of water and add a few drops of concentrated hydrochloric acid and 2 ml of barium chloride solution ( approximately 10 percent ). Transfer to a Nessler tube ( capacity 100 ml ) and dilute to the mark. Carry out a control test in another Nessler tube ( capacity 100 ml ) using the same quantities of the reagents in the same total volume of the reaction mixture and adding standard sulphate solution drop by drop till the turbidity produced matches with the sample solution.

8. MINERAL ASH 8.1 Method-Condition not less than 2 g of material and weigh it immediately after conditioning. For some materials a larger sample ( up to 5 g ) may be necessary for accuracy in weighing the ash.

8.1.1 Add a few drops of sulphuric acid to the test portion and ignite to constant weight at a temperature between 800” and 900” C with all precautions against loss, care being taken to ensure the absence of unburnt carbon in the ash. Weigh the residue of incombustible matter ( ash ) and compute the amount as a percentage of the weight of the conditioned test piece.

8.1.2 Make two determinations of ash content. The higher of the two results is the mineral ash but, if the results do not agree to within 10 percent of the mean value, discard the result and repeat the test.

9. CONDUCTIVITY OF AQUEOUS EXTRACT 9.1 Preparation of Extract - Use low conductivity water having a conductivity not greater than 2 microsiemens/cm. Carry out a blank test before each extraction and if the resultant conductivity exceeds 2 microsiemens/cm repeat the test with the same extraction vessel. If the second result also exceeds 2 microsiemens/cm discard the vessel.

9.1.1 Prepare the extract by cutting the material into pieces not greater than 20 x 3 mm and put a weight of five grams of the pieces to 100 ml of water into a 250 ml glass flask (see IS : 1381-1959t) fitted with a reflux condenser of either the same quality glass or quartz. Use apparatus having interchangeable conical ground-glass joints conforming to IS : 5165- 1969%. Roil the water gently for one hour, care being taken not to char the material. Cool the extract to room temperature and decant directly into the test cell.

NOTE - It is recommended that 5 g to 100 ml be used but in some materials, for examples, capacitor tissue, this volume of material would be too great.

*Specification for hydrochloric acid ( rcviscd ). @pecification for boiling flasks ( narrow-necked ). $Specification for interchangeable conical ground-glass joints.

9

IS : 5596 - 1970

9.2 Apparatus - The apparatus for measurement of conductivity shall comprise of a suitable conductivity cell as in Fig. 1 in conjunction with a bridge circuit supplied with current at a frequency of 50 to 3 000 Hz.

9.2.1 The cell consists of two electrodes of inert metal, for example, platinum, maintained at a fixed distance apart and adequately insulated from each other. In immersion electrode type ceI1, the electrodes are almost enclosed in a glass shield which protects the electrodes and limits the fringing current but allows full access of the test liquid to the electrodes during immersion ( see Fig. 1B ) .

NOTE - It is important that any insulation which is immersed in the test liquid should not be water absorbent or subject to contamination by aqueous electrolytes. The cell should be easy to clean and free from recesses where impurities may be retained.

COMBINED ELECTROOE HOLDER d, TERMINAL

I /-

PARAFFIN WAX

/MERCURY CONTACTS

PLATINUM (BLACK1 ELECTROOES

(APPROX 10 X10)

IA Convrntional Type of Call I B Immersion Electrode Type of Cell

FIG. 1 CELLS FOR DETERMINATION OF CONDUCTIVITY OF WATER EXTRACT

9.2.2 The cell constant (Ic) should preferably be within the range 0.05 to 0.5 cm-‘.

10

IS : 5596 - 1970

9.3 Method of Measurement

9.3.1 Determination of Cell Constant - The cell constant Ic, if not known, is determined by means of a solution of known specific conductivity prepared by dissolving 0.745 5 g of dry potassium chloride in low conductivity water and diluting the solution to 1 000 ml at a temperature of 27”&-2°C. Rinse the cell thoroughly with the solution and then fill. Maintain the temperature at 27”f 1” C for 15 minutes and then measure the resistance R in megohms at that temperature.

Then if P is the specific resistance of KC1 solution, the cell constant Ic is calculated as,

&$

The values of specific resistance for 0.01 N KC1 solution at different temperatures are given in the following table.

‘Temperature Specific Resistance p of Temperature Specif; Resistance P of O’OI N KC1 Solution 0’01 .N KC1 Solution

“C -ohm.cm “C ohm.cm

15 872 23 736 16 852 24 721 17 834 18 817 ;z

708 696

19 800 xi

683

E 782 670 766

E 657

22 751 647

9.3.2 Determination of Conductivity of Blank -After thoroughly cleaning the cell with low conductivity water, fill the cell with the water obtained as a result of the blank extraction test and measure its resistance R, in megohms at 27” f 2°C. The conductivity of the blank in microsiemens/cm is then given by:

z

-F 9.3.3 Determination of Conductivity of Water Extract - Thoroughly rinse

the cell with the extract to be tested and then fill with the decanted extract. Adjust the temperature to 27”f2”C, maintain at that value for 15 minutes and then measure the resistance R,, in megohms, at that temperature.

The conductivity of the water extract in microsiemens/cm is then calculated as:

K x R2 - 3;

11

IS : 5596 - 1970

NOTE - For most purposes, where it is not convenient to test the water extract at 27” -+. 2” C, it is sufficiently accurate to apply the following correction:

Conductivity at 27°C = ._.. __~-_. ._ 1 + 0.02 ( t - 27 )

where G is the conductivity obtained when the measurement is made at t”C.

IO. pH VALUE OF AQUEOUS EXTRACT

10.1 Extraction method

- Prepare an aqueous extract of the material by the described in 9.1.

dioxide. Take precautions to prevent ingress of carbon

10.2 pH Determination - Determine the /JH value by an electrometric method ( w IS : 5741-1970* ) and at a temperature range of 15”~ to 25”~ as soon as possible after the preparation of the extract.

11. CONDUCTIVITY OF ORGANIC EXTRACT

11.1 Purpose - The purpose of this test is to determine whether or not soluble organic materials are present in the insulating material. Their presence is confirmed by an increase in the conductivity of the organic ( trichlorethylene ) extract and the test is considered to have particular significance when applied to insulating materials whichare to be immersed in chlorinated coolants.

11.2 Preparation of Extract - Use reagent grade trichlorethylene purified by stirring in about one percent by weight of Fuller’s earth and filtering through a sintered glass crucible ( G. No. 4 ).

NOTE. - Fuller’s earth becomes ineffective if allowed to absorb moisture and may be dried by heating in clean air at a temperature not exceeding 120°C.

11.2.1 Carry out a blank test before each extraction and if the resultant conductivity consistently exceeds 5 x 10-l ’ siemens/cm, further purify the solvent until its conductivity is not greater than this value.

11.2;2 Prepare the extract by comminuting the material under test as described for conductivity of aqueous extract in 9.1 gently heat the samples in air for about 2 hours at a temperature of 80” to 100°C to remove any appreciable amount of absorbed water, and immediately transfer the material to a. suitable flask and cover it with purified trichlorethylene using a proportion of one gram to 10 millilitres of solvent. Boil the solvent gently for about one hour under reflux conditions using all glass apparatus

*Methods for determination of pH value.

12

IS:5596 -1970

constructed with ground glass joints ( see IS : 5165-1969* ). Firmly stopper the flask and allow it to remain overnight in the dark. Adjust any loss of volume through evaporation by adding pure solvent before making the conductivity measurement.

11.2.3 Purified trichlorethylene is stable if kept in the dark or in a brown bottle, but check its conductivity before use for an extraction. During extraction and measurement shield the solvent from strong light especially direct sunlight and store it in the dark. 11.3 Apparatus - Use a suitable conductivity cell such as that used for determining conductivity of aqueous extract shown in Fig. 1A and lB, or the special cell shown in Fig. 2 in conjunction with an electronic

TERMINAL TAGS SPACER

.LIQUID LEVEL 3.22 1.6 ABOVE TOP OF ELECTRODES

&SPACE BENEATH r. rr2nnnC.Y ,.C

All dimensions in millimetres.

FIG. 2 CELL HOR DETERMINATION OF CONDUCTIVITY OF ORGANIC EXTRACT

*Specification for interchangeable conical ground-glass joints.

13

IS : 5596 - 1970

multi-meghometer using not more than 100 V dc or a sensitive galvanometer and battery. With the special cell ( see Fig. 2 ) use an instrument capable of measurement over the range 500 000 ohms to 100 000 megohms.

11.4 Method of Measurement - If not already known, determine the cell constant K by means of an aqueous solution of known conductivity prepared and tested as described in 9.

11.4.1 Before filling with the trichlorethylene extract, wash the cell thoroughly with distilled water ( if last used with an aqueous electrolyte ), dry it and clean it several times with purified trichlorethylene. Dry the cell before filling and arrange for the transfer of the liquid from one vessel to another to take place in a stream of warm air to avoid risk of moisture condensation resulting from cooling; avoid breathing on the electrodes.

11.4.2 Measure the resistance of the extract at a temperature of 27” f 2”C, one minute after application of the dc voltage. If the special cell shown in Fig. 2 is used, the inner electrode should be negative and the outer electrode earthed.

If R = measured resistance of the extract in ohms, and

X = cell constant ( cm-’ ) v

then#the conductivity of the extract in siemens/cm = --i- conductivity

of the solvent in siemenslcm.

11.5 Results - siemenslcm.

Express the conductivity of the extract of the material in

12. ELECTROLYTIC CORROSION

12.1 Purpose - The purpose of this test is to evaluate quantitatively the corrosion effect that occurs when material is placed in contact with copper wires under a dc potential at an elevated relative humidity and temperature.

12.1.1 The extent to which the material under conditions of damp heat exposure cause the corrosion of fine wires is assessed by measuring the resultant decrease in the tensile strength of the wire.

12.2 Test Samples

12.2.1 Form - Test samples may take several forms depending upon the type and nature of the material. The material is tested in the ‘ as received ’ condition and at least five samples are required.

12.2.2 The material is to be cut so that it covers a glass tube and may be fixed at the bottom of the tube. The covering may be made up of strips of material provided the width is multiple of 12 mm ( approximately ) .

14

IS:5596-1970

12.3 Apparatus- The test apparatus (see Fig 3 ) consists of a glass tube approximately 330 mm long and 90 mm in external diameter suitably secured in a horizontal position at each end above a nickel plated brass framework. The base also carries two insulating strips* running parallel to the axis on opposite sides of the tube and secured at each end to nickel plated brass supports. Soldering tags are attached equally spaced along one strip and leaf springs in corresponding positions on the other strip. The leaf springs should deflect at least 3 mm for a load of 0.49 N.

/-TAPE SPECIMEN7

All dimensions in millimetres.

FIG. 3 APPARATUS FOR DETERMINING ELECTROLYTIC CORROSION

12.3.1 Lengths of bare electrolytically refined copper wire 0.2 mm in diameter and about 380 mm long to serve as anodes and cathodes running across the specimens are secured at one end to the soldering tags and at the other to the leaf springs. Duplicate wires are cut to provide specimens for determining T,, the tensile strength of the unused wire. Ensure that the wires are free from kinks and use new pieces for each specimen.

12.3.2 A standard tensile strength testing machine for wire, preferably a constant rate of traverse machine, is used -for testing the unused and corroded wires.

12.3.3 Use the same rate of jaw separation for both the used and the corroded wires. A suitable rate is approximately 130 mm per minute. Hold the ends of the wires in such a way that the wire is not damaged by the clamp or other support. -__ -

*Porcelain, or Mycalex, is suitable.

15

IS : 5596 - 1970

12.3.4 Tensile strength of unused wire, To is determined by testing five samples of the wire and the readings obtained should not vary more than f 1 percent from the arithmetic mean. If the wire fails to satisfy this requirement, examine a further five test pieces. If any of the readings vary more than f 1 percent from the arithmetic mean, the wire is not considered satisfactory for use. The wire is also regarded as unsuitable if the mean breaking load lies outside the range 7.8 to 9.3 N.

12.4 Method

12.4.1 Cleaning the App arutus - Before setting up the test pieces clean the glass tybe by immersing it in cold chromic-sulphuric acid for 24 hours, followed by thorough rinsing with hot tap water and finally with distilled water.

12.4.1.1 Springs, soldering tags and brass base are cleaned by wiping with nylon fabric dampened with methanol (technical grade) conforming to IS: 517-1967*.

12.4.2 Setting up - Test pieces are assembled circumferentially on the upper surface of the glass tube and may be anchored in position by securing the ends with a piece of material cut from the same sample, or alter- natively, the material may be taken round the tube and secured to itself on the under side of the tube. In the latter case specimens longer than 150 mm are required. The length of material and its means of securing are such that an unrestricted test length is in contact with the wire and the latter is not in contact with a cut edge.

Each length of wire is soldered on to the appropriate tag and then wiped with nylon fabric dampened with methanol ( technical grade) conforming to IS : 517-1967*. During the soldering operation precautions should be taken to avoid contamination of the test pieces or apparatus by spray or fumes. A tension of 0.49 N is applied to the wire during the operation of positioning it on the tape and aligning it; this pressure may be achieved by using a pressure gauge. The spring is then adjusted to ensure that tension of 0.49 N is applied to the wire which is then soldered into position. Maintain a spacing of 6.35 mm between pairs of wires over the entire test length of the specimens. Tweezers may be used for making small adjustments in the positioning of the specimens, but care should be taken to avoid contaminating the specimens, the glass tube or the electrodes in any way.

Repeat the procedure for each test piece.

12.4.3 Electrical Circuit - Apply a dc potential of 120-155 V of adequate capacity betlveen each pair tensioned wires and maintain this voltage

‘Sprcification for methanol ( mrthyl alcohol ) (Jirrt rervkinn ).

16

IS : 5596 : 1970

within the specified limits. A resistor of 4.7 k n should be inserted in series with each specimen to limit the short-circuit current. Measure the potential on the terminal remote from the terminal to which the potential is applied, to ensure that it is maintained within the prescribed limits. Make periodic checks to ensure that the potential is maintained during test,

Spurious corrosive effects between specimens are prevented by keeping the polarity of adjacent wires of adjacent specimens same.

12.4.4 Test Conditions -The specimens arranged on the test apparatus and under dc potential are then subjected to accelerated damp heat conditions in a suitable test chamber in accordance with 7.4.1 of IS : 539 - 1961”.

Nwra - ‘I’o ensure that the relative hunlidity is maintained at saturation the humidity is preferably obtained by means of’ steam injection. The humidity should be checked at least twice in the course of each test.

12.4.4.X When placed in the oven the apparatus should always occupy the same position. Fit an inverted vee shaped baffle inslde the oven above the apparatus to prevent condensation dripping on the specimens.

12.4.4.2 Check the temperature variation at regular intervals.

12.4.4.3 The opening of the door of the oven upsets humidity conditions particularly during the period of cooling. It is essential, both for this reason and to prevent the likelihood of contamination, for the test to be carried out in a special cabinet which may be left undisturbed in the oven during the entire time of the run.

12.4.5 Period oj' Exposure - ‘1’1~~ period of exposure shall be in accordance with 7.4.3 of IS : 539-1961*.

12.4.5.1 At the end of three cycles disconnect the dc potential and remove the test apparatus with the test specimens and wires from the chamber.

12.4.6 Wire ‘Tesliug - Finally cut off at their ends the wires with positive polarity and determine their tensile strength breaking loads being recorded.

12.4.7 Results - For each breaking load recorded, the corrosion liabilit)

factor ( CLF) is calculated as:

T,, - ‘I-,

To x 100

*Basic climatic and mvzhanicai durability tests for electronic componems ( m&cd ).

17

IS : 5596 - 1970

where

T@ = mean tensile strength of the wire on which the blank deier- mination has been made, and

T1 = tensile strength of the wire carrying the positive polarity on the test specimen.

The corrosion liability factor of the tape is then expressed as the mean of these calculated values.

The standard deviation is also computed as follows:

Standard deviation =

Sum of squares of deviations from mean CLF of sample ___ IL- 1

where 11 == number of tests included in the mean.

13. SLUDGE AND OIL ACIDITY TEST

13.1 Conditioning - Condition the test specimen in accordance with Appendix A.

13.2 Test Sample - The ratio of material to transformer oil is based on the total surface area of the material ( all sides being taken into consi- deration ) and is 1 cm’ of material to each gram of transformer oil.

13.3 Procedure - Into a 150 X 25 mm test-tube weigh the required amount of transformer oil. Weigh the required amount of material and introduce it into the oil. Lightly plug the mouth of the tube with cotton wool and place it in a constant temperature bath maintained at 100&0~5” C for 164 hours.

13.3.1 Place a similar quantity of the oil above in a second tube and maintain this under the same conditions as a ‘blank’ sample.

13.3.2 At the end of the specifiecl heating period, remove the tubes from the bath, allow them to cool to room temperature. Determine the sludge content of the oil in which the material has been immersed, as follows.

13.3.2.1 Pour the oil into a 600 ml beaker and wash the test-tube and sample with n-heptane until oil free, adding the washings to the oil in the beaker. Make the contents of the beaker up to appraxlmately 300 ml with lz-heptane. Cover the beaker with a watch-, wlass and allow to stand in the dark for 24 hours at room temperature.

13.3.3 Filter the solution through a tared, dried, sintcred glass crucible ( G No. 4 ) transferrin, v all the sediment to the crucible with the aid of

18

IS : 55% - 1970

n-heptane from a wash-bottle. Dry the crucible at 110°C to constant weight. Express the amount of sediment as n percentage of the original sample weight.

13.3.4 Make the filtrate LIP to 500 ml in a measuring cylinder with n-heptane. Make the ‘blank’ sample up to 500 ml in a second cylinder. Determine the acid values of the heptane solutions as follows.

13.3.4.1 Place 60 ml toluene and 40 ml rectified spirits conforming to IS : 323-1959* ( 66 O.P. ) in a 600 ml conical flask. Add 2 to 3 ml alkali blue indicator solution (2 percent by weight in rectified spirit and one drop of 0.1 N hydrochloric acid ) . Neutralize this mixture, with 0.1 N alcoholic potassium hydroxide, IO give a red colour which persists for 15 seconds. Add 100 ml of the above filtrate to the neutralized solvents and titrate to the same end-point with the 0.1 N alcoholic potassium hydroxide. Repeat the titration on 100 ml of the ‘blank’ solution.

Calculate the acid value of the oil, in mg KOH/g from the expression

Acid value = ( t, - tl ~ 5.61 ~~

where

t, = number of ml 0.1 N KOH required to neutralize 100 ml above filtrate,

t, = number of ml 0.1 N KOH required to neutralize 100 ml, n-heptane, and

W = weight of sample.

/ 13.4 Result - Report the acid value of the ‘blank’ oil together with that of the sample oil and the percentage of ‘sludge’ produced in the latter.

NOTE - The sludge may in fact not be oil oxidation products alone but may also contain particles of the qamplc material or breakdown prndrwt~ of it.

APPENDIX A

( Clauses 3.1 and 13.1 )

CONDITIONING OF TEST PIECES

A-l. CONDITIONING

A-l.1 Where appropriate, subject the test piece for not less than 18 hours to a controlled atmosphere of 65 f. 2 percmt relative humidity ( see Note )

‘Specification for rectified spirit (revised).

19

IS: 5596-1970

at a temperature of 27” & 2°C. Make the relevant test in the controlled atmosphere or immediately on removal of each test piece from it.

NOTE - The tolerance of f 2 percent is customary for paper but f 5 percent is customary for fabrics.

A-I.2 This atmosphere of 65 percent relative humidity may be obtained conveniently in an enclosed chamber in which a saturated solution of sodium nitrate is exposed to the atmosphere in the chamber. Prepare the saturated solution from distilled water and sodium nitrite of a recognized analytical reagent quality.

A-I.3 Expose the saturated solution so that the maximum surface is in contact with the air in the chamber, for example, by covering the floor of the chamber with a tray containing the saturated solution. It is essential to use an ample excess of solid sodium nitrate in contact with the saturated solution. If required a mobile slurry of salt and saturated solution may be used, this being prepared by adding to the solid salt, of suitable particle size, a previously prepared solution of sodium nitrite until the desired fluid consistency is obtained.

A-I.4 The saturated salt solution or slurry will become contaminatea in the course of time; the salt tray should, therefore, be emptied, washed all over, carefully dried and refilled with sufficient saturated solution or slurry at intervals of not more than two months. More frequent changes may be necessary if the chamber is used where conditions of severe contamination are experienced.

A-I.5 To ensure uniform conditions throughout the chamber: a fan should circulate air over the surface of the saturated solution or slurry and around the test pieces. Free access of the conditioning atmosphere to all test pieces is essential. From time to time check that the humidity of the air in the chamber’ is correct.

20

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