ASTM D1169-95

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: D 1169 – 95
Standard Test Method for
Specific Resistance (Resistivity) of Electrical Insulating
Liquids
This standard is issued under the fixed designation D 1169; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.1 specific resistance (resistivity), n—the ratio of the dc
potential gradient in volts per centimetre paralleling the current
1.1 This test method covers the determination of specific
flow within the specimen, to the current density in amperes per
resistance (resistivity) applied to new electrical insulating
square centimetre at a given instant of time and under
liquids, as well as to liquids in service, or subsequent to
prescribed conditions. This is numerically equal to the resis-
service, in cables, transformers, circuit breakers, and other
tance between opposite faces of a centimetre cube of the liquid.
electrical apparatus.
The units are ohm-centimetres.
1.2 This test method covers a procedure for making referee
tests with dc potential.
4. Significance and Use
1.3 When it is desired to make routine determinations
4.1 The resistivity of a liquid is a measure of its electrical
requiring less accuracy, certain modifications to this test
insulating properties under conditions comparable to those of
method are permitted as described in Sections 19-26.
the test. High resistivity reflects low content of free ions and
1.4 This standard does not purport to address all of the
ion-forming particles, and normally indicates a low concentra-
safety concerns, if any, associated with its use. It is the
tion of conductive contaminants.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
5. General Considerations
bility of regulatory limitations prior to use. See Note 5 for a
5.1 Theory and measuring equipment pertaining to this
specific cautionary statement.
method shall be in accordance with Test Methods D 257.
2. Referenced Documents 5.2 Where both ac loss characteristic (dissipation factor or
power factor) and resistivity measurements are to be made
2.1 ASTM Standards:
consecutively on the same specimen, make the ac measurement
D 150 Test Methods for A-C Loss Characteristics and
before applying the dc potential to the specimen, and short
Permittivity (Dielectric Constant) of Solid Electrical Insu-
circuit the cell electrodes for 1 min immediately prior to
lating Materials
making the resistivity measurements.
D 257 Test Methods for D-C Resistance or Conductance of
5.3 Make referee tests for resistivity in an atmosphere of
Insulating Materials
less than 50 % relative humidity. For repeatable results make
D 923 Test Method for Sampling Electrical Insulating
3 these tests under carefully controlled atmospheric conditions.
Liquids
5.4 Aside from the adverse influence of contamination on
D 924 Test Method for Dissipation Factor (or Power Factor)
results of the resistivity test, there are other factors that can
and Relative Permittivity (Dielectric Constant) of Electri-
3 contribute to variations in the test results as follows:
cal Insulating Liquids
5.4.1 The use of an instrument not having an adequate range
E 145 Specification for Gravity-Convection and Forced-
4 for accurately measuring the current flowing in the circuit. (See
Ventilation Ovens
Section 6 for two types of recommended instruments.)
3. Terminology 5.4.2 When the time of electrification is not exactly the
same for every test. Upon the application of voltage the current
3.1 Definitions of Terms Specific to This Standard:
flow through the specimen decreases asymptotically toward a
limiting value. Variation in the time of electrification can result
This test method is under the jurisdiction of ASTM Committee D-27 on
in appreciable variation in the test results.
Electrical Insulating Liquids and Gasesand is the direct responsibility of Subcom-
5.4.3 Undue length of time required for the test specimen in
mittee D27.05on Electrical Tests.
Current edition approved Sept. 10, 1995. Published November 1995. Originally
the cell to attain the desired test temperature. This is one of the
published as D 1169 – 51 T. Last previous edition D 1169 – 89.
main sources of erroneous results. For optimum results, attain
Annual Book of ASTM Standards, Vol 10.01.
3 the test temperature within 20 min.
Annual Book of ASTM Standards, Vol 10.03.
5.4.4 Fluctuations in the test voltage (see 6.1.4).
Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 1169
6. Instrumentation 7. Test Circuit
6.1 Instrumentation listed in Test Methods D 257 is suitable, 7.1 A schematic diagram of the test circuit is shown in Fig.
with the exception of the Voltage Rate-of-Change Method. 1.
However, in order to obtain the greatest precision when making 7.2 Construct the circuitry so that leakage is minimal. To
this test, use the voltage-current method with the following this end, mount the transfer switches on polystyrene or
instruments: TFE-fluorocarbon insulation of sufficient thickness to mini-
6.1.1 Voltmeter, having an accuracy of 2 % or better, oper- mize possible leakage. Make all soldered connections with
ated in the upper one third of its scale range for measuring the low-thermal-emf solder using a soldering flux of resin and
voltage supply. alcohol.
6.1.2 Current-Measuring Device—Any type of instrument
NOTE 2—The use of ordinary solder and flux can result in spurious
having adequate sensitivity and precision and with a suitable
thermal emf’s that will cause erroneous indications.
range for measurement of the wide spread of currents encoun-
7.3 Completely shield the test circuit. Make connections to
tered when making this test on new or used liquids will be
−9 the current-measuring instrument with shielded leads. TFE-
satisfactory. For currents greater than 10 A an Ayrton shunt
fluorocarbon-insulated shielded leads are recommended for
and galvanometer, an appropriate electrometer or picoammeter
−12 connecting the high-voltage electrode and measuring electrode
having a sensitivity of 50 pA (50 3 10 A) per division has
of the test cell to the test circuit.
been found convenient and satisfactory. The galvanometer
deflection shall be not less than 20 divisions for the applicable
8. Sampling
−9
Ayrton shunt ratio. For currents less than 10 A an electronic
8.1 Sample oils and askarels for use in this test in accor-
picoammeter has been found suitable. In using this instrument
dance with Test Method D 923. When possible, obtain samples
the multiplier selected shall be such as to give at least one-half
for testing through a closed system. If exposed to atmospheric
full-scale deflection on the indicating instrument.
conditions, take the sample when the relative humidity is 50 %
6.1.3 Time-Measuring Device, accurate to 0.5 s, for measur-
or less. Some liquids, in certain applications, require special
ing the time of electrification.
handling and processes in the sampling, and these will be
6.1.4 Batteries or other stable direct-voltage supplies are
found in the governing procedures. Consult such procedures
recommended for the steady voltage source.
before samples are taken.
NOTE 1—Rectified high-frequency power supplies cannot be used
8.2 Take a sufficient quantity of sample for this test for at
because the high frequency ripple in these supplies can cause the ac
least three separate resistivity determinations.
component of current to equal or exceed the dc current being measured.
The ac component of current is equal to 2 pi times the product of the ripple
9. Galvanometer Calibration and Sensitivity
voltage, the ripple frequency, and the capacitance of the test cell in farads
9.1 When a dc galvanometer is used to measure the current,
−10
(where pi = 3.14). If the capacitance of the test cell is 100 pF (10 F), the
it shall first be calibrated to ensure that it is properly balanced,
ripple frequency is 100 kHz, and the ripple voltage is 5 mV (0.001 % of
that is, that the deflections on either side of zero are equal when
a 500 volt test voltage), the alternating component of current is 3.14 3 10
−7 amperes. The meter would be unreadable under these conditions. the galvanometer is energized with “direct” and “reverse”
−9
NOTE 1—For measurements of current less than 10 A replace galvanometer and shunt with picoammeter.
NOTE 2—With the S.P.D.T. switch on C terminal the galvanometer may be calibrated while the electrodes of the test cell are short-circuited.
FIG. 1 Circuit Diagram and Connections with Complete Shielding for Measuring Specific Resistance (Resistivity) of Electrical
Insulating Liquids
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 1169
polarities of the test potential. test cell will be broken when the door is opened.
11.4 A cross-sectional view of the test chamber with a
NOTE 3—Throughout this test method the terms “direct polarity” and“
three-electrode test cell in place and with test cables connected
reverse polarity” are used to indicate when the positive and negative
is shown in Fig. 1.
potential leads, respectively, are connected to the outer electrode of the
test cell.
12. Test Temperature
9.2 The galvanometer sensitivity, G , in amperes per divi-
s
12.1 The temperature at which a referee test is made shall be
sion, is used in computing the resistivity and is derived from
mutually agreed upon between the purchaser and the seller.
the following equation:
Resistivity measurements are made at many different tempera-
G 5 ~E/R! [m|]P5 ~S/D!
s
tures. For acceptance tests, it is generally made at a tempera-
ture of 100°C, while for routine testing, it is usually made at
where:
room temperature, 85, or 100°C. In some research investiga-
E = test voltage, V,
tions, tests may be made at considerably higher temperatures,
R = calibrating resistor, V ,
while in other cases, particularly for tests on cable oils in
S = shunt multiplying factor (ratio of galvanometer current
service, tests may be made over a range of temperatures.
to total current), and
D = galvanometer deflection, in divisions.
13. Test Voltage
10. Test Cells
13.1 The average electrical stress to which the specimen is
10.1 The design of test cells that conform to the general subjected shall be not less than 5 V/mil (200 V/mm) nor more
requirements given in the Annex are considered suitable for use than 30 V/mil (1200 V/mm). The upper limit has been set with
in making these tests. the purpose of avoiding possible ionization if higher stresses
10.2 Three types of guarded electrode test cells that con- were permitted. For acceptance testing, the stress and time of
form to these requirements and have been found suitable for electrification should be mutually agreed upon by the purchaser
measuring the resistivity of insulating liquids are shown in and the seller. The time of electrification in general usage is 1
Figs. A1.1, A1.2, and A1.3. In addition, a two-electrode cell
min.
suitable for making routine tests is shown in Fig. A1.4. These
NOTE 4—The dc volume resistivity of new oil, particularly at room
figures and a brief description of each cell are given in the
temperature, has been shown to be a function of both electrical stress and
Annex.
electrode spacing. The resistivity has been found to have a maximum
10.3 Because the configuration of the electrodes of these
value when the applied electrical stress is about 50 V/mil; electrical
stresses either below or above this critical value yield lower values of
test cells is such that their effective area and the distance
6 ,7
volume resistivity.
between them are difficult to measure, each test cell constant,
K, can be derived from the following equation:
14. Conditioning
K 5 3.6p C 5 11.3C
14.1 Store the sample in its original sealed container and
shield it from light. Some liquids, such as oils of petroleum
where:
origin, undergo changes when exposed to sunlight. Allow the
K = test cell constant, cm, and
sealed container to stand undisturbed, in the room in which the
C = capacitance, pF, of the electrode system with air as the
test is to be made, for a sufficient period of time to permit the
dielectric. (For methods of measuring C, see Test
sample to attain room temperature before it is opened.
Methods D 150).
11. Test Chamber 15. Storing Test Cell
11.1 When the tests are to be made above room temperature 15.1 Clean and dry the test cell, when not in use, in
but below 300°C, use a forced-draft, thermostatically con- accordance with Section 16. Store it in a dust-free cabinet until
trolled oven that conforms to Specification E 145 as the test it is to be used again, at which time clean and dry as directed
chamber. For tests at room temperature the unenergized oven by Section 16.
can be conveniently used as the test chamber.
16. Cleaning Test Cell
11.2 Provide the test chamber with an opening in the wall
through which two lengths of TFE-fluorocarbon-insulated 16.1 The cleanliness of the test cell is of paramount impor-
tance when making resistivity measurements because of the
shielded cable will pass to make electrical connection from the
measuring equipment and voltage source, respectively, to the inherent susceptibility of most insulating liquids to contami-
nating influences of the most minute nature. For this reason
test cell. Use a perforated ceramic plate or disk to insulate the
test cell from the metal flooring of the oven if the flooring is not clean and dry the cell immediately prior to making the test. It
is essential that the procedures and precautions outlined in
insulated from the oven.
11.3 Provide a safety interlock on the door of the test 16.2-16.5 be strictly observed.
chamber so that the electrical circuit supplying voltage to the
Gänger, B., and Maier, G., “The Resistivity of Insulating Oil in a Direct Voltage
Information as to where these cells can be purchased and working drawings of Field,” Brown-Boveri Review, Vol 56, October 1969, pp. 525–533.
them may be obtained from ASTM, 100 Barr Harbor Drive, PO Box C700, West Harrison, N. L., “Resistivity of Transformer Oil at Low and Medium Field
Conshohocken, PA 19428–2959. Request ADJD092401. Strengths,” Proceedings IEEE, IEEEA, Vol 115, May 1968, pp. 7
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