1 Scope
This standard specifies the method for determining the breakdown voltage of insulating oils at power frequency. This standard is applicable to determine all types of insulating oils of normal viscosity up to 350 mm2/s at 40℃. It is appropriate both for acceptance testing on unused insulating oils and for assessing the condition of samples taken in monitoring and maintenance of equipment.
2 Normative References
The following normative documents contain provisions which, through reference in this text, constitute provisions of this standard. Unless otherwise specified in the Standard definitely, the following referenced standards are all currently valid.
GB/T 4756 Petroleum Liquids-Manual Sampling
IEC 52 Recommendations for voltage measurement by means of sphere-gaps (one sphere earthed)
IEC 60 High-voltage test techniques
3 Principle
The sample to be tested, which is placed in the specific equipment, is subject to an alternating electric field of which the voltage is continuously increased at a given pace until the sample has been punctured.
4 Reagents
4.1 Acetone: analytical pure.
4.2 Petroleum ether: analytical pure, 60℃~90℃.
5 Apparatus
5.1 The electrical apparatus consists of the following units:
a) Voltage regulator;
b) Step-up transformer;
c) Switching system;
d) Energy-limiting instruments.
Two or more of these units may be integrated in any equipment system for use.
5.1.1 Voltage regulator
Uniform increase of voltage, as required, by manual means is difficult and, for this reason, automatic control is essential. Automatic voltage control may be achieved by one of the following methods:
a) Variable ratio auto-transformer;
b) Electronic regulator;
c) Generator-field regulation;
d) Induction regulator;
e) Resistive type voltage divider.
