IEC 60243-2 pdf download

IEC 60243-2 pdf download Electric strength of insulating materials — Test methods — Part 2: Additional requirements for tests using direct voltage
1General
1.1 scope
This standard gives requirements additional to those in lEC 60243-1 for the determination ofthe electric strength of solid insulating materials under direct voltage stress.
1.2Normative references
Subclause 1.2 of lEC 60243-1 is applicable with the following addition:
IEC 60243-1:1998,Electric strength of insulating materials – Test methods – Part 1: Tests atpower frequencies
Definitions
Clause 2 of lEC 60243-1 is applicable.significance of the test
ln addition to the requirements of clause 3 of lEC 60243-1,the following points shall beconsidered when using direct-voltage tests.
3.1 For a non-homogeneous test specimen，with alternating voltage，the distribution ofvoltage stress within the test specimen is determined by impedance (largely capacitive). Withan increasing direct voltage, the voltage distribution may still be largely capacitive but dependspartly on the rate of voltage increase.The resistive voltage distribution after constant voltageapplication represents the steady-state condition. The choice between direct or alternatingvoltage depends upon the purpose for which the breakdown test is to be used and, to someextent, on the intended application of the material.
3.2 Upon direct voltage application,the following currents result: the capacitive current, theelectric absorption current, the leakage current, and, in some cases, partial discharge currents.
In addition, for materials with dissimilar layers or discontinuities, the voltage distribution acrossthe test specimen is also influenced， as a result of interfacial polarization， by charges ofopposite polarity，which may accumulate on the two sides of the interface and create localfields sufficiently strong to produce partial discharges and/or breakdown of the test specimens.
3.3 For most materials，the d.c. breakdown voltage is higher than the peak value of thepower-frequency breakdown voltage; for many materials，particularly those which are non-homogeneous, the d.c. breakdown voltage will be three times higher than the a.c. breakdownvoltage or even more.
4Electrodes and test specimens
Clause 4 of lEC 60243-1 is applicable.
5 Conditioning before tests
Clause 5 of lEC 60243-1 is applicable.
6 surrounding medium
Clause 6 of lEC 60243-1 is applicable.
7 Electrical apparatus
7.1Voltage source
The test voltage applied to the electrodes shall be provided by a power supply having thefollowing characteristics and components.
7.1.1 A choice of voltage of either positive or negative polarity shall be provided,one of theconnections to the electrodes being earthed.
7.1.2 The alternating voltage ripple on the test voltage shall not exceed 2 % of the voltage atall values greater than 50 % of the breakdown voltage. The test voltage shall also be free fromtransients or other fluctuations exceeding 1 % of the applied voltage.