IEC 62068-1:2003 pdf – Electrical insulation systems – Electrical stresses produced by repetitive impulses – Part 1: General method of evaluation of electrical endurance.
1 Scope This part of IEC 62068 is a basic publication that applies to electrical equipment, regardless of voltage, containing an insulation system, which is – connected to an electronic power supply, and – requires an evaluation of insulation endurance under repetitive voltage impulses. This standard proposes a general test procedure to facilitate screening of electrical insulation systems (EIS) and to achieve a relative evaluation of insulation endurance under conditions of repetitive impulses. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60727-1, Evaluation of electrical endurance of electrical insulation systems – Part 1: General considerations and evaluation procedures based on normal distributions IEC 61649, Goodness-of-fit tests, confidence intervals and lower confidence limits for Weibull distributed data 3 Terms and definitions For the purpose of this document, the following terms and definitions apply. 3.1 electrical insulating material EIM electrically stressed component in an EIS 3.2 electrical insulation system EIS insulating structure containing one or more electrical insulating materials (EIM) together with associated conducting parts employed in an electrotechnical device [IEC 60505:1999, definition 3.1.1 1 ]
3.3 candidate EIS EIS under evaluation to determine its electrical endurance when exposed to repetitive voltage impulses 3.4 reference EIS evaluated and established EIS with either a known service experience or a known comparative functional evaluation under repetitive voltage impulses 3.5 partial discharge PD electric discharge that only partially bridges the insulation between conductors [IEC 60270:2000, definition 3.1 modified ] 3.6 partial discharge inception voltage PDIV lowest voltage at which partial discharges are initiated in the test arrangement, when the voltage applied to the object is gradually increased from a lower value at which no such discharges are observed 3.7 partial discharge extinction voltage PDEV highest voltage at which partial discharges are extinguished in the test arrangement, when the voltage applied to the object is gradually decreased from a higher value at which such discharges are observed 3.8 unipolar impulse voltage impulse, the polarity of which is either positive or negative 3.9 bipolar impulse voltage impulse, the polarity of which alternates from positive to negative or vice versa 3.10 impulse-voltage polarity polarity of the applied impulse, with respect to earth 3.11 impulse-voltage repetition rate inverse of the time between two successive impulses when the time intervals are the same, whether unipolar or bipolar 3.12 impulse rise time 1,25 times the time interval between 10 % and 90 % of the zero-to-peak impulse voltage, on the leading edge of the impulse 3.13 rate of voltage rise 0,8 times the impulse-voltage magnitude divided by the time interval between the 10 % and 90 % magnitude of the zero-to-peak impulse voltage
3.14 voltage endurance coefficient VEC exponent of the inverse power model or exponential model, which together with the coefficient k, describes the relationship between life and voltage 3.15 life either time or number of impulses to failure 4 General test procedures 4.1 Overview This clause describes the general procedures for evaluating the ability of an EIS to resist deterioration due to repetitive impulse voltages. There are two methods, depending on the desired outcome. a) A screening test can be carried out at a single test voltage to assess alternative EIMs or different physical constructions by comparison with the previously evaluated EIS. The purpose is to find the EIM (or construction) which yields better endurance. In addition, a single EIS can be evaluated at a single test voltage under variable test conditions, such as different humidity, different impulse repetition rates, etc. to determine the effect of the variable.