IEC 60034-18-32:2010 pdf – Rotating electrical machines – Part 18-32: Functional evaluation of insulation systems – Test procedures forform-wound windings – Evaluation by electrical endurance.
7 DIagnostic sub-cycle
7.1 General
Following each ageing sub-cycle, a diagnostic sub-cycle can be performed. Failure of any part of the test specimen during a diagnostic test constitutes failure of the whole system and shall be reported as such. The appropnate voltage tests are selected according to the chosen test procedure in 4.2.
7.2 Voltage tests
7.2.1 Mainwall insulation test
The diagnostic test on the mainwall insulation consists of three successia ppI.ctQ J a 1,2150 impulse voltage with a peak value of U, = (4 U + 5 kV). Alternatively, a mainwall power frequency test according to 4,4 of IEC 60034-15 may be used In this case, an voltage of (2 UN + I kV) is applied for 1 mm between coil terminals and earth. The applied voltage is then increased at the rate of I kVls up to 2 (2 UN + 1 kV). and then immediately reduced at a rate of at least I kVIs to zero.
7.2.2 Turn Insulation Impulse test
For test objects comprising multiturn coils wound with a single or stranded conductor the diagnostic test of the turn insulation is carried out by an impulse voltage test. The amplitude (peak) shall be given by the formula Lr = 0.65 (4 UN + 5 kV), where UN is the rated voltage in kV (see IEC 60034-15), The number of impulses to be applied is at least 5.
7.2.3 Turn insulation power frequency test
For test objects comprising parallel isolated conductors a power frequency voltage of an appropriate magnitude shall be applied between the turns for 1 mm. Voltage of an appropriate magnitude should be higher or equal to the highest ageing voltage.
7.3 Other diagnostic tests
Optional diagnostic measurements may be performed for Information or to determine end of test life. These may replace the voltage tests. Factors such as Insulation resistance. loss tangent, and partial discharges are examples. An end-point criterion may be established for each diagnostic test, with suitable justification reported.
For the stress grading system, there are no electrical tests defined for diagnostic purposes but it may be useful to record the condition of the material, viewed with the unaided eye, in regard to colour and surface imperfections, such as blistering and cracking.
8 Failures
8.1 Failure location and verification
Failure of a specamen occurs when any electrical breakdown of the mainwall insulation occurs. This will result In the over-current detection system interrupting current to the high voltage transformer. Failure of the insulation should be verified by re-applying voltage gradually from zero. A specimen Insulation failure will prevent the reapplication of the full test voltage. Locating the failure site Is desirable and may be undertaken by seeing arcing or heating at the failure site as the voltage is raised. When specimen failure has been verified the tailed sample should be isolated to allow testing to continue on the remaining samples.
8.2 Failed specimen observations
Each failed specimen should be examined to ensure that the failure is valid for statistical Interpretation. This may require some specimen dissection In the area around the insulation puncture to identify the failure location and its cause.
8.3 Dimensional measurements
The thickness of the insulation wall (mainwall plus lurn plus strand) shall be determined at or near the voltage endurance failure site
9 Functional evaluation of the data
9.1 General
The evaluation of the test data should follow the guidelines set out below. Under the assumption of a Weibull distribution, the appropriate statistical analysis should be applied to calculate the significance of the candidate sample life with regard to that of the reference sample (see IEC 62539).
The general rule is that the candidate insulation system is considered to be qualified if the 90 % confidence interval of the used probability distribution falls above or within that obtained from the reference system (see 4.1 in IEC 60034-18-1).
9.2 Full evaluation
Electrical endurance graphs of the candidate and the reference system are plotted as a log- log representation of the time to failure (t), as a function of the ratio of test voltage (Ui) and rated voltage (UN), where UN is the rated voltage of the reference system and the candidate system. The candidate system is qualified if.