BS/EN 50305-2020 pdf download.Railway applications — Railway rolling stock cables having special fire performance — Test methods.
6.7 DC stability
A test specimen of minimum length of 5 m of cable shall be immersed in distilled water containing 3 % NaCI, At least 300 mm of additional cable shall protrude at each end. The salt solution shall be maintained at an elevated temperature of (85 ± 2) ‘C for (240 ± 2) h, and the specified voltage applied between the conductor and the salt solution with the conductor at the negative potential. The test shall then be repeated, using a new test specimen, with the conductor at the positive potential.
The current flowing in the circuit shall be measured periodically throughout the test at intervals not greater than 24 h. Continuous measurement is preferred, if possible.
The current measurement data shall be plotted in the form of a current versus time curve and shall indicate an approach to a period of stability.
NOTE A period of stability is, for instance, less than 10 % increase In current leakage averaged over any 24 h period (this is subject to review in the light of practical experience),
On completion of the immersion, the cables shall be removed from the salt solution and subjected to the voltage test specified in 6.2 except that the test voltage shall be the rated voltage (U) of the cable, unless otherwise specified.
6.8 DielectrIc strength
5 m of cable sample shall be immersed in water for a period as given in the cable standard. maintained at a temperature of (20 ± 5) ‘C with at least additional lengths of 150 mm protruding at each end. The voltage test specified in 6.2 shall be appfied for 1 mm between the conductor and the water. The test voltage shall be as specified in the cable specification. Immediately afterwards the voltage shall be increased by 500 V every 30 s until a disruptive discharge occurs.
The recorded value shall exceed the specified minimum.
Samples of completed cables shall be aged in accordance with the time and temperatures given In the
appropriate cable specification. The testing shall be In accordance with EN 60811-401 for single layer.
For multi-layer insulating systems special techniques are given in the particular cable standard (see
4.4).
7.2 Long term ag&ng
7.2.1 General
This test method provides a standardized test and procedure for determining the 20 000 h lifetimes of insulation and sheath materials, The end point selected is 50 % elongation at break. A brief explanation of the significance and use of the test is given in Annex C.
To give a value representative of supplied cables, and to provide comparative data, tests for insulation shall be carried out on samples of insulated cores. Sheath shall be taken from a cable of sufficient size so that, after buffing to remove any indentations, the sample conforms to the requirements of EN 60811-501 (multi-layered systems will therefore require large cross-sections to be tested). This allows customers, if required, to confirm performance on supplied cables. Ageing performance demonstrated on small cross section cables it is deemed to be representative cables with the same design and materials.
7.2.2 Summary attest method
Three or four sets of test specimens of a given sample of insulated wire are exposed to several fixed temperatures. From time to time a set of samples is removed and each specimen is wrapped on a 1 o mandrel to simulate a flexing stress equal to 50 % and then immersed in a water bath where it is subject to a voltage test. A 6 D or values of Table 3 mandrel may be used as an alternative, as this represents the minimum bending radius allowed for installation. Specimens are removed until such time that failure occurs.
The life data at different temperatures are analysed on the basis of the Arrhenius equation which relates exposure time to failure to the reciprocal of the absolute temperature of exposure. The method is based on EN 60216-1.
An initial screening test at 180’C ± 2’C is used to determine the approximate rating of the cable. 45 Samples are placed in the oven, after 4 days the first 3 samples are tested. Each day 3 samples are removed and tested until failure occurs or 50 % elongation is rio longer achieved. Based on the results of the screening test sufficient sets of test specimens of a given sample of insulated wire or sheath are exposed at several fixed temperatures with the lowest temperature selected such that at least 5000 h will be needed for the end point to be reached. At appropriate intervals samples are removed and tested, either by wrapping the sample around a 10 mandrel or around itself to induce 50 % strain. followed by electrical tests, or in the case of sheathing by tensile testing. Using the methods described in EN 60216-1 the time to failure at different temperatures are used to create an Arrhenius plot to detemiine the 20000h I 50 % elongation at break rating. Previous convention dictates that at least 20C higher rating is needed than the designated continuous use temperature.BS/EN 50305-2020 pdf download.