BS EN 61558-2-12:2011 pdf free.Safety of transformers, reactors, power supply unitsand combinations there of Particular requirements and tests forconstant voltage transformers and power supplyunits for constant voltage.
BS EN 61558-2-12 Replacement of the 10th paragraph starting with “Transformers are supplied …” by thefollowing:
The constant voltage transformers are connected to the rated supply voltage and loadedwith an impedance resulting in the rated output, at the rated output voltage and, for a.c., atthe rated power factor. The supply voltage is then increased to the value of the highest inputvoltage variation declared by the manufacturer. After this voltage increase，no change oradjustment is made in the circuit. The test is repeated under no-load condition with thehighest or the lowest input voltage variation if this is a more unfavorable condition.
This clause of Part 1 is applicable,except as follows:Replacement of the 2nd paragraph starting with ” Compliance is checked…” by thefollowing:Compliance is checked by inspection and by the following tests，which are carried outimmediately after the test according to 14.1,at the same ambient temperature,and withoutchanging the position of the constant voltage transformer at the maximum value of therated supply voltage designed for the constant voltage transformer.Inherently short-circuit-proof constant voltage transformers shall be tested as follows:
Before starting the test,it is necessary to determine the highest output current of theconstant voltage transformer at the maximum value of the supply voltage designed for theconstant voltage transformer.The constant voltage transformer is then loaded with themaximum output current or the output winding(s) short-circuited,whichever results inthe maximum temperature.Three additional specimens are required，only for the following test. Constant voltagetransformers used in other tests are not subjected to this test.
Each of the three specimens is mounted as for normal use on a 20 mm thick dull blackpainted plywood surface. Each constant voltage transformer is operated at rated supplyvoltage plus or minus the input voltage variation declared by the manufacturer，the outputwinding which produced the highest temperature during the test of 14.1 being initially loadedwith 1,5 times the rated output current (or, if this is not possible, the maximum value of theoutput current obtainable) until steady-state conditions are reached or the constant voltagetransformer fails (whichever occurs first).
lf the constant voltage transformer fails， it shall comply,during and after the tests, with thecriteria given in 15.5.2.
lf the constant voltage transformer does not fail, the time to reach steady-state conditions isnoted and the chosen output winding is then short-circuited.The test is continued until theconstant voltage transformer fails. Each specimen shall do so within a duration, for this partof the test, which is no longer than that necessary to attain steady-state conditions, but in anycase it shall not exceed 5 h.
The constant voltage transformer shall fail safely. lt shall comply, during and after the test,with the criteria given in 15.5.2.BS EN 61558-2-12 pdf download.