IEC 60034-9-2021 pdf Rotating electrical machines – Part 9: Noise limits

5.1.2 Resilient mounting The natural frequency of the support system and the machine under test shall be lower than a third of the frequency corresponding to the lowest rotational speed of the machine. The effective mass of the resilient support shall be not greater than one-tenth of that of the machine under test. 5.1.3 Rigid mounting The machines shall be rigidly mounted to a surface with dimensions adequate for the machine type (for example by foot or flange fixed in accordance with the manufacturer’s instructions). The machine shall not be subject to additional mounting stresses from incorrect shimming or fasteners. 5.2 Test operating conditions The following test conditions shall apply: a) The machine shall operate at rated voltage(s), rated frequency or rated speed(s) and with appropriate field current(s) (when applicable). These shall be measured with instruments of an accuracy of 1 % or better. – The standard load condition shall be no-load, except for series wound motors. – When required, the machine shall be operated at an agreed load condition. b) Machines shall be tested in their operating position within their specified duty that generates the greatest noise. c) For an AC motor, the waveform and the degree of unbalance of the supply system shall comply with the requirements of IEC 60034-1 . NOTE Any increase of voltage (and current) waveform distortion and unbalance will result in an increase of noise. d) A synchronous motor with adjustable excitation field shall be run with excitation to obtain unity power factor or for large machines tested as a generator. e) A generator shall be either run as a motor or driven at rated speed with excitation to obtain the rated voltage on open circuit. f) A machine suitable for more than one speed shall be evaluated over the operating speed range. g) A motor intended to be reversible shall be operated in both directions unless no difference in sound power level is expected.