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IEC 60034-18-41 pdf free download

IEC 60034-18-41 pdf free download.Rotating electrical machines – Part 18-41: Partial discharge free electrical insulation systems (Type I) used in rotating electrical machines fed from voltage converters – Qualification and quality control tests.
The value of Ub in these formulae is the value shown in Figure 1 for the phase/phase voltage on the machine terminals. The values of the phase/ground voltages estimated from these formulae may be higher or lower in practice, depending upon the grounding system, converter control regime and other factors. It is known that a sudden rise can occur in the machine ground voltage level with respect to the d.c. zero point in the converter. The theoretical rise is determined capacitively to be 1/3 which gives a residual effect of about 0,7. This would apply to simple systems where only travelling wave theory determines the factor, i.e. stress categories A, B and C (see Clause 7).
Exam pIes of the enhancement that is produced for various rise times and cable lengths in the case of a motor driven from a converter are given in Figure 4. In this case, the enhancement to the voltage for an impulse rise time of 1,0 is insignificant below about 15 m and only exceeds 1,2 when the cable length is greater than about 50 m.
Voltages above 2UdC can be produced at the terminals of the machine by drive double transition and by a converter fed drive algorithm that does not allow a minimum time between successive pulses. Double transition occurs, for example, when one phase switches from minus to plus d.c. bus voltage at the same instant that another phase switches from plus to minus. This generates a 2UdC voltage wave which travels to the machine and can then increase in magnitude when reflected at the machine terminals. If there is no minimum impulse time control in the drive and if the time between two impulses is matched with the time constant of the cable between the converter and the machine, an over voltage >2UdC can be generated at the machine terminals. The reflection can be reduced or prevented by using a filter in the converter, at the machine terminals or both.
In the event of an earth fault on one of the phases of a system where the neutral star point is not grounded, the machine may be permitted by the manufacturer to run for a period of several hours until a suitable outage can be arranged for repairs. In this case, the voltage stress on the turn to ground insulation in the other phases will increase.IEC 60034-18-41 pdf free download.

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