Abstract
During synchronization phase of a doubly fed induction machine prototype abnormal high voltages were recorded at stator terminals. By evaluating the measured curves, and the frequency response of a similar machine, these overvoltages could be traced back to differential mode resonance effects within the machine itself. The effect of differential mode resonance is not restricted to doubly fed induction machines but also occurs in other machine types such as squirrel cage induction machines. If not considered in the insulation design, such abnormal voltages will lead to a premature ageing of the insulation. Depending on the operating conditions, premature failures may occur. The measured data presented in the article give an illustrative example what could happen if windings of electric machines are excited near series resonance frequency. As the occurence of this effect becomes more probable the higher the switching frequency of the converter, it is thoroughly important to be aware of it.
Highlights
D OUBLY fed induction generators (DFIGs) with static converters in the rotor circuit are widely used for wind power and pump storage applications
In special industrial drive applications induction machines with wound rotors (WRIMs) and static converters in the rotor circuit are used [5], [6]. For both – DFIGs and WRIMs – voltage harmonics are present at rotor terminals if they are operated with voltage source converters without sinusoidal filters
For a DFIG in the multi-megawatt range, high harmonic voltages have been measured at the stator terminal during synchronization phase
Summary
D OUBLY fed induction generators (DFIGs) with static converters in the rotor circuit are widely used for wind power and pump storage applications. In special industrial drive applications induction machines with wound rotors (WRIMs) and static converters in the rotor circuit are used [5], [6] For both – DFIGs and WRIMs – voltage harmonics are present at rotor terminals if they are operated with voltage source converters without sinusoidal filters. To interpret frequency responses measured by LCR-metres, the scheme introduced in [7] was developed Albeit it was focused on squirrel cage induction machines, it can still be used for DFIG analysis here, since the stator designs are comparable. Numerical simulation data is presented, showing that the stators of machines A and B have similar characteristics This makes the measured frequency response of generator B to a certain degree comparable to generator A.
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