A comparative analysis of methods for calculating the transient voltage distribution within the stator winding of an electric machine subjected to steep-fronted surge

Frequency domain modelling of random wound motor windings for insulation stress analysis

“…Other authors have stated that despite neglecting these losses there is adequate agreement with experimental data [9], nevertheless it is clear from the results presented here that prediction accuracy degrades in the high frequency ranges associated with short pulse rise times. This conclusion is in agreement with some recently published works [6,11].…”

“…The resulting overvoltages, which can reach up to twice the dc voltage level in the inverter, and the short rise times cause a very uneven voltage distribution along the winding, and most of the voltage falls within the first coil of the winding [1][2][3]. Furthermore, there is an uneven voltage distribution within this first coil [4], with higher electrical stresses in the first turns [2,3,5] and last turns [2,6]. In random wound windings this can be a problem because these turns can be in contact and the interturn voltage may exceed the partial discharge inception voltage (PDIV) of the winding insulation.…”

Frequency and Time Domain Characterization of Transient Voltages through Low-Voltage Motor Stator Coils Fed with Inverter Pulses

“…It has been reported that lower rise times provide greater overvoltages and a more uneven voltage distribution, so it is necessary to use models including winding losses [8] and to increase upper frequency limits under study [3,5].…”

“…Moreover, during the surge rise time, nearly the full voltage is displayed across the first coil in each phase [3][4][5][6][7]. Furthermore, there is an irregular voltage pattern within this first coil [7], with higher electrical stresses in the first turns [1,5,6] and Nomenclature ω angular frequency U(ω) frequency domain coil input voltage u(t) time domain coil input voltage U k (ω) frequency domain voltage at tap #k u k (t) time domain voltage at tap #k H k (ω) voltage transfer function at tap #k I j (ω) frequency domain current in mesh #j Zt i (ω) turn #i impedance Zm ij (ω) inductive mutual impedance between turns #i and #j Ztt (ω) turn-to-turn impedance Ztg (ω) turn-to-ground impedance last turns [8], so in random wound coils it is possible to have great voltages between two wires touching each other [5,9]. These are the reasons for identifying turn-to-turn insulation as the weakest point within an inverter fed motor stator winding [9,10].…”

“…Most of the work recently carried out has focused on form-wound coils that have an easier geometrical description [8,12], so the proposal of an accurate model for voltage distribution prediction in random wound coils becomes a complex problem to be solved.…”