Abstract
AbstractThe high electrical stresses in the Electrical Insulation Systems of machines fed by pulse width modulation (PWM) inverters remain a limitation of the lifetime. The stress is caused by repetitive over voltages caused by the short switching times of the PWM inverter power electronic circuit. This paper provides measurements made on an industrial drive connected to the grid with standard cables that include a ground connection wire, following the current standards. The phase-to-phase, phase-to-neutral, and neutral-to-ground voltages are measured focusing on short and repetitive voltage spikes. The causes of these voltage spikes are analyzed using a high frequency equivalent circuit of the whole drive, including the earthing system. The simulations are made with the well-known SPICE circuit simulator. This study focuses on the common-mode currents flowing in the earthing connections and its influence on voltage spikes. A solution that can reduce significantly the phase-to-neutral voltage spikes is proposed.
Highlights
The advances in power semiconductor technologies have brought numerous opportunities to develop motor drivesThe pulse width modulation (PWM) inverters create additional voltage stresses on the motor electrical insulation systems (EISs)
It is well known that the fast-fronted voltage pulses imposed by the inverter create a higher voltage stresses between the winding turns near the phase inputs
The slot capacitances existing between the motor frame have a major importance for estimating the voltage stress endures by the motor coils and their turn-to-turn insulation
Summary
The PWM inverters create additional voltage stresses on the motor electrical insulation systems (EISs). The theoretical study [7] based on partial differential equations representing the propagation of energy in windings details these phenomena This theoretical analysis, made in time-domain, yields results that are confirmed by measurements made on a random-wound motor specially equipped for measuring the turn voltage distribution. The connection cable between the inverter and the motor has a major role [17,18,19] These fast phenomena have been studied with wave propagation theory or equivalent circuits [20,21,22,23,24], considering the voltage fast fronted pulses of the inverter. A specific solution is proposed for the most unfavorable cases
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