The current distribution within multi strand windings is investigated for transient current and voltage supplies. The difference in losses between transient and sinusoidal waveforms is elaborated. Therefore, a wide range of frequencies as well as different kinds of transient waveforms has been investigated. The definition of the skin depth is no longer sufficient. A new parameter is required for transients, which is related to time. This parameter will be defined and called "skin time". A numerical method is developed based upon a finite element transient calculation. The method is applied to the winding as well as to the core. A comparison with measurements verifies the approach described.
Parasitic effects caused by static frequency In cases like emergency breaks the complete overload converters, like shaft voltages, insulation stress, additional capability is used. The control dynamic influences strongly losses, harmonic torque ripple or noise may endanger the the rolling stock quality. reliable operation of drives or turbine shaft arrangements and The second case is a typical compressor or pump application. diminish its lifetime.The compressor or pump drives a fluid mechanic process. The optimal design of the converter depends mainly upon the This process can be controlled in different ways. Either the driven process and the motor type. The converter size is compressor speed is adjusted or the volume flow has to be given by the technical motor data. The chosen motor design controlled by valves. A third possibility is given by hard depends on the driven process but on the chosen converter as switching of complete motor pump lines. Conventional speed well. Three main types of converters are applied to control with the application of slip couplings or slip ring asynchronous machines in this power range. These three asynchronous machines cause strong losses and maintenance types are analysed in the light of the converter caused effects. costs. A reduction in motor speed implements a reduction in load torque as well, no special temperature limitation occurs Keywords: Static frequency converter, shaft voltage, at lower speed operation. The process quality within fluid asynchronous motors, harmonic torque ripple, additional mechanics does not imply high level control requirements. losses, natural frequencies, insulation stress Often strong redundancy, loss and vibration limitations are defined, which have to be fulfilled by the drive, fig. 2. 1IiNTRODUCTION Recent developments in converter driven electrical machines Power cell allow their applications with an adequate return of investment within more and more industrial areas. Cost effective converter designs meet a strong market interest within the steel, aluminium and copper industry as well as I the need for solutions with high efficiencies in the oil and gas industry and in power plants. Three main types of asynchronous machine drive applications can be found within these industries:1l. Constant torque with strong short time overload capability and large field weakening area 2. Torque which is proportional to the square of the speed 3. Short time overload applications with alternating phases of overload and no load Transfortaer The first case is the most challenging for the drive dynamic. It is a standard application for several drives within the steel Fig. 2: Medium voltage converter Perfect Harmony industry. Roll stands, figt1, need to cope with short timean iport tim Onl torque requirements, coilers or shears must be capable to cae.The tidrkind of applicationis givengb short tim overlad accelerte andstop wthin a horttme.caes.eriThe bsdriveluis appledoivnlydrn.tatu fa acceleraeand sop withn a shot time.application. A typical case could be a ponny...
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