Briefly about the negative effects of voltage unbalance currents

5 июля 2015
Briefly about the negative effects of voltage unbalance currents

and higher harmonics on the operation of electric motors, generators,

transformers, rectifiers and installations

for reactive power compensation.

Known:



       
  • The asymmetry of the line voltages of 4% reduces the service life of induction motors in 2 times. When of voltage unbalance greater than or equal to 5% drastically increase the vibration of the engines and heating of windings;

  •    
  • Voltage unbalance of 1% creates asymmetry the currents in windings of electric motors 7-9%, and this additional losses and the reduction of effective moment;

  •    
  • Reduction of the useful torque is approximately equal to the square of the voltage unbalance ratio

  •    
  • In the presence of the supply voltage of the motors of higher harmonics, overheating occurs due to the additional losses in the stator and in the rotor;

  •    
  • Three-phase synchronous generators are very sensitive to current unbalance. Current unbalance of three-phase generators leads to oscillations of active power, mechanical surge shaft, the wear and tear of bearing shields, increased consumption of diesel fuel of diesel generator sets. According to GOST electric car long-term operation in the unbalance current of the generator exceeds 20-25% not valid

  •    
  • In the presence of higher harmonics caused by powerful non-linear loads, there are additional losses of active power, which leads to the generator overheating and reduced efficiency

  •    
  • The asymmetry of the input voltage of the supply transformer, and load leads to the appearance of unbalance and unbalance of output voltages. Depending on the windings connections can cause overheating conditions of the magnetic circuit and windings. Transformers with zero output can significantly overheat the higher currents of zero sequence harmonics, especially the third harmonic;

  •    
  • Voltage unbalance and harmonics increase the dielectric losses in the capacitor units for reactive power compensation due to the fact that their resistance with increasing harmonics decreases exponentially, causing temperature rise and shorten the life of capacitors;

  •    
  • Voltage unbalance and harmonics complicate the job of systems for reactive power compensation due to the possible resonance currents in the network, which is possible at two frequencies.

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