# Electric Current and Components: Questions… 1 answer below »

Q1. What are the main sources/causes of EMI on the supply side of the DC VSD? What are the main harmonic frequencies present?

The causes of EMI on the supply side is by fast switching frequencies,Harmonics are a sinusoidal component of the mains fundamental frequency (50 Hz). Harmonics are generated by equipment such as, power electronics, drives, transformers and arc welders. The supply side harmonic interference is a continuous distortion (up to 3khz) of the normal sinusoidal waveform.The distortion frequencies are multiples of the fundamental 50Hz frequency The main harmonics frequencies present mainly low order odd harmonics.

Q2. Why are motor side harmonics from a VSD not so much of an issue with DC drives as with Ac drives?

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Q3. Explain how a phase controlled 3 – phase rectifier leads to harmonics in the supply network.

Q.4 Explain the difference between Power Factor and Displacement Factor

Q.5 As the DC output voltage from the convert is reduced the firing angle (delay angle) increase and the reactive current required by the VSD increase. Explain

Q.6 Explain how harmonics on the supply side of the VSD may be prevented from entering the supply network.

Q.7 Using torque v/s Speed and Power v/s speed curves explain what happens to the output of the DC motor when it is driven at various speed above and below rated (base) speed.

Q.8 Describe the working of the ‘Ward Leonard’ set. Explain why it’s use has fallen out of favour at the present time. Draw a sketch of the set up.