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Where "h" is the harmonic order, "k" is any integer, and "q" is the pulse number of the device/circuit. 

This can also be achieved by using dual-wound transformers, where the primary is delta and the secondary is wound with two output windings: a wye and a delta. The result is on transformation being 30° apart, creating the equivalent of a 12-pulse unit. The same result is achieved by using two transformers, one wired delta-delta, and the other delta-wye. The figure above shows this application. 

When installed close to the line-side terminals of the equipment, filters provide the lowest impedance path for the harmonics currents to flow. Thus these currents will not be introduced into the rest of the distribution system, where they can cause wave distortion and damage or tripping of power factor correction capacitors. The figure above shows this concept.  

The 5th harmonic is a negative sequence harmonic, and the resulting magnetic field revolves in a direction opposite to that of the fundamental field at a speed five times that of the fundamental field. And the 7th harmonic is a positive sequence harmonic, with a resulting magnetic field revolving in the same direction as the fundamental field at a speed of seven times the fundamental. The net effect is a magnetic field revolving at a speed of six times the speed of the rotor.  

It's said by some experts that harmonics can significantly impact the motors, basically through voltage distortion. This voltage distortion at the motor's terminals translates into harmonic fluxes within the motor. These harmonic fluxes don't contribute much to motor torque. However they do rotate at a frequency different than the rotor synchronous frequency. In turn it induces high-frequency currents in the rotor.  

One way of looking at this is shown in Figigue 2 below, we see a power factor (PF) improvement curve superimposed over a harmonic resonance curve. 

Note that the 5th and 7th order harmonics are shown interfering across a wide area of capacitor addition, specifically in the high power factor (PF) area, in which you would normally want to have their performance characteristic. As you can see from the figure, the interference is significant. 

Power Factor improvement vs. harmonic resonance 

The figure below shows a basic 3-phase, 6-pulse, pulse-width modulation (PWM) drive (VSD). 

All pulse-width modulation (PWM) drives contain the following main parts, with subtle differences in hardware and software components. The input section of the pulse-width modulation (PWM) is the converter, and it contains six diodes (arranged in an electrical bridge). These diodes convert AC power to DC power.  

Compounding this problem is the fact that these nonlinear loads typically have a low power factor (PF), forcing many industrial facilities to use capacitor banks to improve power factor (PF) to avoid utility penalty charges.  

We know that DC motors, unlike AC motors, act like a electrical generator when the motor has been disconnected from the power source. The DC motor functions like a generator due to the DC motors permanent magnet. The resistance to rotation causes the dynamic braking. The voltage and current produced by the DC motor is directed into the dynamic braking resistor to dissipate the heat energy.