Line and Load Reactors for VFDs

Can someone help me with line and load reactors for a VFD application.
1. What is the %impedance for the line and the load that I should use. Are reactors suggested for both 1Hp vs. 100hp?
2. If I have a ~250-300' motor cable length, should I use a load reactor, Common Mode chocke, or terminator? What are the advantage of each or application of each.
3. My application uses 100Hp, 20Hp and 2Hp motors.
4. I have read not to use 5% impedance reactor on the loadside. Why?
5. Also, on another application, I have multiple motors on one drive with motor leads upto 500'. Should I use load reactors? 1 reactor for 15 motors?

Thanks

 

[TheDOG]

DayEng;

It depends on what you are trying to acheive or prevent.

Reactors or chokes are used on the output side of a VSD for a number of reasons. Firstly, the choke will reduce the rate of dV/dt and reduce the effects of cable charging current. It will also be assist in reducing/eliminating overcurrent trips if the motor is subjected to shock loading, by oppposing the sharp change in current. The reason you would not use a 5%z reactor on the load side is because of the voltage drop across it. This means that the motor terminal voltage is reduced, thereby reducing motor torque.

If you are trying to reduce the effects of Reflected Wave, a motor terminator is more effective than a reactor. A terminator works by connecting a LR circuit in parrallel with the motor windings. This reduces the mismatch between motor surge impedence and cable surge impedence, therefore reducing the reflected wave voltage.

Reactors on the input is a totally different story...a 3%z reactor is used for "absorbing" line voltage spikes, thereby reducing overvoltage trips on the drive. A 5%z on the input will reduce THD more effectively than a 3%z. Again, the higher the %z, the higher the voltage drop across the reactor - robbing the motor of torque.

Hope this helps.

 

[jbartos]

Suggestions to DayEng (Visitor) Sep 3, 2002 marked ///\\Can someone help me with line and load reactors for a VFD application.
1. What is the %impedance for the line and the load that I should use.
///Although some values are mentioned in the above posting, it would be better to accept the manufacturer recommended and potentially produced reactors with their %z ratings.\\ Are reactors suggested for both 1Hp vs. 100hp?
///The input reactors are always recommended since they reduce input harmonics, spikes, and inrushes. The output side reactors are usually applied from about 5HP up, although they are definitely somewhat beneficial to smaller sized motors too.\\2. If I have a ~250-300' motor cable length, should I use a load reactor, Common Mode chocke, or terminator?
///It depends on the motor HP. If under about 5HP than the load reactor will not be so much required. However, I suggest that you follow the manufacturer recommendations for the mentioned devices.\\ What are the advantage of each or application of each.
///Load side conditioning is essentially for improvement of the VFD output voltage and current waveforms, reduction of harmonics, conditioning of reflected waves, and suppression of common mode currents.\\3. My application uses 100Hp, 20Hp
///Input reactors (filters) and output reactors (filters) do apply.\\ and 2Hp motors.///Input reactors (filters) apply, and the output reactors (filters) are marginally beneficial. Check with the VFD manufacturer.\\4. I have read not to use 5% impedance reactor on the loadside. Why?
///It may cause a prohibitively large voltage drop.\\5. Also, on another application, I have multiple motors on one drive with motor leads upto 500'. Should I use load reactors? 1 reactor for 15 motors?///There will be need for more reactors. Ideally, one for each motor above 5HP approximately. Again, it is recommended that you contact the VFD manufacturer tech support.\\