# vfd load side questions



## Jlarson (Jun 28, 2009)

Looks like a reflected wave reducer. Is it for a drive with an extra long run out to the motor?

The resistors are dampening resistors. They help prevent resonance because of the cable capacitance.


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## butcher733 (Aug 4, 2012)

jlarson said:


> looks like a reflected wave dampener. Is it for a drive with an extra long run out to the motor?
> 
> The resistors are dampening resistors. They help prevent resonance because of the cable capacitance.


~100'


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## John Valdes (May 17, 2007)

Looks like a load reactor and braking resistor bank mounted close to each other.


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## butcher733 (Aug 4, 2012)

John Valdes said:


> Looks like a load reactor and braking resistor bank mounted close to each other.


Which do what?


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## McClary’s Electrical (Feb 21, 2009)

John Valdes said:


> Looks like a load reactor and braking resistor bank mounted close to each other.


That's exactly what we're seeing.


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## sparkywannabee (Jan 29, 2013)

That's a load reactor, for some reason a lot of times they paint em blue like line reactors. One time we upgraded 250 HP drives from GE to AB, and the line reactors would not fit in the cabinet so we mounted them outside. One of the mechanics welded up a frame to set them on, walked in and told us the "transformer stand' is done. The kid from Rockwell helping us with the commissioning took serious umbrage to that, i dont think anybody was going to get out of that room alive. Half hour lesson on whiteboard followed on why a reactor is not to be referred to as a transformer.


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## ponyboy (Nov 18, 2012)

sparkywannabee said:


> That's a load reactor, for some reason a lot of times they paint em blue like line reactors. One time we upgraded 250 HP drives from GE to AB, and the line reactors would not fit in the cabinet so we mounted them outside. One of the mechanics welded up a frame to set them on, walked in and told us the "transformer stand' is done. The kid from Rockwell helping us with the commissioning took serious umbrage to that, i dont think anybody was going to get out of that room alive. Half hour lesson on whiteboard followed on why a reactor is not to be referred to as a transformer.


 Lol. If some tech guy did that to any of our welders they'd probably get a half hour lesson on why they should go f*ck themselves


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## sparkywannabee (Jan 29, 2013)

ponyboy said:


> Lol. If some tech guy did that to any of our welders they'd probably get a half hour lesson on why they should go f*ck themselves


He had one of our electricians, big ole ex marine so hopping mad one day we just about had to restrain him, good times. I loved whenever he was in the shop though, fountain of knowledge, i learnt a lot from him, reminded you of a young JRaef.


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## JRaef (Mar 23, 2009)

Jlarson is right, that is a load filter for reducing the negative effects of the high pulse switching rate in modern drives. Also called a "sine wave filter" or a "dV/dt filter". 

The fast rise time of the PWM pulses can cause capacitance in the cables and between the stator and the rotor to create voltage spikes. The cable pulses can exceed 2000V on a 480system, way above the insulation rating of the motor windings, especially on older motors. The rotor pulses are lower, but try to go to ground through the bearings so they burn tiny little pits in the bearing races that eventually cause bearing failure. The resistors and reactor combo slow down the rise time of those PWM pulses to prevent creating those capacitive effects. A load reactor itself helps a little, adding the RC filter to it does a much better job. Not likely necessary if you are within 25ft drive-to-motor, but at 100' I would do it too. Cheap insurance.


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## Jabberwoky (Sep 2, 2012)

JRaef said:


> The cable pulses can exceed 2000V on a 480system,



Holy crap, what system have you had 2kv on the cables? I have only ever seen up to 900v spikes on our 10MHz scope at the motor side of a 250' run. I would think if the power modules on the drive side saw those spikes the diodes would break down.


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## JRaef (Mar 23, 2009)

Jabberwoky said:


> Holy crap, what system have you had 2kv on the cables? I have only ever seen up to 900v spikes on our 10MHz scope at the motor side of a 250' run. I would think if the power modules on the drive side saw those spikes the diodes would break down.


Worst case scenario, not common. And yes, it can (does) take out the transistors.


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## Jlarson (Jun 28, 2009)

We get the big spikes a lot on deep ESP installs the well guys had their hands in. I.E. no reactors, no filters and the drive is just setup enough to get water flowing :laughing:


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## CYoung (Apr 19, 2013)

Not sure if this is going to work or not but here is a picture of a waveform before a load reactor was installed.


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