Individual Line Reactor or "Global" Line Reactor?

[egurdian3]

Dealing with replacement of RTUs for a multi-unit residential building. The RTUs are controlled thru VFDs; the largest motor is a 460V, 10HP for the compressor, RTU-FLA = 78A, MOCP = 90A.
Regardless of cost, what is a preferred, more effective application for line reactors:
1) Install individual AC Line Reactors for each RTU.
2) Install 1 AC Line Reactor on the incoming feeder to the 1200A Switchboard?

 

[richwaskowitz]

Not Recommended

Not Recommended

According to MTE,

"Multiple drives or inverters on a common power line require one reactor per controller. Individual reactors provide filtering between each controller (reduce crosstalk) and also provide optimum surge protection for each unit. A single reactor serving several controllers does not provide adequate protection, filtering or harmonic reduction when the system is partially loaded."

It would be nice to use one reactor to cover all, but it just does not work that way. You have to remember that reactors are put in front of drives for several different reasons. One is to add impedance to limit the current inrush charging the power supply caps. Another reason is to reduce harmonics, not just between drives but out beyond the panel in back into the rest of the power system.

Hope this helps.

 

[Besoeker]

According to MTE,

"Multiple drives or inverters on a common power line require one reactor per controller. Individual reactors provide filtering between each controller (reduce crosstalk) and also provide optimum surge protection for each unit. A single reactor serving several controllers does not provide adequate protection, filtering or harmonic reduction when the system is partially loaded."

It would be nice to use one reactor to cover all, but it just does not work that way. You have to remember that reactors are put in front of drives for several different reasons. One is to add impedance to limit the current inrush charging the power supply caps. Another reason is to reduce harmonics, not just between drives but out beyond the panel in back into the rest of the power system.

Hope this helps.

Spot on if I may say so.

 

[Jraef]

According to MTE,

"Multiple drives or inverters on a common power line require one reactor per controller. Individual reactors provide filtering between each controller (reduce crosstalk) and also provide optimum surge protection for each unit. A single reactor serving several controllers does not provide adequate protection, filtering or harmonic reduction when the system is partially loaded."

It would be nice to use one reactor to cover all, but it just does not work that way. You have to remember that reactors are put in front of drives for several different reasons. One is to add impedance to limit the current inrush charging the power supply caps. Another reason is to reduce harmonics, not just between drives but out beyond the panel in back into the rest of the power system.

Hope this helps.

You're right, but in my opinion, we have to consider the source on that comment about multiple reactors; a company (MTE) that directly benefits by selling you on the most expensive option...

A single line reactor still provides the CHIEF benefit offered by that option, the added impedance to slow down the rise time of any transients coming in from the line side. "Cross talk" among drives is not as much of an issue as it was maybe 20 years ago. I have plenty of installations where there is only one large reactor ahead of multiple small drives, no problems with anything taking place between the drives. As for harmonics, reactors are over sold for that purpose in my opinion. Sure, they can drop the ITHD on a 6 pulse drive input from 80% to 40%, but you really need to be under 12% ITHD at most, so you don't really get all the way there with reactors alone anyway, and if you do use a passive filter, you end up with an individual reactor as part of that filter. Harmonics for most people is also more of a regulatory concern than anything else in that they are going to be required to meet IEEE 519 which is based SOLELY on the THD at the PCC (Point of Common Coupling), typically the utility service connection. You may or may not need to address it at all when it is small loads in a larger facility. I still firmly believe that line reactors should be used as cheap insurance for the investment in the VFD, and one reactor ahead of multiple drives is the most cost effective way of getting that if the VFDs are all small.

 

[Besoeker]

You're right, but in my opinion, we have to consider the source on that comment about multiple reactors; a company (MTE) that directly benefits by selling you on the most expensive option...

A single line reactor still provides the CHIEF benefit offered by that option, the added impedance to slow down the rise time of any transients coming in from the line side. "Cross talk" among drives is not as much of an issue as it was maybe 20 years ago. I have plenty of installations where there is only one large reactor ahead of multiple small drives, no problems with anything taking place between the drives. As for harmonics, reactors are over sold for that purpose in my opinion. Sure, they can drop the ITHD on a 6 pulse drive input from 80% to 40%, but you really need to be under 12% ITHD at most, so you don't really get all the way there with reactors alone anyway, and if you do use a passive filter, you end up with an individual reactor as part of that filter. Harmonics for most people is also more of a regulatory concern than anything else in that they are going to be required to meet IEEE 519 which is based SOLELY on the THD at the PCC (Point of Common Coupling), typically the utility service connection. You may or may not need to address it at all when it is small loads in a larger facility. I still firmly believe that line reactors should be used as cheap insurance for the investment in the VFD, and one reactor ahead of multiple drives is the most cost effective way of getting that if the VFDs are all small.

Have you come across notching?

 

[Jraef]

Have you come across notching?

Not in the last 20 years or so, no.