How to solve long line control problem?

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renzespin

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Location
Seoul, South Korea
Hi! everyone in this forum. I would like to ask for your good ideas or proven experiences in solving the problem of long line control. This problem usually happens in the control circuit of motor LCS (Local Control Stations) when control cable length is in the range of 400~600meters (MCC to motor location).

The problem is that the LCS malfunctions due to a small amount of circulating current in the control wires. The control voltage in the MCC is 120VAC. When we applied an AC/DC converter at MCC side in one of our projects, this problem has been avoided. However, at this time only 120VAC shall be used. Therefore, is there any other way to solve the problem keeping 120VAC as the control voltage?
 
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renzespin

Member
Location
Seoul, South Korea
jim dungar said:
This is a resource I have used in the past.

http://static.schneider-electric.us/docs/Motor Control/Lighting Contactors/M-379F.pdf
Click to expand...

Thank you very much for sharing with us the Square D bullletin. It is indeed very helpful to clearly understand the nature of the problem and the possible ways on how to solve it. In my opinion, I believe the best solution to shunt capacitance effect is what is shown in Fig.7, i.e., using Isolating DC Control Relay. Once again, thank you very much Mr. Jim Dungar and to all.
 
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jim dungar

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Location
Wisconsin
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PE (Retired) - Power Systems
renzespin said:
It is indeed very helpful to clearly understand the nature of the problem and the possible ways on how to solve it.
Click to expand...
Different problems have different solutions, so I am glad you were able to narrow down your possibilities.
 
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