M-flex factory VFD panel with bypass problems 1

[jnorris04]

I have 8 Schneider VFD panels that have a bypass with overload protection built in. On 60 hz, the panel works as it should. But, when I turn it down to 30 hz, the overload relay trips within a couple minutes. What is causing this? It is an electronic overload. It is doing this on all 8 panels.

 

[davidbeach]

Bypass problem - bypass is impossible at 30Hz, so something doesn't line up. I think you have a problem that will take 2 or 3 detailed paragraphs before someone can begin to have a clue; a very brief description probably isn't going to get you any useful information.

 

[waross]

Can you describe the overload relay? Does it give any indication of the reason for the trip? Can the under frequency be tripping the phase loss protection feature?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

Very few solid state overload relays are capable of being used down stream of VFDs, and none of the ones Schneider sells are so rated as far as I know. Did Schneider build these bypass panels, or were they built by others? As I recall, NONE of the Schneider SSOLs are capable of being used in a circuit with a VFD, you must use a bi-metal version.

Also, as a general design rule, the OL relay on a VFD bypass is placed in the circuit so that it is only being used when the bypass starter is in use, so it would not even be in the circuit when the motor is running at 30Hz. Sounds to me as though someone built these without a good understanding of all of the potential pitfalls.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington