ATV 71 exceeding speed setting

[MarkWebber]

In a hoisting application, we have an ATV71 with 3 15kw parallel motors and resistor bank.  While decending the hoist which was lightly loaded, the travel speed was exceeded for several seconds then returned to normal motor speeds.  No new fault codes were stored.

I've gotten with the hoist manufacturer who has no suggestions how the VFD can permit this.  

Any thoughts?

[LeoLazzaro]

Dear MarkWebber , Please could you send us more information about the architecture used in the hoisting movement ?  To have optimal control for hoisting movement SE recommend to use 1 drive per motor and closed loop ( encoder feedback). Motor model inside of our ATV71 for 3 motors in parallel will be not the true, drive willsee as 1 big motor but it is not totally correct. For other side will be necessary to double check the size of the resistor.  Could you check that  parameter BRA=No? It is automattically set it to NO if you use the brake logic funtion to control de mechanincal brake . BRA must be in no to send the energy to the resistor .

[BJacqz]

May be the first thing to check is the internal reference of the drive when speed goes over the requested one, may be, this is a simple ripple on the reference sent to the drive...I mean the signal sent to AI1 speed reference signal