PowerFlex 700 Emergency Stop

rleon

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Aug 2008
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Hi:

How can I make an emrgency Stop to a PowerFlex 700? I just have the emergency button in plantnear the motor (not using a safety relay) and I know how to connet it the the VDF and program a paramter to make the motor stop inmediatly, not with coast and without ramp and the stop have to work in any mode (AUTO or MANUAL).

I need a E-Stop without disconnecting power to VDF and without using a contactor between the motor and the VDF output.

Thanks!
 
Last edited:
If I read you post correctly then you are using the E-Stop button as a stop button with a certain stop mode selected and this is not a true E-Stop.
In the past for an E-Stop we use a dual channel safety relay and safety contactors [2] in series on the line side of the VFD but lately we have been using the Drive Guard Safe Off on the Power Flex Dives when it is available and I think you can get that for the 700.


HTH
 
An E-stop shall stop the machine as quickly as possible. To
obtain a quick stop one either removes the power directly
or one lets a frequency converter 'run down' and afterwards
after a little delay, remove the power. An E-stop shall not
create other hazards. Therefore a risk analysis must be made​
for the E-stop to be correctly connected. Also an E-Stop should require a manual reset after the button is released not an automatic one
 
or one lets a frequency converter 'run down' and afterwards
after a little delay, remove the power.

That's the point. I need to make the VDF brakes the motor as quickly as possible and then disconnect the power, for example after a delay or when the motor is under 10 RPM.

If I disconnect the power only, without braking first, the motor will continue running by inertia. If I use normal stop, the VDF will use a ramp. None of this two options works for me.

This are only pump motors, without gear box.
 
This is were the safety relay with time delayed outputs and safety contactors come into play.
In an E-Stop condition you issue an immediate command from the safety relay to stop the drive and then at some time later [Determined by the time delays of the safety relay you have selected] you drop power to your safety contactors which drops power to the line side of the drive.


Again you can search for the Drive Guard Safe Off Option for the Power Flex 700 which eliminates the safety contactors but still uses a safety relay.
 
That's the point. I need to make the VDF brakes the motor as quickly as possible and then disconnect the power, for example after a delay or when the motor is under 10 RPM.

If I disconnect the power only, without braking first, the motor will continue running by inertia. If I use normal stop, the VDF will use a ramp. None of this two options works for me.

This are only pump motors, without gear box.

I would add a resitor bank to the VFD to absorb the DC voltage fed back to the VFD bus, and then use the DC braking settings within the drive. This, of course, in conjunction with a safety relay with the delayed contacts to allow the drive time to stop the motor, then disconnect power to the drive.
 
Ummmm, hold it a minute there, muusicman. A braking resistor is for regenerative braking which only occurs when the drive is on a decel ramp to stop. DC injection braking is a bit different in that the drive goes to coast-to-stop and then DC is injected into the motor to make it resist turning. No brake resistors are needed with DC injection braking because the braking energy stays in the motor. It does not return to the drive as in regenerative braking.

The problem with DC injection braking is that it is not speed-controlled braking. Instead, it is simply torque braking. The difference from a safety and E-stop standpoint is that, with DC injection braking, the stopping time will vary as the load on the motor shaft varies. With regenerative braking, the decel ramp is always enforced making the stopping time the same regardless of load.

As usual with E-stop, you need to think thru the hazard and the best possible solution carefully. I would think with a pump that the load would always be the same and therefore the DC injection brake would produce close to the same stopping time every time. That would be a cheaper and simpler solution if what I said is true.
 
Dick, You are correct, it was late, and my brain was off. Change my response to read "use the ramp to stop settings within the drive."
 

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