category 3 safety circuits for ac drives

[plcsavvy]

I am involved in a project that employs a programmable safety system to meet category 3 safety compliance.
I have chosen to place two contactors in series between an ac drive and disconnect of a motor.Is this permissible or do I have to place the two safety contactors in series with the incoming power to the drive? The drives I am using are the siemens micromaster 420 and 440 sensorless vector types. Keep in mind that the drive on command is being sent to the drive via Profibus-DP. Upon E-stop, the now closed contacts of the series wired contactors will open thereby killing power to the motor. In addition to this, the run signal to the drive will be dropped.

thanks in advance, PLCSAVVY.

 

[Barry1961]

This topic has been gone over a few times in the motors and controls forum. There was some very good posts on it.

Barry1961

 

[ScottyUK]

One such thread was thread248-135444

The Siemens applications guys at A&D in Manchester are very knowledgable and could probably help you with product-specific information. It's a Sunday and I'm not going to spoil it by using the accursed Siemens website, so I haven't got a number handy for A&D.

Are you tied to the Siemens drives? I know for sure that drives from Rockwell (PowerFlex) and Control Techniques (Unidrive) have this feature: I'm using it on a project which will enter service in the next week or so. I'd be amazed if ABB don't also have it on their range.

All the secure shutdown functions require a physical contact from either an ESD button or via a safety relay. You can not run this funtion through a PLC or similar, but I think you probably know that since you're looking at contactors to disconnect the drive.


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One day my ship will come in.
But with my luck, I'll be at the airport!

 

[plcsavvy]

Thanks for the reply guys. I am unfortunately tied to the Siemens drives, since they are customer specified. I did have a look at the AB powerflex drives and their safety circuitry. I noticed that the RUN signal to the drive is also wired to two series wired contactors. In my application I would be using profibus to send the run signal to the drive. Is this appropriate for catgeory 3 safety compliance. There are now so damn many safety contactors on this machine that I am running out of panel space! Seems to me that I will need two more contactors in series with the run signal to the drives.
Any comments?

 

[plcsavvy]

I learned from a Siemens rep today, that profibus-DP is safe to category 4 for communications only. It can therefore, be used to provide the run signal to the drive.
So the two contactors I have provided to remove power from the motor are sufficient.

best regards, PLCSAVVY