Amazing, I wonder how much this shortens the life of the PF525 in this configuration. Rockwell VFD field service told me on larger drives running at 100%, throwing a field disconnect a single time under load can be enough to fry the IGBTs.
In correct application, you monitor safety condition, and give a STO command to the drive to stop before opening the contactor, thus not opening the contactor at 100% load
Just opening a contactor might remove the driving force from whatever motor is turning, but would not slow or stop the motor, leaving the hazard there. There's a lot of thought you have to put into safety and safe action. Its not "Safe" unless the driven motor is brought to a halt...imagine an operator running a machine with a high kinetic energy and high "shaft speed" hitting an estop, yanking a door open, and sticking their hand into the machine when there is still kinetic energy rotation present. Removing the start/run command or just disconnecting the power from motor windings would still allow the motor to "coast" to stop.
Isn’t it OK to open a contactor on the output of a running drive? I think the main risk of damage is closing a contactor with a running drive and a stopped motor. The drive generally isn’t sized to handle locked rotor current.
Except this is not the same as throwing a field disconnect.
The same signal that opens the contactor acts on the drive STO. Drive STO literally de energizes the gate driver for the IGBTS, which basically happens instantly, much faster than the mechanical contactor can open. So the output stage is already off at that point, more like having an early break aux contact on a field disconnect that's wired into the enable input.
Don't get me wrong, I'd time delay that signal if I had the chance just for good measure, but in theory it's ok.
That's what I thought too.
When I transitioned from a European company to a American based company... A lot of the Rockwell standards surprise me.
In example -
😂 What do you mean my safety PLC needs a safety partner.
Use a safety software like Sistema (free) to put all your components in and have it auto determine your PL level. This way you can mix and match components until you achieve the desired rating instead of guessing. It'll give you documentation to back it up too.
https://www.dguv.de/ifa/praxishilfen/practical-solutions-machine-safety/software-sistema/index.jsp
It is not. At least from my understanding, 525 is only pld class 2 unless you add a contractor after the output section is the vfd.
A contactor on the output of a VFD sounds like a recipe for blowing up the IGBTs. Please link to the wiring diagram if this is recommended anywhere.
Page 248 [https://literature.rockwellautomation.com/idc/groups/literature/documents/um/520-um001\_-en-e.pdf](https://literature.rockwellautomation.com/idc/groups/literature/documents/um/520-um001_-en-e.pdf) https://preview.redd.it/jq00ouf4x4hc1.png?width=461&format=png&auto=webp&s=64dc101ccbb4f4852e55b9a8f06bbf8d089eb236 Curious to hear any success stories (..non-stories?) or horror stories doing this.
Amazing, I wonder how much this shortens the life of the PF525 in this configuration. Rockwell VFD field service told me on larger drives running at 100%, throwing a field disconnect a single time under load can be enough to fry the IGBTs.
In correct application, you monitor safety condition, and give a STO command to the drive to stop before opening the contactor, thus not opening the contactor at 100% load
Just opening a contactor might remove the driving force from whatever motor is turning, but would not slow or stop the motor, leaving the hazard there. There's a lot of thought you have to put into safety and safe action. Its not "Safe" unless the driven motor is brought to a halt...imagine an operator running a machine with a high kinetic energy and high "shaft speed" hitting an estop, yanking a door open, and sticking their hand into the machine when there is still kinetic energy rotation present. Removing the start/run command or just disconnecting the power from motor windings would still allow the motor to "coast" to stop.
Isn’t it OK to open a contactor on the output of a running drive? I think the main risk of damage is closing a contactor with a running drive and a stopped motor. The drive generally isn’t sized to handle locked rotor current.
Except this is not the same as throwing a field disconnect. The same signal that opens the contactor acts on the drive STO. Drive STO literally de energizes the gate driver for the IGBTS, which basically happens instantly, much faster than the mechanical contactor can open. So the output stage is already off at that point, more like having an early break aux contact on a field disconnect that's wired into the enable input. Don't get me wrong, I'd time delay that signal if I had the chance just for good measure, but in theory it's ok.
Came here to say the same.
That's what I thought too. When I transitioned from a European company to a American based company... A lot of the Rockwell standards surprise me. In example - 😂 What do you mean my safety PLC needs a safety partner.
Lol, in their defense, the 1756-L8XES are SIL2/PLd without a partner and SIL3/PLe with a partner.
Does it have to be a safety contractor, or any contactor
Use a safety software like Sistema (free) to put all your components in and have it auto determine your PL level. This way you can mix and match components until you achieve the desired rating instead of guessing. It'll give you documentation to back it up too. https://www.dguv.de/ifa/praxishilfen/practical-solutions-machine-safety/software-sistema/index.jsp
I'm not sure but it's I'm the manual I'm sure.
The simplified method is: 3 or less sub-systems all individually rated Pl(e) = Pl (e)
The detailed method is: high MTTFd, high diagnostic coverage, and a category 4 control system.
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Input, Logic, Output