How To E-Stop A Powerflex Drive

[lowdere]

I'm working on a vfd estop application for the first time. I have a belt conveyor driven by a Powerflex 700. Lanyards on the conveyor are for estop.

I'm having trouble understanding exactly what dictates requirements for an estop. Is it acceptable to simply turn off the Enable control signal to the drive, ... or must I install a contactor between the drive and the motor with some sort of relay management module to disconnect the drive safely?

Whatever the answer is... what code dictates my requirements? I have been digging through MSHA, NFPA, and NEC for something, but I have done nothing more than confuse myself.

Thanks,
Eric

 

[dogleg43]

Typically a 3 phase contactor is placed between the output of the drive and the motor leads. This contactor is controlled by the "Hard" E-Stop.

Depending on the application, contacts for a "Soft" E-stop may be placed in series with the stop/run terminals (a Soft E-stop permits a more orderly shutdown.)

***Check with the drive manufacturer and make them tell you where to place the contactor. They do not all have the same answer.

 

[ScottyUK]

A-B's Powerflex 70 range has a specific 'safe off' input for ESD applications called DriveGuard which meets the requirements of EN954-1 Category 3. No doubt it has some form of approval under US standards too. In Europe it is up to the end user to assess the requirements for the integrity of the safety system under what is known as a "SIL assessment", and then design the shutdown system to meet that integrity level.



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I don't suffer from insanity. I enjoy it...

 

[lowdere]

The Powerflex 700 in this application does not have the safe-off option.

 

[cbarn24050]

Putting a contactor between the drive and the motor can damage the drive. Cutting power to the drive is the right way. Over here in Europe the code you need to follow is dependent on the "risk assesment" of the machine.

 

[jraef]

This issue is debated fairly regularly in this forum. There is no universal consensus, mainly because of the universal answer to most questions like this, "it depends". Do a keyword search on "VFD emergency stop" to look at some of the previous discussions, maybe you can get some insight as to how it would apply to your situation.

Aside from that, cbarn2450 is correct in that putting a contactor on the output side is generally risky to the drive. As you will find however, some people consider that to be secondary to life safety requirements if there is a possibility of contact with the motor conductors after the E-stop is activated. I doubt if that is a concern for a conveyor drive. Killing input power will still prevent the drive from running on and carrying someone into a rock crusher or shredder etc., which is what those cable switch systems are about.

My opinion is that I don't think a base block stop command is adequate for life-safety purposes, but again, this has been debated often. I recently attended a presentation on the SIL-2 conformance capability of the new Schneider VFD which they claim is exclusive to them, but I went away unconvinced. To put it another way, if I fall on a belt and grab the cable, I want an air gap in front of the power source to that motor, not a legal conformance document that my widow can use to sue someone after I have been turned into pink goo!

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[jraef]

As if to further emphasize the "it depends" issue, I just erred in the above. If it's a down hill conveyor that is using the motor and drive in a dynamic braking or regen mode to prevent runaway of the overhauling load, then opening a contactor ANYWHERE is exactly the opposite of what you want!

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[Walden]

To emphasise what jraef wrote. As an engineer you have to decide how quickly the plant is to stop in an emergency. For example, two projects I have worked on. In the first, a cable winding machine, we used DC injection braking to stop the drum dead in half a revolution.In the second,the load was driven through a gear box and it was sufficent merely to isolate the drive motor. The load stopped immediately because of the gear box ratio.

 

[ozmosis]

I agree with Walden. The key words are "emergency" and "stop".
You have to determine what sort of stop is required in an emergency. The actual function of your VFD will come a few steps after you have determined the method of stopping. The advent of 'safe-stop' in a VFD means you have a tested and verified method of removing power to the motor, but you still have to determine how you are going to stop the motor and how quickly. Treat the application as you would for a traditional E-stop (without VFD) and if it had a suitable safety category built into the VFD then you can integrate it.
If you do not have the "safe-stop" function in your powerflex then removing the power to the input of the drive should be looked at in the event of an emergency stop as removing the supply to the motor could mean that the VFD is still 'running' even though the motor is not physically connected.

 

[dbaird]

lowdere, take a look at the link below and see if if helps in your determination.

http://www.jicosh.gr.jp/english/guideline/Machinery/SafetyStandards.html

David Baird

Sr Controls Designer
EET degree.
Journeyman Electrician.

 

[jraef]

Lowdere,
I just got of the phone with a friend who works at a mine, so he deals with this issue as it relates to conveyors every day with MSHA. He says MSHA has no requirements for motor power removal per se, but the cable e-stop must be a maintained device requiring physical reset by hand. How it is done at the VFD is strictly up to the user's safety protocol. Most users he has worked for allow the VFD to turn off without the need for an additional isolation contactor, because a common way of handling e-stops like that is to use a Master Control Relay (MCR) that kills control power to everything simultaneously. He suggests that you call your local MSHA inspector anyway just to make sure, because he is going to be the AHJ.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[moltra]

I just installed 7 powerflex 700's and the way I wired the E-stop up was to use a Minatour Estop Relay with the output of the relay connected to Digital input #6.

Hardware Enable Circuitry (Vector Control Option Only)
By default, the user can program a digital input as an Enable input. The
status of this input is interpreted by drive software. If the application
requires the drive to be disabled without software interpretation, a
“dedicated” hardware enable configuration can be utilized. This is done
by removing a jumper and wiring the enable input to “Digital In 6” (see
below).
1. Remove the I/O Control Cassette &
cover as described on page 1-16.
2. Locate & remove Jumper J10 on the
Main Control Board (see diagram).
3. Re-assemble cassette.
4. Wire Enable to “Digital In 6” (see
Figure 1.8).
5. Verify that [Digital In6 Sel],
parameter 366 is set to “1, Enable.”

This is a hardware Stop Not a program stop which makes it a good E-stop circuit.

 

[cbarn24050]

Hi Moltra, it's lucky you don't live in Europe, if you did that here you would be in big trouble if someone got hurt.

 

[ozmosis]

Cbarn
Very true. Here is an extract from the Siemens 'Standard drive' operating manual (without safety integrated):
"This equipment must not be used as an "Emergency Stop Mechanism" (see EN 60204, section 9.2.5.4).
Emergency Stop facilities according to EN 60204, IEC 204 (VDE 0113) must remain operative in all operating modes of the control equipment. Any disengagement of the Emergency Stop facility must not lead to an uncontrolled or an undefined restart of the equipment"

 

[moltra]

Why would it be a problem. It is being controlled by a safety relay that has to be mainly reset fot the machine to be restarted. and the drive must then be restarted.

 

[cbarn24050]

HI Moltra, look at your safety relay. It has DOUBLE output contacts, it has DUAL circuit operation and it has contact monitoring. It's all there for a reason namely single fault operation and muliple fault notification. If your drives disable funtion doesn't work how will you stop the drive? How would you know in advance that it had gone faulty?

 

[moltra]

The hardware enable on a PF700 drive takes the 24 volt control voltage from the SCRs therefore when the safety relay actuates it takes the volts off the SCRs stopping them from firing therefore stopping the motor. IT is a hardware stop not a software stop.

 

[cbarn24050]

It doesn't matter, there is no backup, no fail safe, no monitoring, it would be illegal to do it that way over here.

 

[ozmosis]

Moltra
Unless you have a certified 'Safety Integrated: safe stop (here in Europe it would be classed as a category 3 safety level within EN954-1), you cannot use the function (shutting down the gate driver circuit) as a safe stop. I'm not sure if A-B have this in the Powerflex700 but lowdere advised his particular model does not have it.
More and more drive companies are building this in. Siemens, Danfoss and Control Techniques are three that I know do in 'standard drives'as an option.

 

[moltra]

I understand that in a Cat 3 safety system that you need two ways of taking power a way. I am talking about in a Cat 1 situation.