regulation
regulation
(OP)
I am working at a plant that after many years of denial is being dragged kicking and screaming into our current heath and safety regime
my problem is that the health and safety department are insisting that full isolations be carried out on our machines before the cleaners, who uptill now have relied on estops can work inside the machine. A resonable demand but it causes me problems as the dc drives that contrl these machines dont like being powerd off. pleanty of past experiences tell me that more than occasionally they go off and then stay off.
My intended solution is to interupt the field and armature connections to the motor with a local locable isolator that can be locked off by our electricians.
i have some questions about this approach.
i intend to put the breaker inside an automatically locking box that can be unlocked by the combination of the main contactor open signal on the drive and some sort of access button being pressed i intend the opening of the box to inerupt the stop circuit of the drive to make double sure the drive is not powerd up when the isolator is switched.
some of these signals will be plc controlled, some via a comms link. is this acceptable?
how do i go about rating an isolator for dc are there any funndemental considerations?
Is this really necessary do the regs really request an isolation. how can i find out more about the regs for rotating machinery isolation?
my problem is that the health and safety department are insisting that full isolations be carried out on our machines before the cleaners, who uptill now have relied on estops can work inside the machine. A resonable demand but it causes me problems as the dc drives that contrl these machines dont like being powerd off. pleanty of past experiences tell me that more than occasionally they go off and then stay off.
My intended solution is to interupt the field and armature connections to the motor with a local locable isolator that can be locked off by our electricians.
i have some questions about this approach.
i intend to put the breaker inside an automatically locking box that can be unlocked by the combination of the main contactor open signal on the drive and some sort of access button being pressed i intend the opening of the box to inerupt the stop circuit of the drive to make double sure the drive is not powerd up when the isolator is switched.
some of these signals will be plc controlled, some via a comms link. is this acceptable?
how do i go about rating an isolator for dc are there any funndemental considerations?
Is this really necessary do the regs really request an isolation. how can i find out more about the regs for rotating machinery isolation?





RE: regulation
Also you should be able to turn off the equipment and turn it back on without it failing. If it does fail fine! Improve it when you repair it so it meets reasonable manufacturing reliability standards.
I would not go to some non-conventional technique for safety!! I don not understand your safety scheme from a reading of your post. This means it is too complicated!!! and will be misoperated at some point. Can someone be injured during a misoperation? (Sounds like it to me.)
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: regulation
Are the isolators ever going to be used for load making or breaking? This introduces some very different conditions compared to off load operation.
I would be looking for a recognised isolator / disconnector / breaker with a recognised locking device. I would think very carefully before engineering my own safety system, and given the questions you're asking I'm not convinced that you have the experience to design something which will guarantee to provide 'safety from the system', to quote a phrase beloved of the UK's HSE. That's important if it ever went to legislation because you overlooked something which directly or indirectly lead to an accident. Your defence is much stronger if you have used a recognised product in the way it is intended to be used and within its designed rating.
If you're in North America, Cutler-Hammer's range of MCCB's are available without a tripping unit suitable for 250V DC service, from a few tens of amps up to many hundreds, which are capable of accepting a locking device. If you don't need load switching capability then these are probably overkill.
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Sometimes I only open my mouth to swap feet...
RE: regulation
i intend to interupt the output of the drive before it gets to the motor therefore isolating the motor.lockable. i intend to provide electrical interlocks to prevent the drive being isolated at his point whilst power can be supplied to the motor ie to stop some idiot switching it off whilst its running.
is it resonable to monitor the fact that its running over a comms link.
RE: regulation
RE: regulation
As for using the comm link. You know your own comm system better than we do, and the fact that your asking the question makes me doubt that it is a good idea.
respectfully
RE: regulation
JRaef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: regulation
On even rather small wound field DC motors, opening the field circuit with a contactor results in a horrendous bolt of lightning due to collapsing flux in the motor field.
Any de-energizing of the field circuit should include suppression devices to manage the kickback energy.
RE: regulation
If your modifications fail to do their job, you may KILL someone. I can't see how your management would even begin to contemplate the possibility of risking someones life during a trivial cleaning operation.
The lawyers would have field day and make the cost of fixing the machine to operate correctly seem like peanuts.
TTFN
RE: regulation
How can these modifications fail. maybe i should have mentioned this is a separately exited field dc motor, the isolator will interupt all 4 cables to it so that it can recive no power from the drive. the interlocks i propose are to protect the machine from being turned off with power on for the resons suggested by jraef, to protect the machine for the not the cleaner.
i intend to make sure the e stp citcuit is open, by hard wiring and the field/ main contector is open using a signal from the drive ofver a comms link. two layers of checks to prevent power being supplied to the field or armature before access to the isolator is allowed. once isolated the aux contacts of the isolator would also interupt the stop circuit to prevent the drive being powerd up
There is a field fail routine within the drive logic to detect field current before closing the main contactor also