E-Stop (ESD) System Design Help

Hi everyone,

I have been "volunteered or voluntold" to design a ESD system for a crude oil loading system. I have done searches on the site and have found a lot of info but most of the info I found was on machine ESD systems. Didn't really find anything on pumps or loading systems.

Here is what I have to work with:
2 Pumps with STD Starters
2 Pumps with AB 755 VFD's. I was planning on setting these up to communicate Ethernet/IP with the PLC. No hard start/stop signal.
8 Loading Control Computers. These send request to the PLC for the pump. They also have inputs for permissive to run. One of the permissives will be ESD signal.
PLC is a CompactLogix L33ER.
Edit: There are a total of 8 ESD Mushroom Buttons total in the system.

I designed a ESD system many years ago that used 3 ESD Mushroom Buttons wired in series. They were wired to the coil of a 6 point Industrial Relay. Each point was wired to interrupt the start signal from the PLC to the Motor Starter Coil. I had one point wired to a PLC input so the PLC could shut remove permissives to the loading controllers if a ESD button was pushed.

After reading a bunch of post on this site I realize that my last design was a little lacking in safety since I didn't use a safety relay.

So now I want to really "do it right" and make sure the system is designed better. So if anybody has any ideas at all I am wide open for suggestions. Please fire away.

Thanks!!

You should be doing a proper risk assessment to determine what safety category or SIL level you need to meet.

But at a start, check out this page for wiring examples.

http://www.ab.com/en/epub/catalogs/...768319/11456672/Typical-Wiring-Diagram-s.html

you SHOULD put contactors in front of the vfd's.
if there is an e-stop condition, you meed to kill the power to all drives, you don't need crude spilled.

i say this because we had a vfd input fail on drive and we told the drive to stop and it didn't. we even did an e-stop and it kept running. if a mechanic didn't have the disconnect next to him, it would have been bad for the 3 of them working on the machine.

REMEMBER, this is crude oil, high visibility !!
if you ask what if, you better have an answer.

regards,
james

I wouldn't say ''you should'' but ''you must'' put a contactor and maybe 2 in series according to sil or satefy level returned back from the risk study from engeeners. If the fact that running drives could hurt. (Sometimes stopping them could hurt too if it is holding a weight up and shutting them bring it down etc...)
They will check how much likely it is to hurt or kill people, they will put probability numbers on peoples life but it is the way to do it...
Only few drives have some built in safety logic approved to some degree and managing around it is better because you can use quick ramp down functions that would bring rotating mass to stop faster than a cost to stand still with an opened contactor.

I would rather install it after the VFD if you install a contact and wire back a early break contact back to the vfd to make a quick inhibit pulsing. (Opening a loaded drive may hurt the drive if not done properly but opening primary will create a voltage fault each time...

You will also have to put additionnal contactor to cut power to other motor according to the status of the safety relay connected to them. Your mushrooms will go to that relay using 2 nc contact on each of them that are suitable for safety (Contact only close in middle position so it open even if the contact bloc mecanical holder break) The safety relay will look to have both signal operated simultenously and monitor the proper opening and closing of the safety isolating contactor.

Usually, you would need a reset because the e-stop condition will be latched or a fault from a broken device detected by the safety relay

So yes it is a little bit more complex than wire 1 NC estop in serie with motor contactor coil if you (or the safety survey) want more safety than cat1

Before you go much further, you need to understand that there are VERY different definitions of the acronym "ESD", especially when it comes to the oil and gas business. If your research is done with just the acronym, you could get yourself in trouble.

ESD to the electronics industry means Electro Static Discharge, protecting sensitive electronic components from static electricity discharges when people touch things. Totally different issue, not germane to oil and gas.

ESD in the oil and gas industry means "Emergency Shut Down" typically of pipeline equipment, but also some processing functions.

It's also important to understand the ESD, in the oil and gas sense, is NOT THE SAME as "E-Stop", and cannot be equivocated to Machine Safety Directives in the same way. E-Stop for machine and personnel safety has to do with immediately putting a machine into a safe working condition, i.e. removing all sources of motor power.

Oil and gas ESD is different. In that industry, immediately removing motor power (E-Stop) can have very DISATEROUS effects on a process or the movement of hazardous materials. So they use the term ESD to mean a procedure implementation leading to an orderly and carefully considered shut down of something like a pipeline pump.

If you do not know this and have been given this task, someone is cutting corners that should NOT be cut. ESD for oil and gas is not something that should be handled by rookies, because "trial by fire" is not something you want to do in that environment.

In all cases, ESD wouldn't mean to kill power everywhere regardless of what would happend if done...The study will be for sure more complex in oil and gaz system but even anywhere else, you won't cut power to a braking system or suden stop a pump power when the liquid rebond can harm peoples etc...