Surge and Lighting protection

[Roktgr]

Hi, I'm a new mechanical engineer working at a hospital facility. Recently we had two large power failures that reviled the hospitals power system is very exposed to damage from electrical surges and lightning.

Our system has one three phase source as of now that comes into a set of transformers the split into four branches. Three provide 120/220v to our three main buildings and one provides 480v for our X-ray Lab.

I have a couple of questions that you guys may be able to answer.

The first day we had power failure the power company came out and replaced the 15amp fuses in the power line and first set of transformer boxes. The cause was believed to be from a lightning strike that back fed through our line.

The second failure also blew the 15amp buses on the pole and in the transformer box along with alot of circuit boards, controls, motors, and other expensive equipment. The cause of this failure is not yet known but it could have been a direct hit to our system and fed out of our facility.

The power company returned and after inspecting the transformers they determined that the 15a fuses were underrated and install 40a fuses in their place.

This brings up my first question. Does that seem like a reasonable solution? According to the history of the system the 15a fuses have been in operation for quite a few years, the entire facility is 100 years old, and have not had any major issues and doesn't seem like any additional load has been added so why would you upgrade the fuse size?

Second question is more along the lines of system protection. I see there are surge protectors available for an entire facility. Where are these installed at? Do you install them in the main set of transformers, were the power comes off the line, or on each branch as the power is distributed?

It would seem to me that in order to be protected from surges either up or down the line you would want to have a surge protector somewhere on the incoming power feed side and then also a lightning protection system. Is that correct? Or would there be a better option to prevent surges down through our system.

And since we have quite a bit of three phase powered equipment they would have to be equipped with motor savers in the event that we lost one of the phases.

Thanks for your help, I'm not an EE so this is a new area for me and just trying to make sure I have everything covered.

 

[cranky108]

Question 1: when they replaced the the 15A fuse, did they replace all three, or just the one that blew?

Question 2: where are the fuses? On the transformer primary? And what is the size listed on the name plate, and voltage?

Don't look at the equipment installed, look at the equipment that has recently been replaced. It may do the samething, but it may have a very different inrush.

 

[Roktgr]

They replaced all three. The fuses are on the last pole before the lines drop into the transformers. They also upgraded the fuses I believe on the primary transformer. The transformer is a 100KVA.

There has not been an equipment replaced in probably the last ten years or more. The power guys did not recognize were most of our equipment came from and to make it even better we own the transformers so the power company really doesn't have a good idea of whats all in there.

We had another failure this afternoon, it blew the 40a fuses on the line.

Thought maybe it was a ground leak that has been increased due to the extra wet weather we have been having. Seems like this could be a tough problem to troubleshoot.

 

[burnt2x]

Roktgr,
I sort of caught the slant when you mentioned "we own the transformers so the power company really doesn't have a good idea of whats all in there."
IMO, since it is your transformer, you should get the services of a qualified EE and have your system analyzed to begin with.
OTOH, since the replacement fuses got busted, the problem was never corrected (or similar event occured).

 

[Roktgr]

Yep thats being done, started getting it setup now. Sucks having equipment that you don't know anything about.

 

[cranky108]

From the other side of the fence, power company side, it also sucks having equipment that you don't know anything about.
In your case, they want to help, but they don't know how.
The'll do what they can, but they will have a limit.

From the power company side of the fence, we want to help our customers, but some need more help than we can give (Liability, time, money issues).

Getting a consultant to look at it is a good idea. If your lucky it may just be a cracked bushing that flashes over when wet.

 

[alehman]

As far as surge protection, there are many, many manufacturers of such devices. You are on the right track with multiple devices. It is usually best to have one at the low voltage main distribution and others electrically close to the load. Again, an electrical consultant would be money well spent.