Utility Short Circuit Data Proprietary?

[wbd]

Hello,

I'm performing an arc flash hazard analysis for a company in California. When trying to get the available short circuit data from the utility, I was told that this information is proprietary. Has anyone else expierenced this and how did they handle it?

I think it's preposterous that this would be proprietary information, how does one properly size switchgear, protection devices, etc. without this?

amazed!

 

[mpparent]

Jeez,....never ran into that one. The local utility has always been cooperative.

Mike

 

[HighPotter]

Well first off, which utility? I have experience with most of them.


HP

 

[dpc]

I've dealt with utilities who refuse to provide specific short circuit data. They will tell you that your equipment should be designed for 500 MVA or 1000 MVA or some other worst-case value.

Of course, this is of little help when doing arc-flash or power flow studies.

You might have to contact the PUC.

 

[wbd]

The utility is Pacific Gas & Electric. Anybody have any contacts inside - like Protection Engineering group. This is a first for me, all other utilities have been very cooperative with this information. Maybe they have more lawyers than engineers on staff!

 

[wareagle]

The problem you and the utility face is that the information they give you is subject to change. If the customer is fed from a 300 kva pad mt you get a specific fault level but what if they change the pad mt to a 1000 kva. Also the source of power is subject to change. This is an on going problem with the arc fault study. Thats why the max fault level is given which is not what you want to hear.

 

[wbd]

I understand what your saying but by not using the actual values, the customer may end up spending more money for arc flash gear or changing protective device settings or adding fuses to lower the arc flash hazard. Additional hazards could be introduced because arc flash gear is cumbersome in #4 category. The actual category using the real data could be a #2 and using max possible could result in a #4 category, which requires an arc flash suit.
Additionally, i am asking for the duty on the primary side of a customer owned transformer. As far as getting into changing transformer sizes, that would or could affect more than the arc flash, ie short circut withstands of equipment. This is a responsibility that should fall n the customer to the affects of changing out power equipment.

 

[davidbeach]

I have found that the utilities are a lot more willing to provide real numbers when the customer takes service at primary voltage rather than secondary voltage. Knowing the distribution engineer or the protection engineer responsible for the circuit rather than just dealing with the service planner can help tremendously also.

 

[Dumbo2929]

The utility does not want to be responsible for providing a value today, and due to system changes (reconductoring, changing switching schemes, automation, etc.) that value is now higher. This is the new reality. Distribution automation has made it possible to utilities to reconfigure hourly or daily as load, planned maintainence, etc. changes. Also they do not want to be liable for changing things inside the customers facility, so the customer must assume the worst. Welcome to 2006.

 

[alehman]

I've recently completed short circuit studies for a client with 50+ facilities located around the U.S. Most were able to look it up with an address or transformer number in a few minutes. I wasn't doing arc flash studies, so worst-case fault current was all I needed.

PG&E was one of the most difficult. They made me send a signed letter request along with a service application (this was an existing service!?). There was considerable delay when the service size I listed on the application did not agree with their records. The process took many weeks and numerous phone calls, but I finally did get an answer.

 

[wbd]

Alehman - Thank you, so they were difficult but not impossible!

My concern with using a generic maximum possible, theorectical, design for type value is that it may not produce a conservative value for an arc flash hazard. This is because of having to reduce the bolted fault to an arcing fault which will affect trip times. So an artifically high bolted fault current when reduced to an arcing fault could trip the breaker or blow the fuse faster than would happen using values closer to actual. This could lead to choosing arc flash clothing that is inadequate. This should give the utility lawyers something to think about if they are worried about lawsuits due to giving out accurate fault current information.

 

[resqcapt19]

Here is the statement that one utility gives with their fault current info.

The standard calculated available fault currents are given in amperes, RMS symmetrical, at the secondary bushings of the Company's transformer, assuming an infinite bus and a bolted fault. The intent of these values is to serve as a guide in the selection of the proper service and downstream equipment. These are of no value for the use in determining the proper personal protection equipment since the impedance, fuse size and type, and calculated primary fault current available at the primary bushings of the bank can not be known for any particular installation.

Don

 

[croudk]

I have typically handled utility requests by letting the customer request the information from their utility contact. Of course, for smaller customers, they may not have an individual contact but just the generic customer service call number. I agree that utilities are becoming more and more difficult to deal with when requesting short circuit and overcurrent protection data. Much of this may be due to tightening security restrictions after 9/11. It's probably easier for them to treat every request as a security threat rather than try to deal legitimately with practical requests. Good luck.

 

[resqcapt19]

I think that the real reason is liability issues. Their systems are so dynamic that the fault current that they give you now, may not be correct tomorrow or next week or when ever you use it to do arc flash calculations.
Don