Primary vs. Secondary Metering
Primary vs. Secondary Metering
(OP)
Does it really pay to go primary?
You get a better rate, but now you maintain and replace the transformers...and now have to account for transformer losses...
Unless you directly utilize medium voltage, it seems that primary doesn't make sense once you factor in transformer losses bringing everything down to 480V...
Am I missing something?
Anyone have an example/analysis...
Thanks,
Mike
You get a better rate, but now you maintain and replace the transformers...and now have to account for transformer losses...
Unless you directly utilize medium voltage, it seems that primary doesn't make sense once you factor in transformer losses bringing everything down to 480V...
Am I missing something?
Anyone have an example/analysis...
Thanks,
Mike






RE: Primary vs. Secondary Metering
Bottom line, it can be a great savings, or it can be a great waste of time and resources, you have to do an analysis based on your loads, load profile, and rates.
RE: Primary vs. Secondary Metering
David Castor
www.cvoes.com
RE: Primary vs. Secondary Metering
We could get a $0.003/kWh deduct for going primary, but my understanding is the incentive usually accounts for the transformer losses that are now on the customer, not leaving much if anything for the annual maintenance and eventual replacement of the transformers...
RE: Primary vs. Secondary Metering
RE: Primary vs. Secondary Metering
Utilities normally are in for the long term, so they will buy higher quality equipment.
However, you can construct a substation cheeper with used, and rebuilt equipment.
That's probally how some of the primary metering starts, as the customer normally pays for a special substation (one way or another). The issue of primary metering allows the customer to construct there own substations.
However, we recently saw a customer construct there own substation because they wanted a higher reliabilty than we normally offer (they paid more than we would have).
RE: Primary vs. Secondary Metering
$0.003 x 8,000 hrs/yr x 1500 kw = $36,000 savings per year before accounting for transformer losses. Losses are about 3 kW + 22 kw load loss = 25 kw. A good design could knock that down to 20 kw. $/kwh = $36,000/(20kw x 8,000 h)= $.225/kwh. If your equivalent base rate is $ 0.25/kwh or more, you might be ahead.
Many, many assumptions in this analysis: constant load, no time value of $$, no cost for metering and protection or maintenance, etc, etc.
Like the other gentlemen said, there is a lot more to look at. Several of my clients and employers went for it and have not had large regrets. (Maybe they all went bankrupt before the transformer costs hit.)
RE: Primary vs. Secondary Metering
Back in those days enforcement was a bit different, but now the AHJ is requiring a UL listed switch at point of delivery. That is a 90" tall unit, typically not vandall proof and not appropriate for unsupervised locations.
Typical utililty pad mount transformer is not UL listed and for some duties they will run them all the way up to 220% of nameplate, that too is not allowed on an installation subject to NEC. I am not sure if Load Break Elbows and other elements of URD construction are UL listed, typically NEC primary installations have bolted lugs with stress cones and require more switches than Load Break Elbows.
If a facility has it's own qualified staff to work on primary that might change the analysis, but many local campgrounds with primary systems do not. When a cable fails (not unheard of) they are at a loss for whom to call. When a transformer starts leaking a little they need a major project to replace it.
RE: Primary vs. Secondary Metering
RE: Primary vs. Secondary Metering
One other point is that, depending on the contract, you may be paying for transformer losses with secondary metering as well, as meters have the ability to include transformer loss compensation.
RE: Primary vs. Secondary Metering
I was merely looking for thoughts and experiences about going primary. I have heard from more than one source that there is a "5MW rule" (At least at that level of load primary usually starts becoming more accepted).
Another consideration is the "want" to go primary even if economocally it may not be the best choice. I'm thinking maybe mission critical facilities or the like, where control and ownership may warrant a bit more $$$
RE: Primary vs. Secondary Metering
Another
It depends" is transformer size for a new installation.
I planned a small mill (that was never built due to an abrupt down turn in the economy).
With primary metering we needed a code sized transformer, about 750 KVA. With secondary metering the utility would install a 500 KVA transformer.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Primary vs. Secondary Metering
RE: Primary vs. Secondary Metering
The second scenario was for a million square foot manufacturing and warehouse facility. The load was so large that the utility would only let the owner buy primary power. If I remember correctly, the demand load was around 5000 kVA.
RE: Primary vs. Secondary Metering
If this load can be served either at primary or secondary voltage, it just comes down to an economic analysis, as you say.
David Castor
www.cvoes.com
RE: Primary vs. Secondary Metering
RE: Primary vs. Secondary Metering
I usually only consider primary for large facilities, special control and protection applications and campuses where the maintenance staff is already familiar with it.
Alan
"The engineer's first problem in any design situation is to discover what the problem really is." Unk.
RE: Primary vs. Secondary Metering
Just think about it, who in there right mind would trust the customer to own the cash regester (other than the post office)?
However it would be the customers requirment to own the instrument transformers for protection of there equipment. For most smaller primary metered customers, that would be the CT's. Which normally don't go bad that often.
One exception I've seen is a primary metered wind farm, which owned several sets of PT's for there internal protective uses. And strangly they did not have spares.
RE: Primary vs. Secondary Metering
RE: Primary vs. Secondary Metering
However, I have seen that a requirment for the customer to own the protection, including the breaker, as a requirment. I did have a primary metered customer wanting to use fuses, but we did not allow that as it would have required us to slow down the line protection to accomidate them.
I think they opted for circuit switchers as they were cheeper than breakers (they had two transformers, in case one failed). Strangly the transformers were not what failed and caused them a several month outage (yes we steped in and helped them out, although we probally shoulden't have).
RE: Primary vs. Secondary Metering
Revenue class meters may not be suitable for protection and vice versa.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Primary vs. Secondary Metering
Just another factor that makes primary metering attractive. In some areas local utilities will offer "added facilities" service wherein they will provide on-site distribution, maintenance and metering to multiple buildings and basically finance the primary distribution system in exchange for added charges on top of the regular energy costs the facilities used. Oftentimes however, these costs when analyzed for the long run, will far exceed the costs for the customer to finance, own and maintain the system privately.
Regards,
EEJaime