Analyzing energy at the input to a transformer. You should take measurements both at the input and output terminals to better evaluate loss contributions of the transformer itself.
In my very first column for Fluke News Plus in 2005, “When do you bring in the big guns?,” I discussed some simple measurements that one could make with digital multimeters (DMMs) and clamp meters to detect the presence of power system harmonics. The article also indicated that using a more complex and expensive power quality analyzer, a “big gun,” might be appropriate if significant system rework was contemplated.
Near the end of that column, I said the following:
“In a future column, I'll discuss some innovative examples where the costs of upgrading or replacing outmoded distribution equipment, to deal with transformer efficiency in the presence of harmonics, actually resulted in power savings so significant that the payback for the more expensive transformers was in months, not years.”
Well, that time is now.
In the years since I wrote these words, Fluke has become a major force in power quality testing, with everything from a full stable of DMMs and clamp meters to an impressive line of more capable power quality tools and thermal imaging equipment. But, one problem still existed - how to use all the data collected to justify the needed power system upgrades that might be indicated by those tests.
Today, I can tell you about the new Fluke 434 Series II Energy Analyzer and the Fluke 435 Series II Power Quality and Energy Analyzer. For those of you familiar with the original versions, you might conclude that these new models are pretty much the same, but include some more up-to-date measurements, including power inverter efficiency measurement and a unique way of identifying the cost of energy lost due to power quality problems within the electrical system.
The new 430 Series II includes calculations based on work by two college professors in Spain, in which they addressed the equations defined in IEEE standard 1459-2000 that relate measurements of power system voltages, currents, harmonics, phase angles, and phase balance to the cost of power being consumed from the grid.
At last, I have an answer for the question asked of me by an electrical contractor back in 2005:
“How do you convince a potential customer that the problems that you propose to solve really exist in their system?”
It appears that the Energy Loss Calculator screen on the new 430 Series II may provide the answer. Now, not only can you document the technical details that can cause losses; you can also clearly relate those details to a direct operating cost in dollars and cents.
For example, such an analysis might make it easier to determine priorities in implementing kvar correction versus harmonic mitigation by showing clearly the relative impact of each issue on operating costs.
Electrical system upgrades with successful outcomes
I made the seminar presentation referred to above in 2005, shortly after I retired from Fluke, acting as a measurements consultant for a manufacturer of high efficiency transformers.
Since that time, this one manufacturer has made over 150 transformer upgrade installations in schools, where the buildings remain powered during summer shutdowns. It turns out that significant power losses may occur in standard distribution transformers, as referred to in NEMA Standard Publication TP1-2002, under lightly loaded conditions.
Moreover, all of the specifications and testing specified for these transformers assume linear loading, and with many of the schools now outfitted with computers, the actual operating conditions, even under load, are with significant nonlinear loads that reflect energy-stealing harmonic currents back into the distribution wiring and transformers.
What is Department of Energy (DOE) Candidate Standard Level 3 (CSL-3)?
According to ASHRAE’s Advanced Energy Design Guide for K-12 School Buildings:
“Minimum transformer specifications as of January 1, 2007, are classified by DOE as TP-1 and are the lowest efficiency available. Energy-efficient transformers that are 30% more efficient than the minimum TP-1 are classified by DOE as CSL-3.”
As it turns out, the transformers used in the upgrades of the 150+ schools easily exceed the specs in the CSL-3 classification. Because these transformers reduce direct power losses, they also run cooler, reducing air conditioning loads in equipment rooms for additional savings.
And, even though the replacement transformers cost more than the standard-grade units they replaced, the payback for their installation was well under two years because of the energy savings achieved. An added bonus is that after payback, the schools enjoy the continuing benefits of lower operating costs in terms of the cost of power used.
Proving the claim
The ability to take the complex measurements necessary to evaluate a potential power savings opportunity, and then report the results in an easy-to-understand format that shows the reduced cost of energy using local utility costing information, is an exciting new feature of the 430 Series II tools.
Existing system testing using one of these meters can first help a facilities engineer or electrician communicate the opportunity, and then, assuming an upgrade is made, testing again can quickly verify that the savings goals have been achieved.
The 430 analyzer should be used to measure at the input to the transformer in question. If it is very lightly loaded, then this will record the losses due to excitation current in the transformer itself. If the transformer is loaded, then a second recording at the secondary should provide a clear indication of the losses contributed by non-linear loads such as computers and electronic motor drives. Separate temperature measurements in the equipment room should also be noted.
As mentioned earlier, it would appear that the introduction of the Energy Loss Calculator in the Fluke 430 Series II Power Quality and Energy Analyzers is the answer to the need expressed to me by that electrical contractor so many years ago.