Comparing Electrical Losses Between Standard

Delta-Wye & Harmonic Mitigating Transformers (HMT)

Technical Data TD00904007E

New Information

Introduction

Today’s electrical environments have many “not normally consid-ered” ways of reducing heat and saving money for the customer. This document will discuss the “heart” of the electrical system — the dry-type transformer — and how it is impacted due to today’s non-linear loading from a heating and losses standpoint. Comparing the two sys-tem approaches to harmonic mitigation of “apathy” (using the same electrical components that were used in the past) versus the newer transformer design of the Harmonic Mitigating Transformer (HMT), we will see how each is impacted.

The following BTU / Hour Transformer Comparison Table shows the typical heat output (due to losses) from a dry-type transformer when feeding linear loads of the past (i.e., incandescent light bulbs, resistive heating elements, standard three-phase motors as specified by today’s testing and reporting standards. Knowing these losses are necessary when determining additional cooling that may be necessary to remove the additional heat generated by the trans-former. The unfortunate issue at hand is that this table (due to the lack of requirement from the standards) doesn’t accurately reflect the “real-world” performance of this device when feeding today’s non-linear loading (i.e., computers, monitors, fax machines, printers, TVs, battery rechargers, etc.).

BTU / HOUR TRANSFORMER COMPARISON TABLE

STD = Standard, Delta-Wye Dry-Type, 150ºC Temp Rise, Aluminum,Energy Efficient (meets EPACT 2005)

HMT = Harmonic Mitigating Transformer, Dry-Type, 115ºC Temp Rise,Copper, Energy Efficient (meets EPACT 2005)

KVA SIZE

PERCENT LOADING WITH 100% LINEAR LOAD

25% 35% 50%

STD HMT STD HMT STD HMT

15 426 307 554 384 843 56230 702 469 908 646 1,370 1,04745 904 663 1,208 886 1,898 1,38775 1,402 994 1,824 1,327 2,770 2,082112.5 2,019 1,485 2,646 1,895 4,063 2,814150 2,284 1,810 2,976 2,268 4,544 3,325225 2,749 2,595 3,749 3,172 6,047 4,433300 3,834 2,728 5,011 3,494 7,750 5,311500 5,399 5,088 7,029 6,084 10,762 8,357

KVA SIZE

PERCENT LOADING WITH 100% LINEAR LOAD

65% 75% 100%

STD HMT STD HMT STD HMT

15 1,271 834 1,646 1,081 2,957 1,98230 2,048 1,642 2,642 2,161 4,712 3,96645 2,918 2,124 3,812 2,764 6,933 4,97575 4,160 3,198 5,374 4,175 9,599 7,579112.5 6,173 4,169 8,033 5,352 14,589 9,482150 6,881 4,939 8,944 6,391 16,233 11,666225 9,505 6,244 12,573 7,802 23,462 13,127300 11,965 8,156 15,778 10,763 29,716 20,441500 16,407 11,824 21,448 14,957 39,554 26,434

Eaton Corporation

Electrical Group1000 Cherrington ParkwayMoon Township, PA 15108United States877-ETN-CARE (877-386-2273)Eaton.com

© 2007 Eaton CorporationAll Rights ReservedPrinted in USAPublication No. TD00904007E / Z6015July 2007

To further tell the story of heat dissipation within dissimilar products, Eaton Corporation conducted comparison measurements at their Power Quality Experience Center in Warrendale, Pennsylvania. This facility is especially suited to this type of testing through the ease of quick equipment changes using the same electrical load and doing “side-by-side” comparisons of electrical components in a typical commercial electrical power system. While testing and gathering data, it became important to realize the fundamental property to be minimized — in this case, it all comes back to the utility bill. Most electrical utilities charge by the kilowatt (kW, “1000 watts”). Energy and money can be saved either by reducing the number of machines/processes or through the reduction of losses within those processes. In today’s competitive environment, the need to squeeze any and all wastes to a minimum is paramount. The distribution transformer is a device that has a life span of 20+ years with minimal maintenance to ensure efficiency.

Due to these attributes — it’s imperative that the correct trans-former be chosen at purchasing time, which will have the mini-mal losses when feeding the type of loads within a facility. It also helps to understand that in a standard delta-wye designed trans-former, the triplen harmonic currents coming from the loads will tend to stay “trapped” in the delta portion of the transformer, causing a great deal of heat and waste. The physical construction of the HMT is different so as to ensure that the triplen currents are not carried over to the primary — in this way, the overall heat and losses from the transformer are reduced. Photos 1 and 2 enumerate the quantities and infrared heat scans to visually compare and contrast the two transformers being discussed.

Wasted Watts Within 75 kVA Transformers

LOADED WITH 100% NON-LINEAR (COMPUTER) LOAD

Infrared Heat Scans of the Transformers When Feeding the Same Non-linear, Computer Load

Photo 1 — Standard Delta-Wye Transformer

Photo 2 — Eaton’s Harmonic Mitigating Transformer

The electrical, dry-type transformer represents an opportunity to either save money (if we choose the right type of transformer, at the time of purchase, that's suited to feeding the characteristics of the load in the building) or waste a great deal of “hidden” energy and money in today's electrical systems through higher than anticipated losses within the transformer. In this technical document, we've compared two types of “systems” for performance when feeding non-linear, computer-type loading. It's important to understand that we're discussing “systems” instead of specific products as you would expect a 150°C temperature rise transformer to perform differ-ently than a 115°C transformer from a heat dissipation standpoint. The systems approach says that you'll either choose a “standard/delta-wye” transformer (which is typically 150°C in temperature rise) OR you'll choose a harmonic mitigating transformer (HMT) which has a standard temperature rise of 115°C. What's important to note is the “Wasted Watt” table — as the anticipated losses in the standard/delta-wye are much higher than would be expected (as normal transformer tables only show losses when feeding linear loads of the past). This further shows that the HMT is the correct and most economical dry-type electrical transformer for use when feeding today's non-linear loads during the next 20+ years of its anticipated operational use.

% LOAD

STD HMT

WATTS LOST EFFICIENCY

WATTS LOST EFFICIENCY

15 347 97.0% 199 98.3%25 427 97.8% 243 98.8%35 534 98.0% 298 98.9%50 802 98.0% 473 98.8%75 1,420 97.5% 904 98.5%100 2,170 97.2% 1,513 98.1%