1、852 2004 ASHRAE.ABSTRACT Industrial plants use electrical power equipment todistribute power for lighting, driving motorized devices, oper-ating HVAC equipment, and control of equipment. The mainfocus of this paper is to provide updated information on heatlosses by various types of electric power eq
2、uipment. The infor-mation is organized by equipment type, and practical guidanceon using this information to compute losses under differentconditions is provided. The effect of loading margin used bydesigners in sizing the electric equipment, load diversity, andambient temperature on heat loss is di
3、scussed. Uncertaintiesin the results for different pieces of equipment are presented.Also, a comparison of the results to the previously publishedinformation is provided. INTRODUCTIONEngineers wanting to estimate heat loss to the surround-ing environment from electrical power and control equipmentin
4、 industrial plants and large buildings need updated informa-tion. This paper provides updated heat loss information onmedium-voltage (5 to 15 kV) and low-voltage (below 5 kV)power devices for HVAC load calculations. The equipmentcovered includes both power and lighting transformers,medium-voltage sw
5、itchgear, electric cables and cable trays,motor control centers and combination motor starters, invert-ers, battery chargers, low-voltage circuit breakers, electricmotors, unit substations, series reactors, and adjustable-speedor variable-frequency drives (ASD or VFD). The first part ofthis paper de
6、scribes the types and varieties of informationsources for equipment heat loss, how tests were conducted,and the uncertainties associated with the gathered data. Thesecond part of this paper reports the study results. Helpful information to guide designers on using thisupdated information to compute
7、heat loss is provided for eachpiece of equipment in the form of load diversity, design margin,and the effect of the ambient environmental temperature. Loaddiversity assigns a fraction to a piece of equipment subjected topartial duty over a period of time. This fraction is used to deter-mine the aver
8、age power dissipated by the device over a periodof time, while the load varies in a routine fashion. The diversityfraction definition varies according to the equipment. Thereason for this variation stems from the dissipation of heat vary-ing either linearly with or as the square of the load current.
9、 Thedefinition of the diversity factor or fraction for each equipmentcategory will be presented. Design margin accounts for unan-ticipated increase in demand and opportunity for future growth.The level of design margin assigned by the engineer rangesfrom 100% for well-defined, noncritical applicatio
10、ns to 50%for conceptual designs and highly critical applications. Typi-cally margins of 80% are used for most applications, providinga balance between reliability and initial costs. For example, ifa piece of equipment was expected to require X amps with a50% margin, the equipment would be selected f
11、or a maximumcapacity of 2X amps (X/0.5). Uncertainties in the results are discussed for each piece ofequipment. Many of these uncertainties stem from differencesfrom manufacturer to manufacturer of the same type of equip-ment. A comparison of the final results to previouslypublished results is provi
12、ded in the form of tables or graphs ofdata. The previously published data include Rubin (1979) andMcDonald and Hickok (1985).Heat Loss from Electrical andControl Equipment in Industrial Plants:Part IIResults and ComparisonsWarren N. White, Ph.D. Anil Pahwa, Ph.D. Chris CruzWarren N. White is an asso
13、ciate professor and Chris Cruz is a graduate student in the Mechanical and Nuclear Engineering Department, andAnil Pahwa is a professor in the Electrical and Computer Engineering Department, Kansas State University, Manhattan, Kans.NA-04-9-2b (RP-1104) 2004. American Society of Heating, Refrigeratin
14、g and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions, Vol. 110, Part 2. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission.ASHRAE Transactions: Sy
15、mposia 853RESULTSTransformersThere are a variety of different transformer types. A smallsample of the available data is presented here. Table 1 presentsinformation concerning general purpose dry-type units, withan 80C temperature rise. Other units could have differenttemperature rises. Table 2 conta
16、ins data concerning generalpurpose liquid-filled units. The full-load loss figures in Tables1 and 2 correspond to rated current. The losses at any frac-tional load can be determined byTotal losses = no load losses + load losses (LF)2,(1)where LF = the load fraction, i.e., the fraction of full-load c
17、urrent (between zero and one). Transformer losses are not a strong function of environ-mental temperature; thus, the full-load and no-load losses canbe considered as constant regardless of the ambient tenpera-ture.Those power and lighting transformers (and larger units)built and tested in accordance
18、 with the NEMA TP1 Standard(NEMA 1996) have maximum efficiencies that either exceedor meet those efficiencies shown in Table 3 at a given percent-age of load. For low-voltage units (600, 208, 120 volts), thegiven load percentage for peak efficiency is 35%, while formedium-voltage units, the load val
19、ue for peak efficiency is50%. The efficiencies of these dry-type units are referred to anaverage winding rise temperature of 75C, while the liquidimmersed efficiencies are referred to an average windingtemperature rise of 85C. Losses vary linearly with windingtemperature. Referring the efficiencies
20、to a particular windingtemperature allows comparison between units. The tempera-ture to which the losses are referred is listed at the top of Table3.Given the full capability of the unit in kVA, the full-loadlosses for the NEMA TP1 units are approximately(2)wherepf = power factor,LF = load fraction
21、for peak efficiency (0.35 or 0.5), and = efficiency from Table 3 corresponding to kVA and unit type. Table 1. General Purpose Dry-Type Units Having an 80C Temperature RiseTemperature Rise (C)Rated Voltage (V)Kilo-Volt-AmpsAverage No Load Losses (W)Average Full Load Losses (W)100% Margin Total Losses
22、 (W)80% Margin Total Losses (W)50% Margin Total Losses (W)80 480D-208Y 15 330 277 607 507 39980 480D-208Y 25 530 502 1032 851 65680 480D-208Y 30 415 616.5 1032 810 56980 480D-208Y 37.5 530 671 1201 959 69880 480D-208Y 45 487.5 963.5 1451 1104 72880 480D-208Y 50 700 1371 2071 1577 104380 480D-208Y 75
23、 725 1969.5 2695 1985 121780 480D-208Y 112.5 700 2230 2930 2127 125880 480D-208Y 150 1075 2136 3211 2442 160980 480D-208Y 225 1450 2820.5 4271 3255 215580 480D-208Y 300 1650 3279 4929 3749 247080 480D-208Y 500 2900 4857 7757 6008 411480 480D-208Y 750 3640 8572 12212 9126 578380 15kD-480Y 500 2400 50
24、00 7400 5600 365080 15kD-480Y 750 2800 9000 11800 8560 505080 15kD-480Y 1000 3500 9600 13100 9644 590080 15kD-480Y 1500 5000 11600 16600 12424 790080 15kD-480Y 2000 6500 15500 22000 16420 1037580 15kD-480Y 2500 7200 18500 25700 19040 11825Full load lossespf kVA 1000 1100-2 LF()100-watts , 2004. Amer
25、ican Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions, Vol. 110, Part 2. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior writt
26、en permission.854 ASHRAE Transactions: SymposiaThe power factor in Equation 2 depends upon the electri-cal load, e.g., 0.8 for motor loads or 1.0 for resistive loads.The no load losses are approximately(3)The losses provided by Equations 2 and 3 correspond tothe average winding temperature rises sho
27、wn at the top ofTable 3. The load losses for all dry-type units (general purposeand TP 1) must be corrected for temperature according toTable 4. The load losses for liquid immersed units do notrequire any temperature correction. The temperature correc-tion consists of multiplying the load losses by
28、the factor of(4)whereTK= 234.5C for copper windings and 225C for aluminum windings, andTREF= reference temperature shown in Table 4.Once the temperature corrected load and no load lossesare determined, Equation 1 can be used to calculate the lossesat the given level of loading.Table 2. General Purpo
29、se Liquid-Filled UnitsRated Voltage(V) Kilo-Volt-AmpsNo Load Losses (W)Full Load Losses (W)100% Margin Total Losses(W)80% Margin Total Losses(W)50% Margin Total Losses(W)Substation15kD-480Y 225 760 3400 4160 2936 161015kD-480Y 300 900 4635 5535 3866 205915kD-480Y 500 1330 5540 6870 4876 271515kD-480
30、Y 750 1735 9875 11610 8055 420415kD-480Y 1000 2000 12025 14025 9696 500615kD-480Y 1500 2900 15720 18620 12961 683015kD-480Y 2000 3535 21750 25285 17455 897315kD-480Y 2500 4400 23750 28150 19600 10338Table 3. NEMA TP1 EfficienciesKilo-Volt-AmpsEfficiency %Dry Type, Low Voltage, 75CEfficiency %Dry Typ
31、e, Medium Voltage, 75CEfficiency %Liquid Immersed, Medium Voltage, 85C15 97 96.8 98.030 97.5 97.3 98.345 97.7 97.6 98.575 98 97.9 98.7112.5 98.2 98.1 98.8150 98.3 98.2 98.9225 98.5 98.4 99.0300 98.6 98.5 99.0500 98.7 98.7 99.1750 98.8 98.8 99.21000 98.9 98.9 99.21500 - 99 99.32000 - 99 99.42500 - 99
32、.1 99.4No load losses pf kVA 1000 LF()100- 1LF()2load losses()watts .Temperature correction factorTKTREF+()TK75C+- ,= 2004. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions, Vol. 110, Part 2. For personal use only. Add
33、itional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission.ASHRAE Transactions: Symposia 855Diversity is only applied to the load losses, whereas the noload losses remain constant as long as the unit is energized.Modi
34、fying Equation 1 to account for diversity provides therelation,(5)In order to determine the diversity factor, the time averageof the load fraction in the RMS (root mean square) sense hasto be found by the relation,(6)whereT1= time spent operating with a low load fraction,LFL= low load fraction,T2= t
35、ime spent operating with a high load fraction,LFH= high load fraction, andLFAVE= average load fraction.The diversity factor is then given byDiversity factor = (LFAVE/LF)2,(7)whereLF = load fraction corresponding to expected peak load of the unit (usually LFH).The power loss, taking into account marg
36、in information, isPower loss with margin = no load loss+ load loss (M/100)2, (8)whereM = the margin.The value of M is either 100% for full loading, 80% forexpected (recommended) loading applications, or 50% forcritical applications. Transformer literature states that powerlosses are only weakly infl
37、uenced by the ambient temperature.The loss information presented came from manufacturers thatfollowed relevant IEEE standards for measuring and reportingtransformer losses. As a result, the uncertainty of the lossvalues reported by these manufacturers is 10% or less.Medium Voltage SwitchgearThe heat
38、 loss calculation for medium voltage switchgearis based on a spreadsheet that provides a menu of the variousequipment devices found in them. The losses from mediumvoltage circuit breakers (including enclosure effects) can beestimated for 15 kV breakers and 5 kV breakers as15 kV breaker loss = 13800
39、volts 1.73 Irated (I/Irated)2 pf 0.00006 watts , (9)5 kV breaker loss = 4160 volts 1.73 Irated (I/Irated)2 pf 0.0001 watts , (10)wherepf = power factor (nominally 0.9),Irated= the rated line current for the breaker in amps,(I/Irated) = the load fraction of the breaker.The spreadsheet is shown in Fig
40、ure 1. In order to accountfor diversity, the current flowing in a breaker or bus must beaveraged using the following equation:(11)whereIL= low current flowing through breaker for time T1,IH= high current flowing through breaker for time T2,IAVE= average current in RMS sense.A diversity factor can th
41、en be defined to be used to deter-mine the current values to enter into the spreadsheet of Figure1.Diversity factor = IAVE/IH.(12)The margins for medium voltage switchgear are 100% forfull-load applications, 80% for commercial applications, and50% for critical applications. These numbers were chosen
42、 asthe result of discussions with industrial plant design engineers.The margin of 100% would indicate that equipment would beoperated continuously at its rated capacity, whereas a marginof 80% would indicate that equipment is loaded to the pointwhere 80% of the current capacity is utilized.Table 4.
43、Limits for Temperature Rises for Dry-Type UnitsInsulation System Temperature Class (C) Average Winding Temperature Rise (C) TREF Standard Reference Temperature (C)130 75 95150 90 110180 115 135200 130 150220 150 170Average total losses no load losses=load losses LF()2 diversity factor .+LFAVET1LFL2T
44、2LFH2+T1T2+- ,=IAVET1IL2T2IH2+T1T2+-= 2004. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions, Vol. 110, Part 2. For personal use only. Additional reproduction, distribution, or transmission in either print or digital f
45、orm is not permitted without ASHRAEs prior written permission.856 ASHRAE Transactions: SymposiaFigure 1 Medium voltage switchgear spreadsheet. 2004. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions, Vol. 110, Part 2. F
46、or personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission.ASHRAE Transactions: Symposia 857Cables and Cable TraysThe bulk of cable losses are the resistive losses in the mainconductors. Thus,
47、 if the number of cables and their physicalarrangement in the trays are known, total losses per foot at theroom temperature of that specific cable tray can be computed.There are many combinations of loading, size, and packing ofthe cables in a tray. However, normal industry practice and thefollowing
48、 simplifying assumptions make it possible tocompute losses. Specific factors considered are:1. A cable tray can have cables of only one voltage level at atime.2. All of the cables in a tray are considered to be three-phasecables and are of the same size.3. Total height of the cable bundle does not e
49、xceed 3 in.4. Only single layers are considered for 5 kV and 15 kV cablesfor all sizes because the height of the bundle even for thesmallest size would exceed 3 in. Multiple layers are consid-ered for 600 V cables.5. A packing or fill factor of 40% is considered for the trays.In other words, the total area occupied by the cables
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