In order to size the cooling equipment, the HVAC design engineer
must be able to estimate with certainty the amount of energy added to
the environment from various heat sources and lost through various heat
sinks located in a room. Heat could be added from several sources such
as the presence of people in a classroom or office, solar radiation
through windows, and incandescent room lighting. A heat sink could
consist of outside doors and windows in winter. By closely estimating
the environmental heat gain, the HVAC equipment will not be incorrectly
sized with insufficient capacity or costly unutilized excess capability.
Building and industrial plants utilize electrical power for many
uses such as lighting, driving motorized devices, HVAC, and energy
transmission and distribution throughout the structure. All of this
electrical equipment contributes to the total heat loa d. Estimating the
total amount of rejected heat is a necessary part of sizing the heating
and refrigeration equipment required for the building.
Until recently, the primary source of information available to the
design engineer for estimating the environmental heat gain caused by
electrical equipment is the paper by Rubin (1979). In this well used
document, the rejected power values corresponding to full load operation
for transformers, power distribution equipment, motors, switchgear, and
power cables, to name a few, were presented in tables for a range of
equipment sizes common to indoor equipment. The data presented by Rubin
was obtained from the paper presented by Hickok (1978) and from other,
unspecified manufacturers. Hickok, who worked for GE at the time of
publication of his paper, states, "The data are on General Electric
products ... At no point in either Hickok's paper or in
Rubin's paper is there a discussion of measurement procedure or
measurement uncertainty nor is there any information on the rate of heat
dissipation caused by part loads. Rubin's motivation for publishing
the data was to aid the HVAC design engineer. Hickok's motivation
in his paper was to aid the factory engineer in identifying plant
locations where efficiency could be improved. Hickok's motivation
is easy to appreciate because the energy price shocks provided by Electrician Service two
oil embargoes made increasing the efficiency of existing plants,
buildings, and factories the first choice in reducing the costs of
production. McDonald and Hickok (1985) later co-authored an update of
Hickok's 1978 paper with much of the same data.
The information provided by these papers is dated. Since the oil
embargoes of the 1970' s, many electrical equipment manufacturers
have taken pains to increase the efficiency of their products. At the
same time, advances in power electronics and computer control have made
much of the technology reflected in the 1970 equipment obsolete. Another
change that has occurred since Rubin published his work is that the
manufacturing standards that apply to the various items of power
equipment have been re-issued and updated several times. These standards
could provide details for measuring the power loss in the equipment
where, perhaps, originally none existed. Also, the standards might
specify a maximum level of uncertainty for performing the measurements
and any data reported by a manufacturer claiming to follow the standard
could be deemed reliable. Thus, there is a need to update the 30 years
old information presented by Rubin.
White and Pahwa (2003a) report on work undertaken to prov ide new,
up-to-date equipment power loss data as well as information on losses
corresponding to part load operation. A result of RP - 1104 was the
issuance of a proposed design guide for estimating the environmental
heat gain. The scope of the work was reported in White, Pahwa, and Cruz
(2004a) while a synopsis of the design guide was reported in White,
Pahwa, and Cruz (2004b). While good strides were completed in the work
of White et al., RP-1104 was just a beginning in the development of
accurate ways of estimating the rejected heat of indoor electrical
distribution equipment.
The purpose of this work is to continue and advance the effort
initiated in RP-1104. The scope of the work is outlined in the following
section.
Scope of Work
Table 1 lists the types of indoor electrical equipment that were
investigated. In each row, the capability of estimating the equipme nt
heat loss at the initiation of the project is stated. Also, the
information needed in each equipment category is stated. The scope of
the work to be performed in each equipment instance is stated and,
finally, the work performed is listed. The differences between the
proposed and actual work scope will be explained on a case by case
basis.
Table 1. RP-1395 Scope
Device Type Status at Project Needed Information
Initiation
DC None. Component loss numbers Typical
Switchgear construction data Spreadsheet type
means of evaluating losses
Medium Spreadsheet type Verification of manufacturer
Voltage means of evaluating supplied loss data for breakers,
Switchgear losses bus bars, current transformers,
potential transformer s, relays,
and auxiliary compartments
Influence of enclosures on
losses.
Unit 1) Spreadsheet type Verification of manufacturer
Substation means of evaluating supplied loss data for larger
Low Voltage losses breakers, bus bars, current
Switchgear transformers, potential
transformers, relays, and
auxiliary compartments Influence
of enclosures on losses
2) Laboratory data on
some breaker losses
Bus bars and Manufacturer loss Influence of enclosure on losses
Bus ways data Analytical models for loss
calculations
Motor 1) Spreadsheet type Verification of manufacturer
Control means of evaluating supplied loss data for larger
Centers losses starters, bus bars, and auxiliary
c ompartments Influence of
enclosures on losses
2) Laboratory data on
some (smaller) combo
motor starters
Panelboards Laboratory data on Spreadsheet type means of loss
some breaker losses. calculation. Loss data for lugs
and breakers
Cables and Loss estimates Verification of loss estimates
Cable Trays derived from through comparison with measured
analytical models test data
UPS System Manufacturer loss Loss information of the UPS system
data for battery as a whole Correlation of losses
chargers and with kW-hr rating of UPS system.
inverters
Adjustable Extensive Verification of manufacturer
Speed manufacturer loss published loss data.
Drives data
Device Type Planned Work Scope P roject Work Results
DC Model and test 24 V and -48 V DC 1) Published test
Switchgear systems to calibrate and verify information in the
loss calculation by testing 3 technical literature
switchgear installations. was used to verify
published manufacture
data regarding switch
mode rectifiers.
2) Spreadsheet
created.
Medium Test losses on 3 switchgear 1) The analytical
Voltage installations to calibrate and model presented in
Switchgear verify loss calculation White and Piescio-
spreadsheet Tested items are to rovsky (2009a) and
among 5, 7.2, & 13.8 kV ratings Piesciorovsky and
with 1200, 2000, or 3000 amp White (2009b) is used
breakers. to estimate the heat
losses.
2) Spreadsheet
created.
Unit Test switchgear losses on 3 1) The analytical
Substation installations in order to model used for MV
Low Voltage calibrate and verify loss switchgear was use for
Switchgear calculation spreadsheet Tested LV.
items are to be among 800, 1600,
2000, 3200, and 4000 amp frame
sizes.
2) Breaker tests were
performed.
3) A spreadsheet model
was created.
Bus bars and Literature search on loss models Several different
Bus ways and loss tests. Verify or correct analytical models were
manufacturer loss data. Test if developed and
needed. Compile data on standard compared. The results
sizes. showed good agreement.
Motor Test control center losses on 3 1) The analytical
Control installations to calibrate an d model used for
Centers verify loss calculations switchgear was used
spreadsheet for MCC. Measurements
were made on combo -
starters.
2) A spreadsheet model
was created.
Panelboards Build spreadsheet model and 1) The same analytical
verify through measurements for model used for
120, 240, and 600 V panels for switchgear and MMC was
currents up to 1200 amps. Perform used here. Measured
tests on at least 3 boards of breaker loss data was
each voltage level. obtained.
2) Spreadsheet
created.
Cables and Acquire loss data through testing 1) Successful
Cable Trays and/or literature search to comparisons were made
verify analytical results. Test with test data found
at least three different cable in the technical
sizes if necessary. Cables are to literature.
be both low voltage and up to 15
kV med. voltage.
2) The existing
spreadsheet was
updated.
UPS System Determine UPS system losses 1) A wealth of UPS
through measurements on at least equipment loss data
3 systems of different kW-hr found from tests
rating - tested units are to be performed under IEC
in the 20 - 10kVA single phase standards was located.
range or up to 150 kVA three
phase range.
2) A spreadsheet model
was created.
Adjustable Test 2 ASD from each voltage 1) New manufacturer
Speed level (240, 480, 600V) and data was collected and
Drives compare to loss predictions - compared to RP-1104
tested ASD to be rated from 25 to data.
800 hp.
2) Good comparisons < br>
were made to DOE and
other published data.
In the sections to come, each of the equipment categories will be
covered and the results will be summarized.
PROJECT RESULTS
DC or Telecom Switchgear
DC or telecom switchgear has the technical name of switch mode
rectifiers and consists of 12/24/48 volt rectifiers for battery charging
and powering DC loads. The rectifiers are driven by the AC power supply.
Originally, the plan was to measure the power loss of such devices
and compare the results to published manufacturer data in order to
assess the quality of the numbers provided by manufacturers. Because
switch mode rectifier test results were found in the technical
literature, these published results were used in lieu of tests.
The switch mode rectifier (SMR) unit is a solid state electrical
device that transforms the AC input voltage from the utility power
supply, namely 120/208 VAC for the USA and 220/380 VAC for the EU, into
a DC output voltage consisting of either 12, 24, or 48 VDC. This DC
voltage output is usually used to feed telecommunication applications.
Some SMR units can be packaged with a battery option which provides the
backup power during the AC outages.
The percent of rated load, P, is defined as
P = (100 x [P.sub.l])/([P.sub.r]) (1)
where [P.sub.r] is the SMR rated power in watts (Btu/h) and
[P.sub.l] is DC load in watts (Btu/h). The DC load is given by
[P.sub.l] = [P.sub.r] x [DF x I/[I.sub.r]] (2)
where I is the DC load current in amps, [I.sub.r] is the rated DC
load current in amps, and DF is the load diversity factor. The load
diversity factor is obtained in the same manner as presented in White et
al. (2004b). Given the rated power percent, the percent SMR efficiency,
[eta], is found from the SMR effic iency curve; a typical curve is shown
in Figure 1 which is based on data provided by Smith (2003). The percent
SMR efficiency is given by the ratio of the output power to the input
power and is expressed as
[FIGURE 1 OMITTED]
[eta] = (100 x [P.sub.l])/[P.sub.I] (3)
where [P.sub.l] is SMR output power and [P.sub.I] is the SMR input
power.
The rate of SMR heat loss is the difference between the input power
and the output power which is expressed as
[P.sub.loss] = [P.sub.I] - [P.sub.l] (4)
By solving equation (3) for [P.sub.I] and substituting the result
into equation (4) shows that the SMR heat loss as a function of the load
and the efficiency is
[P.sub.loss] = [P.sub.l] x ([100/[eta]] - 1). (5)
The analysis just presented explains how the SMR power loss
spreadsheet of Figure 2 determines the rate of dissipated heat. In
Figure 2, six SMRs are connecte d in parallel and feed a load of 9000
watts (30708 Btu/h) and 48 volts. Each SMR consisted of a 1500 watt
(5118 Btu/h), single phase 120 VAC input, and 48 DCV output device. The
DC load is working at 75% of capacity with a diversity factor of 0.9.
[FIGURE 2 OMITTED]
During the research of this electrical device, information was
obtained from manufacturer literature. In compiling information from
eight manufacturers on switch ed mode rectifiers, data were collected on
more than 170 separate devices which showed that the efficiency depends
on the load, SMR topologies (ferro resonant, resonant, quasi-resonant,
forward, boost topology, and others), nominal AC input voltage, the
number of phases, and the nominal DC output voltage.
It was decided to separate the SMR topologies into two groups
determined by the maximum efficiency. The classification consisted of a
low efficiency SMR topology group (maximum efficiency < 75%) which
was indicative of the ferro-resonant topology and a high efficiency SMR
topology group (maximum efficiency > 75%) which was indicative of the
resonant, quasi-resonant, forward, and boost topologies. The SMR units
were further divided into other categories according to their type of
topology, number of phases, input AC voltage level and output DC voltage
level. There were nine different groups that were created. This division
was: (1) 120 VAC/12- 24- 48 VDC/ single phase/ low efficiency, (2) 120
VAC/12 VDC/single phase/ high efficiency, (3) 220 VAC/ 12 VDC/ single
phase/ high efficiency, (4) 120 VAC/ 24 VDC/ single phase/ high
efficiency, (5) 220 VAC/ 24 VDC/ single phase/ high efficiency, (6) 120
VAC/ 48 VDC/ single phase/ high efficiency, (7) 220 VAC/ 48 VDC/ single
phase/ high efficiency, (8) 208 VAC/ 48 VDC/ three phase/ high
efficiency, and (9) 380 VAC/ 48 VDC/ three phase/ high efficiency.
Most SMR manufacturers only list the maximum efficiency, usually
occurring around 80% - 90% load, for a given unit. By collecting
manufacturer peak efficiency data on SMRs and grouping the data
according to the scheme of the previous paragraph, the SMR groups were
determined. Nine SMR efficiency curves were built in the mold of typical
SMR efficiency curves from three manufacturers. Depending upon the
nature of the data, the efficiency curve was either represented by a
curve fit or three straight line segments. The straight line segments
were used for the low efficiency curves while the curve fit was used for
the high efficiency curves. The nine SMR efficiency curves were included
in a spreadsheet linked to a Visual Basic program. The different types
of SMRs are listed in Table 2 together with the average maximum
e fficiency and the efficiency as a function of load.
Table 2. Low- and Hiqh-Efficiency Switch Mode Rectifiers
Type of SMR Efficiency Market Average Maximum
Efficiency %
120 VAC - 12 VDC-1 PHASE
120 VAC - 24 VDC-1 PHASE Low USA 75
120 VAC - 48 VDC-1 PHASE
120 VAC - 12 VDC-1 PHASE USA 79.4
220 VAC - 12 VDC-1 PHASE EU 83.3
120 VAC - 24 VDC-1 PHASE USA 80.6
220 VAC - 24 VDC-1 PHASE High EU 86.4
120 VAC - 48 VDC-1 PHASE USA 82.2
220 VAC - 48 VDC-1 PHASE EU 89.5
208 VAC - 48 VDC-3 PHASE USA 90.4
380 VAC - 48 VDC-3 PHASE EU 9l
Type of SMR Load, P, % SMR Efficiency Curve, [eta], %
120 VAC - 12 VDC-1 PHASE 0 to 10 [eta] = 2.3175 x P
120 VAC - 24 VDC-1 PHASE 10 to 50 [eta] = 1.0913 x P + 12.263
120 VAC - 48 VDC-1 PHASE 50 to 100 [eta] = 0.1635 x P + 56.85
120 VAC - 12 VDC-1 PHASE 10 to 100 [eta] = [eta](P) - 13.4
220 VAC - 12 VDC-1 PHASE 10 to 100 [eta] = [eta](P) - 9.5
120 VAC - 24 VDC-1 PHASE 10 to 100 [eta] = [eta](P) - 12.2
220 VAC - 24 VDC-1 PHASE 10 to 100 [eta] = [eta](P) - 6.4
120 VAC - 48 VDC-1 PHASE 10 to 100 [eta] = [eta](P) - 10.6
220 VAC - 48 VDC-1 PHASE 10 to 100 [eta] = [eta](P) - 3.3
208 VAC - 48 VDC-3 PHASE 10 to 100 [eta] = [eta](P) - 2.4
380 VAC - 48 VDC-3 PHASE 10 to 100 [eta] = [eta](P) - 1.8
In order to verify the spreadsheet, comparisons were made between
the spreadsheet results and information contained in refereed journals
and conferences. The comparison used information given by Sh ieh et
al.(1997) and Lin et al.(2000). An example of the results of these
comparisons is shown in Figure 3.
[FIGURE 3 OMITTED]
Medium and Low-Voltage Switchgear
Heat loss from medium and low-voltage switchgear was addressed in
White and Piesciorovsky (2009) and Piesciorovsky and White (2009). Due
to personnel safety issues in association with measurements on live high
voltage wiring, the RP-1395 Project Monitoring Subcommittee decided that
an analytical model was an acceptable research alternate.
The low-voltage switchgear model makes use of information for fused
and non-fused low-voltage power circuit breakers which were developed in
this project. Both low and medium voltage switchgear made use of the bus
bar model developed in this project and reported by White and
Piesciorovsky (2009).
Low-Voltage Circuit Breakers, Fuses, and Switches (up to 0.6 kV)
Ther e are three types of low-voltage circuit breakers which are
molded case circuit breakers (MCCB), insulated case circuit breakers
(ICCB), and low-voltage power circuit breakers (LVPCB). These circuit
breakers have different applications as summarized in Table 3. The
emphasis here is on MCCBs and LVPCBs. Both MCCBs and ICCBs are used in
motor control centers and switchboards. MCCBs commonly use a thermal
magnetic trip mechanism while ICCBs use a solid state trip. For this
reason ICCBs have a smaller power loss than MCCBs. Also, both ICCBs and
LVPCBs use a solid state trip and consequently, they have similar power
losses
Table 3. Characteristics of Low-Voltage Circuit Breakers
Characteristics MCCB ICCB LVPCB
Application Panelboards Switchboards Switchgear
Motor
Swithboards Control Centers S witchboards
Motor Control
Centers
Mounting Fixed mounted Draw out and Draw-out mounted
fixed mounted
Ampere Ratings Up to 2500 amps 400 to 5000 800 to 5000 amps
amps
Trip Mechanism Thermal magnetic -Solid state Solid state trip
fixed trip trip With time with a great
current curve range of time
characteristics current curve
characteristics
Standards UL 489-1996 UL 489-1996 UL 1066-1997
A low-voltage fuse is an electrical protection device, used with an
electrical disconnection device, either a switch or breaker. Fuses are
more commonly used with switches than with breakers. While switches are
classified based on their voltage and current ratings, fuses are
classified based on the voltage rating, current rating which is either
nominal or interrupting, shape, and load application which in this work
is either motor or conductor and lighting. The fuse classification is
given by the standards IEC 60269-2-2006 and UL 248-X-2000.
Molded Case Circuit Breakers and Low-Voltage Power Circuit
Breakers. Circuit breakers used in power panelboards, motor control
centers and switchboards are molded case circuit breakers rated at 600
VAC and between 15 and 2500 amps. They can be used as non-fused circuit
breakers.
Measurements have shown that the breaker enclosure can
significantly influence the amount of the heat loss attributed to eddy
currents in the surrounding structures. These circuit breakers are
classified based on frame sizes.
In RP-1395, many live line measurements were made on MCCBs. These
MCCB measurements are compared to data presented in McDonald and Hickok
(1985) and in updated manufacturer literature in F igure 4 for frame
sizes from 15 to 1200 amps. The MCCB power loss data of Figure 4 are
valid for balanced three phase operation.
[FIGURE 4 OMITTED]
The circuit breakers used in low-voltage switchgear are low-voltage
power circuit breakers and they are rated at 600 VAC and between 800 and
5000 amp. They have higher interrupting current ratings (up to 200 kA)
than molded case breakers. The type of mechanism used to open the
breaker is a stored energy spring system while the trip sensor type is a
microprocessor RMS (root mean square) sensor. Low-voltage power circuit
breakers are draw-out mounted allowing easy inspection operations. They
can be used as fused circuit breakers (non-automatic) and non-fused
circuit breakers (automatic). The heat dissipated by LVPCB depends on
whether the breaker is installed with or without fuses.
Rate of heat loss data for LVPCB was derived fro m manufacturer
literature. Data were collected from three manufacturers. The data was
divided into fused and non fused categories. Table 4 shows the
compilation of the data for both breaker categories.
Table 4. Low-Voltage Power Circuit Breaker Power Losses and Resistances
Low-Voltage Power Circuit Breaker Power Losses and
Resistances
Fused LVPCBs Non-fused LVPCBs
Frame Power Loss, Resistance. R, Power Loss, Resistance, R,
Current, Pbr. W [mu][ohm] Pbr. W (Btu/h) [mu][ohm]
IR, amps (Btu/h)
800 600 (2047) 937 95 (324) 148
1200 1050 (3583) 729 212 (723) 147
1600 1500 (5118) 586 378 (1290) 147
2000 2250 (7677) 562 500 (1706) 125
3000 3375 (11515) 375 1042 (3555) 116
3200 3600 (12283) 351 1150 (3924) 112
4000 4500 (15354) 281 1372 (4681) 86
5000 4700 (16036) 188 1650 (5630) 66
Note: The interpolated value are represented in boldface (no available
data).
The LVPCB and MCCB power losses of Tables 4 and 5 are valid for
balanced three phase operation and frame size currents.
Table 5. Molded Case Circuit Breaker Losses
Molded Case Circuit Breaker Losses at Rated Frame Currents
Manufacturer Literature
Frame Power Loss, W (Btu/h) Average Power
Size, Loss, W (Btu/h)
[I.sub.l],
amps
15 10.8, 9.6, 3.9, 3.0 (36.8, 32.8, 13.3, 6.8 (23.2)
10.2)
20 10.8, 9.6, 3.9, 5. 1 (36.8, 32.8, 13.3, 7.4 (25.2)
17.4)
25 9.9, 6.0, 4.8 (33.8, 20.5, 16.4) 6.9 (23.5)
30 10.8, 10.5, 5.4, 7.2 (36.8, 35.8, 18.4, 8.5 (29.0)
24.6)
35 14.4, 9.0 (49.1, 30.7) 11.7 (39.9)
40 11.4, 18.9, 8.4, 7.8 (38.9, 64.5, 28.7, 11 6 (39.6)
26.6)
50 11.7, 15.9, 9.6, 11.1 (39.9, 54.2, 32.7, 12.1 (41.3)
37.9)
60 23.1, 11.7,13.8, 11.7 (78.8, 39.9, 47.1, 15.1 (51.5)
39.9)
70 13.8, 12.6, 14.1, 15.9 (47.1, 43.0, 48.1, 14.1 (48.1)
54.2)
80 13.8, 18.0, 14.4, 16.2, 14.4 (47.1, 61.4, 15.4 (52.5)
49.1, 55.3, 49.1)
90 22.8 - 15.0 - 20.7 - 18.3 (77.8, 51.2, 19.2 (65.5)
70.6, 62.4)
100 15.6, 21.1, 15.9, 20.4, 23.1 (53.2, 72.0, 19.2 (65. 5)
54.2, 69.6, 78.8)
125 17.1, 19.8, 20.1 (58.3, 67.6, 68.6) 19.0 (64.8)
150 20.7, 26.4, 22.2, 15.0, 48.0 (70.6, 90.1, 26.5 (90.4)
75.7, 51.2, 163.8)
175 27.6. 34.8 (94.2, 118.7) 31.2 (106.5)
200 29.7, 39.6 (101.3, 135.1) 34.7 (118.4)
225 40.5, 45.0 (138.2, 153.5) 42.8 (146.0)
250 41.1, 32.0, 80.0 (140.2, 109.2, 272.9) 51.0 (174.0)
300 36.9 (125.9) 36.9 (125.9)
350
400 175.0 (597.1) 175.0 (597.1)
450
600 120.3, 91.8, 85.0, 230.0 (410.5, 313.2, 131.8 (449.7)
290.0, 784.8)
800 170.0, 250.0, 93.0 (580.0, 853.0, 317.3) 171.0 (583.5)
1000
1200
Molded Case Circuit Breaker Losses at Rated Frame Currents
Measurements Model Pbr =
0.2658 x
[I.sub.r] (Pbr
= (1,9069 x
[I.sub.r])
[I.sub.r]
Frame Size, Power Loss V (Btu/h) Average Power Power Loss,
[I.sub.l], Loss, W (Btu/h) Pbr, W (Btu/h)
amps
15 4.0 (13.6)
20 5.3 (18.1)
25 6.6 (22.5)
30 8.0 (27.3)
35 9.3 (31.7)
40 10.6 (36.2)
50 13.3 (45.4)
60 15.9 (54.2)
70 21.1 (72.0) 21.1 (72.0) 18.6 (63.5)
80 21.3 (72.7)
90 23.9 (81.5)
100 26.6 (90.8)
125 33.2 (113.3)
150 39.9 (136.1)
175 48.1, 47.9 (164.1, 48 (163.8) 46.5 (158.7)
163.4)
200 60.6, 65.3, 60.7, 65.2, 58.7 (200.3) 53.2 (181.5)
41.5 (206.8, 222.8,
207.1, 222.5, 141.6)
225 86.1 (293.8) 86.1 (293.8) 59.8 (204.0)
250 94.2, 94.0 (321.4, 94.1 (321.1) 66.5 (226.9)
320.7)
300 76.6 (2 61.4) 76.6 (261.4) 79.7 (271.9)
350 80.8 (275.7) 80.8 (275.7) 93.0 (317.3)
400 97.8.60.5. 188.7.89.4 109.1 (372.2) 106.3 (362.7)
(333.7. 206.4, 643.8,
305.0)
450 109.4 (373.3) 109.4 (373.3) 119.6 (408.1)
600 142.2 (485.2) 142.2 (485.2) 159.5 (544.2)
800 191.7 (654.1) 191.7 (654.1) 212.6 (725.4)
1000 242.3 (826.7) 242.3 (826.7) 265.8 (906.9)
1200 344.0 (1173.7) 344.0 (1173.7) 319.0 (1088.4)
The rate of dissipated heat of a molded case circuit breaker and
low-voltage power circuit breaker (fused or non-fused type) can be
calculated using https://collegegrad.com/careers/electricians the appropriate power loss value from Tables 4 and 5,
respectively and the relation
[P.sub.loss] = [(DF x [I/[I.sub.r]]).sup.2] x [P.sub.br] (6)
where [I.sub.r] is the rated frame current, [P.sub.loss] is the
rate of heat dissipation, I is the breaker current RMS phase current,
[P.sub.br] is the power loss corresponding to the frame current and is
shown in Figure 4, and DF is the diversity factor. Also, the rate of
dissipated heat loss in watts for the breakers can be found by using the
appropriate resistance from Tables 4 and 5 in the relation
[FIGURE 5 OMITTED]
[P.sub.loss] = [(DF x I).sup.2] x R (7)
where R is circuit breaker loss resistance in ohms.
Low-voltage power circuit breakers are built and tested according
to the standards UL 1066-1997 and IEEE C37.13-2008. These standards show
that the LVPCBs can be used in fused and non-fused situations.
Figure 5 shows the average maximum power loss for fused and
non-fused LVPCB derived from manufacturer literature.
Low-Voltage Fuses. Low-voltage fuse loss information was obtained
for EU fuse types, gG and aM and USA fuse types J and RK1. The European
fuse types are defined in the standard IEC 60629 while American fuse
types are defined in the standard UL 248-X-2000. There are two types of
fuses that are of interest which are the general application fuse used
to protect conductors and the motor application fuse which has the
characteristic of having a sufficient time delay so that it does not
fail during high current motor start ups. Power losses at rated currents
up to 1000 volts and 600 amps from two manufactures were collected and
grouped according to the fuse origin and application. A regression
analysis was performed on each data group. The power loss models for
general application or gG type fuses is
[P.sub.Gfr] = 2 x [10..sup.-7 ] x [I.sub.fr.sup.3] - 2 x [10.sup.-4]
x [I.sub.fr.sup.2] + 0.1063 x [I.sub.fr] (8)
while the power loss models for European and American motor
application fuses are
[P.sub.Mfr] = 2 x [10.sup.-7] x [I.sub.fr.sup.3] - 9 x [10..sup.-5]
x [I.sub.fr.sup.2] + 0.0769 x [I.sub.fr] (9)
and
[P.sub.Mfr] = -4 x [10..sup.-5] x [I.sub.fr.sup.2] + 0.1505 x
[I.sub.fr] (10)
respectively, where [I.sub.fr] is the rated fuse current rating in
amps, [P.sub.Gfr] is the power loss in watts for general application
fuses, and [P.sub.Mfr] is the power loss in watts for motor application
fuses. Equation (10) is used for general purpose applications for US
fuses. Note that equations (8) through (10) provide the power loss at
the rated fuse current. The fuse power loss at part loads is given by
[P.sub.fuse] = [([D.sub.f] x [I/[I.sub.fr]]).sup.2] x [P.sub.fr]
(11)
where [P.sub. fr] is provided by equations (8) - (10) depending upon
the application, [P.sub.fuse] is the fuse power loss in watts or in
Btu/h after multiplying equation (11) by 3.412, I is the given current
in amps, and DF is the load diversity factor of the load protected by
the fuse.
[FIGURE 6 OMITTED]
Low-Voltage Fusible Switches. Low-voltage fusible switches are
formed by a three-pole disconnect switch and three low-voltage fuses.
The switch works as a disconnecting device and the fuses work as a
protection device. The low-voltage switches are rated up to 1000 VAC and
up to 630 amps. The switches are always used with fuses that protect the
main elements of the circuit such as cables, heaters, motors, and
lighting from overloads and short circuits.
In order to develop a model for these switches, rated from 30 to
630 amps, data on power losses at rated load and balanced three phase < br>
operation were collected from three manufacturers. The collected data
was fitted with a regression curve which is found to be
[P.sub.sr] = 0.0003 x [I.sub.sr.sup.2] + 0.0839 x [I.sub.sr] watts
(12)
where [P.sub.sr] is the three phase switch power loss in watts at
rated current and [I.sub.sr] is the rated switch current in amps. By
multiplying the result of equation (12) by 3.412 provides the power loss
in Btu/h. The switch power loss at a given current is determined by
[P.sub.switch] = [(DF x [I/[I.sub.sr]]).sup.2] x [P.sub.sr] (13)
where [P.sub.switch] is the low-voltage switch power loss in watts
(Btu/h), I is the given phase current flowing through the switch in
amps, [I.sub.sr] is the switch current rating in amps, [P.sub.sr] is
determined by equation (12), and DF is the diversity factor applied to
the load connected to the switch. Because each of the three phases of
the switch are connected in series with a fuse, the power loss of the
fusible-switch is
[P.sub.loss] = [P.sub.swich] + 3 + [P.sub.fuse] (14)
where [P.sub.loss] is the fusible-switch power loss in watts.
NEMA Motor Starters
The power loss models of full voltage, non-reversing (FVNR) motor
starters in RP-1104 were verified in RP-1395, using updated literature
and live line testing. The starters tested in RP-1104 did not include
fuses. The recommendation of this project is to add the appropriate fuse
power loss to the motor starter power loss presented in RP-1104. Because
a fuse is placed in series with each phase of the motor starter, the
fuse power loss is three. As a rule of thumb, the motor application fuse
rating is 1.25 times the current rating of the starter. Motor starters
are covered in Piesciorovsky and White (2010).
Bus Bars and Bus Ways
Bus bars and bus ways are divided into three categories being the
isolated phase bus, the non-segregated phase bus, and the segregated
phase bus. The first two categories are common indoor bus arrangements
while the last item is mainly an outdoor type of construction. In the
following section, the isolated phase bus and the non-segregated phase
bus will be examined.
Isolated Phase Bus (Medium Voltage up to 38 kV). Electrical bus
ways can be classified into isolated phase buses, non-segregated bus
ways, and segregated phase bus ways. An isolated phase bus (ANSI
definition 20-2.1.4.3) is one in which each phase conductor is enclosed
by an individual metal housing separated from adjacent conductor
housings by an air space. The bus may be self-cooled or force-cooled by
means of circulating air, gas or liquid. Most generators use copper or
aluminum conductors to transfer the generated power. Howeve r, for
voltages greater than 13 kV and/or currents over 5000 amps, sometimes
this alternative is not the most economical, and the isolated phase bus
is used. The isolated phase bus is classified into two groups which are
the non-continuous and continuous isolated phase bus.
Isolated phase buses with non-continuous enclosures have the
characteristic that conductor enclosures are segmented into a series of
electrically isolated, grounded portions. All successive enclosure
sections are insulated from each other. The three enclosures of each
three-phase group are insulated from each other, except at one end where
they are connected together and grounded. The insulation between each
enclosure section is required to prevent circulating currents from
flowing through the high resistance joints at interfaces between
enclosures and between the enclosure and supporting steel beams.
I solated phase buses with continuous enclosures have the characteristic
that conductor enclosures are electrically continuous and shorted
together and grounded at both ends. Circulating currents almost equal to
the phase currents are induced in the enclosures, in a direction
opposite to the current flow. The resulting magnetic fields tend to
cancel each other.
An isolated phase bus model has been created which can accommodate
both the non-continuous and continuous configurations. It was developed
according to the results and examples of the IEEE Standard for
Metal-Enclosed Bus, C37.23-2003. The isolated phase bus bar spreadsheet
model, shown in Figure 6 estimates the partial heat losses of the
conductor for the continuous and non-continuous enclosure cases together
with the different conductor configurations such as three balanced
conductors, three unbalanced conductors, two conduc tors, and single
phase taps. The numbers shown in the spreadsheet of Figure 6 correspond
to an example presented in C37.23-2003. The spreadsheet determines the
total operating heat loss.
[FIGURE 7 OMITTED]
Good agreement was obtained in comparing the Figure 6 spreadsheet
results with the example that is shown in C37.23-2003. In addition, good
agreement was also obtained when the spreadsheet values were compared
with the measured values reported by Elgar, Rehder and Swerdlow (1968)
and Conangla (1963). The results of this comparison are contained in
White and Piesciorovsky (2010).
Nonsegregated Bus Ways (0.6 k V, 5/15 kV). A segregated phase bus
(ANSI definition 20-2.1.4.2) is one in which all phase conductors are in
a common metal enclosure, but are separated by metal barriers between
phases. A non-segregated phase bus (ANSI definition 20-2.1.4.1) is one
in which a ll phase conductors are in a common metal enclosure without
barriers between phases. When associated with metal-clad switchgear the
primary bus conductors and connections are covered with insulating
material throughout. These definitions are found in EPRI (1999).
A non-segregated bus way is used more frequently than the
segregated phase bus way in power distribution systems. In addition, the
non-segregated bus ways are a good option when higher currents have to
be transmitted and the use of copper power cables does not result in a
viably economical option. White and Piesciorovsky (2009) presented an
analytical model of a non-segregated bus. It is this model upon which
the information presented here is based.
The non-segregated bus ways usually are available in low voltage
(0.6 kV) and medium voltage (5/15 kV). They are three phase power
distribution systems designed with aluminum or copper rectangular
conductors which are inside of a metal bus way enclosure. All conductors
are individually supported on insulating members. The bus duct is
designed, manufactured and tested in accordance with ANSI Standard
C37.20.
The heat loss of this electrical equipment item consists of the
ohmic heat loss of the conductor and that of the enclosure. The
conductor heat losses are given by the skin effect which causes the
effective resistance of the conductor to increase with the frequency of
the current and the proximity effect created by currents flowing through
one or more nearby conductors producing magnetic flux which also
modifies the effective resistance of the conductor. The enclosure heat
loss is given by the stray loss caused by the eddy currents induced in
the metal enclosure by the currents flowing in the conductors.
The heat loss of the non-segregated bu s ways was calculated using
information about the materials and dimensions of conductors and
housings (enclosures) given by two different manufacturers. The skin,
proximity and stray heat loss models used in these calculations were
designed according to Dwight (1947), White and Piesciorovsky (2009), and
Del Vecchio (2003). Having obtained the non-segregated bus way heat
losses per unit length for different current ratings, namely 1200, 1600,
2000, 2500, 3000, 3200, 4000, and 5000 amps, the non-segregated bus way
heat loss spreadsheet was developed for any balanced load situation for
each of these current ratings.
This spreadsheet, shown in Figure 7, assumes three phase balanced
currents at 60 Hz, painted aluminum sheet enclosures, rectangular solid
copper conductors, one conductor per phase, 40[degrees] Celsius
(104[degrees] F) ambient temperature, and 65[degrees] Celsius
(149[degrees] F) conductor temperature rise. The ambient conditions
correspond to data shown in manufacturer publications. Figure 7 shows an
example of a power loss calculation for a 20 meter (65.6 ft), 3000 amp
low-voltage bus way carrying a current of 1200 amp and a load diversity
factor of 0.7.
Using the skin, proximity and stray effect heat loss models
previously covered, the heat loss was calculated for the 0.6 kV and 5/15
kV non-segregated bus ways using the design data of two manufacturers.
These calculated values together with the manufacturer values are
compared in White and Piesciorovsky (2010).
Low Voltage Panel Boards
Low Voltage Panelboards (0.6 kV). The National Electrical Code
defines a panelboard as a "single panel or group of panel units
designed for assembly in the form of a single panel, including buses,
automatic overcurrent devices, and equipped with o r without switches for
the control of light, heat, or power circuits; designed to be placed in
a cabinet or cutout box placed in or against a wall, partition or other
support; and accessible only from the front," (NEC, Article
100-definitions). Panel-boards differ from switchboards and low-voltage
switchgear as shown in Table 6.
Table 6. Panelboard Characteristics (Panelboard versus Switchboard and
Low Voltage Switchgear (120 V, 208V, and 480 V)
Characteristics Panelboard Switchboard Low Voltage
Switchgear
Function or Control light, Load Substation
Application heat, or power distribution application before
circuits before the the switchboard
panelboard
Design Cabinet or cut Stand-alone Stand-alone
out box mounted enclosure enclosure mounted < br>
against a wall mounted away away from a wall.
from a wall. Construction with
Construction internal barriers
with internal between devices
barriers between and busses.
devices and
busses is
optional.
Breakers fully
compartmentalized
with barriers.
Bus Bars Vertical bus Horizontal and Horizontal and
bars--3 phase Vertica bus Vertical bus
bars--3 phase bars--3 phase
and ground
Breaker Rated Up to 1200 amps 150 to 5000 800 to 5000 amps
Current amps
Access Only from the Front and rear Front and rear
front access access
Disconnect Fusible Switch Fusible Switch LVPCB
Devices MCCB MCCB ICCB LVPCB FLVPCB--Fused
low-volta ge power
circuit breaker
The panelboard is designed to handle voltages up to 0.6 kV, to be
connected directly to loads, to be mounted against a wall, to be built
with a vertical three phase bus bar system, to accommodate rated
currents up to 1200 amps, and to be accessible only from the front. The
power panelboard is classified by its current rating which is either
250, 400, 600, 800, or 1200 amps and by its dimensions which consist of
height, bus bar length, width, and depth. These dimensions are a lso used
to determine the total number of branch circuits which consist of
circuit breakers, fusible switches, and motor starters. All of branch
circuits are connected to the vertical main bus. The panelboard
enclosures are made of galvanized steel while the vertical main bus is
made of copper or aluminum with rectangular cross sections. The
dimensions and ampacities of the main bus are given by UL 67-1993. In
order to develop a loss model for panelboards, attention will be given
to MCCB, fusible switch, motor starter, and bus bar with enclosure
losses. The assumption of balanced three phase currents is applied to
all panelboard devices. The loss models of the MCCB, fusible switch and
motor starter were shown in previous sections of this paper, and only
the bus bar and enclosure losses are treated here.
Table 7. Bus Bar and Enclosure Losses per Unit Length--Low Voltage
Panelboard
Bus bar Dimensions, m (ft)
Power Panelboard Height Width Phase-to-Phase
Ampere Ratings, Separation
[I.sub.bus], amps
250 0.0254 (0.0833) 0.0064 (0.0210) 0.0444 (0.1457)
400 0.0508 (0.1666) 0.0064 (0.0210) 0.0952 (0.3123)
600 0.0635 (0.2083) 0.0064 (0.0210) 0.1206 (0.3957)
800 0.0889 (0.2917) 0.0064 (0.0210) 0.1714 (0.5623)
1200 0.0635 (0.2083) 0.0127 (0.0417) 0.1143 (0.3750)
Calculated Enclosure--Bus Bar Power Losses
Power Panelboard Calculated Calculated Calculated
Ampere Ratings, Enclosure Power Three-Phase Bus Enclosure-Bus
[I.sub.bus], amps Loss, W/m Bar W/m (Btu/h Bar W/m (Btu/h
(Btn/h ft) ft) ft)
250 0.13 (0.14) 2 5.84 (26.87) 25.97 (27.01)
400 1.45 (1.51) 33.87 (35.22) 35.32 (36.73)
600 5.01 (5.21) 61.89 (64.36) 66.90 (69.57)
800 16.58 (17.24) 78.71 (81.85) 95.29 (99.09)
1200 23.63 (24.57) 136.63 (142.08) 160.26 (166.65)
0.6 KV - /15 KV NON-SEGRAGTED BUS WAY POWER LOSS SPREADSHEET
FIXED DATA
Heat Loss Resisstance per
Three Phase [OMEGA]/m]
Bus Bar Rating Voltage Level [KV] Bus Bar Enclosure
[Amps]
1200 0.6 KV 1 1758E-04 3.6150E-05
5/15 KV 1.1758E-04 3.6150E-05
1600 0.6 KV 5.6273E-05 3.8160E-05
5/15 KV 5.6335E-05 3.1290E-05
2000 0.6 KV 4.5018E-05 3.6090E-05
5/15 KV 4.5018E-05 2.3140E-05
2500 0.6 KV 4.6207E-05 2.8230E-05
5/15 KV 4.6207E.05 2.4840E.05
3000 0.6 KV 3.5549E-05 1.8360E-05
5/15 KV 3.5549E-05 2.8560E-05
3200 0.6 KV 3.5549E-05 1.8360E-05
5/15 KV 3.5549E-05 2.3160E-05
4000 0.6 KV 2.7781E-05 1.4400E-05
5/15 KV 2.7781E-05 1.4400E-05
5000 0.6 KV 2.1630E-05 1.3710E-05
5/15 KV 2.1211E-05 1.3710E-05
ENTER DATA
Bus Bar Select Load Diversity Bus Way
Rating [Amps] option "1" [Ampere] Factor [< 1] Length [meter]
1200
1600
2000
2500
3000 1 1200 0.70 20
3200
4000
5000
RESULTS
Bus Bar Rating Device Power Enclosure Power Total Power
[Amps] Loss [watts] Loss [watts] Loss [watts]
1200 0.00 0.00 0.00
0.00 0.00 0.00
1600 0.00 0.00 0.00
0.00 0.00 0.00
2000 0.00 0.00 0.00
0.00 0.00 0.00
2500 0.00 0.00 0 00
0.00 0.00 0.00
3000 501.66 259.10 760.76
0.00 0.00 0.00
3200 0.00 0.00 0.00
0.00 0.00 0.00
4000 0.00 0.00 0.00
0.00 0.00 0.00
5000 0.00 0.00 0.00
0.00 0.00 0.00
TOTAL POWER LOSS [watts] 760.76
The power losses in bus bars and enclosures were determined by the
numerical methods of White and Piesciorovsky (2009) and Del Vecchio
(2003). The bus bar and enclosure losses at the 250, 400, 600, 800 and
1200 amps ratings were found and the results were put through a
regression analysis. The enclosure-bus bar power loss was found to be
[P.sub.bus] = [(DF x I).sup.2] x H x (0.00004 + 0.0839 x
[I.sub.bus.sup.-1]) watts (15)
where [P.sub.bus] is the enclosure-bus bar power loss in watts, I
is the load current flowing through a single bus bar in amps,
[I.sub.bus] is the current rating of the bus bar in amps, H is the bus
bar length in meters, and DF is the load diversity factor applied to the
main disconnecti ng device. Multiplying equation (15) by 3.412 provides
the power loss in Btu/h. The main disconnecting device load diversity
factor is
DF = [p.summation over (c=1)][DF.sub.c] x [[I.sub.c]/I] (16)
where [DF.sub.c] is the secondary branch device diversity load
factor and [I.sub.c] is the secondary branch device current in amps.
Equation (16) is not true on an instantaneous basis. Its purpose is to
predict the average long term rates of heat loss.
Figure 8 shows a schematic diagram of a panelboard where there is a
main branch that feeds the secondary branches that consist of circuit
breakers, fusible-switches, and motor starters. The main branch has
power losses from the main disconnecting device (breaker or fusible
switch) and enclosure-bus bar losses, while the secondary branches have
the breakers, fusible switches, and motor starter losses.
The foregoing panelboard analysi s was included in a spreadsheet
linked to a Visual Basic program which calculates the panelboard heat
loss.
[FIGURE 8 OMITTED]
CABLES AND CABLE TRAYS
The spreadsheet developed during RP-1104 for cables and cable trays
is based on an analysis presented by Harshe and Black (1994). The
calculation used in the spreadsheet for predicting the heat losses was
compared to published cable hot-spot measurement data reported by Stolpe
(1971), Lee (1972), Nemeth et al.(1981), and Engmann (1984).
The goal of the analysis presented by Harshe and Black (1994) was
to accurately predict the hotspot temperature in a cable tray bundle. To
do this, the rate of heat generated by [I.sup.2]R losses is set equal to
the rate of heat transferred to the environment through free convection
and radiation. The heat transfer is a function of the cable bundle
surface and the ambient temperatures.
[FIGURE 9 OMITTED]
The cable bundle is assumed to have uniform surface temperature.
Knowing the surface temperature, the hot spot temperature can be
predicted based on the cable bundle thermal resistance. The hot-spot
temperature is used to determine the electrical resistance of the
conductors in the bundle. Using the heat balance, a new surface
temperature can be determined which can be used to produce a new
hot-spot temperature and the final hot-spot temperature is determined
through an iterative process. From the hot-spot temperature, the cable
electrical resistance can be determined and the overall heat loss
determined.
It has been noticed that the hot-spot temperature can be sensitive
to cable and loading parameters such as the ambient temperature, but the
heat loss is not sensitive to environmental parameters. It has been
demonstrated in RP-1104 that conduct or heat loss is not a strong
function of ambient temperature because the losses vary linearly with
absolute temperature. For a 10 [degrees]C (18[degrees] F) change in a
room temperature of 25 [degrees]C (77[degrees] F), the percent change in
electrical resistance (and power loss) will be (10/298 * 100)% = 3.4%.
This percentage is smaller for higher environmental temperatures.
A mistake was found in one of the formulas reported by Harshe and
Black (1994). A constant shown in Eq. (15) of that paper is listed as
1.85x[10.sup.6] ([degrees]C [m.sup.3]) whereas the constant should read
1.85x[10.sup.8] [([degrees]C [m.sup.3]).sup.-1]. Eq. (15) is a curve fit
for g[beta]/[v.sup.2] where g is the acceleration of gravity, [beta] is
the coefficient for thermal expansion of air, and v is the kinematic
viscosity of air. The curve fit describes the variation of
[g[beta]/[v.sup.2]] as a function of temperature. Although it was
noticed that the hot spot temperature changed in subsequent
calculations, the power loss was not significantly influenced.
By obtaining close agreement between the hotspot temperature values
determined in the spreadsheet and the hotspot temperatures measured in
the work of Stolpe (1971), Lee (1972), Nemeth et al. (1981), and Engmann
(1984), the validity of the spreadsheet model was determined. White and
Piesciorovsky (2010) contains greater detail regarding the comparisons.
UNINTERRUPTIBLE POWER SUPPLY
The uninterruptible power supply (UPS) is used for loads that need
a continuous energy supply without any AC wave disturbances (harmonics,
blackouts, spikes, sags, etc). The UPS has batteries which store energy
when the AC main supply is available. The batteries feed the load when
the AC main supply is not available. As the main supply is AC, and the
DC backup supply is provided by the batteries, the UPS has also a
rectifier (AC-DC converter) which charges the batteries, an inverter
(DC-AC converter) which supplies the load from the batteries when the AC
main supply fails, and a static switch which allows the load to be
supplied from either the AC main power or the inverters. A UPS that
includes a battery charger, a power inverter circuit and a static switch
is illustrated in Figure 10.
[FIGURE 10 OMITTED]
A typical UPS contains sufficient battery capacity to support its
fully rated output load for a few minutes or several hours. The time is
dependent on the quantity of batteries. In addition, a secondary power
supplier such as a diesel driven generator can be used to charge the
batteries and supply the lo ad in the event of a main AC power loss. The
UPS transforms the AC voltage input given by the utility power supply
into a DC voltage output of 12, 24, or 48 VDC.
The UPS efficiency is determined by the measurement of the input
and output power in normal operation according to section 6.6.11 of the
standard IEC 6240-3 UPS efficiency test. The UPS efficiency testing is
based on the following fractional load levels of 0%-10%, 10%-20%,
20%-50%, 50%-75%, and 75%-100%.
The UPS percent rated output power is given by
P = 100 x [[P.sub.l]/[P.sub.r]] = [[100 x [P.sub.l]]/[[S.sub.rs] x
cos[theta]]] (17)
where [P.sup.l] is the power output in watts, [P.sup.r] is the
rated output power in watts, [S.sup.rs] is the rated output volt-amps,
and cos([theta]) is the output power factor. If [P.sup.l] and [P.sup.r]
are used to evaluate equation (17), then the units of the power
quantit ies are in the same units. If the volt-amps is used to evaluate
equation (17) then [P.sup.l] must be in watts. The output power is given
by
[P.sub.l] = [P.sub.r] x [(DF x I)/[I.sub.r]] (18)
where DF is diversity factor, I is load current in amps, and
[I.sup.r] is rated output current in amps.
The efficiency is determined from curves which show the efficiency
as a function of the percent output power. Figure 11 show a typical
efficiency curve which is obtained from IEC 62040, pp. 52.
[FIGURE 11 OMITTED]
The percent UPS efficiency is given by the ratio of the output
power to the UPS input power multiplied by 100 or
[eta] = [100 x [P.sub.l]/[P.sub.I]] (19)
where [P.sup.I] is the input power in watts (Btu/h). Equation (19)
provides the correct result as long as the power quantities are in the
same units. The rate of UPS power loss is the difference between the
input power and the output power and is
[eta] = [100 x [P.sub.l]/[P.sub.I]] (19)
where [P.sup.loss] is the rate of heat loss in watts (Btu/h). From
equations (19) and (20), the power loss as a function of the efficiency
and output power is
[P.sub.loss] = [P.sub.l] x ([100/[eta]] - 1). (21)
A UPS is rarely used at full load and the UPS losses are
essentially constant. The typical UPS efficiency value decreases as the
load decreases. UPS devices are typically loaded in the 30% and 50%
range.
The UPS system is usually made up of several UPS units. Depending
on how these are electrically connected, the UPS system can be
classified into one of the configurations listed in Table 8 as described
by Ton and Fortenbury (2005). Illustrations of these configurations or
topologies are shown in White and Piesciorovsky (2010).
Table 8. Uninterruptible Power Supply Configurations
Uninterruptible Power System Configurations
N or Capacity
Isolated Redundant
N + 1 parallel, Single Bus
SN Dual Bus
2(N + 1) Dual Bus
A UPS topology is the technology upon which the UPS operates. The
classification of these topologies is shown in Table 9 according to
their usual operational power ratings. There are other UPS topologies
that are not described in this paper. Also, UPS topologies are
classified according to the UPS manufacturer models and the UPS market
structure as described by Ton and Fortenbury (2005).
Table 9. Uninterruptible Power Supply Topologies
UPS Technology UPS Rating, kVA
Standby Up to 2 kVA
Transformer 5 kVA to 20 kVA
Double Conversion 5 kVA to > 200 kVA
Delta Conversion 20 kVA to > 200 kVA
Flywheel 50 kVA to > 200 kVA
The UPS typical eff iciency curve shows that the higher the load,
the higher the UPS efficiency. For this reason, some manufacturers have
introduced a programmable mode called "High Efficiency Mode"
which is used only in "Double Conversion" UPS units. It is
sometimes referred to as the "power-saver" mode. When the UPSs
do not work with the High Efficiency Mode, they are working under the
"Base" mode which can be used by all UPS topologies. Also, the
UPS efficiency depends on the load power factor as seen by the fact that
the percent UPS efficiency decreases 0.5% when the load power factor
decreases by 0.1 according to Ton and Forten-bury (2005).
The efficiency of a UPS system and consequently its rate of
dissipated heat depends on the topology, configuration, operating mode,
and power factor. In Ton and Fortenbury (2005), efficiency measurements
were made on a variety of UPS units according to the Eu ropean Standard
IEC 62040-3 (1990). For this reason, their work was an important source
in determining the UPS heat loss model developed in RP-1395. Using this
data, eight curves, defined by analytical functions, were constructed
for predicting the UPS power loss. These curves predict the UPS
efficiency as a function of percent of rated output power. The
presentation of these eight UPS efficiency curves for different
topologies, modes, and power factor conditions is contained in the final
report of RP-1395. The range of validity of these functions is between a
lower limit of approximately 10 to 30% to a upper limit of 100% of rated
load. In addition, UPSs are usually operated between 30% and 50% of
rated load.
Given the UPS efficiency functions described in the previous
paragraph and by using equations (17) to (21), the UPS power loss model
was developed as a spreadsheet w hich is linked to a Visual Basic
program. The spreadsheet is shown in Figure 12. The calculation shown in
Figure 12 involves two UPS devices in parallel. Each unit consists of a
750 kVA, double conversion UPS in high efficiency mode. The system
characteristics consist of a redundancy configuration being 2N dual bus
and the number for the redundancy is one. The rated power of the load is
600 kW (2047200 Btu/h) and the rated current is 1000 amps. The load
power factor is 0.9 and the diversity factor is 0.8. The actual load
current is 950 amps.
[FIGURE 12 OMITTED]
The spreadsheet, based on measured data from Ton and Fortenbury
(2005), was used to replicate data presented by two manufacturers. The
results were satisfactory and they are shown in Table 10. It is seen
that in most of the comparisons, the percent difference in heat loss
rate is within [+ or -] 10%.
Table 10. UPS System Power Loss Spreadsheet Verification
Data Entered in Spreadsheet
UPS Data--Manufacturer Literature
UPS Configuration
Number Rate kVA UPS Unit UPS System Redundancy No. UPS UPS
per UPS Technology of kVA Power
UPS per Factor
Unit
1 40-160 Double * N + 1 Parallel 2 160 0.9
2 225-550 Double * N + 1 Parallel 2 275 0.9
Conversion
3 750 Double * Isolated Redundant 1 750 0.9
4 500 Double * Isolated Redundant 1 500 0.9
5 400 Double * Isolated Redundant 1 400 0.8
6 225-300 Double * Isolated Redundant 1 225 0.8
7 225-300 Double * Isolated Redundant 1 300 0.8
8 100-150 Double * Isolated Redundant 1 100 0.8
9 100-150 Double * Isolated Redundant 1 120 0.8
10 100-150 Double * Isolated Redundant 1 150 0.8
Data Entered in Spreadsheet
Load Characteristics
Number Rate kVA per Load Load Load Load Actual
UPS Rated Rated Power Diversity Load
Power, Current, Factor Factor Current,
kW amps amps
1 40-160 288 333 0.9 0.9 249
2 225-550 455 1145 0.9 0.9 638
3 750 675 902 0.9 1 902
4 500 495 1145 0.9 0.9 600
5 400 320 481 0.8 1 481
6 22 5-300 180 270 0.8 1 270
7 225-300 240 360 0.8 1 360
8 100-150 80 120 0.8 1 120
9 100-150 96 144 0.8 1 144
10 100-150 120 180 0.8 1 180
Comparison of Data and Model Values--Efficiency and Power Loss
UPS Load Verification Efficiency And Power Loss
Comparison
Rated Load, % UPS System Efficiency, %
Number Rated kVA per Man. Spreadsheet Man. Data Spreadsheet
UPS Unit Data Value Value
1 40-160 45 45.29 94.65 95.62
2 225-550 25 25.15 90.00 91.62
3 750 100 100 91.75 92.80
< br>4 500 100 100 93.80 92.80
5 400 100 100 94.00 92.30
6 225-300 100 100 92.40 92.30
7 225-300 100 100 92.70 92.30
8 100-150 100 100 92.40 92.30
9 100-150 100 100 92.70 92.30
10 100-150 100 100 92.80 92.30
Comparison of Data and Model Values--Efficiency and Power Loss
Efficiency And Power Loss Comparison
UPS UPS System Power Loss, % Difference between
W (Btu/h) Model and Manufacturer
Data
Number Rated Man. Data Spreadsheet Efficiency Power Loss
kVA per Value [DELTA], % [DELTA], %
UPS
Unit
1 40-160 6930 (23645) 6300 (21496) 1.01 -10.1
2 225-550 12380 (42240) 11390 (38863) 1.77 -8.65
3 750 60700 (207108) 52370 (178686) 1.13 -15.9
4 500 31800 (108502) 34910 (119113) -1.08 8.91
5 400 21420 (73085) 26700 (91100) -1.84 19.8
6 225-300 14800 (50498) 15020 (51248) -0.11 1.46
7 225-300 18800 (64146) 20020 (68308) -0.43 6.09
8 100-150 6580 (22451) 6670 (22758) -0.11 1.34
9 100-150 7560 (25795) 8010 (27330) -0.43 5.62
10 100-150 9310 (31766) 10010 (34154) -0.54 6.99
* High efficiency
Adjustable Speed Drives
The heat loss from an adjustable speed drive is covered in
Piescioro vsky and White (2010).
CONCLUSION
This paper has demonstrated that the ability to accurately estimate
the rejected heat of indoor electric power distribution equipment has
improved. Given the many equipment classifications listed in Table 1, a
summary of the project findings regarding the estimation of dissipated
heat for each equipment classification was presented with the exception
of medium and low-voltage switchgear and adjustable speed drives which
were covered in great depth in companion papers. A major difference in
the conclusion of this project as compared to RP-1104 is that the
results in RP-1395 all consisted of spreadsheets whereas most of the
RP-1104 results consisted of tables and charts. The use of spreadsheets
is necessitated by the amount of accumulated data, complexity of
equipment, and our goal of making the information accessible and easy to
use.
Future work in this area involves the inclusion of new equipment
categories and documenting the successes and or difficulties in applying
this material in order to perform building heat load estimates.
ACKNOWLEDGMENTS
The authors would like to thank the American Society of Heating
Refrigeration and Air Conditioning Engineers (ASHRAE) for funding this
work especially TC 9.2 Industrial Air Conditioning and TC 9.1 Large
Building Air Conditioning Systems.
REFERENCES
ANSI Standard C37.20C-1974, "Standard for Switchgear
Assemblies Including Metal-Enclosed Bus", 1974
ANSI C37.20 d. 1978: "Switchgear Assemblies Including
Metal-Enclosed Bus.", 1978.
Conangla A., "Heat Losses in Isolated-Phase Bus
Enclosures", IEEE Transactions Power Apparatus and Systems, vol 82,
pp. 308-318, June 1963.
Del Vecchio R. M., "Eddy-Current Losses in a Conducting Plate
Due to a Collection of Bus Bars Carrying Currents of Different
Magnitudes and Phases", IEEE Transactions on Magnetics, Vol 39,no
1, pp 549-552, January 2003.
Dwight, H. B., "Effective Resistance of Isolated Nonmagnetic
Rectangular Conductors," Trans. AIEE, vol. 66, pp. 549-552, 1947.
Elgar E. C., R. H. Edler and N. Swerdlow, "Measured Losses in
Isolated-Phase Bus and Comparison with Calculated Values", IEEE
Transactions on Power Apparatus and Systems, vol pas-87,no 8, pp
1724-1730, August 1968.
Electric Power Research Institute, "Isolated Phase Bus
Maintenance Guide," TR-112784, May, 1999.
Engmann, G., "Ampacity of Cable in Covered Tray," IEEE
Transactions on Power Apparatus and Systems, Vol PAS-103, No 2, pp. 345
- 352, February 1984.
Harshe, B.L. and W. Z. Black, "Ampacity of Cables in Single
Open-Top Cable Trays," IEEE Transactions on Power Delivery, Vol. 9,
No. 4, pp. 1733 - 1740, 1994.
Hickok, Herbert N. "Energy Losses in Electrical Power
Systems." IEEE Transactions on Industry Applications, v IA-14 n 5,
Sep-Oct 1978 pp. 373-387.
IEC 62040-3-1990, "Uninterruptable Power Systems", Part
3: Method of Specifying the Performance and Test Requirements,"
International Electrotechnical Commission, 1990.
IEEE Std. C37.23-2003, "IEEE Standard for Metal-Enclosed
Bus", New York, The Institute of Electrical and Electronics
Engineers, April, 2004.
Lee, R.H., "Ampacities of Multiconductor Cables in
Trays," IEEE Transactions on Power Apparatus and Systems, Vol.
PAS-91, No. 3, pp. 1051 - 1056, May 1972.
Lin, Bor-Rin, Y. Lan Hov, and H. Keng Chiang, Implementation of a
Three-Level Rectifier for Power Factor Correction, IEEE Transact. on
Power Electronics, Vo l 15, No 5, pp. 891-900, Sept. 2000.
McDonald, William J.; Hickok, Herbe rt N. "Energy Losses in
Electrical Power Systems." IEEE Transactions on Industry
Applications, v IA-21 n 3, May/June 1985, pp. 803-819.
Nemeth, C.W., G. B. Rackliffe and J. R. Legro, "Ampacities of
Cables in Trays with Firestops," IEEE Trans. on Power Apparatus and
Sys., Vol. PAS-100, No 7,pp. 1051 - 1056, July 1981.
Piesciorovsky, Emilio C. and Warren N. White, "Building Heat
Load Contributions from Medium and Low Voltage Switchgear Part II:
Component and Overall Switch-gear Heat Gains (RP - 1395)," - ASHRAE
Transactions, vol. 115, part 2, pp. 382-394, 2009
Piesciorovsky, Emilio C. and Warren N. White, "Heat Gain from
Adjustable Speed (Variable Frequency) Drives - RP 1395," to be
presented at the 2010 ASHRAE Summer Meeting and to appear in the ASHRAE
Transactions, 2010.
Rubin, I. M., "Heat Losses from Electrical Equipment in
Generating Stations," IEEE Transactions on Power Apparatus and
Systems, vol. PAS-98, no. 4, pp. 1149-1152, July-Aug. 1979.
Shieh J.J, C. T. Pan and Z. J. Cuey, "Modelling and design of
a reversible three-phase switching mode rectifier", IEEE Proc.
Electr. Appl, Vol 144 N 6, pp. 389-396, November 1997.
Smith, P., "Tightening belts: How to make informed power plant
purchasing decisions, System Engineering," TELEPHONY Magazine, May
14, 2003.
Stolpe, J., May 1971, "Ampacities for Cables in Randomly
Filled Cable Best Electrician Service trays," IEEE Transactions on Power Apparatus and
Systems, Vol. PAS - 90, No. 3, pp. 962 - 974.
Ton, M. and B. Fortenbury, December 2010, "High Performance
Buildings: Data Centers Uninterruptible Power Supplies (UPS)",
California Energy Commission.
UL 67-1993, "Standard for Panelboards", Underwriters
Laboratories, Eleve nth Edition, December 8 1993.
UL 248-X-2000, "Low-Voltage Fuses," where X ranges from I
to 15 depending upon the fuse class, Underwriters Laboratories, Second
Edition.
UL 1066-1997, "Low-Voltage AC and DC Power Circuit Breakers
Used in Enclosures", Underwriters Laboratories, Third Edition, May
30, 1997.
White, Warren N. and Anil Pahwa, "Heat Gain from Electrical
and Control Equipment in Industrial Plants," Phase II - Part A
Report, ASHRAE RP-1104, June, 2003a.
White, Warren N. and Anil Pahwa, "Heat Gain from Electrical
and Control Equipment in Industrial Plants," Phase II - Part B
Proposed Design Guide, ASHRAE RP-1104, June, 2003b.
White, Warren N., Anil Pahwa, and Chris Cruz, "Heat Loss from
Electrical and Control Equipment in Industrial Plants: Part I - Methods
and Scope," ASHRAE Transactions, vol. 110 (2) pp. 842 - 851, 2004a.
White, Warren N., Anil Pahw a, and Chris Cruz, "Heat Loss from
Electrical and Control Equipment in Industrial Plants: Part II - Results
and Comparisons," ASHRAE Transactions, vol. 110 (2) pp. 852 - 870,
2004b.
White, Warren N. and Emilio C. Piesciorovsky, "Building Heat
Load Contributions from Medium and Low Voltage Switchgear, Part I: Solid
Rectangular Bus Bar Heat Losses (RP-1395)," ASHRAE Transactions,
vol. 115, part 2, pp. 369-382, July 1, 2009.
White, Warren N. and Emilio C. Piesciorovsky, "Heat Gain from
Electrical and Control Equipment in Industrial Plants, "Part II -
Research Project Report, ASHRAE RP-1395, March 1, 2010.
This paper is based on findings resulting from ASHRAE Research
Project RP-1395.
Warren N. White is an associate professor in the Department of
Mechanical and Nuclear Engineering, and Emilio C. Piesciorovsky is a
graduate student in the Department of Electrical and Co mputer
Engineering, Kansas State University, Manhattan, KS.
Warren N. White, PhD
Emilio C. Piesciorovsky
https://www.thefreelibrary.com/HeatgainfromElectricalandControlEquipmentinindustrial...-a0250825211
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