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UMKCAC Station Service SizingRevision 1prepared for Burns & McDonnell March 20, 2014prepared byUMKC Senior Design (Substation) GroupContents TOC \o "1-3" \h \z \u 1.0Introduction PAGEREF _Toc383175404 \h 1-12.0System Design PAGEREF _Toc383175405 \h 2-13.0AC Loads During Construction PAGEREF _Toc383175406 \h 3-34.0Conclusion PAGEREF _Toc383175407 \h 55.0References PAGEREF _Toc383175408 \h 6IntroductionStation service transformers are required to provide power to all substation auxiliary alternating current (AC) loads. Calculating the power rating of an AC service transformer requires load power consumption data, but the size is not determined strictly by adding all available loads consequently yielding overly conservative results. To properly size the transformer, some electric loads are multiplied by a diversity factor, which scales the load to a value dependent on usage probability. For example, the chances that all receptacles will be used at any one instant at rated power will likely not happen; therefore, the receptacle loads would be multiplied by a very small diversity factor. Another factor to take into account is the climate. In winter, there will primarily be heating loads, and conversely, the summer would primarily be HVAC or transformer fan loads. The objective of this study is to calculate the required station service transformer size to supply the UMKC substation under an assumed worst case scenario.System DesignEnergized Substation AC LoadsThe following table displays the apparent power rating of auxiliary equipment in the substation. In the last three columns, the total, winter, and summer VA show the predicted loads, and the each column is individually summed. The total VA sum portrays a loading scenario for the substation where every load is used simultaneously at rated power; this scenario is assumed to be infeasible considering the diversity factors for both the winter and summer scenarios are neglected. The winter and summer VA totals account for ambient temperatures by reducing temperature dependent loads from the total in order to more accurately mimic power consumption seen in a given season, and additionally, various diversity factors have been integrated independent of temperature accounting for the probabilistic nature of some loads including receptacles.Table STYLEREF 1 \s 2 SEQ Table \* ARABIC \s 1 1Energized Substation AC LoadsLoad DescriptionQTYVolts Req'dVA RatingDiversity Factor (DF)Total VAWinter VA [7]Summer VA [8]WinterSummer69kV Cubicle Strip Heaters (TWO per cubicle) [1]225025010.5500500250138kV Cubicle Strip Heaters (four per cubicle) [1]625025010.51500150075069kV Breakers tank heaters[1]2250150010.0430003000120138kV Breakers tank heaters [1]6250150010.0490009000360138/69 kV Transformer [2]1120/240145000.50.51450072507250Interior Building Lights (33-64W lights) [3]81206411512512512125VDC Battery Charger [4]2240960011192001920019200120V Building Receptacles [5]112015120.080.081512120.96120.96Roof Vent Fans [6]2240426401852808528Substation Up Lights (15-400W lights) [7]1512040010600060000Substation Flood-Lights (6-400W lights) [7]612040010240024000138kV MOAB Heaters412011510.5460460230HVAC 12401500010.67150001500010050Control Room Exhaust Fan112072011720720720Communication Equipment 112072011720720720[#] = Assumptions/Notes?TOTAL LOAD (kVA) =83.55266.3829648.81096Notes and assumptions used for Table 2-1 are as follows:[1] 138kV Breaker load calculated from Siemens manufacturer drawing 72-480-955-422. Two 250W, 250VAC rated cabinet heaters and two 1500W, 240VAC rated tank heaters(assumed). [2] Transformer max load assumed to be 10.5kW based on TR drawings. The transformers have a self cooled rating for 45MVA so the transoformer fans will not be turned on unless two of the four paralleled transformers are out of service. Because of this we have included a 0.5 diversity factor for the transformer AC loading. [3] Interior control building lighting consists of two 32W bulbs at each fixture.[4] Battery charger VA rating calculated per current rating. 40A*240VAC = 9600 VA [5] Five out of the 12 indoor receptacles are assumed to be used at 20% of rating (4A each) which is 8.3% of the total rated load of all indoor receptacles.[6] Loading and diversity factor provided by MCP: 17.68A*240V = 4264VA.[7] Outdoor lighting assumed to be on during winter scenario (assumed to be at night) and off during the summer scenario (assumed to be during the day).Notes: Winter scenario assumes night time for coldest part of day, all photocell controlled lights on, all heaters running full load and two transformer fans running full load.Summer scenario assumes day time for hottest part of day, low temp. thermostatically controlled heaters off and two transformer fans running full load.AC Loads During ConstructionThe energized substation AC loads will be served from permanent station power transformers connected to the 138kV bus in the substation. That source will not be available until engerization of the 138kV bus, however some of the substation loads will require AC service prior to energizeing the bus. The following table displays the apparent power rating of auxiliary equipment in the substation that are presumed to be utilized prior to energization of the substation. The loading analysis for this scenario utilizes similar diversity factors and seasonal loading as the energized substation loads.Table STYLEREF 1 \s 22AC Loads During ConstructionLoad DescriptionQTYVolts Req'dVA RatingDiversity Factor (DF)Total VAWinter VA [7]Summer VA [8]WinterSummer69kV Cubicle Strip Heaters (TWO per cubicle) [12]225025010.33500500165138kV Cubicle Strip Heaters (four per cubicle) [12]625025010.331500150049569kV Breakers tank heaters[9]2250150010.3330003000990138kV Breakers tank heaters [9]6250150010.33900090002970138/69 kV Transformer [1]1120/2401450011145001450014500Interior Building Lights (33-64W lights) [3]81206411512512512125VDC Battery Charger [4]2240960011192001920019200120V Building Receptacles [6]112015120.080.081512120.96120.96Roof Vent Fans [13]2240426401852808528Substation Up Lights (15-400W lights) [14]1512040010600060000Substation Flood-Lights (6-400W lights) [14]612040010240024000138kV MOAB Heaters412011510.5460460230HVAC [4]12401500010.67150001500010050Control Room Exhaust Fan112072011720720720Communication Equipment [5]112072011720720720[#] = Assumptions/Notes?TOTAL LOAD (kVA) =83.55273.6329659.20096Notes and assumptions used for Table 2-1 are as follows:[1] 138kV Breaker load calculated from Siemens manufacturer drawing 72-480-955-422. Two 250W, 250VAC rated cabinet heaters and two 1500W, 240VAC rated tank heaters(assumed). [2] Transformer max load assumed to be 10.5kW based on TR drawings. The transformers have a self cooled rating for 45MVA so the transoformer fans will not be turned on unless two of the four paralleled transformers are out of service. Because of this we have included a 0.5 diversity factor for the transformer AC loading. [3] Interior control building lighting consists of two 32W bulbs at each fixture.[4] Battery charger VA rating calculated per current rating. 40A*240VAC = 9600 VA [5] Five out of the 12 indoor receptacles are assumed to be used at 20% of rating (4A each) which is 8.3% of the total rated load of all indoor receptacles.[6] Loading and diversity factor provided by MCP: 17.68A*240V = 4264VA.[7] Outdoor lighting assumed to be on during winter scenario (assumed to be at night) and off during the summer scenario (assumed to be during the day).Notes: Winter scenario assumes night time for coldest part of day, all photocell controlled lights on, all heaters running full load and two transformer fans running full load.Summer scenario assumes day time for hottest part of day, low temp. thermostatically controlled heaters off and two transformer fans running full load.ConclusionIn Table 2-1, the winter scenario presents the worst case for the energized substation AC load of 73.63kVA. The standard size distribution transformer that meets this loading is rated at 75kVA, which should adequately serve for station service. While the calculated worst case loading of the substation is 98.17% of the station power transformer nameplate rating this does not necessarily mean that any additional AC loading will detrimentally overload the the station power transformer. IEEE C57.12.23-2009 states the kVA rating is developed by measuring the oil temperature near the top of the transformer tank, and the temperature should not pass 55° C for the specified nameplate rating in order to preserve the life of the transformer. In IEEE C57.910-2011, an approximation table illustrates the relationship of dropping ambient temperatures (°C) to increasing kVA (%) as a 1:1 ratio with an assumed average of 30° C as the base point. Even though IEEE state that the relationship is conservative, it is advised to add an additional 5° C margin. Also note that under the worst case scenario loading of 98.17% will take place when the ambient temperature is approximately -7° C or lower considering that is when the 138kV breaker tank heaters are set to turn on which make up 32.4% of the total winter load. When the ambient temperature is -7° C, the rating of the transformer could potentially be increased by 32% [30°C (assumed ambient) – (-7)°C (worst case scenario temperature) – 5°C (IEEE recommended margin)] without compromising the transformer life expectancy. This would provide additional capacity for future loading without comprising the life of the transformers. It should also be noted that industry practice and BMcD operational practices allow for temporary overloading of transformers above the nameplate rating. The construction AC loading anaylsis was performed to provide BMcD with information required to properly size the temporary construction AC service. As outlined In Table 2-2, the winter scenario presents the worst case AC loading for the substation during construction. Per the anaylsis the worst case construction load for substation equipment is 73.63kVA, this load would be adequately fed by a 400A, 120/240V single phase service. This loading is for substation equipment only and does not include any additional construction loads (trailers, equipment, tools etc.). Anticipated additional constuction loads should be served from a separate source or added to the substation equipment loading to determine the total AC service size required for construction. The construction AC service sizing should take into account BMcD transformer loading operational practices and consider that the peak loading is expected during periods of cool ambient temperatures. References[1] IEEE Std C57.12.23-2009, IEEE Standard for Submersible Single-Phase Transformers: 167 kVA and Smaller; High Voltage 25000V and Below; Low Voltage 600V and Below[2] IEEE Std C57.81-2011, IEEE Guide for Loading Mineral-Oil-Immersed Transformers and Step-Voltage Regulators[3] Siemens Type SPS2, 145kV, 3000A, drawing number 72481045425_4, Issue A. [4] Siemens Transformer 138/36kV, 45/60 MVA, drawing number D-10069[5] Southern States Type VM-1 Operator drawing D-139309 Rev. 2[6] Controllix Corporation 36kV Metal Enclosed Capacitor Equipment, drawing 121-041-3[7] Hindle Power AT Series Battery Chargers drawing DC5016-00 Rev 4B[8] Myers Controlled Power, LLC Switchgear drawings 285421 series[9] BMcD Engineering Standards, Section 1, AC Systems. ................
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