Section 2.0 Electrical Depth
2.0 Electrical Depth 2.1 Introduction The electrical distribution system was analyzed to determine if any improvements could be made, to analyze its capabilities, to verify code compliance, and to make any needed adjustments to accommodate the new lighting design. The safety guidelines for the power distribution design were obtained from the National Electric Code 2002, published by the National Fire Protection Association. Most of the calculation methods were obtained from the Electrical Systems in Buildings, by S. David Hughes. Specifications for the electrical equipment used in the design were obtained from manufacturers data. Appendix A-2 has a complete list of all electrical specifications referencing the equipment used. 2.2 Emergency Power Study 2.2.1 Overview/ Existing Emergency Generation System The main tenant of the building, Wegmans Food Markets decided it was crucial for this large supply of standby power to maintain operation during a time of utility power failure. With a large amount of refrigeration equipment and essential computers that are crucial to the operations of the store, the store would have to shut it doors completely without some sort of emergency power. Power failure could generate millions of losses from the store being closed, but also losses in spoiled food, and potential security issues. The first part of the electrical study focused on analyzing the emergency standby power. After some analysis, it was determined that the existing emergency power system could supply the entire building except for a large air-conditioning load (AC-1). The existing emergency system consisted of two 900kW, 480/277V generators connected in parallel which is switched on from an automatic transfer switch when utility power is lost from Dominion Virginia Power Company. The generator power is routed to a 480/277V emergency distribution switchboard with 3200 amp mounted main circuit breaker. The switchboard feeds three branches which each has an automatic transfer switch (ATS). The first branch feeds the life safety loads (lighting and elevators), the second branch feeds critical computers and other crucial receptacle loads. The third branch feeds the remaining power on the distribution system with the exception of air-conditioning load AC-1 which, is shed by the automatic transfer system. Each ATS has a bypass /isolation switch, which provides a safe and convenient means for manually bypassing and isolating the ATS for maintenance and repair. The second branch also includes an uninterruptible power supply to critical computer loads.
2.2.2 Existing Emergency Generation One-Line Figure 2.1 Existing Emergency Power One-Line
2.3 Emergency Power Redesign 2.3.1 Overview First, an engineering analysis was done to determine which loads would be truly essential for Wegmans to maintain operations for the grocery part of the building during power failure. After this, a schematic was developed and three separate branches were created to supply different loads throughout the building. After an analysis of what loads are truly essential, I developed new emergency power panels. It was determined that I would maintain three (3) emergency generations feeds, but the loads in these branches would be significantly changed in an attempt to downsize the emergency generation power, however, still providing equal reliability to crucial loads in the existing system. The first emergency power branch serves the life safety (EM. Lighting/Elevators), the second branch feeds the critical computer loads, and the third branch supply s power to the refrigeration equipment. 2.3.2 New Emergency Generation Panel Boards Although I am decreasing the size of the emergency system, it is important for the emergency system to be designed with adequate capacity and a rating to safely carry the entire connected load to the emergency system at one time. Loads on each new branch were calculated to determine the size of the new emergency generation distribution system and from that the necessary generator size was determined. The KW and KVA loads for lighting and receptacle was calculated by using the given amperes and voltage of each system. To find the KVA and KW for the mechanical equipment the horsepower ratings were used to estimate their loads to size the generators.
New Emergency Lighting Panels: Panel Voltage KVA Demand Spare KVA I j Total KVA I (Amps) PPEM1 480 164.54 32.91 29.6 14.3 197.45 237.49 PPEM2 480 86.34 17.27 15.5 7.5 103.61 124.62 LVEM1 208 5.64 1.13 1.0 0.5 6.77 18.79 Panel Panel Breaker Conductor Size Conduit Size (in) Panel Size (Amps) PPEM1 250A, 3P (4) #4/0 THHN 2 250 PPEM2 250,3P (4) #4/0 THHN 2 250 LVEM1 50A, 3P (4) #4THHN 1 90 New Emergency Lighting Transformer: xtformer Side xtformer KVA Voltage I pri (Amps) Ipri x 1.25 (Amps) TEM1 Primary 25 480 30.07 37.59 TEM1 Secondary 25 208 69.39 86.74 xtformer Side Breaker Used Wire size (Awg or kcmil) Conduit Size (in) TEM1 Primary 50A, 3P (4) #8 THHN 0.75 TEM1 Secondary 100A, 3P (4) #4 THHN 1.00
New Computer Power Panels: Panel Voltage KVA Demand Spare KVA i j Total KVA I (Amps) PPCOMP1 480 46.28 9.256 8.3 4.0 55.536 66.80 LVCOMP1 208 0.86 0.172 0.2 0.1 1.032 2.86 LVCOMP2 240 25.26 5.052 4.5 2.2 30.312 72.92 LCOMP3 208 20.16 4.032 3.6 1.8 24.192 67.15
Panel Panel Breaker Conductor Size Conduit Size (in) Panel Size (Amps) PPCOMP1 400A, 3P (4) #500 THHN 3 400 LVCOMP1 50A, 3P (4) # 3 THHN 1.25 90 LVCOMP2 100A, 3P (4) #2 THHN 1.25 125 LCOMP3 100A, 3P (4) #2 THHN 1.25 125 UPS for LCOMP2: UPS Voltage KVA I (Amps) Breaker Conductor Size Conduit Size (in) 240 40 96.23 100A, 3P (4) #2 THHN 1.25
New Computer Power Panels Transformers: xtformer Side xtformer KVA Voltage I pri (Amps) Ipri x 1.25 (Amps) COMP1 Primary 25 480 30.07 37.59 COMP1 Secondary 25 208 69.39 86.74 COMP2 Primary 30 480 36.08 45.11 COMP2 Secondary 30 208 83.27 104.09 COMP3 Primary 30 480 36.08 45.11 COMP3 Secondary 30 208 83.27 104.09 xtformer Side Breaker Used Wire size (Awg or kcmil) Conduit Size (in) COMP1 Primary 100A, 3P (4) #3 THHN 1.25 COMP1 Secondary 100A, 3P (4) #3 THHN 1.25 COMP2 Primary 100A, 3P (4) #3 THHN 1.25 COMP2 Secondary 250A, 3P (4) #4/0 THHN 2 COMP3 Primary 100A, 3P (4) #3THHN 1.25 COMP3 Secondary 250A, 3P (4) #4/0 THHN 2
New Refrigeration and Elevator Power Panels: Panel Voltage KVA Demand Spare KVA i j Total KVA I (Amps) PPREF1 480 371.24 74.248 59.4 44.5 445.488 535.84 LREF1 208 49.28 9.86 7.9 5.9 59.14 164.15 LREF1A 208 60.9 12.18 9.7 7.3 73.08 202.85 LREF2 208 61.5 12.3 9.8 7.4 73.8 204.85 Panel Panel Breaker Conductor Size Conduit Size (in) Panel Size (Amps) PPREF1 600A, 3P 2 sets of (4) #300 THHN 3 600 LREF1 250A, 3P (4) #500 THHN 3 400 LREF1A 250A, 3P (4) #500 THHN 3 400 LREF2 250A, 3P (4) #500 THHN 3 400 New Refrigeration and Elevator Power Panels Transformers: xtformer Side xtformer KVA Voltage I pri (Amps) Ipri x 1.25 (Amps) PPREF1 Primary 150 480 180.42 225.53 PPREF1 Secondary 150 208 416.36 520.45 PPREF2 Primary 112.5 480 135.32 169.15 PPREF2 Secondary 112.5 208 312.27 390.34 Side Breaker Used Wire size (Awg or kcmil) Conduit Size (in) Primary 250A, 3P (4) #250 THHN 2.25 Secondary 600A, 3P 2 sets of (4) #300THHN 3" Primary 250A, 3P (4) #4/0 THHN 2" Secondary 400, 3P (4) #500 THHN 3"
2.3.3 Generator Sizing: The loads on each of the 3 three newly created emergency branches were summed to determine the necessary generator size. The KW and KVA loads for lighting and receptacles were simply calculated from the given ampacity and the rated voltage. A power factor of 0.9 was assumed for the lighting and receptacle loads. All mechanical and refrigeration equipment was sized from their specified ampacity or horsepower to estimate their KVA and KW. All mechanical equipment was assumed to have a power factor of 0.8. To determine the generator size, I used a method described to me by my electrical consultant John Reese. Sizing the generator starts with sizing the loads for the life safety branch (emergency lighting), the loads were totaled for RKVA and starting KVA. After this, the emergency Computer panels start up, and then the starting load is added to the running load of the life safety branch. Then, the mechanical and refrigeration equipment is started last on the emergency distribution system and added the running RKVA of the previous two branches. After power factors were applied and safety factors were added to the capacity, a total demand KVA was compiled and that total KVA was converted to KW. Assumptions: 0.9 PF for Life Safety (Emergency Branches) 0.9 PF for Computer Branch 0.8 PF for Mechanical Equipment 600% of motor full-load Generator Sizing Emergency Branch Loads SKVA RKVA SKW RKW Total KVA Total KW Life Safety (Emergency Lighting) 124.2 124.2 111.78 111.78 124.2 103.5 Computer Branch 62.5 62.5 56.25 56.25 186.7 149.36 Mechanical/Refrigeration Branch 742.5 123.75 99 186.7 929.2 279.45
Total KVA Total KW Critical Condition 929.20 279.45 25% Growth 232.30 69.86 Design 1162 349 2.3.4 Emergency Power Redesign Conclusion: The redesign of the emergency distribution system accomplished its goals of creating a more simplified, less expensive system. This study started because of Wegmans desire to create a new standard for their emergency distribution system. My study first evaluated what loads were crucial and what loads are not crucial to maintaining operations as close to normal as possible in their main grocery space. From this a detailed list of essential and optional desired power loads for the sized down emergency generation system was found. The vast majority of loads were emergency lighting, computer, and refrigeration loads. The final solution was a single 500kw generator. The redesigned emergency system cannot nearly back-up the entire building like the existing system but a value engineering analysis shows that the decrease in initials cost and maintenance could provide more bang for its buck. Selecting a scaled back approach and basically only keeping critical loads and loads which only allows the grocery portion of the building to operate as normal, the new sized down emergency system provides an alternative to the expensive existing system. The owner would have to make a decision based on whether spending this much additional costs would return profits through being able to keep the entire building open during a power failure. Price Breakdown: Existing System (Twin 900KW w/interlocking system): $486,000 New System (Single 500KW): $105,000
2.4 Fault Current Analysis: Fault current analysis allows us to predict the maximum available current at various points in the electrical system. A fault current analysis was done with the assistance of the Electrical Designer s Reference Program. AIC ratings were given for each panel picked on the critical path which was chosen to travel from the MDP all the way to the end of the paths at LCOMP1, LCOMP2, and LCOMP3. These critical paths were chosen due to the distance of the Panels from the MDP and distance the ampacity has to travel. It is mandatory that all equipment be properly rated for interrupting or withstanding the maximum available fault current at each point in the distribution system. To insure that all applicable electrical equipment is adequately rated to withstand or interrupt the available fault current, the magnitude of the maximum possible fault current must be determined for each point in the electrical distribution system Panel Isc AIC Rating MDP 60,143 65,000 PPCOMP1 47,648 54,000 LLCOMP1 17,900 20,000 LLCOMP2 8,051 10,000 LLCOMP3 6,264 10,000