Thomas R. Proctor High School

Transcription

1 System Overview Thomas R. Proctor High School has been upgraded from an existing radial electrical system to an expanded radial system. The new system incorporates two separate substations, one located in the main electrical room of sector D in the existing building and one located in the main electrical room of sector K in a new wing of the addition (refer to figure 1). Both main electrical rooms are located in the basement of their respective sectors. The incoming electrical service into Thomas R. Proctor High School is provided by Nimo Power Company. Before reaching the school, the 13.2 kv Figure 1 Locations of the two underground service enters new metal enclosed outdoor main substations in Proctor H.S. switchgear, containing a 600A fused disconnect switch. The utility metering equipment is located on the primary side of this switchgear (explanation of primary vs. secondary metering is described in the Utility Rate Structure section of the report). The service is stepped down in each main substation from 13.2 kv to 480Y/277V via a -Y transformer. Each transformer is protected on the primary side by a 600A fused disconnect switch. All the loads in the school that operate at 208Y/120V are stepped down by 480Y/ Y/120 V transformers (explained further in the Transformer Configuration section). Figure 2 Proctor H.S. Expanded Radial Distribution 1

2 Substation 1: The main switchboard in sector D of the existing building is a 4000A, 480Y/277V, 3Ø-4W switchboard with and AIC rating of 65,000A. It generally contains loads in the existing building, as well as most of the larger new and existing HVAC equipment (chillers, boilers, etc.) throughout the entire building. Although the existing 1938 building electrical system needed replacement, some of the 1990 renovated spaces were able to remain. The main distribution panels that did not need replacement in the existing building have been back-fed by this switchboard. Due to the quantity and size of the loads on this switchboard, it is sized larger than the main switchboard located in the new addition. Substation 2: The main substation in sector K of the new addition consists of a 3000A, 480Y/277V, 3Ø-4W switchboard with an AIC rating of 65,000A. This switchboard supplies power to sectors H, J, and K, as well as some renovated areas in the existing building. The loads include general power, lighting, elevators, electric heaters, VAV boxes, unit vents, fan coils, air handling units, fire pump, exhaust fans and relief fans. This substation also contains the school s emergency generator that supplies emergency power to all of the life safety loads in the school (explained further in the Emergency Power/Lighting section). Since the loads on this switchboard (especially the mechanical equipment) are smaller than the substation 1, it is sized accordingly. My electrical system analysis will focus on this substation, however, since the entire electrical system for the new addition gets power from it. Transformer Configuration Unlike many smaller schools, Proctor High School does not have an exterior transformer. Instead, the underground service is transformed in each of the two main switchgear rooms. Both of these transformers are 13.2 kv 480Y/277V. The transformer for substation 1 is 2000 kva while the transformer for substation 2 is 1500 kva. Aside from the two main transformers, there are (21) Δ-Y 480Y/277V transformers of all sizes ranging from 15 kva kva for receptacles and smaller loads. Eleven of the transformers are fed from substation 1 and 10 are 2

3 fed from substation 2 (see one-line diagram in appendix for exact locations of transformers). These transformers are ventilated, low-sound-level units with one leg and coil per phase (in primary and secondary). The K-13 design rating of the transformers prevents overheating when carrying full load with harmonic content. Emergency Power System The large size of the school demands back-up power in case of emergency. Such back-up is provided via a 500 kw/625 kva diesel fuel emergency generator that is fed from the main switchboard. The generator has the following features: 1. Air-intake silencer 2. Battery charger 3. Sub-base mounted fuel tank with double-wall protection 4. Engine generator set 5. Muffler 6. Exhaust piping external to set 7. Remote annunciator 8. Remote stop switch 9. Starting battery 10. Load bank (furnished for initial testing only) 11. Load-bank remote-control panel 12. Fuel tank leak detection system 13. Vibration isolation The generator is designed to supply AC power backup (with an approximate 10 second delay) to different loads throughout the building. The generator supplies back-up power to life safety loads (emergency lighting and fire alarm systems) and select non-life safety loads. Specifically, the emergency generator panel feeds three separate distribution panels and a 100 hp fire pump. One distribution panel controls all of the emergency lighting for the school and certain small power loads. Another distribution panel contains two elevator controllers which each have a 200A switch. The last panel controls select HVAC loads such as boilers, sensible coolers for the main telephone/data room and main electrical room, as well as unit heaters and a storm water ejector pump for the generator room. The fire alarm system in the building also has DC (battery) backup that provides at least 90 minutes of power if AC power fails. The 3

4 telephone system, although not a life safety load, has a similar backup system. The three main emergency panels are linked from normal power (main switchboard 2) to emergency backup power through the use of an automatic transfer switch (ATS) for each emergency panel. It is important to note that shunt trip is provided to be used during generator load shedding to disconnect all but the life safety loads (refer to the appendix for a generator system diagram). Automatic Transfer Switches: The ATS switches used in the building are contained in NEMA 250, Type 1 general-purpose enclosures. The switching arrangement is double-throw so that the switch is incapable of pauses or intermediate position stops during normal function. The switch has an adjustable voltage relay that is pre-set to 90% of the nominal voltage to avoid premature transfer to emergency power. The time delay for re-transfer to normal power is adjustable from 0-30 minutes and is pre-set to 10 minutes. The unit contains a test switch that simulates normal-source power failure. A transfer override switch is provided to supersede automatic retransfer to normal power. This forces the ATS to remain on emergency power regardless of the state of normal power if is so desired. Switchgear and Overcurrent Devices Switchgear: As described in the system overview, the incoming electrical service enters an exterior with a 600A fused disconnect switch. The switchgear maintains its 20 distance from the utility pole, as per the NEC regulations. The switchgear load interrupter switch has the following characteristics: System Voltage: 13.2kV, 3Ø-4W Maximum Design Voltage: 15 kv Amperes Continuous: 600A Fault Close: 61 ka 4

5 Main Substation Room 1 Exterior Switchgear Main Substation Room 2 Figure 4 Site plan of exterior switchgear, manholes, and substation rooms Scale: NTS Enclosed Switches and Circuit Breakers: Enclosed Switches: All enclosed non-fusible switches are NEMA KS 1, type HD, with lockable handle. All enclosed fusible switches are NEMA KS 1, type HD, with clips to accommodate the specified fuse. The switch has a lockable handle with two padlocks and is interlocked with the enclosure cover when it is in the closed position. The fuse associated with each fused switch is a NEMA FU 1, nonrenewable cartridge fuse. Enclosed Circuit Breakers: The circuit breakers are molded-case NEMA AB 1, with interrupting capacity to meet the available fault currents. The following four types of circuit breakers are found in the building Molded-Case Circuit Breaker: contains an inverse time-current element for low-level overloads and an instantaneous magnetic trip element for short circuits 5

6 Adjustable Instantaneous-Trip Circuit Breaker: contains a magnetic trip element with front-mounted, field-adjustable setting. GFCI Circuit Breaker: Single and two-pole configurations with 5- ma trip sensitivity. Molded-Case Switch: Molded-case circuit breaker without trip units. Wiring and Bus Types While the existing building electrical system that has been back-fed by switchboard 1 uses 1200A bus duct as its means of conductors, the new electrical system uses copper conductors. Medium-Voltage Cable: The main service into the building is type MV90, compact class B copper. The conductor interstices are filled with impermeable compound. The rubber insulation complies with AEIC CS 6. The rated voltage is 15 kv. The shielding is copper tape applied over semi-conducting insulation shield. The outside jacket is sunlight-resistant PVC. Conductors: No. 10 AWG and smaller is solid copper conductor that complies with NEMA WC 5. No. 8 AWG and larger is stranded copper conductor that complies with NEMA WC 5. Cables: The following describes the type of cable used in its specific location or application: Service Entrance: Type THWN in raceway. Feeders: Type THHN/THWN in raceway. Branch Circuits: Type THHN/THWN in raceway. Fire Alarm Circuits: Power-limited, fire-protective signaling circuit cable or THHN/THWN in raceway. 6

7 Class 1 Control Circuits: Type THHN/THWN in raceway. Class 2 Control Circuits: Power-limited cable, concealed in building finishes or type THHN/THN in raceway Motor Power Distribution The vast majority of motor loads are in conjunction with mechanical equipment. Most of these loads are distributed via HVAC panelboards. Larger HVAC loads (such as chillers) are fed directly from the main switchboard and protected by individual 800A, 3-pole circuit breakers. The remaining motors are dispersed among regular power panels. No motor control centers are present in the school. Power Factor Correction As is typical with a school building, no capacitors or other components were necessary for power factor correction at Proctor High School. Since buildings of this nature typically have a high power factor (>.95), power factor correction is not an issue. A large portion of the total load in the school is resistive or high power factor lighting loads. Even the motor load, although a very substantial amount of the total load, consists of high efficiency and high power factor energy saving motors. The motor loads, in conjunction with the resistive and lighting loads, rarely results in an overall power factor that drops below.95. UPS Systems The electrical engineering contractor did not need to provide any kind of UPS system anywhere in the building. However, the school district did buy their own mini-ups systems to back-up the school s data servers. These are likely 3-12 KW output UPS units that sit on the floor and provide uninterrupted backup to the network servers. These loads are not backed by the emergency generator, so they rely strictly on their own charged batteries to provide constant power in case of power failure. 7

8 Typical Lighting System The entire lighting system in Proctor H.S. operates at 277V. The majority of the lighting is fluorescent, with compact fluorescent lighting and HID lighting in certain areas. Some lighting in the classrooms, labs, office spaces, corridors, and toilets are controlled using a programmable lighting panel. This lighting control system includes a network control unit, lighting control unit, and lighting control relay panel (with mounted relays). Since manufacturer names are not specified for lamps and ballasts, Philips Lighting lamps and advanced transformer ballasts are used for the purpose of this report. Lamp Schedule: Lamp Wattage Ballast Fluorescent CFTR26W/GX24q/ REZ-1T32 ICF-2S26-H1-LD@120 Ballast Factor Input Watts Operating Voltage Current Power Factor F54T5/835/HO/ALTO 54 ICN4S5490C2LS@ CFT7W/G23/825 7 H-1B-TP-BLS F4OT8/TL835/ALTO 40 ROP-3P32-SC F24T5/835/HO 24 ICN-2S24@277V PL-T 18W/835/4P/ALTO PL-C 13W/835/4P/ALTO 13 RCF-2S13-M1-LS-QS Metal Halide CDM70/TD/ A52M >.9 CDM100/PAR38/SP/3K A53M >.9 MHC100/C/U/MP/3K/ALTO A53M MH175/3K/BU B55N MH250/C/U A57M MS400/3K/BU A60M

9 Fluorescent Lamps: Fluorescent Lamps are specified to be 3500K. The lamps are specified to have a CRI of >85. The rated average life is 20,000 hours at 3 hours per start on a rapid-start circuit. Fluorescent Ballasts: All ballasts are designed for a total harmonic distortion (THD) of <10% and an A sound rating. Electronic ballasts for linear lamps: are energy saving and without potting compound voids. Recessed compact fluorescent ballasts: are electronic, fully encapsulated with a minimum power factor of 90%. The lamps have an operating frequency of <5% and a lamp current crest factor of <1.7. Non-recessed compact fluorescent ballasts: have a power factor of >90% and a coil temperature of 65 degrees C. HID Lamps: All of the metal-halide lamps are specified to have a color temperature of 3600K and a CRI of 70. All of the lamps are a self-extinguishing type. HID Ballasts: All ballasts are to match the system voltage. The minimum starting temperature is -22 degrees F and normal ambient operating temperature is 104 degrees F. The ballasts have open-circuit operation that will not reduce lamp life. The ballasts provide an auxiliary, instant-on, quartz system. This automatically switches quartz lamps on when the fixture is initially energized and when momentary power outages occur. The ballasts also provide an auxiliary emergency transfer system. Lighting Control Devices: The following devices are integrated into the lighting design of the school: Time Switches: Solid-state programmable time switch units with alphanumeric display, complying with UL

10 Photoelectric Relays: consists of a single-pole, double-throw dry contacts. The time delay prevents false operation. Multi-pole Contactors and Relays: These contactors are electrically operated and mechanically held, complying with UL 508. Mechanical Equipment Characteristics Refer to the appendix for mechanical equipment schedules. NEC building Design Load The building design load was calculated for the new addition to Proctor H.S. (substation 1) and compared to the original design load and switchboard size. This was determined by separating the loads in the building into three categories: receptacle/small power, lighting, and motor loads. An estimated power of 180 VA was used for each receptacle in which the actual power was not known. For any dedicated receptacle, or receptacle that is to have a specific appliance associated with it at all times, the known power of the load was used for calculations. The known power of all other small power loads (electric resistive cabinet heaters, etc.) was used for calculations. The lighting system was calculated in two different ways. First, an actual existing lighting load calculation was performed to try to get an accurate impression of the lighting load. The lighting load was also estimated using Table 220.3(A) for general lighting loads by occupancy in the NEC Handbook for. The greater of these two values was used for the final calculation of the demand load for switchboard sizing. The motor loads on switchboard 2 are small in comparison to the overall motor load. The motors on the switchboard consist of elevator control motors, air handling units, VAV boxes, unit vents, fan coils, exhaust fans, relief fans, fire shutters, and the school s fire pump. The loads were calculated by multiplying the largest motor by 0.25 and adding it to the sum of all of the motor loads. To determine the total connected load, power factor assumptions were made for each type of load: Small power:.85 PF Lighting:.95 PF Motors:.85 PF 10

11 Spare Capacity (25%):.85 PF These values were used in order to remain very conservative in the calculations. School buildings would rarely ever have a power factor as low as.85 and lighting power factors are typically >.95. The loads were then separated by utilization voltage and then added together to calculate the total connected load. Total demand load was then calculated by using the proper demand factors for the loads: Receptacles: Lighting: 1.25 Motors: 1 Spare Capacity: 1 1 (for the first 10 kva).5 (remaining kva) Connected and Demand Load Power Calculations: Small Power: Total Connected Load: Total Demand Load: Lighting: Actual Load Total Connected Load: Total Demand Load: PF = j369.7 kva = 702 kva j5.27 kva (1 st 10 kva) + ( kva) (x 0.5) j = 245 kva PF = j53.66 kva ( j53.66) x (1.25) = kva NEC occupancy load Square feet x NEC VA/sq.ft: 124,588 x 3 = 373,764 VA 21,986 x 0.5 = 10, VA 1,240 x 1 = 1,240 VA Total = kva Total Connected Load = PF = j120.5 kva Total Demand Load = ( j120.5) x (1.25) = j kva 11

12 Motors: Total Connected Load: Total Demand Load: Spare (25%): Total Connected Load: Total Demand Load: Fire pump (largest motor): PF x j9.82 kva Motors: PF = j kva j9.82 kva j kva ( ) x (1) = kva PF = j kva j x (1) = j kva The total connected and demand loads were calculated by adding together the loads, making sure to keep the loads on different operating voltages separate, and then adding the combined 480Y/277V load to the combined 208Y/120 load. Then the total current was derived by dividing the demand load power by (1.732 x voltage) since the entire system is three-phase. Once again, it is important to make sure that the loads on different voltages are seaparted and then the currents are added at the end. Results: Total Connected Load (Actual) Total Connected Load (NEC) Total Demand Load (Actual) Total Demand Load (NEC) Total Demand Current (NEC) Total Demand Current (NEC) kva kva kva kva A A Switchboard Power Capacity: P=VIcos(σ) P = (480) (3000)(1) = kva In both the actual and NEC cases, the demand load is well under the switchboard capacity, even with 25% spare capacity. Switchboard Current Capacity: In both the actual and NEC cases, the demand current is well under the switchboard capacity, even with 25% spare capacity. 12

13 Utility Rate Structure Before the electrical service was installed, a rate analysis of primary vs. secondary metering on the exterior switchgear was conducted to determine which system would be the cheapest. Estimated Maximum Demand for Entire Building = 3300 kw 80% Diversity Average Demand = 2640 kw = 2640 kw (summer) = 1980 kw (winter) Primary Usage: Summer Total = 918,000 kwh Winter Total = 688,400 kwh Summer Charges Demand $33,501/ month for 3 months = $100,503 kwh charge $25,633.80/month for 3months = $75,795 Winter Charges Demand $25,633.80/month for 9 months = $230,704 kwh charge $18,947.20/month for 9 months = $170,525 Supply benefit charge (12 months) = $5,240 Service charge (12 months) = $5,240 Supply charge (12 months) = $251,929 Grand Total = $840,176 Secondary Usage: Summer Total= 918,000 kwh Winter Total = 688,400 kwh Summer Charges Demand $39,520/month for 3 months = $118,562 kwh charge $25,326/month for 3 months = $74,978 Winter Charges Demand $30,239/month for 9 months = $272,155 kwh charge $18,933/month for 9 months = $170,939 13

14 Supply Benefit (12 months) = $5,480 Supply Charge (12 months) = $3,122 Supply Charge (12 months) = $261,929 Grand Total = $908,165 Summary Secondary Service Annual Cost = $908,165 Primary Service Annual Cost = $840,176 Savings for Primary Service = $67,989 (Annual) As a result of the cost analysis, the school decided upon primary service metering because of the annual savings. It was determined that the initial cost would be paid back in approximately 4 years. 14

15 APPENDIX 15