POW ER EN GIN EER S, LLC Electrical Engineering, Power, Lighting, Technical Studies and Utility Consulting

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1 POW ER EN GIN EER S, LLC Electrical Engineering, Power, Lighting, Technical Studies and Utility Consulting 37 Fox Den Road Kingston, MA (508) Phone (781) Fax STERLING MUNICIPAL LIGHT DEPARTMENT 50 MAIN STREET STERLING, MA WILES ROAD 2 X 1MW (2MW TOTAL) PV IMPACT STUDY FOR DISTRIBUTION INTERCONNECTION MARCH 2012

2 POW ER EN GIN EERS, LLC Electrical Engineering, Power, Lighting, Technical Studies and Utility Consulting 37 Fox Den Road Kingston, MA (508) Phone (781) Fax Mr. Sean Hamilton March 23, 2012 Sterling Municipal Light Department 50 Main Street Sterling, MA Subject: Sterling Municipal Light Department Wiles Road 2 x 1MW (2MW Total) PV Project Feasibility Study for Distribution Interconnection Dear Sean: Power Engineers, LLC has completed a detailed feasibility impact study for the distribution interconnection of the proposed PV project off of Wiles Road. The attached report contains a review of the preferred route that has been established for a 13.8kV interconnection of the 2 x 1MW PV systems (2MW Total) PV project to connect the existing 13.8kV circuit owned by SMLD. The results of the study are favorable for the interconnection of the proposed PV project to the existing 13.8kV 1501 Circuit, which would be extended from Chocksett Road to Wiles Road to serve this project. If you have any questions, or require additional information, please feel free to give me a call. Sincerely, David J. Colombo, P.E. Principal

3 Sterling Municipal Light Department Wiles Road PV Project Feasibility Study for Distribution Interconnection March 2012 TABLE OF CONTENTS SECTION DESCRIPTION 1 Executive Summary 2 Existing Infrastructure 3 Proposed Installation 4 Computer Analysis 5 Conclusions / Recommendations Attachments 1. Community Energy Solar, LLC Proposed Layout Plan 2. SMLD System One-Line Diagram 3. SMLD Drawings of Proposed Line Extension to Wiles Road 4. SMLD System Load and Feeder Data ( ) 5. Computer Model one-line diagram 6. Computer model input data 7. Time Current Curves (overcurrent protection)

4 EXECUTIVE SUMMARY A detail Feasibility Study for Distribution Interconnection of the Wiles Road 2.0MW (AC) PV project (hereafter referred to as the Study) was conducted for the Sterling Municipal Light Department (SMLD). The purpose of the Study was to review the technical issues related to thermal capacity, voltage performance, short circuit and protection for the SMLD 13.8kV distribution circuit to absorb the power output of the PV System, to be installed on Wiles Road in Sterling, MA. The proposed project is to interconnect two (2) new 1.0MW PV Systems to the Wiles Road location to the existing 13.8kV circuit, for a total interconnection of 2.0MW. The existing distribution system on Wiles Road is supplied from the SMLD 1502 Circuit, out of Chocksett Substation. The proposed project is to be connected to the SMLD 1501 Circuit, which is more heavily loaded on a normal basis. The proposed project would require the extension of the 1501 Circuit from Pole #67 Chocksett Road to the proposed point of interconnection on Pole #7 Wiles Road, about 20 pole sections. The existing SMLD 1501 Circuit runs from the Chocksett Substation to Pratts Road to Heywood Road to Meetinghouse Road. The project would include the extension to Pole #7 Wiles Road as detailed above. The results of the Study contained herein indicates that the proposed interconnection is acceptable. Thermal loading of existing SMLD overhead primary 13.8kV wire on the 1501 Circuit is acceptable with the 2.0MW proposed PV System in operation and the SMLD system under peak load conditions (with and without the Perkins 1MW PV system on-line). The SMLD 1501 Circuit is comprised of 477kcmil and #1/0Awg aluminum conductors. Existing equipment loading, including the upstream substation transformer is also acceptable give present ratings. During light load conditions with the PV System in operation, the voltages on the system are within industry limits and voltage drops through the wire sections are acceptable. Short circuit and power factor contributions are also considered acceptable and should not cause any significant deviations to the SMLD system. The Wiles Road PV project should provide sufficient power factor control at the PV System site or on the 13.8kV circuit to maintain the power factor at the Point of Common Coupling (PCC) to pre-project conditions. A voltage flicker analysis was also performed and determined that the limits are below the industries accepted standard IEEE It is recommended to proceed with the proposed project and commence with detailed design and construction of the new 13.8kV line construction along Wiles Road to the primary of the project site equipment. In addition, it is recommended to work with the PV System vendor to review their on-site design and the inclusion of the proposed protective requirements to protect the SMLD system from islanding. These protective requirements SMLD Feasibility Study for PV System Interconnection March 2012 Page 1

5 could be either installed on the customer-owned equipment or on the SMLD system at the point of interconnection. SMLD Feasibility Study for PV System Interconnection March 2012 Page 2

6 EXISTING INFRASTRUCTURE The existing SMLD system is presently served from the Chocksett Substation. This substation is an 115kV-13.8kV step-down substation. The Substation is supplied by two (2) National Grid 115kV circuits, designated the O-141 and P-142. These transmissions lines tap and feed into two step-down substation transformer, each rated 12/16/20/22.4MVA. The secondary of the transformers each feed into a 2000A, 13.8kV substation bus. Each bus connects in a normally open bus-tie configuration to two feeders. Transformer No. 1 feeds the 1503 and 1504 Circuits, and Transformer No. 2 feeds the 1501 and 1502 Circuits. The available short circuit values on the two 115kV transmission lines from National Grid that serves the SMLD Chocksett Street Substation. The values are listed below. Short Circuit values National Grid Transmission Line P142: 1LG: A= 5.990kA X/R ratio= LG: A= kA X/R ratio= Line O141: 1LG: A= 6.007kA X/R ratio= LG: A= kA X/R ratio= The SMLD system has a system peak just over 13MW (13,284kW) recorded this past July 2011, before peak shaving generation is considered. The monthly system peak for 2011 is as follows (not considering peak shaving): Figure 1 SMLD Peak System Load Month Peak Demand kw January ,850 kw February ,558 kw March ,072 kw April ,067 kw May ,044 kw June ,886 kw July ,284 kw August ,696 kw September ,331 kw October ,618 kw November ,942 kw December ,141 kw SMLD Feasibility Study for PV System Interconnection March 2012 Page 3

7 During the recent summer peak (July 2011), the typical distribution of load amongst the four 13.8kV feeders was as follows: 1501 Circuit 36.2% 1502 Circuit 14.4% 1503 Circuit 18.0% 1504 Circuit 31.3% These values listed above will be the basis for the peak load system model. Data from has been provided by SMLD and reviewed as part of this project. The 1501 Circuit feeds from the Substation along Chocksett Road to Pratts Junction Road to North Row, to Heywood Road, to Rowley Hill Road to Meetinghouse Hill Road. This feeder mainline is approximately 35,000 feet from the Substation to the open point on Pole #29 Meetinghouse Hill Road. The portion of the 1501 Circuit that connects to the proposed Wiles Road PV site is about 3,600 feet from the Substation to the intersection of Pratts Junction Road and Clinton Road, another 820 feet on Clinton Road and 700 feet on Wiles Road to the site. A total of 20 ne pole sections of wire will be needed to extend the 1501 Circuit from Pratts Junction Road to the Wiles Road site. The figure below (Figure 2) shows the new work for the line extension. To PV Site From Substation Figure 2 Proposed 1501 Line Extension Route Figure 3 shows the SMLD Three-Phase Circuit Map. SMLD Feasibility Study for PV System Interconnection March 2012 Page 4

8 Figure 3 SMLD Three-Phase System One-Line Proposed Interconnection Point to Wiles Road & PV project (P7) SMLD Feasibility Study for PV System Interconnection March 2012 Page 5

9 PROPOSED INSTALLATION The proposed installation includes the installation of 2 x 1.0MW AC rated PV systems. The information provided by Community Energy Solar, LLC and SMLD shows a primary underground 15kV cable connection from each 1MW system to a riser pole, owned by SMLD. A detailed one-line diagram from the developer has not yet been provided. It is assumed that SMLD will provide a group-operated air-break switch to isolate the PV system if needed. Upstream of the switch will be SMLD protection in the form of primary pole-mounted fusing or a pole-mounted recloser. If fusing is provided, a fuse size of 140k is recommended. If a recloser is installed the minimum pickup should be on the order of 160A, about 2X the full-load amps of the PV system. Between the PV system and the riser pole disconnect(s), it would be typical for SMLD to install two (2) new padmount 15kV primary metering cabinets. One cabinet would meter the output of each of the 1MW of inverters and customer 1000kVA padmount transformer. It is recommended to have the customer provide a detailed one-line to be able to review the protection of the PV system, for compliance with the SMLD Interconnection Requirements documents. The SMLD work for the proposed installation would be to run the proposed primary wire from Pratts Junction Road to Clinton Road to Wiles Road. It is recommended that SMLD install new 477kcmil aluminum spacer cable up to Wiles Road. New 477kcmil aluminum spacer cable overhead primary wire should be installed between Pole #80 Clinton Road up to Pole #7 Wiles Road from single-phase to three-phase to the project interconnection point, which would be Pole #5 Wiles Road. The proposed PV system, rated at 2.0MW is likely to inject a maximum of amps at 13.8kV into the SMLD system. The riser pole on the PV System site would include a three-phase 15kV group-operated air-break (GOAB) switch to allow the PV System to be isolated with a visible break. Primary metering should be installed as close to the riser pole as practical for a demarcation point. SMLD Feasibility Study for PV System Interconnection March 2012 Page 6

10 COMPUTER ANALYSIS A detailed computer analysis was completed for the normal proposed configuration of the two (1) 1000kW PV systems and two 1000kVA step-up transformer interconnection to the SMLD system through new 13.8kV risers and primary line extension to the SMLD 1501 Circuit. The computer modeling was completed with the PowerTools software suite by SKM Systems Analysis, Inc. Cases Modeled The following three (3) individual cases have been examined: Case #1 This is the Base Case with the existing 1501 Circuit from SMLD extended to the project site. Maximum feeder loads are considered on Circuit 1501, based on July 2011 data. No PV Systems are in-service in this case. Case #2 This Case is the Base Case with the addition of the 2 x 1000kW PV systems online at Wiles Road site. The 1501 Circuit is considered at its peak load condition. The Perkins 1MW PV system is off-line in this case. Case #3 This Case is the Base Case with the addition of the 2 x 1000kW PV systems online at full output. The 1501 Circuit is considered at its light load condition, which would occur on weekends, etc. The existing Perkins 1MW PV system is also on-line in this case. Data Collection Along with a physical survey of the area completed in February of the existing pole lines in Sterling near the site, the following information was requested from SMLD, reviewed and has been the basis for the computer modeling: a. Circuit Maps, showing the existing distribution circuits that could connect to the proposed PV project. b. Substation One-Line for the substations related the distribution circuits that could connect to the proposed PV project. c. Wire Sizes for distribution circuits, if not shown on circuit maps. d. Protective Settings for substation related the distribution circuits that could connect to the proposed PV project SMLD Feasibility Study for PV System Interconnection March 2012 Page 7

11 e. Capacitor locations, sizes and settings, on the distribution circuits that could connect to the proposed PV project. f. Fuse sizes, locations and settings on the distribution circuits that could connect to the proposed PV project. g. Recloser locations, ratings and settings on the distribution circuits that could connect to the proposed PV project. h. Feeder and Substation Transformer loading. Assumptions The following assumptions were made for the computer model: The inverters for the PV project as assumed to be 500kW AC rated output with a power factor, normally at unity (1.0) with excursions of no more than +/ The computer model is of just the AC portion of the system, as the DC system will cause no negative impacts on the SMLD 13.8kV system. The PV Systems will step up through 1000kVA, 5.75% impedance (ANSI standard) padmount transformers from the PV System generator 480 volts. The SMLD peak July loading is assumed to be 13,284kW, without the peak shaving generation in service. System power factor is assumed to be 0.98, based on recent peak load data. The SMLD system feeders are divided by load, with 36.2% on 1501, 14.4% on 1502, 18.0% of 1503 and 31.3% on The substation load tap changers are assumed to regulate the secondary 13.8kV terminals to %, close to 14.1kV. The peak load on 1501 Circuit is 4812kW, based on assumptions from July data. Riser pole fuses at the PV site were assumed to be 140A (k-speed). No upstream fuses are assumed, as this project would tap into mainline 1501 Circuit on Wiles Road, which will backup 1502 Circuit through normally open switch on Pole #8 Wiles Road. Substation relays are set for 360A phase pickup on the 1501 feeder. The following assumption of load split on the 1504 Circuit is being used in the computer model for a lumped load. o The 8 feeder sections modeled were loaded at the end of each section based on the length of the feeder in relation to the total feeder length, large spot loads and existing system data available. SMLD Feasibility Study for PV System Interconnection March 2012 Page 8

12 Load Flow & Voltage Drop Analysis A load flow and voltage drop analysis was conducted to determine if the addition of a 2.0MW Wiles Road PV System would have a negative or unacceptable effect on the SMLD distribution system. The load flow examined thermal loading limits of the existing and new conductors, transformers and other equipment. The voltage drop analysis examined the system voltage with and without the PV System online. Both of these analyses were conducted at peak and minimum system loads on the 1501 feeder. The results of the load flow study are summarized below. Peak system load is based on SMLD data for a recent system peak day, 7/22/2011, with the following feeder loading (out of Chocksett Substation): 1501 Circuit 1502 Circuit 1503 Circuit 1504 Circuit MW MW MW MW The system configuration is assumed to be in the normal state with both transformers in service at the Chocksett Substation, all capacitors in service normally (system power factor 0.98, as recorded during July peak). A review of SMLD data for the past few years shows night time system load being as low as 4.5MW during spring and fall months. Obviously the PV system cannot operate during the 3:00AM 4:00AM when the system load is at its lowest. Based on the data provided, an assumed light system load of 6.5MW was modeled, as could occur on a weekend, holiday or other period of light load. SMLD Feasibility Study for PV System Interconnection March 2012 Page 9

13 LOAD FLOW CASE RESULTS Location Case #1 Case #2 No PV System Peak System Load 2.0MW PV System Peak System Load Case #3 2.0MW PV System Light System Load Chocksett Substation Trans 2 (22MVA rated) 1501 Feeder Main Out of Substation (477kcmil wire) 1501 Feeder Intersection of Chocksett and Pratts Junction (towards North Row) 6.81MW 4.61MW 1.12MW 4.87MW / 203Amps 2.68MW / 111Amps 0.18MW / 8Amps 4.21MW / 177A 4.21MW / 177Amps 2.05MW / 85Amps 1501 Feeder Intersection of Clinton and Pratts Junction Roads (towards Wiles Rd) 0.383MW / 16A 1.80MW / 76Amps (towards SMLD) 1.99MW / 84Amps (towards SMLD) Wiles Road tap off of Clinton Road 0.089MW / 4A 1.99MW / 84Amps (towards SMLD) 2.0MW / 85 Amps (towards SMLD) The voltage drop analysis is used to determine if the system voltage at any point on the new interconnection or the existing SMLD 13.8kV 1501 circuit will be below or above the industry +/- 5% limits, as dictated by ANSI C84.1 American National Standard for Electric Power Systems and Equipment Voltage Ratings (60Hz) and other similar requirements. For the voltage drop analysis all capacitor banks on the 1501 circuit are assumed to be in service. The results of the voltage drop analysis are summarized below. SMLD Feasibility Study for PV System Interconnection March 2012 Page 10

14 VOLTAGE DROP CASE RESULTS Location Case #1 Case #2 No PV System Peak System Load 2.0MW PV System Peak System Load Case #3 2.0MW PV System Light System Load Chocksett Substation Trans 2 (22MVA rated) 1501 Feeder Main Out of Substation (477kcmil wire) 14,179V 14,182V 14,125V 14,177V 14,181V Feeder Intersection of Pratts Junction and North Row 1501 Feeder Intersection of Pratts Junction and Clinton Road 1501 Feeder Meetinghouse Hill Road 1501 Feeder Wiles Road 13,972V 13,996V -0171% VD 14,133V 14,171V % VD 13,784V 13,808V VD 14,132V 14,185V % VD 14,144V -1.23% VD 14,139V -0.04% VD 13, % VD 14,153V -0.15% VD The results of the load flow and voltage drop analysis indicate that during peak and light load conditions on the feeder, there are no thermal overloads of wire, transformers, etc. In addition there are no voltage violations outside of acceptable range. The addition of the PV System raises the primary voltage about 50 volts (about 0.4%) near the site and should not create any high voltage conditions during light load periods. Although there are a number of various cases that could be examined the cases selected cover the normal operation of the 1501 Circuit. The performance should not be impacts in a negative way by single contingencies when load is transferred to other distribution circuits. As a litmus test, the loss of SMLD Chocksett Substation Transformer No. 2 was simulated under peak load conditions (Case #2 above). The remaining Transformer No. 1 is capable of supporting the expected 13.2MW of peak load, and voltage variations are similar to the Case #2 with both transformers in service. The 13.8kV substation bus is about 80 volts below the case with both transformers in service. SMLD Feasibility Study for PV System Interconnection March 2012 Page 11

15 Voltage Flicker Analysis Voltage Flicker is defined as a noticeable or irritation fluctuation of voltage that can cause mis-operation of equipment. The industry standard for interconnection of distributed generation IEEE 1547 addresses the requirements for flicker on new projects as follows: IEEE 1547 states that: Synchronization - The DR unit shall parallel with the Area EPS without causing a voltage fluctuation at the PCC greater than ±5% of the prevailing voltage level of the Area EPS at the PCC, and meet the flicker requirements of Limitation of flicker induced by the DR. The DR shall not create objectionable flicker for other customers on the Area EPS. Flicker is considered objectionable when it either causes a modulation of the light level of lamps sufficient to be irritating to humans, or causes equipment mis-operation DR is the Distributed Resource; PCC is the Point of Common Coupling and EPS is the Electric Power System Flicker is based on measurements in the voltage amplitude, i.e., the duration and magnitude of variations. The table below shows the magnitude of maximum voltage changes allowed with respect to the number of voltage changes per second Voltage Fluctuation Versus Duration Curve The industry now uses a guideline of a 2.0% voltage fluctuation as being noticeable and causing irritation or possible equipment operation, for most projects. Since the proposed PV Systems are not likely to all come on line at the same time, the worst SMLD Feasibility Study for PV System Interconnection March 2012 Page 12

16 case for voltage flicker would occur if the PV Systems all trip off line at the same time, from full output. The results of the flicker modeling are summarized below, for a full load (Case #2) and light load (Case #3) condition. The voltage variation was modeled at the PCC, which is on Wiles Road. The voltage fluctuation would occur quicker than voltage regulating devices (LTC, capacitors, etc.) could react. VOLTAGE FLICKER RESULTS Location Case #2 2.0MW PV System Peak System Load Case #3 2.0MW PV System Light System Load Pre-Trip Voltage Wiles Road at Clinton Road Post-Trip Voltage Wiles Road at Clinton Road 14,209V 14,156V 14,085V 14,039V Voltage Variation 124V (0.87%) 117V (0.82%) The results of the voltage flicker analysis are acceptable with short term voltage fluctuations below 2.0% when all three PV Systems trip off line at full output, before other voltage regulating equipment can react. This level of fluctuation should be below the level or perception. Power Factor Analysis The power factor performance of the proposed PV System interconnection has been reviewed. The proposed inverters should have the ability to maintain a nominal 1.0 unity power factor, with a possible deviation of no more than 0.95 leading to 0.95 lagging. The computer model assumed this standard deviation in power factor. The computer modeling has assumed that all of the capacitor banks are in service during peak load conditions. All feeder loads has been assumed to have a 0.98 power factor. The results of this analysis shows that for Case #1 under peak load, without the PV Systems, the power factor at the substation is 0.98 due to the existing capacitors on the system. With the PV Systems on-line, the power factor at the ends of the feeder is As mentioned earlier, the PV System modeling is conservative regarding the var limits & control and the power factor in reality should be closer to unity here. The power factor at the Chocksett Substation is acceptable with the PV system in operation as summarized below. SMLD Feasibility Study for PV System Interconnection March 2012 Page 13

17 POWER FACTOR RESULTS Location Case #1 Case #2 No PV System Peak System Load 2.0MW PV System Peak System Load Case #3 2.0MW PV System Light System Load Chocksett Substation 13.8kV Bus Feeder Intersection of Pratts Junction and North Row 1501 Feeder Intersection of Pratts Junction and Clinton Road 1501 Feeder Meetinghouse Hill Road 1501 Feeder Wiles Road As can be seen the power factor performance is virtually unaffected by the addition of the 2MW PV system. No additions of capacitor banks are required due to the project. With the other Perkins 1MW PV project on-line at the same time, the results are similar and thus acceptable. System Power Factor Theory All electric equipment requires "VARs" - a term used to describe the reactive or magnetizing power required by the inductive characteristics of electrical equipment. These inductive characteristics are more pronounced in motors and transformers, and therefore, can be quite significant in industrial facilities. The flow of VARs, or reactive power, through a watt-hour meter will not affect the meter reading, but the flow of VARs through the power system will result in energy losses on both the utility and the industrial facility. Some utilities charge for these VARs in the form of a penalty, or KVA demand charge, to justify the cost for lost energy and the additional conductor and transformer capacity required to carry the VARs. In addition to energy losses, VAR flow can also cause excessive voltage drop, which may have to be corrected by either the application of shunt capacitors, or other more expensive equipment. SMLD Feasibility Study for PV System Interconnection March 2012 Page 14

18 Power Factor Triangle The power triangle shown in figure above is the simplest way to understand the effects of reactive power. The figure illustrates the relationship of active (real) and reactive (imaginary or magnetizing) power. The active power (represented by the horizontal leg) is the actual power, or watts that produce real work. This component is the energy transfer component. The reactive power or magnetizing power, (represented by the vertical leg of the upper or lower triangle) is the power required to produce the magnetic fields to enable the real work to be done. Without magnetizing power, transformers, conductors, motors, and even resistors and capacitors would not be able to operate. Reactive power is normally supplied by generators, capacitors and synchronous motors. The longest leg of the triangle (on the upper or lower triangle), labeled total power, represents the vector sum of the reactive power and real power components. Electric power engineers often call total power (kva, MVA) - apparent power, or complex power. Some utilities measure this total power, (usually averaged over a 15 minute load period) and charge a monthly fee or tariff for the highest fifteen minute average load reading in the month. In the power triangle shown above, the reactive power component is decreased by adding shunt capacitors, and the total power will also decrease. This is shown by the decreased length of the dashed lines in the power triangle as the reactive power component approaches zero. Therefore, adding capacitors, which will supply reactive power locally, can reduce total power and monthly kva demand. The ratio of the real power to the total power is called power factor. As the angle gets larger (caused by increasing reactive power) the power factor gets smaller. In fact, the power factor can vary from 0.0 to 1.0, and can be either inductive SMLD Feasibility Study for PV System Interconnection March 2012 Page 15

19 (lagging) or capacitive (leading). Capacitive loads are drawn down, and inductive loads are drawn up on the power triangle. Most industrial customers normally operate on the upper triangle (inductive or lagging triangle). As capacitance is added, the length of reactive (inductive) power leg is shortened by the number of capacitive kvar that were added. If the number of capacitive kvar added exceeds the inductive kvar load, operation occurs on the lower triangle. This is commonly referred to as over compensation, and higher system voltages can result. Short Circuit Review A detailed short circuit review was completed to determine if the addition of the proposed PV Systems would have an effect on the fault interrupting ratings of the existing SMLD equipment. The short circuit review was completed, based on equipment information and drawings provided by the client and manufacturers. The objective was to calculate the available three-phase and line-to-ground fault currents under worst case (bolted fault) conditions and compare these values to the published device interrupting ratings. The maximum symmetrical fault currents occur during the first 1/2 cycle after a fault. The short circuit review has been performed based on the intent of the following applicable industry standards: ANSI/IEEE Std C Application Guide for AC High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis ANSI/IEEE Std C Low-Voltage AC Power Circuit Breakers Used in Enclosures IEEE Std 141 Recommended Practice for Electric Power Distribution in Industrial Facilities. IEEE Std Recommended Practice for Industrial and Commercial Power Systems Analysis Two separate short circuit cases have been examined as part of this Study: Case No. 1 Case No. 2 Base Case No PV System running. 2.0MW PV Systems running. Maximum load on 1501 feeder. The results for the minimum load case (Case #3) would be similar to Case #2. For each case, the initial symmetrical and asymmetrical short circuit currents during the first one-half cycle after a bus fault occurs were calculated. This provides a worst case calculation to be used for comparison with equipment ratings. See Figure below. SMLD Feasibility Study for PV System Interconnection March 2012 Page 16

20 imp peak fault current, first 1/2 cycle dice dc decaying component of fault current I ratio of pre-fault voltage to Thevenin equivalent impedance Figure Short Circuit Current Versus Time After Fault Occurs. The following faults were simulated and calculated for each (3-phase) equipment: Three-phase fault, Single line-to-ground fault, Double line-to-ground fault and Line-to-line fault. The results of the short circuit review as summarized in the table below. The existing fault current on Clinton Road, near Wiles Road close the project site is about 4,314 amps at 13.8kV. This value is well below the 10kA distribution limit for most conventional pole-mount equipment. The addition of the inverters should add no more than 1800A at 480V per 500kW inverter (based on an assumed 3-5X full load amps), which translates to no more than 400A additional fault current on the SMLD 13.8kV system, or a 9.4% increase theoretical maximum at this location. This should create no additional impact for SMLD equipment, or its customer s equipment. Actual inverter information should be provided by the vendor to confirm the maximum short circuit contribution. We have assumed the fault current contribution from the inverters based on what is available in the industry on other similar projects. SMLD Feasibility Study for PV System Interconnection March 2012 Page 17

21 Location Short Circuit Summary Table Case#1 No PV System Running Case#2 2.0MW PV System Clinton Road at Wiles Road ka 3-phase ka 3-phase (9.4% increase) SMLD Chocksett Substation ka 3-phase ka 3-phase (7.0% increase) Protective Coordination Review A review of the existing protective devices on the SMLD 1501 Circuit was completed to determine if any upgrades will be required as part of the PV System interconnection. Presently the existing 1501 Circuit is protected at the Chocksett Substation by SEL overcurrent relays which operate the 13.8kV substation circuit breakers (13.8kV). The overcurrent protection includes phase and ground protection with time overcurrent (51) and instantaneous settings (50). The existing 1501 substation relays are set for 360A phase overcurrent pickup and 144A ground overcurrent pickup. As mentioned there is no other protection between the substation the proposed point of interconnection presently. The proposed PV system is below the daytime feeder minimum load on the 1501 Circuit, and thus no backfeed to the Substation is likely. The feed to Wiles Road is before the existing 1501 reclosers, located on Pole #1 Pratts Junction Road and Pole #10 Heywood Road. Given these facts there are no expected issues with the existing pickup settings of the existing SMLD devices and no relay or recloser settings changes are recommended. As mentioned the recommended fuse size on Wiles Road at the tap location for the 2MW PV site would be 140k fuses at 13.8kV. If each 1000kVA transformer is to be fused individually the recommended fuse size is 50A at the riser pole, to protect the 1000kVA transformer and the primary cable. The proposed time current characteristic (TCC) curve (in the back of the report) illustrates the coordination with the inrush and damage curves of a typical 1000kVA transformer of standard impedance. The proposed transformers should be provided with standard bay-o-net fuses, sized by the manufacturer to protect the transformer from overload. The riser pole fuses will protect the underground primary cable (#1/0Awg aluminum) as well as the primary metering cabinet. For this project the recommended CT ratio should be 35:5 (for each 1000kVA system), as the CT s will have an overload factor of at least 1.25X. This will provide accuracy for periods of light generation. SMLD Feasibility Study for PV System Interconnection March 2012 Page 18

22 The project and Community Energy Solar, LLC should provide documentation showing the coordination of their 480V inverter and/or switchboard circuit breakers with the fuses of the proposed 1000kVA transformer. The Protective Coordination Review was completed based on the intent of the following applicable industry standards: IEEE Std Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems IEEE Std Recommended Practice for Applying Low-Voltage Circuit Breakers Used in Industrial and Commercial Power Systems. IEEE Std Recommended Practice for Industrial and Commercial Power Systems Analysis The proposed design and drawings do not include protective settings, or settings for antiislanding protection. SMLD has published Interconnection Requirements for Distributed Generation. This document includes the following requirements that should be adhered to and demonstrated by the project: Voltage Regulation The DR [distributed resource] shall not actively regulate the voltage at the PCC [unless required by NEPOOL s operating procedures]. The DR shall not cause the Area EPS service voltage at other Local EPSs to go outside the requirements of ANSI C , Range A. Surge Withstand Performance The interconnection system shall have the capability to withstand voltage and current surges in accordance with the environments defined in IEEE Std C or IEEE C as applicable. Voltage The protection functions of the interconnection system shall detect the effective (rms) or fundamental frequency value of each phase-to-phase voltage, except where the transformer connecting the Local EPS to the Area EPS is a grounded wye-wye configuration, or single phase installation, the phase-to-neutral voltage shall be detected. When any voltage is in a range given in Table 1, the DR shall cease to energize the Area EPS within the clearing time as indicated. Clearing time is the time between the start of the abnormal condition and the DR ceasing to energize the Area EPS. For DR less than or equal to 30 kw in peak capacity, the voltage set points and clearing times shall be either fixed or field adjustable. For DR greater than 30 kw the voltage set points shall be field adjustable. SMLD Feasibility Study for PV System Interconnection March 2012 Page 19

23 Frequency When the system frequency is in a range given in Table 2, the DR shall cease to energize the Area EPS within the clearing time as indicated. Clearing time is the time between the start of the abnormal condition and the DR ceasing to energize the Area EPS. For DR less than or equal to 30 kw in peak capacity, the frequency set points and clearing times shall be either fixed or field adjustable. For DR greater than 30 kw, the frequency set points shall be field adjustable. Table 2 Interconnection system response to abnormal frequencies DR size Frequency range (Hz) Clearing time (s) 30 kw > < > 30 kw > < ( ) adjustable setpoint < a DR 30 kw, maximum clearing times; DR > 30 kw, default clearing times Harmonics When the DR is serving balanced linear loads, harmonic current injection into the Area EPS at the PCC shall not exceed the limits stated in Table 3 IEEE Std The harmonic current injections shall be exclusive of any harmonic currents due to harmonic voltage distortion present in the Area EPS without the DR connected. Based on these requirements and typical requirements placed on other similar projects in MA by investor-owned utilities, the proposed project shall have the following requirements placed upon it: 1. The proposed padmount transformer shall be delta on the primary and wye-ground on the secondary to limit harmonic contributions to the primary. 2. The proposed transformer shall be provided with standard under-oil fusing to protect the transformer from overloads. 3. The project shall provide ground fault protection on their equipment as required by the 2011 NEC (typically for 480V breakers over 1000A). 4. The project shall install a dedicated utility-grade relay to prevent islanding and detect fluctuations in voltage and frequency. This relay shall meet the surge requirements for hardened utility-grade equipment as set forth in ANSI C A SMLD Feasibility Study for PV System Interconnection March 2012 Page 20

24 SEL-547 or other similar relay is recommended to be installed on each inverter, at the switchboard level, or at the primary riser pole switch level. 5. The following settings for the under/over voltage and frequency are recommended to be in accordance with the requirements above, other standards, such as NPCC under-frequency load shedding and typical utility practice. Settings are listed on the 480V level, but would be applicable in percentages to 13.8kV level as well. SMLD Feasibility Study for PV System Interconnection March 2012 Page 21

25 Proposed Protective Relay Settings for Anti-Islanding Protection SMLD Feasibility Study for PV System Interconnection March 2012 Page 22

26 CONCLUSIONS / RECOMMENDATIONS The results of the feasibility study for the proposed PV System interconnection of new 2 x 1.0MW PV Systems (2MW total) on the existing SMLD 1501 Circuit is favorable. There are no appreciable impacts to system voltage performance, thermal loading and short circuit contributions. The proposed interconnection to the Wiles Road section of the existing SMLD 1501 circuit is recommended, as this is the closet and most accessible point on the SMLD system. The proposed interconnection would be a tap off of Pole #7 Wiles Road. 1. Load Flow There are no thermal violations with the proposed installation of the PV System (4 x 500kW inverters) connecting to the existing SMLD 1501 Circuit. The SMLD will need to extend three-phase primary to Pole #7 Wiles Road to facilitate the interconnection. 2. Voltage Drop The voltage drop with the additional power flow due to the proposed PV System produces acceptable voltage drop (less than 3% per line section). No upgrades to the SMLD system outside of the three-phase primary line extension are recommended to mitigate voltage issues. The new primary wire should be 477kcmil aluminum 3. Voltage Flicker The voltage flicker which would occur from a sudden disconnect of the PV System from the 13.8kV system does not result in objectionable voltage flicker. The flicker is well below 2%, which is the industry limit. No additional upgrades to the SMLD system are recommended to facilitate the interconnection. 4. Power Factor - The results of the power factor analysis show acceptable power factor on the SMLD system due to the interconnection and the PV System var requirements during full output. The inverters shall demonstrate a power factor variation of no greater than 0.95 lagging to 0.95 leading at all times. 5. Protective Coordination Review There are no changes required to the existing protective settings of SMLD equipment due to the interconnection of the PV System proposed. New fuses are recommended at the three-phase tap to the project site off of Wiles Road (140A). The project needs to include a utility-grade relay to address anti-islanding concerns and satisfy the SMLD interconnection requirements, which are similar to other utilities in MA. Proposed settings have been provided. This relay could be installed at one of the primary metering locations to trip a motor-operated gang switch on the pole as has been done on the other large PV project in Town, or the protective could be installed at the customer s 480V level to trip a switchboard breaker, contactor, etc. SMLD Feasibility Study for PV System Interconnection March 2012 Page 23

27 ATTACHMENTS 1. Community Energy Solar, LLC Proposed Layout Plan 2. SMLD System One-Line Diagram 3. SMLD Drawings of Proposed Line Extension to Wiles Road 4. SMLD System Load and Feeder Data ( ) 5. Computer Model one-line diagram 6. Computer model input data 7. Time Current Curves (overcurrent protection) SMLD Feasibility Study for PV System Interconnection March 2012 Page 24

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32 P S P S P S Open P S P S NGRID P kw kvar NGRID O kw kvar SWITCH DSL1 115KV P KV V VD% 0.05 % PF KV TAP P KV DSL1 SWITCH V VD% 0.05 % PF 0.97 SWITCH DSL2 115KV O KV V VD% 0.06 % PF KV TAP O KV DSL2 SWITCH V VD% 0.06 % PF 0.96 CASE NO. 1 BASE CASE PEAK LOAD CONDITIONS NO PV GENERATION 115KV BUS CS-1 115KV BUS CS-2 CS-1 CS-2 RLY CS-1 RLY CS-2 115KV C S V VD% 0.06 % PF KV BUS T1 115KV C S V VD% 0.06 % PF KV BUS T2 T1 12MVA kw kvar A Tap 0.00 % 13.8KV T1 BUS T1 115KV V VD% 0.06 % PF 0.97 T1 13.8KV V VD% % T2 12MVA kw kvar A Tap 0.00 % 13.8KV T2 BUS T2 115KV V VD% 0.06 % PF 0.96 T2 13.8KV V VD% % 52T1 DISC#1 52T2 DISC#1 52-T1 52-T2 RLY 52-T1 RLY 52-T2 52T1 DISC#2 52T2 DISC#2 13.8KV BUS V VD% % DISC 1F1 #1 DISC 1F2 #1 13.8KV 52T1 BUS FUSE SS#1 5E DISC 52-BT #1 DISC 52-BT #2 52-BT DISC 2F1 #1 13.8KV 52T2 BUS DISC 2F2 #1 13.8KV BUS V VD% % FUSE SS#2 5E 52-1F F F F RLY 1503 DISC 1F1 #2 CBL kw kvar 100 A Ampacity A RISER POLE V VD% % RLY 1504 DISC 1F2 #2 CBL kw kvar 174 A Ampacity A RISER POLE V VD% % TRANS SS#1 75KVA 0.0 kw 0.0 kvar 0.00 A Tap 0.00 % STA SVC 208V # V VD% % PF 0.00 RLY 1501 DISC 2F1 #2 CBL kw kvar 204 A Ampacity A RISER POLE V VD% % PF 0.97 RLY 1502 DISC 2F2 #2 CBL kw kvar 80 A Ampacity A RISER POLE V VD% % TRANS SS#2 75KVA 0.0 kw 0.0 kvar 0.00 A Tap 0.00 % STA SVC 208V # V VD% % PF 0.00 LOAD kw (Input) OH-1504 SEC1A kw kvar A VD0.4 % OH-1501 SEC kw kvar A VD0.3 % LOAD kw (Input) OH-1504 SEC kw kvar A VD0.2 % P43 WORC V VD% % LOAD-1504 SEC kw (Input) OH-1504 SEC kw kvar A RECL-1504 P46 WORC LOAD-1504 SEC1C kw (Input) PRINCETON V VD% % OH-1504 SEC kw kvar A VD0.1 % LOAD-1504 SEC kw (Input) OH-1504 SEC kw kvar A VD0.2 % LOAD-1504 SEC kw (Input) OH-1504 SEC1B kw kvar A VD0.7 % OH-1504 SEC1C kw kvar A VD0.6 % BEAMAN V VD% % CHOCKSETT V VD% % LOAD-1504 SEC1A kw (Input) MAIN V VD% % LOAD-1504 SEC1B kw (Input) PRINCETON@ JEWETT V VD% % FUSE-JEWETT OH-JEWETT 0.2 kvar 0.01 A VD-0.0 % FUSE-PV RISER OH-1501 SEC kw kvar A VD1.2 % OH-1501 SEC kw kvar A VD0.8 % OH-1501 SEC kw kvar A VD0.4 % OH-1501 SEC kw kvar A VD0.2 % LOAD-1501 SEC kw (Input) NORTH ROW V VD% % LOAD-1501 SEC kw (Input) NORTH HEYWOOD V VD% % LOAD-1501 SEC kw (Input) ROWLEY HILL V VD% % LOAD-1501 SEC kw (Input) ROWLEY MEETINGHOUSE V VD% 0.11 % LOAD-1501 SEC kw (Input) PRATTS V VD% % OH-1501 SEC2A kw 76.9 kvar A CLINTON RD V VD% % OH-1501 SEC2B kw LOAD-1501 SEC2A 38.7 kvar kw (Input) 8.04 A WILES ROAD V VD% % OH-1501 SEC2C 89.0 kw LOAD-1501 SEC2B 17.8 kvar kw (Input) 3.71 A WILES ROAD V VD% % LOAD-1501 SEC2C kw (Input) P46 WORC RECL V VD% % LOAD-1504 SEC kw (Input) OH-1504 SEC kw kvar A RECL-1504 P53 BEAMAN OH-1504 SEC kw 93.4 kvar A RECL-1504 P53 PRINCETON PV RISER POLE V VD% % PF 0.00 Open GOAB-PV RISER P53 BEAMAN RECL V VD% % LOAD-1504 SEC kw (Input) P53 PRINCETON RECL V VD% % LOAD-1504 SEC kw (Input) CBL-PV-SEC1 0.0 kw 0.0 kvar 0 A Ampacity A PRI-METER CB-INV#1 CB-INV#2 CB-PANEL PV SWBD 2000A 0.00 V VD% % PF 0.00 PV PRIMARY METER 0.00 V VD% % PF 0.00 FEED TO 7.5KVA TRANS PV MAIN DISC CBL-PV-SEC2 0.0 kw 0.0 kvar 0 A Ampacity A CBL-PV-INV1 0.0 kw 0.0 kvar 0 A Ampacity A CBL-PV-INV2 0.0 kw 0.0 kvar 0 A Ampacity A CBL-PV-MAIN 0.0 kw 0.0 kvar 0 A Ampacity A TR-1000-PRI 0.00 V VD% % PF 0.00 PV-INV1-500KW 0.00 V VD% % PF 0.00 PV-INV2-500KW 0.00 V VD% % PF 0.00 TRANS-1000KVA 0.0 kw 0.0 kvar 0.00 A Tap 0.00 % INVERTER-500KW-1 INV1-GEN 0.00 V VD% % PF 0.95 INVERTER-500KW-2 INV1-GEN V VD% % PF 0.95 TR-1000-SEC 0.00 V VD% % PF 0.00 INV1-500KW kw kvar INV1-500KW kw kvar

33 FEED TO 7.5KVA TRANS P S P S P S Open P S P S P S P S NGRID P kw kvar NGRID O kw kvar SWITCH DSL1 115KV P KV V VD% 0.05 % PF KV TAP P KV DSL1 SWITCH V VD% 0.05 % PF 0.97 SWITCH DSL2 115KV O KV V VD% 0.04 % PF KV TAP O KV DSL2 SWITCH V VD% 0.04 % PF 0.97 CASE NO. 2 PEAK LOAD CONDITION 2 X 1MW WILES ROAD PV SYSTEM ON-LINE PERKINS PV SYSTEM OFF-LINE 115KV BUS CS-1 115KV BUS CS-2 CS-1 CS-2 RLY CS-1 RLY CS-2 115KV CS V VD% 0.06 % PF KV BUS T1 115KV CS V VD% 0.04 % PF KV BUS T2 T1 12MVA kw kvar A Tap 0.00 % 13.8KV T1 BUS T1 115KV V VD% 0.06 % PF 0.97 T1 13.8KV V VD% % T2 12MVA kw kvar A Tap 0.00 % 13.8KV T2 BUS T2 115KV V VD% 0.04 % PF 0.97 T2 13.8KV V VD% % 52T1 DISC#1 52T2 DISC#1 52-T1 52-T2 RLY 52-T1 RLY 52-T2 52T1 DISC#2 52T2 DISC#2 13.8KV BUS V VD% % DISC 1F1 #1 DISC 1F2 #1 13.8KV 52T1 BUS FUSE SS#1 5E DISC 52-BT #1 DISC 52-BT #2 52-BT DISC 2F1 #1 13.8KV 52T2 BUS DISC 2F2 #1 13.8KV BUS V VD% % FUSE SS#2 5E 52-1F F F F RLY 1503 DISC 1F1 #2 CBL kw kvar 100 A Ampacity A RISER POLE V VD% % RLY 1504 DISC 1F2 #2 CBL kw kvar 174 A Ampacity A RISER POLE V VD% % TRANS SS#1 75KVA 0.0 kw 0.0 kvar 0.00 A Tap 0.00 % STA SVC 208V # V VD% % PF 0.00 RLY 1501 DISC 2F1 #2 CBL kw kvar 111 A Ampacity A RISER POLE V VD% % RLY 1502 DISC 2F2 #2 CBL kw kvar 80 A Ampacity A RISER POLE V VD% % TRANS SS#2 75KVA 0.0 kw 0.0 kvar 0.00 A Tap 0.00 % STA SVC 208V # V VD% % PF 0.00 LOAD kw (Input) OH-1504 SEC1A kw kvar A VD0.4 % OH-1501 SEC kw kvar A VD0.2 % LOAD kw (Input) OH-1504 SEC kw kvar A VD0.2 % P43 WORC V VD% % LOAD-1504 SEC kw (Input) OH-1504 SEC kw kvar A RECL-1504 P46 WORC P46 WORC RECL V VD% % LOAD-1504 SEC kw (Input) PRINCETON V VD% % LOAD-1504 SEC1C kw (Input) OH-1504 SEC kw kvar A VD0.1 % OH-1504 SEC kw kvar A VD0.2 % OH-1504 SEC kw kvar A RECL-1504 P53 BEAMAN P53 BEAMAN RECL V VD% % LOAD-1504 SEC kw (Input) LOAD-1504 SEC kw (Input) LOAD-1504 SEC kw (Input) OH-1504 SEC kw 93.4 kvar A RECL-1504 P53 PRINCETON P53 PRINCETON RECL V VD% % LOAD-1504 SEC kw (Input) OH-1504 SEC1B kw kvar A VD0.7 % OH-1504 SEC1C kw kvar A VD0.6 % BEAMAN V VD% % CHOCKSETT V VD% % LOAD-1504 SEC1A kw (Input) MAIN V VD% % LOAD-1504 SEC1B kw (Input) PRINCETON@ JEWETT V VD% % FUSE-JEWETT OH-JEWETT 0.2 kvar 0.01 A VD-0.0 % FUSE-PV RISER PV RISER POLE V VD% % PF 0.00 Open GOAB-PV RISER CBL-PV-SEC1 0.0 kw 0.0 kvar 0 A Ampacity A PRI-METER OH-1501 SEC kw kvar A VD1.2 % OH-1501 SEC kw kvar A VD0.8 % OH-1501 SEC kw kvar A VD0.4 % OH-1501 SEC kw kvar A VD0.2 % PRATTS V VD% % OH-1501 SEC2A PF kw LOAD-1501 SEC kvar kw (Input) A VD-0.1 % CLINTON RD NORTH R OW V V VD% % VD% % PF 0.97 OH-1501 SEC2B kw LOAD-1501 SEC2A LOAD-1501 SEC kvar kw (Input) kw (Input) A VD-0.1 % WILES ROAD NORTH HEYWOOD V V VD% % VD% % PF 0.97 OH-1501 SEC2C kw LOAD-1501 SEC2B LOAD-1501 SEC kvar kw (Input) kw (Input) A VD-0.0 % ROWLEY HILL V WILES ROAD VD% % V OH-1501 TAP TO PV VD% % kw PF 0.97 LOAD-1501 SEC kvar kw (Input) A LOAD-1501 SEC2C kw (Input) VD-0.0 % FUSE-WILES PV RISER ROWLEY MEETINGHOUSE V VD% % GOAB-PV RISER1 LOAD-1501 SEC kw (Input) RISER FUSE-1 50A kw kvar CBL-PV-SEC3 46 A kw Ampacity A kvar 46 A Ampacity A PRI-METER WILES1 PV PRIMARY METER WILES V kw VD% % kw kvar kvar PF A 46 A Ampacity A CBL-PV-SEC4 Ampacity A TR-1000-PRI V VD% % PF 0.97 PV RISER WILES V VD% % GOAB-PV RISER2 PF 0.97 CBL-PV-SEC6 PRI-METER WILES2 PV PRIMARY METER WILES V VD% % PF 0.97 CBL-PV-SEC5 TR-1000-PRI V VD% % PF 0.97 CB-INV#1 CBL-PV-INV1 0.0 kw 0.0 kvar 0 A Ampacity A CB-INV#2 CBL-PV-INV2 0.0 kw 0.0 kvar 0 A Ampacity A CB-PANEL PV SWBD 2000A 0.00 V VD% % PF 0.00 PV MAIN DISC CBL-PV-MAIN 0.0 kw 0.0 kvar 0 A Ampacity A PV PRIMARY METER 0.00 V VD% % PF 0.00 CBL-PV-SEC2 0.0 kw 0.0 kvar 0 A Ampacity A TR-1000-PRI 0.00 V VD% % PF kw kvar 1325 A Ampacity A CB-INV-WILES-1 TRANS-1000KVA kw kvar A Tap 0.00 % TR-1000-SEC V VD% % PF 0.95 CBL-PV-MAIN-WILES-1 PV SWBD 2000A WILES V VD% % PF 0.95 CB-INV-WILES kw kvar 1325 A Ampacity A CB-INV-WILES-3 TRANS-1000KVA kw kvar A Tap 0.00 % TR-1000-SEC V VD% % PF 0.95 CBL-PV-MAIN-WILES-2 PV SWBD 2000A WILES V VD% % PF 0.95 CB-INV-WILES-4 PV-INV1-500KW 0.00 V VD% % PF 0.00 PV-INV2-500KW 0.00 V VD% % PF 0.00 TRANS-1000KVA 0.0 kw 0.0 kvar 0.00 A Tap 0.00 % INVERTER-500KW-1 INV1-GEN 0.00 V VD% % PF 0.95 INV1-500KW kw kvar INVERTER-500KW-2 INV1-GEN V VD% % PF 0.95 INV1-500KW kw kvar TR-1000-SEC 0.00 V VD% % PF 0.00 CBL-PV-INV kw kvar 663 A Ampacity A PV-INV1-500KW V VD% % PF 0.95 INV-500KW-WILES1 CBL-PV-INV kw kvar 663 A Ampacity A PV-INV2-500KW V VD% % PF 0.95 INV-500KW-WILES2 CBL-PV-INV kw kvar 663 A Ampacity A PV-INV1-500KW V VD% % PF 0.95 INV-500KW-WILES3 CBL-PV-INV kw kvar 663 A Ampacity A PV-INV2-500KW V VD% % PF 0.95 INV-500KW-WILES4 INV1-GEN V VD% 0.00 % PF 0.95 INV1-GEN V VD% 0.00 % PF 0.95 INV1-GEN V VD% 0.00 % PF 0.95 INV1-GEN V VD% 0.00 % PF 0.95 INV1-500KW kw kvar INV1-500KW kw kvar INV1-500KW kw kvar INV1-500KW kw kvar