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Outdoor Power Transmission & Distribution

Design Criteria/Facility Standards Manual Page 1 University of Maryland, College Park

Description:

The purpose of the section is to highlight the current applicable UMCP Design Standards and requirements for Outdoor Power Transmission and Distribution, including but not limited to the following:

• Medium Voltage cable

• Medium Voltage Splices and Terminations

• Medium Voltage Loop Switches

• Medium Voltage Transformers

• Underground Ductbank

• Electrical Manholes

• of building service/maintenance support within buildings on the UMCP campus.

Related Sections:

• TBD

Effective Date:

• TBD

Applicable Standards:

• All materials and installation methods shall comply with current NFPA Regulations.

• All work in or around Medium Voltage systems shall comply with current OSHA Safety Regulations.

• All work shall be inspected by a 3rd party electrical inspector certified by the State of Maryland per requirements outlined in section 12-601 and 12-605 of Md Public Safety Code. See section 26.05.00 for more details.

• NEC

• UL Underwriters Laboratories

General Requirements

1. Operations and Maintenance

The Medium Voltage (13,800 volts) distribution system on campus is operated and maintained by MEIP through their contractors (Honeywell). Any modifications, removal or new installations involving the following components shall be forwarded to MEIP’s Engineering Team for review and approval (in addition to the university review process);

• Medium Voltage cables or ductbank

• Medium Voltage loop switches

• Medium Voltage transformer

• Low voltage cables or ductbank from service transformer to service disconnect

• Main service entrance switchgear

2. Short Circuit Calculations New connections to the Medium Voltage system shall utilize SKM software to perform short circuit calculations to allow for integration of the new equipment connections to be integrated into the SKM model maintained by the system operator.

3. Qualifications

• All work on the Medium Voltage system shall be completed by technicians certified to work on high voltage systems. This includes all workers entering Medium Voltage manholes or working in loop switches or transformers.

• All testing of Medium Voltage loop switches, transformers and cables shall be performed by independent testing companies, certified by nationally recognized testing agency to perform such work.

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4. Products

• Basic Materials

• All products shall be UL (Underwriters Laboratories) listed.

• Warning Signs: Provide warning signs for electrical equipment per current OSHA and NFPA guidelines.

• Medium Voltage Cable

• The Medium Voltage feeder cable shall be compact cable with 3-1/c; each rated 15KV, 133% level, 220 mils insulation, EPR (ethylene-propylene rubber) cable.

• The cable shall have a full tape shield, and be rated for 105 degrees C continuous operating temperature (MV-105), and 100 hours per year of “emergency” overload at 130 degrees C for five years of cable life. The Outside Diameter (O.D.) of the 500 kcmil cable and jacket shall be less than

1.5 inches.

• The cable shall be rated for 500 amps in accordance with NEC for three single conductors in one underground raceway, three feet deep with a conductor temperature of 105 degrees C, 100% Load Factor, an ambient earth temperature of 20 degrees C, and thermal resistance (RHO) of 90.

• The cable shall be either 500 kcmil or 750 kcmil cable to match existing rating for replacement or extension of feeders when installed as part of the campus “Loop” Feeder system. The cable may be 4/0 AWG between the Loop Switch and the transformer.

• Manufacturer: Okonite, Prysmian, Rome, or approved equal.

• The ground conductor shall be 2/0 AWG stranded soft drawn bare copper conductor.

5. Medium Voltage Splice And Termination Materials

• Splice Kits

• The splice kits shall match the make and type of Medium Voltage cable provided.

• They shall be “cold shrink” splice kits and be rated for operation at 105 degrees C. If “cold shrink” splice kits are not manufactured for the particular cable application, then “resin filled” kits shall be provided.

• The kits shall include all components, including lugs and connectors, etc., needed to prepare the cables and completely install a splice.

• The kits shall provide water, weather, and mechanical protection, and be suitable for underground and cable tray applications.

• All splices shall be grounded type (outdoor type).

• Splice kits shall be manufactured by Prysmian, “3M” or approved equal.

• Termination Kits

• The termination kits shall match the make and type of Medium Voltage cable provided. They shall be “cold shrink” termination kits. The kits shall include all components, including lugs and connectors, etc., needed to prepare the cables and completely install a termination. The kits shall provide water, weather, and mechanical protection.

• Termination kits shall be manufactured by “3M”, Prysmian or approved equal.

6. Medium Voltage Loop Switches

• Review selection of Medium Voltage Switch with E&E and the MEIP Engineer. Currently the Medium

Voltage Loop Switches shall be either:

• S&C Electric Company “PMU-19” style low profile, pad-mounted switchgear.

• G&W Electric PN 132 276-25-6 style low profile, pad-mounted SF6 switchgear with 12” skirt that raises unit to align connections to match existing campus pad mounted MV switch installations.

• The switch shall be a three phase switch rated 14.4 KV Nominal, 17.0 KV max, and 95 KV BIL minimum. The switch shall be rated 600 amps RMS Continuous, as well as 600 amps RMS for Load interruption (Dropping and Load Splitting) (Parallel or Loop Switching)

• The switch shall have the following Duty-Cycle Fault-Closing, Two Time ratings;

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• Asymmetrical—40,000 Amps RMS

• Symmetrical—25,000 Amps RMS

• Peak—62,500 Amps RMS

• The switch shall have a Momentary rating of 40,000 Amps RMS, and a One-Second rating of 25,000 Amps RMS.

• The switch shall utilize SM-5S fuses and fuse holders or resettable fault interrupters.. Three spare fuses shall be provided with switch. The fuse ratings or RFI settings shall match the transformer Primary protection rating.

• Compartments #2 and #3 shall disconnect the incoming cables from the internal bus. Compartment #4 shall disconnect the internal bus from load side fuses. Compartment #1 shall contain fuses and connect to load side cables.

• The switch shall have physical dimensions of 72” wide x 70” deep by 62” high. The switch shall be dark green.

7. Medium Voltage Transformer

• Transformers shall be outdoor, pad-mounted, oil-filled with primary fusing located at the loop switch.

• Liquid oil shall be biodegradable and non toxic.

• Provide equipment by one of the following; ABB, Eator or Schneider Electric (Square D).

• The transformer shall be three phase(unless UM approved otherwise), 65 degree C rise, 60 hertz, copper windings, rated 30 degree C average ambient.

• The transformer shall be rated 13,800 volts delta on the primary side, with 480/277 volts (or 208/120 volts) on the secondary side. It shall be rated 95 KV BIL, and have 2-2.5% FCAN and 2-2.5% FCBN taps.

Total voltage compensation shall be 5%.

• Impedance values—2.3% min and 5.75% max up through 500kva. 750 kva and larger shall have a design impedance of 5.75%.

• Transformers shall be equipped with externally replaceable, 8.3/14.4kV rated loadbreak bushing wells and inserts suitable for use with loadbreak elbow connectors. Bushings shall be arranged for loop feed in accordance with ANSI C5.12.26 Fig 6A.

• Transformers shall be equipped with metal oxide, distribution class under oil lightning arresters. Arresters shall be rated 10kV.

• Transformer shall be equipped with ground attachment points, one in the primary compartment, and one in the secondary compartment. The secondary ground point shall be a bar capable of supporting up to 12 ground cables. Grounding attachments shall be made using a “taplug” connector with ½” – 13UNC threads.

• Transformer shall be filled with ANSI Type II mineral oil and shall have less than 1 PPM of PCB content at the time of manufacture.

• Transformers shall be equipped with 6-hole spade type connectors. Transformers over 1500 kva shall be equipped with 10 hole spades. Spades shall be capable of accepting copper conductors up to 750 kcmil in size.

• Transformers shall be equipped with a pressure relief device that utilizes a pull-ring to operate the device.

• The transformer shall have the following accessories:

• 5 position tap changer

• Dial type thermometer (measuring current and max temperature achieved)

• Liquid level gauge

• Pressure vacuum gauge

• Gas sample valve

• 1” drain valve and sampler

• Pressure relief valve

• Ground bar in the secondary compartment

• Standard industrial enamel paint (dark green)

• Sound Level Shall not exceed 60 dBa.

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8. Utility Access Holes

• Utility access holes shall be pre-cast reinforced concrete with minimum inside dimension as indicated for each utility access hole (minimum size 6’ wide x 8’ long x 6’ high) and a centered entrance opening of 36 inches diameter (minimum).

• The utility access hole, cover, and collar shall be capable of supporting truck loads on the cover and all other loads imposed by dry or wet earth. Provide engineering computation "sealed" by a registered professional engineer as part of the shop drawing submittals for each size of utility access hole to substantiate that the utility access hole design accommodates the criteria set forth in the Design Loads below

• Design Loads:

• Dead Load:

• Concrete at 150 PCF

• Earth Cover at 120 PCF

• Lateral Earth Pressure on Walls:

• Equivalent Fluid pressure above the water table at 32 PSF per foot of depth.

• Equivalent Fluid pressure below the water table at 81.4 PSF per foot of depth.

• Surcharge on walls equal two feet of dry earth.

• Time Load:

H20-AASHO truck loading rear wheel load of 16,000 lbs. + 30% impact (20,800 lbs. total)

• Utility access holes shall be as manufactured by: Penn Cast, Easi Set, A.C. Miller Products Inc., Smith- Midland or approved equivalent.

• The utility access hole cover shall be cast iron to accommodate a clear opening into the utility access hole of 36 inches diameter (minimum).

• Covers for "Electric" utility access holes shall have the word "Electric" cast as part of the cover.

• The rim supporting the cover shall be cast iron.

• Cover and rim shall be structurally adequate to accommodate a 20 ton truck loading (H20-ASSH) as required for each utility access hole.

• Covers shall be solid except for openings to enable placing and removing the cover, and shall be designed to meet standard U.S. Government designs for underground electric or telephone construction.

• A Ground rod shall be installed, and shall be copper clad steel at least 10 feet long and 3/4 inches diameter (minimum).

• Cable support racks shall be installed on all four interior walls of the utility access hole and shall be non-metallic, adjustable arm, cable racks. Each stanchion (upright) shall be at least 36” long. Install six stanchions in the utility access holes—two on each of the long walls, and one on each of the short walls.

Utilize stainless steel bolts and washers to attach the stanchions. Install a total of twelve 14” support arms on the stanchions. Each arm shall be rated to support 350 lbs. The racks shall be Underground Devices, Inc. or approved equal.

• Each utility access hole shall have a hot dip galvanized steel ladder that reaches from the rim supporting the cover to the floor of the utility access hole. Attachments to secure the removable ladder to the steel rim shall be stainless steel.

• Each utility access hole shall have "hot dip galvanized steel pulling eyes" for each wall. Each "pulling eye" shall be located near the floor and shall be centered in the respective wall.

• Construct manhole with depressed sump pit in one corner of the manhole for collecting standing water.

Size shall be minimum 8”x8” by 6” deep to accommodate a portable pump.

• Provide end bells for all duct penetrations.

• Include “knockouts” where penetrations are not utilized during the initial installation. Provide for up to 8 ducts (including the existing penetrations) at each face of the manhole.

9. Low Voltage Cables

• All low voltage cables for feeders, branch circuits, and control circuits shall be copper conductor, THHN/THWN, 600 volt insulation, rated at 90 degrees C.

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• Use of wire smaller than #12 AWG for feeder and branch circuits, and #14 AWG for control circuits shall not be acceptable.

• Feeder and branch circuit conductors larger than #10 AWG and all control circuit conductors shall be stranded.

10. Main Service Entrance Switchgear

• Service Entrance disconnecting means for services of 400 amps or more shall be a single main breaker--fused disconnects are not acceptable.

• Electrical service entrance conductor from the pad mounted transformer to the building shall be copper. Aluminum is not an acceptable material to be installed for this application and should not be considered a valued engineered (VE) substitute.

11. Grounding Service Entrance

• Grounding systems for buildings served by the Campus 13.8 kV distribution shall be designed based on the NEC definition of a separately derived system. The campus Electrical Distribution System (EDS) is a separately derived system. The secondary feeder is a 3-phase, 4-wire system with the ground. Normally, the University bonded the neutral & ground conductor in the switchboard.

• Grounding systems for buildings served directly by PEPCO and utilize a PEPCO transformer shall be designed based on the NEC definition of the pad mount transformers as a service. Reference NEC 2020-

250. 30 (C).

12. Design

• The Medium Voltage (13,800 volts) distribution system on campus is operated and maintained by MEIP through their contractor Honeywell, and will require their approval. Any modifications, removal or new installations involving the following components shall be forwarded to MEIP Engineer for review and approval;

• Medium Voltage cables or ductbank

• Medium Voltage Loop Switches

• Medium Voltage transformer

• Low voltage cables or ductbank from service transformer to main building switchgear

• Main building service switchgear

• The project tie in request shall be coordinated through FM E&E, to ensure the proposed equipment and service layout complies with the campus Medium Voltage distribution requirements and that sufficient electrical capacity is available for the proposed project.

• The design for new loads to be added to the campus MV looped feeder system shall include the continuing the continuity of the loop by routing out and back from a Medium Voltage switch and powering the transformer from that MV switch (UMD E&E Can provide additional detail upon request).

The connection to the existing Medium Voltage distribution system, through the loop switch and transformer to the first disconnecting device in the main electrical switchgear in the building (point of demarcation) shall be submitted to MEIP for review and approval at each stage of the design.

13. Medium Voltage Cables

• All feeders in manholes shall be labeled. The labels shall be permanent and be readable with auxiliary lighting in the manhole. The labels shall indicate origination and destination locations, as well as the feeder number.

• Install fireproof taping on all phase cables in manholes.

14. Medium Voltage Ductbanks

• All new Medium Voltage cable shall be installed in ductbank. Direct buried cable is prohibited.

• Medium Voltage ductbanks constructed for Medium Voltage loop feeders shall be concrete-encased, 5” diameter (minimum) PVC conduits, with a minimum of four conduits.

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• Ductbanks for feeders between the loop switch and the transformer may utilize concrete-encased, 4” diameter PVC conduits.

• Ductbanks shall utilize “long sweep” elbows.

• Ductbanks terminating in buildings or manholes shall have “bell ends”, where the conduits penetrate the wall, or bushings if terminating in equipment.

• Ductbanks shall have a minimum of 30” cover from the top of the ductbank to the top of grade.

• Ductbanks shall include a minimum of 100% spare conduits.

• Ductbanks should be graded gently sloping down toward each manhole (3” per 100’ minimum).

• If multiple loop switches are installed on a common pad, the Medium Voltage loop ductbanks shall not go from switch to switch but shall go back to the manhole—one 4-conduit ductbank for each switch on the pad.

• Utilize rigid PVC spacers to provide minimum duct spacing and concrete cover depths while supporting conduits during concrete pours.

• Install reinforcement in ductbanks passing through disturbed earth and when running perpendicular across roadways.

• Waterproof floor and wall penetrations of the ductbank, prior to pouring concrete around the conduits

• Provide 6” of separation in combined ductbanks between Medium Voltage conduits and communication or low voltage conduits.

• Provide a minimum of 18” separation when crossing steam or hot water lines. Ductbanks shall cross under steam and hot water lines, unless depth of ductbank exceeds 8’.

• Ductbanks shall not run parallel to steam lines, unless there is at least a 5’ separation between ductbank and steam line.

• Empty conduits shall have pull strings installed, and tied off at both ends.

• A continuous internal grounding conductor, consisting of a 4/0 AWG bare stranded copper conductor, shall be installed within each medium voltage ductbank. The grounding conductor must be interconnected with the grounding system in each utility access hole (manhole) and bonded to the 4/0 ground ring at all pad-mounted switch and transformer locations.

15. Medium Voltage Manholes

• Manholes shall not be greater than 400’ apart.

• Upon completion of the feeder installation, provide “fold-down” drawings of the interior of the manhole, with the duct conduits clearly labeled, and with cables annotated.

• Low voltage cables (less than 600 volts) shall not pass through Medium Voltage manholes (more than

4160 volts).

16. Grounding for Pad-Mounted Equipment

• All pad-mounted loop switches and transformers shall be connected to an underground ground ring using a 4/0 AWG bare tinned-copper conductor.

• The ground ring shall be installed using a tinned-copper conductor buried a minimum of 24 inches below finished grade and located approximately 6 inches from the equipment foundation.

• The ring shall be interconnected to at least two copper-clad steel ground rods (3/4-inch diameter by 10 feet long).

• All grounding connections below grade shall be made using exothermic-welded connectors.

17. Low Voltage Ductbanks

• Low voltage ductbanks constructed for service entrance feeders or emergency power feeders shall be concrete-encased, 4” diameter (minimum) PVC conduits.

• Ductbanks shall utilize “long sweep” elbows.

• Ductbanks terminating in buildings or manholes shall have “bell ends”, where the conduits penetrate the wall.

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• Ductbanks shall have a minimum of 30” cover from the top of the ductbank to the top of grade.

• Ductbanks shall include a minimum of 50% spare conduits.

18. Installation, Inspection and Testing

• Project construction teams shall complete and submit the Medium-Voltage Tie-In Construction checklist prior to the start of work on the MEIP MV system. This includes provisions for testing prior to commencement of work, switching plan and construction safe work plan.

• All Medium Voltage components (loop switches and transformers, etc.) shall be tested after they are placed in their final position. The applicable tests include; Megger, Contact Resistance, and Hi-Pot test.

• All Medium Voltage cables, terminations, and splices shall be tested prior to energizing.

• All test results shall be submitted to MEIP and FM E&E prior to re-energizing the campus Medium Voltage system after a new MV equipment, cable and splice are installed.

• MD Code requires inspection of electrical premise or structure. The requirements are outlined in section

12-601 and 12-605 of Md Public Safety Code.

• The Contractor shall obtain electrical installation inspection from a non-governmental electrical inspector approved by the state fire marshal. The Contractor shall coordinate inspections, coordinate inspection schedule with the owner, and obtain the electrical inspection certificate within 15 days after completion of electrical installation. The Contractor shall obtain electrical inspections of portions of the Work as they are completed and as required by the electrical inspector, and sufficiently ahead of close-in work so that corrections and re-inspections may be made, and in all cases while the area is accessible and visible for inspection.

• The inspection certificate shall be used in lieu of a county or municipal permit for electrical work performed on property belonging to the State of Maryland. The electrical sub-contractor shall file with the independent inspection agency, and pay all fees associated with such filing