SECTION 5 TRANSFORMERS Necessary transformers will be installed and maintained by The City of Aspen. The City of Aspen will not furnish transformers unless they are of standard size and voltage as established by The City of Aspen. The customer shall notify The City of Aspen in advance of any change in the customer's load requirements that may affect the installed transformer capacity. If the customer's power requirement, within six months after the installation of transformers, proves to be less than shown in the application for service, The City of Aspen may make a reduction in the installed transformer capacity and the customer will be required to pay The City of Aspen the cost of making the change. If the customer's power requirement, within six months after the installation of transformers, proves to be more than the installed transformer capacity, The City of Aspen may make an increase in the installed transformer capacity and the customer will be required to pay the cost of making the change to The City of Aspen. GENERAL The City of Aspen shall not be required to furnish primary transformers unless they are of standard size, voltage and impedance as established by The City of Aspen for the locality where the service is rendered. The City of Aspen must be notified in advance of any change in the consumer s load requirements that may affect the installed transformer current of voltage rating. Limitation on the number and size of secondary conductors are discussed under the heading of Point of Delivery. 1. Capacity a. If the consumer s power requirements within six months after the installation of transformers proves to be significantly greater or less than shown in the application for service, The City of Aspen may make a change in the installed transformer capacity and the consumer may be required to pay The City of Aspen the cost of making the change. PADMOUNT b. An increase in the transformer capacity will increase the available fault current and might affect the interrupting capability of the main disconnect. 1. Clearance A minimum of ten (10) ft clearance, for hot stick operation, shall be maintained in front of the doors of the pad mounted transformer. Transformers will not be located under any overhang (roof, balcony, stairs, etc.). Rear and side clearances will be established by the appropriate City of Aspen engineer in accordance with The City of Aspen construction standards. Pad mounted transformers require air circulation for cooling. Clearances required in specific cases may be obtained from The City of Aspen s engineering department. 2. Installation General requirements concerning installation and operation of transformers is discussed under the heading of Transformer/Equipment Installation, Pad Mounted.
3. Vaults Pre-cast concrete vaults are located beneath each pad mounted transformer. The vault provides space to allow extra length of primary (14,400 volt) cable to be coiled in case terminators need to be replaced. The vault also contains the ground rod and grounding conductor for the primary distribution system. All services fed from this transformer will also occupy space in the vault. Refer to Underground Service in Section 4 for additional information.
PAD MOUNTED TRANSFORMER CLEARANCE
PAD MOUNTED TRANSFORMER (CLEARANCE) ILLUSTRATION NOTES A. Top pad of pre-cast concrete transformer vault. Not all pads are the same dimensions. B. Transformers. Not all transformers are the same dimensions. C. Transformer door. Transformer doors hinge at various positions on the transformers. D. Clear areas are required around pad mounted transformers to allow the following: 1. Access to the primary and secondary compartments of the transformer. (Ice, snow water and dirt build up shall be prevented.) 2. Hot stick operation of the elbows, switch and bay-o-net fuse associated with the primary compartment of the transformer. 3. Air circulation for cooling the transformer during peak load conditions. 4. Boom truck access for replacing the transformer. 5. Routine inspection and maintenance. E. Grade shall be level in the clear area. F. The clear area shall have no obstructions that would impede The City of Aspen s personnel in the operation, maintenance, installation, removal, or repair of the transformer or any other City of Aspen s facilities at this location.
SERVICE LATERAL AT PAD MOUNTED TRANSFORMER
SERVICE LATERAL AT PAD MOUNTED TRANSFORMER ILLUSTRATION NOTES A. Installation of underground service laterals is the responsibility of the consumer, not The City of Aspen. B. Prior to excavation, obtain access to the transformer vault (Courtesy Lock) to determine depth and position knockout and other cables. C. The City of Aspen primary cables (14,400 volts line to neutral) are coiled in the bottom of the vault and connect the primary bushings of the transformer. Do not disturb these cables. D. The ground wire and the ground rod located in the vault and transformer compartment are part of the distribution grounding system and are not to be used by the consumer. E. Before you dig call Colorado 811, Dial 811 or (1-800-922-1987) to have all underground utilities located. F. All underground services, commercial or residential, installed ahead of the City of Aspen meters shall be sized to limit the voltage drop to 2% between the transformer and meter and shall be installed in conduit. Direct burial of conductors will not be permitted except for temporary services. G. Service lateral conductors must be long enough to reach the secondary bushings of the transformer. The service laterals must reach a minimum of 60 inches above the transformer pad. H. All conduits must enter the vault through knockouts and must be grouted. It is recommended that all service laterals be installed at a minimum depth of 24 inches. Knockouts provided in our transformer vaults range from 18 to 41 deep depending on vault design. I. Conduits must be sealed. Water, rodents and debris can enter the conduit and exit the other end into metering devices and buildings. J. Backfill of excavation around transformer vault shall be well compacted to avoid settling in the future.
TRANSFORMER/EQUIPMENT INSTALLATIONS, PAD MOUNTED The City of Aspen will provide an outdoor pad-mounted transformer for service to consumers, such as; shopping centers, office buildings, schools, large apartment buildings, etc., under the following conditions: 1. The City of Aspen will own, operate and maintain the primary underground installation between the adjacent distribution facilities and the transformer, including primary cable, ducts, transformers and protective equipment. 2. The City of Aspen will connect all conductors and maintain the low voltage connection at the transformers secondary terminals. 3. Property shall be to final grade (plus or minus 6 inches) except at equipment location, which shall be to exact final grade. Property corner pins are to be in place with the structure staked or the foundation in, prior to installation of the pad-mounted equipment and splice vaults. 4. The City of Aspen should be consulted well in advance of any proposed project for approval of location and transformer capacity. 5. In the event, and in the judgment of The City of Aspen s engineer that the consumer s selected location for the installation of the pad-mounted equipment is not adequately protected from traffic when directed by public authority, consumer shall provide and install either a fence, guardrail or guard posts to protect the pad-mounted equipment. 6. The City of Aspen will not permit current transformers in The City of Aspen s owned transformers. 7. Vehicle access to transformer must be provided. POINT OF DELIVERY It is the policy of The City of Aspen to own, operate, and maintain the electric distribution facilities up to the point of delivery. This policy is applicable to service rendered from either overhead or underground facilities. All such facilities will be installed in accordance with The City of Aspen s Extension Policy and Rules and Regulations on file at its main office in Aspen. In general, the point of delivery will be considered to be at the point of attachment and connection to the service mast and service entrance conductors for consumer s service supplied by an overhead service drop. The point of delivery for a consumer served by an underground service lateral is the pad mounted transformer. Consumer installed service installations shall be 500 kcmil conductor, or smaller, for termination to facilities within The City of Aspen. The number of conductors that may be terminated is limited by the type of installation as follows: 1. Underground service laterals from a three phase pad-mounted transformer are limited to twelve (12) conductors per phase (500 kcmil). 2. Underground service laterals from single phase pad-mounted transformers are limited to eight (8) conductors per phase 500 kcmil maximum size. Conditions other than above should be discussed with The City of Aspen electric department.
GROUNDING All service systems that operate below 1000 volts contain a grounded neutral or a grounded phase conductor used as a circuit conductor in the system. The grounded neutral or grounded phase conductor is grounded at the supply transformer and will be run from the transformer bank to the meter socket and to each service disconnection means in accordance with 2014 NEC Article 250.24(B), or as may be amended. FAULT CURRENT It is the intent of The City of Aspen to address the customer's need for information concerning fault current requirements pertaining to new construction, rewire, or additional load. Refer to 2014 NEC Article 110.9, or as may be amended. SPECIAL RULES The customer shall provide a minimum of ten (10) ft clearance on the door side(s) of pad-mounted transformers for hot-stick operation and ten (10) ft clearance on the door side(s) of pad-mounted primary metering cabinets for instrument transformer maintenance. Transformers shall not be located under any overhang (roof, balcony, stairs, etc.). Clearance requirements are shown in the Illustrations Section, Drawings CR-30, CR-40, CR-50, CR-60, CR-90 and CR100. Clearances required in specific cases may be obtained from the assigned City of Aspen Engineer. (For Separation and General Information on Transformers see NEC, FM Global Transformers, and/or IEEE Guide for Substation Fire Protection.) Construction will be noncombustible (typically insulated metal on steel frame) and gives spacing based on the volume of fluid in the transformer. The separation distances given in this data sheet are the same as those given in NFPA 850 for this type of construction. This data sheet allows separation, barriers or water spray protection to be used to protect transformers, NFPA 850 recommends that oil-filled main, station service and startup transformers be protected by water spray or foam water systems. C.1.3 IEEE Std 979-1984 Fire protection guidance for indoor and outdoor substations is covered in the ANSI/IEEE Std 979-1984. There is a difference with regard to separation distances. This data sheet recommends a 25 ft (7.6 m). Separation between mineral oil insulated transformers containing from 500 to 5,000 gal (1.9 to 19 m 3 ) and 50 ft (15.2 m) separation between transformers continuing in excess of 5,000 gal (19 m 3 ) of mineral oil. Water spray or a 2-hour rated fire barrier are given as alternatives. IEEE 979 recommends 30 ft separation between transformers with more than a 333 kva rating (approximately 100-150 gal (0.380-0.57 m 3 )). An automatic extinguishing system or a one-hour fire barrier are given as alternatives. C.1.3.2 Outdoor Transformers Spacing of transformers from buildings depends on the quantity of oil contained within the transformer. Transformers containing 200 gal (7.6 m 3 ) or more of oil should be a minimum of 20 ft (6.1 m) from an exposed building regardless of protection provided. It is recommended that a minimum separation distance of 50 ft (15.2 m) from buildings be used unless the building has walls equivalent to or are protected by a 2-hour fire barrier. The separation distance for transformers containing smaller amounts
of oil ranges from 10 ft (3 m) for 75 kva or less, to 20 ft (6.1 m) for transformers from 76 to 333 kva, and 30 ft (9.1 m) for more than 333 kva. Oil containment systems are also recommended in the form of yardstone, diked area and pits. A separation distance between large transformers of 30 ft (9.1 m) of clear space or a one hour fire barrier is recommended. Also automatic extinguishing systems should be considered for all liquid-cooled transformers except those that are adequately separated or that contain less than 500 gal (1.9 m 3 ) of combustible transformer liquid. Table 2a. Separation Distance between Outdoor Liquid Insulated Transformers and Buildings (1) Liquid Less Flammable (FM Approved Fluid) Mineral Oil or (unapproved fluid) FM Approved Transformer or Equivalent Two Hour Fire Resistant Construction Horizontal Distance (1) Non-combustible Construction, ft (m) Combustible Vertical Liquid Volume, gal (m 3 ) ft (m) Construction, ft (m) Distance ft (m) Yes N/A 3 (0.9) 5 (1.5) No 10,000 (38) >10,000 (38) N/A <500 (1.9) 500-5,000(1.9-19) >5,000 (19) 5 (1.5) 15 (4.6) 25 (7.6) 5 (1.5) 15 (4.6) 15 (4.6) 25 (7.6) 50 (15.2) 25 (7.6) 50 (15.2) 25 (7.6) 50 (15.2) 100 (30.5) 25 (7.6) 50 (15.2) 25 (7.6) 50 (15.2) 100 (30.5) (1) All transformer components must be accessible for inspection and maintenance. Table 2b. Outdoor fluid insulated Transformers Equipment Separation Distance (1) Liquid Less Flammable (FM Approved Fluid) Mineral Oil or (unapproved fluid) FM Approved Transformer or Equivalent Fluid Volume, gal (m 3 ) Distance, ft (m) Yes N/A 3 (0.9) No 10,000 (38) 5 (1.5) >10,000 (38) 25 (7.6) N/A <500 (1.9) 5 (1.5) 500-5,000 (1.9-19) 25 (7.6) >5,000 (19) 50 (15.2) (1) All transformer components must be accessible for inspection and maintenance.