1.1 Summary

The following specification is intended for use by consultant engineering firms to provide bidding specifications for products with the quality and performance characteristics required for a K-13 Isolation Transformer. The K-13 Isolation Transformer shall be designed to supply isolated power to sensitive computer based equipment. The isolation transformers will meet or exceed the U.S.Federal Government’s strict telecommunications standards for isolation. In order for a response to this request to be considered it shall require submittal of a proposal of adequate depth to fully define and identify the isolation transformer being offered. The isolation transformer hereafter shall be referred to as the “DTS”.

1.2 Furnished with Equipment

  1. Factory Test Report
  2. Protective Packaging
  3. Installation Drawings
  4. O&M Manual
  5. Warranty Statement

1.3 Documents & Standards

American National Standards Institute (ANSI): C-89.2 Impulse Level Capability.

National Bureau of Standards (NBS): HBS-H-28 Screw Thread Standard for Federal Services.

National Electrical Manufacturer’s Association (NEMA):

  1. ST-1 Dry Transformers, 600-Volt and below.
  2. ST-20 Dry Transformers for General Applications.
  3. TR-1 Transformer Sound Levels/
  4. TR-27 Dry Transformers for Industrial, Commercial, and Institutional.
  5. WC-1 Wire.

Underwriter’s Laboratories (UL):

  1. UL 506 Dry Transformers.
  2. USAS C-57 Transformers.

1.4 System Description

1.4.1 The DTS transformers shall be designed to supply isolated power to sensitive computer based equipment. The DTS will met or exceed the U.S. Federal Government strict telecommunications standards for isolation. The DTS will have multiple voltage capability with DELTA primary windings and WYE secondary windings. They are equipped with an electrostatic shield for noise attenuation, as well as, surge protection. They are capable if operation at either 50Hz or 60Hz with no drop in the capacity rating.

1.4.2 The DTS transformers are to be constructed with copper windings for higher reliability and higher efficiency. The core steel shall be high-grade, low-loss, high permeability, non-aging, M6 or better, grain oriented silicon steel. The core steel shall be annealed, coated, and be free of all burrs and turned edges. The core shall be mounted in a NEMA 1 enclosure that is suitable for floor mounting.

1.4.3 A manufacturer’s nomenclature data plate will be attached to the NEMA 1 enclosure with the DTS specified input and output voltages, operating frequencies, kVA rating temperature operating range, primary DELTA input winding and secondary WYE output winding connection methods, isolation shielding between the primary and secondary winding and any other data required by manufacturing standards not listed.

1.4.4 The standard DTS platform will include a minimum rating of K-13 in order to mitigate waveform distortion, high neutral currents, and load harmonics. The DTS will also have multiple taps for maximum flexibility in adjusting to variable or unknown supply voltages.

1.4.5 NEMA 3R enclosure modifications can be added after the units are installed or ordered. The NEMA 3R or other outside rated enclosure covers add 2 inches to the front and back of the DTS unit.

1.5 System Operation

1.5.1 Normal:

1.6 Quality Assurance

1.6.1 The manufacturer shall have a Quality Assurance (QA) program in place with inspection of incoming parts, modular assemblies, and final products. The manufacturer shall have a designated QA manager who is responsible for overseeing the overall QA process, as well as, Quality Control (QC) representatives responsible for actively overseeing the manufacturing process.

1.6.2 Each DTS design shall be tested using a production unit from orders as they are received and the DTS units are built. Each transformer will continue to receive production tests, and these test reports shall be made available upon request. Computer test reports from the design testing shall be submitted for review upon request. Testing shall include: Induced potential test at 400 Hertz, applied voltage test, no-load loss measurements (watts), full-load loss measurements (watts), impedance measurements, exciting currents, and temperature tests at full load to confirm full load losses.

1.6.3 Packing: Unless otherwise specified all isolation transformers shall be individually packed in accordance with level A/A of the export packing specifications (MIL-C-104). Two methods of marking each unit shall be utilized. First, the outer crate shall be stenciled on at least two sides with the Mark/For number and DTS option number. Second, metal tags of approximately one-half inch in height identifying the Mark/For number and DTS option number shall be permanently affixed to the crate at a noticeable location.

1.6.4 Inspection: New transformers should be inspected when received for damage during shipment. Examination should be made before removing the DTS from cars or trucks, and if any injury is evident or any indication of rough handling is visible, a claim should be filed with the carrier at once and the manufacturer shall be notified. Subsequently, covers or panels should be removed and an internal inspection made for injury or displacement of parts, loss or broke connections, cracked porcelain, dirt or foreign material, and for the presence of free water or moisture. Corrective measures should be taken where necessary. Shipping braces should be removed if present. After a transformer is moved, or if it is stored before installation, this inspection should be repeated before placing the DTS in service.

1.6.5 Handling: Ventilated DTS units can be handled very much like liquid-immersed transformers except that somewhat greater care may be required because of the lighter case. If it is necessary to handle ventilated DTS transformers outdoors during inclement weather they should be thoroughly protected against the entrance of rain or snow.

1.6.6 Storage: Ventilated DTS units preferably should be stored in a warm dry location with uniform temperature. Ventilation openings should be covered to keep out dust. If it is necessary to leave a transformer outdoors it should be thoroughly protected to prevent moisture and foreign materials from entering. Condensation and the absorption of moisture can be prevented or greatly reduced by the installation of space heaters or other small electric heaters.

1.7 Submittals

1.7.1 Proposal: Catalog cut sheets and/or data sheets describing the proposed equipment shall be submitted with the proposal. A users listing shall be available upon request giving company names, locations, and systems installed. All deviations from this specification shall be listed and included with the proposal.

1.7.2 Receipt of Order: A minimum of two sets of installation drawings showing outline dimensions, weights, connections, and a one-line diagram of the RFC shall be sent to the purchaser to be used in planning the installation of the system.

1.7.3 Formal Approval: If a formal submitted approval is required for the project then the following should be requested, submitted, and approved before design/construction of the RFC commences:

  1. Equipment Installation Outline
  2. External Cabling Connection Diagram
  3. Equipment One-Line Power Diagram
  4. Equipment Elevation Drawing
  5. “Other” Site Evaluation Diagrams

1.7.4 Delivery of Equipment: As a minimum, the following shall be provided with the equipment upon its arrival to the final destination:

  1. Operation & Maintenance Manual
  2. System Installation Procedures
  3. System Operation Procedures
  4. System Troubleshooting Instructions
  5. System Maintenance Milestones
  6. Recommended Spare Parts List
  7. Final Test Report Copy

1.8 Warranty

1.8.1 The manufacturer shall state the warranty of the equipment, and in no case shall it be less than 12 months after start-up or 18 months after shipment, whichever occurs first. A warranty statement will be provided with the equipment and included as part of the overall O&M manual.


2.1 System Capacity

2.1.1 The DTS will be sized to handle any application up to 1,500kVA.

2.2 Primary & Secondary Voltage

2.2.1 The primary winding shall be DELTA, 3-wire, that is tapped for the following voltages: 480V, 400V, 415V, 380V, and 208V.

2.2.2 The secondary winding shall be WYE, 4-wire, that is tapped for the following voltages: 480/277V, 380/220V, 208/120V.

2.2.3 The DTS shall be capable of any combination of the foregoing primary and secondary voltages.

2.3 Taps

2.3.1 Taps shall be provided as follows: Two each full capacity above nominal (FCAN), and two each full capacity below nominal (FCBN) with each tap step rated at two and half percent/ Copper windings and copper bars with copper screw compression lugs will be provided as specified. AL/CU lugs are not acceptable.

2.4 Environmental 

2.4.1 The equipment shall be suitable for 220 degrees C insulation, 115 degrees C rise over 40 degrees C ambient temperature. Class “H” insulation shall be used.

2.4.2  Site Conditions:

  1. Ambient: 0° to 40°C (32° to 104°F)
  2. Humidity: 0% to 95% Non-condensing.
  3. Audible Noise: 65 dB

2.5 Shielding 

2.5.1 An electrostatic shield shall be provided between the primary and the secondary windings.  This shielding along with the grounding strap shall be terminated on a stud located on the center support leg in the center of the wiring compartment. The grounding lug (size will be comparable to the transformer power rating) shall be provided for external connection by others.

2.5.2 An optional double or triple shielded DTS can be specified depending upon “threat level” requirements.

2.6 Frequency

2.6.1 All DTS unit shall be rated for 50Hz/60Hz regardless of the kVA rating or voltage strapping utilized.

2.7 Sound Levels

2.7.1 10 to 150kVA – 50dB

2.7.2 151 to 300kVA – 55dB

2.7.3 301 to 500kVA – 60dB

2.7.4 501 to 700kVA – 62dB

2.7.5 701 to 1000kVA – 64dB

2.7.6 1001 to 1500kVA – 65dB

2.7.7 DTS cores shall be mounted to rubber vibration isolators to reduce noise levels.

2.8 Corrosion Protection

2.8.1 Protection: All exposed items such as bolts, screws, buts, washers, and other such parts shall be of approved corrosion-resistant material or shall be suitably treated to resist corrosion.

2.8.2 Corrosion Resistant Treatment: Uniform coatings of a sufficient thickness of cadmium, chromium, copper, nickel, silver, or zinc are approved corrosion-resistant treatments.

2.8.3 Dissimilar Metals: Contact between dissimilar metals, which would cause deterioration of parts by galvanic corrosion shall be avoided wherever practicable.

2.8.4 Threaded Parts: All screw threads shall be in accordance with the National Bureau of Standards Handbook H-28.

2.9 Ratings & Wire/Lug Sizes

2.9.1 10kVA – Primary: 1 each #8 AWG per phase. Secondary: 1 each #8 AWG per phase.

2.9.2 15kVA – Primary: 1 each #6 AWG per phase. Secondary: 1 each #6 AWG per phase.

2.9.3 25kVA – Primary: 1 each #2 AWG per phase. Secondary: 1 each #2 AWG per phase.

2.9.4 30kVA – Primary: 1 each #2 AWG per phase. Secondary: 1 each #2 AWG per phase.

2.9.5 45kVA – Primary: 1 each 1/0 AWG per phase. Secondary: 1 each 1/0 AWG per phase.

2.9.6 62.5kVA – Primary: 1 each 4/0 AWG per phase. Secondary: 1 each 4/0 AWG per phase.

2.9.7 100kVA – Primary: 2 each 2/0 AWG per phase. Secondary: 2 each 2/0 AWG per phase.

2.9.8 125kVA – Primary: 2 each 2/0 AWG per phase. Secondary: 2 each 2/0 AWG per phase.

2.9.9 150kVA – Primary: 2 each 350MCM per phase. Secondary: 2 each 350MCM per phase.

2.9.10 225kVA – Primary: 2 each 350MCM per phase. Secondary: 2 each 350MCM per phase.

2.9.11 250kVA – Primary: 3 each 350MCM per phase. Secondary: 3 each 350MCM per phase.

2.9.12 350kVA – Primary: 4 each 350mCM per phase. Secondary: 4 each 350MCM per phase.

2.9.13 500kVA – Primary: 4 each 500MCM per phase. Secondary: 4 each 500MCM per phase.

2.9.14 750kVA – Primary: 6 each 500MCM per phase. Secondary: 6 each 500MCM per phase.

2.9.15 1000kVA – Primary: 8 each 500MCM per phase. Secondary: 8 each 500MCM per phase.

2.9.16 1250kVA – Primary 10 each 750MCM per phase. Secondary: 10 each 750MCM per phase.

2.10 Enclosures

2.10.1 All enclosures above 25kVA rating are to have three (3) steel I-beam support legs equally spaced for floor loading. “J” or “U” nits are to be used to secure the front and rear cover plates. all enclosures are to be painted with one coat of primer and one finish coat.

2.10.2 At installation/maintenance manual and wiring diagram are to be enclosed with each unit. Also provide a red or yellow tag affixed to the front-right mounting bolt stamped “Loosen All 4 Mounting Bolts To Finger Tight Torque”.

2.11 Construction

2.11.1 Quality: All materials, parts, and components used will be new and of the highest grade. Brackets and securing hardware shall be electroplated with corrosion resistant material. Internal wiring conductors shall be combined into cables, or bundles and shall be tried securely together.

2.11.2 Design: The DTS shall use components of adequate rating to provide an expected service life of over twenty (20) years continuous duty and ten (10) years without component replacement, provided that routine maintenance procedures are carried out.

2.11.3 Experience: The manufacturer should have at least ten (10) years experience designing, constructing, and servicing isolation transformers.

2.11.4 Maintainability: No regular maintenance service operations are required except for a yearly Preventative Maintenance (PM) review. Maintenance may be done at more frequent intervals if desired.

2.11.5 System Layout: Modules and sub-assemblies shall be mounted in open construction design so that each may be easily replaced. The equipment shall be constructed so that each component can be replaced without the need for specialized tools.

2.11.6 Installation: At installations where unusual concentrations of moisture, vapors, dust, and other particles may impinge upon windings. Contaminants such as magnetic, metallic, conductive, abrasive, or chemically active materials must be avoided in the airflow by effective filtering. Materials such as dust or lint, which can accumulate and block ventilation passages, must also be filtered.

2.12 Optional Features

2.12.1 Outdoor Rated Enclosures: The DTS will be built to endure the harshest outdoor environments – sand, snow, rain, salt, etc. This enclosures will be built to NEMA 3, 3R, 4, 4X, 12…standards. For large systems (300kVA+) or “turn-key” applications the DTS can be built into an ISO container allowing for easy transportation, installation, and maintenance.


3.1 Manufacturing

3.1.1 The manufacturer shall design, build, and test the DTS. If requested by the customer, the manufacturer shall arrange shipment of the DTS to their requested destination.

3.1.2 The manufacturer shall prepare and deliver the required drawings and manuals with the equipment.

3.2 Site Preparation

3.2.1 The owner shall prepare their site for installation of the equipment.

3.2.2 The owner shall arrange for local electricians to install the equipment.

3.2.3 The DTS shall be installed in accordance with local codes and the OEM’s recommendations.

3.3 Field Service Start-up & Inspection

3.3.1 The DTS is to be checked and inspected by the field service representative from the OEM to confirm proper installation.

3.3.2 The DTS is to be started-up by the field service representative from the OEM to confirm proper operation. The OEM representative should provide commissioning, training, etc. if requested by the customer.