Attachment 3 - 262214 LOW-VOLTAGE TRANSFORMERS.pdf

JUBA ELECTRICAL UPGRADE DEVELOPMENT July 13, 2020

JUBA SOUTH SUDAN Issued for Bid

LOW-VOLTAGE TRANSFORMERS SECTION 262214 - 1

SECTION 262214 - LOW-VOLTAGE

TRANSFORMERS

PART 1 - GENERAL

1.1 SUMMARY

A. This Section includes the following types of dry-type transformers rated 600 V and less, with capacities up to 1000 kVA:

1. Distribution transformers.

2. Buck-boost transformers.

3. Control and signal transformers.

B. Related Sections include the following:

1. Section 033000 “Cast-in-Place Concrete.”

2. Section 260518 “Low-Voltage Electrical Power Conductors and Cables.”

3. Section 260525 “Grounding and Bonding for Electrical Systems.”

4. [Division 26 Section on “Vibration and Seismic Controls for Electrical Systems.”]

1.2 SUBMITTALS

A. Product Data Include rated nameplate data, capacities, weights, dimensions, minimum clearances, installed devices and features, and performance for each type and size of transformer indicated.

B. Shop Drawings: Wiring and connection diagrams.

C. Source quality-control test reports.

D. Output Settings Reports: Record of tap adjustments specified in Article on ADJUSTING.

1.3 QUALITY ASSURANCE

A. Comply with the OBO Electrical Code (NFPA 70, “National Electrical Code as amended by

OBO).

1. Electrical Components, Devices, and Accessories: Listed and labeled in accordance with Chapter 1 of the OBO Electrical Code by a testing agency acceptable to

Contracting Officer/COR based upon input from OBO/PDCS/DE/EE, and marked for the intended use.

B. Comply with IEEE C 57.12.91.

LOW-VOLTAGE TRANSFORMERS SECTION 262214 - 2

C. Energy-Efficiency:

1. Comply with 10 CFR 431 (DOE 2016) efficiency levels.

2. Marked as compliant with DOE 2016 efficiency levels by an NRTL

1.4

DELIVERY, STORAGE, AND HANDLING

A. Temporary Heating: Apply temporary heat according to manufacturer's written instructions within the enclosure of each ventilated-type unit, throughout periods during which equipment is not energized and when transformer is not in a space that is continuously under normal control of temperature and humidity.

1.5

COORDINATION

A. Coordinate size and location of concrete bases. Cast anchor-bolt inserts into bases. Concrete, reinforcement, and formwork requirements are specified in Section 033000 “Cast-in-Place

Concrete.”

B. Coordinate installation of wall-mounting and structure-hanging supports.

C. Lightning and Surge Protection:

1. Main transformers serving the Post buildings shall have distribution class lightning arresters on the primary side and surge protectors on the secondary side of the transformer.

2. Provide surge protection at the service entrance to each building.

PART 2 - PRODUCTS

2.1 MATERIALS

A. Source Limitations: Obtain each transformer type from single source from single manufacturer.

B. Description: Factory-assembled and -tested, air-cooled units for 50 or 60-Hz service.

C. Cores: Grain-oriented, non-aging silicon steel.

D. Coils: Continuous windings without splices, except for taps.

1. Internal Coil Connections: Brazed or pressure type.

2. Coil Material: Copper.

LOW-VOLTAGE TRANSFORMERS SECTION 262214 - 3

2.2 TRANSFORMERS, GENERAL

A. Transformers: Provide a minimum of 20 percent spare capacity above demand load without requiring fan cooling.

B. Utility (Service) Transformers: Provide either oil filled or encapsulated dry type pad mounted outdoor type incoming commercial service transformers. Prove the transformer with a delta connected primary and a grounded wye connected secondary. The transformer shall be capable of being easily replaced or repaired by the local utility company. Provide encapsulated dry type transformers where there are known problems with PCB contamination in locally available mineral oil.

2.3 DISTRIBUTION TRANSFORMERS

A. Distribution Transformers: Locate distribution transformers adjacent to their associated panel and be sized with 20 percent reserve capacity. Transformers shall be specified with two 2.5 percent FCAN (full capacity above normal) and two 2.5 percent FCBN (full capacity below normal) taps. The transformers shall be indoor, dry, heavy-duty type in NEMA-1 enclosures unless otherwise required. Transformers serving loads with high harmonic content (non-linear loads) shall be K-factor rated to compensate for these effects.

B. Comply with NEMA ST 20, and list and label as complying with UL 1561.

C. [Provide transformers that are internally braced to withstand seismic forces specified in

Division 26 Section on "Vibration and Seismic Controls for Electrical Systems."]

D. Cores: Electrical grade, non-aging silicon steel with high permeability and low hysteresis losses: One leg per phase.

E. Coils: Continuous windings without splices except for taps.

1. Coil Material: Copper.

2. Internal Coil Connections: Brazed or pressure type.

3. Terminal Connections: Welded.

F. Enclosure:

1. NEMA 250, Type 2: Core and coil shall be encapsulated within resin compound to seal out moisture and air.

2. KVA Ratings: Based on convection cooling only and not relying on auxiliary fans.

Wiring Compartment: Sized for conduit entry and wiring installation.

3. Finish: Comply with NEMA 250.

G. Wiring Compartment: Sized for conduit entry and wiring installation.

H. Encapsulation: Transformers smaller than 30 kVA shall have core and coils completely resin encapsulated.

LOW-VOLTAGE TRANSFORMERS SECTION 262214 - 4

I. Indoor Transformer Enclosure Finish: Comply with NEMA 250 for “Indoor Corrosion

Protection.”

1. Finish Color: ANSI 61 gray.

J. Insulation Class: 220 deg C, UL-component-recognized insulation system with a maximum of

150 deg C rise above 50 deg C ambient temperature.

K. Taps for Transformers:

1. Transformers Smaller than 3 kVA: One 5 percent tap above normal full capacity.

2. Transformers 7.5 to 24 kVA: One 5 percent tap above and one 5 percent tap below normal full capacity voltage.

3. Transformers 25 kVA and Larger: Two 2.5 percent taps above and four 2.5 percent taps below normal full capacity.

L. Grounding: Provide ground-bar kit or a ground bar installed on the inside of the transformer enclosure.

M. K-Factor Rating: Transformers indicated to be K-factor rated shall comply with UL 1561 requirements for nonsinusoidal load current-handling capability to the degree defined by designated K-factor.

1. Unit shall not overheat when carrying full-load current with harmonic distortion corresponding to designated K-factor.

2. Indicate value of K-factor on transformer nameplate.

3. Neutral: Rated 200 percent of full load current for K-factor-rated transformers.

N. Electrostatic Shielding: Each winding shall have an independent, single, full-width copper electrostatic shield arranged to minimize interwinding capacitance.

1. Arrange coil leads and terminal strips to minimize capacitive coupling between input and output terminals.

2. Include special terminal for grounding the shield.

3. Shield Effectiveness:

a. Capacitance between Primary and Secondary Windings: Not to exceed 33 picofarads over a frequency range of 20 Hz to 1 MHz.

b. Common-Mode Noise Attenuation: Minus 120 dBA minimum at 0.5 to 1.5 kHz;

minus 65 dBA minimum at 1.5 to 100 kHz.

c. Normal-Mode Noise Attenuation: Minus 52 dBA minimum at 1.5 to 10 kHz.

O. Wall Brackets: Manufacturer's standard brackets.

P. [Fungus Proofing: Permanent fungicidal treatment for coil and core.]

Q. Low-Sound-Level Requirements: Maximum sound levels, when factory tested according to

IEEE C57.12.91, as follows:

LOW-VOLTAGE TRANSFORMERS SECTION 262214 - 5

1. 9.00 kVA and Less: [40] <Insert value> dBA.

2. 9.01 to 30.00 kVA: [45] <Insert value> dBA.

3. 30.01 to 50.00 kVA: [45 dBA for K-factors of 1, 4, and 9] [48 dBA for K-factors of 13 and 20] <Insert dBA>.

4. 50.01 to 150.00 kVA: [50 dBA for K-factors of 1, 4, and 9] [53 dBA for K-factors of

13 and 20] <Insert dBA>.

5. 150.01 to 300.00 kVA: [55 dBA for K-factors of 1, 4, and 9] dBA.

2.4 BUCK-BOOST TRANSFORMERS

A. Description: Self-cooled, two-winding dry type, rated for continuous duty and with wiring terminals suitable for connection as autotransformer. Transformers shall comply with

NEMA ST 20 and shall be listed and labeled as complying with UL 506 or UL 1561.

B. Enclosure: Ventilated, NEMA 250, Type 2.

1. Finish Color: ANSI 61 gray.

2.5 CONTROL AND SIGNAL TRANSFORMERS

A. Description: Self-cooled, two-winding dry type, rated for continuous duty, complying with

NEMA ST 20, and listed and labeled as complying with UL 506.

B. Ratings: Continuous duty. If rating is not indicated, provide at least 50 percent spare capacity above connected peak load.

2.6 SOURCE QUALITY CONTROL

A. Test and inspect transformers according to IEEE C57.12.01 and IEEE C57.12.91.

1. Resistance measurements of all windings at rated voltage connections and at all tap connections.

2. Ratio tests at rated voltage connections and at all tap connections.

3. Phase relation and polarity tests at rated voltage connections.

4. No load losses, and excitation current and rated voltage at rated voltage connections.

5. Impedance and load losses at rated current and rated frequency at rated voltage connections.

6. Applied and induced tensile tests.

7. Regulation and efficiency at rated load and voltage.

8. Insulation-Resistance Tests:

a. High-voltage to ground.

b. Low-voltage to ground.

c. High-voltage to low-voltage.

9. Temperature tests.

LOW-VOLTAGE TRANSFORMERS SECTION 262214 - 6

B. Factory Sound-Level Tests: Conduct sound-level tests on equipment for this Project.

PART 3 - EXECUTION

3.1 EXAMINATION

A. Examine conditions for compliance with enclosure- and ambient-temperature requirements for each transformer.

B. Verify that field measurements are as needed to maintain working clearances required by

NFPA 70 and manufacturer's written instructions.

C. Examine walls and floors for suitable mounting conditions where transformers will be installed.

D. Verify that ground connections are in place and requirements in Section 260526 "Grounding and Bonding for Electrical Systems" have been met. Maximum ground resistance shall be 5 ohms at location of transformer.

E. Proceed with installation only after unsatisfactory conditions have been corrected.

3.2

INSTALLATION

A. Install wall-mounting transformers level and plumb with wall brackets fabricated by transformer manufacturer.

1. [Brace wall-mounting transformers as specified in Division 26 Section on "Vibration and Seismic Controls for Electrical Systems."]

B. Install floor-mounting transformers level on concrete bases. Construct concrete bases of dimensions indicated, but not less than 100 mm larger in both directions than supported unit and

100 mm high.

1. [Anchor transformers to concrete bases according to manufacturer's written instructions, seismic codes at Project, and requirements in Division 26 Section on

"Vibration and Seismic Controls for Electrical Systems."]

C. Secure transformer to concrete base according to manufacturer's written instructions.

D. Secure covers to enclosure and tighten all bolts to manufacturer-recommended torques to reduce noise generation.

E. Remove shipping bolts, blocking, and wedges.

LOW-VOLTAGE TRANSFORMERS SECTION 262214 - 7

3.3 CONNECTIONS

A. Ground equipment according to Section 260525 "Grounding and Bonding for Electrical

Systems."

B. Connect wiring according to Section 260518 "Low-Voltage Electrical Power Conductors and

Cables."

C. Tighten electrical connectors and terminals according to manufacturer's published torque-tightening values. If manufacturer's torque values are not indicated, use those specified in

UL 486A and UL 486B.

D. Provide flexible connections at all conduit and conductor terminations and supports to eliminate sound and vibration transmission to the building structure

3.4

ADJUSTING

A. Record transformer secondary voltage at each unit for at least 48 hours of typical occupancy period. Adjust transformer taps to provide optimum voltage conditions at secondary terminals.

Optimum is defined as not exceeding nameplate voltage plus 10 percent and not being lower than nameplate voltage minus 5 percent. Submit recording and tap settings as test results.

B. Adjust buck-boost transformers to provide nameplate voltage of equipment being served, plus or minus 5 percent, at secondary terminals.

C. Output Settings Report: Prepare a written report recording output voltages and tap settings.

3.5

CLEANING

A. Vacuum dirt and debris; do not use compressed air to assist in cleaning.

END OF SECTION 262214