Powell Electrical Systems, Inc.
Guide Specification
Medium Voltage Isolated Phase Bus
1.0
2.0
General
1.1
This specification describes the electrical and mechanical requirements for metal-enclosed,
isolated phase bus duct through 38kV applications. The bus duct system described is to be suitable
for indoor and outdoor installations with nominal current ratings operating in ambient temperatures
to 40oC.
1.2
This specification covers only the general requirements of the bus duct assemblies. The specific
requirements of each assembly (plan, arrangement, components, etc.) will be shown on drawings
provided by the purchaser. These drawings will form the basis for developing the drawings to
manufacture and install.
Standards and Codes
2.1
3.0
4.0
The assemblies shall be constructed, wired and tested in accordance with all applicable sections of
the following latest listed standards and codes.
2.1.1
American National Standards Institute (ANSI IEEE-C37.23)
2.1.2
National Electric Code (NEC) (NFPA No. 70)
2.1.3
National Electrical Manufacturers Association (NEMA)
2.2
It shall be the manufacturer's responsibility to be knowledgeable of the requirements of the above
Standards and Codes. In instances where standards or codes conflict, ANSI IEEE-C37.23 shall be
the governing document.
2.3
Site Conditions
2.3.1
Ambient air temperature limits (-30oC to +40oC)
2.3.2
Altitude above sea level ______ feet.
2.3.3
Maximum wind velocity ______ miles per hour.
2.3.4
Ice load ______ pounds per square foot.
2.3.5
Snow load ______ pounds per square foot.
2.3.6
Seismic zone ______.
.
Basic Construction
3.1
The bus duct shall be of the isolated phase type with the conductor of each phase contained in its
own, separate metal housing, and with adequate air space between phases.
3.2
The bus construction shall be electrically continuous, welded, with low external flux.
3.3
End plates or shorting plates shall be welded to the enclosure to provide a continuous path for
currents in the enclosure.
3.4
Bus duct shall be designed for indoor and outdoor installations and shall be totally enclosed, nonventilated, and weather resistant.
3.5
The bus enclosure, conductor and supports shall be designed to withstand the electrical,
mechanical and thermal forces imposed by electrical tests, continuous application loads, short
circuit conditions, and shipping.
3.6
The bus system shall have provisions for both expansion and contraction to prevent damage due to
the stresses caused by temperature changes and short-circuit conditions.
Ratings (Current ratings based upon 40oC ambient)
4.1
Maximum voltage ______ V/kV rms
4.2
Basic impulse insulation level ______ kV
Publication No. 05185
02/2010 v0
©2010 Powell Industries, Inc. All rights reserved.
Page 1 of 4
Powell Electrical Systems, Inc.
Guide Specification
Medium Voltage Isolated Phase Bus
5.0
6.0
7.0
8.0
4.3
Rated frequency withstand ______ kV (1 min. dry) 60Hz
4.4
Rated continuous current ______ Amperes
4.5
Momentary withstand current ______ kA Asymmetrical
4.6
Conductor total temperature limited to 105oC for silver/tin plated surfaces or equivalent bolted bus
joints.
4.7
Enclosure total temperature limited to 80oC.
Conductors
5.1
Conductors shall be of electrical conductor (EC) grade aluminum.
5.2
The shape of the conductor shall be the manufacturer’s standard.
5.3
The bus conductor shall be sized to carry rated continuous current without exceeding the
limitations of hot-spot temperature rise as determined by the applicable standards. All bus shall be
designed for continuous operation at an ambient of 40 oC unless otherwise specified.
Bus Joints
6.1
Temperature rise of bus bar joint shall not exceed 65oC above a maximum 40oC ambient, or a total
of 105oC operating temperature.
6.2
The joints shall be welded to the maximum extent possible within shipping limitations.
6.3
Contact surfaces of bolted joints shall be silver plated.
6.4
Flexible joints shall be provided in the bus runs to accommodate relative movement due to
temperature changes or vibration. Similarly, flexible joints shall be provided at the apparatus
terminations to facilitate connections.
6.5
Bolts for bus joints shall be of non-corrosive material and shall be non-magnetic.
Conductor Support Systems
7.1
Bus conductors shall be supported within the enclosure by means of a single porcelain insulator at
each support point.
7.2
Conductor supports shall be designed and located to withstand short-circuit and momentary
currents and remain functional after short-circuit has been experienced.
7.3
At each insulator location, an inspection and servicing port will be provided which includes a
gasketed inspection cover.
Enclosures
8.1
In general, the bus enclosure shall be constructed in the form of a continuous cylinder of
electrically-conductive aluminum.
8.2
Enclosures shall be dust-tight and drip-proof for indoor service and weatherproof for outdoor
service.
8.3
Enclosures shall be of continuous design in which the enclosure lengths are welded at shipping
joints and connected together at each end.
8.4
Enclosures shall have electrical insulation at connections to generators and transformers in order
to prevent longitudinal currents from flowing through generator frames or transformer tanks.
8.5
Enclosures shall have expansion bellows to allow for temperature changes and vibration.
8.6
Removable gasketed covers shall be provided for access to all insulators, connectors, terminals,
bushings and disconnect links for inspection, maintenance and testing.
Publication No. 05185
02/2010 v0
©2010 Powell Industries, Inc. All rights reserved.
Page 2 of 4
Powell Electrical Systems, Inc.
Guide Specification
Medium Voltage Isolated Phase Bus
9.0
8.7
End plates or shorting plates shall be welded to the enclosure to provide a path for circulating
currents at equipment terminations.
8.8
The exterior of the enclosure shall be painted and finished per the manufacturer’s standard color
and standard painting procedure.
Space Heaters
9.1
10.0
Wall Entrances
10.1
11.0
12.0
13.0
14.0
Thermostatically controlled space heaters shall be provided as appropriate for the application and
as is feasible for the overall design of the bus system being furnished.
A minimum two-hour fire rated seal shall be provided where the bus penetrates any wall including
transformer fire walls.
Equipment Connections
11.1
Terminal compartments shall be furnished for enclosing the line terminals and bushings of all
primary apparatus to which the bus is to be connected.
11.2
The bus shall be designed to coordinate with the generator termination enclosure, the generator
voltage transformer and surge arrestor, the generator step-up transformer, the generator breaker,
the generator excitation transformer and the auxiliary transformer as applicable.
11.3
Equipment connections will include bolting hardware, bus adapters (where required), insulating
materials and assembly drawings.
Bus Duct Supporting Structures
12.1
Outdoor bus duct supports shall be rigid, self-supporting, galvanized steel.
12.2
The design and construction of indoor supports will be dependent on the building structure and
associated requirements and limitations of the application.
12.3
Supports shall be designed to withstand applicable site conditions which include wind velocity and
seismic requirements.
Testing
13.1
All equipment will be subjected to ANSI-C37.23 standard production tests.
13.2
Any field tests required will be performed using procedures and test criteria provided by the
manufacturer.
Documentation Requirements
14.1
Dimensioned drawings with plan, elevation, and other views necessary for clarity.
14.2
Bus termination drawings showing details of the connecting equipment (transformers, generators,
etc.).
14.3
Drawings giving location of space heaters, and diagrams indicating the applications other terminal
locations.
14.4
Installation and Operating Instructions on all of the equipment furnished.
Publication No. 05185
02/2010 v0
©2010 Powell Industries, Inc. All rights reserved.
Page 3 of 4
Powell Electrical Systems, Inc.
Guide Specification
Medium Voltage Isolated Phase Bus
For assistance regarding these specifications or with support questions, please contact Powell directly:
Powell Electrical Systems, Inc.
Delta/Unibus Division
515 Railroad Avenue
Northlake, IL 60164
708.409.1200
708.409.1211 fax
Email: info@powellind.com
Website: powellind.com
Publication No. 05185
02/2010 v0
©2010 Powell Industries, Inc. All rights reserved.
Page 4 of 4