Quantcast Design Guidance for Electrical Power Systems Serving Nonlinear Harmonic Loads

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DEPARTMENT OF THE NAVY
NAVAL
FACILITIES
ENGINEERING
COMMAND
200 STOVALL STREET
ALEXANDRIA.
VA
22332.2300
IN REPLY REFER TO
04Al/CMM
27 Jan 1992
Design Policy Letter DPL-92-0001
FROM:
Commander, Naval Facilities Engineering Command
Subj:
DESIGN GUIDANCE FOR ELECTRICAL POWER SYSTEMS SERVING
NONLINEAR HARMONIC LOADS
Ref:
(a) Federal Construction Council Report No. 112, dtd 1 Nov 91
1.  Purpose :  To provide design guidance for electrical power systems serving
large concentrations of personal computers and industrial loads. This
guidance applies to all facilities where the estimated harmonic load exceeds
15 to 20 percent of the total building electrical load.
2 .  Background:  The majority of new government facilities and retrofit design
project8 will Include upgraded Electrical Utility Services for personal
computers, automatic data processing systems, electronic office equipment,
electronic ballasts, and solid state motor control equipment which may
contain switching mode power supplies.
This equipment, when connected to conventional building wiring systems,
can create overheating of transformers, generators, motors, and the
interconnected building wiring system.  The excessive neutral currents are the
result of harmonic currents within the office equipment switching mode power
supplies.  The resulting overtemperature conditions may damage the insulation
within transformers, motors, generator8 and cable systems. Reference (a),
recently issued by the Federal Construction Council, provide8 additional
information and references.
3 .  Policy Statement:  It is Naval Facilities Engineering Command
(NAVFACENGCOM) policy to use the following design practice8 when designing
electrical distribution systems for facilities which must accommodate
nonlinear and harmonic loads. Typical facilities Include communications
center8 laboratories, data processing and administrative building8 with
15 to 20 per cent of connected harmonic load.
(a) Electrical Design Analysis Shall include a calculation of estimated
nonlinear loads.
(b) Transformers shall he selected using procedure8 outlined in ANSI
C57.lll-1986.  This standard provide8 a simple calculation method for
determining derating factors for low voltage, dry type distribution
transformers.  Electrical Designers should consider using "K" rated
transformers which are rated for 220 degree centigrade maximum hot spot
temperature operation. This design procedure will ensure that the
transformer life expectancy will not be reduced when connected to
nonlinear loads.
APPENDIX X





 


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