1、_ SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising there
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4、0 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/AIR5387 AEROSPACE INFORMATION REPORT AIR5387 Issued 1999-08 Reaffirmed 2015-09 Ai
5、rport Electrical Power System Harmonics RATIONALE AIR5387 has been reaffirmed to comply with the SAE five-year review policy. INTRODUCTIONQuality of the airport electrical power is receiving increased attention due to the increased use of critical equipment such as computers and other equipment that
6、 demand high quality power. Much of the new equipment being installed today in airports causes harmonic distortion of the electrical power. At the same time, other new equipment being installed requires electrical power with little or no harmonic distortion. This document will explore the polluting
7、effects of certain electrical equipment that degrade power quality and suggest some solutions. Poor power quality manifests itself in many ways:a. Overheated neutral conductors, transformers, and other electrical distribution equipment that can bring on premature failures.b. High voltage distortion.
8、c. Neutral to ground voltage.d. Poor power factor.In extreme cases, poor power quality can be a direct contributor to subsequent problems with equipment such as:a. Computer operational problems.b. Hardware component failures and reduced equipment life expectancy.c. Motor burnouts.d. Generator voltag
9、e regulation and frequency control problems.e. Uninterrupted power supply (UPS) and generator overheating.f. Failure of power factor (PF) correction capacitors.In nearly every case, the loads themselves, not the supply, produce the voltage distortion found in the electrical distribution system. Norm
10、ally the generators that are found in utility companies, as well as those in use for stand-by power around airports, all produce clean, high quality sinusoidal AC power. Alternating current (AC) in its purest form, follows a sine wave as it alternates 50 or 60 times per second (50 or 60 Hz) (see Fig
11、ure 1).FIGURE 1 - Effect of Third Harmonic on a Sine WaveSAE INTERNATIONAL AIR5387 2 OF 81. SCOPE:This SAE Aerospace Information Report (AIR) is intended to cover all airport 50 or 60 Hz electrical systems as well as all electrical utilization equipment that is attached to those systems.1.1 Purpose:
12、This document is intended to instruct users about electrical power system problems caused by harmonic distortion of the electrical current. This distortion is generated by certain pieces of electrical utilization equipment commonly found in use on airports.2. REFERENCES:2.1 A. H. (Tony) Hoevenaars,
13、P.E., Taming the Rogue Wave: Techniques for Reducing Harmonic Distortion, EC&M, June 1997.2.2 Thomas Landers, P.E., Are Harmonics Overheating Your Neutrals and Panel Boards?, Power Quality Assurance, September/October 1997.2.3 Marina Dishel, P.E. and John R. Nasto, P.E., Meeting IEEE 519 THD Limitat
14、ions: A Case Study, EC&M, December 1997.2.4 Richard Redl, Paolo Tenti, J. Daan Van Wyk, Power Electronics Polluting Effects, IEEE Spectrum, May 1997.2.5 IEEE-519-1992 Recommended Practices and Requirements for Harmonic Control on Electrical Power Systems.2.6 IEC 1000 3-2 Limits for harmonic current
15、emissions (equipment input current 16 A per phase).3. ORIGIN OF POLLUTION:3.1 More of the electrical equipment in use today is nonlinear, meaning it consumes current in a nonsinusoidal manner. According to Ohms Law, when a voltage is applied across an impedance, current will flow that is equal to th
16、e voltage divided by the impedance. Until recently, electrical loads were essentially linear, offering constant impedance that caused little fluctuation to the current flow. This meant that the current flow through the electrical power system was essentially a continuous unpolluted 50 or 60 Hz sinus
17、oidal wave. Nonlinear electrical loads are placed on the system by much of todays energy saving equipment such as:3.1.1 Adjustable speed drives.3.1.2 Battery chargers.3.1.3 Computer and other electronic equipment power supplies.SAE INTERNATIONAL AIR5387 3 OF 83.1.4 400 Hz solid state frequency conve
18、rter type ground power units.3.1.5 Electronic lighting ballasts.3.2 Power electronics experts estimate that about 50 to 60% of the electrical power in industrialized countries is flowing through some kind of power electronic system, and the percentage is growing. This equipment cycles on and off sud
19、denly within each cycle of line voltage, so that it continuously varies the amount of current it draws from the electrical power system. Impedance is no longer a constant in a nonlinear load, but instead, varies during each sine wave of the current flow. This creates distortions to the current, whic
20、h are often multiples, usually odd multiples (3, 5, 7, etc.), of the fundamental 50 or 60 Hz sinusoidal wave of the current. For example, if the fundamental frequency is 60 Hz, the 3rd harmonic is 180 Hz and the 5th harmonic is 300 Hz, etc. These nonlinear currents, called harmonics, can adversely a
21、ffect the flow of current and the quality of power being delivered throughout the airport electrical system designed for 50 or 60 Hz sinusoidal power (see Figure 1).3.3 Uncorrected 6-pulse diode rectifier circuits, such as found in many battery chargers and solid state frequency converters, produce
22、approximately 40% harmonic current at full load. If the rectifiers in these pieces of equipment are silicon controlled rectifiers (SCR) their harmonic current can exceed 60% of the fundamental.3.4 Severe problems caused by harmonics begin to occur as nonlinear loads on an electrical power distributi
23、on system approach 20 to 30% of the facilitys total load.4. MEASUREMENT OF HARMONIC DISTORTION OF VOLTAGE AND CURRENT:4.1 Total harmonic distortion (THD) of the current drawn by one or more pieces of electrical equipment is usually expressed as a percentage of the fundamental current. THD is calcula
24、ted as the square root of the sum of the squared values of each of the harmonic currents (known as root-mean-squared or RMS) divided by the fundamental current. The relationship, is:(Eq. 1)4.2 As the harmonic currents pass through the systems line and load impedances they produce voltage drops at ea
25、ch harmonic frequency in relation to Ohms Law. The voltage drops appear as harmonic voltages and the accumulation of these voltages at all of the harmonic frequencies produces the voltage distortion. The relationship, total harmonic distortion (THD) of the voltage is:(Eq. 2)Special instrumentation i
26、s required to measure harmonic currents and voltages.IthdI32+ I52+ + Ih2I1=VthdV32+ V52+ + Vh2V1=SAE INTERNATIONAL AIR5387 4 OF 84.3 It is not uncommon to find electrical equipment being used in airports today that have harmonic current levels of 30 to 40% of the fundamental current. If this equipme
27、nt constitutes a sizable portion of the total loading on the electrical distribution system, it may cause any or all of the problems noted in the Introduction.5. ALLOWABLE CURRENT DISTORTION IN RELATION TO DEMAND LOAD CURRENT FOR GENERAL DISTRIBUTION SYSTEMS (120 V TO 69 kV):5.1 IEEE-519-1992 Recomm
28、ended Practices and Requirements for Harmonic Control on Electrical Power Systems sets limits for allowable current distortion caused by a piece of electrical equipment drawing power from an electrical power system (see Table 1).NOTE: The point of common coupling (PCC) is the point at which a nonlin
29、ear load is connected to a source that also serves other adjacent loads. The PCC is usually the point where the nonlinear load feeder leaves a bus energized by a power source.IEC 1000-3-2, Limits for Harmonic Current Emissions, also sets limits for the amount of distortion that can be caused by a pi
30、ece of electrical equipment drawing 16 A per phase from an electrical power system.TABLE 1 - Allowable Current Distortion per IEEE 519-1992Harmonic, nMaximum AllowableOdd-HarmonicCurrent Distortion,Isc/ILas aPercentage1100011 4.0 7.0 10.0 12.0 15.011n17 2.0 3.5 4.5 5.5 7.017n23 1.5 2.5 4.0 5.0 6.023
31、n35 0.6 1.0 1.5 2.0 2.535n 0.3 0.5 0.7 1.0 1.4Total demanddistortion25 8 12 15 20.01Iscis the short-circuit current available at the point of common coupling.ILis the fundamental value of load current during maximum demand.2Total harmonic distortion of the maximum demand load current averaged over 1
32、5 to 30 min.3No power generation equipment may exceed these values of current distortion regardless of the acual value of Isc/I1.SAE INTERNATIONAL AIR5387 5 OF 85.1 (Continued):Class A: Balanced three phase equipment and all other equipment, except that stated in one of the following classes.Class B
33、: Portable tools.Class C: Lighting equipment, including dimming devices.Class D: Equipment having an input current with a “special wave shape” as defined in IEC 1000-3-2 and an active input power , P600W, measured under the test conditions given in IEC 1000-3-2.TABLE 2 - Limits for Class A Equipment
34、 per IEC 1000-3-2TABLE 2A - Odd HarmonicsHarmonic OrdernMaximum PermissibleHarmonic CurrentA3 2.305 1.147 0.779 0.4011 0.3313 0.2115 n 39 0.15 15/nTABLE 2B - Even HarmonicsHarmonic OrdernMaximum PermissibleHarmonic CurrentA21.084043608 n 40 0.23 8/nSAE INTERNATIONAL AIR5387 6 OF 86. EFFECT OF HARMON
35、IC DISTORTION ON POWER FACTOR:6.1 Harmonic currents, especially those produced by equipment using SCR rectification, are often out of phase with the fundamental current drawn by the equipment. The resultant current is then out of phase with the voltage and this causes low power factor. Using equipme
36、nt that produces excessive current harmonics may result in higher power bills if its electrical utility company charges the airport a lagging power factor penalty.7. HARMONIC DISTORTION SOLUTIONS:7.1 A variety of techniques can be used to solve harmonic problems. Often the best and most cost effecti
37、ve solution is found by using a combination of techniques.7.1.1 Installing neutral conductors having 30 to 40% higher ampacity than the phase conductors can solve neutral conductor overheating.7.1.2 Zigzag or phase shifting transformers are sometimes used to reduce or eliminate harmonic currents.7.1
38、.3 Oversized transformers and generators can be used to increase an electrical systems thermal capacity. If the nonlinear load is less than 15% of the total load on an electrical system, it is less likely that harmonic currents produced by the nonlinear loads will cause problems.7.1.4 K-rated transf
39、ormers should be used for high levels of nonlinear loads. However, while K-rated transformers address the higher neutral current in the secondary winding and increased eddy current losses due to higher frequencies, they do not address certain other problems. They do not address the higher temperatur
40、e created on the primary winding of a delta-wye transformer by certain circulating currents and, therefore, the transformer may need to be de-rated to 75 to 80% of its rating. K-rated transformers, when properly applied, can handle higher currents caused by high THD, however, they do not reduce the
41、higher currents caused by THD.7.1.5 Delta-wye transformers can be installed between the harmonic creating electrical equipment and the other part of the facilitys electrical system to keep the unwanted triplen (3rd, 9th, etc.) harmonics from propagating into other parts of the system. This technique
42、 can enable a cluster of nonlinear load type equipment to draw only fundamental current from the power source, canceling the harmonics and enabling the system to maintain consistent voltage to current relationships.7.1.6 Wire routing should also be considered. If wires to nonlinear loads are in clos
43、e proximity to wires feeding sensitive loads, such as in the same wire trough, the higher harmonic currents can be electromagnetically coupled into the sensitive wiring.7.1.7 12-pulse or 18-pulse rectifiers can be used in the utilization equipment instead of 6-pulse rectifiers to reduce THD.7.1.8 Pa
44、ssive or active filters can be used to reduce THD.SAE INTERNATIONAL AIR5387 7 OF 87.1.9 Many vendors of new electrical equipment can now offer harmonic correction as an option or standard feature on their equipment.7.2 Before any of these solutions are implemented, the entire distribution system sho
45、uld be reviewed to determine the best solution for the site. Choosing the wrong solution could introduce new problems and the wrong combination of solutions can be disastrous.8. CONCLUSION:8.1 Harmonic currents can cause many problems in airport electrical power distribution systems and sensitive el
46、ectrical equipment. Care in selecting the equipment and care in designing the power system feeding this equipment will prevent such problems.PREPARED BY SAE SUBCOMMITTEE AGE-2C, VEHICLE MAINTENANCE AND AIRCRAFT SERVICING OF COMMITTEE AGE-2, AIR CARGO AND AIRCRAFT GROUND EQUIPMENT & SYSTEMSSAE INTERNATIONAL AIR5387 8 OF 8
