ASTM F2490-05(2013)
(Guide)Standard Guide for Aircraft Electrical Load and Power Source Capacity Analysis
Standard Guide for Aircraft Electrical Load and Power Source Capacity Analysis
SIGNIFICANCE AND USE
4.1 To show compliance with 14 CFR 23.1351, you must determine the electrical system capacity.
4.2 14 CFR 23.1351(a)(2) states that:
4.2.1 For normal, utility, and acrobatic category airplanes, by an electrical load analysis or by electrical measurements that account for the electrical loads applied to the electrical system in probable combinations and for probable durations; and
4.2.2 For commuter category airplanes, by an electrical load analysis that accounts for the electrical loads applied to the electrical system in probable combinations and for probable durations.
4.3 The primary purpose of the electrical load analysis (ELA) is to determine electrical system capacity (including generating sources, converters, contactors, bus bars, and so forth) needed to supply the worst-case combinations of electrical loads. This is achieved by evaluating the average demand and maximum demands under all applicable flight conditions. A summary can then be used to relate the ELA to the system capacity and can establish the adequacy of the power sources under normal, abnormal, and emergency conditions.Note 1—The ELA should be maintained throughout the life of the aircraft to record changes to the electrical system, which may add or remove electrical loads to the system.
4.4 The ELA that is produced for aircraft-type certification should be used as the baseline document for any subsequent changes. When possible, the basic format of the original ELA should be followed to ensure consistency in the methodology and approach.
4.5 The original ELA may be lacking in certain information, for instance, time available on emergency battery. It may be necessary to update the ELA using the guidance material contained in this guide.
SCOPE
1.1 This guide covers how to prepare an electrical load analysis (ELA) to meet Federal Aviation Administration (FAA) requirements.
1.2 The values given in SI units are to be regarded as the standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: F2490 − 05 (Reapproved 2013)
Standard Guide for
Aircraft Electrical Load and Power Source Capacity
Analysis
This standard is issued under the fixed designation F2490; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
3.1 Definitions of Terms Specific to This Standard:
1.1 This guide covers how to prepare an electrical load
analysis(ELA)tomeetFederalAviationAdministration(FAA)
3.1.1 abnormal electrical power operation (or abnormal
requirements. operation), n—occurs when a malfunction or failure in the
electric system has taken place and the protective devices of
1.2 The values given in SI units are to be regarded as the
the system are operating to remove the malfunction or failure
standard.
fromtheremainderofthesystembeforethelimitsofabnormal
1.3 This standard does not purport to address all of the
operation are exceeded.
safety concerns, if any, associated with its use. It is the
3.1.1.1 Discussion—The power source may operate in a
responsibility of the user of this standard to establish appro-
degraded mode on a continuous basis when the power charac-
priate safety and health practices and determine the applica-
teristics supplied to the using equipment exceed normal opera-
bility of regulatory limitations prior to use.
tionlimitsbutremainwithinthelimitsforabnormaloperation.
3.1.2 alternate source, n—secondpowersourcethatmaybe
2. Referenced Documents
used instead of the normal source, usually on failure of the
2.1 FAA Aeronautics and Space Airworthiness Standards: normal source.
14 CFR 23.1309Normal, Utility, Acrobatic, and Commuter
3.1.2.1 Discussion—The use of alternate sources creates a
Category Airplanes—Equipment, Systems, and Installa-
new load and power configuration and, therefore, a new
tions
electrical system that may require separate source capacity
14 CFR 23.1351Normal, Utility, Acrobatic, and Commuter
analysis.
Category Airplanes—General
3.1.3 cruise, n—condition during which the aircraft is in
14 CFR 23.1353Normal, Utility, Acrobatic, and Commuter
level flight.
Category Airplanes—Storage Battery Design and Instal-
lation 3.1.4 electrical source, n—electrical equipment that
14 CFR 23.1419Normal, Utility, Acrobatic, and Commuter produces, converts, or transforms electrical power.
Category Airplanes—Ice Protection
3.1.5 electrical system, n—consists of an electrical power
14 CFR 23.1529Normal, Utility, Acrobatic, and Commuter
source, the electrical wiring interconnection system, and the
Category Airplanes—Instructions for Continued Airwor-
electrical load(s) connected to that system.
thiness
3.1.6 emergency electrical power operation (or emergency
14 CFR 91General Operating and Flight Rules
operation), n—condition that occurs following a loss of all
14 CFR 135.163Operating Requirements: Commuter and
normalelectricalgeneratingpowersourcesoranothermalfunc-
On Demand Operations and Rules Governing Persons on
tion that results in operation on standby power (batteries or
Board Such Aircraft—Equipment Requirements: Aircraft
other emergency generating source such as an auxiliary power
Carrying Passengers under IFR
unit (APU) or ram air turbine (RAT)) only, or both).
3.1.7 ground operation and loading, n—time spent in pre-
paring the aircraft before the aircraft engine starts.
This guide is under the jurisdiction of ASTM Committee F39 on Aircraft
Systems and is the direct responsibility of Subcommittee F39.01 on Design,
3.1.7.1 Discussion—During this period, the APU, internal
Alteration, and Certification of Electrical Systems.
batteries,oranexternalpowersourcesupplieselectricalpower.
Current edition approved July 1, 2013. Published September 2013. Originally
ε1
approved in 2005. Last previous edition approved in 2005 as F2490–05 . DOI:
3.1.8 landing, n—condition starting with the operation of
10.1520/F2490-05R13.
navigational and indication equipment specific to the landing
AvailablefromU.S.GovernmentPrintingOfficeSuperintendentofDocuments,
732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401. approach and following until the completion of the rollout.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2490 − 05 (2013)
3.1.9 nominalrating,n—thisratingofaunitpowersourceis 5. Basic Principles
its nameplate rating and is usually a continuous duty rating for
5.1 Aloadanalysisisessentiallyasummationoftheelectric
specified operating conditions.
loadsappliedtotheelectricalsystemduringspecifiedoperating
3.1.10 normal ambient conditions, n—typical operating
conditions of the aircraft. The ELArequires the listing of each
conditions such as temperature and pressure as defined by the
item or circuit of electrically powered equipment and the
manufacturer’s technical documentation.
associated power requirement. Note that the power require-
ment for an item may have several values, depending on the
3.1.11 normal electrical power operation (or normal opera-
utilization for each phase of aircraft operation.
tion) , n—assumesthatalltheavailableelectricalpowersystem
is functioning correctly with no failures or within the Master
5.2 To arrive at an overall evaluation of electrical power
Minimum Equipment List (MMEL) limitations, if a MMEL
requirement, it is necessary to give adequate consideration to
has been approved (for example, direct current (DC)
transient demand requirements, which are of orders of magni-
generators,transformerrectifierunits,inverters,mainbatteries,
tude or duration to impair system voltage or frequency
APU, and so forth).
stability, or both, or to exceed short-time ratings of power
sources, that is, intermittent/momentary and cyclic loads. This
3.1.12 normal source, n—provides electrical power
is essential, since the ultimate use of an aircraft’s ELA is for
throughout the routine aircraft operation.
the proper selection of characteristics and capacity of power-
3.1.13 takeoff and climb, n—condition starting with the
source components and the resulting assurance of satisfactory
takeoff run and ending with the aircraft leveled off and set for
performance of equipment under normal, abnormal, and emer-
cruising.
gency operating power conditions.
3.1.14 taxi, n—condition from the aircraft’s first movement
5.3 A large majority of general aviation aircraft uses only
under its own power to the start of the takeoff run and from
DCpower.IfanaircraftalsousesACpower,theELAwillhave
completion of landing rollout to engine shutdown.
to include the AC loads as well.
4. Significance and Use
6. Procedure for Preparation of Electrical Load Analysis
4.1 To show compliance with 14 CFR 23.1351, you must
6.1 Content—The load and power source capacity analysis
determine the electrical system capacity.
report should include the following sections:
4.2 14 CFR 23.1351(a)(2) states that: 6.1.1 Introduction,
6.1.2 Assumptions and Criteria,
4.2.1 For normal, utility, and acrobatic category airplanes,
by an electrical load analysis or by electrical measurements 6.1.3 Load Analysis—Tabulation of Values,
6.1.4 Emergency and Standby Power Operation, and
that account for the electrical loads applied to the electrical
system in probable combinations and for probable durations; 6.1.5 Summary and Conclusions.
and
6.2 Introduction:
4.2.2 Forcommutercategoryairplanes,byanelectricalload
6.2.1 The introduction to the ELA report should include
analysis that accounts for the electrical loads applied to the
informationtoassistthereaderinunderstandingthefunctionof
electrical system in probable combinations and for probable
the electrical system with respect to the operational phases of
durations.
the aircraft.
6.2.2 Typically, the introduction to the ELAshould contain
4.3 The primary purpose of the electrical load analysis
the following:
(ELA) is to determine electrical system capacity (including
6.2.2.1 Brief description of aircraft type, which may also
generating sources, converters, contactors, bus bars, and so
include the expected operating role for the aircraft;
forth) needed to supply the worst-case combinations of elec-
6.2.2.2 Electricalsystemoperation,whichdescribesnormal,
tricalloads.Thisisachievedbyevaluatingtheaveragedemand
abnormal, and emergency operations, bus configuration with
and maximum demands under all applicable flight conditions.
circuit breakers, and connected loads for each bus. A copy of
A summary can then be used to relate the ELA to the system
the bus wiring diagram or electrical schematic should also be
capacity and can establish the adequacy of the power sources
included in the report;
under normal, abnormal, and emergency conditions.
NOTE 1—The ELA should be maintained throughout the life of the 6.2.2.3 Generator, alternator, and other power source de-
aircraft to record changes to the electrical system, which may add or
scription and related data (including such items as battery
remove electrical loads to the system.
discharge curves, inverter, emergency battery, and so forth).
4.4 The ELA that is produced for aircraft-type certification Typical data supplied for power sources would be as shown in
should be used as the baseline document for any subsequent
Table 1;
changes. When possible, the basic format of the original ELA 6.2.2.4 Operating logic of system (for example, automatic
should be followed to ensure consistency in the methodology
switching, loading shedding, and so forth); and
and approach. 6.2.2.5 List of installed equipment.
4.5 TheoriginalELAmaybelackingincertaininformation, 6.3 Assumptions and Criteria—All assumptions and design
for instance, time available on emergency battery. It may be criteria used for the analysis should be stated in this section of
necessary to update the ELA using the guidance material the ELA. For example, typical assumptions for the analysis
contained in this guide. may be identified as follows:
F2490 − 05 (2013)
TABLE 1 Typical Data for Power Sources
certification of the airplane and should include calculations
Identification 1 2 3 appropriatetothesecases.AllMMELitemsmustbeaccounted
Item DC Generator Inverter Battery
for in the load analysis to ensure that the electrical system
Number of units 2 1 1 capacity is not exceeded when all items are functional.
Continuous rating 250 A 300 VA (total) 35 Ah
6.4.1.5 Circuit Breaker—Identify each circuit breaker by
(Nameplate) . . . . . . . . .
5-s rating 400 A . . . . . . circuit name or identification number.
2-min rating 300 A . . . . . .
6.4.1.6 Load at Circuit Breaker—The ampere loading for
Voltage 30 V 115 VAC 24 VDC
Frequency . . . 400 Hz . . . each circuit.
Power factor . . . 0.8 . . .
6.4.1.7 Operating Time:
Manufacturer ABC XYZ ABC
(1)The operating time is usually expressed as a period of
Model number 123 456 789
Voltage regulation ±0.6 V ±2 % . . .
time (seconds/minutes) or may be continuous, as appropriate.
Frequency regulation . . . 400 Hz ± 1 % . . .
Equipment operating time is often related to the average
operatingtimeoftheaircraft.Ifthe“on”timeoftheequipment
is the same or close to the average operating time of the
6.3.1 Most severe loading conditions and operational envi-
aircraft, then it could be considered that the equipment is
ronment in which the airplane will be expected to operate are
operating continuously for all flight phases.
assumed to be night and in icing conditions;
(2)In such cases in which suitable provisions have been
6.3.2 Momentary/intermittent loads, such as electrically op-
made to ensure that certain loads cannot operate
erated valves, that open and close in a few seconds are not
simultaneously, or there is reason for assuming certain combi-
included in the calculations;
nations of load will not occur, appropriate allowances may be
6.3.3 Motor load demands are shown for steady-state op-
made. Adequate explanation should be given in the summary.
eration and do not include starting inrush power. The overload
(3)In some instances, it may be useful to tabulate the data
ratingsofthepowersourcesshouldbeshowntobeadequateto
using a specified range for equipment operating times, such as
provide motor starting inrush requirements;
follows:
6.3.4 Intermittent loads such as communications equipment
5-s Analysis All loads that last longer than 0.3 s
(radios, for example, VHF/HF communication systems) that
should be entered in this column.
may have different current consumption depending on operat-
5-min Analysis All loads that last longer than 5 s
should be entered in this column.
ing mode (that is, transmit or receive);
Continuous Analysis All loads that last longer than 5
6.3.5 Maximum continuous demand of the electrical power
min should be entered in this column.
system must not exceed 100% of the load limits of the
(4)Alternatively, the equipment operating times could be
alternator(s) or generator(s) that are equipped with current
expressed as actual operating time of equipment in seconds or
monitoring capability;
minutes or as continuous operation. In the example given in
6.3.6 Cyclicloadssuchasheaters,pumps,andsoforth(duty
Appendix X1, the approach taken is to show either continuous
cycle); and
operation or to identify a specific operating time in seconds/
6.3.7 Estimation of load current, assuming a voltage drop
minutes.
between bus bar and load.
6.4 Load Analysis—Tabulation of Values—A typical load 6.4.1.8 Condition of Aircraft Operation—Phase of preflight
and flight (such as ground operation and loading, taxi, takeoff,
and power source analysis would identify the following details
in tabular form: cruise, and land). For aircraft, the conditions in Table 2 could
be considered.
6.4.1 Connected Load Table—See Appendix X1.
6.4.1.1 Aircraft Bus—Identify the appropriate electrical bus
6.4.2 Calculations:
being evaluated. In a multiple bus configuration, there will be
6.4.2.1 The following equations can be used to estimate
a set of tables for each bus (that is, DC Bus 1, DC Bus 2,AC
totalcurrent,totalcurrentrate,andaveragedemandforeachof
Bus 1, Battery Bus, and so forth).
the aircraft operating phases (ground operation and loading,
6.4.1.2 Condition of Power Sources—Normal, abnormal
engine start, taxi, takeoff and climb, cruise, and landing):
(abnormal conditions to be specified, for example, one genera-
TotalCurrent ~A! 5SumofAllCurrentLoads (1)
tor inoperative, two generators inoperative, and so forth), and
emergency.
Operatingata GivenTime
6.4.1.3 Aircraft Operating Phases—The following aircraft
operating phases should be considered for the ELA. Assume
“night” conditions as the worst-case sce
...
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