SAE AIR 769-1964 GROUND FAULT PROTECTION ON 400-CYCLE GROUND POWER UNITS.pdf

1、l C3 . .r; .1/ SOCIETV OF AUTOMOTIVE ENGINEERS. ,. A E R 0 S P A C E A I R 769 495 LEXINGTON AVENUE NEW YORK 17, N.,. I N f 0 R M A T I 0 N R E P 0 R T - I GROUND FAULT PROTECTION ON 400 CYCLE GROUND POWER, UrTITS I ued 9-15-6li I Rsvised dcm. rd ?E u10 a o =Ad m e Adm md W, do , a_ d 3 L Eda owd uE

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3、 Aerospace Information Report defines the characteristics of a Ground Fault Protection System to be used in conjunction with 400-cycle ground power units for servicing civil aircrat. This suggested system is intended to acquaint the airlines with one system which will eliminate possible shock hazard

4、s to operating personnel. HISTOR.Y - Stationa.ry mounted 400-cycle ground power units use a grounded neutral sy- stem in which the generator neutral is tied solidly to the frame of the unit. In addition, the ground power unit frame is grounded electrically to the airport building ground system. No s

5、hock ha,zards prevail in this installation. Portable ground power units have generator neutral grounded to the frame of the mobile equipment. However, no means are available to ground the frame of the mobile power unit to earth. This information report outlines the circuitry recommended for opening

6、the output contactor (or contactors) or de-energizing the;,generator of the ground power unit if any phase of the output cable (or cables) becomes grounded to earth. Serious da.mage to the operator can occur if one phase becomes grounded to earth. Any operator touching earth and the power unit or ai

7、rcraft being ser- viced could receive up to 120-volts 400-cycle. FAiTLT PROTECTION SYSTEM - A ground strap insulated from the frame of the portable ground power unit is connected to one side of the coil of a sensitive relay which operates on 1-milliampere or less at 20 - 30 volts. The other side of

8、the relay coil is connected to the frame of the power unit. When a 20 - 30 volt differential exists between earth ground and power unit or aircraft ground, this sensitive relay is energized which actuates a latching relay. The latching relay opens the output contactor (or contactors) to remove power

9、 from the output cable (or cables) and also energizes a push-totest light that indicates that a ground fault condition exists. An optiona.l system de-energizes the generator instead of opening the contactor (or contactors) if additional protection to operating personnel is be- lieved necessary. A re

10、set circuit re-establishes the condition for normal operation when the ground fault condition is .corrected. Periodic checking of the protection system is im- perative to insure proper functioning when a fault condition exists . PREPARED BY SAE COMMITTEE AGE-2, CIVIL AIRCRAFT GROUND SUPPORT EQUIPMENT Cooyrisht 1964 bY 800ibr of AutomotW nsinrs. Ina PIeNd In U. 8. A.