Abstract:
A method and system for responding to a fast trip protective element trip in a generator system that re-excites the generator when a fast trip protection element trips and determines whether the generator immediately retrips the fast trip protection element, thereby determining whether a fault is located in the generator or in an attached load. If it is determined that the fault is located in the load, the system re-excites and reconnects the load after disabling the fast trip protection element for a specified period to allow for the load to clear its fault.

Description:
BACKGROUND 
       [0001]    Modern aircraft power generation systems often use variable frequency generators (VFGs). The VFGs are designed to carry required overloads at the lowest operating speeds of the VFGs. This results in the generator having a higher capacity at the highest operating speeds. As a result of this design consideration, some faults in a generator control unit or the generator can cause significant over voltages at higher operating speeds if the faults are not identified quickly. 
         [0002]    To protect against such faults, fast trip protection devices are included in the generator and trip whenever an overvoltage is present. Due to the fast nature of the fast trip protection devices, it is also possible for nuisance trips to occur. A nuisance trip occurs when a fault is present in the load and the fast trip protection device falsely detects a fault in the generator. When a nuisance trip occurs, it is imprudent to disconnect the generator from the load and connect an alternate power source. 
       SUMMARY 
       [0003]    Disclosed is a method for responding to a fast protective trip in a generator system having the step of re-exciting the generator when a fast trip protection element trips and determining whether the generator retrips the fast trip protection element. 
         [0004]    Also disclosed is a method for responding to a fast trip protection trip device in a generator system comprising detecting a fast trip protection element tripping, isolating a generator from a load by opening a generator line contactor, de-exciting the generator, re-exciting the generator while the generator line contactor is open, connecting the load to an alternate power source when the generator retrips, determining the fast trip protection element trip is a nuisance trip when the generator re-excites without tripping the fast trip protection element, temporarily disabling the fast trip protection element when the trip is a nuisance trip, re-exciting the generator when the trip is a nuisance trip, reconnecting the generator to the load by closing the generator line contactor when the trip is a nuisance trip, re-enabling the fast trip protection element after a pre-determined duration when the trip is a nuisance trip. 
         [0005]    A power supply is defined as a generator and a generator line connection connecting the generator to a power distribution bus. The power distribution bus is operable to distribute power to at least one load. A fast trip protection device is incorporated into the generating source such that the fast trip protection device can detect a fault and open the generator line connection when a fault is detected. A controller is operable to control the generator and the fast trip protection device. The controller further has a computer readable means storing instructions for causing the power supply to perform the step of re-exciting the generator when a fast trip protection element trips and determining whether the generator immediately retrips the fast trip protection element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
           [0007]      FIG. 1  illustrates a single channel power distribution system. 
           [0008]      FIG. 2  illustrates a two channel power distribution system. 
           [0009]      FIG. 3  illustrates an automatic fault isolation methodology that can be used with the illustrated examples of  FIGS. 1 and 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0010]      FIG. 1  illustrates a single channel power distribution system  10  having a single generator  20  acting as a power source. The generator  20  includes a fast trip protection device  22  and a controller  26 . A power output feeder  24  delivers electric power from the generator  20  to a power distribution bus  30  through a generator contactor  28 . The generator contactor  28  is controlled via a signal line  27  from the fast trip protection device  22 . Multiple loads  40  are connected to the power distribution bus  30  and receive operational power from the power distribution bus  30  via power connections  32 . Typically, a second generator  60  driven by an Auxiliary Power Unit (APU) provides a backup power source. The second generator  60  is connected to the power distribution bus  30  via a generator contactor  68 . The power output feeder  64  provides power from the second generator  60  to the generator contactor  68  through line contactor  68 . 
         [0011]      FIG. 2  illustrates an alternate two channel configuration for a power distribution system  100 . As with the power distribution system  10  of  FIG. 1 , each channel of the power distribution system  100  has a generator  120   a ,  120   b , with a controller  126 , and a fast trip protection device  122 . Each channel includes a power distribution bus  130  that provides power to multiple loads  140 . Each generator  120   a ,  120   b  is connected to the corresponding power distribution bus  130  via a power output feeder  124 , and a generator line control (GLC) switch  128 . The GLC switch  128  is controlled using signal lines  127  from the fast trip protection devices  122 . 
         [0012]    The two channel configuration illustrated in  FIG. 2  also includes a bus tie connector  150  connected to each power distribution bus  130  via a bus tie contactor  152 . An auxiliary power unit  160  is also connected to the bus tie connector  150  via an auxiliary generator line control (AGLC) switch  168  and a power feeder  162 . The bus tie contactor  152  can be controlled by switch control lines  127  from either of the fast trip protection devices  122  or an independent controller (not pictured). 
         [0013]    With continued reference to  FIGS. 1 and 2 ,  FIG. 3  illustrates a mode of operation of the generator  20 ,  120   a ,  120   b . Initially, the fast trip protection device  22 ,  122  detects a fault within the system  10 ,  100  and trips in a “fast trip protection device trips” at  310 . The tripped fast trip protection device  22 ,  122  causes the controller  26 ,  126  to open the generator line contactor  28 ,  128 , thereby isolating the generator  20 ,  120   a ,  120   b  from the loads  40 ,  140  in a “generator line contactor opened” at  312 . Once isolated, the generator  20 ,  120   a ,  120   b  is de-excited (powered down) in a “generator is de-excited” at  314 . 
         [0014]    After being isolated and de-excited, the generator  20 ,  120   a ,  120   b  is re-excited in a “generator is re-excited” at  316  to determine if the fast trip protection device  22 ,  122  retrips while isolated from the loads  40 ,  140  at “does fast trip device immediately retrip?” at  318 . If the fast trip protection device  22 ,  122  retrips, the generator controller  26 ,  126  determines that a fault exists within the generator  20 ,  120   a ,  120   b  in a “fault is identified as within generator” at  320 . When a fault is identified within the generator  20 ,  120   a ,  120   b , the generator  20 ,  120   a ,  120   b  is taken offline by the controller  26 ,  126  in a “generator taken off line” at  322 . The controller  26 ,  126  then connects an alternate power source such as an APU  60 ,  160 , or a second generator  120   a ,  120   b  channel to the loads  40  in a “load connected to alternate power source” at  324 . 
         [0015]    Alternately, if the fast trip protection device  22 ,  122  does not retrip when the generator  20 ,  120   a ,  120   b  is re-excited, the generator controller  26 ,  126  determines that the fault exists within the loads  140  and the tripping of the fast trip protection device  22 ,  122  was a nuisance trip in a “fault identified as within load” at  330 . When a nuisance trip occurs, it is imprudent to disconnect a functioning generator  20 ,  120   a ,  120   b  as the generator is still able to provide power, and the loads  40 ,  140  containing the fault may need power to clear the fault. Thus, when a fault is identified as being within the load  40 ,  140 , the controller  26 ,  126 , temporarily disables the fast trip protection device  22 ,  122  in a “fast trip protection device disabled” at  332  and then generator  20 ,  120  is re-excited in a “generator is re-excited” at  334 . The controller then closes the generator line contactor  28 , thereby reconnecting the generator  20 ,  120   a ,  120   b  to the loads  40 ,  140  in a “generator line contactor closed” at  336 . The fast trip protection is temporarily disabled to prevent the load fault from re-tripping the power system. 
         [0016]    The duration of the temporary disablement of the fast trip protection is predetermined and stored within the controller  26 ,  126 . Alternately, the duration can be determined a priori by the controller  26 ,  126  based on the number and types of connected loads  40 ,  140  at the time of the fault. Once the temporary disabling of the fast trip protection device has completed, the power distribution system  10 ,  100  is returned to its original state and the load is allowed to clear its fault. 
         [0017]    It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom. Although particular step sequences are shown, described, and claimed, it should also be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention. 
         [0018]    Although the different examples have specific components shown in the illustrations, embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples. 
         [0019]    The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.