DC GROUND FAULT ANALYZER,  Model:  GFAL-A

 
Analyzer Unit, GFAL-A
                                                Model:  GFAL-A
              Highlights

    *   Test for ground fault resistances in  multi-feeder distribution systems 

    *  Help to calculate the fault resistance in each polarity with respect to ground 

      *   Analyze and functional test the DC ground fault alarm unit

    *   Detect spikes and AC power contamination in battery distribution  systems 

    *   Will perform the function of a DC ground fault detector and indicator unit 

    *  Create a DC tracking signal for troubleshooting with the GFAL-B
            tracking unit


               


                                       Model:  GFAL-A
 


        Performance

        *    Operate on 12 VDC to 250 VDC ungrounded DC systems
           Variable load resistance selection for safety operation
        *     Plant operation remains uninterrupted during test
        *    Does not use or inject AC signals to operate

        Background

    Multi-feeder DC distribution systems utilize ungrounded 12 VDC to 250 VDC battery assemblies for control, instrumentation and plant
    equipment operations.

    DC ground faults in one polarity of a multi-feeder system will diminish the reliability of the system if they remain uncorrected.

    Multiple DC ground faults in opposite polarities can cause an electrical short and system failure.

    If a DC alarm unit fails to operate and indicate the presence of a ground fault [that would have tripped the alarm] the reliability of the
    DC system is in jeopardy.

    The presence of AC power on a DC multi-feeder distribution system can produce none, partial or total system failure and the possibility 
    of electrocution to any person who comes in direct contact with the DC system.

        Present methodology to indicate DC ground faults

    The existence of a DC ground fault in a multi-feeder DC distribution system, is commonly indicated by voltmeters that test for voltage imbalance.

    The voltmeters are attached to the DC distribution system and will indicate ground faults; however, if a second ground fault with a equivalent
    resistance is present in the opposite polarity, the voltage imbalance with respect to ground is restore and the voltmeters WILL NOT  
    indicate the ground faults.

    There  are many other variations of this voltage imbalance test measurement, a few examples are:  the replacement of voltmeters with light bulbs,
    ground fault detector/alarm relays, or a current meter connected at the center point of a voltage divider.

    The major problem with all the cited DC ground fault indication methods is that they use the voltage imbalance technology for indication. 
    Consequently, as mentioned earlier, these methods and instruments will have erroneous indication on multiple ground faults, if those faults are
    located on opposite polarities.

                                                 GFAL-A Operation and Applications 

         DC distribution system ground fault test

    For this application, a selected resistance is applied to the polarity with the bigger voltage indication.
    A set of voltage data and appropriate calculation will find the value of the total fault resistance from each polarity with respect to site ground.
    There is another method design by Samco Engineering that will find the fault resistance on each polarity for 250 VDC dual battery
    distribution system.  

        Site DC Alarm

    This test is performed to verify and adjust the operation and response of the DC Alarm System. 
    A variable selected resistance is connected to one polarity at a tine to control the amount of fault resistance being introduced to the DC system
    with respect to site ground. 

    If the site DC Alarm  it is properly working should trip when the introduced resistance is below the set point needed to trip the alarm.

    Disconnected, out of commission and out of specifications  site DC alarms are quickly exposed by the GFAL-A instrument.

        AC Power and spikes on DC systems

    The more common AC contamination on DC systems with respect to ground is either wiring connections errors or paths of leakage resistance
    between the DC system and the AC power system.
    A spike is produce when a leakage fault resistance is intermittent.

    The GFAL-A has an AC voltage detector circuit that will reveal spikes and AC power that is superimposed on the DC distribution system
    respect to site ground

        Predictive Maintenance Programs

    A periodic testing on-line on DC multi-feeder distribution systems can produce a database file to support a predictive maintenance program.
    Important data to save are: Voltage with respect to ground, DC ground fault magnitude from each polarity, DC alarm response and
    AC contamination.

    All the above data can be obtain with the help of the GFAL-A Unit.

        Typical users for the GFAL-A

    The DC ground fault analyzer GFAL-A is utilized in situations where a high degree of service reliability and safety from the multi-feeder
    DC distribution system is required and desirable.

        *    All type of Generating Power Plants
        *
    Distribution Substations
        *
    Refineries 
        *     Cogeneration Facilities 
        *     All locations with ungrounded DC distribution system

         References for DC ground faults

        ANSI/IEEE:
        Standard 450-1987, 484-1987 and Std. 946-1992 “Recommended Practiced for Maintenance, Testing and Replacement
        of Large Lead Storage Batteries for Generation Stations and Substations”.

        NRC: (Nuclear Regulatory Commission)
        Information Notice 88-86.       “Operating with Multiple Grounds”
        EPRI : ( Electric Power Research Institute”   “DC Distribution Systems” Book.


        Specifications for the Model GFAL-A  

        Operating DC range                             12 VDC to 270 VDC   
        Impedance range                                  5 Kohm to 80 Kohm (also 10 Mohm)
        Switching pseudo grounds                  5 Kohm to 80 Kohm “Cold opto switching”  
        Accuracy                                                 Volts and milliamps a minimun 2%
        Environmental operation                    30 to 125 Degrees F
        Power adapter input                            12-18 VDC  (Center point positive polarity}
        Internal battery operation                  24 hr, rechargeable
        Display (volts and ma)                         Two 3 1/2 digit LCD
        Dimensions                                           13 3/8” x 11 5/8” x 6.0”
        Weight                                                   6 Lb
        Case (2 colors)                                      Gray and yellow
        Warranty                                               1 year parts and labor


     If you need more information, please contact us at
               
Samco Engineering  
            Fountain Valley, CA 92708
            Phone: (714) 235 - 5901
            E-mail: samcoeng@aol.com                                                                                      Return to Home page

              2017