*
Test for ground fault resistance in
multi-feeder distribution systems
*
Help to calculate the fault resistance
in each polarity with respect to ground
* Analyze and
functional test the DC alarm system operation
*
Detect spikes and AC power contamination in
battery distribution systems
*
Will perform the function of a ground fault
indicator unit
*
Create the DC tracking signal for troubleshooting with
the GFAL-B
tracking
unit
Model: GFAL-A, Analyzer unit
Performance
*
Operate on 12 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 on 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 measurements test, 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 DC ungrounded systems
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 to 240 VDC
Impedance range
5 K to 10
Mohm
"Switching pseudo grounds”
5 K to 80 K “Cold opto switching”
Accuracy
2%, full scale
Environmental operation
30 to 125 Degrees F
Power adapter input
+ 12-18 VDC
Internal battery operation
24 hr, Rechargeable
Display
Volts and milliamps
Dimensions
12” x 7.5” x 11”
Weight
6 Lb
Case (2 colors)
Gray and yellow
Warranty
1 yr. 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
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