AVTM246100C
Revision 1
Nov 2014
Instruction Manual
for
Dual Range
Battery Ground Fault Tracer
Patent No. 4,546,309
HIGH-VOLTAGE EQUIPMENT
Read this entire manual before operating.
APARATO DE ALTO VOLTAJE
Ante de operar este producto lea este manual enteramente.
M
Valley Forge Corporate Center
2621 Van Buren Avenue
Norristown, PA 19403 U.S.A.
610-676-8500 (Telephone)
610-676-8610 (Fax)
www.megger.com
Dual Range
Battery Ground
Fault Tracer
Instruction Manual
Copyright © 2014 by Megger. All rights reserved.
The information presented in this manual is believed to be adequate for the intended use of the product. If the product
or its individual instruments are used for purposes other than those specified herein, confirmation of their validity and
suitability must be obtained from Megger. Refer to the warranty information below. Specifications are subject to
change without notice.
WARRANTY
Products supplied by Megger are warranted against defects in material and workmanship for a period of one year
following shipment. Our liability is specifically limited to replacing or repairing, at our option, defective equipment.
Equipment returned to the factory for repair must be shipped prepaid and insured. Contact your Megger representative
for instructions and a return authorization (RA) number. Please indicate all pertinent information, including problem
symptoms. Also specify the serial number and the catalog number of the unit. This warranty does not include
batteries, lamps or other expendable items, where the original manufacturer’s warranty shall apply. We make no other
warranty. The warranty is void in the event of abuse (failure to follow recommended operating procedures) or failure
by the customer to perform specific maintenance as indicated in this manual.
M
Valley Forge Corporate Center
2621 Van Buren Avenue
Norristown, PA 19403 U.S.A.
610-676-8500 (Telephone)
610-676-8610 (Fax)
www.megger.com
Contents
1 INTRODUCTION ...........................................................................................................................................1 About the Dual Range BGFT… ....................................................................................................................1 How the Dual Range BGFT Works ..............................................................................................................2 Applications for the Dual Range BGFT .......................................................................................................3 Upon Receipt of the Dual Range BGFT ......................................................................................................3 Safety First ..........................................................................................................................................................4 How to Use This Manual .................................................................................................................................4 Typographic Conventions............................................................................................................................4
2 SAFETY..............................................................................................................................................................7 Overview .............................................................................................................................................................7 Connection to Power Source ...........................................................................................................................8 Fuse Replacement..............................................................................................................................................9
3 CONTROLS, INDICATORS AND CONNECTORS .......................................................................... 11 Overview .......................................................................................................................................................... 11 Transmitter ...................................................................................................................................................... 12 Receiver ............................................................................................................................................................ 14 Current Probe ................................................................................................................................................. 15
4 OPERATION ................................................................................................................................................. 17 General ............................................................................................................................................................. 17 Transmitter Connections ............................................................................................................................... 17 Configuring the BGFT .................................................................................................................................. 18 Applying Transmitter Test Voltage ............................................................................................................. 19 Receiver Connections and Applying Power ............................................................................................... 20 Defining The Fault ......................................................................................................................................... 20 Bridge Operation ............................................................................................................................................ 21 Tracing The Fault ........................................................................................................................................... 22 Instrument Shutdown Procedure ................................................................................................................. 22
5 APPLICATION NOTES ............................................................................................................................. 23
6 MAINTENANCE & REPAIR .................................................................................................................... 29 Maintenance .................................................................................................................................................... 29 DC fuse Test and Replacement ............................................................................................................... 30 Amplifier Output Fuse Test and Replacement ...................................................................................... 31 AC line Fuse Test and Replacement ....................................................................................................... 32 Changing voltage selector settings ........................................................................................................... 32 Battery Replacement (Receiver) ............................................................................................................... 33 Repair ............................................................................................................................................................... 33 Specifications & replaceable parts .................................................................................................................... 35 Specifications ................................................................................................................................................... 35 Environmental ............................................................................................................................................ 35 Transmitter .................................................................................................................................................. 35 Operational ................................................................................................................................................. 36 Receiver ....................................................................................................................................................... 36 Standard Accessories ................................................................................................................................. 36 Replaceable Parts List .................................................................................................................................... 37 i
AVTM246100C Rev 1 Nov 2014
LIST OF FIGURES
Figure 1: Dual Range Battery Ground Fault Tracer and Accessories ............................................................ 4 Figure 2: Transmitter Control Panel .................................................................................................................12 Figure 3: Receiver Case (Front/Back) ..............................................................................................................14 Figure 4: Test Connections.................................................................................................................................19 Figure 5: On-Line Diagram of Example ..........................................................................................................24 Figure 6: Panel 31 AB..........................................................................................................................................26 Figure 7: Terminal Block MM ............................................................................................................................27 Figure 8: Main Distribution Panels ...................................................................................................................28 Figure 9: Voltage Selector Card Orientation ....................................................................................................32 ii
AVTM246100C Rev 1 Nov 2014
1
INTRODUCTION
About the Dual Range BGFT…
NOTE: Before attempting to use the Dual Range BGFT,
be sure that you read and understand the safety requirements
and operating procedures contained in this manual.
Thank you for selecting a Megger product. This instrument has been
thoroughly tested and inspected to meet rigid specifications before being
shipped.
It is ready for use when set up and operated as described in this manual.
This manual contains instructions for the operation of the Dual Range
Battery Ground Fault Tracer. See Figure 1. The equipment comprises a
transmitter, receiver, source leads, current probe, feedback cable, and
instruction manual. The transmitter is housed in a rugged plastic
enclosure; the other items are housed in a separate accessories bag.
The Dual Range Battery Ground Fault Tracer locates ground faults in
ungrounded DC battery systems. Various standards require action when
the impedance between any battery polarity and earth ground falls below
a specified limit. In the case of nuclear-fueled plants, the Nuclear
Regulatory Commission (NRC) requires audits and appropriate action
when this impedance is deemed unsafe. Other facilities come under the
guidelines of the National Electric Code, NFPA, IEEE standards, and
OSHA requirements for safe operation of DC battery systems in an
ungrounded environment.
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How the Dual Range BGFT Works
The Dual Range Battery Ground Fault Tracer applies a 20 Hz signal
between the battery bus and station ground. This is accomplished by
connecting the transmitter via the source leads to an accessible
battery bus and to a ground bus located in a distribution cabinet. A
two-step process then begins to identify both the magnitude and
location of the fault. First, suspect feeder cables are identified by
measuring the flow of fault current to ground on all the output
circuits from the cabinet.
The amplitude of the 20Hz signal can be limited to either 15VAC, in
the low range or 50VAC in the high range. The low range should be
used when tracing low impedance faults below 100K ohms. The high
range should be used for high impedance faults above 100Kohms;
such as those caused by water ingress.
A bridge balance measurement can be performed to determine the
value of the capacitance and resistance of the suspected ground fault.
This is typically performed if more than one feeder cable is found
that contains a fault current.
The resistance and capacitance bridge located on the transmitter is
used to determine the value of the fault impedance in real and
imaginary terms (resistance and capacitive reactance) while the
amplitude of the signal current injected into the suspect feeder cable
is monitored with the receiver. Three stages of amplification can be
selected to identify and find faults to 399 kΩ. The red feedback wire
(supplied) is used as a canceling feature for the injected signal as
compared with the bridge selected impedance.
Isolating the fault to a specific location may require moving the
equipment downstream in a distribution system. Once a fault
resistance is quantified, the bridge and feedback portion of the
procedure can be dismissed and the fault can be tracked by evaluating
feeder lines of a subpanel. If the current value decreases after several
steady or increasing readings, then the location is in the opposite
direction.
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SAFETY
Applications for the Dual Range BGFT
The BGFT, Dual Range Battery Ground Fault Tracer, can find
ground faults in ungrounded battery systems in:·




Substations
Generating Stations
UPS Systems
Any other ungrounded DC system
For information about other installations that might benefit from
impedance testing, contact Megger.
Upon Receipt of the Dual Range BGFT
Check the equipment received against the packing list to ensure that
all materials are present. Notify Megger of any shortage.
Telephone (610) 676-8500.
Examine the instrument for damage received in transit. If any
damage is discovered, file a claim with the carrier at once and notify
Megger or its nearest authorized sales representative, giving a detailed
description of the damage.
This instrument has been thoroughly tested and inspected to meet
rigid specifications before being shipped. It is ready for use when set
up as indicated in this manual.
The BGFT instrument is shown in Figure 1. The BGFT includes the
following components and accessories.
 transmitter
 receiver with 9-volt
battery
 current source leads
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 clamp-on current sensor (CT)
 feedback loop
 line cord
 instruction manual
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Figure 1: Dual Range Battery Ground Fault Tracer and Accessories
Safety First
Be sure to read the safety information in Section 2 thoroughly and
observe all safety precautions and recommendations.
How to Use This Manual
Typographic Conventions
Figures and tables are numbered in sequence by section.
Numbered lists show procedural steps.
Bullets list items and options.
Buttons represent elements on the Dual Range BGFT control panel.
Cautions alert you to possible damage to equipment.
G
CAUTION
Never allow water to enter the case of the
BGFT.
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SAFETY
Warnings alert you to conditions that are potentially
hazardous to people.
F
WARNING
Always power off and disconnect the Dual
Range BGFT before cleaning it.
NOTE: Very high impedances exhibit low resolution readings
Notes provide important information.
on the receiver. To obtain better resolution, wrap an additional
turn around the clamp-on jaws of the current probe thereby
doubling the fault current. Remember to divide the bridge
capacitance by the number of turns and to multiply the bridge
resistance by the number of turns to identify the fault impedance.
Margin notes offer extra information and assistance.
Symbols used on the instrument are:
G
F
Caution: refer to accompanying notes.
Warning: refer to accompanying notes.
Equipment complies with current EU directives.
WEEE
The crossed-out wheeled bin placed on Megger products is a
reminder not to dispose of the product at the end of its life with
general waste. Megger is registered in the UK as a Producer of
Electrical and Electronic Equipment. The Registration No is
WEE/DJ2235XR.
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2
SAFETY
Overview
The Dual Range BGFT and its recommended operating procedures
have been designed with careful attention to safety. However, it is not
possible to eliminate all hazards from electrical test equipment or to
foresee every possible hazard that may occur. The user not only must
follow the safety precautions contained in this manual, but also must
carefully consider all safety aspects of the operation before
proceeding.
It should be understood that any use of electricity inherently involves
some degree of safety hazard. While every effort has been made by
Megger to reduce the hazard, the user must assume responsibility for
his own safety. Any work on large batteries is hazardous and requires
constant attention to safety; particularly guard against the possibility of
acid spills, explosion, and electrical shock.
The responsibility of the user is not limited to his/her own safety;
he/she must also be responsible for all persons in the vicinity. The
distribution system to which the Dual Range Battery Ground Fault
Tracer is connected can be extensive and therefore the user must be
aware of the consequences of applying up to 50 Vac to the DC system
and the effect on the operation and safety of the entire system.
The Dual Range BGFT has been designed to the IEC61010-1 safety
standards. Observe all industry standard safety rules for tracing
ground faults.

The Dual Range Battery Ground Fault Tracer is designed for
connection to energized systems. Keep the power on/off
switch set to 0 (off) when making connections or
disconnections at the battery. The output of the Dual Range
Battery Ground Fault Tracer and the system to which it is
connected are sources of high voltage. Always wear rubber
gloves during these operations.

Safety is the responsibility of the user.

The purpose of this equipment is limited to use as described
in this manual. Do not use the equipment or its accessories
for any purpose other than specifically described.

Do not operate in an explosive atmosphere. Explosive gases
can be present around batteries. A properly vented battery
environment is considered safe, but it is the responsibility of
the user to verify conditions prior to using the Dual Range
Battery Ground Fault Tracer.
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
Wear protective clothing and eye protection to guard against
skin and eye damage from battery acid.

Ensure that test leads and probes are in good condition, clean
and free of broken or cracked insulation.
Observe the following cautions marked on the transmitter panel.
1. For use on ungrounded systems only.
2. Set power switch to off prior to connecting or disconnecting
output leads to battery.
3. Connect output leads to J3 before connecting to battery system.
4. Ensure output ground connection is made to system earth ground.
5. Adhere to all industry standards for testing battery systems.
This instrument is only to be used by suitably trained personnel who
are familiar with the hazards involved in testing high-voltage DC
systems.
G
CAUTION
Refer fuse replacement to qualified service personnel
only. To prevent electric shock and fire hazard, use only
the fuse specified in the parts list which is identical in
respect to type, voltage rating, and current rating.
Connection to Power Source
The power input plug must be inserted only into a mating receptacle
with a ground contact. Do not bypass the grounding connection. Any
interruption of the grounding connection can create an electric shock
hazard. Make sure that the receptacle is properly wired before inserting
the plug.
Connect the transmitter to a ground outlet using supplied AC power
cord.
The BGFT test instruments operate from a single-phase power source.
The three-wire power cord requires a two-pole, three-terminal, live,
neutral, and ground type connector.
Before connecting to the ac power source, determine that the
instrument rating matches the voltage of the power source and has a
suitable two-pole, three-terminal grounding type connector.
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SAFETY
Fuse Replacement
.
Refer fuse replacement to qualified personnel only. To prevent electric
shock and fire hazard, use only the fuse specified. See Section 7 Specifications & Replaceable Parts.
F
G
WARNING
No user serviceable parts inside! Refer all servicing to the
factory or a qualified authorized service company!
CAUTION
Use only factory supplied mains cord! Mains cord shall
not be substituted!
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3
CONTROLS, INDICATORS AND
CONNECTORS
Overview
This chapter explains the locations and functions of the controls and indicators
for the Dual Range BGFT transmitter and receiver. The first section covers
the Dual Range BGFT transmitter and second covers the receiver.
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Transmitter
Figure 2: Transmitter Control Panel
J1 receptacle ― 115 VAC, 50/60 Hz or 230 VAC 50/60 Hz receptacles for ac
power. Power on/off switch controls power entry.
The switch is electrically connected to two fuses rated 2A Time Delay at 250
VAC or two fuses rated 1A Time Delay at 250 VAC. Over-current due to an
internal fault condition removes ac power to the power supplies.
Refer to Section 6, Maintenance and Repair, for fuse replacement instructions. Use
standard three wire line cord supplied with this instrument.
G
WARNING
Under no circumstances should the third wire ground
(green/yellow wire) connection to the ac power line be
disconnected or its continuity altered in any way.
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CONTROLS, INDICATORS & CONNECTIONS
VOLTAGE SELECTOR ― The voltage selector configures the input of the
unit to either 115VAC or 230VAC. The 115 VAC setting will operate on
voltages from 103.5 VAC to 126.5 VAC. The 230 VAC setting will operate on
voltages from 207 VAC to 253 VAC
The BGFT catalog number 246100C is set to 115 VAC at the factory.
The BGFT catalog number 246100C-47 is set to 230 VAC at the factory.
To alter the settings see Section 6 - Maintenance and Repair.
NOTE: If the voltage selector setting is changed in the field then the internal fuses
MUST be replaced as well.
F1 - FUSES ― The BGFT catalog number 246100C (115 VAC model) has 2A
fuses installed at the factory. Only use factory recommended fuses. For Fuse
type, see Section 7 - Specifications and Replaceable Parts.
The BGFT catalog number 246100C-47 (230 VAC model) has 1A fuses installed
at the factory. Only use factory recommended fuses. For Fuse type, see Section 7 Specifications and Replaceable Parts.
J2 FEEDBACK ― dual banana jack colored red and black receives connections
from the feedback cable supplied. The dual banana plug end of the lead should
match up with the dual banana jack receptacle.
J3 VOLTAGE OUTPUT jack ― receptacle for the current source leads. Insert
by lining up the keyway with the receptacle slot and push in and turn to the
right.
F
WARNING
The wiring for this connector is specific. A hazard to personnel
and equipment could result if the connections to either end of this
connector are compromised.
OUTPUT VOLTAGE meter ― Three-digit LCD shows representative
terminal voltage at J3. This voltage is controlled by the VOLTAGE CONTROL
dial mounted directly below the meter. Turning the VOLTAGE CONTROL
clockwise increases output voltage.
OUTPUT CURRENT meter ― Three-digit LCD indicates any current in
excess of 10 mA produced by the transmitter. This includes the feedback current
as well as the fault current.
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OUTPUT VOLTAGE SELECTOR – Allows the operator to limit the output
voltage to 15VAC open circuit, in the low range mode. This is an added safety
feature to ensure that most miss-operations of the unit will not result in system
faults. The output range can also be set to 50VAC open circuit in the high range
mode. This will allow the unit to use its full range of power to locate high
impedance faults; such as those caused by water ingress. It is recommended that
all tests start on the low range.
OUTPUT VOLTAGE / READY / CONNECT/DISCONNECT switch
― This illuminating switch, situated below the OUTPUT CURRENT meter,
illuminates with an amber light when the transmitter has completed charging of
the DC blocking capacitors located on the output and feedback circuits. The
output can now be enabled by pressing the switch to its IN position or disabled
by pressing the switch to its OUT position.
FEEDBACK CONTROL switches (manual bridges) ― Six switches, three
CAPACITANCE and three RESISTANCE, control the bridge mechanism.
Turning clockwise increases the respective component value.
Receiver
Figure 3 shows the receiver case.
Current Probe
Inputs
Gain Selector
Switch
Manufacturing
Information
Label
Battery
LED
Battery
Compartment
Meter
Figure 3: Receiver Case (Front/Back)
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CONTROLS, INDICATORS & CONNECTIONS
GAIN selector switch ― Four-position lateral switch for selecting
power on, 1, X10, and X100 gain. There is also an OFF position and a
latched BAT. TEST position which tests internal 9 V battery supply
voltage.
BAT. LED ― This green LED indicates an adequate internal 9 V
battery voltage. This LED lights when the selector switch is depressed
fully to the BAT. TEST position.
CURRENT PROBE inputs ― Two banana jacks are provided. These
should correspond to the mating plugs of the current sensor.
Meter ― Three and one-half digit display shows the magnitude of signal
current sensed by the current probe and amplified by the selected gain.
Battery compartment ― Situated on the reverse side of the receiver,
access to the battery can be made by turning the slotted screw
counterclockwise until loose.
Manufacturing information label ― Contains catalog number and
serial number.
Current Probe
Current probe jaw opening control ― Press the handle extensions
together until the opening is sufficient to encompass the cable under
test.
Direction arrow ― Since the probe aids in locating fault direction, the
consistent orientation of the probe needs to be maintained by observing
the red marking.
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4
OPERATION
General
Once a ground fault condition is revealed either through monitoring
equipment or inspection, the Dual Range Battery Ground Fault
Tracer can be used to identify, track, and locate the fault or faults in
the DC distribution system. The Dual Range Battery Ground Fault
Tracer should be positioned at the highest level of distribution
known to be fault free. Obviously, the farther away from the fault
the unit is located, the longer it takes to locate. The distributed
capacitance of cabling masks the resistive portion of the fault as
distance is increased.
Once a distribution cabinet is selected, locate the nearest appropriate
AC outlet and position the transmitter within the maximum AC line
cord length supplied with the unit. As previously mentioned, only a
grounded three-wire AC line cord should be connected to the
transmitter and the ground wire should not be interrupted by
extension cords or adapters. Refer to Section 2 - Safety, before
connecting and operating the Dual Range Battery Ground Fault
Tracer.
Transmitter Connections
The Dual Range Battery Ground Fault Tracer can be used while the
distribution system is in full operation. If safety regulations require
otherwise, follow all operating and maintenance procedures specified
at your facility.
1.
Remove sufficient cabinetwork to expose the DC supply bus
and feeder connections. Identify the ground bus and the
various supply bus connections. Some DC distribution
systems have taps on their battery to supply two voltage
systems. Common labeling is "P" for the most positive
battery terminal; "PN" to identify the tap connection; and
"N" to identify the most negative terminal. Other identifiers
such as "A" system and "B" system are also used. Consult
distribution schematics before connecting to the system if
there is any question or if labeling is not clear.
2.
Connect one side of the ground lead to the ground
connection on the BGFT. Connect the clip side of the
ground cable to earth ground.
3. Once the cabling for feeders and the DC bus is exposed,
locate the source leads in the accessories bag. This two-wire
cable can be identified by the four-pin connector at one end
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and two alligator clip type connectors at the other end. The
connectors on the clip end are distinguished from each
other by their labels, which denote where the clips should be
connected.
F
G
WARNING
The source lead with the “Connect to Earth Ground”
label should be attached only to the ground bus bar or
frame ground.
CAUTION
The source lead with the “Connect to Faulted Side of
String” Label should be attached only to the battery
bus connections. Inadvertent connection of the red
source lead to the ground bus bar or frame could result
in equipment damage.
4. Attach the source lead connector to J3 of the transmitter by
inserting with the key positioned and turning the locking
collar clockwise until snug.
5. Attach the source leads between the system ground and the
faulted side of the battery string, per the labeling on the
connectors.
6. Ensure that the power switch marked 0 (off) and │ (on) is
set to 0. Insert the female end of the AC line cord into the
power receptacle located in the lower left corner of the
transmitter and marked J1. Insert the male end into the
appropriate AC outlet.
All connectors for the transmitter front panel should now be
connected with a cable. Proceed to the next step, "Applying
Transmitter Power."
Configuring the BGFT
Before applying power, check all connections, set the following
controls as specified, and adhere to all cautions listed on the upperright portion of the transmitter control panel and those outlined in
this manual.
1. Set VOLTAGE CONTROL fully counterclockwise to
MIN.
2. Set the OUTPUT VOLTAGE switch to the OUT position.
3. Set the OUTPUT VOLTAGE range to 15V.
4. Set the RESISTANCE selector switches fully clockwise with
the left-most switch set to OPEN (blue numbers)..
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OPERATION
5. Set the power switch at J1 to │ (on). After a delay of
approximately 30 seconds, the amber READY light should
light, indicating that the transmitter is ready for operation.
The receiver is a battery-powered device, activated by moving the
slide switch from the OFF position in an upward direction and
selecting a gain position. Depending on signal strength, which is
inversely proportional to the fault impedance, the necessity for
increased gain will be a choice of receiver display resolution.
6. Connect the two parts of the receiver, the clamp-on current
probe that surrounds the cable to be examined and the
display and metering unit, by placing the clamp-on wiring
terminations (banana plugs) into the top part of the receiver
at the mating banana jack connectors.
Disconnect the ground lead of any battery ground fault monitor or
isolate it from the circuit if possible. (Battery ground fault monitors
can add a path to ground).
Applying Transmitter Test Voltage
NOTE: The amount of test voltage required will greatly
depend upon the magnitude of fault impedance to be
located and the system requirements for injected signals
onto the distribution bus. The larger the signal applied, the
more current will be available to the fault impedance and the
more resolution capability the receiver will exhibit.
1. Determine if the ground fault is on negative or positive side
of the battery string by finding which side measures the
lower voltage.
2. If the ground fault is on the positive side of the string then
connect the BGFT output transmitter cable between the
positive battery terminal and earth ground.
3. If the ground fault is on the negative side of the string then
connect the BGFT output transmitter cable between the
negative battery terminal and earth ground.
4. Set the receiver to (x1) and place the receiver CT around the
red transmitter lead of the BGFT. As shown in Figure 4.
Figure 4: Test Connections
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Receiver Connections and Applying Power
NOTE: Do NOT connect the transmitter across the
plus and minus terminals of the battery string.
Turn on the output of the BGFT by setting the output voltage push
button on the transmitter to the IN position (CONNECTED).
Slowly raise the transmitter’s output voltage, by turning the
transmitter output control know in a clockwise position. Slowly raise
the voltage until the receiver measures current. (0.1 is sufficient).
If the receiver does not measure current then increase the scale to
(X10) then (X100) if needed. (0.1 is still sufficient on either range).
Open the main panel and place the receiver clamp around each
circuit individually.
Locate the circuit with the current flow. This will be the circuit with
the ground fault.
If 2 or more circuits display the current then use the bridge in the
unit to tune out any false paths (see Bridge Operation).
Defining The Fault
The contributing impedance to ground can be defined by using the
feedback cable and the bridge section of the transmitter. During the
search for the fault, the initial connection is usually made at an
upstream cabinet and may be some distance from the actual fault
location.
This distance to the fault involves much wiring and many switch
mechanisms. The distributive capacitance of this cable and switch
mechanism may mask the true fault path with a high capacitance to
ground. This capacitance at 20 Hz could present a low impedance to
ground and prompt a search on the wrong feeder cable (phantom
fault).
To help eliminate false impedance to ground, a feedback cable
coupled to a decade bridge that defines the true impedance and
allows a true resistance value of the fault to be recognized. This is
accomplished by looping the feedback cable through the clamp-on
current probe and thereby canceling the effect of resistance and
capacitance on the measured injected fault current.
NOTE: Very high impedances exhibit low resolution
readings on the receiver. To obtain better resolution,
wrap an additional turn around the clamp-on jaws of
the current probe thereby doubling the fault current.
Remember to divide the bridge capacitance by the
number of turns and to multiply the bridge resistance by
the number of turns to identify the fault impedance.
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OPERATION
Bridge Operation
Capacitance
With the FEEDBACK CONTROL switches set to the blue
numbers as described in the paragraph on "Transmitter Connections,"
start with the capacitance section of the bridge. Observe the receiver
display and dial in a capacitance from the bridge section. If the
feedback cable is properly aligned, the displayed reading should start
to decrease or remain the same.
If the displayed value starts to increase, then the feedback cable is
entering the current probe from the wrong direction. Either reverse
direction at the transmitter panel or change the orientation of the
cable at the current probe.
If the displayed value remains the same, then the fault impedance is
resistive in content and no further capacitance nulling is required.
However, it is common for the displayed value on the receiver unit
to reflect some capacitive effect. This is caused by the capacitance to
ground in the feeder cable being investigated. Continue to dial in the
capacitance values until either the displayed value reverses direction
or the meter reaches minimum. If there are multiple turns of the
feedback cable around the current probe, multiply the null balance
capacitance displayed on the transmitter dials by the number of
turns.
When the travel of the displayed value reverses direction, then the
feedback capacitance is contributing to rather than canceling the
capacitive impedance effect. Adjust to a minimum and proceed to
the resistive balance. If the displayed value reaches zero or some
minimal value and increasing the gain of the receiver does not
provide any more resolution, then the path chosen contains no
resistive path to ground measurable to the specifications of this
device. Resistances at this point will be close to 1 MΩ.
Resistance
After the feeder cable capacitance has been determined and no
further addition of feedback capacitance reduces the displayed value,
and may even start to increase the value, then the remaining fault
impedance can be identified using the resistive portion of the bridge
and feedback circuitry.
Move the left-most or highest value switch to the OPEN position
and decrease the resistance selected until the displayed value reaches
a null condition. Increasing the gain selector on the receiver provides
resolution when required. Use the marked resistance dials to
determine a value of fault resistance measured to ground. If there are
multiple turns of the feedback cable around the current probe, divide
the null balance resistance displayed on the transmitter dials by the
number of turns.
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Tracing The Fault
Once the fault impedance is defined and a suspected downstream
path is determined, tracing the fault can begin. Trace the fault by
moving the receiver downstream. If it becomes necessary to move
the transmitter, then follow the procedure below.
Continue tracing faults by:
1. Shutting down the transmitter by following the Instrument
Shutdown Procedure below.
2. Move the transmitter to the next location and reconnect to
the buss.
3. Follow the Bridge Operation procedure in the previous
section to locate the resistive faults. Keep the polarity of the
current probe correct, at all times. When the displayed value
decreases or reverses polarity, the location of the fault has
been passed.
4. Repeat Steps 1 through 3 until all faults are located in the
DC system.
Instrument Shutdown Procedure
It is important to the safety of the operator and to the future
operation of the Dual Range Battery Ground Fault Tracer that an
orderly shutdown and removal from the DC bus under test be
accomplished.
1. Turn the VOLTAGE CONTROL fully counterclockwise.
2. Set the OUTPUT VOLTAGE switch to the OUT position
(DISCONNECTED).
3. Set the ac power switch to 0 (off).
4. Remove the clamp-on device and the feedback cable from
the receiver and transmitter cases, respectively.
5. Remove the red source lead first and then the black source
lead from the DC bus under test.
6. Disconnect the ac power cord from the system source.
7. Disconnect the ground lead from earth ground then from
the BGFT transmitter.
8. Carefully replace all components in the accessory bag and
secure the transmitter case.
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5
APPLICATION NOTES
Shortcuts
The following shortcuts can be used to save time when locating
grounds:
1. A typical utility environment will have four main DC panels
represented by one ground recorder. If physically possible,
check the main cables or bus work feeding each cabinet
(negative and positive) for the injected signal.
2. If a large imbalance of injected signal is observed with the
receiver, start with the cabinet containing the largest signal
level. The feedback circuit can be used, but remember that
the resistance found is a total of all feeder resistances in
parallel.
3. If a main feeder cable having ground current is detected and
the cable is traced to a cabinet with many jumpers, divide and
conquer. Move the receiver at a distance halfway from the
last measurement point until the fault current disappears and
reverse direction until the fault is located.
4. It is not necessary to move the transmitter every time you
relocate to another cabinet during tracing. Moving is only
necessary if the signal splits and the validity of the signal
(resistive or capacitive current) requires the feedback circuit.
5. Remember to disable the ground monitor test resistor to
ground before tracing a suspected fault. The low impedance
of this test resistor may mask the parallel fault impedance.
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Example of Test
Power generating station XYZ requires assistance in locating a DC
negative ground on its 120 V control battery bus. The Dual Range
Battery Ground Fault Tracer is made ready in accordance with the
instruction manual, making sure that the black lead is connected to
the ground bus or suitable grounded point. Power system regulations
limit bus perturbations to 10 V rms, so the transmitter output signal
amplitude is pre-adjusted to that level. A data sheet is used to record
the results and to help determine a pattern of search along with
sufficient system one-line diagrams. The main distribution panels
marked 10 AJ and 20 AJ are checked for signal strength (Fig. 5).
There is no large difference between the negative and positive bus so
a decision to start at panel 10 AJ is made.
Figure 5: On-Line Diagram of Example
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AVTM246100C Rev 1 Nov 2014
APPLICATION NOTES
All feeder cables are checked (10 AJ 01-20) with the largest signal
strengths on circuits 6, 11, and 19. Using the feedback circuit, circuits
6 and 11, impedances are determined to be capacitive in nature.
However, circuit 19 presents a 5 kΩ resistance in addition to
capacitive reactance on the balance bridge. A check of panel 20 AJ
produces no significant signal levels when checked with the receiver.
The negative bus ground alarm coincides with the significant ground
located in panel 10 AJ. A starting point is determined and station
prints indicate that circuit 19 feeds distribution panel 31 AB.
Panel 31 AB is located in another room and the decision is made to
leave the transmitter connected as is to the main bus and use the
receiver to track the signal. A reading is recorded with the feedback
circuitry removed and the receiver is moved to panel 31 AB (Fig. 5).
At panel 31 AB, the main cable 1SY016 repeats the reading on its
negative lead that was last taken at panel 10 AJ. With the receiver gain
at X10 and the preset signal amplitude the same as before, the display
indicates 0.200. The panel contains six circuit breakers and the signal
is traced to the negative lead of cable 1ST405. Prints indicate that the
cable enters cabinet 19 BAJ and connects to terminal block TB-MM4. Furthermore, TB-MM-4 is jumpered to points 6, 8, 10, 12, 14, 16,
18, 20, 22, 24, 26, 28 (Fig. 6).
To conserve time and energy, a reading at the entry point, terminal 4
and a midpoint in the jumper string is selected. Terminal 4 signal level
is 0.200; however, jumper 16 to 18 halves the signal to 0.100. Then
proceed back through jumpers 6, 8, 10, 12 and 14 and determine
signal strength at their outputs. Signal levels are 0.060 and 0.040 at
terminals 8 and 14, respectively.
Since capacitance was present on the line during initial measurements
at main panel 10 AJ, there is a good possibility that this split in signal
may be capacitive in nature. To determine the true resistance path, the
transmitter must be relocated to this panel and the feedback circuitry
used.
The output of the transmitter is connected to point 4 of terminal
block TB-MM and the black lead to an appropriate ground point. The
output wires of the remaining terminal output points are checked with
the bridge and the only resistive circuit to ground is discovered on
terminal output point number 26.
Prints indicate that point 26 feeds into field cable 101 and proceeds to
the transformer yard (Fig. 7). Leaving the transmitter connected as is,
the receiver minus the feedback lead is moved to the transformer in
the yard. Checking cable 101, we find no signal is present. This
indicates that the ground lies between the cable 101 transformer
connection and point 26 on TB-MM.
This is verified by obtaining permission to lift this circuit and seeing
the ground alarm return to normal. All equipment is de-energized and
packed up for future use.
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Figure 6: Panel 31 AB
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APPLICATION NOTES
Figure 7: Terminal Block MM
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Figure 8: Main Distribution Panels
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6
MAINTENANCE & REPAIR
Maintenance
Since the instrument and its components may be used in dirty and
corrosive environments, periodically clean all components and test
leads with a mild detergent and a soft cloth. Do not immerse the
transmitter or receiver in water or allow moisture to enter the cases.
Maintenance should only be carried out by qualified personnel.
Periodically (every six months) inspect and clean the case, as previously
described, all test leads, and connections. Inspect the current probe
leads and transmitter source leads for effects of corrosion and wear.
The power on/off switch on the transmitter panel contains a line fuse
to protect the instrument from current overloads. These primary side
fuses are rated for 2A Time Delay at 250 VAC or 1A Time Delay at
250 VAC. A line output fuse rated at 2 A ac 600 VAC is located inside
the instrument.
The current output leads have a set of fuses, ATM-2 to protect the
operator. These are fast acting, with high interrupting capacity. These
fuses are designed to protect the user from catastrophic component
failure.
F
WARNING
Under no circumstances should these fuses be defeated
or replaced with another type fuse. Replace with the type
specified in Section 7 Specifications & Replaceable Parts.
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To verify that the problem is DC fuse related, move the instrument
from the DC distribution system under test by de-energizing the
equipment and detaching the source leads. With the transmitter source
leads connected to J3, short the two clip ends together, turn the
VOLTAGE CONTROL fully counterclockwise and apply power to
the transmitter. Verify that the ac power remains on and that after the
time delay, the amber READY lamp lights. Observe the ac OUTPUT
CURRENT meter on the transmitter panel, and set the OUTPUT
VOLTAGE switch to CONNECT. Turn the VOLTAGE CONTROL
clockwise until the displayed current value increases from zero. If there
is no output, then the DC fuse is likely damaged or a break has
occurred in the test leads circuit.
DC fuse Test and
Replacement
If suitably trained personnel are available and fuse replacement is
required, follow this procedure for fuse replacement.
1. Turn the VOLTAGE CONTROL fully counter-clockwise.
2. Set the OUTPUT VOLTAGE switch to DISCONNECT.
3. Remove all ac power to the transmitter by setting the power
on/off switch to 0. Disconnect the AC line cord. Set the
OUTPUT VOLTAGE switch to DISCONNECT.
4. If the current source leads are still connected, remove from the
DC distribution bus under test.
5. Remove the source leads from their J3 connection on the
transmitter front panel.
6. Disconnect the ground lead from earth ground then from the
BGFT transmitter.
F
WARNING
This instrument contains several large capacitors. During
operation some or all of these capacitors could become
charged up to the capacity of the DC bus under test.
Normally these capacitors are automatically discharged
when the leads are disconnected and the switches are set
to the positions as described in steps 1 through 3.
However, under certain fault conditions, these capacitors
may be left charged. Always use a voltmeter to check the
state of the charge and wear rubber gloves as necessary
when touching the capacitors and the circuits connected
to them.
7. Remove 14 Phillips head screws from the transmitter panel
and lift the chassis to the top of the instrument case. Remove
the entire chassis and rest it on a clean flat surface.
8. Find the fuse located in a double fuse holder. Only one slot of
the fuse holder is wired; the remaining slot houses the spare
fuse.
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MAINTENACNE & REPAIR
9. Remove the damaged fuse and replace with the spare. Using
an ohmmeter, verify that the fuse is indeed bad.
10. Visually inspect all components within the transmitter chassis
assembly for damage. Since the fuse was installed and sized to
protect under component fault situations, this may indeed be
the case. If no damage is observed, proceed to the next step. If
damage is observed, return the transmitter to the Megger
Repair Department.
11. Replace the chassis in the instrument case, replace the 14
screws and test again as described above. If the instrument still
does not respond correctly, return it to the Megger Repair
Department.
Amplifier Output Fuse
Test and Replacement
The output amplifier section is configured in a push-pull arrangement
that requires a measure of DC balance between each output transistor
array. In the event of component failure or radical calibration drift, the
outputs become unbalanced and one phase works harder than the
other. This causes an imbalance in the current available and also causes
the individual phase protection fuse to interrupt. Inadvertent
connection to an ac bus could also cause one or both of the fuses to
interrupt.
An indication of this problem is a reduction in current and voltage
available to the output. Normal current available to shorted output
source leads at maximum clockwise adjustment of the VOLTAGE
CONTROL is approximately 0.5A ac at a voltage of 15VAC or 1.7 A
ac at a voltage of 50 VAC rms. Neither of these values is attainable in
the event of an amplifier output fuse interruption.
If both fuses interrupted, there would be no output indication
whatsoever, and a symptom similar to an interrupted DC fuse would
be evident.
1. Perform steps 1 through 4 of the procedure for replacement of
the DC fuse.
2. Locate the FET DRIVER PRINTED CIRCUIT BOARD in
the middle of the transmitter chassis assembly. The two
amplifier output fuses are located directly beneath the heat
sink and mounted to the printed circuit board in clip fuse
holders.
3. Remove the damaged fuse and replace with a new one. Refer
to Section 7 - Specifications & Replaceable Parts, for rating and size.
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AC line Fuse Test and
Replacement
If the transmitter does not respond to the application of AC line
voltage, check the fuses protecting the ac input circuitry. To check
and/or replace these fuses, perform the following steps.
1. Perform steps 1 through 3 of the procedure for replacement of
the DC fuse.
2. Using a small flat blade screwdriver, insert the tip into the slot
located at the top of the ac power entrance module J1. The
front face of the module will swing outward.
3. Remove the fuse cartridges located within the module and
marked with an arrow pointing to the right of the transmitter.
4. Replace the fuses and restore the fuse cartridges to their
previous location. Replace the line fuses with direct
replacements as specified in Section 7 - Specifications & Replaceable
Parts.
5. Close the front face cover of the ac entrance module and retest
the transmitter. If the fuses continue to interrupt, it is
recommended that the entire unit be sent to the Megger
Repair Department.
Changing voltage
selector settings
1. To change the selected voltage: open the fuse cover using a
small blade screw driver or similar tool. Pull the voltage
selector card straight out of the housing, using the indicator
pin. Orient the indicator pin ton point up when the desired
voltage is legible at the bottom. Insert the voltage selector card
into the housing with the printed side of the card facing
forward toward the IEC connector and edge containing the
desired voltage first. Replace cover and verify the indicator pin
shows the desired voltage.
Figure 9: Voltage Selector Card Orientation
NOTE: When the voltage selector is set to either the 100V or 120V
position the BGFT will be configured for 115VAC operation. For
115VAC operation the input module will require 2A fuses.
When the voltage selector is set to either the 230V or 240V position the
BGFT will be configured for 230VAC operation. For 115VAC
operation the input module will require 1A fuses.
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MAINTENACNE & REPAIR
Battery Replacement
(Receiver)
BATTERIES
The crossed-out wheeled bin placed on the batteries is a reminder not
to dispose of them with general waste at the end of their life.
This product contains a 9 V alkaline battery.
They are located in the BGFT receiver. (P/N 30001-1)
They can be safely removed by performing the following steps.
1. Remove the battery compartment cover by turning the slotted
screw with a flat blade screwdriver counterclockwise until the
cover separates from the case.
2. Remove the battery and disconnect the battery supply leads.
3. Replace with an adequate substitute battery (refer to Section 7 Specifications & Replaceable Parts), reconnect the supply lead, and
insert the battery into the case.
4. Replace the battery compartment cover and reinstall the screw
being careful not to over-tighten or cross-thread the
restraining screw.
Spent batteries are classified as Portable Batteries and should be
disposed of in accordance with Local Authority requirements. Megger
is registered in the UK as a producer of batteries.
The Registration number is BPRN01235
Repair
Megger offers complete repair service and recommends that its
customers take advantage of this service in the event of equipment
malfunction. Please call 610-676-8500 and ask for Customer Service to
obtain an RA #, then ship to:
TEL: 610-675-8500
Megger
ATTN: Repair Department
Valley Forge Corporate Center
2621 Van Buren Avenue
Norristown, PA 19403 U.S.A.
It is best if you return the entire instrument, including leads, to help us
find the source of the problem. Many times the problem appears to be
the transmitter, but the problem is eventually found to be in the
receiver. Please indicate all pertinent information, including problem
symptoms and attempted repairs. Equipment returned for repair must
be shipped prepaid and insured and marked for the attention of the
Repair Department.
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Preparation for Storage and Shipment
Remove the battery from the receiver before shipment or long-term
storage. Storage temperature for the Battery Ground Fault Tracer
should not exceed the range -5 to 130°F (-20 to 55°C). Pack in a carton
or box (original shipping container if available) in accordance with best
commercial practice. Seal container with waterproof tape.
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AVTM246100C Rev 1 Nov 2014
7
SPECIFICATIONS & REPLACEABLE PARTS
Specifications
Environmental
Operating temperature range:
32 to 105°F (0 to 40°C)
Storage temperature range:
-5 to 130°F (-20 to 55°C)
Humidity:
20 to 95% RH non-condensing
Transmitter
Mechanical
Dimensions:
7.5 x 18.5 x 14.6 in. (H x W x D)
(19 x 47 x 37 cm)
Weight:
35 lb (15.9 kg)
Electrical
Maximum voltage to ground:
250 VDC
Mains:
115 VAC ±10% for the 246100C @ 50/60 Hz,
200 VA max.
230 VAC ± 10% for the 246100C-47 @ 50/60
Hz, 200 VA max.
Source voltage:
variable 0 to 15 V rms in low range
variable 0 to 50 V rms in high range
Source current:
load dependent 0 to 1.7 A rms
Source frequency:
20 Hz ±2%
Display (volts):
three-digit LCD ±5%
Display (current):
three-digit LCD ±5%
Fuses:
DC output, ATM2, 2 A, 600 VDC
FET Driver, time-delay, 2 A, 250 V (internal)
AC line, 5 x 20mm., 2A, 250 VAC, time delay
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AC line, 5 x 20 mm, 1A, 250 VAC, time delay
Operational
Fault resistance:
1 to 399 kΩ @ 50 V
bridge accuracy ±10%
Line capacitance:
0.01 to 11.1 μF
bridge accuracy ±20%
Receiver
Electrical:
9 V alkaline battery
Power (max.):
11 mA at 9 VDC
Battery life:
40 hours continuous use at 20°C (estimated)
Standard Accessories
Source leads: Two single conductor, 14 AWG, 600 V insulation, each conductor
fused at 2 A, 600 VDC
Current probe
AC line cord
Feedback cable, single conductor, 18 AWG, 600 V insulation
Instruction Manual
Accessories bag
Ground Cable
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AVTM246100C Rev 1 Nov 2014
SPECIFICATIONS & REPLACEABLE PARTS
Replaceable Parts List
Description
Part Number
Accessories bag
29996
US style AC line cord
17032-7
EU style AC line cord
17032-13
UK style AC line cord
17032-12
Battery, 9 V alkaline
1482-1
Clamp-on current probe
29999-1
Feedback cable assembly
29998
Fuses, source lead, ATM 2 A, 600 VDC
29440-2
Fuses, FET Driver, time delay, 2 A, 250 V
2567-27
F1 AC line fuse, 5 x 20 mm 2A Time Delay, 250 VAC
27708-3
F1 AC line fuse, 5 x 20 mm 1A Time Delay, 250 VAC
27708-5
F2 DC fuse, ATM2, 2 A, 600 VDC
29440-2
Instruction manual
AVTM246100C
Receiver assembly
30001-1
Source lead assembly, 20 ft long, fused leads TYPE ATM, 2 A
29386-3
Ground Cable
1004-648
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AVTM246100C Rev 1 Nov 2014
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