Megger AVTM6514J User manual

AVTM6514J
Rev. A
March 2003
Instruction Manual AVTM6514J
for
Impulse Generator
Catalog Nos. 651403 and 651404
High-Voltage Equipment
Read the entire manual before operating.
Aparato de Alto Voltaje
Antes de operar este producto lea este manual enteramente.
PO Box 9007
Valley Forge, PA 19485-1007 U.S.A.
610-676-8500
Shipping Address:
Valley Forge Corporate Center
2621 Van Buren Avenue
Norristown, PA 19403 U.S.A.
www.megger.com

AVTM6514J Rev. A (03/2003)
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Copyright 2003 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. Specifications are subject to change without notice.

AVTM6514J Rev. A (03/2003) i
Table of Contents
SECTION 1 ............................................................................................................................................................ 1
introduction......................................................................................................................................................... 1
Receiving Instructions .................................................................................................................................. 1
General Information ..................................................................................................................................... 1
SECTION 2 ............................................................................................................................................................ 5
Safety.................................................................................................................................................................... 5
SECTION 3 ............................................................................................................................................................ 9
Specifications ...................................................................................................................................................... 9
Electrical ......................................................................................................................................................... 9
Physical............................................................................................................................................................ 9
Environmental ............................................................................................................................................... 9
SECTION 4 .......................................................................................................................................................... 11
Description........................................................................................................................................................ 11
Circuit Descriptions .................................................................................................................................... 11
Controls And Connectors .......................................................................................................................... 13
SECTION 5 .......................................................................................................................................................... 15
Setup .................................................................................................................................................................. 15
SECTION 6 .......................................................................................................................................................... 19
Operation .......................................................................................................................................................... 19
Operating Procedure................................................................................................................................... 19
Interpreting The Output Current Meter .................................................................................................. 19
Shutdown Procedure................................................................................................................................... 20
SECTION 7 .......................................................................................................................................................... 21
Operation Notes .............................................................................................................................................. 21
Theory ........................................................................................................................................................... 21
Impulse Testing ........................................................................................................................................... 22
Operation With An Electromagnetic Impulse Detector ....................................................................... 22
Proof Testing Cable .................................................................................................................................... 22
SECTION 8 .......................................................................................................................................................... 23
Service................................................................................................................................................................ 23
Maintenance ................................................................................................................................................. 23
Performance Check..................................................................................................................................... 24
Troubleshooting And Repair..................................................................................................................... 25
SECTION 9 .......................................................................................................................................................... 29
Replaceable Parts List...................................................................................................................................... 29
GLOSSARY.......................................................................................................................................................... 31

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WARRANTY........................................................................................................................................................ 33
APPENDIX .......................................................................................................................................................... 35
Brief Operating Instructions...................................................................................................................... 35
FIGURE LIST
Figure 1: Impulse Generator................................................................................................................................. 2
Figure 2: Schematic Diagram.............................................................................................................................. 12
Figure 3: Typical Fault Diagram........................................................................................................................ 21

AVTM6514J Rev. A (03/2003) 1
SECTION 1
Introduction
RECEIVING INSTRUCTIONS
Check the equipment received against the packing list to ensure that all materials are
present. Notify Megger of any shortage. Telephone [phone].
Examine the instrument for possible 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.
GENERAL INFORMATION
This instruction manual describes the operation and maintenance of Impulse
Generators having Catalog No. 651403 and 651404. Catalog No. 651403 is the 120 V,
50/60 Hz, 300 VA model, and Catalog No. 651404 is the 240 V, 50/60 Hz, 300 VA
model.
The Impulse Generator produces periodic pulses up to 15 kV for locating faults in
cables by the high-voltage, impulse-tracing method. No larger than a medium-sized
suitcase and weighing only 41 pounds, the Impulse Generator is contained in a
fiberglass carrying case that is rugged and durable to withstand transportation from site
to site. See Figure 1.
The Impulse Generator uses low-voltage storage capacitors on the primary side of a
pulse transformer. Every six seconds, a solid-state switch discharges the capacitors into
the pulse transformer, which steps the voltage up to the required level. The resultant
output is a high-voltage impulse with a steep front and an exponentially decaying "tail"
—an ideal waveform for cable fault location. The waveform travels along the cable
until it reaches the fault, where a sparkover occurs. High-voltage sparkover causes a
significant current to flow, and the fault is located by detecting this current or the noise
made by the sparkover.
An ammeter on the Impulse Generator displays peak fault current in percentage of the
available output. When the meter indicates a cable fault, its location is pinpointed by
tracing the fault current with a detector carried along the cable path. Two such detectors
are available from Megger:

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Figure 1: Impulse Generator

AVTM6514J Rev. A (03/2003) 3
Catalog No. 653000 Surge Detector (for direct buried cable)
Catalog No. 651113 Electromagnetic Impulse Detector (for ducted and buried
cable)
A rotary switch allows the selection of 3, 6, 9, 12, or 15 kV. The switch also has a
ZERO START position which discharges the capacitors and provides a zero-voltage
start-up for safety. Input and output cables are permanently attached; storage for cables
is provided in the lid of the carrying case. An integral fan provides cooling.

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AVTM6514J Rev. A (03/2003) 5
Section 2
Safety
This equipment and the cable to which it is connected are sources of high-voltage
electrical energy. All persons performing or assisting in tests must use all practical safety
precautions to prevent contact with energized parts of the test equipment and related
circuits. Persons actually engaged in the test must stand clear, by at least 3 ft (0.91 m), of
all parts of the complete high-voltage circuit unless the system is de-energized and all
parts of the test circuit are grounded. Persons not directly involved with the work must
be kept away from test activities by suitable barriers, barricades or warnings. Be aware
that impulses applied to the cable will be present at the remote end(s) and any other
exposed part of the cable, usually out of sight of the operator. To avoid inadvertent
contact with hazardous live parts, always ensure that access to all exposed parts of the
cable or connected equipment is restricted, by using suitable barriers or barricades.
§Safety is the responsibility of the user.
§Misuse of this high-voltage equipment can be extremely dangerous.
§The purpose of the test equipment is limited to use as described in this manual. Do
not use the equipment or its accessories with any device other than specifically
described.
§Never connect the test equipment to energized equipment.
§Never use the test equipment if there is any possibility that the test equipment or
cable under test is in an explosive atmosphere.
§A qualified operator should be in attendance at all times while the test equipment is
in operation.
§The safety ground jumpers and surge ground must be properly connected (refer to
Section 5).
§Refer to IEEE 510-1983 "IEEE Recommended Practices for Safety in High-
Voltage and High-Power Testing," and follow the applicable safety
recommendations.
§Observe the safety warnings marked on the equipment.
Treat all terminals of high-voltage power equipment as a potential electric shock hazard.
There is always the potential of voltages being induced at these terminals because of
proximity to energized high-voltage lines or equipment. Always use a safety grounding
stick to ground the high-voltage conductor. A safety ground jumper must then be
installed between the high-voltage conductor and ground of the cable under test. The
ground connection must be the first made and the last removed.

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Systems of this type should not be used to locate faults on direct-buried unshielded or
secondary cable. Dangerously high differences in potential may be developed in the
current return path to the system.
Systems of this type should not be used to locate faults on any cable that is likely to be
near enough to an energized cable to allow a burn through of the insulation of the
energized cable. This situation may occur when the cables are located in a common
trench, duct, or tray.
On completion of a test, even after power has been removed from the system, energy
can still be stored in the impulse capacitor and cable under test. To discharge the cable
and capacitor, immediately after use, set the OUTPUT KILOVOLTS switch to ZERO
START. This places a solid ground on the output cable, power supply, and impulse
capacitor.
F
WARNING
Never assume that the coaxial output cable or the cable under
test is completely discharged, even after following the above
procedures. Always use a safety grounding stick to ground any
conductive part of the circuit and then apply safety ground
jumpers before touching any connections.
This system operates from a single-phase power source. It has a three-wire power cord
and a two-pole, three-terminal grounding type connector. The voltage to ground from
either pole of the power source must not exceed the maximum rated operating voltage,
120 V ac for Catalog No. 651403 and 240 V ac for Catalog No. 651404. Before making
connection to the power source, determine that the system is suitable for the voltage of
the power source, and has a suitable two-pole, three-terminal grounding type connector.
The power source must have a high rupture fuse or circuit breaker rated no higher than
15 A.
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. Determine that the receptacle is
correctly wired before inserting the plug.
To avoid electric shock hazard, operating personnel must not remove the system
protective covers. Component replacement and internal adjustments must be made by
qualified service personnel only.
Users of high-voltage equipment should note that high-voltage discharges and other
sources of strong electric or magnetic fields may interfere with the proper functioning
of heart pacemakers. Personnel using heart pacemakers should obtain expert advice on
the possible risks before operating this equipment or being close to the equipment
during operation.
If the system is operated in accordance with the safety precautions in this manual and if
all grounds are correctly made, rubber gloves are not necessary. As a routine safety
procedure, however, some users require that rubber gloves be worn, not only when
making connections to the high-voltage terminals, but also when manipulating controls.
Megger recommends this excellent safety practice.

AVTM6514J Rev. A (03/2003) 7
The following warning and caution notices are used in this manual where applicable and
should be strictly observed.
F
WARNING
Warning, as used in this manual, is defined as a condition or
practice which could result in personal injury or loss of life.
G
CAUTION
Caution, as used in this manual, is defined as a condition or
practice which could result in damage to or destruction of the
equipment or apparatus under test.
Megger has made formal safety reviews of the initial design and any subsequent
changes. This procedure is followed for all new Megger products and covers areas in
addition to those included in applicable ANSI standards. Regardless of these efforts, it
is not possible to eliminate all hazards from electrical test equipment or to foresee every
possible hazard that may occur. It is therefore essential that the user, in addition to
following the safety rules in this manual, also carefully consider all safety aspects of the
test before proceeding.

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AVTM6514J Rev. A (03/2003) 9
Section 3
Specifications
ELECTRICAL
Input voltage: 105 to 125 V ac (Cat. No. 651403)
210 to 250 V ac (Cat. No. 651404)
Input frequency: 50/60 Hz
Power consumption: 300 VA
Surge interval: 6 seconds
Surge generator equivalent
capacitance:
2.5 µF at 15 kV
Stored energy: 300 joules
Surge output voltage: 3 to 15 kV (switch selected)
Surge output current: Approximately 600 A into a short circuit
Output cable length: 20 ft (6 m)
PHYSICAL
Weight: 41 lb (18.6 kg)
Dimensions: 14.5 x 17.5 x 8.5 in. (D x W x H)
(36.8 x 44.5 x 21.6 cm)
ENVIRONMENTAL
Temperature range: -4 to 122°F (-20 to 50°C) (operating)
-22 to 131°F (-30 to 55°C) (storage)
Altitude: 7500 ft (2286 m) maximum
Voltage derates at higher altitudes
Humidity: Operation and storage limits 5 to 95% rh noncondensing
conditions
Climate: Operation prohibited in rain or snow

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Section 4
Description
CIRCUIT DESCRIPTIONS
The electronics of the Impulse Generator are described in the following and shown in
the schematic diagram of Figure 2.
The Impulse Generator has a bank of energy storage capacitors, a high-voltage dc
supply for charging the capacitors, a switch to discharge the capacitors, a damping
resistor, and an output circuit. Capacitive energy storage and switching take place at a
low voltage on the primary side of a pulse transformer, which in turn steps the voltage
up as high as 15 kV for output to the cable under test. This means that the capacitors
may be 800 to 1000 V devices, rather than the usual large 15,000 to 25,000 V type. The
lower voltage allows use of a solid-state switch, an SCR.
The circuit schematic is divided into five functional parts:
1. Energy storage capacitor charging circuit: This circuit is composed of transformer
T1 and diode CR8, which provides a rectified voltage to charge the main capacitor
bank C7.
2. Solid-state switch SCR: This switch (Q7) is used to discharge the capacitor bank C7.
3. Discharge circuit: The energy in the capacitor bank is discharged into pulse
transformer T3 through a damping resistor R19. T3 steps the voltage pulse up as
high as 15 kV (open circuit) for output to the cable under test. The output voltage
under load varies between 3 and 15 kV in five steps of 3 kV each, depending on
which secondary tap of T1 is used to charge C7.
4. Pulse transformer and output metering circuit: A current transformer T4 monitors
the output current and provides an input to meter M1, which indicates peak current.
M1 has a 0 to 100 percent scale; it is calibrated to read approximately 100 percent
with 15 kV into a short circuit. Lower output voltage taps provide a proportionately
lower indication; e.g., 3 kV into a short circuit produces only 20 percent deflection.
5. Timing and firing circuits: The periodic pulse which gates the main SCR Q7 is
developed in the following manner. Every six seconds a voltage pulse is discharged
through transformer T2, gating pilot SCR Q6. In turn, Q6 switches the gating
voltage to the main SCR Q7, thus completing the firing sequence for the high-
voltage output pulses.

Figure 2: Schematic Diagram

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A zero start circuit uses a latching (self-sealing) relay K1 in the primary of T1. A sixth
position on the T1 secondary tap-changing switch discharges capacitor bank C7 and
simultaneously shorts the latching contact of K1. This ensures that on start-up, no high-
voltage pulses can be generated until the rotary switch is first turned to its (zero-output)
position.
Line-voltage fan B1 cools the heat sink of the charge and discharge resistors. If the heat
sink temperature rises excessively due to a fan failure or for any other reason, thermal
switch SW3 shuts the unit down.
ON/OFF circuit breaker CB1 protects the Impulse Generator and provides immediate
shutdown whenever required. FL1 and transient voltage suppressor CR15 are provided
across the main line voltage input. Pilot light DS1, across a third secondary tap of T1,
indicates that high-voltage output pulses are available.
CONTROLS AND CONNECTORS
AC INPUT: 10-ft (3 m), permanently attached line cord; two-
pole, three-wire grounding plug mates with a
standard NEC socket
HV OUTPUT: 20-ft (6 m), permanently attached output cable is
terminated with two heavy duty copper spring
clips, covered with rubber boots (one red, one
black).
POWER lamp: red pilot light on the panel indicates that the input
circuits are working and the high-voltage output
should be available.
ON/OFF switch: 3.5 A breaker provides circuit protection and acts
as ON/OFF switch.
OUTPUT KILOVOLTS switch: rotary switch selects the output voltage from 0 to
15 kV in steps of 3 kV and also provides the
ZERO START feature.
OUTPUT CURRENT meter: indicates percentage of the maximum peak output
current: 600 A at 15 kV into a short circuit

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Section 5
Setup
The following steps serve as a general guide for setting up operation. Before proceeding,
read, understand, and observe all safety precautions contained in this manual. Refer to
Section 2.
1. Observing all safety precautions, be sure all equipment is de-energized. Identify the
faulted cables, obtain access to both ends, and erect barriers.
2. Discharge the cable under test by applying a ground using a safety grounding stick
(not supplied). Connect a safety ground jumper (not supplied) from the high-voltage
conductor of the cable under test to the specimen ground (the ground conductor of
the cable under test).
F
WARNING
Failure to apply a safety ground jumper to the cable under test
prior to system connection can be extremely dangerous.
3. Choose a location that meets the following conditions:
a. Both the high-voltage conductor and shield of the cable to be tested must be
accessible.
b. An electrical service suitable for the system must be available within 10 ft (3 m)
of the chosen location. The service ground wire must be connected to a secure
low-resistance ground.
c. The system must be within 20 ft (6 m) of the terminal of the cable under test.
d. The test area should be as dry as possible.
e. There should be no flammable material stored in the vicinity.
f. There should be adequate ventilation in the test area.
g. Warning lights or beacons are recommended.
4. Connect the output surge ground (low-voltage return lead of the HV OUTPUT
cable, black boot) to the specimen ground (grounded shield of the cable under test).
F
WARNING
Do not extend the surge ground. Be sure that this connection is
made to a secure low-resistance ground (less than 5O), usually
the driven ground of the power system located in the vicinity of
and connected to the specimen ground.

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5. Connect the HV OUTPUT cable high-voltage lead (red boot) to the faulted high-
voltage conductor of the cable under test. Be sure that the exposed conductor and
clamp are sufficiently insulated to withstand the test voltage.
6. Connect any other conductors of the cable under test to the specimen ground.
7. Be sure that the ON/OFF switch is set to OFF and the OUTPUT KILOVOLTS
switch is set to ZERO START.
F
WARNING
Use only a three-terminal grounded outlet; instrument is
grounded through the line cord. Do not use a three-terminal to
two-terminal adaptor.
8. Connect the AC INPUT cable to the service outlet.
9. For vehicles having a motor-driven generator:
a. Make sure that the ground and neutral of the generator are securely tied to the
machine frame and the chassis of the vehicle.
b. Start the engine-generator and allow it to warm up sufficiently to ensure normal
stable operation.
c. Check the engine-generator voltage to ensure proper input voltage for the
system.
10. Operation from a portable engine-generator:
The system can be operated from a portable engine-generator when a service line is not
available. An engine-generator suitable for sustained operation must be rated at a
minimum of 0.5 kVA. It must be equipped with a good governor that responds to load
change rapidly but without excessive overshoot. The electrical output should be
matched to the rated input voltage, frequency, and power.
a. Locate the engine-generator in a well-ventilated area less than 10 ft (3 m) from
the system.
b. Store spare fuel in a suitable safety container well away from both the engine-
generator and the system.
c. Be sure that the green neutral wire is bonded to the engine-generator frame.
This lead should be no longer than 10 ft (3 m) and should be equivalent to No.
12 AWG or larger.
d. Start the engine-generator and allow it to warm up sufficiently to ensure normal
stable operation.
e. Check the engine-generator voltage to ensure proper input voltage for the
system.
f. Connect the test system to the motor-generator using the input cord.