KEHUI T-305E User manual

T-305E High Voltage Surge Generator
User Manual
Kehui International Ltd.
2 Centrus, Mead Lane, Hertford
Hertfordshire, SG13 7GX
United Kingdom
Phone: [phone]
Fax: [phone]
Website: http://kehui.com

T-305E User Manual Version 3.5 | 2
Legal Notices
The copyright of this material belongs to Kehui International Ltd. No company or individual may
extract, copy or translate in any way without the written permission of the copyright owner.
Copyright infringement will be investigated.
This product complies with the design requirements for environmental protection and personal
safety.
This product is a professional instrument specially designed for power cable faults. Please do not use
it for any other purpose. The company assumes no responsibility or loss if it is used for other
purposes.
The safety regulations in this user manual should be strictly adhered to.
The storage, use and disposal of the product should be in accordance with the product manual,
relevant contracts or relevant laws and regulations.
As part of Kehui’s continual product development this product is subject to design or technical
changes without prior notice. When product improvement or technical changes occur, you can check
the information through Kehui International Ltd. website http://www.kehui.com.
Disclaimer: Every effort has been made to make this material complete, accurate, and up-to-date. In
addition, changes are periodically added to the information herein; these changes will be
incorporated into new editions of the publication. Kehui International Ltd reserves the right to make
improvements and/or changes to the product(s) and/or the program(s) described in this document
without notice, and shall not be responsible for any damages, including but not limited to
consequential damages, caused by reliance on the material presented, including but not limited to
typographical errors.
NOTE: Windows is a registered trademark of Microsoft.
Revision history:
Data version
Revision date
Revision reason
Person
3.0
2019.05.01
New block diagram and front panel added,
final edit
TonYip/DiaKib
3.1
2019.05.01
New block diagram P8
DiaKib
3.2
2020.02.10
Clarified grounding and T-H200 operation
BilKib
3.3
2021.03.17
Updated technical data, more detail on 2048J
version
BilKib
3.4
2021.04.10
Replacement of diagrams with photographs.
Page numbering & Order codes
BilKib/DiaKib
3.5
2021.07.16
Layout change and additional instructions
following customer feedback
BilKib
Document number: T305E_UM_V3.5_EN

T-305E User Manual Version 3.5 | 3
Foreword
Thank you for purchasing the new product of Kehui - T-305E, the high voltage surge
generator (hereinafter referred to as T-305E)
The T-305E is a high-performance high voltage surge generator with a maximum output
voltage of 32kV and with versions providing a maximum surge energy of 1024J or 2048J. It is
used for pre-location and pinpointing of high impedance and intermittent flashing faults of
underground power cables.
The T-305E provides either DC or single-shot high voltage surge voltage signals to the faulty
cable to break down the fault for pre-location purpose. It works in conjunction with Kehui’s
T-906, cable fault locator, to pre-locate cable faults. T-305E supports the Secondary/
Multiple Impulse Methods (SIM/MIM) and the Impulse Current Method (ICM) for fault pre-
location.
T-305E works in conjunction with the T-506 for cable fault pinpointing. It provides cyclic
impulses to the faulty cable to periodically break down high impedance and flashing faults.
A magnetic field and an acoustic signal are produced during this process. The signals are
used by the T-506 to trace and to pinpoint the fault by the magnetic field and sound
coincidence method. The unit can also be used as a DC power source for the T-H200 sheath
fault locator.
Kehui constantly improves its products, and the individual instruments provided may differ
from the instructions in this manual without prior notice. We are always at your service if
you have any queries or should you require further information.

T-305E User Manual Version 3.5 | 4
Table of Contents
1. SAFETY INSTRUCTIONS ..............................................................................................................5
2. PRODUCT OVERVIEW..................................................................................................................6
2.1 Product features........................................................................................................................6
2.2 Main use and scope of application ..............................................................................................6
2.3 Product nomenclature ...............................................................................................................6
2.4 Environmental conditions...........................................................................................................6
2.5 Standard Configuration ..............................................................................................................6
2.6 Technical Data Sheet..................................................................................................................7
3. WORKING PRINCIPLE...................................................................................................................8
3.1 Basic Operation .........................................................................................................................8
3.2 DC operation .............................................................................................................................9
3.3 Surge operation .........................................................................................................................9
3.4 Low-voltage cable break-down .................................................................................................10
4. EQUIPMENT CONSTRUCTION...................................................................................................11
4.1 User interface Description ........................................................................................................11
4.2 Rear Panel Description .............................................................................................................13
4.3 Side Panel Description..............................................................................................................14
5. GETTING STARTED ....................................................................................................................15
5.1 Using the discharge rod............................................................................................................15
5.2 Wiring connection ...................................................................................................................15
5.3 Modes of operation .................................................................................................................16
6. FAULT PRE-LOCATION...............................................................................................................17
6.1 DC flashover method ...............................................................................................................17
6.2 Impulse flashover method ........................................................................................................18
6.3 Impulse Current Method (ICM) Testing......................................................................................18
6.4 Secondary/Multiple Impulse Method (SIM/MIM) .......................................................................19
7. DC VOLTAGE WITHSTAND TEST ..............................................................................................19
7.1 Cable Connection.....................................................................................................................19
7.2 Performing the Test .................................................................................................................19
7.3 Power off the T-305E ...............................................................................................................20
8. PINPOINTING FAULTS USING THE CYCLIC MODE .................................................................20
9. SHEATH FAULT LOCATION USING THE KEHUI T-H200..........................................................22
10. SHUT-DOWN PROCEDURE.....................................................................................................23
11. MAINTENANCE AND TROUBLESHOOTING...........................................................................23
12. PACKING LIST - T-305E PACKING LIST..................................................................................24

T-305E User Manual Version 3.5 | 5
1. Safety Instructions
Safety Note:
This user manual is the basic commissioning and on-site operation guide for
the T-305E. All operators who will use the T-305E should read the entire
contents of this manual in advance. The manufacturer of this product is not
responsible for any loss caused by the operator's failure to comply with the
operating procedures of this manual or for violation of the safe working
procedures of the operator.
Meaning of the
manual symbols
Important instructions concerning personal safety, operating procedures,
technical safety, etc., are marked with the following symbols:
Symbol
Meaning
Indicates a potential hazard that could result in fatal
or serious injury
Indicates a potential hazard which, if not avoided,
may result in minor personal injury or property
damage.
Indicates that it contains important information and
useful guidance for using this product. Failure to
heed this information will result in the test not
functioning properly.
Indicates that this is a useful guideline based on field
practice.
Use of
accessories:
Please be sure to use Kehui’s spare parts to ensure the safe and reliable use
of this instrument. Using accessories made by other companies will make any
warranty null and void.
Repair and
maintenance:
This instrument must be repaired and maintained by Kehui or an agent
authorised by Kehui. If you have any questions such as maintenance, cable
fault detection, on-site test consultation, etc., please contact
[email protected]

T-305E User Manual Version 3.5 | 6
2. Product Overview
2.1 Product features
The product has the following characteristics:
1. Three modes of operation: DC, pulse or periodic.
2. Different capacitor bank connection to provide different capacitance by a switch
operation. The energy of the surge is directly proportional to the capacitance value.
3. Interlocking features prevent the equipment from HV operation if the ground is not
securely connected.
4. Automatic discharge facility to remove the charges for the equipment and the cable’s
capacitance after test.
2.2 Main use and scope of application
T-305E is used together with Kehui’s power cable fault locator T-906 and pinpointer T-506, to pre-locate
and to pinpoint underground power cable faults
The equipment consists of voltage conversion and rectification to produce high DC voltage for the
test. Interlocking and safety features ensure safe and reliable operation of the equipment during test.
2.3 Product nomenclature
Product model naming method:
T–3 05 E
Enhancement
Design Number
High voltage surge generator
Cable Test Equipment
2.4 Environmental conditions
1. Working environment temperature: -10°C to 40°C
2. Working environment humidity: 20-90% RH at 25 °C
3. Storage environment temperature: -10°C to 60°C
4. Atmospheric pressure: 86 to 016kPa
2.5 Standard Configuration
1. T-305E instrument
2. Cable for triggering and signalling
3. Earthing cables
4. A user manual

T-305E User Manual Version 3.5 | 7
2.6 Technical Data Sheet
Technical Parameters
Parameter Value
Output Voltage
0-32kV, 0-16kV, 0-8kV, Adjustable negative DC
DC Voltage
0-32kV/25mA negative polarity
Rated capacitance for
1024J version
2μf (when output voltage is from 0 to 32kV)
8μf (when output voltage is from 0 to 16kV)
32μf (when output voltage is from 0 to 8kV)
Rated capacitance for
2048J version
4μf (when output voltage is from 0 to 32kV)
16μf (when output voltage is from 0 to 16kV)
64μf (when output voltage is from 0 to 8kV)
Impulse energy
1024J: (32kV/2μF, 16kV/8μF, 8kV/32μF)
2048J: (32kV/4μF, 16kV/16μF, 8kV/64μF)
Operating mode
DC / Pulse / Cyclic
Testing method
SIM(MIM) / ICM
Discharge period
4 - 15s adjustable continuously when in Cyclic mode
Discharge device
Built-in
Working voltage
220/240Vac10% (110V through step-up transformer)
Mains Frequency
50/60Hz20%
Maximum Power
consumption
1500W
Dimensions
1024J Version: 500x400x960mm
2048J Version: 500x400x1100mm
Weight
75kg for standard (1024J) version
120kg for 2048J version
HV Cable length
3.6m
Ground cable length
4m
Working ground cable
1.1m
Discharge rod cable
2m
Power cable
1.8m
Operating temperature
-10oC to +50oC
Storage temperature
-40oC to +60oC
Ingress Protection
IP21

T-305E User Manual Version 3.5 | 8
3. Working principle
3.1 Basic Operation
At its simplest level the surge generator can be considered to be a capacitor C which is
charged to a selectable voltage (via the transformer) and discharged into the cable through a
contactor S1. The value of the capacitor and the voltage can be changed to optimise the
surge to break down the fault.
The equipment has an internal safety discharge feature. When the equipment is powered
off, the selected capacitors and the cables will be connected to earth/ground through the
safety facility. This works by closing the switch S2 which allows the charge stored in the cable
capacitance and the surge generator capacitor to be safely “dumped” through a resister. A
simplified scheme is shown in figure 3.1. The switch S1 can be controlled by a timer to give
periodic surges required for pinpointing.
Note: References to earth/earthing and ground/grounding are used throughout and are
interchangeable.
Figure 3.1 Surge Generator schematic diagram

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The design of a practical surge generator is more complicated as can be seen in the block
diagram Figure 3.2 for the T-305E.
3.2 DC operation
The surge generator can be used as a DC source by closing switch S1 and applying the
rectified voltage signal directly to the cable. In this way the device may be used to check the
voltage withstand of the cable.
If a fault on the cable breaks down under this voltage, it sets up a travelling wave which
reflects between the fault and the surge generator which can be measured on a suitable
instrument (e.g., The Kehui T-906) through an inductive coupler on the earth lead. The
distance to the fault can be calculated from the time between the voltage peaks on the
resultant waveform and knowledge of the velocity of propagation of the surge.
DC mode can also be used to power a sheath fault locator, such as the Kehui T-H200. Using
the surge generator for this application makes it unnecessary to use a separate power
source such as the Kehui T-100C. Further details can be found in Section 5.
3.3 Surge operation
If the fault cannot be broken down by simply raising the voltage, it will be necessary to send
a surge of energy in to the cable. This is achieved by charging capacitor C to the required
voltage and discharging it into the suspected cable core through switch S1.
The surge of energy in the cable will be reflected from the far end of the cable, such that the
fault is subjected to a voltage approaching twice the value injected (e.g., a surge at 32kV
setting will subject the fault up to 64kV).
The ability to break down the fault is not just a function of the voltage; it is also dependent
on the available energy which is a function of capacitance where the energy in Joules is
equal to ½ CV2where C is in µF and V in kV.
Figure 3.2 T-305 Block diagram

T-305E User Manual Version 3.5 | 10
The stored energy is discharged into the cable with a steep-fronted, high energy surge.
Examples of these waveforms are shown in Figure 3.3.
Figure 3.3. Surge characteristics
This is a series of curves with axes; V (kV) and t (µs). The black line represents a typical fault
characteristic showing that it will not break down instantaneously.
It is a common misconception that the ability of a surge to break down the fault is solely
dependent on the magnitude of its voltage. Figure 3.3 shows that this is not always the case.
If the green 15kV (4µF) curve is considered, it only cuts the fault characteristic after 6 µs,
when it is past its peak. Meanwhile with twice the voltage but a much lower capacitance,
the blue 30kV curve fails to cut the fault characteristic at all and does not result in a
breakdown. Increasing the capacitance by a factor of two, as shown in the red curve causes a
breakdown after around 4µs. The increase in capacitance serves to increase the energy
delivered in the surge, allowing the breakdown to be achieved at a lower voltage, which may
be the difference between a successful and unsuccessful test.
A further benefit of increasing the capacitance is that the extra energy should result in a
louder sound and more vibration at the fault point which will enhance the pinpointing
process.
The T-305E is available in versions with either 1024J output or 2048J, the disadvantage of
the higher value being an increase in the surge generator’s size and weight.
3.4 Low-voltage cable break-down
The term “low voltage cable” refers to cables rated below 400V and hence, the insulation
rating is also low. In order to protect the healthy sections of the cable, the operator should
be careful to ensure the discharge voltage does not exceed 5kV. If it is difficult to break-
down the fault point at this level, it is better to increase the capacitor value. Typically, 5kV
with 10µF should be sufficient to break-down the fault.

T-305E User Manual Version 3.5 | 11
4. Equipment Construction
The surge generator is housed in a rectangular case, mounted on a pair of wheels to provide
mobility, facilitated by the rear mounted handles. At the front, castors, fitted with brakes,
ensure the equipment in immobile whilst in use. The difference between the 1024J and
2048J versions of the equipment, is the size of the internal capacitors. This makes the 2048J
device heavier and slightly taller (see section 2.6 Technical data).
The T-305E is fitted with a collapsible shelf, which provides a convenient space to position
the Kehui T-906 TDR fault locator. The cables are contained in a bag at the front of the unit.
Figure 4.1 T-305E in use, showing wheels, castors, cable bag and shelf
4.1 User interface Description
The user interface is situated on top of the unit. The layout of the 1024J and 2048J versions
is identical except for the values on the capacitor bank switch. The details of the user
controls are shown in figure 4.3.
Figure 4.2 Top panel (user interface) on the 2048J version

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1. HV Voltmeter: Shows the magnitude of the high voltage output. The analogue meter
allows the voltage fluctuations to be observed during discharge.
2. Ammeter: Indicates the leakage current during insulation testing.
3. Grounding alarm: Provides a red indication when the protective ground is not properly
connected. When the alarm is activated, the HV circuit will also be disabled.
4. Stop: Pressing this button will open the HV circuit. The red “start” indication will be
switch off and the green “stop” indication will turn on.
5. Power switch: The key prevents the unit being turned on when the by unauthorised
personnel.
6. Timer: The timer sets the cyclic discharge from 4 –15.
7. Start: Pressing this button will close the HV circuit. The internal discharge switch will
operate. The red “start” indication will be on and the green “stop” indication will be off.
8. Mode –Allows the selection of DC, pulse or cyclic modes of operation.
9. Surge –When the pulse mode is selected, pressing this button will produce a single
surge pulse in to the cable under test.
10. Capacitor bank switch –Consists of three capacitor bank settings, selectable for
different cable types and different fault types (note the capacitance values vary
between the 1024J and 2048J versions).
11. Test Voltage Control –Has a zero voltage interlocking during power-up. Before power-
up, the voltage must be adjusted to zero, otherwise the HV circuit cannot start.
12. Test method switch: To switch between two test methods: Impulse current method
(ICM) and Secondary/Multiple impulse method (SIM/MIM).
13. Emergency Stop: In an emergency situation, pressing this button will cut off the power
supply and automatically discharge any residual charge.
Figure 4.3 1024J T-305E Front panel

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4.2 Rear Panel Description
The back panel of the instrument consists of the high voltage output cable, the protection
grounding cable and auxiliary grounding cable.
i. High-voltage output cable: The core of the high-voltage cable is connected to the
faulty cable, the transparent grounding wire is connected to the metallic protective
sheath of the faulty cable. The metallic protective sheath must be grounded, which is
called the working ground (Working GND).
ii. Protection grounding cable: The protection grounding cable is connected to the
ground using the grounding clamp. The protection ground (Protection GND) must be
separated from the working ground. If separate grounding points are not available,
the protection ground can also be connected to the substation earth bar but it must
be as far away as possible from the point where the 'working ground' is connected.
iii. Auxiliary grounding cable: The auxiliary grounding cable is connected to the ground
using the grounding clamp. The auxiliary ground (Auxiliary GND) must be separate
from the protection ground. If separate grounding points are not available, the
auxiliary ground can also be connected to the substation earth bar but it must be as
far away as possible from the point where the 'working ground' is connected.
Additionally, it must not be clamped together with the auxiliary ground, but
connected at a separate point on the substation earth bar.
Note: The protection ground and the auxiliary ground must be grounded separately,
otherwise the high voltage output cannot start.
Figure 4.4 T-305E Back panel

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4.3 Side Panel Description
The side panel consists of the power socket and the interface to T-906, the cable fault locator.
i. Power socket: Connect 220/240V AC input to provide power for the normal operation
of the device.
ii. Trigger/Signal port: For connection to the trigger/signal port of T-906. For the impulse
current method, the output signal is the impulse current. For the secondary/multiple
impulse method, the output signal is the secondary impulse, the input trigger is the
Time Domain Reflectometry (TDR) pulse.
Figure 4.5 T-305E Side panel connections
Trigger connection to T-906 fault
locator to implement the SIM/MIM
or ICM method, depending on the
mode selected.

T-305E User Manual Version 3.5 | 15
5. Getting started
Before operating the instrument, ensure that the cable under test is without power, fully
discharged (see below) and totally isolated.
5.1 Using the discharge rod
The discharge rod supplied with T-305E is multi-sectional and retractable, and in the first
section a discharge resistor is embedded. The discharge procedure consists of three stages:
air ionisation discharge, resistance discharge and direct grounding discharge.
i. Connect the discharge rod cable to the rod and attach it securely to a suitable
grounding point using the crocodile clip.
ii. Holding the handle of the rod, slowly let its metallic point approach the HV test item.
During this process, a crackling discharge sound can be heard. This is air ionization
discharge.
iii. After the air ionisation discharge becomes weak, the point of the rod can make
contact with the HV test item directly. At this time, the item will be discharged
through the discharge resistor inside the rod. The reading of the KV voltmeter will
drop down.
iv. When the reading of the KV voltmeter drops to less than 5kV, use the earth contact tip
of the discharge rod to directly ground the item.
5.2 Wiring connection
i. Preliminary work: disconnect the faulty cable with other devices and ground the metal
sheath. This is the Working Ground, the zero-volt reference point during the discharge
process.
ii. Position the T-305E at about 2m away from the faulty cable, and put the cable fault
locator on the tray at the side panel for easy operation.
iii. Connect the testing cables according to the figure shown below:
Note: The protection ground and the auxiliary ground must be grounded separately,
otherwise the system is not safe.
Figure 5.1 T-305 Connections

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There are five cables that are connected to the device, these are:
1. High Voltage Test Cable - The red high voltage cable should be connected to the
faulty core of the cable under test, the transparent cable should be connected
to the metal sheath, and the metal sheath should be grounded (the Working
GND).
2. Protective GND Cable - This cable should be connected to a separate grounding
point from the Working GND for safety reasons.
3. Auxiliary GND Cable - Use a metal drill rod for grounding. Again, for safe
working, this needs to be separated from the Protective GND.
4. Power Cable - This is to connect to the 220/240V AC supply.
5. TRIGGER/SIGNAL Cable –This is to connect to the TRIGGER/SIGNAL port of the
cable fault locator T-906.
Note: The Protective GND should be electrically separated from the Working GND (GND).
This is to protect the shell of the instrument from the inducing voltage during high voltage
discharge. This is also to protect the user from being injured in case of any T-305E current
leakage.
Warning: Separate the Working GND with the Protective GND, they cannot be connected
to one point. When it is discharging, the voltage of the working GND point will be raised to
thousands of volts in a second. If the Protective GND is not separated from the Working GND,
the high voltage may transmit through the protective earth lead onto the shell of the T-305E,
causing damages to the instrument and injury to the user.
iv. Ensure that the retractable discharging rod is securely attached then clip the other end
on the Working GND point. The discharge rod should be readily accessible beside theT-
305E.
v. After examining all the cables to ensure the connections are correct, the T-305E can
then be powered-on.
5.3 Modes of operation
The T-305E has three modes of operation selectable from the mode switch (figure 4.3 item
8), these are DC mode, Pulse mode and Cyclic mode.
5.3.1 DC mode
The DC mode is used for the DC Flashover method (section 6.1), the DC Voltage Withstand
Test (section 7) and it can also be used as a power source for sheath fault testing with the
Kehui T-H200 (section 9).
5.3.2 Pulse mode
The Pulse mode is used for the other pre-location methods; the Impulse flashover method
(section 6.2), the Impulse current method, or ICM (section 6.3) and the Secondary/Multiple
impulse method or SIM/MIM (section 6.4).
5.3.3 Cyclic mode
The Cyclic mode is used for pinpointing using a separate acoustic/electromagnetic detector
such as the Kehui T-506 (section 8).

T-305E User Manual Version 3.5 | 17
6. Fault pre-location
Warning:
•Cable fault location must be performed by properly trained personnel. A minimum of
two people should be present during the test, to ensure safety.
•The operators must be at least 0.5 meters away from the HV connections during testing.
•Before switching between different modes of operation, the user must completely
discharge the T-305E and switch it off.
•When the test is complete, discharge the cable and surge generator manually using the
discharge rod.
T-305E allows several different methods of fault location. Where a triggered TDR unit is
required, the instructions assume the use of the Kehui T-906 which can be connected directly
to the TRIGGER/SIGNAL output port of the T-305E.
6.1 DC flashover method
The DC Flashover method requires a DC output from the T-305E which is increased until the
fault breaks down, the resulting current flow will trigger the T-906 fault locator.
This method can only be used when the fault resistance is very high, as otherwise, most of
the voltage drop is across T-305E’s internal resistance and the voltage at the fault point will
be too low to cause a break-down. In this case, the reading on the kV voltmeter will not
increase and there is a significant buzzing sound from the instrument.
Approximately 20% of cable faults can be located using the DC Flashover methods and most
faults that occur during preventive maintenance tests belong to this category.
The waveform obtained by the DC Flashover method is relatively easy to interpret. However,
the resistance of the fault point will decrease after several discharges, until the method can
no longer be applied. Therefore, the DC Flashover method must be used sparingly.
Operational procedure:
i. Turn the MODE to the DC position.
ii. Power on the T-305E, the green STOP button lights up.
iii. Turn the voltage ADJUST knob to the zero position, to enable the START control.
iv. Press the START button, which then lights-up and the green STOP light turns off. The
sound of the HV protective device inside the instrument can be heard.
v. Turn the ADJUST knob slowly, the HV voltmeter will display the voltage applied across
the fault point. When the voltage is high enough, the fault will break down,
accompanied by the capacitor discharge. Repeat the charge and discharge process, the
pointer of the kV meter swings back and forth periodically. Stop the voltage adjustment
and check the T-906 unit to confirm that it has triggered. The resulting waveform can
be used to measure the distance to the fault.
When adjusting the voltage, if the HV voltmeter pointer goes up slowly or remains static
and there is a loud buzzing sound from the instrument, it indicates that the DC Flashover
method is not suitable. The voltage ADJUST knob should be immediately returned to
the zero position. Under these circumstances a different mode must be used.
vi. Once the process is completed, discharge the cable and surge generator manually using
the discharge rod (see section 5.1 Using the discharge rod)

T-305E User Manual Version 3.5 | 18
6.2 Impulse flashover method
This mode is used to locate the range of faults with low resistance and high DC leakage
current. The corresponding testing method is called the Impulse Flashover method. This
works by initially charging the capacitor bank and, when the voltage reaches a certain value,
the contactor operates connecting the capacitor to the faulty cable to break-down the fault.
The resulting current flow will trigger the Kehui T-906 connected to the internal current
coupler via the TRIGGER/SIGNAL port.
The Impulse Flashover method is suitable for most flashover faults. As with the DC method,
the waveform obtained by the DC Flashover method is relatively simple and easy to
interpret.
Operational procedure:
i. Turn the MODE knob to the PULSE position.
ii. Power on the T-305E, the green STOP button lights up.
iii. Turn the voltage ADJUST knob to the zero position, which enables the START button.
iv. Press the START button, which then lights-up and the green STOP light turns off. Inside
the instrument, the noise of the HV protective device can be heard.
v. Turn the ADJUST knob slowly until the voltage rises to the chosen value, press the PULSE
button to ascertain whether the voltage is sufficient to break-down the fault. If the fault
does not break-down, raise the voltage further and repeat the process until break-down
occurs.
vii. The swing of the pointer of the kV meter will indicate the fault status. A small swing
indicates the fault has not broken down; if it is large, the operation is successful.
viii. When the break-down voltage value has been found, check whether the T-906 has
triggered. If it has but the waveform is not satisfactory, the discharge voltage should be
increased and the process repeated until a suitable waveform is obtained.
ix. Once the process is completed, discharge the cable and surge generator manually using
the discharge rod (see section 5.1 Using the discharge rod).
6.3 Impulse Current Method (ICM) Testing
In this case other suitable makes of TDR unit can be used, connected using a suitable current
sensor attached to the earth wire on the HV output. If the Kehui T-906 is used, an external
current sensor is not required, as it can be directly connected to the TRIGGER/SIGNAL port
using the Lemo cable supplied.
Operational procedure:
i. Turn the MODE knob to the PULSE position.
ii. Turn the TEST METHOD to ICM.
iii. Select a suitable capacitor bank setting.
iv. Power on the T-305E, the green STOP button lights up.
v. Turn the voltage ADJUST knob to the zero position, which enables the START button.
vi. Press the START button, which then lights-up and the green STOP light turns off. Inside
the instrument, the noise of the HV protective device can be heard.

T-305E User Manual Version 3.5 | 19
vii. Turn the ADJUST knob slowly until the voltage rises to the chosen value, press the PULSE
button to ascertain whether the voltage is sufficient to break-down the fault. If the fault
does not break-down, raise the voltage further and repeat the process until break-down
occurs.
viii. When the break-down voltage has been found, press the PULSE button again and check
the waveform on the T-906, which should allow the fault position to be identified.
ix. Once the process is completed, discharge the cable and surge generator manually using
the discharge rod (see section 5.1 Using the discharge rod).
6.4 Secondary/Multiple Impulse Method (SIM/MIM)
The T-906 should be connected to the internal SIM filter of the T-305E through the
TRIGGER/SIGNAL port using the Lemo cable supplied.
Operational procedure:
i. Turn the MODE knob to the PULSE position.
ii. Turn the TEST METHOD to SIM.
iii. Select a suitable capacitor bank setting.
iv. Power on the T-305E, the green STOP button lights up.
v. Turn the voltage ADJUST knob to the zero position, which enables the START button.
vi. Press the START button, which then lights-up and the green STOP light turns off. Inside
the instrument, the noise of the HV protective device can be heard
vii. Turn the ADJUST knob slowly until the voltage rises to the chosen value, press the PULSE
button to ascertain whether the voltage is sufficient to break-down the fault. If the fault
does not break-down, raising the voltage further and repeat the process until break-
down occurs.
viii. When the break-down voltage has been found, press the PULSE button again and check
the waveform on the T-906, which should allow the fault position to be identified.
ix. Once the process is completed, discharge the cable and surge generator manually using
the discharge rod (see section 5.1 Using the discharge rod)
7. DC Voltage Withstand Test
For power cables rated at 6kV or below, after the fault has been repaired, the T-305E can be
used to perform a DC voltage withstand test.
7.1 Cable Connection
Before commencing the test, disconnect the faulty cable and ground the metal sheath.
Note: This is the Working Ground, the zero-volt reference point during the discharging
process.
7.2 Performing the Test
Because the remaining charge on the cable may be significant, it should be thoroughly
discharged before the test. As a guide, it usually needs 5 minutes for the discharge process
(see section 5.1 Using the discharge rod).

T-305E User Manual Version 3.5 | 20
Operational procedure:
i. Turn the MODE knob to the DC position.
ii. Power on the T-305E, the green STOP button lights up.
iii. Turn the voltage ADJUST knob to the zero position, which enables the START button.
iv. Press the START button, which then lights-up and the green STOP light turns off. Inside
the instrument, the noise of the HV protective device can be heard
v. Increase the voltage by slowly turning the ADJUST knob, the voltmeter shows the
voltage applied to the cable. When it reaches 75% of the test voltage, the rate of rise
should increase to roughly 2% per second avoiding undue stress to the cable.
vi. If the cable fails the test, the voltage will collapse and the current will increase due to
the breakdown of the insulation. On a healthy cable, no breakdown will occur.
7.3 Power off the T-305E
After the test is finished, turn the ADJUST knob to zero to discharge the cable. The T-305E
can then be powered down.
Warning:
The power off procedure for DC Voltage Withstand Test is different from that for break-
down test. There is no discharge loop for this test, the energy on the cable can only be
discharged by the discharge rod. Therefore, the user MUST follow the correct discharge
procedure using the discharge rod as described in section 5.1.
8. Pinpointing faults using the cyclic mode
This mode is used for pinpointing the fault position of the cable using the Kehui T-506
pinpointer or any similar device . In this mode, the T-305E will discharge to the cable at a
frequency determined by the TIME dial setting. The flow of current through the fault point
as it breaks down, generates periodic magnetic and acoustic signals, which can be picked up
by the T-506 pinpointer for precise location of the fault.
Figure 8.1 Pinpointer in use, with the resultant magnetic and acoustic waveforms