Low Voltage Fault Locating Revised

1. 1
LV Low Voltage Cable Fault Locating
Impact of the actual Cable Design on
- understanding the nature of a fault
- selecting the correct method
- applying the correct connection diagram
to successfully fault locate LV Cables
Henning Oetjen, Product Mgr Cable Products, Megger Valley Forge, USA

2. …..what are the alternatives ??

3. 3
Facts to know about Fault Locating of LV Power Cables
1. There are many more designs, materials and construction
types for LV cables compared to MV cables
2. There are many more different types of LV circuit designs
worldwide
3. As a result, there is a multitude of different LV CFL methods
all over the world unlike to MV power cable fault locating

4. Important Statements about fault locating
on LV Power Cables
1. LV power cables typically operated between 120
and 600V
2. Typical voltage rating max. 1.1kV
3. The required voltage to fault locate has
no correlation to the voltage rating of the cable
4. The required voltage depends on the nature of
the fault and the geometry of the cable
construction, many times between 3 and 6kV are
required

5. What are the fundamental differences in construction?
 1. insulated neutral vs. concentric neutral
 2. insulated neutral vs. bare neutral
 3. armoured vs. un-armoured cable
 3. PVC vs. XLPE vs. EPR vs. PILC insulation
What are the fundamental differences in application?
 1. direct buried vs. cable in conduit
 2. Energized = live vs. de-energized
 3. Point to Point circuit vs. Branched network

6. What are the most common LV Fault Locating methods
worldwide ?
 1. LV TDR “phase” comparison (Prelocation)
 2. Conditioning / Burning
 3. HV TDR ARM Method (Prelocation)
 4. ICE Plus (Prelocation)
 5. Tone Tracer = Line Locator (Prelocation of ground faults)
 6. SMART Fuse (Prelocation of intermittend faults)
 7. Voltage gradient method, measuring step potential (Pinpointing)
 8. Surge Generator, thumping (Pinpointing)
 9. LV Bridge Method
10. Fault Sniffer (Pinpointing)

7. What are the most common LV Cables worldwide ?
 1. Triplex, insulated neutral
 2. Concentric neutral type
 3. 3/N Phase un-shielded with Armour
 4. Typical unshielded
 5. Special French Cable
 6. Special Dutch “Combi Cable”

8. All E-Tray Products feature the very same,
most commonly used LV Fault Locating Methods
Especially well qualified are the 3kV and 4kV EZ-THUMP units
 1. LV TDR “phase” comparison
(Prelocation)
 2. HV TDR ARM Method (Prelocation)
 3. Voltage Gradient Method, measuring step potential
(Pinpointing with Galvanometer)
 4. Surge Generator, thumping (Pinpointing)

9. 9
Which methods should be used on what cable type ……..
“Triplex Cable” North America, all Aluminum wires
- single Phase +120V / -120V / Neutral (Residential)
- also available as 3Ø plus Neutral (industrial)
- typically directly buried, sometimes in pipe
TDR phase comparison identifies the following “faults”
- phase to earth ground (often), Ground fault
- phase to phase (rare), Low resistance or
- open neutral (often)
- neutral or phase internally corroded
How to connect TDR - between wires, 3 wires = 3 (combinations) pairs
4 wires = 6 (combinations) pairs
How is defect located - impedance comparison between pairs of wires,
distance to impedance mismatch (higher or lower)

10. 10
Which methods should be used on what cable type ……..
“Triplex Cable” cont’d
- single Phase +120V / -120V / Neutral (Residential)
- also available as 3Ø plus Neutral (industrial)
- typically directly buried, sometimes in pipe
Thumping between wire & earth ground identifies the following faults
- damaged insulation in phase wire or neutral
How to connect unit - HV lead to one wire, HV Return & Ground to ground rod
How is defect located - using the Digiphone Plus as a pinpointer
Step-Potential Method identifies ground (earth) faults of phase or neutral wires
How to connect unit - HV lead to one wire, HV Return & Ground to ground rod
How is defect located

11. 11
Which methods should be used on what cable type ……..
TDR phase comparison identifies the following “faults”
- phase to armor = earth ground (often)
- phase to phase (rare),
How to connect TDR - between wires, 4 wires = 6 (combinations) pairs
- between wire and armor (armor grounded)
How is defect located - impedance comparison between pairs of wires,
distance to impedance mismatch (higher or lower)
Typical 3Ø plus Neutral Cable for LV city networks or
heavy industrial loads, all Copper Conductor
- 3 Ø plus insulated Neutral, with heavy ARMOR
- typically directly buried, sometimes in pipe

12. Which methods should be used on what cable type ……..
HV TDR ARM identifies the following “faults”
- phase to armor = ground fault (typical)
- phase to phase (rare)
- broken armor(rare)
How to connect TDR - between wires, 4 wires = 6 (combinations) pairs
- between wire and armor (armor grounded)
How is defect identified - comparison between pairs of wires
Thumping between wires or between wire & armor identifies the following faults
- damaged phase wire insulation between ground or each other
How to connect unit - HV lead to one wire, HV Return to armor or second wire
How is defect located - using the Digiphone Plus as a pinpointer
Typical 3Ø plus Neutral Cable cont’d

13. 13
Which methods should be used on what cable type ……..
“EDF / ENEDIS” France, all Aluminum wires
- 3 insulated Ø wires plus bare Neutral plus
metallic armor tape wrapped around all wires
- typically directly buried
TDR phase comparison identifies the following “faults”
- phase to earth ground (often), Ground fault
- phase to phase (rare), Low resistance
- open neutral (often)
- neutral or phase internally corroded
How to connect TDR - between 3 wires = 3 (combinations) pairs
- between each wire and neutral wire
How is defect located - impedance comparison between pairs of wires,
distance to impedance mismatch (higher or lower)

14. 14
Which methods should be used on what cable type ……..
“EDF / ENEDIS” France cont’ d
HV TDR ARM identifies the following “faults”
- phase to neutral / armor / ground (typical)
- phase to phase (rare)
How to connect HV TDR - HV lead to one phase, HV Return to neutral/armor
- HV lead to one phase, HV Return to second phase
How is defect located - impedance comparison between HV & LV TDR traces,
distance to impedance mismatch (lower
Thumping between wire & neutral / armor identifies the following faults
- damaged insulation in phase wire
How to connect unit - HV lead to one phase wire, HV Return neutral
How is defect located - using the Digiphone Plus as a pinpointer

15. Application driven matrix for selecting best suited Method
Concen-
tric Neutral
Insulated
Neutral
Bare
Neutral
Direct
buried
Cable in
conduit
Energi-
zed
De-ener-
gized
Intermit-
tent
Branched
system
LV TDR Yes Yes Yes Yes Yes depends yes depends Limited
HV TDR
ARM
Yes No Yes Yes Yes No Yes No Limited
ICE Plus Yes Yes Yes Yes Yes No Yes No Yes
Tone
Tracer
No Yes Yes Yes Typically
Yes
depends Yes No No
SMART
Fuse
Yes Yes Yes Yes Yes Yes No Yes Yes
Voltage
Gradient
No Yes Yes Yes No No Yes No No
Surge
/Thumper
Yes Yes Yes Yes Limited No Yes No Yes
Fault
Sniffer
Yes Yes Yes Yes No Yes Yes No Yes

16. Voltage Gradient Method (direct buried cables)
“Bar graph” “Quasi” analogue display (momentary reading)
“Histogram” display, response of up to 7 pulses = approx.15
seconds is displayed (reading over time)

17. Voltage Gradient Method = Step voltage Method
Histogram type visualization
Advantage:
Changes are much easier recognizable .

18. Case Study in Buenos Aires, LV Circuit EDESUR
Actual
 1. LV TDR “phase” comparison
(Prelocation)
 2. HV TDR ARM Method (Prelocation)
 3. Surge Generator, thumping (Pinpointing)
30,1m

19. Particular area of concern: LV lighting systems in public
areas to address general security concerns, airports
operates 24 hrs
Case Study International Airport Kuala Lumpur

20. 20
Case Study Kuala Lumpur International Airport

21. Case Study International Airport Kuala Lumpur

22. Summary
By applying one or several of the 4 commonly
applied methods presented today
 1. LV TDR “phase” comparison (Prelocation)
 2. HV TDR ARM Method (Prelocation)
 3. Voltage gradient method, measuring step potential (Pinpointing)
 4. Surge Generator, thumping (Pinpointing)
all typical faults in underground LV power Cables can be located

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Questions?
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