Distribution Utility Reliability Improvement Initiative

1. LT XLPE Cable & HT ABC Redesign:
Distribution Utility Reliability
Improvement Initiative

2. 2
 Cables are like Artery & Veins
of a distribution utility
 Failures of cables hamper
reliability & customer
satisfaction
Cables

3. Inner
Sheath
Armour
Outer Sheath
Conductor
XLPE
Insulation
Construction of LT XLPE Cable
as per IS 7098- I
About LT XLPE

4. Customer Supply Interruption & Analysis Data (FY 11-12, 12-13 &
13-14)
300000
310000
320000
330000
340000
350000
FY: 11-12 FY: 12-13 FY: 13-14
Nos. 316032 330604 342769
Nos.
No Current Complaints
0.00
5.00
10.00
15.00
20.00
25.00
30.00
S/L
Broken/Bu
rnt
Feeder Trip Cons. Int.
Ckt. Fault
Supply
Failure/BD
FY: 11-12 21.80 11.80 11.20 4.70
FY: 12-13 28.02 10.19 9.47 9.19
FY: 13-14 29.80 10.07 8.97 10.89
%
Top 4 Highest contributor
Service Cable
Failure
 30% of No Supply attributed to Service Cable
Failures
 Financial Loss (FY 13-14)
 Revenue Lost due to unserved power : INR 2.5
Cr/Yr
 Repair & Replacement Cost : INR 2 Cr/Yr
Reasons for failure :-
Cracking of insulation in exposed portion
Probable Reasons of CRACKING :-
1. Improper Bending but not so as Cracking is
throughout the exposed surface only
2. Ultra Violet Rays
Trigger

5. UV Rays are penetrable in RYB Pigmented XLPE Resulting in
Cracking & Failure.
* Refer IEEE Paper: UV Ageing
Need to Re-look LT Cable Design
Is IEC 60502(I)/IS:7098(I) adequate ??
How to make XLPE UV retardant?
I0 = intensity of incident light
I = intensity of transmitted light
 = molar absoptivity coefficient
in cm2 mol-1
c = concentration in mol L-1
b = pathlength of absorbing
solution in cm-1
Beer-Lambert Law
Photo-chemical ageing
due to UV Rays
Describes ageing of XLPE under UV
Light as per following equation
UV Effect on XLPE (Scientific Theory & Field Observation)

6. Carbon
Additive for all
3 cores
Use of TiO2 for
all 3 cores
throughout
Use of UV
retardant
termination kit
Cost Escalation
by 30 %
UV test in hot silicon oil also
confirmed that UV is penetrable
through RYB coloured XLPE but not
penetrable through Black Pigment
LAB Test with UV Source
Lab Test & Probable Solution

7. EUREKA:
UV Retardant by
redesigning all
XLPE cores with
black pigment at
Zero Cost
Conventional design of LT XLPE as per IS: 7098-
I
New Design with all black core & extruded colour coding
EUREKA/New XLPE Cable Design

8. Technical Evaluation
Parameter
"As Is"(RYB & Black Pigment
Neutral)
Proposed Solution (Black Pigment for
all cores)
UV Retardant No Excellent
Water Ingress
(Probability)
High Very Low
UV retardant Accessories Required No Requirement
Probability of exposed
insulation failure
Very High No
Safety of Man & material Unsafe Safe
Economic Evaluation
Parameter
"As Is " Design (RYB Pigmented
Core)
Proposed Design (All Black Pigments
Cores)
Cost of UV Protective
accessories
High, approx. Rs. 50 Lacs/
Annum
Zero
Repair Cost (Mat. + Lab) High, Approx. Rs. 1.5 Cr. / Annum Zero
300000
305000
310000
315000
320000
325000
330000
335000
340000
345000
FY: 11-12 FY: 12-13 FY: 13-14 FY: 14-15
Nos. 316032 330604 342769 329066
Nos.
No Current Complaints
0.00
5.00
10.00
15.00
20.00
25.00
30.00
S/L
Broken/Bur
nt
Feeder Trip Cons. Int.
Ckt. Fault
Supply
Failure/BD
FY: 11-12 21.80 11.80 11.20 4.70
FY: 12-13 28.02 10.19 9.47 9.19
FY: 13-14 29.80 10.07 8.97 10.89
FY: 14-15 22.62 11.01 10.17 9.77
%
Top 4 Highest contributor
Technical & Economic Analysis of New Design

9. HT
ABC
A very novel
concept as
compared to the
conventional over
head bare
conductor.
ABC provides
higher safety
and reliability.
Best choice in
congested urban
areas with narrow
lanes & bi-lanes.
ABC: Aerial Bunched Cable

10. Conductor
Semi-conducting Conductor
Screen
Insulation
Semi-conducting Insulation
Screen
Semi-conducting water
blocking tape
Copper Screen
Outer Sheath
No IS available for HT ABC
IS 7098-II (HT U/G XLPE) is followed by
OEM
All distribution utilities use copper screen
Construction of HT ABC

11. 0
500
1000
1500
2000
2500
FY:09-10 FY:10-11 FY:11-12 FY:12-13 FY:13-14
Nos. 775 1261 1810 1853 2465
Nos.
Nos. of ABC Failure
0
0.2
0.4
0.6
0.8
1
1.2
FY:09-10 FY:10-11 FY:11-12 FY:12-13 FY:13-14
MU Loss 0.5351 0.6654 0.9101 0.9227 1.174
MU
MU Loss
 Increasing trend of ABC Failure
 High MU Loss
 High interruption & Customer Dissatisfaction
Trigger

12. Sparking
spot
Outer sheath burnt
Insulation damage
due to sparking
Cause of Sparking
Sparking & Hissing
sound is developed
between Copper
screen & Messenger
wire due to floating
screen(Disconnected
from messenger)
Initial
stage
Outer Sheath burnt
along with damage of
XLPE insulation due to
heat & sparking.
Later
stage
The design of HT ABC is such that a substantial capacitive voltage is induced at
copper screen if metallic screen is in floating state, resulting in sparking & discharging
sound and capable to puncture the outer sheath.
Issues with ABC

13. When screen is not connected with messenger/earth @ NO LOAD
Voltage Measured at conductor of ABC : 6.06 KV
Voltage measured at copper screen: 4.49KV (Approx. 80% of Ph
Voltage)
MF: 1000
Design Snag

14. 11 KV
150mm2
Aluminium
Conductor
Messenger
100 mm2
6.5 KV
8 Volts
100 mm2
Aluminium
Screen
11 KV
150mm2
Aluminium
Conductor
Messenger
100 mm2
6.5 KV
4.8 KV
2.5 mm2
Copper
Screen
Design Snag

15. • Faults generally occurs due to
substandard material/Design
snag
INTERNAL
FAULTS
• Birdage /tree
fault/equipment/Network
failures.
EXTERNAL
OR THROUGH
FAULTS
Our fault analysis reveals that around 70% faults are of Internal
fault in nature.
Type of ABC Failure

16. Screen
Messenger
Fault CurrentOwing to its lower resistance,
messenger wire will carry about
36 times more current than
copper screen
Conductor
Fault Study: External Fault

17. (f ile test2.pl4; x-v ar t) c:XX0054-XX0002 c:XX0054-XX0004
0.00 0.04 0.08 0.12 0.16 0.20[s]
-10.0
-7.5
-5.0
-2.5
0.0
2.5
5.0
7.5
10.0
[kA]
Earthing of HT ABC Screen - Simulation
Messenger
Current
Screen Current
Fault current distribution in case of External Fault
Fault Analysis: Ext. Fault

18. Conductor
Screen
Messenger
Fault Current
In case of internal fault, almost total
fault current travels through the copper
screen thus Burning the screen as well
as damage of XLPE Insulation
Fault Study: Internal Fault

19. Earthing of HT ABC Screen - Simulation
Fault current distribution in case of Internal Fault
Screen Current
Messenger Current
Fault Analysis

20.  Missing/Damage/
disconnected Earthing
 Capacitive Voltage: 80% of
Phase Voltage on Screen
during floating earth
 Insufficient cross section of
Copper screen to withstand
high fault current
Shortcomings

21.  Existing short circuit current rating of
the Cu tape which is 2.5mm² was
reviewed so as to withstand a short
circuit current of 10kA for 1sec.
 70 mm ² Copper is required for
10KA which will increase the
cost by 4 times & weight by 2
times
 So 100mm² Aluminium is opted
instead of copper
 Reduction in capacitive voltage due
to increased cross section
Old HT ABC with
copper tape screen for
0.25KA for one sec
fault current rating
New HT ABC with Al
wire screen for 10KA
for one sec fault
current rating
Eureka: New ABC Design

22. When screen is not connected with
messenger/earth @ NO LOAD
Voltage Measured at conductor of ABC : 6.06
KV
Voltage measured at Aluminium screen: 8V
Voltage Measured with new ABC Design

23. Technical Evaluation
Parameter Conventional ABC ABC with Al Screen
Fault Current capacity 0.25kA for 1sec 10kA for 1sec
Probability of insulation
failure
Very High Low
Induced Voltage at Cu
Screen @no load
80% of Ph Voltage Close to Zero
Aging of cables Very Fast Very Slow
0
500
1000
1500
2000
2500
FY:09-10 FY:10-11 FY:11-12 FY:12-13 FY:13-14 FY:14-15
Nos. 775 1261 1810 1853 2465 1624
Nos.
Nos. of ABC Failure
0
0.2
0.4
0.6
0.8
1
1.2
FY:09-10 FY:10-11 FY:11-12 FY:12-13 FY:13-14 FY:14-15
MU Loss 0.5351 0.6654 0.9101 0.9227 1.174 0.8521
MU
MU Loss
Economic Evaluation
Parameter Conventional ABC ABC with Al Screen
Cost of Cable/m(150sqmm) INR 600 INR 650
Repair/Replacement Cost Very High Low
Technical & Economic Analysis of New Design

24. Cable&ABCRedesign
Specification revised for both LT XLPE Cable & HT ABC
Patent Filed for LT XLPE Cable Design. Reg. No. 1301/DEL/2014
Replicable across all distribution utility
Proposal sent to BIS to revise IS: 7098-I for LT XLPE Cable
Already Shared with nearby utility & implemented at DHBVNL,Haryana
Journey So Far

25. Thank You