lt xlpe cable & ht abc redesign
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LT XLPE Cable & HT ABC Redesign: Distribution Utility Reliability Improvement
Initiative
2
Cables are like Artery & Veins of a distribution utility
Failures of cables hamper reliability & customer satisfaction
Cables
Inner Sheath
Armour
Outer Sheath
Conductor
XLPE Insulation
Construction of LT XLPE Cable as per IS 7098- I
About LT XLPE
Customer Supply Interruption & Analysis Data (FY 11-12, 12-13 & 13-14)
FY: 11-12 FY: 12-13 FY: 13-14300000305000310000315000320000325000330000335000340000345000
No Current Complaints
Nos
.
S/L Broken/
Burnt
Feeder Trip Cons. Int. Ckt. Fault
Supply Failure/BD
0.00
5.00
10.00
15.00
20.00
25.00
30.00
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
UV Rays are penetrable in RYB Pigmented XLPE Resulting in Cracking & Failure.
* Refer IEEE Paper: UV Ageing
Need to Re-look LT Cable DesignIs IEC 60502(I)/IS:7098(I) adequate ??
How to make XLPE UV retardant?
I0 = intensity of incident light
I = intensity of transmitted lighte = 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)
Carbon Additive for all
3 coresUse 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
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
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
FY: 11-12 FY: 12-13 FY: 13-14 FY: 14-15300000305000310000315000320000325000330000335000340000345000
No Current Complaints
Nos
.
S/L Broken/
Burnt
Feeder Trip Cons. Int. Ckt. Fault
Supply Failure/BD
0.00
5.00
10.00
15.00
20.00
25.00
30.00
Top 4 Highest contributor
%
Technical & Economic Analysis of New Design
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
Conductor
Semi-conducting Conductor Screen
Insulation
Semi-conducting Insulation Screen
Semi-conducting water blocking tape
Copper Screen
Outer Sheath
No IS available for HT ABCIS 7098-II (HT U/G XLPE) is followed by
OEMAll distribution utilities use copper screen
Construction of HT ABC
FY:09-10 FY:10-11 FY:11-12 FY:12-13 FY:13-140
500
1000
1500
2000
2500
Nos. of ABC Failure
Nos
.
FY:09-10 FY:10-11 FY:11-12 FY:12-13 FY:13-140
0.2
0.4
0.6
0.8
1
1.2
MU Loss
MU
Increasing trend of ABC Failure
High MU Loss
High interruption & Customer Dissatisfaction
Trigger
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
When screen is not connected with messenger/earth @ NO LOAD Voltage Measured at conductor of ABC : 6.06 KVVoltage measured at copper screen: 4.49KV (Approx. 80% of Ph Voltage)
MF: 1000
Design Snag
11 KV 150mm2
Aluminium Conductor
Messenger 100 mm2
6.5 KV
8 Volts100 mm2 Aluminium Screen
11 KV 150mm2
Aluminium Conductor
Messenger 100 mm2
6.5 KV
4.8 KV2.5 mm2 Copper Screen
Design Snag
• 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
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
(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
Conductor
Screen
MessengerFault 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
Earthing of HT ABC Screen - Simulation
Fault current distribution in case of Internal Fault
Screen Current
Messenger Current
Fault Analysis
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
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
When screen is not connected with messenger/earth @ NO LOAD Voltage Measured at conductor of ABC : 6.06 KVVoltage measured at Aluminium screen: 8V
Voltage Measured with new ABC Design
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
FY:09-10 FY:10-11 FY:11-12 FY:12-13 FY:13-14 FY:14-15 0
500
1000
1500
2000
2500
Nos. of ABC Failure
Nos
.
FY:09-10 FY:10-11 FY:11-12 FY:12-13 FY:13-14 FY:14-15 0
0.2
0.4
0.6
0.8
1
1.2
MU Loss
MU
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
Cab
le &
AB
C R
edes
ign
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
Thank You
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