distribution cable asset management of hk...

Distribution Cable Asset Management of

HK Electric

November 2014

Presented by: S. T. Ip

Chief Construction & Maintenance Engineer

2

Content

- Introduction to HK Electric

- Asset Management System

- Design Review

- Quality Control

- Data Management

- Performance Evaluation

- Maintenance Strategy

- Condition Monitoring

- Way Forward

Distribution Cable Asset Management of HK Electric

3

Introduction to HK Electric Operating Environment

Supplying electricity to Hong Kong Island,

Lamma Island and Apleichau

Total service area is about 88km2 with day time population of more than 2.5 million

Commercial and financial centers located along the northern shore – load density as high as 250MVA/km2

Densely populated with limited supply of land space --> high rise buildings & high load density

Congested underground facilities and active road excavation work

Extremely high demand on supply reliability & power quality


4

Introduction to HK Electric Transmission and Distribution System

Distribution Substation


275kV Zone Station

275kV Switching Substation

132kV Zone Station

132kV Switching Station

275kV Cable

Interbus Transformer

132kV Cable / Overhead Lines

275kV Cable

Zone Transformer

Zone Transformer

Distribution Transformer

Distribution Transformer

Direct to Customer

LV Cable

LV Cutout / Endbox

11kV Cable

22kV Cable

N/O

Generation 275kV 132kV 22/11kV LV


Generation

5

Asset Management System

- Distribution cable defined as one of the asset

groups of T&D Asset Management System

.Comply with PAS-55 /ISO 55001

- Objectives

.To manage the assets effectively for sustaining

a world class supply reliability

. To excel in services rendered to customers and

the general public


6

Asset Management System

- Distribution Cable Asset Group shall: . Establish asset management strategy . Produce specific asset management objectives, performance targets and management plans . Identify, evaluate and mitigate risks, failure modes and consequences . Carry out regular asset management review every 3 years


7

- Life Cycle & Risk Based Approach For Asset Management

Design of New

Apparatus

Equipment

Manufacturer

Replacement Periodic

Review

End of life / product

obsolescence /

Costly modification or

improvement

O&M

experiences Latest system

requirements

Improvement/ Upgrading

of In-service Apparatus

Retired asset may serve as

strategic spares

International

standard /

Market available

technology with

proven track

record

Improvement

needs

Consultancy /

technical

support

QA/QC

meeting

SMS/AMS *

Skill transfer/

engineering

supervision

Operation, Maintenance &

Refurbishment


8

Design Review 11kV Network

- Open ring design, simple,

flexible and high feeder

utilization

- 100% remote monitoring and

control

- 100% underground cable

- Inter/Intra feeder group

connector to provide additional

back feed sources for feeder with

more than 6 substations, to cater

for double faults. N/O N/O N/O N/O N/O N/O N/O N/O N/O

Source A Source B Source C Source D

Primary

Substation

Level

Distribution

Level

Switching Centre

Clean Feeder



9

INTRA-FEEDER

GROUP

INTERCONNECTION

INTER-FEEDER

GROUP

INTERCONNECTION

SOURCE

A

SOURCE

B

SOURCE

C

SOURCE

D

SOURCE

E

SOURCE

F

FEEDER GROUP 1 FEEDER GROUP 2

N/O

N/O

N/O N/O

N/O

SIX

S/S

SIX

S/S

SIX

S/S

SIX

S/S

SIX

S/S

SIX

S/S

Design Review Typical Inter/Intra Feeder Group Interconnection


10

Design Review 22kV Close Ring Network

- Introduced in 2003 to overcome underground congestion problem

-Closed ring configuration adopted for higher supply reliability and power quality

N/O

SOURCE A SOURCE B

N/O

To other rings



11

Design Review

22kV Rings Interconnection

Full SCADA system for system monitoring and control of each distribution substation


12

Design Review: Joint

Mastic compound

Water Blocked

Joint Remarks:

1st generation – Joint without mastic compound

2nd generation – Joint with mastic for water blocking

3rd generation – Breakout glove at one end & pressure tube on cable core

to stop free water flow along cable body and cores

4th generation – Breakout glove on both ends

Breakout glove Pressure tube

Greatest challenge is to

block the water from

getting into the joint but

keeping the joint small and

cool.

One Typical Example of Continuous Refinement on 11kV Joint


13

Design Review: Cable


Circular core cables to

reduce electric stress

XLPE insulation is

manufactured by dry

curing technologies. The

XLPE insulation is water

tree retardant materials.

High purity compound is

used.

Triple extrusion cable

cores to enhance the firm

contact of the insulation

screen

MDPE oversheath for

better mechanical and

anti-termite protection

GI wire with

bituminous for better

mechanical protection

and anti-corrosion

14

Quality Control Reliability of Jointing

- Cable jointing by in-house resources - Structured trade test system to ensure the quality of jointing skills - Regular refreshment on jointing skills - Regular seminar on latest joint and cable design - Jointer Certification System - Certification by joint manufacturer for newly designed joint


15

Quality Control Reliable Manufacturing

- Good quality and reliable cable/joint comes from precise manufacturing process, stringent quality assurance, and continual quality review - Quality assurance & quality control

meeting/factory visit & audits inward inspection to ensure the quality of cable/joint/termination supplied and provide feedback to the manufacturers

- Cable inward inspection arrangement: 2 samples per cable drum, one keep by the factory and one inspected by HK Electric.

Wavy pattern

found on XLPE

Conductive pick

off on XLPE after

peeling off of

insulation screen

Conductor screen

residual found in

between of copper

strands


Examples of defects found in inwards inspection:

16

Congested Underground Situations


Data Management

17

To facilitate ease of identification at site, different cable outer sheath colours adopted for cable of different voltage class


Data Management

Cable Outer Sheath Colour

Voltage Class Outer Sheath Colour

22kV Turquoise

11kV Red

380V Green

22kV Cable

11kV Cable

380V Cable

18

Data Management

HV Distribution Cable

Routes Map

HV Distribution Cable

Schematic Diagram

HV Distribution Cable Front Page –

recording the details of cable sections,

joint types, cable/joints/termination

installation dates, links to detailed

jointing records , etc.

Geographical Information System(GIS) for cable asset inventory management.


19

Performance Evaluation of 11kV Cable System

Causes of Joint faults

Majority of joint faults attributed to

water ingression

Insulation breakdown

due to water tree

Connector overheat

Overcut at paper

insulation

18%

41% 14%

5%

1%

1% 20%

Distribution of Causes of Cable

Joint Faults

Fault Induced by 3rd Party Disturbances

Water Ingress

Connector Overheat

Workmanship

Water Tree

Termite Attack

Unknown


20

Performance Evaluation of 11kV Cable System Causes of cable body faults

-3rd party disturbances,

water tree and cable

damage are the 3 main

factors for cable body faults

Cable damage

water tree Water tree faults account for ¼ of the cable body fault

24%

21%

33%

22%

Distribution of Causes of Cable Body

Faults

Fault Induced by 3rd Party Disturbances

Water Tree

Cable Damaged

Unknown


21

Performance Evaluation of 11kV Cable System Water Tree Statistics

-Water tree analysis started

in 1996

-No. of XLPE cables with

water tree in insulation is on

average around 5-6% and in

a small rising trend.

- ‘B’ and ‘C’ cables are

classified as Water Tree

Prone Cable (WTPC) and

will be replaced with priority.

0

10

20

30

40

50

60

70

80

90

100

Water Tree Distribution among Cables

0.00%

1.00%

2.00%

3.00%

4.00%

5.00%

6.00%

7.00%

8.00%

2007 2008 2009 2010 2011 2012

% of Core Samples foubd with Water Tree


22

Maintenance Strategy Actions Done in The Past to Improve Reliability

1. Cable damage prevention - Legislation

2. Enhancement in cable & joint design

3. Phasing out of PILC cable termination

4. Phasing out of 1st generation non-water-proofing joint


23

Maintenance Strategy On-going Measures

1. Cable patrol by dedicated cable damage prevention patrol team.

2. Pro-active replacement of unreliable joint types.

3. The design of XLPE-PILC transition joint is enhanced to strengthen

water blocking capability .

4. Short length PILC cable will be replaced in conjunction with other cable

work to eliminate transition joints.

5. Pro-active replacement of water tree prone cables

Additional sleeve installed to

PILC side to strengthen the

water blocking capability in

enhanced transition joint


24

Condition Monitoring

- Condition monitoring based approach - Off line diagnostic testing - On line Partial Discharge monitoring - Proactive water tree analysis


25

TD 3.2kV 6.5kV 10kV L1 123.75 x10-3 91.16 x10-3 76.50 x10-3 L2 12.15 x10-3 13.67 x10-3 33.07 x10-3 L3 6.17 x10-3 7.38 x10-3 13.62 x10-3 Std. Dev 3.2kV 6.5kV 10kV L1 1.657 x10-3 6.140 x10-3 0.391 x10-3 L2 0.045 x10-3 0.067 x10-3 2.641 x10-3 L3 0.045 x10-3 0.010 x10-3 1.054 x10-3

Abnormal reflection

from either joint at

1144m/1149/1201m

Serious corrosion on inner

sleeve sealing interface due

to water penetration

Water was found on

cable core copper screen

tape which was corroded

as well

Water accumulated

inside the inner sleeve

Condition Monitoring Experience on Off Line Diagnostic Testing Example of Successful Cases in Pinpointing Weak Component

High TD measured after

cable overlaid

These cable

sections were

overlaid

TDR indicated water in joints

The joints were

replaced. TD pattern

returned to normal

and dissection

indicated water in

joints and in serious

corroded state.


26

Condition Monitoring Cable Condition Classification

- Based on VLF testing system manufacturer’s proposal, test records, joint

dissection & re-testing results,

Health Index , 5 levels : 5, 4, 3, 2 & 1

HI=5: Immediate action required

HI=4: Re-test in 1 year, HI=3: Re-test in 3 years, HI=2: Re-test in 10 years,

HI=1: Re-test in 20 years

- By mid 2014, 25% of Cable

circuits tested

- Confidence level of revised

classification :

HI=5 > 82.86%, HI=4 >95.00%,

HI=3 > 98.33%, HI=2 >99.37%

& HI=1 > 99.44%

82.86%

95.00% 98.33% 99.37% 99.44%

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

HI(5) HI(4) HI(3) HI(2) HI(1)

Confidence Level of Classification


27

Condition Monitoring On-Line PD Monitoring

-For continuous monitoring the 11kV cable condition, trial installation of on line PD monitoring systems at primary stations for monitoring 11kV and outgoing feeders commenced in 12/2012 and completed in mid 2013

- Three Substations are installed with on line PD monitoring and their performance are under evaluation


28

Way Forward

1. Continue the replacement of weak components in conjunction with network

reinforcement and new supply schemes.

2. Water tree deterioration is irreversible and the water tree infected cables will continue

to deteriorate as reviewed in the slight rising trend of water tree as shown by the

analysis in the previous slide. An accelerated program for replacement of water tree

prone and PILC cables is formulated to phase out these weak cables in 15-20 years

3. Extend the on-line cable monitoring system for all primary stations if the trial is

promising. This can effectively help to reduce tripping incidents at 1st & 2nd cable legs.

4. Cable joint identification by passive device

5. Collaboration with university on designing device for identifying energised unloaded

cable using tunneling electromagnetic resistive principle


29

Thank You


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