theme 1 - smart grids architecturessgemfinalreport.fi/files/s1-1 ug-cabling 2011-eng.pdf · based...

Theme 1 - Smart Grids architectures

WP1.1: Significance of electricity and Smart Grids

4.4.2011 1

Institute of LUT Energy Energy Technology | Electrical Engineering | Environment Technology

Underground Cabling

Juha Haakana, Jukka Lassila

Footer

4.4.2011 3

1. Strategy process2. Cabling process3. Economic analyses4. Case study

The effects on reliability and operational costsThe effect on price of distribution Risk analysis of long interruptions

5. Conclusions

Contents

4.4.2011 4

Underground cablingDrivers

Aging of networkNeed of better reliabilityEconomic regulationTechnical challengesEnvironmental issuesEnergy policyNeeds of society

0,0 %

0,5 %

1,0 %

1,5 %

2,0 %

2,5 %

3,0 %

3,5 %

4,0 %

4,5 %

5,0 %

1950 1954 1956 1958 1960 1962 1964 1966 1968 1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008

Per

cent

age

valu

e of

all

woo

d po

les

Poles that are already at the end of their lifetime, or that are nearing the end

Age of poles +30 years65 % of the poles

4.4.2011 5

Underground cablingStrategy process

Strategic analyses• Comparison of

technologies• Reliability evaluation• The goals of network

development• Evaluation of the state

of present network• Assessment of

parameters

Strategicdecisions

Assessment of the underground cablingprocess (Cabling concept)• Locating of suitable

targets• Evaluation of the

timing• Priority of the targets

in the renovation• etc

Network structure is changing towards underground cabling

A) B) C)

General strategic planning

Assessment of the considered method:Underground cabling

30 fault during last 4 years, network length 100 km

7,5 fault/100 km

Reliability of the distribution should be improved

Aged network structure

Reliability analysis

Network topology

Consideration of the potential of exploitation of different network structures

< 10 a

< 20 a

< 30 a

< 40 a

> 40 a

110/20 kV

4.4.2011 6

Underground cablingStrategy process

Cabling process1. Where the cabling is implemented?2. When the cabling is started?3. How the cabling is implemented?4. What is the priorization of the cabling sections?5. Is there any opportunity to decrease costs with

cooperation with other service providers (tele operation, district heating, water distribution, etc)?

4.4.2011 7

Underground cablingCabling process

Rural area feeder

What is the age and line structure in the studied areas

Where the cabling is implemented?

Urban area feeder with lower load density

Urban area feeder with high load density

4.4.2011 8


a) Step by step carried out renovation (small section are renovated each year) is suitable for networks that have lines from all age groups

When the cabling is started?

< 10 a

< 20 a

< 30 a

< 40 a

> 40 a

110/20 kVFeeder sections that have exceeded their techno-economic lifetime and which are in bad condition

b) Rapidly carried out cabling (renovation is completed fast) process removes workable lines from the network if age varies significantly between the line sections

Is the cabling needed to start within the next years or is it reasonable to delay the starting point by 10 years

4.4.2011 9


When the cabling is started?

< 10 a

< 20 a

< 30 a

< 40 a

> 40 a

110/20 kV

Step by step renovation:Gradual cabling can be focused on the targets, where it is most necessary.

Rapid cabling process:This provides an opportunity to improve reliability in the renovation area remarkably with lower unit costs [€/km], but on the other hand it may cause massive write downs because of removal of the workable lines

4.4.2011 10


How the cabling is implemented?Utilization of cabling techniques

1. Traditional excavation 2. Plowing method

3. Use of chain excavator

Significant part of the total excavation costs consist of the cost component that depends on the used cabling method or technique.

The costs of the cable installation can vary significantly between the techniques. In the suitable ground the costs from the plowing can be only a fraction of costs of traditional excavation. It has been studied that costs from plowing are averagely 50 % from the costs excavation and the suitable ground to plowing method can represent even 80% of the targets.

4.4.2011 11

1. year110/20 kV

= reserve connection (normally open point)


What is the priorization of the cabling sections?

An example of priorization order in the examined networkA. Technical restrictionsB. Age of the linesC. Faulting vulnerabilityD. Suitability of groundE. Branch linesF. Other reasons

In this case the priority is: An old branchline locating in conditions where faulting vulnerability is high

4.4.2011 12


Co-operation with the other infrastructure operators

• Planning of the infrastructure investments togetherwith other operators

• Utilization of excavation for several purposes e.g. electricity distribution cable, optic fiber, water pipes.

• The unit price of cabling can be significantly lower

4.4.2011 13

Underground cablingCompensation of earth fault currents

Centralized compensation• Compensation coil is located to substation• Typical size of the unit is from 50 A to 100 A• Can be used to reduce autoreclosing• Automatic control of system• Big unit size -> risk of failure

Decentralized compensation• Can be divided all over network• Suitable for changing network topologies

• Flexible in renovation that is carried out steply

• Adapts well into exceptional situation such as back-up supply

• Technique is developing

Centralized

Combined compenstion

For instance:100 A = 100 k€

1 k€/A

For instance: 5 A = 10 k€

2 k€/A

4.4.2011 14

Underground cablingBack-up power arrangements

Reserve connections• More loops into networks

Movable aggregates• What is needed amount of aggregates• Requirements for the network

• Connection points: substations, RMU units in the network• Restriction of fault, power of aggregate has to be enough

to supply the interrupted load

Back-up cables• Length of reserve cable (0.5 km)?• Operation with crossing of the roads• Requirements for the network

• Connection points: substations, RMU units in the network

4.4.2011 15

Underground cablingNetwork topology

1) Open questions- What are suitable technical structures to rural area cable networks

- The costs and interaction of solutions to network topology

2) Substations- Satellite substations with simple structures (price approximately 5 k€ without

transformer)

- With one or zero disconnect device

- Possibility to connect reserve power

3) Disconnectors- MV link box, which includes air insulated line disconnector or 2+1 SF6

disconnectors

- RMU devices are installed into substation structures

- Costs are approximately equal to polemounted disconnector stations (+10-20 %)

- RMU-units always remotely controled

MV link box

Substation

4.4.2011

4.4.2011 16

P < PreserveL > Lboundary

P > PreserveL < Lboundary

P > PreserveL > Lboundary

- Each cable is possible to disconnect so that faulted area includes max. one distribution substation

- In case of branch lines the solution depends on the power of load, length of branch, costs of disconnectors and back-up supplies


4.4.2011 17


Profitability of installing cable with or without ring main unit (RMU)

Initial branch line

Excavation 10000€/km, Plowing 5000€/km + RMU 5000 €/unit

100

120

140

160

180

200

220

35 mm2 70 mm2 95 mm2 120 mm2 150 mm2 185 mm2 240 mm2

Cross section of cable

Leng

th o

f bra

nchl

ine

[m]

Marginal cost of excavation

Profitable to excavate and install cable into excavation

Profitable to use plowing and RMU unit

Branch line + RMU

Without RMU

4.4.2011 18

For instance 70 mm2

25 €/m

Excavation:10-15 €/mPloughing (plowing):2-4 €/m

Depending on transformer density in the area, for instance5 €/m

Depending on technology (centralised or distributed), for instance

1-3 €/m

For instance 500 kVA 50 k€/unitCase area 500 km:

0.1 €/m

CABLE CABLING RENOVATION OF DISTRIBUTION TRANSFORMER

COMPENSATION OF EARTH FAULT CURRENTS

BACKUP POWER

Underground cablingCost components

tCtCtCtCtC

tCressubs

compexccabinv

where Ccab =material costsCexc =excavation costsCcomp =compensation costsCsubs =substation costsCres =reserve power costs

Investment costs of cabling consists of:

4.4.2011 19

Underground cablingEconomic analyses

0

200

400

600

800

1 000

1 200

1 400

1 600

1 800

2 000

2 4 6 8 10 12 14 16 18 20

Joht

oläh

dön

huip

pute

ho [k

W]

Roadside (from 5 1 faults/100km,a)Based on long-term statistics:

Fault rate UG cable OH forest OH roadside - Sustained faults 1 10 5 faults/100km,a- HSAR - 25 14 pcs/100km,a- DAR - 10 5 pcs/100km,a- Maintenance 58 153 124 €/km,a- Fault repair 44 100 60 €/km,a

HSAR = High-speed autoreclosing (~ 0.3–0.5 s)DAR = Delayed autoreclosing (~ 1–2 minutes)OH = Over head lineUG = Underground cable

z

z

110/20 kVFeeder 1

Feeder 2

a) Line in forest

b) Line next to road

Forest (from 10 1 faults/100km,a)

9

When road side OH-line is renovated to underground cable, sustained fault rate will decrease from 5 to 1 faults/100km,a (= change 4 faults). If peak power of the feeder is more than 1700 kW, renovation is profitable.

When forest OH-line is renovated to underground cable, sustained fault rate will decrease from 10 to 1 faults/100km,a (= change 9 faults). If peak power of the feeder is more than 700 kW, renovation is profitable.

Analysis includes:- Investment costs- Operational costs- Outage costs

P [kW]

Change in number of sustained faults [faults/100km,a]

4.4.2011 20

< 10 a

< 20 a

< 30 a

< 40 a

> 40 a

110/20 kV

Underground cablingCase study, network renovation

Initial information

Forest rate: 45 %

Average age: 30 a

Length: 52 km (20 kV)

Locates in rural area

Studied medium-voltage feeder

4.4.2011 21

2. year

4. year3. year

110/20 kV

110/20 kV110/20 kV

Priority:1) Age, condition2) Reliability (forest)3) Ground properties

1. year 110/20 kV

= reserve connection (normally open point)

Total length of the feeder is 50 km.

Step by step renovation

4.4.2011 22

0

50 000

100 000

150 000

200 000

250 000

300 000

350 000

400 000

450 000

500 000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Year

Inve

stm

ent [

€/a]

0 %

10 %

20 %

30 %

40 %

50 %

60 %

70 %

80 %

90 %

100 %

Cha

nge

in re

liabi

lity

indi

ces

Investment SAIFI SAIDI MAIFI

100 %

SAIDI

SAIFI

MAIFI

Cha

nge

in re

liabi

lity

indi

ces

Underground cablingCase study, network renovationStudied feeder:Annual investments and development of the reliability indices

4.4.2011 23

0 €

5 000 €

10 000 €

15 000 €

20 000 €

25 000 €

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 %

20 %

40 %

60 %

80 %

100 %

120 %

Outage costs

Maintenance

Fault repair

Cost

s [€

/a]

Year100 % overhead line network

100 % underground cable network

Underground cablingCase study, network renovationStudied feeder:Development of operational costs (Fault repair and maintenance) and Customer outage costs

4.4.2011 24

SAIFI: -72 %

SAIDI: -63 %

MAIFI: -100 %

Outage costs: -77 %


Alternative 1: UG cabling vs. Line renovation to the existing line route (= wooden pole renovation)

Investments: UG 2 M€ vs. OH 0.6 M€ Distribution fee: + 1.4 snt/kWh (+ 1.3 snt/kWh if OPEX benefits included)

OPEX benefits = long term (40 a) economic benefits in maintenance and fault repair costs

Vs.

P = 5 %, t = 40 aE = 100 MWh/km

UG-cabling Pole renovation OH-line to roadside

Alternative 2: UG cabling vs. Line renovation to roadside (= fully new OH-line)

Investments: UG 2 M€ vs. OH 1.2 M€ Distribution fee: + 0.8 snt/kWh (+ 0.7 snt/kWh if OPEX benefits included)

or

Effect of cabling on distribution fee

4.4.2011 25


Alternative 1: UG cabling vs. Line renovation to the existing line route (= wooden pole renovation), difference in investments 1.4 M€

Alternative 2: UG cabling vs. Line renovation to roadside (= fully new OH-line), difference in investments 0.8 M€

0

1

2

3

4

5

6

7

8

9

10

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Average power of the feeder [kW]

Incr

ease

in th

e di

strib

utio

n fe

e [c

nt/k

Wh]

Cabling vs.overhead line pole change Cabling vs. Overhead line next to roadside

Alternative 1 Alternative 2

P = 5 %, t = 40 a

For instance, if average power of the feeder is 1MW, the effect of cabling on distribution fee is ca. 0.9 cnt/kWh in alternative 1 and 0.5 cnt/kWh in alternative 2

Vs.

UG-cabling Pole renovation

or

OH-line to roadside

Effect of cabling on distribution fee

4.4.2011 26

Probability of customer to exceed 6 hours cumulative interruption duration

0 %

5 %

10 %

15 %

20 %

25 %

30 %

35 %

0 500 1000 1500 2000 2500

Customer number

Exce

edin

g pr

obab

ility

Present network (mostly overhead line)

Underground cable network

Underground cablingCase study, network renovationThe effect of underground cabling on risk of experiencing long interruption times within a year

Total number of customers in the case network 2300

In the present overhead line network 250 customer has over 15% probability to experienceover 6 hours cumulative interruptions per year

In the underground cable networkthe risk to experince over 6 hoursannual cumulative interruption is under 15% within all customers

Decrease in the risk of the customer with worst reliability is approximately17 percentage unit that is under 50% from the initial value

References• T. Kaipia, J. Haakana, J. Lassila, J. Partanen, “A Stochastic Approach for Analysing Availability of Electricity Supply,”

Nordac 2010 – Nordic Distribution and Asset Managament Conference, Aalborg, Denmark 2010.• J. Haakana, T. Kaipia, J. Lassila, J. Partanen, “Simulation Method for Evaluation of the Challenges in the Reliability

Performance of Medium-Voltage Networks,” Accepted to be presented in PSCC 2011 Stockholm• ET (Finnish Energy Industries). Report ”Sähkönjakelun toimitusvarmuuden kriteeristö ja tavoitetasot” in Finnish, 2010

4.4.2011 27

Underground cablingConclusions

• Underground cabling needs a lot of ground work• Cabling process includes several phases or questions such as

where, when and how it is carried out• Operational costs decrease because reliability is improved• Customer outage costs decrease because of improved reliability• Effect of cabling on the distribution fee is moderate, for instance in

a case where average power of the feeder is 1000 kW, the increase in the price can vary between 0.5 to 1 cnt/kWh

• The risk level of customers to experience long interruptions decreases significantly

4.4.2011 28284.4.2011

4.4.2011 28

Institute of LUT Energy Energy Technology | Electrical Engineering | Environment Technology

theme 1 - smart grids architecturessgemfinalreport.fi/files/s1-1 ug-cabling 2011-eng.pdf · based...

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