Theme 1 - Smart Grids architecturessgemfinalreport.fi/files/S1-1 UG-cabling 2011-Eng.pdf · Based...
Transcript of 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
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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
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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)?
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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
Underground cablingCabling process
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
Underground cablingCabling process
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
Underground cablingCabling process
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.
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1. year110/20 kV
= reserve connection (normally open point)
Underground cablingCabling process
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
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Underground cablingCabling process
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
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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
Underground cablingNetwork topology
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Underground cablingNetwork topology
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
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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]
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< 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
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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 %
Underground cablingCase study, network renovation
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
Underground cablingCase study, network renovation
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