Production and Distribution of Electricity
Vesa Linja-aho — Spring 2013http://www.flickr.com/photos/31119160@N06/8007585111/
Technical details of the course Classes:
Mon 14:00-16:45 @ ETYA1124 (Leppävaara) Wed 14:00-15:45 @ G406 (Kallio)
Excursion: Ensto Group @ Porvoo, Tuesday 5th of February 2013 at 10:00-12:40 We must depart at about 8:30 and we’ll be
back at about 13:30, more information about transportation will follow later.
The final exam is on Monday 25th of February Attending the class is not mandatory, but
highly recommended. All course material will be shared through
Tuubi2
About me Vesa Linja-aho, M. Sc. in electrical and
electronics engineering. Professional background:
7 years at Aalto university (research and teaching)
1 year in Computerworld Finland magazine (editor)
3 years at Metropolia, senior lecturer in automotive electronics.
[email protected], +358404870869
My office is at Kalevankatu 43, Helsinki
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We start with prerequisite exam
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Why… is electric power usually generated in large
plants instead of local generators? are high voltage levels used in power
transmission and distribution? is alternating current used in power
transmission and distribution?
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It is fairly easy to distribute electricity with low losses The distribution losses (from plant to end
user), for distances of couple of hundreds of kilometers, are couple of percents (< 5 %).
There are certain advantages with large-scale production of electricity Emission control Large electric machines have an efficiency
near 100 %.
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Homework Read the following article:
http://en.wikipedia.org/wiki/War_of_Currents
We will discuss it on Monday
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Homework Read the following article:
http://en.wikipedia.org/wiki/War_of_Currents
We will discuss it on Monday
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War of Currents Why was DC more common in the very
early power systems? What inventions lead to the victory of AC? Why was DC transmission inferior to AC
transmission? How about the future? Does DC have any
advantages?
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Three-phase system http://www.wolframalpha.com/input/?i=sin
%282*pi*50*t%29%2C+sin%282*pi*50*t%2B2pi*%281%2F3%29%29%2C+sin%282*pi*50*t%2B2pi*%282%2F3%29%29
Smooth power flow The currents cancel each other -> saves
wiring material. Rotating magnetic field -> easy to design
electric machines.
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AC Pros
Easy to change the voltage level with transformers.
Arcing will cease automatically (zero-point)
Cons Ventricular fibrillation hazard Losses via inductive and capacitive
coupling
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DC Pros
Low losses with long distances Modern electronic and electric appliances
use DC. Many alternative power sources output DC Easy to use with batteries
Cons Changing the voltage level is not simple This is changing with development of power
electronics. Arcing hazard Efficient electric generators produce AC
by nature.12
Second coming of DC? Using DC in buildings can result in 10-20 %
savings. Solar panels, wind power, fuel cells, … Greater capacity for power lines Lower EMI.
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The change is slow The life cycle of the main components
(cables and transformers) is very long For underground cables: 100 years For transformers overhead power lines >
50 years.
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How much? 110 kV overhead power line: 80 000 €/km 20 kV overhead power line: 20 000 €/km 110 kV / 20 kV substation: 0,5-3 M€
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How much power and how far? 110 kV: tens of megawatts for about 100
km. 20 kV: couple of megawatts for about 20-
30 km.
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The pricing The cost of the transmission is typically 15-
50 % of the total price of the electricity. (average for consumers: 30 %).
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What if I used a personal generator? Cost of fuel? Heat of Combustion? Cost of equipment? Efficiency?
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Environmental aspects in distribution and transmission of electricity Landscape protection Wood preservation agents Transformer oil leaks SF6 in circuit breakers Noise
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Landscape protection Where to put the power lines?
On open fields? In the forest? Next to roads? Under ground? 20 kV:
uninsulated: 20 k€/km coated: 26 k€/km underground: 43-100 k€/km
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Tricks for landscape protection When crossing a road, hide the poles in the
forest. In hilly landscape, locate the line so that
it’s silhouette is not against the sky. By using coated wires, the line can be
made more compact and the wires can be camouflaged.
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Wood preservation agents 20 kV and 110 kV lines usually have
wooden poles (they are cheap). Preservation agents raise the life cycle of
the poles from 10 years to over 50 years. Chrome, copper and arsenic (CCA)
preservation agents are forbidden in new constructions and they are handled as toxic waste.
Creosote oil is toxic also, but it is currently the best option
Experimental: Pine oil and other oils.
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Transformer oil Transformer oil is an insulator and coolant. Large substation transformers have a
leakage pool under them, but small pole transformers do not (and they can contain 30-300 liters of oil).
Leakage to ground water is a large risk, but oil leaks are very rare.
In areas with ground water, dry and resin-insulated transformers can be used to eliminate the risk.
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SF6 - Sulfur hexafluoride Used as insulating agent in circuit breakers
very strong insulator arc-suppressive does not corrode switchgear
Very strong greenhouse gas
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Recycling of equipment Wires Poles Transformers
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Noise 50 Hz / 60 Hz hum High voltage switchgear
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Electric and magnetic fields Lot of research is done and AC electric
power lines have existed for 100 years. The safety limits have a lot of overhead Currently:
there is no scientific evidence on harmfullness of low frequency fields (with low intensity)
same concerns the cell phone radiation
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How to increase efficiency? Raise the voltage Use an extra 1 kV step in distibution (for
distances of couple of kilometers).
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Environmental aspects of Electricity Production Heat CO2 Particles Accidents Water usage Nuclear waste Mining and refining Loss of land …
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Most significant sources in the world Coal 41 % Natural Gas 21 % Hydroelectric 16 % Nuclear 13 % Oil 5 % Other 3 %
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Renewable Hydroelectric 92 % Wind 6 % Geothermal 1,8 % Solar photovoltaic 0,06 % Solar thermal 0,004 %
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Efficiency Depends greatly on the fact is the extra
heat used for district heat or similar (cogeneration).
For simple coal or nuclear power plant, the efficiency is about 33 %.
For combined cycle gas turbine plants, the efficiency is over 50 %.
If the waste heat is used for district heating, the total efficiency can be over 80 %.
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Environmental aspects of Electricity Production Heat CO2 Particles Accidents Water usage Nuclear waste Mining and refining Loss of land …
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Most significant sources in the world Coal 41 % Natural Gas 21 % Hydroelectric 16 % Nuclear 13 % Oil 5 % Other 3 %
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Renewable Hydroelectric 92 % Wind 6 % Geothermal 1,8 % Solar photovoltaic 0,06 % Solar thermal 0,004 %
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Efficiency Depends greatly on the fact is the extra
heat used for district heat or similar (cogeneration).
For simple coal or nuclear power plant, the efficiency is about 33 %.
For combined cycle gas turbine plants, the efficiency is over 50 %.
If the waste heat is used for district heating, the total efficiency can be over 80 %.
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Examples of power output Average electric power in world: 2,3 TW Average electric power in Finland: 10 GW Hoover Dam (1936): 2 GW Three Gorges Dam (2008): 22,5 GW Petäjäskoski (Finland’s largest HPP): 182
MW Kashiwazaki-Kariwa NPP: 8,2 GW Olkiluoto NPP 1,2 GW
Additional 1,6 GW in construction Inkoo CPP: 1 GW
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Fossil fuel power generation Basic idea: burn something, generate
steam for turbine. Efficiency: 33-48 %
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Cogeneration, CHP combined heat&power Efficiency: over 80 %.
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Combined cycle power plant Gas turbine + steam turbine. Efficiency over 60 % (even 90 % with CHP)
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Hydroelectric power plant Water rotates a turbine Efficiency little over 90 %
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Nuclear power PWR (Pressurized water reactor) BWR (Boiling water reactor) Efficiency: about > 30 %
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Pressurized water reactor PWR
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Boiling water reactor (BWR)
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Turbogenerators Large electric generators can achieve over
99 % efficiency , if cooled with hydrogen. Why hydrogen?
Low density High specific heat and thermal
conductivity
Rotating speed: typically 3000 or 1500 rpm Output voltage typically 2-30 kV and
output power up to 2 GW.
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Elements of the transmission and distribution system Substations
Transformers Protective equipment
Transmission and distribution lines
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Transmission and distribution voltage 400 kV 220 kV 110 kV (45 kV) 20 kV (10 kV) (1 kV) 400 V (230 V between neutral and phase)
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Other voltage levels in Finland 25 kV (railway overhead lines) 750 VDC (subway) 600 VDC (tram overhead lines) Estlink HVDC: 150 kV Fenno-Skan 1: HVDC: 400 kV Fenno-Skan 2: HVDC: 500 kV
Damaged by ship anchor Feb 2012 Estimated damage to electricity consumers: 80
M€
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Insulators The length of the insulator is about 1 m /
100 kV 110 kV: 6-8 insulator disks 220 kV: 10-12 insulator disks 400 kV: 18-21 insulator disks 20 kV lines have usually small pin
insulators, or couple of disks. Near the insulator, there are vibration
suppression plates on the wire Insulators may have a thin conductive
coating, for de-icing the insulators. Arcing horns protect the insulator from
significant over voltage51
Voltage drop in distribution In cities: 2-3 % In rural areas: 5 % According to SFS-EN 50160, the voltage
can vary +6 %/-10 % (207-244 V).
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Reliability 90 % of blackouts are caused by middle
voltage network failures. Under 10 % are from low-voltage network. High-voltage network failures are very infrequent.
Automatic fast reconnect typically solve 75 % of the failures. Delayed reconnect will solve 15 % of the failures and the remaining 10 % require repair work.
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Electric safety in Finland Electric work is regulated
Typical: degree from vocational school + 1 year of experience.
Electric safety course every 5 years. In the company, a nominated head of
electric work, who has a degree (vocational, bachelor or master) 0.5-2 years of electric work experience passed the electric safety examination
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Three classes of electric qualification EQ 1 (general). EQ 2 (low-voltage). EQ 3 (low-voltage repair).
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Electric deaths in Finland (moving average)
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professionals
non-professionals
Electric deaths in Finland 2012
Electric shock from railway wire 2011
Electric shock from railway wire 2010
Young electrician died when measuring a newly built transmission line.
A person died from a shock from self-repaired extension cord.
Electric shock from railway wire. A detail: last time a small child has died in
electric accident was in year 1996.
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Most common causes for electric accidents Plain stupidity (railway wires) Self-made dangerous connections (protect
earth misconnected). Professionals do not follow the safety
regulations Typical one: after disconnecting the
voltage, the electrician does not verify that the installation is really dead.
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Electric network in buildings
Small buildings: 400 V / 230 V Larger buildings: own 20 kV transformer Industry: 110 kV input
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Approximating the peak power: one way One way:
Lighting: 10 W/m2
Appliances: 6 kW for < 75 m2, 7,5 kW for > 75 m2
+ power of sauna The other way:
Like the first, but appliances: 6 kW + 20 W/m2
With electric heating: the total maximum power heating power
of the radiators, 3 kW for appliances
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Structure of the network All wall sockets are grounded (since 1997). Three-wire system Wiring color system:
Black (or brown or purple or white) = live Blue = neutral Yellow-green: protect earth
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Class I plug + socket
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Protection systems Basic insulation (Class 0) Protect earth (Schuko) (Class I) Double insulation (Class II)
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Basic protection The ”traditional” wall socket and plug. For new buildings, illegal since 1997. The appliances can be used. Problem: single insulation fault can make
the chassis live.
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Protect earth The chassis of the equipment is grounded If the PE wire is intact, there is no way the
chassis would hold a dangerous voltage. Ground fault will blow the fuse
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Safety insulation (Class II) All devices to be sold in EU are either Class
I or Class II devices (or Class III with extra low voltage).
In Class II, no single fault can make the chassis live.
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RCD residual-current device (RCD) = residual-
current circuit breaker (RCCB) = ground fault condition interrupter (GFCI), ground fault interrupter (GFI) or an appliance leakage current interrupter (ALCI)
Monitors the current difference between live and neutral connectors.
http://upload.wikimedia.org/wikipedia/commons/9/91/Fi-rele2.gif
Mandatory in new installations (with certain exceptions)
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Distributed production of electricity Centralized vs. distributed?
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Benefits of centralized production Economics of scale Higher efficiency Low-loss transmission Reliability Environment (plants away from cities)
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Why distributed production? Less pollution Better total efficiency More diverse energy source distribution Easier placement of power plants Back up generation Generation during power peaks Price level of power generators has
decreased and will decrease
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Distributed generation in EU (2004)
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Less pollution ”Free” fuel (hydroelectric, wind) Production near the end user less
transmission losses. Easier cogeneration
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Economic benefits Lower threshold for entering the market Modularity and easy expandability Faster construction Lower capital costs
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Support from the state Subvention for production Tax relief Product development aid Obligation for network company to buy the
electricity in fixed price.
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Examples Small wind farm Small CHP for greenhouses Fuel cell, solar, combustion engine or
microturbine plant
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Challenges The network sees a generator as a
negative load. The voltage at the end of the line will rise -
> less losses. Sizing of the wire can usually not be
altered. Very high power output can cause
problem with overvoltage. The protection equipment should be aware
of the generation.
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Group work Article: Rural Electrification in Developing
Countries. From book Lakervi, Partanen: Sähkönjakelutekniikka. 3. ed. 2008. Otatieto. Pp. 286—295.
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Rural electrification (in developing countries) Form three groups and each group will take
one topic: Social aspects in rural electrification Economical aspects in rural electrification Technical aspects in rural electrification
Read from the article (about 20 minutes): intro + one of the chapters (area data, economical issues or technologies applied)
It is great if your add aspects from your home country, was it industrialized or developing country. Write down your findings.
After this, one will stay at the group and the others will go to next table.
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Rural electrification in developing countries About 4 billion people have access to
electricity (of 7 billion people). Social impact. Economic impact. Environmental impact.
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Conditions vary considerably Some relatively poor countries have high
percentage in rural electrification (Costa Rica, Tunisia).
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Area data Small houses + lamps = 100-200 W /
person Refridgerators & TV:s = 400-500 W / person Electric heating of small houses = 1000-
1500 W / person. If cooking is included = practically same as
in industrialized countries.
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Solutions Hydroelectric power, if available, is the
best solution (almost zero maintenance). Diesel unit a popular choice.
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Challenges Governmental intervention accelerate the
electrification process. In turn, governmental intervention may
include corruption. For sustainable distribution systems, a
long-term financial balance is necessary. A well-functioning supply of electricity
promotes social stability.
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Challenges The wealthy demand high reliability and
voltage stability. The poor demand low tariffs and fast
progression of electrification.
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Smart Grid
Grid + modern automation technology + ICT = smart grid.
Smart grid is a bunch of technologies to make grid more reliable, efficient and flexible.
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History Electricity metering Dual tariff system
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Problems with traditional grids How to cope with demand peaks?
Use peaking generators. Black out certain areas. Suffer from low power quality.
Reliability in crisis situations: Power distribution is pretty sensitive to
terrorist attacks. Reading the electricity meters costs
manpower.
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Solutions
Here already: smart metering. Dynamic demand management: for large
customers. Real-time electricity pricing: in power peak,
raise the price in real time until the demand sags.
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Reliability Automatic fault detection and healing.
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Efficiency Many high-power equipment work with
duty cycle (they run with full power or are off). Example: many air conditioning units.
Making these equipment demand-aware can reduce the peak power requirement without impact to the end user.
Another example: a popular tv-show begins. Demand-aware tv sets would have small delay for powering on and they operate with reduced brightness, so that the power plants have time to increase their output.
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Flexibility Traditional network protection gear is
designed for one-way power flow.
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Sustainability Large amounts of renewable energy need
sophisticated network automation. For example, solar power output changes
suddenly.
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Charging electric vehicles When electric vehicles become more
general, they will impact the sizing of the grid.
During demand peaks, it is reasonable to pause the charging.
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Concerns and challenges Privacy: who can access your electricity
usage data? Complex tariff system – easy to unfairly
trick the customers. Remote shutdown of electric supply. RF emissions (although not scientifically
confirmed, people are afraid of them). Cyberterrorism Relatively high cost of investment
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Asset management in electricity distribution Grid development Grid maintenance Grid operation
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Grid development process Based on the network strategy
(environment, basic principles, present state, main measures for development)
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The current state of the network Voltage drop Voltage elasticity (= how much does the
voltage drop when adding more power demand to certain point).
Loading of the wires Power losses Short circuit / earth fault currents Cost of power interruptions
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Investment planning and prioritization If the yearly growth of the load is small,
the driving factor for reconstruction is the useful life of the network components.
The most important goal is to keep the grid to qualify the requirements of legislation.
The task is a complex optimization process.
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Grid maintenance Fixing maintenance Preventive maintenace
TBM = time based maintenance CBM = condition based maintenance RBM = reliability based maintenance
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Reliability based maintenance
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condition
significance
repair
overhaul
testService if necessary
Reliability based maintenance According to safety standards, overhead
power lines must be inspected every 5 years.
The inspection data is used to decide when to, for example, renew the pylons.
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Examples of routine maintenance Clearance of the right-of-way of the power
lines. Monitoring the oil temp of transformers Thermal imaging
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Grid operation Grid operation = maintaining the short-
term power quality, safety, customert service quality and economy.
The operation is lead from control room …which can be the operator’s laptop .
The head of operation has very strict liability of the electric and work safety.
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Main functions of grid operation Follow-up and control of the grid state. Planning the operation procedures of the
grid Fault management Practical arrangements for maintenance of
the grid components
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Monitoring the grid High voltage and middle voltage network is
highly automated. The low voltage network is not. The only
way the operator gets the information of the fault, is usually customer report. The situation is changing, thanks to AMR
systems.
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High voltage, middle voltage, low voltage In terms of electric safety:
High voltage = HV: > 1000 VAC, > 1500 VDC
Low voltage = LV: > 50 VAC, > 120 VDC Extra low voltage: ELV: < 50 VAC, < 120
VDC
In terms of electricity distribution: Middle voltage: 1…45 kV
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SCADA Supervisory Control and Data Acquisition:
Logging the events Control of the state of the switches in
grid. Remote control Distant reading Reporting
SCADA = high reliability information system for operating the grid
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Communications Radio link Optical fiber (sometimes with 110 kV shield
wires). DLC (Distribution Line Carrier):
20 kV, 3-5 kHz carrier. Will pass the distribution transformers. Typical application: day/night tariff control.
In low-voltage network, a carrier of 150-200 kHz is used.
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Power quality (SFS-EN 50160) Frequency (+/- 1 %) Voltage (+10 %, - 15 %) Fast transients Voltage dips Transient overvoltage (1,5 kV, 6 kV) Short blackouts (< 3 min) Long blackouts Harmonics
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