Production and distribution of electricity

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.

firstname.lastname@metropolia.fi, +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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