POWER GENERATION&DISTRIBUTION Assistant Professor Suna BOLAT Office: ee 106 Phone: 366 2197
Electric power system overview
Electric Power System Generation Transmission & Distribution Consumption
Generation and Consumption Konsumenten Produzenten The frequency increases Konsumenten Produzenten The frequency decreases Relationship between generation and consumption Source: ETRANS 19 September 2012 Electric Power Systems
Distributed / Decentralized Generation Centralized Generation Big power plants Transmission Distribution Consumption Distributed / Decentralized Generation (DG) Small power plants close to the consumers Wind, Photovoltaic, fuel cells, micro turbines, small CHP,... Often renewable primary energy sources Often private owners (households, small companies, ) Many DGs in Denmark, Netherlands, Finland,
Decentralized Generation From: Centralisation and decentralisation in strategic municipal energy planning in Denmark Karl Sperling, Frede Hvelplund, Brian Vad Mathiesen, Energy Policy Volume 39, Issue 3 2011 1338 1351 http://dx.doi.org/10.1016/j.enpol.2010.12.006
Connected Grids Advantages: Higher reliability of supply in overall network Exchange of energy internationally. Coupling: Synchronously (via 3-phase AC connections) Asynchronously (via HVDC connections)
TRANSMISSION&DISTRIBUTION
High Voltage Grid Long Distance Transmission (Country, Continent) Import/Export Infeed from large power plants 110 kv, 230 kv, 400 kv AC, power lines and cables HVDC Medium Voltage Grid Regional (sub-)transmission (Bigger cities, cantons) 10 kv, 30 kv, 50 kv AC, power lines and cables Low Voltage Grid Distribution to end consumers (homes, offices, ) 230/400 V Transformations in sub-stations
Overhead line 3-phase systems
Singal phase systems Double single phase system
Power cable
Gas insulated line (transmission)
Transmission&distribution
Grid structures single lines are not sufficient to enable a reliable supply of electricity. A grid of power lines is needed through which the energy can be transported on alternative paths in the event of a line outage. This is referred to as redundancy. In order to provide a high degree of power availability, power grids should be operational under the following two system conditions: under normal operation: when all components, including power stations, transformers, and lines work properly, and under outage operation: when a defined number of operating components have failed.
Examples of grids with different security levels N-0 secure N-1 secure
Distribution grid
High&medium voltage distribution grid Voltage levels: Medium voltage: 3 6 10 15 20 34.5 kv High voltage: 66 154 220 380 500 kv Extra high voltage: 765 1100 kv Distribution in Europe: 20 kv Turkey: 34.5 kv Cypus:?
High&medium voltage distribution grid Radial grid s s s s
High&medium voltage distribution grid Ring grid s 500 kw cos =0,8 500 m 400 m 630 kva cos =0,6 10 kv 800 m 600 m 500 m 380 kw 500 kva 36 A
High&medium voltage distribution grid Meshed grid ~
Low voltage distribution grid 380 (220 1-φ) 400 (231 1-φ) 415 V (240 1-φ) 500 660 V Energy is usually delivered by underground cables
Low voltage distribution
Network operation characteristics 1. NETWORK VOLTAGE: determined according to the load and area Low voltage: 380, 415, 500, 600 V Medium voltage: 3, 6, 10, 15, 20, 34.5 kv High voltage: 66, 154, 220, 380 kv
Network operation characteristics 2. NETWORK FREQUENCY f = 50 Hz 3. NUMBER OF PHASE CONDUCTORS 3-phase 4. NUMBER OF LINES High voltage: 3 wires Low voltage: power consumers; 3 wires composite consumers (lighting and power); 4 wires
Network calculations Thermal considerations Mechanical withstand Economical considerations (loss) Voltage drop Withstand to short circuit currents
Thermal considerations Maximum operating temperature Cross-sectional area of a conductor is determined by the Tables giving the current carrying capability
Current carrying capacity table for copper Size mm 2 Number of loaded conductors and type of insulation Two PVC Three PVC Two XLPE Three XLPE 1.5 22 18 26 22 2.5 29 24 34 29 4 38 31 44 37 6 47 39 56 46 10 63 52 73 61 16 81 67 95 79 25 104 86 121 101 35 125 103 146 122 50 148 122 173 144 70 183 151 213 178 95 216 179 252 211 120 246 203 287 240 150 278 230 324 271 185 312 258 363 304 240 361 297 419 351 300 408 336 474 396
Mechanical considerations In tables, minimum cross-sectional area for conductors is given according to the mechanical strength
Economical considerations Power loss during energy delivery will decrease with the increase in cross-sectional area but the cost will increase! total cost Installation cost q e loss cost Cross-sectional area
Voltage drop In low voltage networks, cross-sectional area of conductors are determined with regard to VOLTAGE DROP!! After that, all the other conditions are cross-checked. Type of installations Lighting circuits A low-voltage service connection from a LV 3% 5% public power distribution network Consumers MV/LV substation supplied from a public distribution MV system 6% 8% Other uses (heating and power)
Short circuit current In high voltage networks, cross-sectional area of conductors are determined with regard to SHORT CIRCUIT CURRENT!! After that, all the other conditions are cross-checked.