Fakultät für Elektrotechnik und Informationstechnik Lehrstuhl für Energiesysteme und Energiewirtschaft Prof. Dr.-Ing. E. Handschin Universität Dortmund Distribution networks in Germany Lecture at the Universidad de Chile Prof.-Dr.-Ing. E. Handschin

2 Content Basic data of the German electricity network Decentralised power supply Supply reliability Communication networks for the power supply Powerline in low tension networks Operating state diagnostic Conclusion, Outlook

3 German Extra-High Voltage Network Basic data of the German electricity network 1 EnBW Transportnetze AG 2 E.ON Netz GmbH 3 RWE Net AG 4 Vattenfall Europe Transmission GmbH Control areas

4 Grid type Circuit lengths in km Cable rate in % eHV and HV MV LV total Cables and overhead lines age pattern of the cables age pattern of the equipment

5 Electricity network operators approx. 900 mains supply operators Distribution networks in Germany Point of origin supply interruption (in %) Plants ~ 0 (except heavy troubles) 220-/380-kV- Grids ~ 0,1 (except heavy troubles) 110-kV-Grids~ 2 MT-Grids~ 80 LT-Grids~ 20

6 Average electricity bill of a three-person-household per month in € (Source VDEW)

7 installed power in Germany Power capacity 2002 till 2030 Replacement of Investment ? Water Wind Other thermal Oil Natural Gas Hard Coal Lignite Uranium

8 regenerative kW h/a kW h/a kW h/a kW h/a kW h/a kW h/a DC AC DC AC DC AC DC AC ~ ~~ Stirlingmotor DC AC ~ natural and bio-gas Decentralised Energy Conversion Systems Fuel Cell Gasmotor Gasturbine Wind energyHydroPhotovoltaic Microturbine Technologies of DECS

9 Characteristics of dispersed generation plants TechnologyElectricity networkHeat / Cooling energy Other functions Biomass CCPBase- /Middle-Load Connection: MV-/HV-Net Heat production in all temperature ranges Reserve and balance power Heat storage Geothermal plant Base- /Middle-Load Connection: MV-/HV-Net Temperature range < 200 °C Short term for peak load possible Wind energy conversion Medium load Connection: MV-Net noneLarge wind farms may produce hydrogen PhotovoltaicConnection: LV-NetTemperature range ≤ C none Micro gas turbine Medium-/ peak load Connection: LV Net Temperature range 200 – 500 °C Large building supply Load management Control and reserve power in combination with a virtual power plant Alternative fuels Low temperature FC Medium-/ peak load Connection: NS Temperature range < 200 °C High temperature FC Base-/ middle load Connection:MV Net Temperature range > 200 °C

[TWh] HydropowerWind powerBiomassPhotovoltaic Contribution of the renewable energies to power generation 1990 – 2004 (source:BMU)

11 Power plants Large power plants supply all customers 110/220/380 kV 10/20 kV 0,4 kV HouseholdIndustry Problems: Flexibility of generation and distribution Operating costs Approval of projects Supply quality Developing countries Present Structure of Electric Power Systems

12 Power Quality Storage Industry Solar Household Fuel Cell Wind Combined cycle plant Storage Advantages: Dispersed generation Energy storage Power quality + Intelligent communication systems + Decentralised energy management systems = The Electric Power Network of the Future The Electric Power Network of the Future 0,4 kV 10/20 kV 110 kV Metering Centralized / Decentralized Electric Power Systems

13 ~ 10 kV 0,4 kV 10 kV PV Yesterday ~ ~ ~ 10 kV 0,4 kV 10 kV PV WEC Today ~ ~ ~ ~ ~ 10 kV 0,4 kV 10 kV ~ ~ ~ PV FC WEC Tomorrow Electricity Heat/Cold IT Water The Distribution Grid Structure in Comparison

14 Integration of DG in the Distribution Network + Superposition of perturbations, in particular for f > 2,5 kHz + Installed Protection must be re-designed + Liberalization + Ancillary Services +... Definition of supplementary supply conditions Technical + Economical + legal = Integration Individual Integration Fixed Integration Distribution Capacity Spectral Network Impedance Network Protection Certification Need for Action

15 h h h h h h h h Extended connecting conditions spectral grid impedance I Household supply connection with inverter, load and source of interference ZÜ2 h ZÜ1 ZÜ4 ZTZT ZNZN ZIZI h IVIV h I Um h UNUN CK 10 kV 0,4 kV System- capacities Transformer Cable / overhead line 1 Grid impedance at PCC 1 Z h 1 UNUN Z 1 UNUN h Measurement at PCC 1 I M External AC-Source PCC Point of Common Coupling PCC Z = f ( Z N, Z T, Z I, Z Ü, x, t, h ) 1 h

16 Extended connecting conditions spectral Grid impedance Current characteristic curve Inverter Compatibility level for U Individual Compatibility level Connection Spectral Grid-impedance characteristic curve as basic connection condition Mathematical result measurement Impedance characteristic curve at PCC Individual compatibility level

17 U soll,UW = 10,6 kV U soll,UW = 10,2 kV load: P L = 4,3 MW Q L = 2,1 MVar U= 9,7 kV U= 9,4 kV feeding: P= 4,3 MW Q= 2,1 MVar U= 10,9 kV U= 10,6 kV  Main operators are obliged to supply customers in the LV-grid with supply voltage in interval U n -10% < U< U n + 10% (DIN IEC 38).  Voltage control for MV- and LV- grids takes place centrally at the power substation (PS).  Problems for voltage control in grids with distributing poles (dp) with high load and feeding  voltage decrease for the right distributing pole  voltage increase for the left distributing pole load flow voltage drop Voltage scheduling

18 G G G G G G G G high voltage bus MV- unit MV- unit  Dimensioning of the dynamic short circuit power considers only the contribution of the feeding grid.  At the 100 % level of the dynamic strength determined by the feeding network increased risk in the direct vicinity of the substation. short-circuit power Short circuit power

19 Failure Disconnection Maintenance Disconnection 10 kV Grid ~ 10 kV / 0,4 kV K01K03 K02K04 ONT  Lost of the MV-Grid because of failures or unbalanced Power  Lost of the LV-Grid at service entrance box because of failures  Operational disconnection at local grid transformer by the power company  NO zero voltage operation warranted  short-term feeding of short circuits  High thermal load of inverters and other Grid components  Voltage procrastination in case of single-phase connection  Lost of the selective protection (error location) Islanding can occur in grid coupled operation Consequences of islanding in grid coupled operation DG in grid coupled Mode Islanding

20 System Configuration

21 Powerline Source: Voltage inhouse

22 coordination WT1 WT2 WT3 PV1 PV2 FC1 FC2 MT2 visualization coordination visualization coordination visualization coordination visualization MT3 PV3 FC3 coordination visualization FC: fuel cell WT: wind turbine PV:photovoltaic MT: micro turbine MT1 Distributed Hierachical Energy Management System

23 Asymmetry Unbalanced allocation of 1-phase loads, as well as the operation of 2-phase loads stress transformers and grids asymmetric. Asymmetric operation of the grid can have different effects  unbalanced transformer load, -losses, -hum  Motors are running unbalanced  high losses  short durability  abrasion of bearings  undefined reactive current compensation (Costs) Asymmetry

24 Maintenance and replacement strategies of distribution networks Summarising of single devices to classes, which are characterised by same lifetime-cycles Statistical model of aging- and innovation processes Evaluation of expected failure rates Long-term prediction of maintenance and replacement Comparison of different maintenance and replacement strategies

25 Maintenance and renewal strategies of distribution networks Modelling of aging processes Maximum age Aging process influenced by maintenance measures Simulator routine Maintenance and replacement strategy (chronological or budget) History of maintenance and replacement of each class Failure rates planned Requirement Maintenance Renewal unplanned Replacement

26 Influence of different replacement strategies 2,5% replacement per year failure rate per year 2% replacement per year failure rate per year 0 0,01 0,02 0, Year Replacement and failure rate [1/a] Period of rising replacement requirement in case of strategy “2% per year” failure rate > 2%

27  Currently there is only limited experience with dispersed generation (DG) within the distribution network  A high penetration of dispersed generation requires detailed investigations, concentrating on protection devices and power quality; existing distribution networks were planned under different operating conditions  Increasing penetration of DG leads to new requirements of the network operation  Economic operation of virtual power plants needs a new energy management system (Multi agent real-time system)  The virtual power plant characterizes the future vision of distribution systems  Maintenance and replacement strategies have to be optimized to reduce distribution network costs CONCLUSIONS