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Probabilistic Reliability Analysis Supporting Distribution Network Expansion

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## Probabilistic Reliability Analysis Supporting Distribution Network Expansion

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**Probabilistic Reliability AnalysisSupporting Distribution**Network Expansion Klaus Schilling**Overview**• Introduction • System Modelling and Data • Study Results • Summary**Aspects Influencing System Reliability in Liberalized**Markets Reduced maintenance Risingcomponent age Increasingcomponent load Component availability Staff reduction,loss of know how Simplifiednetwork structure System reliability [Schwan et al., 2003]**Loadflow**• Short-Circuit • Dimensioning of LV Networks • Optimal Branching • Multiple Fault • Harmonics • Ripple Control • Stability • ElectromagneticTransients • Eigenvalues / Modal Analysis • Optimal Loadflow • Load Profile Calculation • Load Development • Contingency Analysis • Distance Protection • Over Current Time Protection • Simulation of Relay Tripping • Motor Starting • Line Constants • Reliability For analysis and planning purposes in all network levels with integrated data base and schematic or topological graphics SINCALSiemens Network Calculation**Generation of a failure combination list**Examination of a failure combination Network status analysis Identification of supply interruptions Measures for the rectifying ofsupply interruptions ReliabilityIndices Statistical recording of results Details on Reliability Calculation Determination through probability or order AC load flow Supply restorationstrategies**Models and Data**• Clear boundary of the system and components • Network model which corresponds to operation • Load flow / short-circuit model • Load model • Protection model • Models of failure events • Status of operating equipment • Failure models • Failure sequence • Supply restoration models**Failure Models**• Independent single failure (IS) Failure of one single component • Common-Mode failure (CM) Simultaneous failure of several components due to a common cause • Multiple earth faults with multiple tripping (ME) Independent failure of two components in network with resonant earthing on the bases of an existing earth fault • Malfunction of protection device (PM) Stochastic secondary failure due to failure of the primaryprotection and tripping of the backup protection device • Unnecessary protection operation (UP) Stochastic secondary failure due to non-selective tripping of the protection device**Reliability Indices of the ComponentsExample of the**Distribution System IS: Independent single failure ME: Multiple earth fault PM: Protection malfunction UP: Unnecessary protection operation A: Expected value of failure frequency in yr-1 bzw. km-1yr-1 B: Expected value of outage duration in min. C: Expected value of conditional probability of failure**Probabilistic Reliability Indices**Expected values**Study Task**• A German 110 kV subtransmission system feeding some 20 kV distribution networks should be analysed with special focus on: • The impact of the 110 kV network and the 20 kV structure on the reliability indices of the medium voltage customers • The comparison of the present reliability level of different distribution networks with benchmarks • The comparison of scenarios of network expansion with respect to investment costs and reliability**Supply Area**110 kV OHL 110/20 kV Substation Feeding Substation 110 kV Subtransmission Network and Supply Area**Boundaries of the 110 kV Network**• The infeed from transmission network is 100 % reliable • The MV networks are modeled as bulk load on the 20 kV busbar**Schematic Diagram of the 110 kV Network**E F A C D K J G H B**B**B D D F F Reliability Indices of the Existing 110 kV Network 0.4 Frequency of Supply Interruptions 16 Unavailability 4 Energy Not Served in Time**Boundaries of the 20 kV Network**• The infeed from subtransmission network is 100 % reliable • All MV backup connections are modeled • The load is modeled on the MV side of the distribution transformer**Rural 20 kV Network – Area E**Substation E**Benchmark Rural Area**Average Reliability Indices of a Rural 20 kV Network**Urban 20 kV Network – Area B**Substation B**Benchmark Urban Area**Average Reliability Indices of a Urban 20 kV Network**Existing Substation B**Variant„Switchgear“ Improvement of Substation B**Variant„Overhead Line“**Variant„Underground Cable“ Improvement of Substation BReinforcement of Subtransmission Network**Significance of Probabilistic Reliability Analysis**• Additional tool for planning and operation • Support and addition to (n-1) criterion • Important tool in deregulated networks • Comparison of equal (n-1) variants (e. g. switchgear concept) • Support for network restructuring • Quality level for customer • Basis for risk assessment • Maintenance management