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Advanced Protection Scheme for DG Islanding Detection Using DLC in MV Networks

This study explores the challenges and solutions related to Distributed Generation (DG) islanding detection through a novel DLC-based protection scheme. By analyzing the coupling capacitance, signal propagation, and feasible transmission distances in medium voltage networks, we demonstrate the potential to mitigate islanding risks. Our findings reveal good agreement between theoretical and measured values, establishing an effective approach to prevent DG islanding. The proposed method optimizes signal integrity and provides guidelines for practical implementation in urban and rural feeder scenarios.

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Advanced Protection Scheme for DG Islanding Detection Using DLC in MV Networks

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  1. THE ISLANDING PROBLEM After system switching operation, a section of the utility network remains connected to the DG ! HV Busbar MV Busbar PASSIVE PROTECTIONS AS Max/min voltage relaying Over/under frequency relaying Rate of change of frequency relays Phase displacement monitoring DEMONSTRATE THE POSSIBILITY OF FAILING THE ISLAND DETECTION

  2. DLC-BASED PROTECTION SCHEME Guard frequency injected at MV busbar Under normal conditions, guard frequency detected by RX

  3. When the breaker is opened there is a loss of guard frequency for the DG receiver

  4. FEASIBILITY OF DLC PROTECTION THE CARRIER SIGNAL PROPAGATION IN MV NETWORKS CAN FIND DIFFICULTIES DUE TO: Ø     overhead and cable line attenuation; Ø     the presence of capacitor banks; Ø     different line segments; Ø     branching; Ø     mismatching and standing wave patterns.

  5. DEVELOPMENT OF A TOOL FOR THE CARRIER SIGNAL TRANSMISSION ANALYSIS OPTIMAL MISMATCHING ZONE STANDING WAVE CONDITIONS Cable Lines ZM = 460  Overhead Lines ZM = 3000  Combination of OHL and CL ZM = 1500 

  6. 0.70 1.25 Conductors ACSR =15.85 mm CC =10.70 mm 10.25 m MV overerhead line Attenuation as a function of receiver impedance ZM less than 0.5 [dB/km] about 1.54 [dB/km] OVERHEAD AND CABLE LINE ATTENUATION

  7. Electric circuit The Coupling Capacitance : EXAMPLE OF A CAPACITIVE COUPLING DEVICE

  8. Comparison between computed and measured values MEASUREMENT CAMPAIGN I URBAN FEEDER ATTENUATION at 72 kHz = 20 db GOOD AGREEMENT !

  9. TX: 20 db on 75  RX: -49.37 db ATTENUATION: 70 db MEASUREMENT CAMPAIGN II RURAL RADIAL FEEDER This measurement campaign seems to be representative of the DLC transmission length limit without the use of repeater devices.

  10. CONCLUSION • A novel protection method to prevent DG islanding; • A suitable analysis procedure has been developed; • Good agreement of test results with the theoretical calculations  (accuracy of the multiconductor matrix procedure); • Distance limit between TX and RX about 10  15 km for a typical Italian radial branched MV feeder; • (If longer distances are needed, the use of repeaters must be taken into consideration).

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