BENATO IT Session 4 – Block 3 – Question 6 Barcelona May 2003 THE ISLANDING PROBLEM PASSIVE PROTECTIONS AS DEMONSTRATE THE POSSIBILITY OF FAILING THE ISLAND DETECTION 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 HV Busbar MV Busbar After system switching operation, a section of the utility network remains connected to the DG !

BENATO IT Session 4 – Block 3 – Question 6 Barcelona May 2003 DLC-BASED PROTECTION SCHEME Under normal conditions, guard frequency detected by RX Guard frequency injected at MV busbar

BENATO IT Session 4 – Block 3 – Question 6 Barcelona May 2003 When the breaker is opened there is a loss of guard frequency for the DG receiver there is a loss of guard frequency for the DG receiver

BENATO IT Session 4 – Block 3 – Question 6 Barcelona May 2003 FEASIBILITY OF DLC PROTECTION THE CARRIER SIGNAL PROPAGATION IN MV NETWORKS CAN FIND DIFFICULTIES DUE TO:  overhead and cable line attenuation;  the presence of capacitor banks;  different line segments;  branching;  mismatching and standing wave patterns.

BENATO IT Session 4 – Block 3 – Question 6 Barcelona May 2003 DEVELOPMENT OF A TOOL FOR THE CARRIER SIGNAL TRANSMISSION ANALYSIS STANDING WAVE CONDITIONS OPTIMAL MISMATCHING ZONE Cable Lines Z M = 460  Overhead Lines Z M = 3000  Combination of OHL and CL Z M = 1500 

BENATO IT Session 4 – Block 3 – Question 6 Barcelona May 2003 OVERHEAD AND CABLE LINE ATTENUATION Attenuation as a function of receiver impedance Z M Attenuation as a function of receiver impedance Z M m MV overerhead line ACSR  =15.85 mm CC  =10.70 mm Conductors less than 0.5 [dB/km] about 1.5  4 [dB/km]

BENATO IT Session 4 – Block 3 – Question 6 Barcelona May 2003 EXAMPLE OF A CAPACITIVE COUPLING DEVICE Electric circuit The Coupling Capacitance :

BENATO IT Session 4 – Block 3 – Question 6 Barcelona May 2003 URBAN FEEDER MEASUREMENT CAMPAIGN I Comparison between computed and measured values ATTENUATION at 72 kHz = 20 db GOOD AGREEMENT !

BENATO IT Session 4 – Block 3 – Question 6 Barcelona May 2003 RURAL RADIAL FEEDER MEASUREMENT CAMPAIGN II This measurement campaign seems to be representative of the DLC transmission length limit without the use of repeater devices. TX: 20 db on 75  RX: db ATTENUATION: 70 db

BENATO IT Session 4 – Block 3 – Question 6 Barcelona May 2003 CONCLUSION A novel protection method to prevent DG islanding; A novel protection method to prevent DG islanding; A suitable analysis procedure has been developed; A suitable analysis procedure has been developed; Good agreement of test results with the theoretical calculations  (accuracy of the multiconductor matrix procedure); 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; 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). (If longer distances are needed, the use of repeaters must be taken into consideration).