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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
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DLC-BASED PROTECTION SCHEME
Guard frequency injected at MV busbar
Under normal conditions, guard frequency detected
by RX
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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.
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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 ?
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OVERHEAD AND CABLE LINE ATTENUATION
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EXAMPLE OF A CAPACITIVE COUPLING DEVICE
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MEASUREMENT CAMPAIGN I
URBAN FEEDER
ATTENUATION at 72 kHz 20 db
GOOD AGREEMENT !
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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.
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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).