Barcelona 12-15 May 2003
THE ISLANDING PROBLEM
HV Busbar
MV
MVBusbar
Busbar
After system switching operation,
a section of the utility network
remains connected to the DG !
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
BENATO IT Session 4 – Block 3 – Question 6
Barcelona 12-15 May 2003
DLC-BASED PROTECTION SCHEME
HV
network
HV/MV
Rx
MV Lines
MV/LV
MV/LV
Line Breaker
LV loads
Tx
Capacitor
Bank
DG
Guard frequency
injected at MV
busbar
Rx
MV/LV
Overhead Line
DG
Cable Line
Tx
Transmitter Location
Rx
Receiver Location
MV/LV
Under normal conditions, guard frequency
detected by RX
BENATO IT Session 4 – Block 3 – Question 6
Barcelona 12-15 May 2003
HV
network
HV/MV
Rx
MV Lines
MV/LV
MV/LV
Line Breaker
OPENS
Tx
DG
LV loads
Capacitor
Bank
Rx
MV/LV
Overhead Line
DG
Cable Line
Tx
Transmitter Location
Rx
Receiver Location
MV/LV
When the breaker is opened
there is a loss of guard frequency for the DG receiver
BENATO IT Session 4 – Block 3 – Question 6
Barcelona 12-15 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 12-15 May 2003
DEVELOPMENT OF A TOOL FOR THE
CARRIER SIGNAL TRANSMISSION
ANALYSIS
24
50
ZM=3000 
ZM=100 
22
20
Attenuation [dB]
Attenuation [db]
40
f= 72 kHz
30
20
18
16
15 dB
R1
14
12
ZMR2 =460 
10
8
10
R2
OMZ
6
0
0
0.5
1
1.5
2
2.5
3
Receiver Location x [km]
STANDING WAVE CONDITIONS
4
0
100
200
300
400 500 600
ZMR1 []
700
900 1000
OPTIMAL MISMATCHING ZONE
Cable Lines
ZM = 460 
Overhead Lines
ZM = 3000 
Combination of OHL and CL ZM = 1500 
BENATO IT Session 4 – Block 3 – Question 6
800
Barcelona 12-15 May 2003
OVERHEAD AND CABLE
LINE ATTENUATION
14
Line lenght 2 [km]
CL paper - insulated S=185 mm2
0.70
CL EPR - insulated S=185 mm2
12
1.25
OHL ACSR
Conductors
ACSR =15.85 mm
CC =10.70 mm
S=150 mm2
10.25 m
MV overerhead line
Attenuation [dB]
10
Cable Lines
8
6
5
4
3
OverHead Line
2
1
0
0 100
460 500
1000
1500
2000
2500
3000
Impedance Matching ZM 
Attenuation as a function of receiver impedance ZM
less than 0.5 [dB/km]
BENATO IT Session 4 – Block 3 – Question 6
about 1.54 [dB/km]
Barcelona 12-15 May 2003
EXAMPLE OF A CAPACITIVE
COUPLING DEVICE
C
L
phase R
Coupling
Side
Tr1
PG
CR Tr2
Transmitter/
Receiving
Side
X
20 kV
phase S
S
C:
L:
Tr1:
PG:
X:
Tr2:
S:
Coupling Capacitance;
Tuning Inductance;
Insulating Transformer;
Protective Gaps;
Compensation Reactance;
Impedance Trasformer;
Protection Screen.
Electric circuit
The Coupling Capacitance :
BENATO IT Session 4 – Block 3 – Question 6
BW
10  10 3
Cc 

 6700 pF
2  f 2 Z M 2  72  103 2  46


Barcelona 12-15 May 2003
MEASUREMENT CAMPAIGN I
Tx CD
6 lines
HV/MV
2528 m
EPR-insulated cable
S=185 mm2
CD Rx
310 m
Paper-insulated cable
S=240 mm2
MV/LV
95 m
3.6 Mvar
URBAN FEEDER
ATTENUATION at 72 kHz = 20 db
GOOD AGREEMENT !
BENATO IT Session 4 – Block 3 – Question 6
Comparison between
computed and measured
values
Barcelona 12-15 May 2003
MEASUREMENT CAMPAIGN II
IMP 150 
HV/MV
#2
#4
#5
MV/LV
CD Rx
4 lines
#3
450 m
7542 m
5667 m
50 m
3.6 Mvar
-10
Cursor -49.37 dB / 72.000 kHz
Signal Strength [dB]
Tx CD
0
#1
BWTH: 25 Hz START: 70.000 kHz
STOP : 78.000 kHz
-20
-30
-40
-50
-60
# Line
#1
#2
#3
#4
#5
Total Lenght
Km
47.7
5.8
48.6
26.4
4.8
OHL lenght
Km
45
1.7
44.7
23.8
0.4
CL lenght
Km
2.7
4.1
3.9
2.6
4.4
-70
-80
70
71
72
73
2 khZ/Div
TX: 20 db on 75 
RURAL RADIAL FEEDER
74
75
76
Frequency [kHz]
77
78
RX: -49.37 db
ATTENUATION: 70 db
This measurement campaign seems to be representative of the DLC
transmission length limit without the use of repeater devices.
BENATO IT Session 4 – Block 3 – Question 6
Barcelona 12-15 May 2003
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
Italian radial branched MV feeder;

(If longer distances are needed, the use of repeaters must be taken into
consideration).
BENATO IT Session 4 – Block 3 – Question 6
 15 km for a typical