G. Ziegler. Digital Differential Protection
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G. Ziegler, 10/2005 page85
Differential Protection Symposium
Belo HorizonteNovember 2005
Frequently used vector groups (IEC 60076-1)
G. Ziegler, 10/2005 page86
Differential Protection Symposium
Belo HorizonteNovember 2005
Proceed in the following steps:
1. Starting on the high voltage winding, the phase connection terminals are
numbered with 0, 4, 8 (always 4 x 30
O
= 120
O
phase shift).
2. The opposite end of each winding is labelled with a number incremented
by +6 relative to the phase connection (6x 30
O
=180
O
).
3. The secondary windings are numbered the same. In this context it is
assumed that the polarity of the windings is the same in the diagram. (If in
doubt, polarity marks may also be applied.)
4. The phase connection is labelled with the average value of the
corresponding terminal designations belonging to the winding terminals
connected to this phase terminal, e.g. (6+4)/2= 5
5. The difference between the high and low voltage side terminal numbers of
same phases corresponds each with the vector group number, beingYd5 in
this case.
Finding the vector group by using the clock principle
G. Ziegler, 10/2005 page87
Differential Protection Symposium
Belo HorizonteNovember 2005
∆I
∆I
L1
L2
L3
∆I
4
0
8
6
0
6
4
8
2
10
10
2
5
9
1
1
5
9
7
3
11
7
3
11
0
4
8
6
10
2
2
10
12
6
4
8
612
10
4
8
2
Yd5
Yd5
Checking the connections of transformer differential protection
using the clock-wise notation method
G. Ziegler, 10/2005 page88
Differential Protection Symposium
Belo HorizonteNovember 2005
G
G
3
G
1
3
1
3
Current distribution in Y-∆-transformer circuits
for different external fault types
G. Ziegler, 10/2005 page89
Differential Protection Symposium
Belo HorizonteNovember 2005
L1
L2
L3
∆I
∆I
∆I
Dy5
Yd5
3
1
3
3
3
3
3
=
3
Checking the connections of transformer differential protection
using the arrow method (two-phase fault)
G. Ziegler, 10/2005 page90
Differential Protection Symposium
Belo HorizonteNovember 2005
L1
L2
L3
∆I
∆I
∆I
Dy5
Yd5
1
3
3
Checking the connections of transformer differential protection
using the arrow method (single-phase earth fault)
G. Ziegler, 10/2005 page 87
Differential Protection Symposium
Belo HorizonteNovember 2005
Digital Differential Protection
Communications
Gerhard Ziegler
G. Ziegler, 10/2005 page 88
Differential Protection Symposium
Belo HorizonteNovember 2005
Comparison protection
Absolute selectivity by using communication
A
B
Communication
samples, phasors,
binary signals
Relay
•Directialcomparison
distance protection
Exchange of YES/NO signals
(e.g. fault forward / reverse)
• Current comparison (phasors)
differential protection
| ∆I | = |I
A
-I
B
| > I
pick-up
I
A
I
B
| ∆I |
I
A
I
B
Relay
Protection
Protection
G. Ziegler, 10/2005 page 89
Differential Protection Symposium
Belo HorizonteNovember 2005
Signal transmission channels for differential relaying
Pilot wires
- AC (50/60 Hz), voice frequency and digital communication (128 -kbit/s)
-for short distances (< about 20 km)
-influenced by earth short-circuit currents!
Optical fibres
-wide-band communication (n ·64 kbit/s)
-digital signal transmission (PCM)
-up to about 150 km without repeater stations
-noise proof
Digital microwave channels 2 -10 GHz
-wide-band communication (n ·64 kbit/s)
-digital signal transmission (PCM)
-up to about 50 km (sight connection)
-dependent on weather conditions (fading)
G. Ziegler, 10/2005 page 90
Differential Protection Symposium
Belo HorizonteNovember 2005
3
3
87L
87L
• Pilot wires are normally operated insulated form earth
• Voltage limiters (glow dischargers) connected to earth ,
as used with telephone lines, are not allowed!
Analogpilot wire differential relaying