Siemens
Numerical Pilot Protection 7SD52
using digital wide-band communication
Protection and Substation Control
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1
Siemens
Numerical pilot protection relay 7SD52
n Universally applicable to power system
configurations up to six ends ,
containing :
q
OH-Lines
q
Cables
q
Transformers
n For digital data transmissen
Protection and Substation Control
q
Via dedicated optical fibres
q
Via Communication networks
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2
Siemens
Numerical Pilot Differential Protection Principle
IA
IB
IAS , IAC
DI
DI
IBS , IBC
ID
+j
operate
IA
IAC
stabilize
IB
ID
IBS
IAS
IB
+
Operate :
ID = IA +IB
Bias:
IB = IA + IB
Operating
Criterium:
ID  K1 + K2 . IS
IBC
IA = IAS + j IAC
IB = IBS + j IBC
Protection and Substation Control
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3
Siemens
Definition of Synchronous Phasor:
measured at different locations based on a common time reference
Time reference
i
i
A
B
Location :
A
B
Location :
B
I
M
I
Relay A
B
I
R
E
B
Relay
B
Protection and Substation Control
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4
Siemens
Numerical pilot protection: Advanced Fourier analysis of
the currents - Supress DC components, harmonics
sin 2 i
n
0 1 2 . .
.
n
IS(k)
i(k ni)
i
k-n
I(k)  IS(k)  j IC(k)
k
IC(k)
I (k )
j
IC(k)

cos 2 i
n
Protection and Substation Control
IS(k)
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Siemens
Advanced Fourier Transformation - Optimized filtering
coeffizients for 7SD52 -> Suppress DC 4 times better than
conventional Fourier-filters -> Archieve high sensitivity
i0
i1
i2
iN
Dt
0
1
2
3 ....
N
2
N1
IS   sinω n Δt in
N n1

n
0
1
2
3 ...
Protection and Substation Control
N
 iO iN N1

2
IC      cosω n Δt in
N  2 2 n1

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6
Siemens
Advanced Full Cycle Fourier analysis: Filter characteristic
Protection and Substation Control
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7
Siemens
Orthogonal Current Components
(Advanced Fourier Filter)
wt
I(wt)
1 Ø
IS 
I (wt)  sin wt dt
2 Ø -360 
=0
I (Ø)  I S  j I C
I 0
1 j 0
I
1
IC 
2
Ø

I (wt)  coswt dt
Ø - 360
I 30
3
1

j
I
2
2
j IC
I
I 60 1
3
 j
I
2
2
wt
t=0
IS
I 90
 0  j1
I
Protection and Substation Control
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8
Siemens
Numerical Pilot Differential Relay
Propagation Time Measurement and Phasor Angle Correction
A
B
DI
DI
tA1
tL1
tB1
tA2
tB2
tV
tA3
tB3
tA4
tL2
tB4
tA5
IB(tA3)
Propagation time: tL1= tL2= 1/2 x (tA-reception - tA1- tV)
Corrected sampling instant: tB3= tA-reception -tL2

IB(tB3)
= (tB3 - tL2) x (360O/Tperiod)
Protection and Substation Control
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Siemens
Example for the delay time calculation
Flight from Berlin <-> New York
You can not calculate the duration of a flight if you look at the clock in Berlin on departure and later
note the local New York time on arrival. The reason are the different time zones.
The relays are also in two time zones.. Each relay has it´s own 1 us resolution timer.
Tdepart / B->NY (6:00) --------------------> Tarrival / B->NY (8:00)
From the flight back from New York to Berlin the local departure time in NY and the arrival time in Berlin is:
T arrival / NY->B (23:00) <--------------- T depart / NY->B (9:00)
Under the assumption, that the flight to New York and the flight back from NY have the same duration
the relevant time results can be calculated.
The time difference between NY and B and the duration of the flight (transmission time)
Duration = ( T arrival / B->NY - T depart / B->NY+ T arrival / NY->B - Tdepart / NY->B ) / 2
Time difference = (Tdepart / B->NY - Tarrival / B->NY + Tarrival / NY->B - Tdepart / NY->B ) / 2
Duration = (8:00 - 6:00 + 23:00 - 9:00) / 2 = 8 hours (-> delay time)
Time diff. = (6 Uhr - 8 Uhr + 23 Uhr - 9 Uhr)/2 = 6 hours (-> difference between the time zones)
Protection and Substation Control
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Siemens
Coded message of current differential protection 7SD52
HDLC FRAME FORMAT
Opening
Flag
01111110
Address
Field (A)
16 bits
relays
address
Control
Field (C)
8 or 16
bits
Synchronizing
Information
Field (I)
any length
0 - N bits
time data
status + command
Frame
Check
Seqence
(FCS)
Closing
Flag
32 bits
01111110
message
validation
Current vectors
Protection and Substation Control
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11
Siemens
Numerical pilot differential protection: Communication options
Monomode fibre
1300 ober 1550 nm
DI
DI
a) Dedicated optic fibre
DI
DI
Wire, G.703
Optic fibre or Microwave
Further services:
Telefon,
Data transmission,
etc.
Further services:
Telefon,
Data transmission,
etc.
b) Channel of a data transmission system or of a data transmission network
(Protection and PCM-device in the same room)
PCM
MUX
PCM
MUX
Multimode optic fibres
850 nm
DI
O.F.
Multimode optic fibres
850 nm
O.F.
G.703
G.703
Wire G.703
Optic fibre or microwave
Further services:
Telefon,
Data transmission,
etc.
DI
Further services:
Telefon,
Data transmission,
etc.
b) Channel of a data transmission system, or of a data transmission network
PCM
MUX
PCM
MUX
(Protection and PCM-device not in the same room)
Protection and Substation Control
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12
Siemens
Application for a three terminal configuration
Monomode fibre optic cable
up to 10 km (1300 nm modul)
Monomode fibre optic cable up to 35 km with 1300 nm interface
Distance relay
7SA52
X21
G703.1
820 nm
Option:
I-REGB
time
synchronisation
max.
3 km
e
o
PCM
multiplexer
SDH
comms-network
PCM
multiplexer
o
e
Commsconverter
G703.1: 64 kBit
X21: N*64 kBit (1N8)
Protection and Substation Control
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13
Siemens
Numerical line differential protection 7SD52
Scope of functions / Hardware options
3Iph, and IE
4U
8 binary inputs
16 contacts
1 - 2 protection interfaces
System interface
PC-interface
Time synchronisation
- For system configurations with up to 6 terminals
- Fast high set charge comparision (subcycle trip)
- Sensitive current phasor differential
- Inrush restraint (2nd harmonic) and
vector group adaption
½*19´´
- CT saturation detector
16 binary inputs
24 contacts
- Autoreclosure 1/3 pole
24 binary inputs
32 contacts
- Overload protection
Option: 5 fast
trip contacts
- Switch on to fault protection
- 4 remote commands, 24 remote signals
Protection and Substation Control
1*19´´
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Siemens
Communication Options
O
820 nm
1,5 km / 3 km
FO5:
FO6 :
distance 1,5 km (with clock feed-back)
distance 3km
1300 nm
10 km
FO7 :
distance 10km
1300 nm
35 km
FO8:
distance 35km
internal
O
internal
O
internal
E
O
X21
G703
KU : hook-up to communication network
external
Km data for worst-case conditions
Protection and Substation Control
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15
Siemens
Hardware option of the comms interfaces
Protection interface 2
Port E
Remote line end 2
Synchronous N x 64kB/sec
Plug in
modules
Remote line end 1
Protection interface 1
Port D
Synchronous N x 64kB/sec
Subst. control interface
communication modules
FO (Fibre optic) or RS485
or RS232
Available Protocols
IEC - standard
Interfacemodul 2
RS485 or FO
Substation control
service-interface
Interfacemodul 1
RS485 or FO
or RS232
DIGSI
local
Browser
local-PC
interface
Serial time
sync. input
Protection and Substation Control
DIGSI 4; also for
modem connection
and Browser
GPS-receiver
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16
Siemens
Main board of the relay with it´s
Communication - Interfaces
Main processor
board of the relay
Sockets for the
communication
modules
Protection and Substation Control
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17
Siemens
Adaptive Algorithm: Fast Charge comparison and very
sensitive Phasor differential
Charge comparison
Fast normal trip stage
IDiff>> Setting: 0,67*ILoadmax/IN
Fast, <1cycle
5
 i dt
5
 i dt
Phasor differential
For high resistive faults
IDiff> Setting: 0,1-0,2 IN
0
1 cycle Phasor,
fundamental frequency
87L
0
87L
Every 5ms (128-512 bBit), 10 ms (64 kBit)
Protection and Substation Control
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18
Siemens
Adaptive differential relaying
Consideration of CT- and communication-errors
IDiff
IN,load.
trip
I2
I3
I1
I2
restrain
IDiff>
0,15
I3
I1
Through fault
load
I1
0.5
Irestr
IN,Betr.
Calculated Phasor sum:
Minimum pick-up:
Restrain:
IDiff = I1 + I2 + I3
IDiff = Ilow set
IRestrain =  c.t. tolerance + Syncronising tolerance
 trip condition: IDiff >Ilow set and IDiff > IRestraint
Protection and Substation Control
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19
Siemens
Spill Current through Line Charging Capacitances
Protected Zone defined by c.t.1 and c.t.2
I2
I1
I1
C.t.2
C.t. 1
Source V1
IDiff
IC
Source V2
Kichhoff equation:
I1 + I2 - IDiff - IC = 0
Service conditions:
IDiff = 0, IC = I1 + I2
 Difference equals
charging current
IDiff> >2,5.. 4 • IC  sensitive set point
at short lines,
Pick-up value:
minimum 0,1 IN
Protection and Substation Control
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20
Siemens
Setting above spill currents: c.t. error and line charging
I1´=0,95•I1
I2  I1  IC
I1
-I1
I1
I2´=1,05•I1
IC  j U L wCL
IDiff=0,1 • I1
Resulting
set point
Set points:
Percentage bias
related to c.t. errors
IDiff
IDiff = |- I1´ + I2´| = f1• I1 + f2 • I2
Load: I1 = IN
IDiff
= 0,1 • I1 = 0,1• IN
IDiff>
Minimum pick-up
related to line charging
current
I1
Through Fault: I1 = 10 • IN
• IDiff> set point > line charging current
IDiff = 10,5 • IN - 9,5 • IN = IN
• Percentage bias > Sum of c.t. errors
Protection and Substation Control
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21
Siemens
Approximated c.t. Tolerance
Basis for the restraint current calculation
IDiff
I1
Fault current tolerance
Tolerance of
a real CT
Load current tolerance
ALFe / ALFN • IN,c.t
I1
: parameter 7SD52
Example: 10P10, fB < 3%, fK at ALFN = 10%
Protection and Substation Control
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22
Siemens
Current transformer data
C.t. Parameter
c.t. e.g. 5P20, 10VA
% tolerance at ALFN
ALFe = ALFN
Pi + PN
Pi + PB
With PB = Pleads +
Prelay (0,1 VA)
Thumb rule:
Ri  0,1...0,2 * RN
RN at 10 VA  10
=> Ri  2 
ALFe
2 VA + 10 VA
=
ALFN
= 4
2 VA + 1 VA
Resulting Relay Parameter:
• effective ALF / nominal ALF = 4 (calculation as per above)
• IEC 44 -1:
tolerance in load area up to ALFe / ALFN : 1% with 5P, 3% with 10P c.t.s
total error at accuracy limit nN = 5% with class, 5P and 10% 10 P
Protection and Substation Control
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23
Siemens
Internal restraint current calculation due to CT-errors
The restraint current is the sum of the maximal expected CT-errors
5P20 20 VA
1600:1
ALFe/ALFN = 5
fLoad 1 = 1% (0,01)
fSC 1 = 5% (0,05)
800 A
4800 A
IC = 100 A
10P10 10 VA
400:1
ALFe/ALFN = 1
fLoad 3 = 3% (0,03)
fSC 3 = 10% (0,1)
5P20 20 VA
1600:1
ALFe/ALFN = 2
fLoad 2 = 1% (0,01)
fSC 2 = 5% (0,05)
IN,load = 1600 A
1200 A
5600 A
400 A
800 A
IStab = 2.5 • line charge currents (basic restraint value) + c.t. error currents
IDiff = actual deviation of vector summation and charge summation
Case 1 (Through load)
IRest = 2,5 • 100 A + 800 A • 0,01 + 1200 A • 0,01 + 400 A • 0,03 = 282 A
Idiff = 100 A
I restr / IN,load = 0,176
IDiff / IN,load = 0,063
Case 2 (Through fault)
IRest = 2,5 • 100 A + 4800 A • 0,01 + 5600 A • 0,05 + 800 A • 0,1 = 658 A
IDiff = 40 A
I restrain / IN,load = 0,41
I Diff / IN,load = 0,025
Protection and Substation Control
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24
Siemens
CT Saturation detector based on harmonic analysis
ct I2
ct I1
Harmonic content of the differential current
2
|fn|
|f1|
0
t
Id = I1 - I2
0
0
Harmonic order
10
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25
t
Protection and Substation Control
Siemens
Charge comparison: Operating Principle
I1
I3
protected Line configuration
I4
Q diff=Q 1+Q 2+Q 3+Q 4
Q1
I2
Q part1=Q 1
7SD52
Q part2=Q 2+Q 3+Q 4
1
Protection and Substation Control
Q2

Qdiff
2
Q3
Q part2=Q 1+Q 2
Q4
Q part3=Q 1+Q 2+Q 3
7SD52
Q part3=Q 3+Q 4
7SD52
Q part4=Q 4
3
4
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26
Siemens
Charge Comparison:
Charge calculation, Operating characteristic, Tripping times
|Q |
diff
Operate
(internal fault)
Charge calculation by
numerical integration
t
0
t
1
Q
Q
1
t
2
t
3
t
4
DIFF
>
Settable pick-up value
=IDiff>>
Restraint Area
t
5
qdiff12.dsf
t
6
Calculated charge restraint value
from CT-errors , synch. errors
Current Measuring window
5 ms (50 Hz)
Corrected time instants
after end-to-end time synchronisation
Protection and Substation Control
QRest
Relay calculates the charge. Setting as current value IDiff>>
speed
64 kbit/s
128 kbit/s
512 kbit/s (FO)
2 relays
21 ms
16 ms
14 ms
3 relays
21 ms
16 ms
14 ms
EV S
6 relays
41 ms
24 ms
17 ms
27
Siemens
7SD52 Pilot Protection: Sliding data windows
faultinception
current,
voltage
voltage
current
time
5 ms charge and
20 ms phasor data windows
Protection and Substation Control
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28
Siemens
Familiar with digital communication networks
Features of the relay to relay communication
n Synchronous data transmission by HDLC- protocol
n Permanent supervision of the data transmission
n Measurement and compensation of signal transmission time
(max. 20 ms)
n Counts number of invalid telegrams
Blocking the diff.protection if transmission failure rate is too high
n Settings for the data transmission
(N*64 kBit/s, N settable from 1 - 8, synchronous HDLC-protocol)
n Communication device addresses
(Protection devices are clearly assigned to a defined protection
section)
n Detection of reflected data in the loops in comms- network
n Step 2: Microsecond exact time synchronisation
via satellite (civil - IRIG-B)
(If signal transmission time depends on the transmission direction,
Online high resolution fault recorder)
Protection and Substation Control
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29
Siemens
Ring and Chain topologie
Automatic change from
closed ring to chain, if
one connection is lost
or not available
side 2
side 2
I2
side 3
I2
Connection to
side 3
I3
I3+I1
I2
I1+I2
I1
other diff. relays
I3
I3
I1
I3+I1
I1+I2
side 1
Closed ring
Protection and Substation Control
side 1
Partial current summation
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30
Siemens
Breaker-and-a-half Scheme, Through Fault Stabilisation
87L
To remote end
busbar 2
If = through fault current
If = through fault current
busbar 2
busbar 1
Partial differential
Protection and Substation Control
87L
To remote end
87L
busbar 1
Full differential
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31
Siemens
Topologies: Chain topology for max. 6 line ends
1
PI1
PI1
2
PI2
PI1
3
PI2
PI - Protection Interface
PI1
6
PI1
Protection and Substation Control
PI2
5
PI1
PI2
4
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32
Siemens
Topologies: Ring topology, 6 line ends
1
PI2
PI1
2
PI2
PI1
3
PI1
PI2
PI2
PI1
6
PI1
PI2
5
PI1
PI2
4
PI - Protection Interface
Protection and Substation Control
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33
Siemens
Web-Browser based commissioning tool
Protection and Substation Control
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34
Siemens
7SD52: Commisioning and Monitoring using Web-Browser
Protection and Substation Control
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35