SPECIAL PROTECTION SCHEMES
IN OPERATION AT
ITAIPU POWER PLANT
RUI JOVITA G. C. DA SILVA *
JOSÉ BENEDITO MOTA JÚNIOR
ROBSON ALMIR DE OLIVEIRA
JOSÉ GREGÓRIO ACHA NAVARRO
MARCELINO PEREIRA DE ALMEIDA
EVONYR BORDIN FILHO
FERNANDO VEGA DAHER
ALEXANDRE GONÇALVES LEITE
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TRANSMISSION SYSTEM
6.300 MW
23 %
7.000 MW
94 %
1.300 MW
6%
6.300 MW
90 %
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INSTALLED CAPACITY EVOLUTION:
GENERATION X TRANSMISSION.
50 Hz Sector
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INSTALLED CAPACITY EVOLUTION:
GENERATION X TRANSMISSION.
60 Hz Sector
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DESCRIPTION OF THE SPECIAL
PROTECTION SCHEMES
60 HZ - 17 ACTIONS
stability 7
self-excitation 1
overvoltage 1
overfrequency 3
overload 3
voltage collapse 1
damping 1
50 HZ - 14 ACTIONS
overfrequency 5
frequency collapse 3
overvoltage 4
overload 2
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CS U10
TRIP U10
Frequency
Rate Scheme
CS U11
TRIP U11
CS U12
TRIP U12
CS U13
TRIP U13
CS U14
TRIP U14
CS U15
81D1
Taxa 1
f
t
 1,2 Hz
TRIP U15
CS T1
CS U16
TRIP U16
s
CS U17
Taxa 3
f
t
TRIP U17
 2,4 Hz
CS U18
s
OR
81D2
Taxa 2
f
t
1,4 Hz
TRIP U18
Send signal to open 765
kV lines in Foz do Iguaçu
CS T2
s
Taxa 3
f
t
 2,4 Hz
s
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SCHEME TO AVOID FREQUENCY
COLLAPSE
U01
And
U02
And
And
And
Off
Separate U01
Separate U02
And
signal from ST-FI of the
blocking of 4
or more converters
And
disconect one unit of
U01, U02, U03 ou U04
And
Relé 81
f t 
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OVERLOAD ON LINES
Overload LT IPU-MD 1
t = 5s
And
Open circuit breaker
84LI2
And
+
t = 3s
43MD1
Overload LT IPU-MD 2
And
t = 5s
And
+
t = 3s
43MD2
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Open circuit breaker
44L22
Open circuit breaker
84LI1
Open circuit breaker
44L11
8
PERFORMANCE
60 Hz
Time to re-synchronize
was reduced about 5 min.
Its 1 min 30 s now.
50 Hz
switches manually
controlled
=> self-excitation
=> operators are more
familiarized
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PERFORMANCE
60 Hz
159 PLCs actuations
13 errors - associated with maintenance, PLCs
design and auxiliary equipments failures.
Logic 02
Logic 04
Logic 05
Logic 06
Logic 08
Logic 09
Logic 11
Logic 12
Logic 13
Logic 14
Logic 15
Total Number of Actuation of the PLCs Logics
76
2
25
3
15
13
4
8
5
3
5
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PERFORMANCE
60 Hz
Logic
Logic 2
Misoperation Causes
Tripping of generators due to failure in auxiliary equipment, which
provide to PLC the status of transmission line.
Tripping of generators due to short circuit in DC source of the Ivaiporã
PLC, without transmission lines opening. This wrong actuation caused
load interruption in Brazilian power system.
Refusal of operation due to design error.
Tripping of generators due to: communication and auxiliary equipment
(which provide the status of series capacitor to PLC) failures.
Tripping of one, instead of two, generating unit due to wrong period of
load set in PLC. There weren’t stability problems to the power system.
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PERFORMANCE
60 Hz
Logic
Logic 8
Logic 9
Logic 6
Logic 13
Misoperation Causes
Tripping of generators due to failure in auxiliary equipment, which
provide to PLC the status of transmission line.
Communication problem caused generating units tripping without event
in the system.
No tripping of generating units due to failure in auxiliary equipment,
which provide the power flow on transformers to PLC.
Tripping of generators due to PLC software error, without overload in
transformers.
Three actuations with disconnection of generating units during
overload relay maintenance at Ivaiporã substation.
Tripping of generators due to PLC software error.
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PERFORMANCE
60 Hz
SCHEMES INDEPENDENT FROM PLCs:
* scheme against self-excitation - one correct
actuation during 2002 major blackout.
* scheme to increase damping with Brazil
Southern region - one correct actuation during
an opening of 765 kV S-SE interconnection.
* scheme to control overfrequency in Brazil
Southern region - one incorrect actuation in
1994 during relay maintenance, tripping all
765 kV lines in Foz do Iguaçu substation.
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PERFORMANCE
50 Hz
scheme to avoid the separation of the
interconnected system Itaipu-Ande – two correct
actuation, with generating unit tripping by
frequency rate to control overfrequency.
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PERFORMANCE
50 Hz
One was during the 1999 major blackout, and
the interconnection Itaipu-Ande was opened by
the actuation of the 220 kV overvoltage relay
(overvoltage above 286 kV for more than 1s),
causing blackout in Ande power system.
Because of this occurrence the scheme to
avoid frequency collapse in the Ande power
system was created.
The other actuation avoids blackout in Ande
power system during HVDC bipole blocking.
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PERFORMANCE
50 Hz
About SPSs incorrect actuation, there were only
one, which occurred in 1995 during
maintenance, when there was an accidental
operation of the 500 kV line protection,
signalizing a two-phase fault. This resulted in
interconnection Itaipu-Ande opening and
blackout in Ande power system.
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CONCLUSIONS
Despite the number of Special Protection
Schemes installed at Itaipu power plant, they
can be characterized by their simplicity and
good performance. They were installed since
the beginning of plant operation and have been
provided security to the electrical system and
equipments.
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CONCLUSIONS
Most of SPSs are designed to act during
complex problems in the interconnected system,
the exception are the SPSs implemented by
PLCs in 60 Hz system, which act during simple
contingencies too.
The SPSs actuations avoided interruption of
load, or even major blackout, throughout
Brazilian and Paraguayan power system, mainly
those designed to maintain system stability and
to avoid voltage and/or frequency collapse.
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CONCLUSIONS
It´s important to highlight the familiarization of
Itaipu operators with all these schemes and their
actuations, characterized mainly by the right
auxiliary switches positioning, on 50 Hz sectors,
and by the short period to re-synchronize
generating units disconnected by SPSs, in 60 Hz
sector.
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CONCLUSIONS
The SPSs have been presented very good
performance. The misoperations are associated
with equipment maintenance and with failures of
PLCs design or auxiliary equipments.
The SPSs implemented by PLCs present less
than 10 % of incorrect actuations and/or
refusals.
The others SPSs have so few actuations to allow
a statistics calculation, but the incorrect
actuations didn’t repeat for years.
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SPECIAL REPORT
Question 2.3
How important are communication issues
(availability, reliability, etc.) for the
implementation of SPS ?
Deve-se procurar alcançar uma disponibilidade
o mais próxima possível de 100 % para os
recursos de comunicação utilizados em SPS.
Qualquer redução implica em indisponibilidade
do SPS. O mesmo vale para uma recepção
correta do sinal enviado. Para garantir isso
pode-se enviar os sinais por meios diferentes.
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SPECIAL REPORT
Question 2.3
Have any risk been identified involving
overfunction in case of duplication/triplication of
equipments ?
É uma possibilidade. O projeto do SPS deve
sempre prever que a sua possibilidade de falha
deve ser mínima face a solicitação mais crítica.
Assim, uma duplicação/triplicação tem o objetivo
de evitar atuações desnecessárias, mas não
podem aumentar a possibilidade de falha na pior
condição.
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SPECIAL REPORT
Question 2.3
Have any misoperation been experienced that
have had an influence on decision concerning
systems’ maintenance ?
Sim. Muitas. As rotinas e procedimentos de
manutenção dos SPSs requerem determinadas
condições do sistema que muitas vezes
podemimplicar em restrições eltro-energéticas.
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