Dehui Chen

Salvatore Mantuano

Wei Liu

Yi Xia

Springer - Publisher Connector

Analysis and discussion of a dead-zone protection mal-operation case in Brazil

Analysis and discussion of a dead-zone protection mal-operation
case in Brazil
Dehui CHEN (&), Yi XIA, Wei LIU,
Salvatore MANTUANO
Abstract A mal-operation case of busbar protection
caused by a dead-zone protection abnormality in the Bra-
zilian Midwest Grid on September 19th, 2012, is briefly
described. The operation process of pilot distance, auto-
matic re-closure, busbar differential and dead-zone pro-
tection, and the emphasis on the logic scheme of dead-zone
protection are analyzed. The time delay between the
breaker’s main pole and auxiliary contact during re-closure
was the main cause in this case, and a defect in the logic
allowed it to occur. The differences in dead-zone protec-
tion logic between Brazil and China are discussed. A test
platform was constructed in the laboratory, and a site
simulated experiment was also performed. Possible causes
are suggested and test activities are carried out to verify
them. Results show the values of practical engineering
approaches to the solution. Experience also contributed to
avoiding future mal-operations and strengthening the reli-
ability of the protection system, and thus of the power
supply in Brazil.
Keywords Brazilian power system, Power system, Relay
protection device, Dead-zone protection
1 Introduction
Conventional protective relays cannot cover the whole
power supply configuration because of the combined
effect of economy and technology on the configuration of
current transformer (CT) used in the design and con-
struction of the power grid. A fault occurring between a
circuit-breaker and the CTs cannot be eliminated by
busbar protection. Similarly, the fault also cannot be
isolated by breaker failure protection rapidly because of
the time delay involved. As a supplementary form of
protection, dead-zone protection can be installed to isolate
faults quickly to avoid affecting the operation of the
segments of the power system grid that are 220 kV and
above [1, 2].
A mal-operation of dead-zone protection occurred in
the 500 kV Cuiaba´ substation within the Brazilian Mid-
west Grid on September 19th, 2012, because of the time
delay mismatch between the circuit-breaker main pole
and auxiliary contact when its position changed from
‘‘OFF’’ to ‘‘ON’’ during re-closure. The defects in the
protection scheme are identified by analyzing the opera-
tion behavior of the functional component. Promotion
plan are suggested and verified by experiment using a test
platform.
2 Operation process
2.1 System single line pre-fault
There are three 500 kV outgoing lines, two main
transformers and two shunt reactors in the Cuiaba´ substa-
tion shared by two different transmission companies, TME
(Transmissora Matogrossense de Energia) and ITE (Itum-
biara Transmissora de Energia). The assets to the left of the
dotted line in Fig. 1 belong to TME and to the right belong
to ITE. Figure 1 shows the system single diagram, in which
a fault occurred at location F. The primary equipment are
all air insulated system (AIS) and all circuit-breakers’
positions in the ‘‘ON’’ condition.
Received: 30 October 2012 / Accepted: 31 July 2013 / Published
online: 12 February 2014
 The Author(s) 2014. This article is published with open access at
Springerlink.com
D. CHEN, NARI Technology Co., LTD, Nanjing 210003, China
(&) e-mail: chendehui@sgepri.sgcc.com.cn
Y. XIA, W. LIU, S. MANTUANO, State Grid Brazil Holding
S.A., Rio de Janeiro 20071-004, Brazil
123
J. Mod. Power Syst. Clean Energy (2014) 2(1):87–91
DOI 10.1007/s40565-014-0044-4
2.2 Protection configuration
REB500 decentralized busbar protection system and
REL531 pilot distance protection were adopted for the
busbar and line, respectively. The configuration for line
protection was redundant and there was one set of busbar
protection. Each busbar protection set consisted of one
center unit and four bay units. Communication between the
center and bay units was through an optical cable [3–5].
Automatic re-closure was employed with line protection,
and the timer setting was 700 ms. Breaker failure protec-
tion, dead-zone protection, over-current protection and
current measurement of each branch were implemented in
the bay units, while busbar differential protection was
completed in the center unit.
The configuration of CTs for the line protection zone
and busbar protection overlapped, and the current trans-
formers in bay A had 2,000:1 CT ratio, while the others had
2,000:5 CT ratios.
In addition, the busbar protection system belonged to the
ITE company. The circuit-breaker (TME’s assets) position
that busbar protection needed was wired from an inter-
mediate relay within the auxiliary protection because of
limitations of the position signal contact.
2.3 Process of protection operation
On September 19th, 2012, shutdown occurred on the
500 kV Cuiaba´-Jauru´ line (LT_JAURU) because of a short
circuit that involved phase A and the earth. It was elimi-
nated by the operation of pilot distance protection on this
line. After 702 ms, automatic re-closure of the line acted,
but failed because of the permanent fault and thus triple
tripping occurred, caused by the operation of the same
protection unit. After 40 ms all the breakers connected to
busbar I also tripped because of the differential protection
of this busbar (The wrong configuration resulted in the
operation of the busbar protection because of the link
between the measuring component and bay’s circuit-
breaker position) [6]. Table 1 shows the sequence of
events.
3 Analysis and comparison
In this accident, four protection components operated,
including pilot distance, automatic re-closure, dead-zone
protection and busbar differential. It was confirmed later
from the disturbance recorder report and a site inspection
that phase A had a permanent fault with earth.
3.1 Behavior analysis on dead-zone protection
operation
The operation of dead-zone protection, which will not
operate unless faults occur between the CTs and the
breaker, is the most likely cause of this accident, while the
breaker was normal after later examination. By analyzing
the dead-zone logic scheme of the REB500 (see Fig. 2), the
breaker position signal appeared to be the probable source
of the problem. In the operation, the time delay of the
breaker position changing from ‘‘OFF’’ to ‘‘ON’’ was about
92 ms, which was greater than the typical value (37 ms).
Figure 3 shows the sequence of dead-zone protection
[4].
Upon inspection, the ‘‘close command’’ signal men-
tioned in Fig. 2 was seen to be absent in the adopted busbar
Bus I
Bus II
9338
9328
9238
9228
9218
9128
9118
9038
9028
9018
Cuiabá/
Jaurú
Reactor
Tansfomer
Transformer
Cuiabá/
Ribeirãozinho II
Reactor Cuiabá/
Ribeirãozinho I
ETIEMTBay A Bay B Bay C Bay D
F
Fig. 1 System single diagram pre-fault
Table 1 Sequence of events
No Component operation Absolute
time
Relative
time/ms
1 Operation of LT_JAURU pilot
distance protection
14:12:10.17 0
2 9338 circuit-breaker position is
‘‘OFF’’
14:12:10.312 295
3 Operation of LT_JAURU automatic
re-closure
14:12:10.719 702
4 Triple trip command of LT_JAURU 14:12:10.724 794
5 Operation of busbar 1 differential
protection
14:12:10.851 834
6 9338 circuit-breaker position is
‘‘ON’’
14:12:10.853 836
7 Operation of 9338’s dead-zone
protection
14:12:10.861 844
8 9338 circuit-breaker position is
‘‘OFF’’
14:12:10.904 887
88 Dehui CHEN et al.
123
protection in this substation, and was the same in other
substations.
The recorder picture shows that the fault current existed
for 78 ms, and the time delay between the main pole and
auxiliary contact was more than 36 ms. During this period,
when the breaker’s main pole was ‘‘ON’’, and the fault
current detected by the relay was 0.77 A, which was
greater than the setting value (0.1 A). Thus, the condition
in logic scheme (see Fig. 2) that the current of any phase is
greater than setting was considered true. Another condition
indicates that the breaker position is ‘‘OFF’’ was also
considered to be correct because the breaker position was
detected by protection device as ‘‘OFF’’ during the time
delay between the main pole and the auxiliary contact. In
addition, the ‘‘close command’’ signal had no influence on
the logic because of absence, and thus dead-zone protection
acted after 36 ms. This was consistent with the site
situation.
3.2 Analysis of dead-zone protection scheme adopted
[7, 8]
Figure 2 shows the operation scheme for dead-zone
protection adopted in the Brazilian system, which was
determined by the following conditions: first, the breaker
position signal, second, the current of any phase, and
finally the block signal (‘‘close command’’). Dead-zone
protection will be activated after a further time delay (set to
36 ms) when all the above items are true. To ensure that
the protection bases its decision on an effective image of
the circuit-breaker status, the position signal ‘‘OFF’’ was
delayed with a configured timer while the circuit-breaker
was actually opening. In addition, the timer t2 (set to
200 ms) was the width of the tripping command. The
purpose of this timer (36 ms) was to enable the detection of
a circuit-breaker close command that was subject to
internal signal transit times and breaker contact bounce
times [6]. This logic adopted by protection has the fol-
lowing three drawbacks.
• Poor ability to avoid mal-operation
It is simple for the operation of dead-zone protection,
which has a strong effect on the power system, depending on
the circuit-breaker position and the current detected. It is
also very easy to meet these items above in normal condi-
tions, such as when the circuit-breaker opens on its own.
• Application of the signal is ambiguous
It is not clear whether the ‘‘close command’’ occurs
because of a re-closure signal, manual close signal or a
combination of the two. In addition, the requirements for the
time delay between the auxiliary contact and main pole are
also not clear, especially when the circuit-breaker position is
wired from an intermediate relay or other middle stages.
• Logic diagram fails to reflect the protection function as
originally intended
On analyzing the logic scheme, there is the misunder-
standing that the dead-zone protection should act as long as
the circuit-breaker position is ‘‘ON’’ and the current is greater
than the settings, which runs counter to the original intention.
3.3 Analysis of dead-zone protection logic adopted
in the Chinese power grid
The dead-zone protection scheme applied in China has a
different logic scheme according to the different system
single diagram, such as one-and-a-half or double busbar,
Trip command
Breaker(A) position is  “OFF”
Breaker(B) position is  “OFF”
Breaker(C) position is  “OFF”
&
&
t1 0
t2
Internal trip 
signal
Internal trip 
signal
Close command
Current of any one phase is 
greater than settings
Fig.2 Logic scheme adopted for dead-zone protection
Fault current
Main pole position of 
9338 breaker
OFF
ON
Auxiliary contact 
position
OFF
ON
Close command 
Exist
None
36ms
78ms
Fig. 3 Sequence chart for dead-zone protection
Analysis and discussion of a dead-zone protection mal-operation case in Brazil 89
123
etc. Figure 4 shows the protection logic adopted in the one-
and-a-half single diagram. The dead-zone protection will
act after a setting time delay when the following conditions
are met: the protection has already received triple trip
signals or a trip signal of phase A, B, C simultaneously, the
over-current component has already acted, and protection
has already received the position signal which indicates
that the circuit-breaker position was ‘‘OFF’’.
The logic applied in China is not perfect compared with
dead-zone protection logic adopted in the Brazilian power
grid, but it has certain advantages.
• Criterion is well thought out and easily achieved
Besides the circuit-breaker position signal, operation
signals of the protection system such as line, etc, are also
adopted by protection, in addition, settings and criteria are
shared by the over-current component and failure protec-
tion, all these keep the implementation straightforward.
The protection logic also reflects the original intention of
dead-zone protection that the fault cannot be removed at all
after the protection has operated.
• Good ability to prevent mal-operation
The condition, in which the circuit-breaker position is
‘‘OFF’’ and a triple trip occurs when the protection acts, is
not simultaneously satisfied by the logic scheme in a nor-
mal situation.
• Flexibility in coordinating time
It is clear that dead-zone protection sends a trip com-
mand to the next circuit-breaker, activates the remove trip
command and isolates all sides of the transformer after t1,
t2, and t3 time delays, all of which better reflect the
‘‘Selective’’ feature of the relay protection and avoid fur-
ther development of the accident.
4 Solutions and verification
Three measurements were made when defects similar to the
characteristics of the Brazilian power grid were applied. First,
the signal, such as the circuit-breaker position, which has an
influence on protection performance, should be wired directly
from an auxiliary contact if possible, and avoid an intermediate
relay that can add an uncertain time delay. Second, a test should
be launched to measure the time delay between the auxiliary
contact and main pole of the circuit-breaker. If the time delay is
greater than 30 ms, the ‘‘close command’’ signal should be
wired. The time delay value ensures that instrument error and
the transformer time needed for the signal should be taken into
account. Third, if the time delay tested is less than 30 ms, the
port for wiring the ‘‘close command’’ signal may link directly to
ground to avoid mal-operation of the dead-zone protection.
A test platform was constructed and a disturbance
recorder used to ensure the output was the same when the
fault occurred [9]. The same model devices installed on-
site were adopted to ensure that the environment was the
same as the substation site. The pulse duration of binary
operations, such as the circuit-breaker position, was con-
figured according to different situations. The correct
operation of the solution was verified by the results.
5 Conclusions
By analyzing this accident, we acquire insights for the
construction and application of relay protection in China.
Triple trip of line protection
Triple trip of generation and 
transformer protection
Trip phase A
Trip phase B
Trip phase C
&
&
1
t3
&
Activate 
remove trip
Trip next 
breaker
t2
t1
Trip all sides of 
transformer
Current of any one phase is greater 
than settings
Breaker(A) position is  “OFF”
Breaker(B) position is  “OFF”
Breaker(C) position is  “OFF”
Fig. 4 Logic scheme of dead-zone protection adopted in China
90 Dehui CHEN et al.
123
5.1 To further strengthen standardized construction
of relay protection design
With the need for construction of a Smart Grid, especially
with the wide application of the IEC 61850 standard in
substations, standardized design and construction, including
component modeling, function interface, function configu-
ration and function test on the relay protection design should
be further strengthened based on the achievements in pre-
vious standardizations to keep pace with the trend for the
gradual integration of relay protection technology with
information and communication technology.
5.2 Adhering to correct and mature application
principles of relay protection
Brazilian upgrades in electrical power systems and their
operation have accumulated much successful experience,
some of which has developed into a standard, but their
practical application is not mandatory. During the devel-
opment of a Smart Grid in China, we should adhere to
correct technological and application principles proved by
practice, such as the ‘‘Four Features’’ of relay protection,
principle of distribution independence, redundant configu-
ration and various anti-accident measures, which can
remove those potential faults and will influence the reli-
ability of relay protection, giving full recognition to relay
protection as the ‘‘First Line of Defense’’ for power grids in
general.
5.3 Focusing on the influence of the construction mode
on building reliability into the relay protection
system
The construction of the Brazilian power grid mostly
adopts the EPC (Engineering Procurement and Construc-
tion) model, which optimizes its function and design as
well as reducing the cost of construction to some extent.
Conclusions can be drawn from the analysis of many faults,
and experience in operation, that these potential faults are
systemic and built in during design and construction, and
are difficult to detect by experiments before commission.
The construction of the power grid in China is changing
from one based on professional and system integration to
merging with the primary, secondary and EPC model. We
should not reduce the reliability of relay protection and
influence the safety and stability of the electrical power
system because of the cost savings and optimization of
design and function. Thus, we should place emphasis on
the effects of transforming the construction model.
Open Access This article is distributed under the terms of the
Creative Commons Attribution License which permits any use, dis-
tribution, and reproduction in any medium, provided the original
author(s) and the source are credited.
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Dehui CHEN received the master degree in 2007 in Telecommuni-
cation System Engineering from Nanjing University of Posts &
Telecommunications, Nanjing, China. He is currently an engineer for
power system protection and automation at NARI Technology Co.,
Ltd.
Yi XIA received the master degree in 2007 in Electrical Engineering
from China Electric Power Research Institute, Beijing, China. He is
currently an electrical engineer in State Grid Brazil Holding S.A.
Wei LIU is the director of O&M Department in State Grid Brazil
Holding S.A.
Salvatore MANTUANO is currently an electrical engineer in State
Grid Brazil Holding S.A.
Analysis and discussion of a dead-zone protection mal-operation case in Brazil 91
123


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