Operation of Circuit Breakers: Data and Analysis

Abstract

An attempt has been made for the analysis on Circuit breakers (CBs) this paper. First, the types and arcing phenomenon of Oil and SF6 Circuit breakers were briefly discussed. However, various CBs were analyzed in terms of certain outage frequencies and reliability indices to ascertain the most reliable CB. This was possible using data collected from the 33kV Transmission Company of Nigeria (TCN) New Haven, Enugu. After the analysis, Emene Industrial CB had the highest value of availability of 0.9999 and the lowest tripping report while Ezillo had the highest failure rate of 0.1032.

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Operation of Circuit Breakers: Data and Analysis
V.C. Maduemea , M. J. Mbunwea*, T. C. Maduemea , M. Ayaz Ahmadb ,
C. V. Anghel Drugarinc
aDepartment of Electrical Engineering, University of Nigeria Nsukka, 410001, Nigeria
bPhysics Department, Faculty of Science, P.O.Box 741, University of Tabuk, 71491, Saudi Arabia
cDepartment of Electronics and Informatics Engineering, “Eftimie Murgu”, University of Resita,
Resita, Romania
*Corresponding author: muncho.mbunwe@unn.edu.ng & mayaz.alig@gmail.com
Received: 16 January 2021; Accepted: 12 June 2021; Published: October 2021
Abstract
An attempt has been made for the analysis on Circuit breakers (CBs) this paper. First, the types and
arcing phenomenon of Oil and SF6 Circuit breakers were briefly discussed. However, various CBs
were analyzed in terms of certain outage frequencies and reliability indices to ascertain the most
reliable CB. This was possible using data collected
from the 33kV Transmission Company of
Nigeria (TCN) New Haven, Enugu. After the analysis, Emene Industrial CB had the highest value
of availability of 0.9999 and the lowest tripping report while Ezillo had the highest failure rate of
0.1032.
Keywords: Circuit breaker; Outage; Failure rate; Availability; Reliability
To cite this article: Madueme, V.C., Mbunwe, M.J., Madueme, T.C., Ayaz Ahmad, M., Anghel Drugarin,
C.V. (2021). Operation of Circuit Breakers: Data and Analysis. Multidisciplinary Journal for Education,
Social and Technological Sciences, 8(2), 60-73. https://doi.org/10.4995/muse.2021.12406

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1. Introduction
Once a power system is established it is necessary to protect it from internal and external faults. So
we use some protecting and sensing device like circuit breakers, Relays, Fuses etc (Saxena, Singh,
Ali, Gandhi, 2012). Power circuit breaker is one of the most important protection and control
apparatus in the power system (Suwanasri, Hlaing and Suwanasri, 2014).
A circuit breaker is a switching device that interrupts the abnormal or fault current. It is a
mechanical device that disturbs the flow of high magnitude (fault) current and in addition, performs
the function of a switch. The circuit breaker is mainly designed for closing or opening of an
electrical circuit, thus protects the electrical system from damage. Circuit Breakers represent one of
the most critical power apparatus in the power system. They are used to change topology of the
power system to accommodate various configurations in routing the load.
CBs are also used to isolate faulted parts of the system as a part of the protective relaying operation
(Kezunovic, Ren, Latisko, Sevcik, Lucey, Cook, and Koch, 2005). Circuit breaker essentially
consists of fixed and moving contacts. These contacts are touching each other and carrying the
current under normal conditions when the circuit is closed. When the circuit breaker is closed, the
current carrying contacts, called the electrodes, engaged each other under the pressure of a spring.
During the normal operating condition, the arms of the circuit breaker can be opened or closed for a
switching and maintenance of the system. To open the circuit breaker, only a pressure is required to
be applied to a trigger (Circuit globe, 2017).
Figure 1: Diagram of an Oil Circuit Breaker (Circuit globe, 2017)
Whenever a fault occurs on any part of the system, the trip coil of the breaker gets energized and
the moving contacts are getting apart from each other by some mechanism, thus opening the
circuit.
According to Pinnekamp (2007), Several GVA of power can be tamed by a circuit breaker within
fractions of a second. Such is the importance of this single device that tens of billions of dollars
have been spent on its development over the last 100 years.

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2. Types of Circuit Breaker
Circuit breakers are mainly classified on the basis of rated voltages. Circuit breakers below rated
voltage of 1000V are known as the low voltage circuit breakers and above 1000V are called the
high voltage circuit breakers.
The most general way of the classification of the circuit breaker is on the basis of the medium of
arc extinction. Such types of circuit breakers are as follows :-
[1] Oil Circuit Breaker
a. Bulk Oil Circuit Breaker
b. Minimum Oil Circuit Br eaker
[2] Minimum Circuit Breaker
[3] Air Blast Circuit Breaker
[4] Sulphur Hexafluoride Circuit Breaker
[5] Va c u um Circuit Breaker
[6] Air Break Circuit Breaker
All high-voltage circuit breakers may be classified under two main categories i.e oil circuit
breakers and oil-less circuit breaker (Electrical concepts, Circuit breaker and Arc Phenomenon,
2017).
3. Arc Phenomenon in Circuit Breaker
When a short-circuit occurs, a heavy current flows through the contacts of the circuit breaker
before they are opened by the protective system. At the instant when the contacts begin to separate
the contact area decreases rapidly and large fault current causes increased current density and hence
rise in temperature.
The heat produced in the medium between contacts (usually the medium is oil or air) is sufficient
to ionize the air or vaporize and ionize the oil. The ionized air or vapour, acts as conductor and an
arc is struck between the contacts. The potential difference between the contacts is quite small and
is just sufficient to maintain the arc. The arc provides a low resistance path and consequently the
current in the circuit remains uninterrupted so long as the arc persists.
During the arcing period, the current flowing between the contacts depends upon the arc resistance.
The greater arc resistance will repres ent to the smaller the current flow bet ween the contacts. The
arc resistance depends upon the following factors:
• Degree of ionization - the arc resistance increases with the decrease in the number of
ionized particles between the contacts.
• Length of the arc - the arc resistance increases with the length of the arc i.e. separation of
contacts.

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• Cross section of arc - the arc resistance increase with the decrease in the area of cross
section of the arc (Electrical Systems, 2017).
Figure 2: Diagram of the SF6 Circuit breaker (Electrical Systems, 2017)
When the contacts of a circuit breaker are separated under fault conditions, an arc is struck between
them. The current is thus able to continue until the discharge ceases. The production of arc not only
delays the current interruption process but it also generates enormous heat which may cause
damage to the syst em or to the breaker itself. Therefore, the main problem in a circuit breaker is to
extinguish the arc within the shortest possible time so that heat generated by it may not reach a
dangerous value (Electrical Systems, 2017).
4. Data and Analysis
The data for our analysis was collected from the 33kV Transmission Company of Nigeria (TCN)
located in New Haven, Enugu (TCN, Tripping reports, 2016). It contained data of up to 59
feeders/CBs in Enugu region for the period of three (3) months (April – June 2016). The data
contained the outage (tripping) report for the feeders together with the tripping time, restoration
time, type of fault, time duration before restoration.
As a result of enormity of the data, we tried to group the number of outages per feeder in terms of
their outage frequencies such as:
i. Most Frequent Outages: for outages greater than 100 times.
ii. Very Frequent Outages: Outages between 31-99
iii. Less frequent Outages: between 10 -30
iv. Occasional: between 3 -9
v. Rare: between 1-2

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The tables and their corresponding chart representations are given to further illustrate the frequency
of outages of each feeder between April and June 2016.
Table 1: Most Frequent Outages (>100)
Feeder Outages
Ezillo
152
Ya h e
140
Itigidi
133
Nnewi
131
Agulu
127
Ehamufu
116
Obosi
115
Barracks Rd.
104
North Bank
104
Umu nya
102
Table 2: Very Frequent Outages (31-99)
Feeder
Outages
Achi
76
Nnpc
76
Nicuss
74
Neni
73
Neni 33
70
Atani
70
Amechi
69
Isieke
67
Ankpa
63
New Nnpc
62
Udi
62
Army Barracks
59
Oju
47
Govt House
42
Wukari
40
Katsina-Ala
39
Taraku
36
Emene Ind. Layout
33
Table 3: Less Frequent Outages (10-30)
Feeder
Outages
Enugu-Ukwu
27
Ind.Layout
26
Ituku/Ozalla
25
Yandev
22
Kingsway Line2/9th
Mile
20
Asaba
18
Awada Ii
18
Emene
17
Feeder 1
17
Makur di
16
Water Wo r k s
16
Feeder 2
13
Feeder 4
12
Mobtr
10
Table 4: Occasional Outages (3-9)
Feeder
Outages
Afikpo
9
Golden Oil
9
Thinkers Corner
8
Aguleri
7
Unn
7
Feeder 3
6
Kingsway Line 1
5
Ibagwa
4
Nsukka
3
Table 5: Rare Outages (1-2)
Feeder
Outages
Feeder 5
2
Mobtr 2
2
Mob 45
2
Oji
2
Agbor
1
Bcc 1&Ii
1
Emene Industrial
1
Oji Local
1

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(a) (c)
(b) (d)
(e)
0
5
10
15
20
25
30
ENUGU-UKWU
IND. LAYOUT
ITUKU/OZALLA
YANDEV
AWADA II
FEEDER 1
EMENE
MAKURDI
WATER WORKS
FEEDER 2
FEEDER 4
MOBSTR
Less frequent outages (10-30)
0
2
4
6
8
10
Occasional outages (3-9)
0
0,5
1
1,5
2
2,5
Rare outages (1-2)
0
20
40
60
80
100
120
140
160
EZILLO
YAHE
ITIGIDI
NNEWI
AGULU
EHAMU…
OBOSI
BARRA…
NORTH…
UMUNYA
Most frequent outages ( >100)
0
10
20
30
40
50
60
70
80 Very frequent outages (31-99)

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Figure 3: Charts showing the various frequency of out age of the CBs (a) most frequent outages (b)
very fr equent outages (c) less frequent outages (d) occasional outages (e) rare outages
5. Reliability Analysis
According to Anyaka B.O. (2012), Some reliability indices were calculated from the data obtained
such as:
• Mean Time to Repair (MTTR)
 =  
  (1)
• Mean Time between Failures (MTBF)
 = −    
  =   
  (2)
• Failure Rate, λ
λ= 1
 (3)
• Availability, A
A = 
 + (4)
It should be noted that the total period stands for the total time in consideration (i.e. 3 months =
2184 hours). After calculations, the results are shown in Tables and graphs. Table 6 and Figure 4
shows Most Frequent Outages Reliability results.
Tab l e 6. Most Frequent Outage Reliability results
FEEDER
Outages
Duration
MTTR
MTBF
Failure
rate
Availability
EZILLO
152
711
4.68
9.69
0.1032
0.6743
YA H E
140
544.43
3.89
11.71
0.0854
0.7506
ITIGIDI
133
863.12
6.49
9.93
0.101
0.6048
NNEWI
131
672.55
5.13
11.88
0.0842
0.6984
AGULU
127
487.97
3.84
13.35
0.075
0.7766
EHAMUFU
116
357.3
3.08
15.75
0.0635
0.8364
OBOSI
115
621.29
5.4
13.59
0.0736
0.7156
BARRACKS
RD.
104
314.48
3.02
17.98
0.0556
0.8562
NORTH
BANK
104
374.64
3.6
17.4
0.0575
0.8286
UMUNYA
102
564.83
5.54
15.87
0.063
0.7412

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Figure 4: Availability and failure rate characteristic for most frequent outages.
Table 7 and Figure 5 show very Frequent Outage Reliability results.
Tab l e 7: Very frequent Outage reliability results
FEEDER
Outages
Duration
MTTR
MTBF
Failure rate
Availability
ACHI
76
534.68
7.04
21.7
0.0461
0.755
NNPC
76
170.85
2.25
26.49
0.0378
0.9217
NICUSS
74
328.73
4.44
25.07
0.0399
0.8495
NENI
73
408.04
5.59
24.33
0.0411
0.8132
33
70
571.7
8.17
23.03
0.0434
0.7381
ATANI
70
207.03
2.96
28.24
0.0354
0.9051
AMECHI
69
435.48
6.31
25.34
0.0395
0.8006
ISIEKE
67
475.55
7.1
25.5
0.0392
0.7822
ANKPA
63
175.12
2.78
31.89
0.0314
0.9198
NEW NNPC
62
89.29
1.44
33.79
0.0296
0.9591
UDI
62
677.78
10.93
24.29
0.0412
0.6897
ARMY
BARRACKS
59
194.7
3.3
33.72
0.0297
0.9109
OJU
47
247.58
5.27
41.2
0.0243
0.8866
GOVT
HOUSE
42
61.33
1.46
50.54
0.0198
0.9719
WUKARI
40
232.01
5.8
48.8
0.0205
0.8938
KATSINA-
ALA
39
399.93
10.25
45.75
0.0219
0.817
TARAKU
36
254.88
7.08
53.59
0.0187
0.8833
EMENE
IND. L AY.
33
77.9
2.36
63.82
0.0157
0.9604
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
Availability
Failure rate

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Figure 5: Availability and failure rate characteristic for very frequent outages
Table 8 and Figure 6 show the most Frequent Outages Reliability results.
Tab l e 8: Less frequent outage reliability results
FEEDER
Outages
Duration
MTTR
MTBF
Failure
rate
Availability
ENUGU-UKWU
27
425.42
15.76
65.13
0.0154
0.8052
IND.LAYOUT
26
44.85
1.73
82.28
0.0122
0.9794
ITUKU/OZALLA
25
106.53
4.26
83.1
0.012
0.9512
YANDEV
22
151.62
6.89
92.38
0.0108
0.9306
KINGSWAY
LINE2/9TH
MILE
20
38.3
1.92
107.29
0.00932
0.9824
ASABA
18
133.1
7.39
113.94
0.00878
0.9391
AWADA II
18
21.17
1.18
120.16
0.00832
0.9903
EMENE
17
67.85
3.99
124.48
0.00803
0.9689
FEEDER 1
17
57.1
3.36
125.11
0.00799
0.9738
MAKURDI
16
44.8
2.8
133.7
0.00748
0.9795
WATER WORKS
16
187.33
11.71
124.79
0.00801
0.9142
FEEDER 2
13
50.9
3.92
164.08
0.00609
0.9767
FEEDER 4
12
45.3
3.78
178.23
0.00561
0.9792
MOBTR
10
6.63
0.66
217.74
0.00459
0.997
0
0,2
0,4
0,6
0,8
1
1,2
ACHI
NNPC
NICUSS
NENI
33
ATANI
AMECHI
ISIEKE
ANKPA
NEW NNPC
UDI
ARMY BARRACKS
OJU
GOVT HOUSE
WUKARI
KATSINA-ALA
TARAKU
EMENE IND.…
Availability
Failure rate

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Figure 6: Availability and failure rate characteristic for less frequent outages
Table 9 and Figure 7 show the most Frequent Outages Reliability results.
Tab l e 9: Occasional outage reliability results
FEEDER
Outages
Duration
MTTR
MTBF
Failure rate
Availability
AFIKPO
9
193.2
21.47
221.2
0.00452
0.9115
GOLDEN OIL
9
45.75
5.08
237.58
0.00421
0.9791
THINKERS
CORNER
8
18.15
2.27
270.73
0.00369
0.9917
AGULERI
7
357.95
51.13
260.86
0.0038
0.8361
UNN
7
56.95
8.14
303.86
0.00329
0.9739
FEEDER 3
6
16.68
2.78
361.22
0.00277
0.9924
KINGSWAY
LINE 1
5
3.83
0.766
436.03
0.00229
0.9982
I B A G WA
4
26.2
6.55
539.45
0.00185
0.988
NSUKKA
3
91.72
30.57
697.43
0.00143
0.958
0
0,2
0,4
0,6
0,8
1
1,2
Failure rate
Availability

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Figure 7: Availability and failure rate characteristic for Occasional outages
Table 10 and Figure 8 show the most Frequent Outages Reliability results.
Tab l e 10: Rare outage reliability results
FEEDER
Outages
Duration
MTTR
MTBF
Failure rate
Availability
FEEDER 5
2
100.11
50.06
1041.95
0.00096
0.9542
MOBTR 2
2
1.07
0.54
1091.47
0.000916
0.9995
MOB 45
2
1.67
0.84
1091.17
0.000916
0.9992
OJI
2
3.35
1.68
1090.33
0.000917
0.9985
AGBOR
1
4.75
4.75
2179.25
0.00046
0.9978
BCC 1&II
1
37.73
37.73
2146.27
0.00047
0.9827
EMENE
INDUSTRIAL
1
0.12
0.12
2183.88
0.000458
0.9999
OJI LOCAL
1
1.93
1.93
2182.07
0.000458
0.9991
0
0,2
0,4
0,6
0,8
1
1,2
Availability
Failure rate

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Figure 8: Availability and failure rate characteristic for rare outages.
6. Observations and Conclusion
From the reliability analysis carried out, the following observations are made:
• In the most frequent outage result, we can observe low availabilities at Itigidi and Obosi
Feeders with corresponding high failure rates.
• The very frequent outage result showed low availability values and high failure rates at
Achi, 33kV Onitsha and Udi feeders.
• The Feeder at Enugu-Ukwu has the lowest availability in the less frequent outage results.
• Aguleri CB has the highest failure rate in the occasional outage results
• Feeder 5 in Asaba station has the lowest availability in the rare outage results.
The availability of a system shows how reliable the system is. From our analysis, the high outages
as a result of over-current and earth faults imply that the particular feeder is less reliable. By
calculation, Ezillo CB has the lowest availability value (0.6743) and Emene Industrial CB has the
highest availability value (0.9999). Hence, Emene Industrial CB has the highest reliability.
However, this does not necessary mean that this feeder is the most reliable one because any CB can
fail at any time due to some factors such as overloading, malfunction, weather conditions, human
errors and so on. The earth-fault and over-current directional and inverse time relays should be
employed in the power system to reduce the high outages due to faults on the system.
0
0,2
0,4
0,6
0,8
1
1,2
Availability
Failure rate

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Compensation should also be done on areas with high loading to improve voltage profile and
reactive power and hence increase transmission line load ability.
Acknowledgement: The authors are immensely grateful for the financial support from “African
Centre of Excellence (ACE-SPED) University of Nigeria, Nsukka” to enable us to achieve the
research (Muncho J. Mbunwe et al., 2019-2021).
Conflicts of Interest: The authors declare no conflict of interest.
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