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Short Circuit Analysis for Effective Relay Coordination in Nigerian Port
Authority, Rivers state
Article · December 2022
DOI: 10.5281/zenodo.7431713
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Journal of Emerging Trends in Electrical Engineering
Volume 4 Issue 3
DOI:https://doi.org/10.5281/zenodo.7431713
Short Circuit Analysis for Effective Relay Coordination in
Nigerian Port Authority, Rivers state
Kingsley Okpara Uwho*, Hachimenum Nyebuchi Amadi, Promise Obire
Department of Electrical Engineering, Rivers State University, Port-Harcourt, Nigeria
*Corresponding Author
E-Mail Id: kingsley.uwho@ust.edu.ng
ABSTRACT
This study seeks to address the poor order of operation of relays in Nigerian Ports Authority
(NPA) for effective relay coordination. NPA is fed from Marine Base distribution substation
of 2 X 15MVA, 33kV. Short circuit analysis is used and Inverse Definite Minimum Time
(IDMT) for prompt response of the relay and hence, the circuit breakers. Modelling and
simulation of the network is carried out using Electrical Transient Analyzer (ETAP 19.0.1)
using data obtained from the Port-Harcourt Electricity Distribution Company and the
Transmission Company of Nigeria. The outcome of the analysis shows that in the existing
case, the order of tripping of the primary feeder relays with their respective backup is
wrong.When a 3-phase fault is initiated on the existing NPA feeder, the order of time of
operation in response to fault is 82.9ms, 137ms, 213ms and 110ms, with the sequence from
feeder breaker 33kV to line breaker, 33kV control panel breaker and then to 11kV incomer
control breaker. The improved case gives an order of 226ms, 343ms, 411ms and 420ms.
420ms.The existing case means that fault occurs in the order of 1,4,3,2. This negates the right
sequence, which is 1,2,3,4. Proper and effective relay coordination is necessary because it
protects both the equipment connected in the network and the personnel working on such
equipment from danger.
Keywords: Circuit breaker, distribution network, nigerian ports authority, short circuit
analysis, relay coordination.
INTRODUCTION
The sole work of a protective relay in a
network is to foresee a fault and therefore
energize the breaker to open the circuit as
fast as possible. Directional over current
relays have been used most often as an
economic means for the protection of subtransmission and distribution networks or
sometimes, as secondary protection of
transmission system [1].
The setting of over current relays must
meet all likely networks prone to faults.
Time and current settings are mostly used.
Over current relays have current setting
multipliers within 50 – 200% in steps of
25% called the plug setting. The plug
setting is dependent on the minimum fault
HBRP Publication Page 1-9 2022. All Rights Reserved
current and the maximum load current [2].
The reliability of a power network is
largely dependent on an efficient
protection scheme for it disconnects only
the faulty part of a system while supply
continues in the rest part of the system.
Primary and secondary protections are
employed in every power network for a
proper relay coordination. In a situation
where the primary protection fails to act,
the back protection should as a matter of
fact acts to save the network from a total
collapse [3]. Over current relays act when
the load current is more than the preset
number. The duty of the TSM of the relay
is to determine the time required for the
relay to energize the circuit breaker while
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Journal of Emerging Trends in Electrical Engineering
Volume 4 Issue 3
DOI:https://doi.org/10.5281/zenodo.7431713
the plug setting dictates the current needed
for the relay to pickup [4]. The
coordination of an over current relay is set
up at the design stage as a result of the
fault current calculation. To clear off a
fault properly within a given time, a relay
must network with other protective relays
found at adjacent buses [5].
The Resistance of a conductor is given as
SHORT CIRCUIT ANALYSIS
Short circuit analysis is used to determine
the magnitude of the short circuit current
that the system is able to yield and
compares the magnitude of the circuit
current with the interrupting rating of the
over current protective device [6]. The
following are the model equations
(Ω)
(2.1)
Where𝜌 is conductor resistivity at a given temperature in Ω/m
𝑙 is conductor length in meter
A is conductor cross-section area in m²
Cross - sectional area (A) is given:
Then calculation of diameter becomes d = 2r
(2.2)
(2.3)
From equation (3.3), radius can be evaluated as r =
Per kilometer reactance of one phase can be evaluated as:
Xo = 0.1445log10 (
) + 0.0157
(2.4)
DGMD- Geometric mean distance between the line conductors and ‘r’ is taken as radius of the
conductors.
Also, determination of line reactance X is given as:
X= 𝑥ₒ 𝑙ₒ
(2.5)
Thus, the distributed series impedance becomes:
Z₁ = R + jX
(2.6)
Also, the equivalent admittance which is a measure of how easily a circuit or device will
allow the flow of electric current, can be represented by:
Zₒ = Y = = G + jB
(2.7)
From the above equation (2.7)
G=
and
(2.8)
(2.9)
If transmission line constants for the route length 𝑍₁ 𝑎𝑛𝑑𝑍ₒ are known, then transmission
line constants referred to base MVA in p.u can be evaluated as:
HBRP Publication Page 1-9 2022. All Rights Reserved
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Journal of Emerging Trends in Electrical Engineering
Volume 4 Issue 3
DOI:https://doi.org/10.5281/zenodo.7431713
Z1P.U =
(2.10)
For a known source Impedance and Base MVA, source impedance becomes:
Source Impedance =
(2.11)
Total fault impedance at Marine Base 2×15MVA, 33/11kv injection substation in p.u can be
evaluated as:
ZF = ZS + Z1+Zt
(
Zt= Zp.u =
)
(2.12)
(2.13)
For a 3 phase 11kv line fault at the injection substation,
Fault MVA =
(2.14)
Fault current at Marine Base injection substation can be determined as:
Fault current=
√
(2.15)
Where VL-L = Line -Line Voltage
MATERIALS AND METHOD
Materials
Materials employed for this analysis are
obtained from the Port Harcourt Electricity
Distribution Company (PHEDC) and the
Transmission Company of Nigeria (TCN)
and are tabulated in table 3.1
Table 1: Data for Calculations and Simulation from PHEDC and TCN[7].
S/N
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Parameter
Route length of 33kv line
Maximum load on 33kv line
T1B 30MVA Impedance at Transmission station
T1 15MVA Impedance at Marine Base Injection Substation
T2 15MVA Impedance at Marine Base Injection Substation
Peak load on Churchill 11kv Feeder
Peak load on NPA 11kv Feeder
Peak load on Station Road 11kv Feeder
Peak load on Amadi North 11kv Feeder
Conductor Size
Conductor type
Cable size
CTRs Incomer
CTRs Outgoing
Base MVA
Relay Type
Conductor Resistivity at 32 °
33kv line spacing
HBRP Publication Page 1-9 2022. All Rights Reserved
Assumptions
4.5km
15.3MW
12.5%
10.52%
10.6%
2.8Mw (168Amps)
2.7MW (162Amps)
3.5MW(210Amps)
3.3 MW (198Amps)
150mm sq.
AAC
240mm sq.
1250-800/1
600-300/1
100
Schneider O/C and E/F Relay
2.83×10-8
3ft= 914.4mm
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Journal of Emerging Trends in Electrical Engineering
Volume 4 Issue 3
DOI:https://doi.org/10.5281/zenodo.7431713
Method
Short circuit analysis and Inverse Definite Minimum Time (IDMT) are used for effective
coordination.
Electrical Transient Analyzer Program (ETAP 19.0.1) is used for the modelling and
simulation.
NPA Feeder
Relay 7 – NPA Feeder Protective Relay
Maximum load of NPA 11kV feeder = 162Amps
TMS = 0.081 (Simulated Set Value)
Taking time difference between two Relays as 100ms
CT Ratio = 600/1A
PS = 40%
Curve Type: Standard Inverse
Fault current (ETAP) on NPA Feeder = 4.494kA
PSM =
=
= 18.725
T=
T=
= 188ms
Relay 4: T2 11kV Incomer Relay
Time of operation of Relay 2 = 100 + 188 = 288ms
If = 3.505KA
PSM =
=
= 7.3
0.288=
TMS = 0.083
MS
Relay 2: T2 33kV Control Panel Relay
Time of Operation of Relay 3 = 100 + 288 = 388ms
If = 1.168kA
PSM =
=
= 6.49
0.388=
TMS = 0.1
MS
RESULTS AND DISCUSSION
Relay Coordination on 33/11kV NPA Feeder (Existing Case)
HBRP Publication Page 1-9 2022. All Rights Reserved
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Journal of Emerging Trends in Electrical Engineering
Volume 4 Issue 3
DOI:https://doi.org/10.5281/zenodo.7431713
Fig. 1: Circuit Breaker Tripping Sequence for Fault on NPA Feeder (Existing case).
Figure 1 clearly shows the order of
tripping sequence for a 3-phase simulated
fault of the existing case injected on NPA
feeder. The tripping sequence is in the
order of: Feeder circuit breaker, 33KV line
Breaker, 33KV Control Panel Breaker,
11KV Incomer Breaker. This response to
fault violates the right order of operation.
CB7 – NPA
CB4 – T2A 11KV INCOMER
CB3 - 33KV CONTROL PANEL
CB1 - 33KV LINE BREAKER
Table 2: Relay response sequence with time of operation for Existing Case.
Table 2 represents the operation of relays
with its associated circuit breakers and the
corresponding tripping time (ms) for 3phase fault on NPA feeder of the existing
HBRP Publication Page 1-9 2022. All Rights Reserved
case. There is a clear violation of relay
response to fault when compared with the
proper sequence.
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Journal of Emerging Trends in Electrical Engineering
Volume 4 Issue 3
DOI:https://doi.org/10.5281/zenodo.7431713
Improved Relay Coordination
TRIPPING SEQUENCE ON NPA FEEDER (EXISTING CASE)
250
213
TIME (ms)
200
137
150
100
50
110
82.9
1
4
NPA
T2A 11KV INCOMER
3
2
33KV CONTROL PANEL
33KV LINE BREAKER
0
TRIPPING SEQUENCE
TRIPPING SEQUENCE
TIME (ms)
Fig. 2: Graph showing Sequence of Circuit Breaker Operation for Fault on NPA Feeder
(Existing case).
Figure 2 represents a graph of the various
circuit breaker tripping sequence with its
associated time of operation in response to
a 3-phase fault on NPA feeder of the
existing case.
Fig. 3: Circuit Breaker Tripping sequence for Fault on NPA Feeder (improved case).
Figure 3 explains the simulated sequence
of tripping for a 3-phase fault on NPA
11kV outgoing feeder for the modified or
new case. This mode of operation shows
HBRP Publication Page 1-9 2022. All Rights Reserved
the right order, which is from Feeder
Circuit Breaker to 11kV Incomer Breaker
to 33kV Control Panel Breaker and to
33kV line Breaker.
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Journal of Emerging Trends in Electrical Engineering
Volume 4 Issue 3
DOI:https://doi.org/10.5281/zenodo.7431713
Table 3: Relay response be sequence with time of operation (improved Case).
Table 3 represents the operation of relays with its associated circuit breakers and the
corresponding tripping time (ms) for the improved case for a 3-phase fault on NPA feeder.
TIME (ms)
TRIPPING SEQUENCE ON NPA FEEDER (NEW
CASE)
600
343
411
420
400
226
200
1
2
3
4
NPA
T2A 11KV INCOMER
33KV CONTROL PANEL
33KV LINE BREAKER
0
TRIPPING SEQUENCE
TRIPPING SEQUENCE
TIME (ms)
Fig. 4: Graph showing Sequence of Circuit Breaker operation for fault on NPA feeder
(improved case).
Fig. 4 shows a graph of the numerous
circuit breaker tripping sequence with its
associated time of operation in response to
a 3-phase fault on NPA feeder for the
improved case.
Table 4: Comparison of Existing and Improved Relay Coordination on NPA Feeder.
Comparison of Existing Case With New Case on NPA Feeder
Feeder
Tripping Sequence Time (ms)
EXISTING NEW
NPA
1
82.9
226
T2A 11KV Incomer 2
137
343
33KV Control Panel 3
213
411
33KV Line Breaker 4
110
420
Table 4 clearly shows the difference between the existing and improved case regarding
sequence of operation of various circuit breakers to fault on NPA 11kV outgoing feeder
HBRP Publication Page 1-9 2022. All Rights Reserved
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Journal of Emerging Trends in Electrical Engineering
Volume 4 Issue 3
DOI:https://doi.org/10.5281/zenodo.7431713
COMPARISON BETWEEN EXISTING CASE WITH NEW CASE
420
411
450
400
343
TIME (ms)
350
300
250
226
213
200
150
100
137
110
82.9
50
0
NPA
T2A 11KV INCOMER
33KV CONTROL PANEL
33KV LINE BREAKER
TRIPPING SEQUENCE
TRIPPING SEQUENCE
EXISTING
NEW
Fig. 5: Graph Comparing Sequence of Circuit Breaker Operation for fault on NPA Feeder
(Existing case vs improved Case).
Fig 4 represents the different behaviour of
circuit breakers in response to a 3-phase
fault on NPA feeder when comparing
existing with improved case.
Table 5: Relay Operating time for fault on NPA feeder.
Relay Time Operations (Sec)
Relay
Theoretical Calculations
/ (SOP)
0.081
(1)
Relay 7
0.083
(2)
Relay 4
0.1
(3)
Relay 2
0.34
(4)
Relay 1
ETAP
Modified
Network/ (SOP)
0.08
(1)
0.082
(2)
0.09
(3)
0.34
(4)
Table 5 shows a clear similarity between
manually calculated relay response time
with simulated time for a 3phase fault on
NPA 11kV feeder for both existing and
modified cases.
CONCLUSION
A reliable and efficient system is the aim
of every designer. An efficient relay
operation prevents downtimes and
guarantees the safety of personnel on site.
The relay coordination of NPA has been
improved as the right order of tripping has
been corrected and is now from Feeder
Circuit Breaker to 11kV Incomer Breaker
to 33kV Control Panel Breaker and then to
HBRP Publication Page 1-9 2022. All Rights Reserved
ETAP
Existing
Network/ (SOP)
0.082
(1)
0.11
(4)
0.09
(3)
0.19
(2)
Curve Type
SIT
SIT
SIT
Definite Time
33kV line Breaker, which means 1,2,3 and
4.
REFERENCES
1. Noghabi, A. S., Sadeh, J., & Mashhadi,
H. R. (2009). Considering different
network
topologies
in
optimal
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2. So, C. W., & Li, K. K. (2000).
Overcurrent relay coordination by
evolutionary
programming. Electric
power systems research, 53(2), 83-90.
3. Alam, M. N., Das, B., & Pant, V.
(2015). A comparative study of
metaheuristic optimization approaches
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Journal of Emerging Trends in Electrical Engineering
Volume 4 Issue 3
DOI:https://doi.org/10.5281/zenodo.7431713
for directional overcurrent relays
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Expansion. Journal of Newviews in
Engineering
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Cite as: Kingsley Okpara Uwho,
Hachimenum Nyebuchi Amadi, &
Promise Obire. (2022). Short Circuit
Analysis
for
Effective
Relay
Coordination in Nigerian Port
Authority, Rivers state. Journal of
Emerging Trends in Electrical
Engineering,
4(3),
1–9.
https://doi.org/10.5281/zenodo.74317
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