Performance Analysis of Utility Scale Photovoltaic Systems Integrated Into An Islanded Nigeria Electric Power Grid

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Performance Analysis of Utility Scale Photovoltaic Systems Integrated Into An Islanded Nigeria Electric Power Grid

S.I. Ibuodinma, O.J. Onojo, L.O Uzoechi

Department of Electrical and Electronic Engineering Federal University of Technology,

Owerri, NIGERIA.

Abstract:- This paper is on the performance analysis of photovoltaic (PV) system integrated into an islanded Nigeria electricity grid. Electricity supply in Nigeria is abysmal and the effects on the economy and quality of life of Nigerians. This work carried out load flow studies of a part of the existing network, namely Afam Power Substation to Yenegoa Transmission Substation and the network with utility scale PV system integrated. Contingency analysis of the system was carried out using a set of possible contingency scenarios. PowerWorld Simulator was deployed in carrying out these analyses. With the incorporation of PV systems, stability was achieved when there was loss of generation. For example, when Afam Generation station was opened, system violations went from 14 (without PV) to 3 (with PV). Finally, the levelized cost of electricity (LCoE) for combined cycle gas turbines and PV systems was conducted. The LCoE for PV systems was 0.08985$/KWh which is less than LCoE of 0.245$/KWh as at 2013. The results also show that such hybrid generation planning can provide a high degree of redundancy in our fragile network.

Keywords: Utility Scale PV systems, Power Flow Analysis, Contingency analysis, PowerWorld.

1.0 INTRODUCTION

The issue of electric power demand supply in Nigeria has been seemingly intractable over the years. Several government and industry players have done a lot to improve the system, yet outcomes remain abysmal. Sambo (2008) showed that based on the so- called reference scenario, at 7% GDP growth, electricity demand projections for Nigeria is expected to peak at 119,200MW in the year 2030. With a base year of 2005, this would have implied a yearly addition of 4,538MW. It is estimated the installed capacity of off grid generation in Nigeria is about 14 GW (African-EU Renewable Energy Corperation Programme, 2016). This capacity exceeds the overall installed capacity. It has been shown that with average generation of 4000 MW, the per capita consumption is 0.03KW, a very poor performance (Ezirim, Eke, & Onuoha, 2016). Many manufacturing industries rely mostly on off grid generators for their electricity needs. In addition, overall, electricity consumption only accounts for one fifth of our final energy demand today, but contributes about 40% of energy related CO2 emission. (International Energy Agency, 2018). Therefore, to improve generation capacity in Nigeria and reduce carbon emission it will be necessary to deploy as

many as possible renewable energy sources in our energy mix.

Utility scale solar power plants are energy generating facilities capable of producing large amounts of electricity that can be fed into the electricity transmission grid; they range in size from 10 MW to over 200 MW(Xoubi, 2015). The integration of photovoltaic systems into the grid is gaining more traction today as a very important application of PV systems. According to levelized cost studies conducted by Lazard, an international financial advisory and asset management firm, the mean levelized cost of energy of utility-scale PV technologies is down approximately 13% from 2017 and the mean levelized cost of energy of onshore wind has declined almost 7% (Lazard, 2018). Utility scale photovoltaic systems promise to be a viable option in ramping up generation capacity of Nigeria, while protecting the environment.

Nigeria has recorded a total of 18 total system collapse and 6 partial system collapse between 2018-2019. The Nigeria National Grid is highly vulnerable to voltage instability. It was observed that the high rate of system collapse is largely due to faults (technical challenges) on the network, the state of the power system equipment and to some extent political issues (Samuel, Katende, Daramola, & Awelewa, 2014).

This reinforces the need for intentional power system islanding. Islanding refers to the condition in which a portion of the grid becomes temporarily isolated from the main grid but remains energized by its own distributed generation resource(s). Islanding may occur accidentally or deliberately. Traditionally, islanding has been seen by utilities as an undesirable condition due to concerns about safety, equipment protection, and system control(Greacen, Engel, Quetchenbach, & Berkeley, 2013). Islanding operation can be intentional and may be desired in cases where the central grid is prone to reliability problems. This reflects the Nigeria electric power scenario.

There is the need to conduct thorough analysis before integrating alternative and variable PV systems. In doing this, Powerworld a userfriendly and highly interactive power system analysis and visualization platform is employed. It integrates many commonly performed power system tasksContingency Analysis, TimeStep Simulation, OPF, ATC, PVQV, Fault Analysis, SCOPF, Sensitivity

Analysis, Loss Analysis, Transient Stability, etc (PowerWorld Corporation, 2019).

    1. METHODOLOGY

    2. Procedure for the project.

      The algorithm for the project is as stated below;

      1. Collection of data: This involves the data of the generation stations, transmission lines, inter-bus transformers and connected loads.

      2. Model system in PowerWorld: This will include creating models of the network the system without Utility Scale PV systems and with PV systems integrated.

      3. Carry out load flow analysis of the system: This will include load flow analysis of the system

        1. Without PV systems integrated

        2. With PV systems integrated

      4. Develop a contingency list.

      5. Conduct contingency analysis.

      6. Carry out cost analysis of the different plants.

    3. Data Collection.

      The data used for this study are generation Stations, inter- bus transformers and transmission line data. These are shown in Tables 1, 2 and 3.

      Table 1: Generation station Voltage and power ratings.

      S/N

      Generating Stations

      Voltage (kV)

      Power (MW)

      1

      AFAM PS

      330

      1396

      2

      GBARAIN PS

      132

      120

      Table 2: Data of the inter-bus transformers

      S/N

      T r a n s f o r m e r s

      Power (MVA)

      Reactance P,u

      % impeda nc e

      1

      330/132kV Tx @Alaoji (T2)

      150

      0.07573

      11.36

      2

      330/132kV Tx @Alaoji (T3)

      150

      0.07573

      11.36

      3

      330/132kV Tx @Alaoji (T4)

      300

      0.04523

      13.57

      4

      330/132kV Tx @Afam (T1)

      164

      0.07074

      11.46

      5

      330/132kV Tx @Alaoji (T2)

      150

      0.07573

      11.36

      Table 3: Transmission line data.

      1

      S/N

      Lines

      Voltage kV

      Power MW

      Len KM

      R p.u

      X p.u

      Afam—Alaoji L1

      330

      400

      25

      0.0009825

      0.0073898

      2

      Afam—Alaoji L2

      330

      400

      25

      0.0009825

      0.0073898

      3

      Afam—Alaoji L1

      132

      300

      30

      0.0047001

      0.058801

      4

      Afam—Alaoji L2

      132

      300

      30

      0.0047001

      0.058801

      5

      AlaojiPH Main L1

      132

      144

      37

      0.0002121

      0.0770005

      6

      AlaojiPH Main L2

      132

      144

      37

      0.0002121

      0.0770005

      7

      AlaojiAba L1

      132

      100

      7

      0.0011204

      0.01412

      8

      AlaojiAba L2

      132

      100

      7

      0.0011204

      0.01412

      9

      AlaojiUmuahia L1

      132

      80

      57

      0.0022401

      0.016845

      10

      AlaojiUmuahia L2

      132

      80

      57

      0.0022401

      0.016845

      11

      AlaojiOwerri L1

      132

      100

      60

      0.0112947

      0.1412004

      12

      AlaojiOwerri L2

      132

      100

      60

      0.0112947

      0.1412004

      13

      Owerri—Ahoada L1

      132

      100

      74

      0.0029084

      0.021869

      14

      Owerri—Ahoada L2

      132

      100

      74

      0.0029084

      0.021869

      15

      Ahoada—Gbarain L1

      132

      50

      37.5

      0.0014542

      0.0109345

      16

      Ahoada—Gbarain L2

      132

      50

      37.5

      0.0014542

      0.0109345

      17

      GbarainYenogoa L1

      132

      50

      37.5

      0.0014542

      0.0109345

      18

      GbarainYenogoa L2

      132

      50

      37.5

      0.0014542

      0.0109345

    4. Load Flow Analysis.

      The derivation of power flow equations for power system networks are shown in Fig. 1.

      Vi = Vii, V = Vi i and Yik = Yikik, (2.8)

      i

      i

      The real and reactive powers in polar form are expressed

      Vi Real power = Pi = V n Yik Vk cos (ik + k i)

      yi1 V1

      i

      (2.9)

      k=1

      Reactive power = Qi = V n Yik Vk sin (ik + k i)

      V2 i k=1

      yi2

      Ii

      yin

      yio

      (2.10)

      Due the non-linearity of the above equations, numerical methods are employed in the evaluation of the solutions to the

      Vn equations. Several techniques exist like the Newton Raphson,

      Gauss Seidel and the Fast Decouple methods. The Newton Method is employed in this project.

    5. PowerWorld Load Flow Simulation

      The PowerWorld model of the islanded network and the modified network are shown in Figs. 2 and 3.

      Figure 1: Typical Power System Network The current entering the ith bus is given as

      Ii = yioVi + yi1(Vi V1) + yi2(Vi V2) + + yik(Vi Vk)

      (2.0)

      Collecting like terms in equation 2.0, we have,

      1

      GS

      AFAM

      PH Main 132kV SS

      4

      3

      T2

      T3 T4

      5

      ABA

      6 132kV SS

      Owerri 132kV SS

      Ahaoda

      9 132kV SS Yenogoa 132kV SS

      Ii = (yio

      + yi1

      + yi2

      + + yik

      )Vi yi1 V1

      yi2 V2

      T1 T2 PS 330kV

      Alaoji 330kV/132kV

      10

      8 Ahaoda 11 12

      132kV SS GS

      7

      yikVk (2.1)

      2

      AFAM PS 132kV

      Umuahia 132kV SS

      GBARAIN PS 132kV

      er

      d

      er

      d

      The term (yio + yi1 + yi2 + + yik) is the self-admittance and the coefficients of V1, V2, Vk are the mutual admittances.

      We simplify equation (2.1) as

      Figure 2: Single Line Diagram of the network

      PH Main 132kV SS

      5

      ABA

      6 132kV SS

      4

      k=1

      k=1

      Ii = n

      Yik Vk; i = 1,2 , n (2.2)

      1 3 Owerri

      T3

      T4

      T3

      T4

      T2 132kV SS

      Ahaoda

      9 132kV SS

      Yenogoa 132kV SS

      The complex power injected into the ith bus of the pow

      system is

      i

      i

      Si = Pi + jQi = ViI ;where i = 1,2 , n (2.3)

      Where Vi is the ith bus voltage with respect to the earth an

      i

      i

      I is the conjugate of the current . The power conjugate

      GS

      AFAM PS 330kV

      PVGS

      2

      AFAM PS 132kV

      Alaoji 330kV/132kV

      8

      7

      Umuahia 132kV SS

      10

      Ahaoda

      132kV SS

      PVGS

      11

      12

      GS

      GBARAIN PS 132kV

      therefore becomes,

      i

      i

      Si = Pi Qi = VIi ; where i = 1,2 …, n (2.4) Substituting into eqn 2.4

      Figure 3: Single Line Diagram of the modified network

      The data of the various part of the network were input in the PowerWorld Simulator. This was used to calculate the voltages, power flows, the voltage angles of the busses. The

      S = P jQ = V n Y V ; where i = 1,2 ,, n

      PowerWorld base settings include

      i i i i k=1 ik k

      (2.5)

      Separating the real and reactive components of the above equation

      1. Base MVA = 100

      2. Voltage tolerance = ±5%

        Real power = Pi = Re {V n Yik Vk} (2.6)

        i k=1

      3. Maximum number of iterations = 100

        Real power = Si = Im {V n Yik Vk} (2.7)

        i k=1

      4. Range of Voltage angle= ± 10°

        The Voltage and the admittance in polar form as given as

      5. Power Factor = 0.8

      6. Slack bus voltage and angle = 1.05 0.00°

      7. Slack Bus = Afam 330kV

      8. Machine models: REG-C (Renewable Energy

        + Fuel Price * Heat Rate (2.11)

        CRF = capital recovery factor, turning capital costs into annual values (if capital is financed at discount rate D)

        Fixed O & M = Fixed Operation and maintenance Costs. Variable O & M = Variable Operation and maintenance Costs. T= Tax rate, DPv = Depreciation Factor

        Generator- Controller) for PV generators and GENTPF for Combined Cycle Gas Turbine.

    6. Contingency Analysis

      CRF = D (1+D)

      N

      N

      (1+D)N1

      D = Discount rate

      N= Lifetime of System.

      (2.12)

      The cost components for evaluating LCOE are itemized in Table 4.

      Since the Photovoltaic system is a still a budding development,

      it is crucial to explore the behaviour of the system under anTable 4: Cost Components of the LCoE for CCGT and PV unexpected or planned system outage to detect the weakness thatsystems(Roche, Ude, & Donald-Ofoegbu, 2017)

      PARAMETERS

      UNIT

      CCGT

      Photovoltaic

      Capital Cost

      $/KW

      1000

      1150

      Fixed O & M

      $/KW-Yr

      /td>

      15.50

      17.30

      Variable O & M

      $/KWh

      0.006

      0

      Capacity Factor

      %

      80

      19

      Discount Rate

      %

      11

      11

      Fuel Cost

      $/MMBtu

      7

      0

      Depreciation

      %

      10

      10

      Tax Rate

      %

      5

      0

      Heat Rate

      Btu/KWh

      11039

      0

      PARAMETERS

      UNIT

      CCGT

      Photovoltaic

      Capital Cost

      $/KW

      1000

      1150

      Fixed O & M

      $/KW-Yr

      15.50

      17.30

      Variable O & M

      $/KWh

      0.006

      0

      Capacity Factor

      %

      80

      19

      Discount Rate

      %

      11

      11

      Fuel Cost

      $/MMBtu

      7

      0

      Depreciation

      %

      10

      10

      Tax Rate

      %

      5

      0

      Heat Rate

      Btu/KWh

      11039

      0

      the network will bear. Contingencies can exist as the result of the outages of the system elements such as: generator, network transmission lines and system transformer for the purpose this work, we focus on the effect of outages of generating stations, particularly with the PV systems integrated and the effect of variability of the photovoltaic source on the system.

    7. Contingency List

      The contingency list is set in order to identify the effect of contingencies on the system operation and to experience which critical contingencies causes most violation of the system.(Alex, 2015) In this project, the contingencies tested are

      1. Open Afam 330kV power station without the photovoltaic systems

        Assuming N = 30 years and calculating the LCoE using equation

      2. Open Gbarain 132kV power station without th(e3.18)

        30

        30

        photovoltaic systems

        1. For combined cycle gas turbine.

      3. Open Afam 330kV power station with the photovoltaic systems

        CRF = 0.11(1.11) = 0.1150

        (1.11)301

        LCoE =( 10000.1150(1(0.050.1))) + ( 15.50

        )+ 0.006 +

        87600.8(10.5) 87600.8

      4. Open Gbarain 132kV power station with the

      photovoltaic systems

      ( 7

      106

      * 11039 ) = 0.1027$/KWh

        1. Zero Insolation at Afam 132kV Photovoltaic Station

          1. For PV systems

          LCoE = ( 11500.1150(1(00.1))) + ( 17.30

          )+ 0 + (0 * 0 )

        2. Zero Insolation at Gbarain 132kV Photovoltaic Station

      87600.19(10)

      = 0.08985 $/KWh

      87600.19

      The PowerWorld simulator was used for the simulation of each of the contingencies.

    8. Cost Analysis

The levelized cost of electricity (LCoE) was evaluated for the two different power generation sources namely natural gas and solar energy. The Nigerian Electricity Regulation Council employs the US Department of Energy method of calculating LCOE. The formula is given by equation 11.

    1. RESULTS AND DISCUSSION

      This chapter presents results and discussion of the of the objectives in chapter 3:

      1. Load flow analysis of the network without PV system

      2. Load flow analysis of the network with PV system integrated

      3. Contingency analysis of the network without PV system integrated.

      4. Contingency analysis of the network with PV system integrated.

      5. Cost Analysis of the system.

      LCOE = Capital CostCRF(1TDpv )

      8760Capacity factor(1T)

      Variable O &M

      + Fixed O & M +

      8760Capacity Factor

    2. Results from Load Flow Analysis of The Network Without PV System

      From the results of the load flow analysis of the system as shown in Table 5, the following is deduced.

      1. All the bus voltage magnitudes are within the acceptable limit of ±5%

        Voltage p.u

        Voltage p.u

      2. There are violations of buses 8, 9, 10, 11, 12, which are not within the ± 10° range. This is explained by the fact that Gbarain PS is not sufficient to boost the real and reactive power supply at that end and there are reactors installed at the downstream station for compensation of losses. Hence the need for a system that can boost supply and compensate for losses. The Photovoltaic system comes as a viable option.

      3. The major active and reactive power demand is on Afam 330kV.

      4. which will definitely have impact on system stability. Therefore, the system is always close to the tipping point and this explains clearly the partial collapses often experienced in this segment. The graphical representation of the bus voltage and voltage angle profile in Figs. 4 and 5 further explains the results.

    3. Results from Load Flow Analysis of the Network with PV System

      The results in Table 6 and Figs. 6 and 7 show a clear improvement when the PV systems were integrated into the select segment of the grid. The following can be clearly seen.

      1. All the bus voltage magnitudes are within the acceptable limit of ±5%, even with more improvement in values.

      2. There are no violations of buses angles as all are within the ± 10° range. This is due to the fact that the PV systems assisted in improving the bus angle by supplying more active power.

      Bus No

      Name

      Pu Volt

      Ang. Deg

      Gen MW

      Gen MVar

      1

      Afam PS

      1.05

      0.00

      537.8

      225.97

      3

      Alaoji TS

      1.04238

      -0.72

      2

      Afam PS

      1.03063

      -2.82

      4

      Alaoji PS

      1.01356

      -5.10

      7

      Umuahia TS

      1.01151

      -5.39

      5

      Aba TS

      1.01006

      -5.68

      6

      PH Main TS

      0.998

      -8.24

      11

      Gbarain PS

      0.96317

      -12.02

      120

      30

      10

      Ahaoda TS

      0.96164

      -12.07

      8

      Owerri TS

      0.96089

      -12.28

      12

      Yenogoa TS

      0.96286

      -12.36

      9

      Ahoada TS

      0.95593

      -13.12

      Bus No

      Name

      Pu Volt

      Ang. Deg

      Gen MW

      Gen MVar

      1

      Afam PS

      1.05

      0.00

      537.8

      225.97

      3

      Alaoji TS

      1.04238

      -0.72

      2

      Afam PS

      1.03063

      -2.82

      4

      Alaoji PS

      1.01356

      -5.10

      7

      Umuahia TS

      1.01151

      -5.39

      5

      Aba TS

      1.01006

      -5.68

      6

      PH Main TS

      0.998

      -8.24

      11

      Gbarain PS

      0.96317

      -12.02

      120

      30

      10

      Ahaoda TS

      0.96164

      -12.07

      8

      Owerri TS

      0.96089

      -12.28

      12

      Yenogoa TS

      0.96286

      -12.36

      9

      Ahoada TS

      0.95593

      -13.12

      Table 5: Results of the PowerWorld Load Flow Simulation without PV.

      Bus Voltage Profile

      1.2

      1

      0.8

      0.6

      0.4

      0.2

      0

      Bus Name

      Bus Voltage Profile

      1.2

      1

      0.8

      0.6

      0.4

      0.2

      0

      Bus Name

      Ahaoda

      Yenogoa Owerri Ahaoda Gbarain PH Main Aba Umuahia Alaoji PS Afam PS Alaoji PS

      Afam PS

      Ahaoda

      Yenogoa Owerri Ahaoda Gbarain PH Main Aba Umuahia Alaoji PS Afam PS Alaoji PS

      Afam PS

      Figure 4: Bar chart of the Bus voltages without PVsystem.

      Voltage Angle Profile

      0.00

      -2.00

      -4.00

      -6.00

      -8.00

      -10.00

      -12.00

      -14.00

      Bus Name

      Voltage Angle Profile

      0.00

      -2.00

      -4.00

      -6.00

      -8.00

      -10.00

      -12.00

      -14.00

      Bus Name

      Ahaoda 132kV SS

      Yenogoa 132kV SS Owerri 132kV SS Ahaoda 132kV SS Gbarain PS 132kV PH Main 132kV SS Aba 132kV SS Umuahia 132kV SS Alaoji PS 132kV Afam PS 132kV Alaoji PS 132kV

      Afam PS 330kV

      Ahaoda 132kV SS

      Yenogoa 132kV SS Owerri 132kV SS Ahaoda 132kV SS Gbarain PS 132kV PH Main 132kV SS Aba 132kV SS Umuahia 132kV SS Alaoji PS 132kV Afam PS 132kV Alaoji PS 132kV

      Afam PS 330kV

      Angle deg.

      Angle deg.

      Figure 5: Bar chart of Voltage angles without PV system.

      Table 6: Results of the PowerWorld Load Flow Simulation with PV.

      Bus No

      Name

      Nom kV

      PU Volt

      Volt (kV)

      Angle (Deg)

      1

      Afam PS 330kV

      330

      1.05

      346.5

      0

      2

      Afam PS 132kV

      132

      1.03328

      136.392

      2.46

      3

      Alaoji TS 132kV

      330

      1.04438

      344.646

      -0.24

      4

      Alaoji TS 132kV

      132

      1.0173

      134.283

      -1.85

      5

      Aba 132kV TS

      132

      1.0138

      133.822

      -2.43

      6

      PH Main 132kV TS

      132

      1.0018

      132.238

      -4.97

      7

      Umuahia 132kV TS

      132

      1.01525

      134.013

      -2.14

      8

      Owerri 132kV TS

      132

      0.97648

      128.895

      -4.00

      9

      Ahaoda 132kV SS

      132

      0.97086

      128.153

      -4.82

      10

      Ahaoda 132kV TS

      132

      0.98055

      129.433

      -2.23

      11

      Gbarain PS 132kV

      132

      0.98171

      129.586

      -1.79

      12

      Yenogoa 132kV TS

      132

      0.97948

      129.291

      -2.12

      Bus No

      Name

      Nom kV

      PU Volt

      Volt (kV)

      Angle (Deg)

      1

      Afam PS 330kV

      330

      1.05

      346.5

      0

      2

      Afam PS 132kV

      132

      1.03328

      136.392

      2.46

      3

      Alaoji TS 132kV

      330

      1.04438

      344.646

      -0.24

      4

      Alaoji TS 132kV

      132

      1.0173

      134.283

      -1.85

      5

      Aba 132kV TS

      132

      1.0138

      133.822

      -2.43

      6

      PH Main 132kV TS

      132

      1.0018

      132.238

      -4.97

      7

      Umuahia 132kV TS

      132

      1.01525

      134.013

      -2.14

      8

      Owerri 132kV TS

      132

      0.97648

      128.895

      -4.00

      9

      Ahaoda 132kV SS

      132

      0.97086

      128.153

      -4.82

      10

      Ahaoda 132kV TS

      132

      0.98055

      129.433

      -2.23

      11

      Gbarain PS 132kV

      132

      0.98171

      129.586

      -1.79

      12

      Yenogoa 132kV TS

      132

      0.97948

      129.291

      -2.12

      Voltage

      Voltage

      1

      0.8

      0.6

      0.4

      0.2

      0

      Bus Low Volts

      Bus(1)

      0.567

      0.95

      59.75

      Bus Low Volts

      Bus(2)

      0.567

      0.95

      59.75

      Bus Low Volts

      Bus(3)

      0.567

      0.95

      59.75

      Bus Low Volts

      Bus(4)

      0.567

      0.95

      59.75

      Bus Low Volts

      Bus(5)

      0.561

      0.95

      59.13

      Bus Low Volts

      Bus(6)

      0.537

      0.95

      56.61

      Bus Low Volts

      Bus(7)

      0.564

      0.95

      59.39

      Bus Low Volts

      Bus(8)

      0.829

      0.95

      87.35

      Bus Low Volts

      Bus(9)

      0.823

      0.95

      86.64

      Bus(5)

      Bus Low Volts

      Bus(1)

      0.567

      0.95

      59.75

      Bus Low Volts

      Bus(2)

      0.567

      0.95

      59.75

      Bus Low Volts

      Bus(3)

      0.567

      0.95

      59.75

      Bus Low Volts

      Bus(4)

      0.567

      0.95

      59.75

      Bus Low Volts

      0.561

      0.95

      59.13

      Bus Low Volts

      Bus(6)

      0.537

      0.95

      56.61

      Bus Low Volts

      Bus(7)

      0.564

      0.95

      59.39

      Bus Low Volts

      Bus(8)

      0.829

      0.95

      87.35

      Bus Low Volts

      Bus(9)

      0.823

      0.95

      86.64

      Bus Name

      Gbarain PS

      Gbarain PS

      Ahaoda

      Ahaoda

      Owerri

      Owerri

      Ahaoda

      Ahaoda

      Umuahia

      Umuahia

      Yenogoa

      Yenogoa

      Aba 132kV SS

      Aba 132kV SS

      PH Main

      PH Main

      Alaoji TS

      Alaoji TS

      Afam PS

      Afam PS

      Figure 6: Bar chart of the Bus voltages with PV System.

      0

      -2

      -4

      -6

      -8

      -10

      -12

      -14

      Bus Name

      0

      -2

      -4

      -6

      -8

      -10

      -12

      -14

      Bus Name

      Angle Deg

      Angle Deg

      Figure 7: Bar chart of the Bus voltages without PV System.

    4. Results from Contingency Analysis of the Network Without PV System

      The contingency lists and the results of the simulations are shown in Tables 7, 8 and 9.

      The results above registered 14 violations when Afam PS was suddenly lost. The violations are severe as seen from the 9 bus voltage violations and 5 transmission line violations, thus whenever Afam PS is lost, the segment must collapse. Again, losing Gbarain PS recorded 5 bus voltage violations which exceeded the ±5% voltage limits and overloaded Alaoji-Owerri line with above 30%, this could lead to loss of that transmission line thus compromising the system. Thus, this network as is, requires further redundancies as this contingency tested can trigger a system collapse of the entire grid.

      VIOLATION SUMMARY WHEN AFAM 330kV PS WAS OPENED WITHOUT PV

      Category

      Element

      Value

      Limit

      Percent

      Branch MVA

      Bus(4)-Bus(8)

      247.2

      125

      197.82

      Branch MVA

      Bus(4)-Bus(8)

      247.2

      125

      197.82

      Branch MVA

      Bus(8)-Bus(10)

      779.8

      125

      623.85

      Branch MVA

      Bus(10)-Bus(11)

      404.3

      62.5

      646.99

      Branch MVA

      Bus(10)-Bus(11)

      404.3

      62.5

      646.99

      VIOLATION SUMMARY WHEN AFAM 330kV PS WAS OPENED WITHOUT PV

      Category

      Element

      Value

      Limit

      Percent

      Branch MVA

      Bus(4)-Bus(8)

      247.2

      125

      197.82

      Branch MVA

      Bus(4)-Bus(8)

      247.2

      125

      197.82

      Branch MVA

      Bus(8)-Bus(10)

      779.8

      125

      623.85

      Branch MVA

      Bus(10)-Bus(11)

      404.3

      62.5

      646.99

      Branch MVA

      Bus(10)-Bus(11)

      404.3

      62.5

      646.99

      Table 7: Results of the Power World contingency analysis without PV system

      Table 8: Results of the Power World contingency analysis without PV system

      VIOLATION SUMMARY WHEN AFAM 330kV PS WAS OPENED WITHOUT PV

      Category

      Element

      Value

      Limit

      Percent

      Bus Low Volts

      Bus(12)

      0.8661

      0.95

      96.23

      Bus Low Volts

      Bus(8)

      0.882

      0.95

      98

      Bus Low Volts

      Bus(9)

      0.8757

      0.95

      97.31

      Bus Low Volts

      Bus(10)

      0.8712

      0.95

      96.8

      Bus Low Volts

      Bus(11)

      0.8686

      0.95

      96.51

      Branch MVA

      Bus(4)-Bus(8)

      173.07

      125

      138.46

      Branch MVA

      Bus(4)-Bus(8)

      173.07

      125

      138.46

    5. Results from Contingency Analysis of the Network with PV System

      The contingency lists and the results of the simulations are shown in Table 9.

      The results showed improvements when the Afam 330kV PS was opened. The following could be deduced.

      1. There were only 3 violations which is far removed from the 13 violations recorded without PV system.

      2. There were no bus voltage violations.

      3. The percentage violations of the transmissions are negligible compared to the results got without PV systems. These line overload can be remedied by simply increasing line capacities.

      Hence, the PV systems will provide a high degree of stability when there is outage of any of the generation plants. As expected, no violations occurred when Gbarain PS was lost.

      Table 9: Results of the Power World contingency analysis with PV system

      VIOLATION SUMMARY WHEN GBARAIN 132 kV PS WAS OPENED WITH PV

      Category

      Element

      Value

      Limit

      Percent

      Branch MVA

      Ahaoda(10)- Owerri(8)

      135.79

      125

      108.63

      Branch MVA

      Gbarain(11)- Ahaoda(10)

      67.98

      62.5

      108.76

      Branch MVA

      Gbarain(11)- Ahaoda(10)

      67.98

      62.5

      108.76

    6. Results from Contingency Analysis of the Network when there is Zero Insolation at the PV Power Stations

      The basic challenge faced with PV systems is the variability of the source. The results here tested the effect of losing any of the PV systems. The violations observed in Table 10 are transmission lines overload occasioned by the demand for more active power from

      1. Gbarain PS when there was zero insolation at Afam 132kV PVGS, Owerri- Ahoada line2 and Gbarain-Ahoada Line1&2 being the trunk lines in this case (see appendix for branch flows).

        Table 10: Results of the Power World contingency analysis without PV system

        Branch MVA

        Violations when there is Zero insolation at AFAM PVGS

        Category

        Element

        Value

        Limit

        Percent

        Branch MVA

        Ahaoda TS ( 10) –

        Owerri TS (8)

        135.79

        125

        108.63

        Branch MVA

        Gbarain PS

        (11) –

        Ahaoda SS (10)

        67.97

        62.5

        108.76

        Branch MVA

        Gbarain PS

        (11) –

        Ahaoda SS (10)

        67.97

        62.5

        108.76

        Violations when there is Zero insolation at GBARAIN PVGS

        Alaoji TS(4)

        – Owerri TS (8)

        163.88

        125

        131.1

        Branch MVA

        Alaoji TS (

        4) – Owerri TS (8)

        163.88

        125

        131.1

      2. Afam PS when there was zero insolation at Gbarain PVGS, Alaoji-Owerri transmission lines.

      electricity tariff because while deploying the system, cheaper electricity costs are likely going to be achieved.

    7. Results from Cost Analysis

The LCoE calculation in chapter three was based on 2017 variables. The tax rate was based only on the VAT for gas supply. The calculated LCoE for the combined cycle gas turbines is 0.1027$/KWh, while LCoE for PV system is 0.08985$/KWh. This implies that the PV systems over its lifetime will provide cheaper electricity than the conventional sources.

4.0 CONCLUSION

The performance analysis of Nigeria electricity network was effectively carried out with the clear set objectives in focus throughout the study. Using PowerWorld simulator, the load flow analysis and contingency analysis of the modified network, that is the network with PV system integration, were studied. The results showed that PV systems whose source is in abundance in Nigeria can help us achieve power system adequacy and stability to reasonable extent.

This work is recommended for all power generation companies in Nigeria (Gencos). Once Nigeria power network is strengthened, the next challenge will be low generation

capacity. This will lead to more electricity supply challenges in Nigeria. Generation companies can use the PV systems as relief stations when there is good insolation and gas supply is low. They can also use PV systems integrated to the grid to control

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