Hardware Complexity

55

Table 3.2: Transmission system costs for energy in Nigeria at 2016

N/MWh

TSP 2975.12

SO 330.08

MO 22.21

NERC ISO 5.28 Ancillary Services 50.69

Total 3383.38

This charge translates to N3.38338/kWh of energy transmitted on the Nigerian grid network.

Table 3.3: Distribution Companies tariff for energy consumed in Nigeria at 2016

DisCo Tariff

56

3.2 Flow Chart for the Execution of the Load Flow Program

Figure 3.1: Load flow chart

Figure 3.1 shows a sketch of the load-flow chart that was used to run the load-flow program of the simulated networks using the NEPLAN software to obtain the results. The Newton-Raphson

Iteration index = 1

Calculate all ∆P and

∆Q mismatches

Converged?

Iteration index

= maximum?

Iteration index = iteration index +1

Form Jacobian Matrix

Solve mismatch equations for all ∆ϴ and ∆V

Update ϴ and V Print

Yes

No

Yes

No Start with initial voltages

57

method was used for the solution of the load-flow algorithm. The figures of the different simulated networks are shown in Chapter 4 along with the results obtained for each.

3.3 Network Modelling

In analysing the impact of the integration of the DG technology on the Nigerian power system, following their installation in the 33kV distribution voltage network, the expanded 330kV grid network, which is a 60-bus network, was modelled and simulated using the NEPLAN software.

Data from the National System Planning (NSP) office and the National Control Centre (NCC) were used in the modelling.

3.3.1 Transmission Network Modelling

The Nigerian power system has an installed capacity of 7,652MW as at May 2019, which is a mix of 18.30% hydro and 81.70% natural gas and steam. Its peak power generation is 5,375MW at 7th February 2019 (Osuoha K., ―Daily Operational Reports‖ 2019).

The Transmission Company of Nigeria network is made up of 5,650kM of 330kV lines and 6,687kM of 132kV lines which connects 32 330kV and 105 132kV substations (Energypedia,

―Nigeria Energy Situation‖ 2019), all linked to the various generating stations and distribution networks, who are guaranteed free access to the networks. These make up the national grid network. The Distribution system comprises of all networks, substations and equipment operating from 33kV and below.

In modelling the grid network in the NEPLAN software, the impedance of each transmission line was taken from real life values (see appendix III). Each phase of the transmission lines has double, bundled conductor made of steel reinforced aluminium. The cross section of every conductor is 350mm

and the gap maintained between the diameters of two conductors in phase is 0.45M while the gap maintained between the phases is 8.65M (Ezeakudo C. P., Ezechukwu O.

A., Ani L. U., Ocheni A., ―Voltage Stability Control Through Reactive Power Regulation in the

Nigerian 330kV Grid‖ 2015). The line impedance and shunt admittance which were used for the

simulation are as shown in table 3.4. The impedance of every phase is symmetrical and

transposition of conductors was assumed done along the lines.

58

Table 3.4: Line parameters used for simulation

Conductor Type R-line X-line Xc -line G-line

Bison 0.038175 0.3264310 0.0111 3.487

The above line parameters were used to model the lines in the NEPLAN software. Stations in load area were treated as load busses. Power transfer was simulated from the generation busses to load busses through the lines. To investigate voltage stability, the behaviour of bus voltage magnitude in the load area was observed.

The Nigerian national grid system is divided into eight operational regions following a geographical disposition of the networks and alongside the political divide of the Country. These regions are: Bauchi, Benin, Enugu, Kaduna, Lagos, Osogbo, Port-Harcourt and Shiroro.

The generating stations were modelled according to the voltage at which they generate but were all stepped up to 330kV, which is also the reality on ground. The generation dispatch scenarios used were as provided by the National Control Centre (NCC) while the loads used represent the maximum demand scenario of the various generating stations and load busses.

3.3.2 Location Criteria and Capacity of DG Installation

In defining the zones to install the DG systems, two different criteria were used:

i. Nodal factors and

ii. Premises provided by the NCC cum NSP according to the declarations of the investors.

3.3.3 Nodal Factors

Nodal factors can be defined as factors that indicate changes in network losses as a result of changes in active power demand in a defined node. They are determined by (Camilo T., Hernando D. and Angela C., ―Technical and Economic Impacts of Distributed Generation on the Transmission Networks‖ 2011)

𝑁𝐹 = 1 − ∆𝑃

∆𝑃

(3.1)

59

In line with these factors, regions and nodes to install DG are those with the highest nodal factors. These nodes have highest levels of losses and voltage problems as well. DG installation capacities were selected as a percentage of the total supplied demand in the corresponding region.

Figure 3.2: Average Nodal Factors for each region of the 330kV grid network

From the above chart, it is observed that Bauchi region has the highest nodal factors while Lagos region has the least. Bauchi region, a net importer of electricity, is characterised by very long transmission lines. The region has a very charged network and relatively low voltages requiring capacitive compensation. Enugu, Benin and Osogbo regions have very close nodal factors and have high voltage issues often. This results to quite high losses in the regions.

3.3.4 Premises Provided by NCC/NSP

The Transmission grid network expansion plan obtained from the NSP was used for the simulation and studied and zones in the country that have attractive potentials for the installation of DG of different technologies were identified. The installation of the different technologies in the regions were modelled and analysed.

3.3.5 Modelling the DG

Given its technical characteristics, DG is installed in medium voltage networks which correspond to 33kV voltage networks in Nigeria. The modelled capacities were installed as a

Bauchi Benin Enugu Kaduna Lagos Osogbo

Port-Harcourt Shiroro Series1 -11.288 -8.9076 -9.2131 -7.02 -3.6457 -8.7804 -7.1053 -5.4842

-12 -10 -8 -6 -4 -2 0