1. Introduction
The incorporation of renewable energy [
1] sources in power systems is a worldwide [
2] trend in the transition toward more sustainable energy systems [
3]. The implementation of these renewable energy sources, such as solar and wind energy, has a significant impact on the behavior of the power system in terms of the stability, security, and quality of the energy supplied [
4]. Expanding the energy mix to include a greater proportion of renewable energy sources (RES) forms a crucial element of Colombia’s energy strategy, aimed at achieving a sustainable and more reliable energy system [
5].
The significant rise in renewable energy generation demands greater standards and poses increased challenges for power system management [
6]. The volatility and difficulty of forecasting non-dispatchable [
7] generation plants imply that the system operator must always have a dispatchable generation capacity sufficient to cope with a significant variation in the forecast of such generation [
8]. Likewise, one of the challenges inherent to the adoption of renewable energy sources is their intermittent nature. This intermittency has substantial implications for the stability and reliability of electricity systems [
9]. Solar energy stands as the most widely available and abundant renewable energy source on a global scale. Technological advancements and reduced production costs have paved the way for the widespread adoption and utilization of solar power as a sustainable energy technology [
10].
The incorporation of intermittent renewable energy sources, such as wind and solar photovoltaic (PV), requires meticulous planning to mitigate potential operational outages that could jeopardize power system reliability. Intermittent renewable energy sources generate fluctuating and unpredictable power output over various time scales, which adds complexity to the imperative of constantly aligning generation with varying load demand [
11].
The energy transition in Colombia [
12] poses complex challenges in terms of the current and projected demand, as well as in the planning and operation of the existing power system. In this context, the Mining and Energy Planning Unit (UPME) plays a key role in leading energy planning and promoting a new, more efficient, and sustainable market model. It is crucial to consider the diversification of the energy matrix [
13], promoting the integration of renewable sources and the adoption of clean technologies. In addition, adequate coordination and regulation mechanisms must be established to guarantee the reliability, stability, and optimization of the power system in this transition process toward a more resilient and environmentally friendly energy model [
14].
For the specific case of the Colombian Caribbean region, the integration of 65.50% of the total capacity of generation projects with photovoltaic and wind generation sources is projected, and 79.76% of these projects will be integrated into the power system of GCM and Atlantic, as shown in
Table 1 [
15].
Persistent demand growth, delays in expansion projects, and the increasing embrace of renewable energy sources underscore the crucial need to maintain power systems within secure operational limits [
16]. In [
17], the authors compare solar PV and wind power generation systems in various regions of Pakistan. The results of this study can facilitate evidence-based decision-making processes in the renewable energy sector and contribute significantly to Pakistan’s effort to move toward a sustainable energy system.
No detailed analysis of Poland’s wind power sector’s electricity generation perspective has been conducted yet. With wind power development at a plateau, the authors of [
10] offer crucial insights and correlation analysis for the Polish power system, aiding system assessment and market model development.
In this context, the integration of photovoltaic and wind systems in the Colombian Caribbean region is an opportunity to improve the quality and reliability of the energy supply, as well as to strengthen the national electricity system and reduce vulnerability to extreme weather events associated with El Niño and La Niña phenomena [
18]. However, the incorporation of these types of generation systems presents significant technical challenges, such as the variability and intermittency of generation that affect the stability and security of the electrical system [
19,
20].
Integrating solar photovoltaic and wind systems in a power system reduces energy losses by generating electricity closer to consumption points, which reduces transmission distances and associated losses [
21]. It also optimizes existing infrastructure by utilizing available space without the need to build costly new infrastructure. This avoids unnecessary expansion of the grid and optimizes the use of existing resources, thus contributing to the technical and operational improvement of the power system [
22,
23,
24].
The combination of solar and wind generation improves grid stability by diversifying generation sources and compensating for fluctuations [
22]. This results in a more stable and reliable supply, reducing interruptions and voltage variations. In addition, the use of renewable systems reduces dependence on fossil fuels [
22,
25,
26], reduces greenhouse gas emissions, and promotes energy efficiency, supporting the transition to a more sustainable and resilient energy model [
22,
25,
26].
This paper will address the technical aspects related to the behavior of the voltage, frequency, and losses of the electrical system in the Colombian Caribbean region from the integration of variable renewable energy, considering the connection to the National Interconnection System and the existing technical limitations. The impacts on the stability and security of the electrical system before and after the incorporation of variable renewable energy will be discussed, as well as the mitigation strategies and solutions to the technical challenges that may arise in the process.
The rest of this paper is structured as follows: the first part deals with the load-flow analysis in power systems, which is applied to evaluate the behavior of the voltage and power magnitudes of the system. Then, it focuses on the integration of photovoltaic and wind systems in 2033, underlining the relevance of renewable energies for a sustainable electricity supply. In the next part, PowerFactory is used to model the Colombian Caribbean region, presenting details on the infrastructure, transformers, and generation plants. Next, the impact of the integration of variable renewable energies in 2033 is examined, taking 2023 as a base scenario, providing details on substations and the addition of these energy sources. The next section shows the results obtained and makes a discussion along with the analysis of these; it analyzes voltage and power variations in busbars with renewable energies, specifying the modifications in substations and the consequences of these changes and delves into the effects of adding renewable systems, evaluating the transient stability of the system, and observing responses in the voltage, frequency, and angle. Finally, the conclusions show some of the aspects considered most relevant to the research.
2. Materials and Methods
2.1. Theoretical Basis
Load-flow analysis [
27] is a fundamental tool to study and evaluate the behavior of a power system. It is based on the calculation of the magnitude and phase angle of the voltages at each bus and, secondarily, the currents, powers, and losses of the system are obtained, considering the characteristics of the components such as generators, loads, transformers, and transmission lines. It is composed of a set of non-linear equations known as power balance equations and current balance equations.
The power balance equations establish that the sum of the active and reactive powers injected at a node must be equal to the sum of the active and reactive powers absorbed at that node. These equations are expressed as follows [
28]:
where
P(
i) and
Q(
i) are the active and reactive power at node
i, respectively,
V(
i) is the voltage at node
i,
G(
i) and
B(
i) are the respective conductance and susceptance at node
i, and
θ(
i) is the phase angle at node
i.
The current balance equations state that the sum of the currents injected at a node must equal the sum of the currents absorbed at that node. These equations are expressed as:
where
I(
i) is the current at node
i,
Y(
i,
j) is the admittance between busbars
i and
j,
V(
j) is the voltage at node
j,
θ(
i,
j) is the phase difference between bus
i y
j [
27].
These equations are simultaneously solved using a numerical method, such as the Newton–Raphson method, to obtain the voltage and current magnitudes at each bus of the system. The load flow allows for analyzing the operating state of the system, determining the energy losses, and evaluating the performance under different load conditions and contingencies. It is an essential tool in the design, operation, and planning of efficient and reliable power systems [
27,
28].
2.2. Base Case Study
To evaluate the impact of integrating photovoltaic and wind power systems, load-flow and transient stability simulations are carried out, considering the scenario of average demand in 2023 and 2033, and considering both conventional generation sources and the generation sources mentioned above. By comparing the load-flow results in both scenarios, the performance of the power system is analyzed in terms of the stability, supply capacity, and voltage variation. This approach provides information on the need to expand generation capacity, improve infrastructure, and promote the use of these types of renewable energy sources to ensure a reliable and sustainable supply in 2033.
Figure 1 shows a schematic and simplified representation of the electricity infrastructure of the Caribbean region, which in turn is divided into two operational subareas: GCM and Atlantic.
The GCM subarea has an infrastructure composed of 22 substations and two thermal power plants: Termonorte and Termoguajira. It should be noted that alternative energy projects are being integrated into this subarea, to diversify the energy mix and improve the resilience of the system. Among the substations, Cuestecita and La Loma have been identified as key nodes, hosting several of these alternative energy projects [
29].
At the same time, the Atlantic subzone is characterized by its 21 substations and two thermal power plants: TEBSA and Las Flores. These power plants play a crucial role in sustaining the region’s energy needs. What distinguishes the Atlantic subzone is the strong integration of alternative energy generation projects. Most of these projects find their nexus in the Sabanalarga and Baranoa substations, which signifies their strategic importance in the regional energy network [
13,
29].
An outstanding feature of the Caribbean region’s electricity system is its interconnection. Both the GCM subzone and the Atlantic subzone are interconnected to the national power grid, see
Table 1 [
13,
29].
Regarding renewable energy projects, La Guajira is one of the areas with the greatest wind potential; however, the region has high solar irradiation. There are more than 50 renewable energy projects in the planning, development, or operation in these systems [
13,
15].
These systems have a solid infrastructure of electrical substations to manage the generation and distribution of electricity. They have 43 electrical substations in GCM and Atlantic plus 4 thermal power plants. In each of the substations, there are different voltage levels (110 and 220 kV) and different amounts of connected demand (load) to be served [
29].
In this study, the PowerFactory 2023 (DigSilent) simulation tool is used to model the power system of the Colombian Caribbean region. The choice of PowerFactory as a load-flow analysis tool with the integration of photovoltaic and wind generation projects is based on its accurate and realistic ability to represent the renewable generation components and to evaluate the effects of their variability on the operation and stability of the power system [
30,
31].
The model of the electrical system under study is composed of the transmission infrastructure, power transformers, and conventional and variable renewable generation plants, among other elements. A capacity expansion is foreseen, reaching 50,153 MW. This expansion represents a growth of 1.7 times the installed capacity in 2022. In this scenario, there are limitations in the implementation of offshore wind generation, so a total capacity of 1500 MW of this technology is contemplated. However, supply from natural gas is strengthened through the addition of 600 MW starting in 2037, reaching a total of 5622 MW of installed capacity from this energy source. This represents an approximate doubling compared to the 2823 MW available in 2022. On the other hand, a growth of approximately three times the installed capacity of wind parks in 2022 is projected, with a capacity at the end of the time horizon of 72,330 MW [
12].
Through simulations of the average demand scenario in 2023 and 2033, the impact of integrating renewable energies in the electric system of the Colombian Caribbean region will be evaluated, contemplating different levels of penetration of these energy sources, and analyzing the system behavior before and after their integration. This approach will allow for obtaining valuable information on the feasibility and potential benefits of adopting renewable energies in the Colombian Caribbean region.
Table 2 shows the capacity and voltage level of the substations selected for the analysis of the electrical power system of the Colombian Caribbean region, as shown in
Figure 1. These busbars in the selected substations are because these are projected to have the most significant integration in the capacity of the generation projects with non-conventional RES; some of the other substations, such as Nueva Barranquilla and Santa Marta, are part of the area of influence of the electrical substations in which the impact of the integration of RES in these substations should be evaluated [
30].
2.3. Methodology
In this paper, a methodology is presented to carry out a voltage and frequency stability analysis in an existing power system. Two scenarios are considered: one for the year 2023 without the integration of intermittent renewable energy and one for the year 2033 with the incorporation of intermittent renewable energy sources.
The methodology is applied using DigSilent software and focuses on the evaluation of system stability.
- -
Data Gathering
In this stage, comprehensive data about the existing power system are meticulously collected. This includes information on the network topology, load characteristics, generation data, as well as the location and capacity of intermittent renewable energy sources. Having up-to-date data for the years 2023 and 2033 is paramount.
- -
System Modeling
DigSilent software is employed to develop a detailed and accurate model of the power system. This model must encompass all relevant components, such as generators, transformers, transmission lines, switches, loads, and intermittent renewable energy sources. Precise representation of the location and capacity of these sources is critical.
- -
Simulation Scenarios
Two simulation scenarios are defined: one for the year 2023, reflecting the state of the system without the presence of intermittent renewable energy, and one for the year 2033, considering the integration of these sources. The generation and load parameters are adjusted according to the expectations for each year. Simulations of power flow, transients, and short-term stability are performed in both scenarios.
- -
Stability Evaluation
The results of the simulations are carefully analyzed to evaluate the voltage and frequency stability in each scenario. Special attention is paid to critical indicators, such as frequency swings and voltage sags, to identify potential stability issues. It is sought to determine if the integration of intermittent renewable energy harms the system stability.
- -
Display of results and graphics (year 2023 and 2033)
The findings are thoroughly documented, including graphs and tables to support the results obtained. Conclusions are made on the voltage and frequency stability of the system in the years 2023 and 2033.
Figure 2 shows the flow chart of the process followed to carry out the simulations using the PowerFactory software.
4. Analysis of Results
To verify the impact of the incorporation of the variable renewable energy projects into the system, transient stability events are analyzed in the busbars of
Table 2. A stability analysis in the Copey 220 kV substation is performed, for which a three-phase short-circuit event is performed in 0.1 s in each of the busbars and a switch event for the protections in 0.15 s from the beginning of the simulation in the Sabanalarga 500 kV substation. The generators at the Tebsa and Cerromatoso substations are studied since they are the closest generators to the substation under study.
Likewise, to verify the impact of the incorporation of the variable renewable energy projects into the system, transient frequency stability events are analyzed in the busbars of
Table 5. The values are within the regulatory range; however, in these cases, some variations may affect the proper operation of the power system [
33].
Figure 3a,
Figure 3b, and
Figure 3c show the voltage, frequency, and angle responses, respectively. As for the voltage with the integration of RES in 2033, the voltage value in substations with the thermal energy injection is shown to be non-stable.
Regarding the frequency, the peak value of the transient is reduced, but the value of the transient is maintained for a longer time, while the frequency is maintained when stability is achieved. The results are used to know if they are within the regulatory range.
For this case, the behaviors are observed in substations with the thermal energy injection. These behaviors are represented in
Figure 3a,
Figure 3b, and
Figure 3c, which represent the responses in terms of the voltage, frequency, and angle, respectively.
Figure 4a emphasizes the voltage response within the substations. With the incorporation of RES, it is evident that the voltage in these substations exhibits a specific characteristic: it tends toward instability. This observation is of particular interest since voltage stabilization is crucial for the proper functioning and efficiency of the electrical grid. An unstable voltage can lead to power quality issues and potential system failures.
On the other hand,
Figure 4b illustrates the frequency response. One of the most notable findings is that, with the thermal energy injection, the transient peak value undergoes a reduction. This behavior can be interpreted as a decline in the initial frequency oscillations following disturbances in the system. However, an aspect that warrants detailed consideration is that, despite this reduction in the peak value, the transient persists for a more extended period. This could have implications for the control and management of the frequency under real-world scenarios. Nevertheless, it is encouraging to observe that the frequency attains a stable state in a shorter time, suggesting a swift system recovery post-disturbance.
Figure 4c, focusing on the angle response, completes the triad of observations. Although the original text does not provide specific details about the angle behavior, it would be pertinent in future research to analyze how the thermal energy injection and the presence of RES affect this variable, given its significance in the synchronization and coherence of machines within an electrical grid.
The responses of the voltage, frequency, and angle in substations with the thermal energy injection provide profound insight into how the presence of RES and other factors can influence the behavior and stability of the electrical system. These findings are pivotal in guiding future research and strategies for the design and control of modern electrical grids.
Similarly,
Figure 5a,
Figure 5b, and
Figure 5c show the voltage, frequency, and angle responses, respectively. As for the voltage, with the presence of RES, the voltage value in substations with the thermal energy injection shows a non-stabilization tendency. Regarding the frequency, the value of the transient is increased which is outside the regulatory range. However, the variation is less than 0.2 Hz, which is the maximum allowed value. The transient value is maintained for a longer time while the frequency achieves stability at a similar time.
Figure 6a,
Figure 6b, and
Figure 6c show the voltage, frequency, and angle responses, respectively. As for the voltage, with the presence of RES, the voltage value in substations with the thermal energy injection shows a non-stabilization tendency. Regarding the frequency, the maximum value of the transient is increased by more than 0.2 Hz. However, the transient value is maintained for a longer time while the frequency achieves stability in less time.
When performing the stability analysis in the Las Jaguas 110 kV substation, under the same fault conditions with the integration of the La Jagua, with 9.9 MW solar generation, no voltage variations are obtained that threaten the correct operation of the system.
In the totality of the simulated disturbances, they show that the network with the connection of photovoltaic and wind generation systems continues to present stable dynamic responses, keeping the system within the tolerated ranges, i.e., there is no non-compliance for the operation of the electrical system of the area GCM.
Likewise, the rotor angle of the synchronous generators in the area shows a high tendency to stabilize and synchronize recovery in the event of severe faults.
It should be noted that in the event of a three-phase fault in one of the GCM lines, in this case, the Codazzi–La Jagua 1 110–In La Jagua (1%) lines were selected, the momentary output of the transformers of La Jagua and the photovoltaic generation project is generated. Once the line is open and the fault is isolated, the La Jagua substation equipment can be normal.
According to the results obtained, it can be affirmed that the connection of a 9.9 MW solar photovoltaic park to the system does not affect the condition of the National Interconnection System in terms of stability.
The analysis of the results of the different simulations of the GCM and Atlantic power system of the Colombian Caribbean region, with the integration of solar photovoltaic and wind systems, reveals slightly significant behaviors in voltage variations.
5. Conclusions
This paper presented the study of the integration of variable renewable energy systems in the Colombian Caribbean region in 2023 and 2033.
Delving further into the analysis, the observed voltage variations in the lower voltage levels hold considerable significance for the overall stability and reliability of the power system. The fact that there was minimal to no variation in levels higher than 220 kV suggests that these upper voltage tiers are better equipped to handle the intermittent nature of renewable energy generation.
In contrast, the voltage fluctuations in the lower voltage levels, ranging from 1% to 3.1%, indicate potential challenges in maintaining voltage stability. These variations can adversely affect the quality of the energy supply, potentially causing voltage sags or swells that may disrupt sensitive equipment and affect end-users.
Successful integration of solar photovoltaic and wind systems requires careful planning and coordination. It is essential to assess the capacity and quality of the power grid, as variations in active power of up to 65% are observed. Appropriate control and management strategies must be designed to ensure a smooth and efficient integration of renewable generation. To mitigate these fluctuations and improve the voltage quality, it is crucial to implement strategies such as voltage regulation devices, grid reinforcement, and enhanced coordination of renewable energy sources with grid operations. By doing so, the power system can ensure a more consistent and reliable energy delivery, especially in areas where the voltage quality is critical.
It is important to note that this type of study has not been rigorously carried out for the Colombian Caribbean region, so it is considered relevant given that in this area of the country, a large number of projects are expected to be integrated into the SIN, as indicated in [
12], to have reliable technical information to design operation and planning strategies focused on safety, reliability, and efficiency.
In summary, the analysis of the simulation results shows that the integration of solar photovoltaic and wind systems into an existing power system leads to an improvement in the voltage variations, system reliability, load-matching capability, and eventual reduction in energy losses. The integration of solar and wind systems into the Caribbean region’s power system increases the available power generation capacity.