# Development of an Integrated Transmission-Distribution Simulation Model for Coordinated TSO-DSO Interface Management

Mohammed Nadir Bouhadda, Mohamed Moez Belhaouane, Arnaud Davigny, Benoit Robyns, Abdelhadi Qasimi, Sébastien Haye, Stéphane Monthe, Vincent Berbesant

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Mohammed Nadir Bouhadda, Mohamed Moez Belhaouane, Arnaud Davigny, Benoit Robyns, Abdelhadi Qasimi, et al.. Development of an Integrated Transmission-Distribution Simulation Model for Coordinated TSO-DSO Interface Management. The 26th European Conference on Power Electronics and Applications, GDR SEEDS France & EPE Association, Mar 2025, Paris, France. 10.34746/epe2025-0316. hal-05075619

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# Development of an Integrated Transmission-Distribution Simulation Model for Coordinated TSO-DSO Interface Management

Mohammed Nadir BOUHADDA, Mohamed Moez BELHAOUANE, Arnaud DAVIGNY and Benoit ROBYNS

Univ. Lille, Arts et Métiers Institute of Technology, Centrale Lille, Junia, ULR 2697 - L2EP, Lille, France.

E-Mail: [mohammed-nadir.bouhadda@junia.com](mailto:mohammed-nadir.bouhadda@junia.com), [mohamed-moez.belhaouane@junia.com](mailto:mohamed-moez.belhaouane@junia.com), [arnaud.davigny@junia.com](mailto:arnaud.davigny@junia.com), [benoit.robyns@junia.com](mailto:benoit.robyns@junia.com)

URL: [https://l2ep.univ-lille.fr](https://l2ep.univ-lille.fr)

Abdelhadi QASIMI and Sébastien HAYE

GÉRÉDIS Deux-Sèvres, Research and Development Department, 79000 Niort, France.

E-Mail: [aqasimi@geredis.fr](mailto:aqasimi@geredis.fr), [shaye@geredis.fr](mailto:shaye@geredis.fr)

URL: [http://www.geredis.fr](http://www.geredis.fr)

Stéphane MONTHE and Vincent BERBESANT

Réseau de Transport d'Electricité (RTE), Research and Development Department, 92073 Paris La Defense, France.

E-Mail: [stephane.monthe@rte-france.com](mailto:stephane.monthe@rte-france.com), [vincent.barbesant@rte-france.com](mailto:vincent.barbesant@rte-france.com)

URL: [https://www.rte-france.com](https://www.rte-france.com)

## Acknowledgements

This work was supported and funded by RTE, the French Transmission System Operator (TSO), and GÉRÉDIS Deux-Sèvres, the French Distribution System Operator (DSO) under concession from SIEDS (Intermunicipal Energy Syndicate of Deux-Sèvres).

## Keywords

« Distribution of electrical energy», « Distributed generation», « Transmission of electrical energy», « Medium voltage grid», « System modeling», «Co-simulation».

## Abstract

This paper presents a comprehensive methodology for integrated TSO/DSO modeling, aimed at enhancing coordinated management of transmission and distribution networks. The proposed approach allows to perform a unified numerical load-flow model that effectively integrates both transmission and distribution electrical systems, accounting for technical constraints of each grid operator. The validation of the detailed joint TSO/DSO model is carried out using real-world scenarios provided by grid operators, ensuring its practical applicability.

## Introduction

Distribution grids are currently undergoing significant transformations driven by several key factors. One of the most impactful changes is the increasing integration of Distributed Generation (DG) systems, such as solar photovoltaic (PV) systems, wind turbines, and small hydroelectric plants, which are located close to the end-users. These distributed energy resources (DERs) are reshaping traditional grid structures, moving away from centralized power plants towards more decentralized networks. Moreover, the evolution of load demand in distribution networks adds another layer of complexity where the load profiles are becoming more dynamic and less predictable.

Indeed, distribution networks, once primarily passive recipients of energy, have now become active and dynamic players, essential for maintaining the stability and efficiency of the overall electrical system. This evolution is marked by the massive integration of decentralized energy production, resulting in bidirectional energy flows at HV (High Voltage) /MV (Medium Voltage) substations. In addition, the nature of loads is changing, with the rise of more flexible loads, such as electric vehicles, which require adaptive management to integrate
smoothly into the power grid. Thus, significant challenges arise for both DSOs and TSOs, particularly due to the inherent intermittency of energy sources and the changing nature of electrical loads.

As a result, distribution networks are susceptible to increased voltage profiles and changes in reactive power flows, sometimes leading to reactive power flowing upwards at the distribution/transmission system interface. These flows can affect voltage control and reactive power management strategies in both MV and HV networks. The coupling between HV and MV systems has therefore become stronger, but also more erratic, variable, and difficult to predict. In addition to this technical evolution, any new distribution system must comply with the regulatory framework defined by the European Grid Codes [1]. For instance, under the Demand and Connection Code [2], any new distribution system must be capable of limiting the upward flow of reactive power to the HV grid during periods of low consumption [3].

To address emerging operational challenges and comply with regulatory requirements, it is crucial to develop new strategies at the interface between transmission and distribution systems [4]. Several approaches have been proposed in the literature to tackle this issue. The topic of voltage control in distribution networks with high penetration of Distributed Generation (DG) has been extensively studied, and there exists a substantial literature proposing a variety of methods [5].

For example, the authors of [6] demonstrated that, in the context of high Renewable Energy Sources (RES) penetration, voltage rise is primarily influenced by two factors: voltage imbalance and reverse power flow (PF). Thus, mitigating either of these factors can help regulate voltage. In [6], voltage imbalance is addressed by injecting negative-sequence current to reduce the maximum line-to-line voltage. Similarly, [7] proposes a coordinated real-time voltage control system based on optimal control strategies via a global controller. Based on real-time voltage control, advanced methods such as Model Predictive Control (MPC) have been developed, using an optimal multi-step algorithm that can handle various constraints, manage time delays, and anticipate predictable disturbances [8]. However, the issue of reactive power exchanges at HV/MV interface is not addressed except in

[9], where the authors propose to integrate a constraint either on voltage or reactive power at the HV side of the transformer with an MPC approach. In [10], a control scheme based on the evolution of the real-time Volt Var Control (VVC) of distribution networks and a joint coordination for the reactive power management of a HV system has been proposed. Another significant result focused on the stochastic optimization of voltage planning and reactive power management at the HV/MV interface is proposed in [11]. The proposed control approach actions on the distribution networks include the On Load Tap Changer (OLTC), the reactive power of decentralized generators, and capacitor banks.

Therefore, active coordination between TSOs and DSOs is essential to assess the mutual interactions at the HV/MV interface and to optimize the use of available flexibilities, such as storage, renewable energy, and production/consumption, while adapting planning methods accordingly [12]. Moreover, to investigate and study the interaction between TSO and DSO at the interface, the integrated modelling of the entire electrical system is a reliable way to capture the effects of the emerging high-growth decentralized energy resources connected to the grid [13].

This paper presents the development methodology of an integrated Transmission-Distribution (T&D) steady-state simulation model based on a real-world case study. The main objective is to demonstrate the feasibility of creating a unified numerical model within a single simulation environment, without relying on co-simulation, as is commonly done in most published works. The aim is to provide TSO and DSO with a model capable of simulating various scenarios and capturing potential interactions at the HV/MV interface. The development and validation processes of the load-flow simulation model will be discussed, highlighting the benefits of such a model in replicating real events that may occur across both transmission and distribution grids.

The paper is structured as follows. First, the new challenges arising from the interaction between Transmission and Distribution grids at the HV/MV interface, highlighting the need for joint TSO-DSO coordination and integrated modeling are presented. Then, the development strategy of an integrated Transmission-Distribution (T&D)
numerical simulation model is detailed. Finally, the validation of the integrated TSO-DSO simulation model is demonstrated through a real-world scenario to confirm the effectiveness of the proposed modeling approach.

## Interaction between Transmission-Distribution grids at HV/MV Interface

Despite the physical interconnection between transmission and distribution systems, these networks are managed separately by the TSO and DSO, with only limited coordination. The TSO operates without insight into potential power flow variations or the control capabilities available to the DSO. In this context, the distribution system is treated as a load, the value of which is simply measured at the distribution substation. Similarly, the DSO typically views the transmission side as a voltage source, also measured at the substation. Consequently, both the TSO and DSO are largely “blind” to the conditions and control actions within each other’s systems [14].

With the increasing variability of loads and the high penetration of inherently stochastic renewable energy sources, energy flow may fluctuate or even reverse direction in some feeders or transmission lines. This challenges the traditional top-down energy transfer model of conventional power systems. As a result, mutual interaction can occur in terms of voltage regulation and reactive power exchange at the HV/MV interface [15].

As shown in Fig.1, this HV/MV interface is located at the substation, where high-voltage electricity in transmission networks is converted to lower voltage levels. The focus is on how energy flows, control mechanisms, and operational strategies between the high-voltage transmission network and medium-voltage distribution systems impact the overall stability, efficiency, and resilience of the grid.

## Emerging Challenges and Scientific Implications

As mentioned earlier, distribution networks have been experiencing significant changes that challenge the effectiveness of traditional voltage control and reactive power management schemes. These changes include the large-scale integration

of Distributed Generation (DG), the replacement of overhead lines with underground cables, and the evolution of loads. As illustrated in Fig. 2, these factors collectively contribute to the shifting dynamics of the distribution network, necessitating new approaches to power system management. The main consequences are associated with voltage rises at the MV and HV levels, the saturation of HV/MV On-Load Tap Changers (OLTC), and increased difficulty in managing of bidirectional active and reactive power flows.

<figure><img src="image_2.png" /><figcaption>Fig.1: General structure of modern power system network</figcaption></figure>

Consequently, the interactions between HV and MV grids have become more erratic, exhibiting greater variability.

<figure><img src="image_3.png" /><figcaption>Fig.2: Location of MV network evolutions and their consequences [10].</figcaption></figure>

Thus, in terms of scientific challenges, the design of advanced real-time control for voltage regulation is essential, particularly to address the issue of voltage fluctuations relative to the
nominal value (overvoltage and undervoltage problems) at the HV/MV interface. Nevertheless, power electronics-based solutions, such as Static Synchronous Compensator (STATCOM) systems connected to the HV/MV interface, should be an optimal solution for voltage support. Additionally, joint coordination between the TSO and DSO is necessary for the optimal management of voltage and current constraints, including maintaining HV within contractual limits and managing power flows (e.g., congestion management). Furthermore, a generalized coordination methodology is needed to optimize data exchange mechanisms and enhance security protocols, ensuring information confidentiality. In addition, reliable and updated medium- and long-term joint planning strategies between the TSO and DSO are also crucial to support the integration of distributed generation sources without compromising the operations of each operator, while offering cost-effective alternatives to network reinforcement. Finally, it is essential to consider the establishment of a new regulatory framework regarding demand and grid connections.

## Necessity of Coordinated TSO-DSO Collaboration and Integrated Modeling

By combining advanced simulation tools with accurate operational data, it becomes possible to develop robust integrated models. These models enhance coordination between TSOs and DSOs, allowing for more agile and proactive responses to the complex challenges posed by the ongoing evolution of the electrical system.

For instance, the integration of renewable energy sources, which are often intermittent and unpredictable, can significantly impact the stability and performance of both transmission and distribution networks. Joint modeling allows for the anticipation of these effects by synchronizing the operations of TSOs and DSOs. This approach not only contributes to forecasting and proactively managing potential issues such as overvoltage and undervoltage but also enhances the overall resilience of the electrical system.

Furthermore, it is essential to consider the stochastic behavior of electrical sources and load, as well as uncertainties, in this type of modeling. Indeed, the stochastic modeling of distribution networks under uncertainty is crucial for studying interactions at the TSO/DSO interface. This

approach accounts for forecast errors, consumption, and production uncertainties, as well as the operation of On-Load Tap Changers at substations.

There are several types of modeling approaches for developing a joint TSO-DSO model, which can be classified into three main categories: steady-state models, dynamic models, and numerical models. For more detailed information on these different modeling approaches, please refer to [16]. Recently, several studies have focused more on numerical modeling, introducing a new dimension to the modeling of TSO/DSO systems. This approach enables real-time simulations and online optimization of parameters of the integrated electrical networks. Indeed, Co-simulation platforms such as IGMS (Integrated Grid Modeling System), HELICS (Hierarchical Engine for Large-scale Infrastructure Co-Simulation), and FNCS (Framework for Network Co-Simulation) allow for the separate simulation of generation and distribution systems while interconnecting them through coupling circuits. This hybrid approach combines the advantages of both static and dynamic models, enabling a more flexible and detailed analysis of interactions between networks, while also reducing computational complexity.

The following section outlines the approach for developing a unified simulation model that integrates both transmission and distribution grids within a single environment. The specific modeling steps taken by each network operator to create a joint simulation model are detailed in the next section.

## Joint TSO/DSO modeling for coordinated management between transmission and distribution networks

The purpose of this section is to depict the strategy for developing a portion of the transmission system operated by the French TSO, RTE (Réseau de Transport d'Électricité), and a segment of the distribution system managed by GÉRÉDIS Deux-Sèvres, the local French DSO operating under concession from SIEDS, the public authority responsible for electricity and gas services in the Deux-Sèvres department of France. The objective is to develop a load-flow
simulation model that enables effective
coordination between RTE and GÉRÉDIS.

## Definition of the study area and physical constraints

The study area is in the southern part of the Deux-Sèvres department, near the borders of Charente, Charente-Maritime, and Vienne. The distribution networks between these three departments are completely separated, meaning there is no possibility of interconnection between feeders, rendering each network independent.

As shown in Fig.3, the power supply to the
southeastern area is provided by four HV (90
kV)/MV (20kV) substations located in Saint-
Maixent, La Mothe-Saint-Héray, Melle, and Sud
Deux-Sèvres (Brioux). In addition to these
substations, the area is also served by three Extra
High Voltage/High Voltage substations, EHV
(225 kV)/HV (90 kV), located in Lezay,
Pamproux, and Melleran. These infrastructures
are crucial for ensuring efficient and continuous
electricity distribution in the region, meeting
consumer needs and maintaining service quality.

<figure><img src="image_4.png" /><figcaption>Fig.3: The geographical study area</figcaption></figure>

For the southwestern area, the power supply is
provided by four substations, which include a
total of eight HV/MV (90kV/20kV) transformers.
The substations are in Saint-Florent, Niort Nord,
Trévins, and Benêt, which the latter is managed
by ENEDIS, the principal French DSO.

The study of the southern area is prioritized due
to the numerous constraints observed on both the
consumption and production sides, along with the
issues identified by the TSO, particularly the
transit constraints between certain substations. In
addition, overvoltage problems at some

substations and interruptions in the regulator must
also be considered.

Methodology for Developing an
Integrated Transmission-
Distribution Simulation Model

First, as is typically done, the transmission and distribution networks have been modeled and simulated separately in two different simulation environments. In this study, the modeling and simulation of the transmission grid have been carried out using *PowSyBl* (Power System Blocks). Note that *PowSyBl* is an open-source framework widely used by TSOs for both static and dynamic studies. This simulation tool is supported by *LF Energy*, an initiative of the Linux Foundation dedicated to accelerating the global energy transition through open-source software. Indeed, the developed detailed model under *PowSyBl*, allow modeling a part of the transmission network around the distribution substations mentioned above. On the other hand, the modeling and simulation of the distribution grid have been performed using *PowerFactory DigSilent*. The *PowerFactory DIgSILENT* simulation software is primarily used by DSOs for both static analyses and dynamic testing. Then, the main idea is to merge both simulation models in the same environment such as *PowerFactory (PF) DigSilent*.

To ensure the conversion of the transmission
network model initially developed in PowSyBl to
PowerFactory DigSilent, an intermediate step
is required. This step involves exporting the
transmission network model in CIM (Common
Information Model) standard to ensure
interoperability between the simulation tools, as
shown in Fig.4. Indeed, to implement such model
and ensure proper interoperability between the
TSO, the DSO, and the stakeholders, the IEC
CIM family of standards IEC61970, IEC61968,
and IEC62325 is adopted in this work.

Once both models are available in the same
simulation environment, and before proceeding
with the merging of transmission and distribution
models in PowerFactory (PF) DigSilent
environment, some adjustments to both models
are necessary. In fact, it is important to verify the
layouts of substations and distribution stations, as
well as the voltage levels. In addition, it is
necessary to adjust the characteristics of the lines,
transformers, loads, and generators in the distribution model.

<figure><img src="image_5.png" /><figcaption>**Fig.4:** Conversion procedure to a unified simulation environment.</figcaption></figure>

The procedure for merging the integrated Transmission-Distribution simulation model is highlighted through the following flowchart summarized in four main steps, as shown in Fig.5.

<figure><img src="image_6.png" /><figcaption>**Fig.5:** Flowchart of the merging procedure of TSO/DSO model</figcaption></figure>

The method described in Fig.5 for creating an integrated transmission-distribution numerical model has been applied to merge the zone of the Deux-Sèvres distribution network managed by GEREDIS with the transmission network in the southern area managed by RTE. The merged

model, following the integration of the TSO/DSO for the MELLE substation, is illustrated in Fig. 6. The validation of the developed TSO-DSO numerical simulation model is given in the next section. Note that for the validation process of the integrated simulation model, the reference model is based on real measurements taken primarily at the HV/MV interface. State estimators are used to reconstruct the network state, ensuring a low mean square error between the measured and estimated electrical quantities.

<figure><img src="image_7.png" /><figcaption>**Fig.6:** Merged model after the integration of TSO/DSO (MELLE substation).</figcaption></figure>

## Validation of the integrated TSO-DSO simulation model

As mentioned previously, the purpose of this section is to ensure that the model accurately reflects actual operating conditions and that it meets the requirements for stability, regulation, and management of energy flows within the two networks.

## Implementation of actual scenario and case study

The model validation is based on the use of real chronicles supplied by TSO, incorporating the active and reactive powers of the loads, as well as the active powers and setpoint voltages of the generators. Moreover, actual measurements provided by the DSO in terms of voltage, active power, and reactive power are exploited in the validation process. To assess the integrated TSO/DSO model, the proposed validation strategy focuses on HV/MV interface of the MELLE substation, depicted by the single-line diagram in Fig.7.
<figure><img src="image_8.png" /><figcaption>Fig.7: Single-line diagram of MELLE substation.</figcaption></figure>

The key parameters of the HV/MV transformers and the voltage-regulating generators are summarized in Table I and Table II, respectively.

<table><caption>Table I: Transformers Parameters</caption><thead><tr><td>Transformer</td><td>Ratio [kV/kV]</td><td>S<sub>nom</sub> [MVA]</td><td>Report X/R</td><td>Copper losses [kW]</td></tr></thead><tbody><tr><td>TR1</td><td>90/20</td><td>36</td><td>32</td><td>188</td></tr><tr><td>TR2</td><td>90/20</td><td>36</td><td>29</td><td>205</td></tr><tr><td>TR4</td><td>90/20</td><td>36</td><td>29</td><td>205</td></tr></tbody></table>

The validation strategy of the integrated Transmission-Distribution model consists of comparing the simulation results from the PF numerical model with the actual measurements provided by both network operators, in terms of voltage levels at the HV/MV interface (MELLE substation).

<table><caption>Table II: Voltage-Regulating Generators of the studied scenario</caption><thead><tr><td>Generators</td><td>Voltage set-point (kV)</td><td>Rated voltage (kV)</td><td>Power set-point (MW)</td></tr></thead><tbody><tr><td>Generator 1</td><td>403</td><td>380</td><td>910</td></tr><tr><td>Generator 2</td><td>403</td><td>405</td><td>910</td></tr><tr><td>Generator 3</td><td>403</td><td>405</td><td>910</td></tr><tr><td>Generator 4</td><td>403</td><td>405</td><td>0</td></tr><tr><td>Generator 5</td><td>406.6</td><td>380</td><td>0</td></tr><tr><td>Generator 6</td><td>406.6</td><td>380</td><td>385.8</td></tr><tr><td>Generator 7</td><td>406.6</td><td>380</td><td>0</td></tr><tr><td>Generator 8</td><td>406.6</td><td>380</td><td>0</td></tr><tr><td>Generator 9</td><td>408.3</td><td>380</td><td>1397</td></tr><tr><td>Generator 10</td><td>408.3</td><td>380</td><td>1487</td></tr></tbody></table>

After integrating the time series data provided by the TSO (input data) into the integrated Transmission-Distribution numerical model, load flow calculations have been performed for various operating conditions. First, load flow tests have been conducted on an unconstrained network, and the results will be presented and discussed in the following sections. Then, to evaluate the accuracy limits of the developed model, load flow simulation tests have been performed under constrained operating conditions, such as the loss of an AC line and the shutdown of a three-phase transformer. Note that under constrained operating conditions, satisfactory validation results have been obtained also, but they require further analysis and improvements, which are currently in progress. Hence, only the load flow test results for unconstrained operating conditions will be presented and discussed in the sequel.

## Simulation results and validation

As mentioned above, the validation of the integrated Transmission and Distribution (T&D) model based on load flow calculations is carried out under unconstrained grid conditions. Once the input data based on real chronicles is correctly configured and incorporated into the merged T&D model, a load flow calculation is then executed based on Powerfactory DigSilent software. The simulation results obtained at the MELLE substation are presented in Table III, detailing the steady-state phase-to-phase (Ph-Ph) voltages and corresponding angles for both the HV and MV levels.
<table><caption>**Table III: Load-flow results from the T&D simulation model**</caption><thead><tr><th>Terminal/Subsection (MELLE Substation)</th><th>Ph-Ph Voltage (kV)</th><th>Ph-Ph Voltage (p.u)</th><th>Angle (deg°)</th></tr></thead><tbody><tr><td>Terminal 32</td><td>94</td><td>1.044</td><td>21</td></tr><tr><td>Terminal 31</td><td>94</td><td>1.044</td><td>21</td></tr><tr><td>Terminal 28</td><td>94</td><td>1.044</td><td>21</td></tr><tr><td>Subsection of Feeder (Secondary of TR4)</td><td>20.4</td><td>1.020</td><td>25.7</td></tr><tr><td>Subsection of Feeder (Secondary of TR2)</td><td>20.4</td><td>1.020</td><td>25.5</td></tr><tr><td>Subsection of Feeder (Secondary of TR1)</td><td>20.4</td><td>1.020</td><td>22.4</td></tr></tbody></table>

The reference data (i.e., reference model) based on the TSO's actual measurements from the transmission grid are provided in Table IV, with a time step of 5 minutes.

<table><caption>**Table IV: Reference data based on TSO's measurements**</caption><thead><tr><th>Time (Hour)</th><th>HV Measurement (kV)</th></tr></thead><tbody><tr><td>08:00</td><td>95.38</td></tr><tr><td>08:05</td><td>95.30</td></tr><tr><td>08:10</td><td>95.35</td></tr><tr><td>08:15</td><td>95.38</td></tr><tr><td>08:20</td><td>95.34</td></tr><tr><td>08:25</td><td>95.29</td></tr><tr><td>08:30</td><td>95.34</td></tr><tr><td>08:35</td><td>95.35</td></tr><tr><td>08:40</td><td>95.49</td></tr><tr><td>08:45</td><td>95.42</td></tr><tr><td>08:50</td><td>95.46</td></tr><tr><td>08:55</td><td>95.45</td></tr><tr><td>09:00</td><td>95.38</td></tr><tr><td>Voltage average value</td><td>95.38</td></tr></tbody></table>

The reference data (i.e., reference model) based on the DSO's actual measurements from the distribution grid are given in Table V, with a time step of 10 minutes.

<table><caption>**Table V: Reference data based on DSO's measurements**</caption><thead><tr><th>Time (H)</th><th>Primary HV (kV)</th><th>Secondary MV of TR1 (kV)</th><th>Secondary MV of TR2 (kV)</th><th>Secondary MV of TR4 (kV)</th></tr></thead><tbody><tr><td>08:00</td><td>92.98</td><td>20.47</td><td>20.47</td><td>20.35</td></tr><tr><td>08:10</td><td>92.98</td><td>20.41</td><td>20.41</td><td>20.66</td></tr><tr><td>08:20</td><td>92.98</td><td>20.41</td><td>20.47</td><td>20.66</td></tr><tr><td>08:30</td><td>92.98</td><td>20.41</td><td>20.47</td><td>20.66</td></tr><tr><td>08:40</td><td>92.98</td><td>20.41</td><td>20.47</td><td>20.66</td></tr><tr><td>08:50</td><td>93.26</td><td>20.41</td><td>20.47</td><td>20.66</td></tr><tr><td>09:00</td><td>92.98</td><td>20.41</td><td>20.54</td><td>20.66</td></tr></tbody></table>

The average values of HV and MV from the DSO's measurements are depicted in Table VI.

<table><caption>**Table VI: Average values of reference data based on DSO's measurements.**</caption><tr><td>Primary Average HV (kV – p.u)</td><td>93.02</td><td>1.033</td></tr><tr><td>Secondary Average MV of TR 1 (kV – p.u)</td><td>20.418</td><td>1.021</td></tr><tr><td>Secondary Average MV of TR 2 (kV – p.u)</td><td>20.471</td><td>1.023</td></tr><tr><td>Secondary Average MV of TR 4 (kV – p.u)</td><td>20.615</td><td>1.030</td></tr></table>

The load flow simulation results (Table III) are compared with the reference data (Tables IV–VI) for the unconstrained operation of both transmission and distribution networks. Then, as shown, the simulation results are highly consistent with the measurements collected from both networks.

The error between the simulation results and the DSO's actual measurements is approximately 0.01084 p.u. (1.053%), while the difference with the TSO's actual measurements amounts to 0.0157 p.u. (1.447%). Given the minimal discrepancies, the developed simulation model accurately reproduces the physical behavior of the integrated transmission and distribution grids, confirming both the validation strategy and the effectiveness of the joint TSO/DSO simulation model.

As mentioned above, several simulation studies have been conducted also under constrained network conditions, including overvoltage, voltage drops, and network congestion. The obtained simulation results closely match with measured or estimated values, further validating the robustness of the integrated T&D detailed simulation model.

## Conclusion

In this paper, a comprehensive methodology for developing a load-flow simulation model has been proposed, based on a collaborative modeling effort between the TSO and DSO, using actual data from both transmission and distribution networks. The integrated model has been implemented in the *PowerFactory DIgSILENT* environment and, by leveraging standardized data exchange formats such as the Common Information Model (CIM), provides
accurate and detailed simulations of electrical
network performance under various operating
conditions.

Validation tests under normal and stressed grid conditions highlight the crucial role of joint modeling in identifying and mitigating grid constraints. This approach improves the accuracy of load-flow analyses and strengthens grid management by precisely assessing transmission and distribution interactions at the HV/MV interface.

By integrating the operational dynamics of both
TSO and DSO networks into a unified simulation
framework, this model fosters greater
coordination between the two grid operators.

As a future perspective, the aim is to leverage the
integrated T&D model developed in this work to
provide valuable insights into the optimal
coordination between the TSO and DSO. This
will help identify and address potential
constraints in both transmission and distribution
networks. This approach will be particularly
useful in tackling challenges associated with
modern power systems, including the integration
of renewable energy sources, demand-side
management, and the increasing complexity of
grid operations.

References

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