Notes:
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This Use Case handles the coordination mechanism between TSO and DSO regarding the voltage control and reactive power management within the DSO and TSO networks based on: <br/>· The reactive power flexibility assessment in the DSO and TSO networks.<br/>· The coordination between the DSO and TSO regarding the constraints management for the reactive power and voltage control.<br/>· Optimal control of voltage and reactive power sources in power systems with presence of DER.<br/>· The exact required information and operational requirement that are exchanged between the stockholders in timely manner in order to manage optimally the reactive power and voltage control at different parts of the grid.<br/><br/>The energy resources in the DSO can contribute to optimising the reactive power in the TSO network, which requires to represent the different SGUs in the DSO network within the operational planning strategy. <br/><br/>On the other side, the TSO can guaranty some voltage setpoints demanded by the DSO to avoid or decrease the voltage constraints in the network managed by the DSO.<br/><br/>The collaboration can takes the following modes/scenarios to support the voltage level on the distribution network by TSO and on the transmission network by DSO: <br/><br/>- Scenario 1: The Voltage control assets at the DSO network could be controlled by the DSO upon inquire by the TSOs (real time and operational planning). This service can be voluntary or mandatory depending of the rules in each country. For mandatory participation of DSO, a remuneration scheme should be considered.<br/><br/>- Scenario 2: The DSO could inquire the TSO to set voltage levels at the interface areas (real time and operational planning) <br/><br/>The output reactive power from the Significant Grid Users (SGU) could be used to contribute in supporting the TSOs’ voltage as in the following process: <br/>· The DSOs can contribute in supporting the voltage in the TSOs’ network by managing the flow of the reactive power in the distribution network.<br/>· The TSO performs the reactive power flow calculations and issue the voltage set-point at the interface point. <br/>· The DSOs estimate the reactive power capabilities of SGU, and perform the power flow calculations to reach the agreed and issued set-points of reactive power flow at TSO-DSO interface.<br/>· Both of the TSO and DSO agree on a certain level of reactive power flow at the interface point in which doesn’t violates the distribution voltage and loading limits.<br/>· The online tap-changer transformers and the voltage in the primary of power transformer could be combined to support the voltage in the distribution network<br/><br/><b>Scenario 1 description:</b><br/>1. Agreement in the DSO participation in voltage control:<br/>If the participation of DSO in the voltage regulation was mandatory, the TSO and DSO should agree in the amount of contribution for each period of time and for each primary substation. This agreement should be inquired by the TSO and the DSO should perform an analysis in operational planning to inform the TSO concerning the maximum participation (reactive power maximum and minimum limits). After the agreement, the participation of the DSO in the service is mandatory.<br/><br/>2. TSO notifies the DSO concerning a reactive power setpoint:<br/>The TSO sends to the DSO the required reactive power value and its duration at each primary substation at different timeframes (several hours or days ahead). The reactive power information can be done in three formats: value of Q; value of tg phi; P/Q operation region. <br/><br/>3. Activation of DSO flexibilities to meet the setpoint not violating quality of supply standards in distribution network<br/><br/>When the moment of activation arrives, the DSO should try to achieve the setpoint requested by the TSO using its the existing reactive power flexibility at the distribution network: <br/>· The reactive power that can absorb or supply the SGU connected in MV networks<br/>· The reactive power that can injected/absorbed by the capacitors banks and by the reactors. The DSO can also adjust the OLTC of the transformers to avoid constraints in the distribution network<br/>· Even if the DSO can’t achieve the setpoint, they will try their best to be as close as possible from the target.<br/><br/><b>Scenario 2 description:</b><br/>1. The DSO send to the TSO the required voltage level and set points for several interface areas to releases the voltage constraints at several parts of the DSO network.<br/>In case of constraints in transmission network, the TSO will do its best to reach the closest voltage level from the targeted level.<br/><br/>2. The TSO activate its assets, including the reactive power flexibilities, for voltage control after the agreeing on the DSO inquire in which doesn’t violates the transmission voltage and loading limits. <br/>
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