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Content for  TR 22.867  Word version:  18.2.0

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5.20  Use case of power distribution grid state estimation serviceWord‑p. 75

5.20.1  DescriptionWord‑p. 75

The State Estimation (SE) service [52] supports the monitoring of the power grid. The goal of SE is to create insight into the operational state of the power network at any given instant in time, by processing the measurement information collected by the instrumentation deployed in the field. The SE service provides monitoring data which can be used by grid operators to assess the performance of their network and to detect possible anomalies in the grid operation. In addition, it can serve as an input for more complex management functions implemented by the Distribution System Operators (DSOs) to more reliably and efficiently operate. An example of a service which could use the SE monitoring data is the power control service [52]. Other services which could use the SE monitoring data include, but are not limited to, network topology reconfiguration, Volt-VAR control and, in the future, demand side management and demand response services.
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5.20.2  Pre-conditionsWord‑p. 75

The measurement devices are deployed in the field and capable to send the data to the DSO control centre (or whatever data concentrator).

5.20.3  Service flowsWord‑p. 75

5.20.3.1  IntroductionWord‑p. 75

The SE service relies as input on the information of the electric grid topology, the electric line parameters and the real-time measurements provided by the instrumentation deployed on the field. Given this set of inputs, the SE service processes the received data to provide the most likely operating state of the network at the considered instant of time (the same time at which the measurements are collected). Finally, the results of the SE service are sent to the control centre (or whatever data concentrator) to give situational awareness to the DSO and, if needed, are made available for other control functions requiring this information. SE results are usually also stored in a database for possible a posteriori analysis.
For its operation, the SE service thus needs as input some important information of the grid characteristics, the deployed measurement infrastructure, as well as the real-time measurement data collected from the measurement units in the field. In addition, if the electric grid is reconfigurable (i.e. topology changes can be applied), the status of the switches and breakers should be also provided in input to the SE tool to make sure that the service is always considering the correct topology of the grid.
Beyond the grid data, which can be determined by the DSOs with a different degree of accuracy as the information of low voltage grids may be incomplete and inaccurate, the key point for enabling the SE service is the availability of measurement devices with real-time communication capabilities. Different from the transmission system, where a large coverage of devices is often available, the instrumentation penetration at the distribution level is usually poor with only few devices installed in specific points, like primary substations (high/medium voltage substations). As a matter of fact, the main power system requirement to enable the grid monitoring via SE is thus the deployment of devices providing the needed measurement data. Due to the large size of the distribution grids and obvious economic constraints, guaranteeing a full observability of the grid is mostly impractical and hardly achievable. The SE solution duly takes into account this aspect and aims at enabling the SE service using only few low-cost measurement devices deployed at strategic points of the grid (chosen by means of ad hoc meter placement strategies). Moreover, the conceived SE solutions are designed to maximize the accuracy performance even in presence of few measurement units in the field. However, it is worth noting that the accuracy of the estimation results strongly depends on the number of available measurements.
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5.20.3.2  Power system requirements of SE serviceWord‑p. 76

Needed components in the field:
sensors and meters.
Information about the electrical grid:
topology of the network; grid parameters (line impedance, transformer data, etc.); nominal power of connected loads and generators; location of the meters.
Type of measurements:
voltage (both magnitude and phase angle), current (both magnitude and phase angle), active and reactive power are the measurements that can be used for SE purposes (it is not mandatory to have all the types of measurements reported).
Measurements number:
the higher the number, the better the results.
Measurement accuracy:
the higher the better; information on the uncertainty characteristics of both sensors and measurement units has to be known.
Measurement synchronization:
highly recommended.
Additional data needed from the field:
notification of switching events leading to a change in the network topology.
Real-time communication capability:
yes, required.
Bi-directional communication:
not required; the communication flow is mono-directional from the meters to the control centre.
Use of edge cloud:
The concept of SE is based on a distributed architecture where both low voltage and medium voltage grids are divided in multiple, smaller areas. This is a solution to reduce the computational cost and execution time of the SE service, as the SE analyses for all areas may operate in parallel. One benefit of this solution is guaranteed scalability of the proposed architecture for SE. Given this framework, it is highly feasible that each local SE runs on a dedicated edge cloud.
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5.20.4  Post-conditionsWord‑p. 76

The operating state of the network provided to DSO at a given instant of time.

5.20.5  Existing feature partly or fully covering use case functionalityWord‑p. 76

Table 5.20.5-1 shows communications requirements for the State Estimation service.
Characteristic parameter Influence quantity
Communication service availability: target value Communication service reliability: mean time between failures End-to-end latency: maximum (notes 1, 2) Service bit rate: user experienced data rate (note 2) Message size [byte] (note 2) Transfer interval: target value (note 2) Survival time (note 2) UE speed # of UEs Service area
99.99%100 ms to few seconds~ 5 kbit/s< 10001 s Stationary< 30 per km²several km² up to 100,000 km²
NOTE 1:
Unless otherwise specified, all communication includes 1 wireless link (UE to network node) rather than two wireless links (UE to UE).
NOTE 2:
It applies to UL.
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5.20.6  Potential New Requirements needed to support the use caseWord‑p. 77

None.

5.21  Use case of power distribution grid power control serviceWord‑p. 77

5.21.1  DescriptionWord‑p. 77

The Power Control (PC) service [52] optimises the management of the distribution grid power flows (at both medium voltage and low voltage level) for preventing possible contingencies, such as violation of the voltage limits, and overloading of grid components. The service also fosters a more efficient and reliable system operation. This is obtained through the smart control of the active and reactive power injected (or consumed) by converter-based components connected to the grid, such as Distributed Generation (e.g. photovoltaic plants, wind turbines) and energy storage units. For the management of the Distributed Generation based on renewable energy sources, an additional objective is to maximize the use of green energy while respecting the operational constraints of the electric grid, thus minimizing as much as possible the power curtailment of renewable generation. The use of smart power control service in the power grid with high penetration of renewable energy sources is expected to significantly improve the efficient operation of the grid, the power quality, and the grid reliability. This service can be defined as an "active service", since it actively acts on some of the power system components to modify their operation.
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5.21.2  Pre-conditionsWord‑p. 77

The State Estimation service (see clause 5.20 "Use case of power distribution grid state estimation service" above) is deployed and active in the power distribution grid. Output of the State Estimation service can be used by the PC service.

5.21.3  Service flowsWord‑p. 77

5.21.3.1  IntroductionWord‑p. 77

The developed PC service is based on the operating conditions of the grid and processes this information to determine the optimal setting of active and reactive power generation for the distributed generation or, when available, of storage units. Different goals can be pursued to enhance the operation of the distribution grid, such as: the reduction of power losses during the operation with normal conditions; the minimization of voltage unbalance in case of high differences in the status of the three phases of the system; the minimization of possible active power generation curtailments during circumstances with over-voltage issues in the grid. The output of the PC service is a list of set points of active and reactive power (PQ set points) for the converter-based components connected to the grid. Consequently, the service needs bi-directional communication with the field to ensure proper delivery of the generated control commands.
The design of the PC service is coupled with the State Estimation service. According to this idea, the PC service takes as input the results of the State Estimation service, namely the voltage profile at the different buses and the information about the branch power flows and the power consumption (or injection) at the nodes. Together with this information, the service needs as input also the model of the electric grid, expressed in terms of network topology and line characteristics. More specifically, the list of inputs needed to enable the PC service includes the following data.
Static grid data:
  • Electric grid topology (information about the nodes and the connection among the different nodes in the grid).
  • Electric component parameters (e.g. impedances of the lines, impedances of transformers, etc.).
Real-time data:
  • Estimation of the bus voltages, power flows in the branches, power consumption or injection at the nodes (as provided by the State Estimation service).
  • Real-time notification of a change in a switch or breaker status.
The output of the PC service is the pair of active and reactive power set points for each converter-based component in the grid. The output of the power control service has to be sent to the converters in the field through communication technologies available in the field for control commands. Results can also be sent to the control room of the Distribution System Operator (DSO) for monitoring and can be stored in the database for possible a posteriori analysis.
Since the PC service relies on the results of the State Estimation service, some of the power system requirements for this service are in common with the State Estimation service. First, measurement devices with real-time communication capabilities are needed to guarantee meaningful monitoring of the electric grid. The accuracy of the estimated results provided by the State Estimation service can also affect the performance of the PC service. Similar to the case of the State Estimation service, a critical challenge for the application of PC at distribution level is the large size of the distribution grids. This calls for the design of distributed approaches where PC services act on small areas, possibly sharing some data with an upper level controller to ensure the coordination of the power control strategy in the whole grid.
Due to the active nature of this service, a bi-directional communication is needed with the field. Data are collected from the grid to enable the State Estimation service, while the output of the PC service is sent to the converter-based components for the control of their power generation (or consumption). This also implies the need to have converters able to communicate remotely, both for sending measurement data (if available) and for receiving the actuation commands. While converters available today do not always guarantee this behaviour, this requirement can be considered as realistic in future scenarios where the availability of communication capabilities is essential to enable the Smart Grid.
The PC service runs continuously and synchronously with the State Estimation service. In particular, a new iteration of the service is triggered by the collection of a new set of estimation results provide by the State Estimation service. Similar to the case of State Estimation service, there are not strict requirements on the reporting rate for the PC service. However, due to the highly intermittent behaviour of renewable energy sources and the possibility of sudden changes in the operating conditions of the distribution grid, it is recommended to run the PC service with at intervals shorter than one minute and possibly close to a few seconds.
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5.21.3.2  Power system requirements of PC serviceWord‑p. 78

Needed components in the field:
inverters (controllable from remote), sensors and meters.
Information about the electrical grid:
topology of the network; grid parameters (line impedance, transformer data, etc.); nominal power of connected loads and generators; location of the meters.
Type of measurements:
the State Estimation service results are used in input to the PC service, so the same requirements as to the State Estimation service apply for this point.
Measurement number:
the State Estimation service results are used in input to the PC service, so the same requirements as to the State Estimation service apply for this point.
Data volume:
limited. In typical operations, one set of setpoints (i.e., active and reactive power, P and Q) is transmitted per minute with volt-reactive volt ampere curve; as an alternative, dynamic voltage control is recommended in case of disturbances. In such situations, the solution will transmit approximately 1 set of setpoints per second. P and Q are floating point numbers. The communication should be scalable, i.e., supporting changing grid topology with an increasing number of actors in the electrical grid.
Measurement accuracy:
the State Estimation service results are used in input to the PC service, so the same requirements as to the State Estimation service apply for this point.
Measurement synchronization:
the State Estimation service results are used in input to the PC service, so the same requirements as to the State Estimation service apply for this point.
Additional data needed from the field:
notification of switching events leading to a change in the network topology.
Real-time communication capability:
yes, required
Bi-directional communication:
yes required; needed to collect measurement and switch notifications in one direction (uplink) and to apply the control signals to the inverter in the other direction (downlink).
Communication reliability and security:
very high. PC service uses only a limited amount of command messages per actor, typically one actor for each switch, transformer, or major power generation unit. Since there will be only a limited set of such actors, the reliability of the data communication becomes particularly important, because losing just a single actor would impact the impact of the PC service. Likewise, it is essential that the data are transmitted in a secure way ensuring full data integrity because of automatic modification of grid edge settings; and in this context, higher security than for monitoring services expected.
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5.21.4  Post-conditionsWord‑p. 79

The management of the distribution grid power flows is optimised in terms of preventing possible contingencies and overloading of grid components. The efficient operation of the power grid, the power quality and the grid reliability are significantly improved.

5.21.5  Existing feature partly or fully covering use case functionalityWord‑p. 79

None.

5.21.6  Potential New Requirements needed to support the use caseWord‑p. 80

Characteristic parameter (KPI) Influence quantity
Communication service availability Communication service reliability: mean time between failures Max Allowed End-to-end latency (notes 1, 2) Service bit rate: user-experienced data rate Message size [byte] (note 2) Survival time UE speed # of UEs Service area
99.99 %< 30 msUL: < 100 Kbit/s< 1000Stationary< 300 per km²several km² up to 100,000 km²
NOTE 1:
Unless otherwise specified, all communication includes 1 wireless link (UE to network node or network node to UE) rather than two wireless links (UE to UE).
NOTE 2:
It applies to both UL and DL unless stated otherwise.
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