Practical Implementation of Adaptive Protection and Control in a Medium Voltage Microgrid

Authors: D. Ishchenko, ABB, USA, A. Oudalov, ABB, Switzerland, H. Laaksonen, A. Kostiainen and S. Sundfors, ABB, Finland, S. Vahakuopus and H.-M. Pekkala, Elenia Oy, Finland

IEC 61850 suite of utility automation protocols combined with OPC client/server technology and application logic engine executed by the grid automation controller installed at the point of common coupling, provides a flexible and powerful platform for the development of advanced adaptive (microgrid state dependent) protection and control system. 

Microgrid control system extracts the information received from the communications infrastructure, performs the real-time analysis and if necessary executes the control action by sending a control command back to the automation system. Both Ethernet and wireless cellular communications are used. Commands to remotely control the diesel generator as well as measurement data reported to the microgrid controller by the diesel generator and remote circuit breaker status have been implemented as IEC 61850 MMS reports.  The controller includes the following key functions that are described in the article:

  • Protection settings adaptation engine based on the network topology, which is implemented with IEC 61850 Setting Group Control Block feature to switch between pre-configured settings
  • Intentional islanding initiated by the distribution system operator, and unintentional islanding initiated automatically due to the loss of voltage on the source side of the recloser for a pre-determined time period
  • Network control for simplified load balancing in the island, which includes several system-level measures to ensure that the transition to the islanded mode is feasible
  • Automated or manual reconnection to the main grid with remote diesel re-synchronization, including modification of the diesel control modes as appropriate and consecutive disconnection of the diesel generator
  • Black start in case automatic resynchronization fails with automated shutdown of the DG units and reconnection to the grid

 

The final application always needs to be designed in full compliance with local safety regulations and standards as related to, for example, touch voltages in islanded operation mode.

Hailuoto Electrical System
Hailuoto Pilot System: The general intention in the Hailuoto pilot was to demonstrate a generic concept for islanded microgrid operation in a medium voltage (MV) distribution system. Hailuoto is the largest island of Finland and the Northern Gulf of Bothnia in the Baltic Sea with 1000 regular inhabitants and 600 holiday houses. The system configuration is shown in Figure 1, where the islanding area includes a portion of 20-kV overhead distribution feeder with recloser, two controllable disconnect switches, and two distributed generators (DGs): 0.5 MW wind turbine (directly connected induction generator) and 1.4 MW diesel generator (directly connected synchronous generator), which support islanding operation. Today, normally the diesel generator is not running. It is only used when intentional island operation is required, for example, due to fault in the submarine cable (Figure 1). The centralized grid automation controller is installed at the recloser station. It can execute the control scenarios through wireless radio communications with the DGs and disconnect switch controls.

The diesel generator in the planned island area has two possible control modes. In the first mode, if the diesel generator is for example running in parallel with the utility grid before planned outage (e.g. due to maintanence) and transition to island operation, the automatic voltage regulator (AVR) is in reactive power control mode, and the speed controller is in active power control mode, i.e. PQ-control. After transition to islanded mode, the AVR is operating in voltage control mode and the speed controller in speed (frequency) control mode. Switching command for diesel generator to change control mode from first (PQ-control) to islanded (voltage and speed control) is issued by the centralized grid automation controller. In case of low load (near minimum, possible minimum and maximum loads - Figure 1) it may be necessary to trip the wind turbine before transition to islanded operation to avoid a pick-up of under-power protection of the diesel generator and blackout of the whole island. The tripping decision is dependent on current load in the corresponding island area which can be calculated by the MV grid automation controller if the power production of diesel generator and wind turbine as well as the power flow in connection point (Viinikantie recloser) are both known.

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