12591 Islanded Operation

Brief mention was made in Chapter 10 of this type of DG system, which was referred to as load transfer. Operation typically begins with starting the DG prime mover and then transferring load to it. The typical protective/permissive relaying functions found in the islanded system will include Dev. 27 on the grid source and Devs. 27 and 81 on the DG source. Because these types of systems are typically installed for emergency and standby service, Dev. 27 on the grid source terminals of the transfer switch will initiate starting of the DG when the grid voltage falls below a preset value for a preset time. Because fault current clearing takes more than six cycles and the grid distribution circuit may have a recloser, it is undesirable to start the DG unless the outage is extended. Therefore, there will be a time delay on the operation of Dev. 27 to start the DG. This delay is approximately one to six seconds long. Devs. 27

and 81 are used to prevent load transfer to the DG until it has achieved acceptable voltage and frequency levels. In the protective role, these two devices will initiate load transfer to the grid (when it is acceptable) if the DG fails. Load transfer in this mode is open transition transfer.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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