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Capstone Turbine Corporation • 21211 Nordhoff Street • Chatsworth • CA 91311 • USA Telephone: (818) 734-5300 • Facsimile: (818) 734-5320 • Website:

Technical Reference

Protective Relay Functions for Capstone MicroTurbines


The Capstone MicroTurbineTM generator may be connected in parallel to a utility grid to power local grid connected loads. When installed in this fashion, power generated by the MicroTurbine is supplied to these loads only when the utility grid voltage is present. Utilities commonly require that protective relay devices be installed with generators connected to their grid. The primary purpose of these devices is to ensure that the local generator will not energize utility wires de-energized by the utility. Typically, these protective relay devices are dedicated relays or solid-state power analyzers that provide control signals to disconnecting devices. This document presents information for the protective relay functions incorporated into Capstone MicroTurbines.

Capstone MicroTurbines include intelligent power controllers, which operate as self- commutated, current controlled inverters when connected to a utility grid. The power controller is referred to as a Digital Power Controller (DPC) in the Model C30, or the combination of the Engine Control Module (ECM) and Load Control Module (LCM) in the Model C60/C65 MicroTurbine. To maintain consistency and ease of reference to both the Model C30 and Model C60/C65 MicroTurbines, the DPC (Model C30) or ECM and LCM (Model C60/C65) will be referred to as the “Power Controller” throughout this document.

The MicroTurbine has protective relay functions built into the Power Controller unit. Programmable settings for the protective relay functions are stored in nonvolatile memory within the Power Controller. As a result, any changes remain set even after an interruption in utility power. Detailed information on the Capstone MicroTurbine may be found in the MicroTurbine User’s Manual (400001).

During utility grid voltage interruptions, the MicroTurbine senses the loss of utility voltage and disconnects from the grid and the local loads. When the grid voltage returns to within its specified limits, the MicroTurbine may be programmed to restart and supply power to the connected loads. Figure 1 shows the relationship between the MicroTurbine, local loads and the utility grid.

Figure 1. Capstone MicroTurbine Grid Connect System Configuration

410033 Rev. D (February 2006) Page 1 of 10

This information is proprietary to Capstone Turbine Corporation. Neither this document nor the information contained herein shall be copied, disclosed to others, or used for any purposes other than the specific purpose for which this document was delivered. Capstone reserves the right to change or modify without notice, the design, the equipment specifications, and/or the contents of this document without incurring any obligation either with respect to equipment previously sold or in the process of construction.

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