Zero Speed Detector

DCS Independent Turbine Protection

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   DCS independent protection system - the zero speed detector - increases reliability and safety of the operation of combustion, steam turbines or any other rotating machines. Measured machines speed is compared with the preset threshold. When the speed is out of the preset limit and DCS live signal is not available, an output signal is set to start the turning gear.

   Implemented solution is performed by small PLC with operator panel integrated (Unitronics series M91). Two speed probes (type enabling to detect pulses with frequencies from 0 Hz upwards - i.e. Jacquet DSS EH10) connected to the two high speed counter channels are used to determine machine speed RPM. When one of two channels determine speed less then threshold and DCS fail signal is achieved contact output changes its state. The output can be used as a signal to start turning gear or to perform any other required actions.

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Key features:

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• Local rotation speed indicator;

• Local maximal speed before trip remembering and indication;

• Underspeed detection;

• DCS status detection;

• Event log.

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Advantages:

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1. Easy and compact PLC construction:

• Three high speed counter/frequency measurement inputs and six contact outputs are available in the PLC itself. No additional I/O modules required;

• User interface display and keyboard available directly on the PLC front panel. No additional display and keyboard required;

• Serial communication is available in the PLC itself (RS232/RS485 port, protocol Modbus supported). OPC communication is available. No additional module required;

• A small mounting place is required.

2. With a separate power supply this solution offers DCS independent protection to start the turning gear in case zero speed is reached. This can increase turbine operation safety and extend turbine operating time.

3. DCS fault signal can be detected and processed by PLC’s internal logic or hardware.