Speed measurement / alarm
A generator is necessary in a coal-fired power plant to produce electricity.
A turbine-driven electrical generator contains a stationary stator and spinning rotor. In operation, it generates up to 21,000 amperes at 24,000 volts of three-phase alternating current (approx. 500 MW).
The rotor spins in a sealed chamber cooled with hydrogen gas. The system requires special handling during startup, with air in the chamber first displaced by carbon dioxide before filling with hydrogen. This ensures that a highly explosive hydrogen-oxygen environment is not created.
In this application, monitoring the speed of the rotor using a two-wire NAMUR sensor is very important to avoid over-speed. A solution for rotor over-speed protection is to use the PR 5725D programmable frequency indicator adding local readout and 2 relays for over-speed alarms and sensor error detection. The 4...20 mA output signal from the PR 5725 is connected directly to the control PLC.
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