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If the steam turbine motive steam pressure becomes lower than the actual pressure, let's say 30 bar operating pressure and dropped to 20 bar, can you please elaborate what is the effect of pressure on the governor — will it trip the compressor on what basis?

Jul-2021

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Anant Chourikar, HCL Technologies Limited, anandashok.chourikar@hcl.com

Steam turbine governors are of typically two types-namely sliding pressure control and other is fixed pressure control. The output of steam turbine is directly proportional to turbine first stage pressure. so maintaining pressure at first stage is very important to get the desired results.

In a sliding pressure control mode, the out varies as per the pressure at the first stage and governor doesn't necessarily correct the drop in pressure whereas in case of fixed pressure control, the governor value position is modified to correct the pressure and maintain it at first stage.

In this situation, when the pressure is dropped to fixed operating level, the valve needs to modify its position to correct or fuel firing in steam generator has to increase to uplift the pressure to the level desired otherwise the output power of steam turbine will continue to drop because of less enthalpy (Pressure, Temperature and Flow) being supplied at first stage. If the turbine speed starts decreasing further to its critical speed then turbine to trip due to chances of high vibration near to critical speed range. Hope this helps. Please write to me in case you need further info on this.

Nov-2021
Muhammad Usman Saeed, PARCO, ing.usmansaeed@gmail.com

Generally for most of Steam Turbine Vendors, they specify minimum, maximum and normal operating conditions of motive steam (Pressure Temperature mostly) for steam turbines. If the steam pressure drops and temperature remains same, steam will remains in superheated region and that will cause only reduction in RPMs of steam turbine. Governor will adjust its opening to tackle reduction in RPM up to certain limits. If steam pressure & temperature both dropped, steam will become saturated and will condense in steam turbine which can damage mainly impeller and other parts of steam turbine. Condensate in turbine cause high axial and radial vibrations. To avoid damage to equipment, Vibration Monitoring System (If Available for your case) generally used for steam turbine and compressor monitor vibrations and will trip turbine if that increase beyond its trip value.

Hope you got your Answer!

Jul-2021