Vacuum Reduced in Turbine Home Load

Leakage around vacuum breaker valve, or another condition is causing the vacuum breaker valve to open?

Low oil pressure?

Your literature should contain a trouble shooting section on vacuum loss. There is more than one thing that can cause it, and possible causes vary among different systems.

Here's a copy and paste of a copy and paste from another site.

5. LOSS OF VACUUM IN MAIN CONDENSER. When the main condenser vacuum starts to drop below normal, which is usually 28-29 inches of vacuum, the watch team starts to take action. Once the condenser has been verified not to be "hot," an investigation for the cause is started. Items checked are: make-up feed tank levels (since a low tank level may allow air to be sucked into the condenser), condenser hotwell level (too high and there is no room for the vacuum, too low and there may be no condensate providing a seal), the loop seal from the air ejector condenser may be lost (allowing air to be sucked into the condenser), there may be an air leak in a fitting under vacuum, the condensate or air ejector condenser temperature may be too hot inhibiting the vacuum, there may be insufficient air ejector motive steam, there may be a problem with gland sealing steam, the main condenser tube sheet may be clogged and the main circ water pump may not be operating properly or not even started.

We really need more information. At full load is the vacuum normal or is it low to begin with. If it is normal at full load, (28" - 29") and the vacuum goes low as you reduce load, at what point does it trip, (25" -26")? If it is tripping at 25 or 26 then you have an air in leakage and the vacuum trip is taking it out. If it trips at a higher number than 25 or 26, it means that your vacuum trip is not set correctly and also you still have an air in leak. We also need to know at what Mega Watt load it is tripping at. Your leak can be in any number of places. 1- Steam seals HP and LP end of the turbine 2- Condenser exhaust flange 3- Condenser dog bone (expansion joint) 4- It cannot be the loop seal on the steam air ejector as you could not pull vacuum 5- pipe flanges on any piping connected to the condenser 6- any pump packing connected to the condenser 7- Condenser tubes (holes in the tubes or leaks at the rolled tube ends) Hope you find your problem. Let us know what you find,

Please have following checks:

1. Is hotwell temp & level maintained while the turbine load is reduced from 20 ~ 6 mw.

2. Is there any change in sealing steam pressure during load shading.

Hopefully you'll find your answer in above checks.

When you are shifting to home load from full load where is the rest of the steam going? Is it getting dumped to the condenser? If so, since it is high enthalpy steam, it may reduce the the vacuum and trip the turbine. Condenser should have sufficient capacity to meet this requirement.

Double-check that no air is getting into the condenser. First.