What is condenser vacuum and why is it important?

• A. A negative pressure in the condenser; higher vacuum reduces backpressure but has little effect on efficiency.
• B. A positive pressure in the condenser; higher pressure improves efficiency.
• C. A pressure near atmospheric; the vacuum is not important.
• D. A negative pressure in the condenser; higher vacuum improves turbine efficiency by reducing backpressure.

Answer: (D)

Condenser vacuum means the condenser operates at sub-atmospheric pressure, created by the vacuum system. This low pressure pulls the exhaust steam from the turbine into the condenser and allows it to condense at a lower temperature. Keeping the condenser at a strong vacuum reduces the backpressure on the turbine exhaust, so the steam can expand further and do more useful work before condensing. In other words, more of the steam’s energy goes into producing turbine power rather than being wasted as backpressure. That higher turbine efficiency translates into better overall cycle efficiency. It’s important to balance vacuum level with practical limits, since deeper vacuum requires more pumping power and tight seals to prevent air ingress, which would spoil condensation.