What is Turbine Differential Expansion?
2 Answers
Turbine differential expansion: Conventionally, it is stipulated that when the rotor expansion is greater than the cylinder expansion, the differential expansion value is positive; when the cylinder expansion is greater than the rotor expansion, the differential expansion value is negative. According to cylinder classification, it can be further divided into high differential, medium differential, low I differential, and low II differential. The differential expansion value is a crucial operational parameter. If the differential expansion exceeds the limit, the thermal protection will act to trip the main unit, preventing collisions between moving and stationary parts and avoiding equipment damage. The reasons related to turbine differential expansion are as follows: 1. Causes of excessive positive differential expansion: This may be due to insufficient warm-up time during startup, rapid speed increase or load increase, or the heating steam temperature of the cylinder interlayer and flange heating device being too low or the flow rate being too low, resulting in weak heating effect. It could also be due to poor sliding performance or sticking of the sliding pin system or bearing base plate. Another possible cause is excessive shaft seal temperature or high shaft seal air supply, leading to excessive elongation of the shaft neck. 2. Causes of excessive negative differential expansion: This may be due to rapid load decrease, unit load shedding, sharp drop in main steam temperature, or inlet steam temperature during startup being lower than the metal temperature, causing water impact. It could also be due to excessive heating of the cylinder interlayer and flange heating device. Another possible cause is the shaft seal steam temperature being too low.
The turbine differential expansion, this thing is quite important, especially when we are maintaining power plant equipment. Simply put, during the startup or shutdown of a steam turbine, temperature changes cause the rotor (the rotating part) and the casing (the outer shell) to expand at different rates. This difference in expansion is called differential expansion. The rotor heats up faster and expands more quickly, while the casing is slower and expands less. If the difference becomes too large, it can cause friction, vibration, or even damage the entire machine. In our work, we use expansion detectors to monitor it in real-time, such as carefully controlling the heating rate during hot or cold starts to avoid issues. In fact, this is often related to abnormal noises in older machines. I've seen many cases where improper maintenance or faulty monitors led to shutdowns. Preventive measures include regular cleaning of probes and calibration of instruments, as downtime for core equipment like steam turbines can result in significant losses.
