Steam Turbine Overspeed Trip Device with Mechanical Overspeed Protection 3300 r/min Trip Speed and Interlock Protection
The overspeed trip device is a mechanical overspeed-protection apparatus for steam turbines, serving as a vital actuator terminal for DEH (Digital Electro-Hydraulic Control System) and ETS (Emergency Trip System). Generally mounted at the front end of the turbine rotor or inside the bearing box, it is directly interlocked with the oil-hydraulic control system of main steam valves and control valves.
- Overspeed protection: Automatically triggers unit trip when rotating speed exceeds 10%-12% above rated speed (e.g. 3300 r/min)
- Interlock protection: Receives signals of vibration, axial displacement, low oil pressure and other parameters to realize comprehensive emergency shutdown
- Manual shutdown: Operators can perform emergency trip via handle or push-button
Two widely-used types of overspeed trip devices are listed below:
Components: Trip weight, spring, adjusting nut, housing, striker pin, etc.
Working Principle:
- During normal operation, spring force holds the trip weight inside the rotor
- As rotating speed rises, centrifugal force increases
- Once centrifugal force exceeds spring preload, the trip weight flies out, strikes the trip lever, actuates the trip oil circuit, closes main steam valves and shuts down the unit
Advantages: Simple construction, reliable performance and power-independent. It acts as the final mechanical protection barrier for the turbine.
It follows similar operating principle as weight-type version, but adopts an annular mass block sliding axially for triggering action. Mostly applied in large-capacity units with higher sensitivity and smoother actuation.
| Component | Function | Precautions |
|---|---|---|
| Trip weight / Trip ring | Senses centrifugal force to initiate tripping action | Smooth surface, free from jamming |
| Spring | Provides preload and sets tripping speed | Periodic spring-force test to prevent fatigue failure |
| Adjusting nut | Sets actuation speed | No arbitrary adjustment; calibration is mandatory |
| Striker pin & lever | Transmits triggering signal | Check flexible inter-linkage movement |
| Overspeed trip slide valve | Controls on-off of safety oil pressure | High sealing requirement; oil leakage prevention |
- Observe status of overspeed-trip indicator lamp
- Perform reset operation before unit startup
- Forbid masking or short-circuiting trip signals
- Overspeed test: Mandatory for newly-commissioned units or after major overhaul, to verify actual tripping speed
- Oil injection test: Available on certain units under running condition, used for checking jamming risk of trip mechanism
- Manual trip test: Conduct at least once per month to confirm emergency-shutdown function
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