Principles of torque limiters
The clutch slips when subjected to a load that surpasses its set torque transmission capacity, so that the torque in excess of the set capacity is never transmitted to the loaded side. This slipping behavior is used as a torque limiter function.
Characteristics of commercial power outage countermeasures using torque limiters
The diagram below is a process flow chart for a GT (gas turbine) generator with an integral torque limiter.
The main characteristics of commercial power outage countermeasures using torque limiters are stated below.
- When a power outage (momentary voltage dip) causes excessive torque, the torque limiter slips momentarily to protect the GT from transmission of excessive torque. While that slipping happens, heat is generated in the torque limiter clutch. The time that elapses between detection of an incident and the generator breaker opening is generally around 200ms in a normal guard system that combines an undervoltage relay and a general-purpose vacuum breaker (3cycleVCB). In that time, slipping continues and heat is generated in the torque limiter. Designing the torque limiter for adequate resistance to heat generation enables us to configure systems with low-cost general-purpose vacuum breakers (3cycleVCB) as the generator breakers.
- If a shear pin system is used, the connection between the GT and the generator is broken when the pins break, and no torque is transmitted, but with a torque limiter, slipping occurs and torque transmission continues uninterrupted. Therefore, when an incident is detected, the generator breaker opens, and then the generator side is automatically recoupled once the excess torque stops. The GT continues to run unaffected, and is either unladen or supplying power to loads in the building within the rated generator capacity.
Overview of a GT generation system with integral torque limiter