How often do you test your overspeed trips? mechanical trip bolt and electrical speed pickups? We are testing it every three years or after a major overhaul (tripping at 110% speed) and would like a concensus on each users testing parameters. thanks

We test out ST trips every couple of months. We have 7mw ST is part of a cogen pant so shutdown to waterwash the GT and we perform some kind of trip on The ST if either a mech. overspeed,local ST trip,low L/O trip. keeps us refreshed and make sure the trips work.

Three years time for testing a turbine overspeed protection is too much. It must be checked atleast twice a year.
While testing, we actually set overspeed trip setting to 104% maximum(actual trip setpoint is 110%) to make sure that turbine is not subjected to unnecessarily high vibration & I think that its enough to determine the integrity of overspeed tripping.
While testing, we take a close look of turbine vibration on all bearings.

Three years time for testing a turbine overspeed protection is too much. It must be checked atleast twice a year.
While testing, we actually set overspeed trip setting to 104% maximum(actual trip setpoint is 110%) to make sure that turbine is not subjected to unnecessarily high vibration & I think that its enough to determine the integrity of overspeed tripping.
While testing, we take a close look of turbine vibration on all bearings.

I think 3 years is a long time between OS trip testing. But if that works for you than i guess it would be ok. We test our 120 Mw unit yearly, because we only shut it down yearly for maintenance. We check over speed, and LO trips and reverse power. This has done us well. Possibly if your unit is down more often than every 3 years than you should check the OS trips.
Doug

We test our 750MW turbines yearly- 2 electrical checks, 1 mechanical.

Chrisd,
Do you actually run the unit up to rated 110% speed to test the overspeed? How do you test the electrical check and the mechanical bolt? Is the mechanical bolt set at the same pickup as the electrical check?
thanks

We first run up to OPC, which takes control of the governer valves and shuts the Reheat stop valves at 103%. We then electrically disable this feature and run up to 108% electrical trip setpoint. After that, we'll disable (via logic point force) the electrical trip and run up to 110% for the mechanical overspeed verification. During all this testing, we verify with a reed tach locally as well as indicated on DCS. Vibration monitoring is also crucial. There is a complete approved procedure we follow, it also states that we must be online at min. 10% load for 4 hours prior to testing. These are completed annually, usually post-overhaul.