don't understand your question.

If you are asking about performing an actual over speed where the generator is NOT tied to the grid and the speed is increased above rated, then generator excitation is normally removed prior to accelerating above rated speed

Oh. By the way. If you break your turbine-generator by doing tests you do not understand nor are qualified to run by training and experience, your boss will not be happy when he fires you for destroying the power plant.

Well said racookpe1978!

I've seen plenty of thoroughly destroyed machinery, but never for such an obviously silly reason as this one!

Mechanical over-speed governors are normally tested on a test stand rather than on the turbine.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

I think the original post was double-posted on the electrical engineering page and then mangled when he transferred it to the turbine page. Please do not double-post.
Here is the original message.

"Hi, I am an automation expert and we have a turbine siemens the question is when we want to do a test turbine overspeed it triggers a default of over-frequency programmed in siprotec 4 .the tie circuit breaker is open and the voltage regulator remains in mode on"

excellent comment Racookpe1978.
I would suggest googling "Eskom Duvha Unit No.4 9 February 2011" to view some photos of an overspeed test gone bad.
intersting finding, when I googled to verify the first hits would find the slide show, there was a recent news report where another accident occured at that station

does he want to exercise test the overspeed trip valve with machine running?
if this is the case, this is a special feature only included if asked for at design stage...

"If you want to acquire a knowledge or skill, read a book and practice the skill".

With respect to CCfowler's comment (and the comment by rotw) I would disagree.

A lot of insurance companies require testing of overspeed once a year as part of regular maintenance. Many OEM require it after major overhauls with turbine/compressor blade replacement. Normally the mechanical overspeed is done installed on the turbine, though can be done in the spin pit, if during an outage it can be removed and tested. I have never worked on a turbine, gas or steam that did not have a built in test program to conduct a "live" overspeed test. I personally have live tested dozens of electrical and mechanical overspeed tests at 3300 and 3960RPM

Many steam turbines are designed to run to overspeed for testing purposes. This is generally done uncoupled from the driven machine. The testing frequency depends on the particular design and any on-line testing such as exercise of the trip and throttle valve. I have tested many turbines to overspeed at speeds up to 12000 rpm. You must consult with the equipment manufacturer.

Johnny Pellin

First I thank Mr. byrdj and csk62 for their agreement and if there are no gents as you can be no improvement in the industrial area

the problem is that in siemens paper are no requirements for the overspeed test must be eliminated in AVR (voltage regulator) with the speed will increase to 7070 t / m and the SIPROTEC has a threshold of 52.5 H (a little meadows 6700t / m) speed so it will trip the turbine speed before reaching the progamme

Most times the instruction books and procedures provided by the OEM are not written to be performed verbatum, but should be used as guide lines by a person familiar with the entire plant (or at least the systems interrelated for a particulair event)

The instructions provided by the turbine OEM may not consider what type of device is being driven and thus how to include the driven must be decided upon by the plant. several have posted (and I have been involved with) that mechanical drive turbine instruction for the overspeed do not state the driven must be physically uncoupled. I have been questioned by several plants about requesting to seperate a feedpump from the turbine because neither supplied manual actually states to do so, My reply is that I am there for the turbine and have nothing to do with pump and refuse to allow it to "ride along" during over speed. and luckily the generations of designers before me included a method to seperate the two!

I must agree with racookpe1978 in that if must ask, you should not make any recomendations about how to perform these test, but seek the recomendations of someone knowledgable. the recomendation I have provided is what I have experance on a particular designed configuration. I hope you looked at the slideshare of the over speed test gone wrong.

BTW what is T/M? I'll assume revolutions per minute. given the couple values provided, am I correct in that your system frequency is 50 hertz with the turbines rated speed about 6425 rpms?

The sync speed is 6436revolution per minute (50Hz)

The sync speed is 6436 (50Hz)