Having issue with Woodward Governor 505 for 75 MW steam turbine unit. Till 3000 RPM no issue is observed by speed control mode. After sync, unit it not going to minimum set point and valve opening is not increasing. Hence tripping due to reverse power. After repeated tries, just after sync load set point increased to 9 MW after which valves started opening. Issue not clear

 

@turbine engineer,

505s are pretty simple devices, and the instruction manual is relatively clear (except the parts about cascade control...).

Have you gone through the manual to see if there is some external signal (an input to the 505) that might be preventing the 505 from opening the valve after the generator breaker closes? Does the 505 "know" that the generator breaker has closed (in other words, is the generator breaker status input working properly--not just "inside" the 505, but from the contact on the breaker all the way to the 505 terminal board)?

Again, these are fairly simple devices and the manuals aren't very complicated (except the part about cascade controls...) and there aren't that many inputs to the 505. Logically go through the inputs and make sure the entire circuit of each related input works properly. If some work has been done recently on the generator breaker or it's "cubicle" then something might have been inadvertently disturbed.

 

@turbine engineer,

By the way, I presume no one changed the 505 configuration BEFORE the problem started or as part of the troubleshooting.

I don't recall if the 505 (and I'm also presuming it's a 505 and NOT a 505e) has an input for load (watts/kW/MW) and if it does I'm presuming it's working properly.

Finally, I'm presuming the steam turbine-generator is being synchronized to other machines (prime mover and their generators) and is operating in Droop Speed Control after the generator breaker closes. (If I recall correctly the 505 starts and operates in Isochronous Speed Control until the generator breaker closes and if there is a tie-line breaker status input to the 505. It's obviously been a long time and I don't want to download the 505 manual and study it (ever again).

 

@WTF?
Thanks for your reply. Here are the observations:

1. Unit was made online after 3 months.
2. No change in settings done before rolling.
3. There are utility tie breaker contact which is shorted to always closed. GT breaker contact checked ok.
4. There is kw input into 505. the transducer was replaced with a spare one and it is healthy as after last sync the load is showing properly
5. Till 3000 RPM following speed setpoint, EHG is changing valve opening and increasing the speed.
6. At 3000 RPM, it is maintaining the speed.
7. Just after sync, there is a dip in actuator opening command from 33% to 22% resulting in steam flow reduction which in turn leads to reverse power.
8. During previous rolling, there was dip at sync from 33% to 32% and then increase of actuator opening command.
9. I understand, 505 converts all load raise/cascade raise signal to speed setpoint and then by PID controller increases the actuator opening command. We are seeing that after sync, there is increase in speed setpoint but no increase in actuator opening command, rather it is decreasing.
10. We have checked the manual, but there is no trouble shooting guide.
11. 505 is getting the command that it is synced from GT breaker, hence increase in speed setpoint to 3012 and higher, but it is not converted to actuator demand setpoint.
12. We have also checked the signal from GT breaker to 505 terminal and found ok.

we are still investigating the issue why it would try to close the actuator although the speed setpoint has already increased. would love some suggestions

 

@turbine engineer,

Previously you mentioned you were able to load the machine during one start/synchronization attempt--how was that done?

You mentioned an EHG (Electro-Hydraulic Governor??), and many 505s use a 4-20 mA or 0-200 mA output to drive a control valve (through an electro-hydraulic servo-valve or pneumatic actuator). If this is the case and there is a linear output from the 505 to the EHG is it possible to, while the unit is not running and the steam supply is isolated and they hydraulic system is running, to use a mA simulator of some kind to "stroke" the control valve (move it through its operating range, or at least part of its operating range)? You also said the unit had sat for several months, and oil quality can sometimes affect EHG servo operation. (Do you regularly check oil quality through testing?)

I would also suggest using some kind of meter (ammeter; voltmeter) to monitor the EHG output when the machine is running and being synchronized and should be loading. You could set this meter up to monitor the current being output to the EHG during simulation as above to record some data for comparison against actual running data (current vs. position). This would tell you if the problem is the 505 or the EHG/servo.

I'm a big one for "dividing and conquering"--trying to to narrow a problem down by eliminating possible sources/reasons/causes one at a time. It starts by analyzing the problem to the best of one's ability to identify possible sources/reasons/causes and deciding which ones are the most likely and then working to discover if they are or if they are not. In this case, I would be trying to find out if the problem is the 505 or the EHG (servo) or the actuator.

I would also be very interested to learn what is causing this drop in reference from 32% to 22% when trying to raise load. That just seems very odd--and more or less points to the 505 as the source of the problem. Is there some kind of control valve position feedback (mA or LVDT) to the 505 that might be failing or failed at some particular position? This could also be monitored during the simulation/stroking as a check.

In my experience the 505 doesn't have a lot of "user-serviceable/replaceable" parts/components. (It also doesn't have a very usable troubleshooting capability.) If you have a spare 505 it could be powered up on a bench and configured ("copying" the settings/parameters/configurations) from the existing 505 to the replacement 505 and then swap it out for the 505 which seems to be having problems. Sometimes, this is the best option, as long as one is sure all of the inputs and output devices (such as the EHG servo!) are working properly so as not to damage the replacement 505. I don't know if Woodward has a repair-and-return option you could use if the replacement 505 works properly to have a low-cost option for replacing the 505 in the warehouse.

 

@WTF?
Thanks again for the replies. Here are my observations:
Previously you mentioned you were able to load the machine during one start/synchronization attempt--how was that done?
During fourth attempt, after sync, the load setpoint was quickly increased to 9 MW, and the actuator opening command started increasing and unit did not trip. However, the reverse power relay operated but luckily, as it was within 5 sec delay, Generator did not trip
You mentioned an EHG (Electro-Hydraulic Governor??), and many 505s use a 4-20 mA or 0-200 mA output to drive a control valve (through an electro-hydraulic servo-valve or pneumatic actuator). If this is the case and there is a linear output from the 505 to the EHG is it possible to, while the unit is not running and the steam supply is isolated and they hydraulic system is running, to use a mA simulator of some kind to "stroke" the control valve (move it through its operating range, or at least part of its operating range)? You also said the unit had sat for several months, and oil quality can sometimes affect EHG servo operation. (Do you regularly check oil quality through testing?)
Oil quality tested ok. EHG gives signal to Voith I/H converter through 4-20 mA signal output. Voith converts the signal to oil pressure and the actuators opens on the actual oil pressure. There is no feedback from the Voith or valve to 505. The valve calibration is non linear and the calibration over the full 0-100% checked by valve stroking and found ok.

I would also suggest using some kind of meter (ammeter; voltmeter) to monitor the EHG output when the machine is running and being synchronized and should be loading. You could set this meter up to monitor the current being output to the EHG during simulation as above to record some data for comparison against actual running data (current vs. position). This would tell you if the problem is the 505 or the EHG/servo.
The issue is the output from 505 is 0-100 % converted to 4-20 mA to the Voith I/H converter. Now if the signal output is not increasing from 505 as can be seen in the DCS and 505 panel, then there is no question of I/H converting that signal to oil pressure and subsequent valve opening. Out issue is 505 is giving output command to decrease the Voith signal and the Voith converter is following that command. 505 should have given command to increase the Voith. The issue of I/H and corresponding actuator would pop up if even after command from 505, valve was not opening.

I'm a big one for "dividing and conquering"--trying to to narrow a problem down by eliminating possible sources/reasons/causes one at a time. It starts by analyzing the problem to the best of one's ability to identify possible sources/reasons/causes and deciding which ones are the most likely and then working to discover if they are or if they are not. In this case, I would be trying to find out if the problem is the 505 or the EHG (servo) or the actuator.
From my experience, this is not the issue of servo or actuator. It is the issue of 505 as it is not giving the command to open the actuators.

I would also be very interested to learn what is causing this drop in reference from 32% to 22% when trying to raise load. That just seems very odd--and more or less points to the 505 as the source of the problem. Is there some kind of control valve position feedback (mA or LVDT) to the 505 that might be failing or failed at some particular position? This could also be monitored during the simulation/stroking as a check.
There is no feedback from either the Voith converter or the actuator. 505 only gives the output command and based on speed and/or load, the command changes. The drop in reference on synchronisation is the main point of concern to us. I understand the output command, after sync is the lowest amongst 'Valve Limiter', 'Load setpoint' and 'Droop control feedback.' we are trying to find out if the droop control or the valve limiter is overriding as being the lowest setpoint.

In my experience the 505 doesn't have a lot of "user-serviceable/replaceable" parts/components. (It also doesn't have a very usable troubleshooting capability.) If you have a spare 505 it could be powered up on a bench and configured ("copying" the settings/parameters/configurations) from the existing 505 to the replacement 505 and then swap it out for the 505 which seems to be having problems. Sometimes, this is the best option, as long as one is sure all of the inputs and output devices (such as the EHG servo!) are working properly so as not to damage the replacement 505. I don't know if Woodward has a repair-and-return option you could use if the replacement 505 works properly to have a low-cost option for replacing the 505 in the warehouse.
Yes, 505 does not have any servicable parts. We are planning to swap the controllers on next shut down if nothing is found till then. I am not for replacing the voith converters as then the actuators would have to be calibrated again for the whole range. As they are only controlled by oil pressure generated from the voith and the scale is non linear, it is very difficult to calibrate the actuators.

 

A couple of things that will cause a 505 to decrease the actuator output:

1. Measured speed is higher than the speed setpoint.

2. Measure kW is higher than the load setpoint.

Have you observed these analog input signals in the 505 at the time of breaker closure? I see that you have replaced the kW transducer and checked it after synchronization. But it could be temporarily outputting an erroneous signal immediately after breaker closure. Or the speed / kW signals could be picking up some noise when the breaker closes. I'm not saying either of these scenarios is likely, but it wouldn't hurt to rule them out.

Also, does your 505 have either the Cascade control or the Aux control configured?

What generation of 505 is this? The latest 505 has a small built-in screen. The previous generation had a two-line display.