GE Mark V Electronic Overspeed Test on Cooldown

Control System: GE Mark V TMR

We currently have a procedure for testing the primary and emergency overspeed test on the Mark V TMR system. It was written by our controls engineer, however, he is no longer around to further pick his brain as to why he wrote it as he did. The procedure was written to perform the test OFFLINE and while the unit was OFF cool down. I will paraphrase it below since i don't have it in front of me:


1. Turn off the EX2000, both the AC and DC breakers. This will trip the 86G-2 Lockout.

2. Open breakers for the follow AUX motors (Both AC and DC Lube Oil, Atomizing Air, Bearing Evac, LO Mist Eliminator, Both Cooling water pumps, Both exhaust frame blowers, Hydraulic, and maybe one more that is escaping my mind)

3. For the primary OS, Parallel 2/3 core speed sensors located on QTBA.

4. Source the frequency 3960 (Sine wave, .433 volts) and monitor the trip/speed signals (TNH, L12 something)

5. for the emergency overspeed test, parallel the three speed sensors on <P> core.

6. Force L4_XTP to "0" and Force L20FG1X to "1"

7. Test across the leads for L20FG1X Trip solenoid on the markV board to ensure the solenoid is energized.

7. Source the frequency 3960 (Sine wave, .433 volts) and monitor the trip/speed signals (TNH_OS, the L12 signal for emergency OS)

8. Test across the leads for L20FG1X trip solenoid on the markV boards to ensure the solenoid is deenergized after the trip.

I was recently asked to test the EOS (primary and emergency) while the unit was on cool down. I was unsure of this just based on it going against the procedure. Looking through the CSP to see the outcome of simulating TNH while the unit is offline for its various effects, It seems our procedure had us kill the breakers for some of the AUX motors because as TNH increases, it gives the permissive to start the motors and this was more or less for equipment protection. I looked at GE's procedure in the manual for EOS checkout, it does not aline with our procedure either but we accomplish the same result. As far as killing the EX2000, i cannot find much logic on this. I can see from the block logic diagram that the EX2000 does reference turbine speed possibly to flash the field at a certain RPM, this may be why he had the breakers turned off. The risk i see with having the unit on cool down and forcing L4_XTP to "0" and L20FG1X to "1" is that now you have the trip solenoid closed with oil pressure and the gas system NOT locked out. I understand L4 energized is required for the SRV to open and if L4_XTP is forced, L4 can never be energized. But it is GE and weirder things can happen. In the event something did internally short, or we touched the wrong wire on a terminal board, this is why, i am assuming, he wrote to have the LO and HYD motor breakers open.

To paraphrase, I am wondering if it is okay to test the Primary and Emergency Electronic Overspeed while the unit is on Cooldown? I get site conditions and versions of Mark V can be different so blanket statements are not generally advised, just looking for a little clarification if possible. Lastly, should the frequency be sourced to the Mark V using a square wave vs. sine wave at 50% duty?
The test you describe is actually a commissioning test. A actual overspeed test is performed later.

The procedure is described in your control spec.

Lifting the leads from the speed pickups invites problems. If leads are lifted then an actual overspeed test should be performed.

We no longer perform actual overspeed tests because it seems that management is no longer is willing to allow the turbine to exceed rated speed.

However, some relief for management may be there.

When removing the turbine from service, lower load and open the generator breaker manually with the HMI. At full speed no load use logic forcing to force L12_H. This will test the shutdown sequencing in real time without actually overspeeding the turbine.
We do 2 tests without actually overspeeding the turbine. The first is for the Primary Overspeed system. We reduce the overspeed trip constant, start the unit. While the unit has flame and ramping, it trips at 25%. This proves the the trip will close gas valves.

The second is to the Emergency overspeed system. That is done offline using frequency generator connected to the speed pickup inputs.

CTG Primary Overspeed Trip Test Procedure:

I. Purpose/Background:

This procedure will demonstrate the functionality of the Turbine Control System Primary Overspeed Trip. The trip set point is lowered to reduce turbine stress. By increasing the speed above the trip set point, we will observe an actual trip. This test will verify proper operation of the speed pickups, appropriate trip logic, contact outputs, and hydraulic system; to close the steam valves (and stop the turbine.)

II. Precautions:

1. At the completion of testing ensure that all forces are removed.
2. Monitor to ensure seal oil is not lost during the test.
3. Hardware Diagnostic Alarms will come in while the constant is changed.
4. Allow 30 minutes additional time to perform the test.

III. Procedure:

1. Open the Trender window for Overspeed Test and go online.
2. Start the unit.
3. Wait until unit reaches cranking speed (~845RPM) then adjust the Overspeed Trip (OST) constant, TNKHOS, from 110% to 25%:
1. Select the record button (to bring up the live value) then double-click the point value for TNKHOS in the Trender window.
2. Change the value to 25, change the ramp rate to 100 then Send the value.
3. Multiple Diagnostics will alarm due to a difference in data tables. They will clear when the constant is returned to normal.
4. You may choose to stop or pause the recording until you get closer to the ramp and trip.
4. The unit will complete the purge, roll down to ~475RPM, ramp back up TO ~500RPM, and fire then accelerate normally.
5. The unit will trip when the speed reaches the 25% (900RPM) setpoint
6. After the trip occurs re-set the OST constant TNKHOS back to 110 % (3960 rpm).
1. With the Trender still on line and in the record mode, double click on the point value for TNKHOS.
2. Change the value back to 110, change the ramp rate to 100, then select send and close.
3. Reset the Diagnostics alarms.
7. With the turbine rolling down, reset it and hit start. (It may roll down below 450RPM before restarting.)
8. The unit rolling down from a trip and fuel valves closing confirms the proper operation of the Primary Overspeed Trip system; speed pickups, control logic, output contacts, and hydraulic system.

Unit: CT11 CT12
Date Performed: ____________ Performed By:

CTG Emergency Overspeed Trip Test Procedure:

I. Purpose/Background:

This procedure will demonstrate the functionality of the Turbine Control System Emergency Overspeed Trip. This is done without stressing the rotating parts. Since the Primary Overspeed test proves the proper operation of the speed pickups, control logic, output contacts, and hydraulic system, to close the fuel valves (and stop the turbine) we can simulate the Overspeed condition and monitor the logic state to confirm that the Emergency Overspeed Trip system is working properly. A frequency generator is used to simulate the speed pickups and verification will be done to show the Emergency Overspeed logic operates when the speed signal increases above the 111% set point.

II. Precautions:

1. Use caution while working inside the Mark 6e panel as 120VAC and 125VDC are present.
2. At the completion of testing ensure that all forces are removed after the speed
3. Prior to disconnecting the speed sensor signal leads, ensure that the leads are legibly marked so that they may be reconnected to their proper terminals.
4. Ensure that seal oil is not lost at any time during this test.

III. Procedure:

1. Open the Trender window for Overspeed Test. Go online then press Record to start and then stop recording, save when done.
2. Connect a function generator to the speed pickup inputs on the <P> core to simulate turbine speed: <pre>
TB Terminal # Wire # Device Signal
PTBA 001 (+) 320 77HT-1 TNH_OS
PTBA 002 (-) 321 77HT-1 TNH_OS
PTBA 005 (+) 322 77HT-2 TNH_OS
PTBA 006 (-) 323 77HT-2 TNH_OS
PTBA 009 (+) 324 77HT-3 TNH_OS
PTBA 010 (-) 325 77HT-3 TNH_OS
(You should get the "control speed trouble" alarm due to the speed pickups being disconnected.)

3. A Fluke 725 set to KHZ step from 3.9KHz to 4KHz, or Velleman HGP1 set to sweep from 3500Hz to 4000Hz, 1Hz step and 0.01Hz speed. Do a Master Reset while the RPMs are below the tip point. The unit will trip at 111% or 3996Hz.
4. Increase the frequency on the function generator until THN_OS increases above 111% (3996Hz = 3996RPM = 111%). Verify l12h_p_hw changes state.
5. Reduce frequency below the Overspeed set point and perform a Master Reset. Verify l12h_p_hw and the “protective module Overspeed trip” alarm clears.
6. Restore the system to the normal lineup.

Unit: CT11 CT12
Date Performed: ____________ Performed By: