Which is the best method for Over speed test for a Frame VI, Mark V Controlled Gas Turbine?

Manual says two ways:

1. Under operating conditions by reducing the constant for the trip setpoint.
2. At shutdown condition by simulating the overspeed condition.

There is no Overspeed bolt for trip in this unit, Under operating condition we have to reduce TNKHOS to below TNKR3?

TNKR3 - 107 set point high speed stop
TNKHOS -110 (same for <P> and <Q>)
TNKHOST-113.5 (same for <P> and <Q>)

There is an another method also there, In the screen ‘Over speed test display’ Overspeed test for <P> or Over speed test for <Q> Both set points are same for <P> and <Q>

When <P>-Test is selected, the turbine speed can be increased to max. 113.5% speed. The <P> over speed set point is at 110%. The <Q>-Overspeed protection set point is shifted to the value 113.5% during <P>-Test.

When <Q> test is selected, the turbine speed can be increased to max. 113.5% speed. The <Q> overspeed setpoint is at 110%. The <P>-Overspeed protection setpoint (110%) is then disabled.

There is Note written below:
The constant K_TEST_EN has to be set to a value greater than zero to enable the selection of one of the overspeed tests. After completion of the test, K_TEST_EN must be set back to zero!

I could not find K_TEST_EN in the control constant and in the CSP.

Anybody can help???

Thanks & Regards

Joy

 

Very difficult question, made more difficult by the fact that a standard for overspeed test CSP (Control Sequence Program) sequencing doesn't exist in GE--nor even for overspeed test displays... It would be necessary to look at your CSP to determine how overspeed testing on a running unit could be performed.

There are two, independent electrical/electronic overspeed detectors in the Mk V turbine control panel. The first is performed in <Q> at the scan rate of the CSP (typically 8 Hz). The high-pressure shaft primary speed pick-up inputs to <Q> are connected to the QTBA terminal boards on <R>, <S>, and <T> on terminals -51 and -52. They are monitored by sequencing in the CSP and compared to TNKHOS, and if TNH exceeds TNKHOS the unit is tripped by picking up L12H, L4T, and dropping out L4--which will drop out the primary trip relays (PTRs) on the TCTG card in <P> core and de-energize the trip solenoid(s) if the unit is running. This is sometimes referred to as the Primary Electrical or -Electronic Overspeed.

The second electrical/electronic overspeed detection is performed in <P> on the three TCEA cards (<X>, <Y>, and <Z>). The high-pressure shaft emergency overspeed speed pick-up inputs are connected to the PTBA on <P> at terminals -1 & -2, -5 & -6, and 9 & -10. Overspeed detection software on the TCEA cards monitors the speed inputs at a scan 128 Hz scan rate. If the speed inputs exceed the setting in the I/O Configurator--which must match the hardware ("Berg") jumper settings for overspeed detection)--the emergency trip relays (ETRs) on the TCTG card are dropped out and the trip solenoid(s) are de-energized (if the unit is running). This is sometimes referred to as the Emergency Electrical or -Electronic Overspeed.

Do you, your company, your management, or your insurance company (or, in some locales, the local fire marshal), have a requirement to perform overspeed testing with the turbine running (sometimes referred to as "on-line" even though the unit cannot be synchronized to perform overspeed testing...)? Or, does your comapny, or your insurance company (or local fire marshal), permit overspeed testing with the unit shut down (sometimes to referred to as "off-line", even though the unit must not be running when simulating speed...) using a frequency generator to simulate shaft speed?

"Off-line" overspeed testing only tests the overspeed detection circuitry of the Mk V; it doesn't (can't easily) test the trip solenoids and the Trip Oil circuitry which actually shuts off the fuel flow to the turbine.

Making a decision to test "off-line" or "on-line" (with the unit not running, or with the unit running, respectively) involves making a decision about what the testing needs to demonstrate/prove, as well as any requirements (insurance company, internal procedures, etc.). Then a test plan needs to be worked-up for the type of testing to be performed.

Changing Control Constants to perform overspeed testing was a bad "work-around" to the poor overspeed sequencing provided from the factory with many new units. It would be necessary to change TNKR3 to be greater than TNKHOS to allow a test of the "primary" electrical overspeed (<Q>) to be certain it tripped at 110%.

One last thing to note about speed pick-ups: The intent of the Mk V was to use six independent speed pick-ups--three for <Q>, and three for <P>. Some engineers did and some didn't; some used four pick-ups, some five, and some three--with the requirement of six inputs satisfied by jumpering a single input to more than two inputs. One needs to review the I/O Report and the actual physical wiring to be certain about the number and configuration of speed pick-ups.