[Tasker] Woodward 505 LST [Tech Support Index]

Woodward 505 LST
Product Questions Pertaining to the Behavior of the
Failed Speed Signal Trip and Associated Override for Start
Related to 505 LST Type 3 turbine configurations (Full Arc with Non-Modulating 2 Position Stop Valves)
To address issues related to an Accelerated Unit Start Program (AUS)
where un-governed turbine speed at startup follows the boiler firing with the governor and stop valves fully open

The Initial Question List relevant to this issue is posted here on February 8th, 2014.  Updates are pending dialog from Woodward.
2010 note, Scott Taylor was Tom Truax's initial Woodward consulting contact for the 505 LST in 2008, but Scott is no longer with Woodward as of 9/2010.  Scott worked with Tom on a previous list of questions in 2008 and 2009.  That discovery documentation is partially listed at the bottom of this page under [Previously Resolved Questions].  Some of those answered questions are relevant to this AUS issue.  Other Woodward personnel who previously assisted Tasker in clarifying 505 LST issues include Calum Maclean, Walter Grassens, and Rich Kamphaus, Dennis Carlton, and Neg Vue.

Open Questions  (response in blue from Aaron Russo / Woodward) follow up question (in red)
Contact Tom Truax (805 680-7727 cell) if username and password are needed to access any protected links

No unresolved questions currently open

Resolved / Answered Questions
Updated 2/11/2014

• (2/8/2014 / Tasker) Is it possible to adjust the speed value that will "arm" the failed speed signal (disarm the override) during start acceleration?  Scott Taylor's review of the GAP code in 2008 indicated that function would "arm" at 200 RPM on the way up, and "trip" at 100 RPM on the way down.  (Note that Tasker's commission testing notes from 2009 seem to indicate that there was no hysteresis and the turbine would trip on loss of speed signal at 200 rpm when costing down)  We would like to increase the speed value so the function arms at 800 RPM (rather than 200 RPM) because during an accelerated unit start the only throttle control is the boiler firing, and due to boiler issues, the speed can sometimes wander, rising above 200 rpm (up to 600 rpm) and then coasting back down to a lower value or all the way to zero.  We don't want the 505 to trip "Loss of Speed Signal" unless the speed has climbed above 800 RPM.
  • There is no adjustment for the value in the 505 LST "Program Mode" or the "Service Mode", so we are inquiring if there is an adjustment in the "De-Bug Mode".
    • (2/10/14 / Aaron Russso) As the code currently stands, you can adjust the “Loss of Speed Signal” trip over-ride level in De-bug mode through the tunable SPEED_CTRL.SPD_OVRD.IN_1.  This value has a tunable range from -5 to 1000 RPMs.
      • (2/11/2014 Tasker) Could you please list the 505 LST De-Bug Mode “path” (Category > Block > Field ?) to access the tunable SPEED_CTRL.SPD_OVRD.IN_1
        • The De-Bug path:
          Category: SPEED_CTRL
          Block: SPD_OVRD
          Field: IN_1
        • This parameter adjusts the level which speed must surpass in order to activate the “loss of speed signals” trip.  This trip indicates a sudden loss of the speed signals.  Once speed surpasses this threshold, a trip will be issued if the speed sensor fails (speed falls below 100 RPMs suddenly).  If speed falls below the value set by SPEED_CTRL.SPD_OVRD.IN_1, but not suddenly, the “loss of speed signals” trip is again overridden and speed can again fluctuate anywhere from zero to the SPEED_CTRL.SPD_OVRD.IN_1.
  • If there is no field to adjust the valve in the De-bug Mode, would it be possible to have Woodward "Re-Code" the value in the Gap Program?  We understand that it would entail returning the 505 LST control to Woodward and a new part number being issued.  The customer has a Spare 505 LST, so they could cycle their spare through as they sequentially implement their accelerated unit start program on multiple units.  NA due to tunable value
     
• (2/8/2014 / Tasker) Another issue has to do with the Valve Position that will initiate a trip if no speed is sensed on start.  This value is adjustable in the Program Mode Block VP MPU OVRD DISBLE under the Speed Configure Header (Woodward 505 LST Manual 26440 Rev D page 35).  The functionality is described at the top of page 62 under the heading Zero Speed Signal Override.  (note: the manual has not changed since revision A, and is not entirely accurate because the 20% value is adjustable and the hysteresis is not clarified)
  • During an Accelerated Unit Start, we want to fully open the governor valve rack, but even with the configurable value set all the way to 100%, fully opening the governor valve will result in a trip on no speed signal.  We can implement a work around by modifying the start procedure to manually raise the valve limiter to some value slightly less than 100%, but it would be our preference to simply turn the function off.  The standard version of the 505 has a similar feature that will disable the MPU Override based on configured elapsed time rather than valve position, but the standard 505 version has a provision to turn the function off in the Service Mode (USE MPU OVERRIDE TIMER block under the MPU Override Header, 505 Manual 26347V2 Rev G).
    • Is there an option to turn the 505 LST VP MPU OVRD DISBLE function off in the De-Bug Mode?
      • (2/10/2014 / Aaron Russo) there are not any handles to turn the 505 LST VP MPU OVRD DISBLE off.
    • Ideally, we would prefer to have the function enabled and adjusted for a legacy start under pressure, and turned off for an Accelerated Unit Start with the Governor Valve fully open because the units will occasionally need to execute a legacy start under governor control.  Is there some method (via a contact input or modbus command) to select when we want the functionality enabled or disabled?  I suspect that presently there is not, so a follow-up question is:
      • Would it be possible to add that capability as a custom Woodward Project.  As the Utility Industry Business Case evolves requiring units to cycle rather than staying on-line for extended run times, more utilities will be implementing Accelerated Start Programs to mitigate the cycle stress on their units and reduce their startup cost.
        • (2/10/2014 / Aaron Russo) Due to the current number of engineering projects and limited engineering capacity, we do not have the capacity to perform the requested changes within the 505LST controller for the next 2-3 years.
• If Woodward is able to do custom GAP coding for the 505 LST, our wish list to accommodate both Accelerated Unit Starts and Legacy Pressure Starts would be:
  • Make the Failed Speed Signal (Loss of MPU) arming speed configurable, or hard code the value to 800 RPM.
  • Make the VP MPU OVRD DISBLE function selectable as either on or off (used or not used) via a Modbus discrete input or some other selectable method.
  • Tie the VP MPU OVRD DISBLE value to a configurable table in the service mode.  If the unit trips during an Accelerated Unit Start, the governor will need to control the start under pressure, but the throttle pressure may range from a low value around 100 PSI up to a high value of 1800 PSI (for this immediate applilcation), so a fixed value is of little to no use because the valve travel needed to roll the turbine will vary significantly with throttle pressure.

Pending

Previously Resolved Questions that relate to the Failed Speed Signal and the Valve Limiter
Excerpts from the [initial installation questions in 2008-2009]
Updated 4/1/09.  2010 note, Scott Taylor was Tom Truax's initial Woodward contact for the 505 LST, but Scott is no longer with Woodward as of 9/2010.

• What is the mpu fail speed on the way up and the way down?
  • Scott reports the code indicates it is 100 RPM on the way down, and arm on the way up at 200 RPM
  • Testing at WPS W2 indicated it is 200 RPM either direction.
     
• Valve limiter / go and hold / If the control is started in auto with a go command, the valve limiter will begin to ramp open.  If a hold command is issued, the speed setpoint ramp will stop, but the limiter ramp will continue toward 100%.  A raise or lower command will drop the control into manual and stop the valve limiter.  The limiter ramp can be restarted by placing the control back into auto and giving a go command.
   
• Valve Limiter start ramp.  Should it move up out of the way at a fast rate after start? manual 26440 page 64. No, the manual is wrong.  You can move it out of the way faster manually, but automatically, it will continue ramping toward 100% at the start rate otherwise.
   
• Rate Selection
  • When selecting Slow, Medium, or Fast Rates via Modbus, does the selection pertain to all ramps?  Speed, Valve Position, and Valve Limiter?
    • Scott Taylor 9/17 – The same selection is applied to Speed and Valve Position ramps when the operator can specify a rate.  There are cases where predetermined, and sometimes instantaneous, rates are used based on operational state (as Walter has described).
    • Walter Grassens - The Speed and Valve Position ramps are affected by this Modbus selection.  The valve limiter is explained in response to the question below.
  • How do you select which ramp rate is used for the valve limiter?  The manual does not detail what is in the valve limiter menu. Reference Manual 26440 Pg 59 & 77.
    • 11/11 The Valve Limiter ramp rate is not user selectable.  It is determined by logic based on whether the system is starting (Start Rate) or when speed is in control of the LSS including during a shutdown when speed demand is switched to ‘0’, the fast rate will be used. Otherwise the Valve Limiter ramp will use the Normal rate (Medium) as a default.  The rates are tunable in the service mode
      • Note: the Modbus output for valve limiter rate will not display the correct valve.  The GAP block is based on incorrect logic (bug).
    • As noted by Walter, the normal rate for the valve limiter is the medium rate, so if fine resolution is desired, then the medium rate should be set to a low value.  For example, if the valve limiter will be used for pre-warm then set the medium rate to about 5% per minutes to achieve fine resolution of the valve position.
       
• On a rolling start, how does the valve limiter behave?  Will it ramp from zero at the selected rate?  The speed setpoint will match the actual rolling speed at the time of the run command, but if the valve limiter is slow to open, speed will continue to decay for some time.
  • Phone Conference on 11/21/08 Scott suspects it behaves like a regular 505.  The limiter will go to zero and need to ramp up to the value to support the current speed at the start ramp rate, which is a fixed value (but tunable in the service mode).
     
• What does the Pre Warm Valve Stroking function do?
  • The manual is incorrect.  The manual indicates you can stroke the governor valve, but the pre-warm function is intended to stroke the TV on a type 1 or type 2 valve configuration.  It does not stroke the governor valve.  On a type 3 valve configuration, there is no throttle valve, so there is nothing to stroke.  The manual indicates that if the speed goes above 100 rpm, the throttle valve will trip.  Again, this is only a throttle valve trip, not a turbine trip.
  • To pre-warm a type 3 configuration with stop valve rather than throttle valves.
    • Reset the governor trip and the turbine trip oil
    • Raise the speed setpoint above the actual speed (turning gear speed).  The PID will try to open the valve, but the LSS is controlled by the valve limiter and the limiter will still be at zero .  There are a number of ways to raise the speed setpoint, including use of the raise command via either a contact input or Modbus.
    • Manually take control of the valve limiter.  The valve limiter can be raised via a Modbus valve limiter raise and lower command, or from the keypad by selecting the limiter menu and using the adjust key.
    • Without the speed pid in control, it appears that the limiter will use the medium rate, so recommend setting the valve limiter medium rate to a low value to enhance resolution
       
• The customer prefers to do the valve raise / lower for pre-warm over hardwired discrete inputs because they send pulses and their network is slow. We need to confirm that we can do the pre-warm valve control raise / lower via the contact inputs on terminals 14 and 15.
  • Verbal response from Scott Taylor indicates that the hardwired contact inputs cannot be used for pre-warm VPC.  Scott's email response was:
  • Looking at the code for the Prewarm. It can be enabled / disabled from modbus through BW14 (if REMOTE mode is true – I believe this is consistent for all modbus commands). When enabled a manual ramp is used to stroke the TV. This can be controlled in LOCAL from the keypad or in REMOTE the open command it from BW30 and the close command is from BW29
  • Also note that the manual is incorrect.  Pre-Warm controls the throttle valve, not the governor valve, so for a type 3 configuration pre-warm won't do anything because there is no throttle valve.
     
• Does the shutdown output clear after a reset when there is still an active trip input?  How do we deal with looped shutdown logic?
  • There is timer called Reset Trip Delay.  The manual indicates that the External Trip Input is ignored for a time after reset, but the unit will trip if the external trip is not cleared within the configured time.  What the manual does not explain is that there are 2 external trip inputs.  One on terminal 12 (DI:1) and another on terminal 27 (DI:16).  The tune-ability override functionality is only available on DI:16.  The trip input on DI:1 is direct acting and immediate.  There are no provisions to break looped logic on a DI:1 External Trip Shutdown.  If looped logic is an issue, then use DI:16 and jumper DI:1 if DI:1 is not used for some other shutdown input.
     
• How do you change the Modbus address
  • Adjust in the De-Bug mode
    • [Gap Modbus blocks] and how to get into the [De-Bug Mode]
    • This same general location also had the comm time out value, changed from the default of 3 seconds to 10 seconds
    • From Scott Taylor: You are correct about some values being accessible only from DEBUG. I don’t know the best way to inform uses about these options. In other controls we do have some special functions that would not be required by most users that are only accessible by Debug. We don’t want to complicate configuration for the majority of users but we do include some special functions that are available with “help” from Woodward.
       
• Do we need to use the inputs for valve position?  What are the consequences of not configuring?
  • Reading of the manual seems to indicate that the control may function, but will there will be an alarm if the valves are not open or closed depending on the operating mode, running or shutdown?  There is no trip indication for the valves, but it is not clear if there is a start permissive, or what other logic (other than alarming ) might be affected.
  • The valve position inputs, analog or discrete, are optional and do not need to be wired if valve testing is not utilized.  There are no permissive tied to the valve position outside the scope of valve testing.  There may be an advantage of having the position input because it will then be available over the Modbus Comm Link.
  • If valve position input is not desired, then the config blocks can be set to no.  If the inputs are routed to the 505, but not used, then the values should still be available over Modbus.
     
• Speed Sensor Probes.
  • 9/4/08
    • Can we use Active pickups. the short answer from Woodward is Yes
    • The manual shows an active pickup, but indicates it is not used.  Also, there are numerous references to passive pickups in the manual, but none for active pickups.
    • If Active Pickups cannot be used, why not?
    • Spoke with Rich Kamphaus on 9/4.  Rich does not see a reason why you couldn't use the active pickups.
    • Spoke with Scott Taylor.  Scott noted that the hardware is exactly the same, but will look into the code.
  • 9/5/08 Email Reply from Scott
    • I saw exactly what you were describing in the manual, both on page 20 in the wiring examples, where it says not used above proximity probe wiring example, and in the Speed Sensor Input section were all references to proximiter inputs were removed (when compared to the standard 505 manuals).
      The hardware is not different and the software includes the switch that would allow the inputs to read the low speeds that could only come from an active speed probe – so technically there should be no problem using a proximiter.
      I have a voice mail with the engineer that wrote this software and will forward any information he provides.
  • 9/9/08 Email Replay from Scott
    •  ... I did talk to the original engineer on the 505LST – He’s no longer at Woodward otherwise I’d put you in touch with him directly. There should be no problem using an active speed probe. His only concern was that with the max speed selected the resolution might be poor.