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I have 20MW HItachi GT. Initial load is set 2.5 MW in MarkV. I would like to change this setting to 1.0 mw temporarily. Can I do it? How can I change this setting? please help?
I'm nervous about replying to this one because I don't know the turbine (heavy duty or aero-derivative) and I'm not clear about the term "initial load".
For most GE-design heavy duty gas turbines using Mark Vs with autosynchronization done using the capability of the Mark V there is something (inappropriately) called "Spinning Reserve" which is the load to which the turbine will go *in the absence of any other load being selected* immediately after being automatically synchronized. In other words, if Base- or Pre-select Load is not selected prior to initiating an auto synch, the unit will synchronize, close the breaker and load/unload to the load defined as "Spinning Reserve". This is set by the value of a Control Constant, usually called (but not always!) LK90SPIN, which can be changed.
The value of LK90SPIN is usually set by experience with stable low-load operating values for a particular unit, or after some consultation with the purchaser when the turbine or control system is being purchased and configured.
<b>BUT, beware!</b> If you make the value of LK90SPIN too low, the load may be unstable because the fuel control valve may not be operating in a stable region, so the load might oscillate ("hunt"), a little, or a lot. It all depends on the unit, the fuel, the type of control valve, etc. If you need to maintain this load for any period of time, you might not be very happy with the oscillations which could occur at such a low load. And those oscillations would be function of the entire control system and its condition as well as the fuel being burned, not just the value of a single parameter or setting.
When the breaker closes, the operator can immediately use the RAISE and/or LOWER SPD/LOAD targets to increase or decrease load to whatever value is desired, so if this is a temporary change why not just have the operators lower load as soon as the breaker closes?
Another problem which might happen is that, in general, the FSNL speed is typically set to something around 100.3% speed, and synchronization occurs at or near this "offset" which will result in the unit possibly taking on more than 1.0 MW upon initial breaker closure. In which case, the operator will still be required to manually lower load with the LOWER SPD/LOAD target. For a unit with 4% droop rated at 20 MW the load increase on initial synchronization with a TNR of 100.3% would be approximately 1.5 MW, which is above the 1.0 MW you are looking to achieve.
So, there are really a couple of things that should be considered if trying to make the unit go to or maintain a particular load upon synchronization, if that interpretation of this question is correct: that the originator wants to change the load which the Speedtronic will go after synchronization.
The best way to do this temporarily is to just have the operator manually adjust load with the RAISE- and LOWER SPD/LOAD targets after synchronization. But, the same problem of unstable unit operation because of the control valve might occur. 1 MW is pretty low, and the fuel control valve might just be on the edge of its controlling region/ability for the fuel at that point.
If the problem is that the unit is taking too much load on synchronization, then it's likely that the FSNL and automatic synchronization parameters need adjustment.
If autosynchronization is not being done with the Mark V, then most of the above is not applicable. If load control is done with some external load reference, then most of the above is not applicable.
So, it's hoped that you understand the apprehension about responding. This is not a simple question because we don't know enough about the application, and the question wasn't really clear.
For most GE-design heavy duty gas turbines using Mark Vs with autosynchronization done using the capability of the Mark V there is something (inappropriately) called "Spinning Reserve" which is the load to which the turbine will go *in the absence of any other load being selected* immediately after being automatically synchronized. In other words, if Base- or Pre-select Load is not selected prior to initiating an auto synch, the unit will synchronize, close the breaker and load/unload to the load defined as "Spinning Reserve". This is set by the value of a Control Constant, usually called (but not always!) LK90SPIN, which can be changed.
The value of LK90SPIN is usually set by experience with stable low-load operating values for a particular unit, or after some consultation with the purchaser when the turbine or control system is being purchased and configured.
<b>BUT, beware!</b> If you make the value of LK90SPIN too low, the load may be unstable because the fuel control valve may not be operating in a stable region, so the load might oscillate ("hunt"), a little, or a lot. It all depends on the unit, the fuel, the type of control valve, etc. If you need to maintain this load for any period of time, you might not be very happy with the oscillations which could occur at such a low load. And those oscillations would be function of the entire control system and its condition as well as the fuel being burned, not just the value of a single parameter or setting.
When the breaker closes, the operator can immediately use the RAISE and/or LOWER SPD/LOAD targets to increase or decrease load to whatever value is desired, so if this is a temporary change why not just have the operators lower load as soon as the breaker closes?
Another problem which might happen is that, in general, the FSNL speed is typically set to something around 100.3% speed, and synchronization occurs at or near this "offset" which will result in the unit possibly taking on more than 1.0 MW upon initial breaker closure. In which case, the operator will still be required to manually lower load with the LOWER SPD/LOAD target. For a unit with 4% droop rated at 20 MW the load increase on initial synchronization with a TNR of 100.3% would be approximately 1.5 MW, which is above the 1.0 MW you are looking to achieve.
So, there are really a couple of things that should be considered if trying to make the unit go to or maintain a particular load upon synchronization, if that interpretation of this question is correct: that the originator wants to change the load which the Speedtronic will go after synchronization.
The best way to do this temporarily is to just have the operator manually adjust load with the RAISE- and LOWER SPD/LOAD targets after synchronization. But, the same problem of unstable unit operation because of the control valve might occur. 1 MW is pretty low, and the fuel control valve might just be on the edge of its controlling region/ability for the fuel at that point.
If the problem is that the unit is taking too much load on synchronization, then it's likely that the FSNL and automatic synchronization parameters need adjustment.
If autosynchronization is not being done with the Mark V, then most of the above is not applicable. If load control is done with some external load reference, then most of the above is not applicable.
So, it's hoped that you understand the apprehension about responding. This is not a simple question because we don't know enough about the application, and the question wasn't really clear.
B
Brian Hall
I'm not familiar with the Hitachi CT but on the GE 7f turbines with MK5 controllers there is a constant in the MK5 logic that controls the spinning reserve MW setpoint. In my documentation it shows up as LK90SPIN.
Thanks a lot CSA. You are right. Operator can reduce the load after synchronisation. We did that and found unit is stable at 1.3 mW load. I tried to change LK90SPIN set to 1.5 MW. But setting reduce only to 2.3 MW. Then I reduced LK90PSMN from 2.5 MW to 1.5 MW. Then the setting reduced to 1.5 MW. What is this factor LK90PSMN.
You're very welcome, and thank you for the feedback!
LK90SPMN is a minimum limit on the setpoint of LK90SPIN. (LK90SPMX is a maximum limit.) LK90SPMN serves as a lower limit for stable operation. If you find that unit operation is not stable below a certain value, you can set the minimum limit to that value to maintain stable operation on synchronization.
LK90SPMN is a minimum limit on the setpoint of LK90SPIN. (LK90SPMX is a maximum limit.) LK90SPMN serves as a lower limit for stable operation. If you find that unit operation is not stable below a certain value, you can set the minimum limit to that value to maintain stable operation on synchronization.
