Title of Invention	A METHOD IN A TURBINE ELECTRO HYDRAULIC CONTROLLER FOR IMPLEMENTING A FREE GOVERNING MODE OPERATION TO RESTRICT THE EFFECTS OF WIDE FLUCTUATIONS OF THE GRID FREQUENCY
Abstract	The invention relates to a control method in a turbine electro hydraulic controller for implementing a free governing mode of operation to restrict the effects on wide fluctuations of the grid frequency, the method comprising the steps of integrating a previous value of the actual frequency to generate a floating frequency set point, the set point is reset to new values in a gradual manner corresponding to a time constant of an integrator; generating a hold signal when change in frequency exceeds the new frequency set value, the hold signal freezes the set value to the last value held; generating a load correction signal corresponding to the frequency error within the frequency band of 49.0 to 50.5 Hz, the proportional load correction value is limited to +/-5% of rated load and added to the load set point; removing the hold signal when the frequency stabilizes to the new value, the load returning to the original value as the frequency error becomes zero(Automatic Supplementary Control); carrying out a load change according to droop characteristics if frequency falls below 49 Hz, the load change is limited to 10%; carrying out load change according to droop characteristics if frequency goes above 50.5 Hz, the load change is limited to 10%; and transmitting a load change signal to modify turbine load set point, and simultaneously transmitting a signal to boiler controls to make the changes in fuel firing with a feed forward action.

Title of Invention

A METHOD IN A TURBINE ELECTRO HYDRAULIC CONTROLLER FOR IMPLEMENTING A FREE GOVERNING MODE OPERATION TO RESTRICT THE EFFECTS OF WIDE FLUCTUATIONS OF THE GRID FREQUENCY

Abstract

The invention relates to a control method in a turbine electro hydraulic controller for implementing a free governing mode of operation to restrict the effects on wide fluctuations of the grid frequency, the method comprising the steps of integrating a previous value of the actual frequency to generate a floating frequency set point, the set point is reset to new values in a gradual manner corresponding to a time constant of an integrator; generating a hold signal when change in frequency exceeds the new frequency set value, the hold signal freezes the set value to the last value held; generating a load correction signal corresponding to the frequency error within the frequency band of 49.0 to 50.5 Hz, the proportional load correction value is limited to +/-5% of rated load and added to the load set point; removing the hold signal when the frequency stabilizes to the new value, the load returning to the original value as the frequency error becomes zero(Automatic Supplementary Control); carrying out a load change according to droop characteristics if frequency falls below 49 Hz, the load change is limited to 10%; carrying out load change according to droop characteristics if frequency goes above 50.5 Hz, the load change is limited to 10%; and transmitting a load change signal to modify turbine load set point, and simultaneously transmitting a signal to boiler controls to make the changes in fuel firing with a feed forward action.

Full Text	FIELD OF THE INVENTION: The invention generally relates to frequency support method implemented in electro-hydraulic governing system of steam turbines. More particularly the invention relates to a control method in a turbine electro hydraulic controller for implementing a free governing mode of operation to arrest wide fluctuations of the grid frequency. BACKGROUND OF THE INVENTION: Electricity grid in many countries are generally susceptible to frequent fluctuations in grid frequency, varying between 48 hertz to 51.5 hertz. Such fluctuations are obviously detrimental to Power Plant equipment, the utilities and the consumers which result in grid collapse leadikng to loss of industrial production including great inconvenience to domestic consumers which in turn affects the law and order situation. One of the influencing factors for wide fluctuations in grid frequency is the disallowance of the governor system of the steam turbine to operate freely and modify the Turbine-Generator load depending on fluctuation of the grid frequency. The restrictions imposed on the governing system generally are in the form of switching off the frequency support device, forcing the turbine admission valve to be wide open irrespective of load or frequency, and introducing dead bands and delay in actuating the frequency support device. Further, the frequency support device provided with the steam turbines are generally equipped with an electro-hydraulic governing system which is based on the objective of maintaining the grid frequency at a fixed value i.e. 50 or 60 Hz. The prior art device however provides a yery limited support in maintenance of the grid frequency, where frequency variations are very large. However, the grid authorities generally operate under the principle that in an electricity scarce country, the grid frequency can be maintained anywhere between 49 to 50.5 Hertz. But the frequent and sharp fluctuations in grid Frequency must be restricted through an appropriate frequency support mechanism designated as Free Governor Mode of Operation(FGMO). OBJECTS INVENTION: It is therefore an object of the present invention to propose a control method for implementing a Free Governor Mode of Operation in the steam turbines to restrict wide fluctuations of the grid frequency. Another object of the present invention is to propose a control method for implementing a Free Governor Mode of Operation in the Steam turbines which arrest transient swings in grid frequency by generating a floating frequency set point. An yet another object of the present invention is to propose a control method for implementing a Free Governor Mode of Operation in the Steam turbines which limits load change due to frequency fluctuation such that fluctuation in steam parameters are restricted within tolerance limits to avoid harmful cycling effect on various equipment. A further object of the present invention is to propose a control method for implementing a Free Governor Mode of Operation in the Steam turbines which is capable of effecting larger load corrections if frequency goes beyond IEGC band of 49 to 50.5 Hz. A still further object of the present invention is to propose a control method for implementing a Free Governor Mode of Operation in the Steam turbines which is capable of exercising automatic supplementary control to bring the load back to the original value. A still another object to propose a control method for implementing a Free Governor Mode of Operation in the Steam turbines which avoids constant fluctuations in load by introducing a small dead band in frequency support mechanism. SUMMARY OF INVENTION Accordingly, there is provided a control method in a turbine electro hydraulic controller for implementing a free governing mode of operation to restrict the effects on wide fluctuations of the grid frequency, the method comprising the steps of integrating a previous value of the actual frequency to generate a floating frequency set point, the set point is reset to new values in a gradual manner corresponding to a time constant of an integrator; generating a hold signal when change in frequency exceeds the new frequency set value, the hold signal freezes the set value to the last value held; generating a load correction signal corresponding to the frequency error within the frequency band of 49.0 to 50.5 Hz, the proportional load correction value is limited to +/-5% of rated load and added to the load set point; removing the hold signal when the frequency stabilizes to the new value, the load returning to the original value as the frequency error becomes zero(Automatic Supplementary Control); carrying out a load change according to droop characteristics if frequency falls below 49 Hz, the load change is limited to 10%; carrying out load change according to droop characteristics if frequency goes above 50.5 Hz, the load change is limited to 10%; and transmitting a load change signal to modify turbine load set point, and simultaneously transmitting a signal to boiler controls to make the changes in fuel firing with a feed forward action. RIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS: Figure 1 shows a schematic diagram of the control logic for implementing the control method according to the invention. DETAILED DESCRIPTION OF THE INVENTION: As shown in figure-1, the method includes:- - Previous value of actual frequency is integrated to generate the floating frequency set point. If frequency changes, set point changes to the new value in a gradual manner as per the integrator time constant. - For frequency changes more than a set value, a hold signal is generated which freezes the set value to the last value held. - Within the frequency bank of 49.0 to 50.5 Hz the proportional controller generates a load correction signal corresponding to the frequency error. The proportional load correction value is limited to +/-5% of rated load and is added to the load set point. - When the frequency stabilizes to the new value, hold signal is removed and the load comes back to the original value as error becomes zero. Also the system is ready to make the next correction if the frequency changes again. - If frequency falls below 49 Hz, the load change shall be carried out as per droop characteristics and is limited to 5%. If frequency goes above 50.5 Hz, load change is carried out as per droop characteristics and is limited to 10%. - While load change signal acts on turbine load set point, a signal Is given to Boiler controls to make the changes in fuel firing with a feed forward action. By implementing the method according to the invention, it is possible to arrest sharp swings in grid frequency by unloading or loading the steam turbine and further prevent inadmissible fluctuation in steam parameters. The control logic for implementing the method is shown in Figure -1 . A brief description of the control logic to be implemented in EHTC is given below: 1. Floating frequency set point: The speed actual signal is used to generate the floating signal. The time delayed set point generated by the actual value of speed. In the event of any change in frequency, the set point changes to a value equal to the new frequency (speed) value. This change happens in a slow ramp. 2. For frequency changes more than the set value, for a duration varying between minimum 3 minutes to a maximum of 6 minutes (proportional to frequency change) a HOLD signal is generated. This signal forces the floating frequency set point to the last set value held. This is done to ensure a proportional correction for sufficient duration to effect changes in boiler parameters. 3. A proportional controller compares the set value and actual value and generates a frequency influence signal with a proportional gain corresponding to droop setting. This proportional component is given in full magnitude at the beginning and starts coming down as the deviation reduces on account of frequency set point slowly approaching the new actual value. 4. The proportional values of frequency influence is added to the load set point to form the final load set point going to load controller, This will increase the load signal. This signal is in addition to the pressure dependent load correction (already available) 5. After the frequency stabilizes to a value within the dead band then the hold signal is removed. After the removal of hold signal the set point will now settle to the new frequency value and proportional frequency influence starts coming down as the deviation reduces. With this the system is now available for the next frequency change. 6. In the frequency range beyond IEGC band i.e. blow 49.0 Hz & above 50.5 Hz the frequency influence as per droop characteristic will become effective and drives the frequency influence signal to ± 10% (this limit can be decided as per site conditions). 7. While the frequency influence acts on turbine load set point a signal is given to Boiler control to make changes in fuel firing with a feed forward action for a quick response. 8. The pressure controller of EHTC In Limit Pressure mode ensures that the load is reduced to maintain the boiler header pressure, in the event of a sudden pressure drop more than set limit value. The performances of the boiler parameters are monitored and the controls tuned for optimum performance to ensure that the load changes do not cause any disturbances in the boiler parameters. Depending on the other conditions of the plant, the limitations of load change can be adopted keeping in view the regulatory requirements for FGMO. WE CLAIM: 1. A control method in a turbine electro hydraulic controller for implementing a free governing mode of operation to restrict the effects on wide fluctuations of the grid frequency, the method comprising the steps of: - integrating a previous value of the actual frequency to generate a floating frequency set point, the set point is reset to new values in a gradual manner corresponding to a time constant of an integrator; - generating a hold signal when change in frequency exceeds the new frequency set value, the hold signal freezes the set value to the last value held; - generating a load correction signal corresponding to the frequency error within the frequency band of 49.0 to 50.5 Hz, the proportional load correction value is limited to +/-5% of rated load and added to the load set point; - removing the hold signal when the frequency stabilizes to the new value, the load returning to the original value as the frequency error becomes zero(Automatic Supplementary Control); - carrying out a load change according to droop characteristics if frequency falls below 49 Hz, the load change is limited to 10%; carrying out load change according to droop characteristics if frequency goes above 50.5 Hz, the load change is limited to 10%; and - transmitting a load change signal to modify turbine load set point, and simultaneously transmitting a signal to boiler controls to make the changes in fuel firing with a feed forward action. 2. The method as claimed in claim 1, wherein the main and Reheat steam parameter fluctuations in the turbine are contained within allowable limits during the automatic load changes. 3. The method as claimed in claim 1, wherein a supplementary control is carried out to automatically relieve the operator from repeated manual intervention on each frequency variation in the grid. 4. A control method in a turbine electro hydraulic controller for implementing a free governing mode of operation as substantially described and illustrated herein with reference to the accompanying drawings.

Full Text

FIELD OF THE INVENTION:
The invention generally relates to frequency support method implemented in
electro-hydraulic governing system of steam turbines. More particularly the
invention relates to a control method in a turbine electro hydraulic controller for
implementing a free governing mode of operation to arrest wide fluctuations of
the grid frequency.
BACKGROUND OF THE INVENTION:
Electricity grid in many countries are generally susceptible to frequent
fluctuations in grid frequency, varying between 48 hertz to 51.5 hertz. Such
fluctuations are obviously detrimental to Power Plant equipment, the utilities and
the consumers which result in grid collapse leadikng to loss of industrial
production including great inconvenience to domestic consumers which in turn
affects the law and order situation.
One of the influencing factors for wide fluctuations in grid frequency is the
disallowance of the governor system of the steam turbine to operate freely and
modify the Turbine-Generator load depending on fluctuation of the grid
frequency. The restrictions imposed on the governing system generally are in the
form of switching off the frequency support device, forcing the turbine admission
valve to be wide open irrespective of load or frequency, and introducing dead
bands and delay in actuating the frequency support device.
Further, the frequency support device provided with the steam turbines are
generally equipped with an electro-hydraulic governing system which is based on
the objective of maintaining the grid frequency at a fixed value i.e. 50 or 60 Hz.
The prior art device however provides a yery limited support in maintenance of
the grid frequency, where frequency variations are very large.

However, the grid authorities generally operate under the principle that in an
electricity scarce country, the grid frequency can be maintained anywhere
between 49 to 50.5 Hertz. But the frequent and sharp fluctuations in grid
Frequency must be restricted through an appropriate frequency support
mechanism designated as Free Governor Mode of Operation(FGMO).
OBJECTS INVENTION:
It is therefore an object of the present invention to propose a control method for
implementing a Free Governor Mode of Operation in the steam turbines to
restrict wide fluctuations of the grid frequency.
Another object of the present invention is to propose a control method for
implementing a Free Governor Mode of Operation in the Steam turbines which
arrest transient swings in grid frequency by generating a floating frequency set
point.
An yet another object of the present invention is to propose a control method for
implementing a Free Governor Mode of Operation in the Steam turbines which
limits load change due to frequency fluctuation such that fluctuation in steam
parameters are restricted within tolerance limits to avoid harmful cycling effect
on various equipment.
A further object of the present invention is to propose a control method for
implementing a Free Governor Mode of Operation in the Steam turbines which is
capable of effecting larger load corrections if frequency goes beyond IEGC band
of 49 to 50.5 Hz.

A still further object of the present invention is to propose a control method for
implementing a Free Governor Mode of Operation in the Steam turbines which is
capable of exercising automatic supplementary control to bring the load back to
the original value.
A still another object to propose a control method for implementing a Free
Governor Mode of Operation in the Steam turbines which avoids constant
fluctuations in load by introducing a small dead band in frequency support
mechanism.
SUMMARY OF INVENTION
Accordingly, there is provided a control method in a turbine electro hydraulic
controller for implementing a free governing mode of operation to restrict the
effects on wide fluctuations of the grid frequency, the method comprising the
steps of integrating a previous value of the actual frequency to generate a
floating frequency set point, the set point is reset to new values in a gradual
manner corresponding to a time constant of an integrator; generating a hold
signal when change in frequency exceeds the new frequency set value, the
hold signal freezes the set value to the last value held; generating a load
correction signal corresponding to the frequency error within the frequency band
of 49.0 to 50.5 Hz, the proportional load correction value is limited to +/-5% of
rated load and added to the load set point; removing the hold signal when the
frequency stabilizes to the new value, the load returning to the original value as
the frequency error becomes zero(Automatic Supplementary Control); carrying
out a load change according to droop characteristics if frequency falls below 49
Hz, the load change is limited to 10%; carrying out load change according to

droop characteristics if frequency goes above 50.5 Hz, the load change is limited
to 10%; and transmitting a load change signal to modify turbine load set point,
and simultaneously transmitting a signal to boiler controls to make the changes
in fuel firing with a feed forward action.
RIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 shows a schematic diagram of the control logic for implementing the
control method according to the invention.
DETAILED DESCRIPTION OF THE INVENTION:
As shown in figure-1, the method includes:-
- Previous value of actual frequency is integrated to generate the floating
frequency set point. If frequency changes, set point changes to the new
value in a gradual manner as per the integrator time constant.
- For frequency changes more than a set value, a hold signal is generated
which freezes the set value to the last value held.
- Within the frequency bank of 49.0 to 50.5 Hz the proportional controller
generates a load correction signal corresponding to the frequency error.
The proportional load correction value is limited to +/-5% of rated load
and is added to the load set point.

- When the frequency stabilizes to the new value, hold signal is removed
and the load comes back to the original value as error becomes zero. Also
the system is ready to make the next correction if the frequency changes
again.
- If frequency falls below 49 Hz, the load change shall be carried out as per
droop characteristics and is limited to 5%. If frequency goes above 50.5
Hz, load change is carried out as per droop characteristics and is limited to
10%.
- While load change signal acts on turbine load set point, a signal Is given
to Boiler controls to make the changes in fuel firing with a feed forward
action.
By implementing the method according to the invention, it is possible to arrest
sharp swings in grid frequency by unloading or loading the steam turbine and
further prevent inadmissible fluctuation in steam parameters.
The control logic for implementing the method is shown in Figure -1 . A brief
description of the control logic to be implemented in EHTC is given below:
1. Floating frequency set point: The speed actual signal is used to
generate the floating signal. The time delayed set point generated by
the actual value of speed. In the event of any change in frequency,
the set point changes to a value equal to the new frequency (speed)
value. This change happens in a slow ramp.
2. For frequency changes more than the set value, for a duration
varying between minimum 3 minutes to a maximum of 6 minutes
(proportional to frequency change) a HOLD signal is generated. This
signal forces the floating frequency set point to the last set value
held. This is done to ensure a proportional correction for sufficient
duration to effect changes in boiler parameters.

3. A proportional controller compares the set value and actual value and
generates a frequency influence signal with a proportional gain
corresponding to droop setting. This proportional component is given
in full magnitude at the beginning and starts coming down as the
deviation reduces on account of frequency set point slowly
approaching the new actual value.
4. The proportional values of frequency influence is added to the load
set point to form the final load set point going to load controller,
This will increase the load signal. This signal is in addition to the
pressure dependent load correction (already available)
5. After the frequency stabilizes to a value within the dead band then
the hold signal is removed. After the removal of hold signal the set
point will now settle to the new frequency value and proportional
frequency influence starts coming down as the deviation reduces.
With this the system is now available for the next frequency change.
6. In the frequency range beyond IEGC band i.e. blow 49.0 Hz & above
50.5 Hz the frequency influence as per droop characteristic will
become effective and drives the frequency influence signal to ± 10%
(this limit can be decided as per site conditions).
7. While the frequency influence acts on turbine load set point a signal
is given to Boiler control to make changes in fuel firing with a feed
forward action for a quick response.

8. The pressure controller of EHTC In Limit Pressure mode ensures that
the load is reduced to maintain the boiler header pressure, in the
event of a sudden pressure drop more than set limit value.
The performances of the boiler parameters are monitored and the controls
tuned for optimum performance to ensure that the load changes do not cause
any disturbances in the boiler parameters. Depending on the other conditions of
the plant, the limitations of load change can be adopted keeping in view the
regulatory requirements for FGMO.

WE CLAIM:
1. A control method in a turbine electro hydraulic controller for implementing
a free governing mode of operation to restrict the effects on wide
fluctuations of the grid frequency, the method comprising the steps of:
- integrating a previous value of the actual frequency to generate a floating
frequency set point, the set point is reset to new values in a gradual
manner corresponding to a time constant of an integrator;
- generating a hold signal when change in frequency exceeds the new
frequency set value, the hold signal freezes the set value to the last value
held;
- generating a load correction signal corresponding to the frequency error
within the frequency band of 49.0 to 50.5 Hz, the proportional load
correction value is limited to +/-5% of rated load and added to the load
set point;
- removing the hold signal when the frequency stabilizes to the new value,
the load returning to the original value as the frequency error becomes
zero(Automatic Supplementary Control);
- carrying out a load change according to droop characteristics if frequency
falls below 49 Hz, the load change is limited to 10%;
carrying out load change according to droop characteristics if frequency
goes above 50.5 Hz, the load change is limited to 10%; and
- transmitting a load change signal to modify turbine load set point, and
simultaneously transmitting a signal to boiler controls to make the
changes in fuel firing with a feed forward action.

2. The method as claimed in claim 1, wherein the main and Reheat steam
parameter fluctuations in the turbine are contained within allowable limits
during the automatic load changes.
3. The method as claimed in claim 1, wherein a supplementary control is
carried out to automatically relieve the operator from repeated manual
intervention on each frequency variation in the grid.
4. A control method in a turbine electro hydraulic controller for implementing
a free governing mode of operation as substantially described and
illustrated herein with reference to the accompanying drawings.

Documents:

00401-kol-2006-claims.pdf

00401-kol-2006-correspondence other.pdf

00401-kol-2006-correspondence others-1.1.pdf

00401-kol-2006-description complete.pdf

00401-kol-2006-drawings.pdf

00401-kol-2006-form-1-1.1.pdf

00401-kol-2006-from 1.pdf

00401-kol-2006-from 2.pdf

00401-kol-2006-from 3.pdf

00401-kol-2006-gpa.pdf

401-KOL-2006-ABSTRACT.pdf

401-KOL-2006-AMANDED CLAIMS.pdf

401-KOL-2006-AMANDED PAGES OF SPECIFICATION.pdf

401-kol-2006-claims.pdf

401-kol-2006-correspondence.pdf

401-kol-2006-correspondence1.1.pdf

401-KOL-2006-DESCRIPTION (COMPLETE) 1.1.pdf

401-kol-2006-description (complete).pdf

401-KOL-2006-DRAWINGS 1.1.pdf

401-kol-2006-drawings.pdf

401-KOL-2006-EXAMINATION REPORT REPLY RECIEVED.pdf

401-kol-2006-examination report.pdf

401-kol-2006-form 1.1.pdf

401-kol-2006-form 1.pdf

401-kol-2006-form 18.1.pdf

401-kol-2006-form 18.pdf

401-KOL-2006-FORM 2-1.1.pdf

401-kol-2006-form 2.pdf

401-kol-2006-form 3.1.pdf

401-kol-2006-form 3.pdf

401-kol-2006-gpa.pdf

401-kol-2006-gpa1.1.pdf

401-kol-2006-granted-abstract.pdf

401-kol-2006-granted-claims.pdf

401-kol-2006-granted-description (complete).pdf

401-kol-2006-granted-drawings.pdf

401-kol-2006-granted-form 1.pdf

401-kol-2006-granted-form 2.pdf

401-kol-2006-granted-specification.pdf

401-KOL-2006-OTHERS.pdf

401-KOL-2006-PA.pdf

401-kol-2006-reply to examination report.pdf

401-kol-2006-specification.pdf

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Patent Number

251686

Indian Patent Application Number

401/KOL/2006

PG Journal Number

13/2012

Publication Date

30-Mar-2012

Grant Date

28-Mar-2012

Date of Filing

02-May-2006

Name of Patentee

BHARAT HEAVY ELECTRICALS LIMITED

Applicant Address

REGIONAL OPERATIONS DIVISION (ROD), PLOT NO: 9/1, DJBLOCK 3RD FLOOR, KARUNAMOYEE, SALT LAKE CITY, KOLKATA-700091, HAVING ITS REGISTERED OFFICE AT BHEL HOUSE, SIRI FORT, NEW DELHI-110049, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	BATRA KUL BHUSHAN	BHARAT HEAVY ELECTRICALS LIMITED, RANIPUR, HARIDWAR
2	RANGANATHA SRIGIRIPURA KRISHNASWAMYIYENGAR	BHARAT HEAVY ELECTRICALS LIMITED, RANIPUR, HARIDWAR
3	BANSAL NARESH KUMAR	BHARAT HEAVY ELECTRICALS LIMITED, RANIPUR, HARIDWAR
4	SATHYAKUMAR YALAMANCHILI NAGALINGA RAVI NAGA	BHARAT HEAVY ELECTRICALS LIMITED, RANIPUR, HARIDWAR
5	VISHWANATHAN BANAVARA SUBBARAYA	BHARAT HEAVY ELECTRICALS LIMITED, RANIPUR, HARIDWAR

PCT International Classification Number

N/A

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA