|Title of Invention||
"JOINT CONTROL OF TURBINES IN A POWER PLANT"
|Abstract||A joint control device generator sets in a powder plant comprising digital governors (GOV1-GOV n) of individual machines connected in a token ring or multi-drop configuration, thereby permitting any individual machine to be the master communicating with the other machines in the ring for joint control.|
|Full Text||JOINT CONTROL OF TURNBINES IN A POWER PLANT
Field of Application
This invention relates to joint control device for turbines in a power plant by connecting the governors of individual machines in a token ring (multi-drop) configuration.
Back ground of the Invention
In general an electric generating station (power plant) may comprise of several turbine-generator sets (machines) of similar or different ratings.
Each turbine has a governor to regulate its output and speed. To facilitate control from a control room which may be located at a distance, a remote control desk is provided in the control room for each governor. The remote control desk provides the necessary control and instrumentation to start, stop and regulate the turbine. From the individual remote control desk each machine is started and synchronized to the grid, one machine at a time. After all the machines are synchronized, the output of each machine has to be adjusted depending on the grid requirements. When a centralized load dispatch center is deciding on the required generation from each utility, the operator will be given a target for the total generation requirement. The operator has to load all active machines uniformly to meet the demand. In the absence of joint control, the operator has to operate each machine from its own remote control desk.
A suitable joint control, which will enable control of all active machines uniformly from a single set point control, will greatly simplify this task. Two set points, viz. load setting and permanent droop setting of each machine in joint control are controlled by the joint control mechanism.
In the existing method, joint control is realized by having a separate joint control desk, which is interfaced to each of the governors. In the analog hardware based electronic governors, the joint control feature is realized in the manner described hereunder.
To interface to the joint control desk, each electronic governor has to be equipped with separate hardware comprising motorised potentiometers, and set-point tracking and follow-tip circuit. In each governor, individual motorised potentiometers are used for the purpose of generating set points such as speed, load and permanent droop.
When the machine is on individual control, the load and permanent droop set point motorised potentiometers are controlled by the RAISE and LOWER push buttons on the remote control desk of that machine. The governor's control circuit use the set-point signal generated by these individual potentiometers.
When the machine is selected from individual to joint control, the individual motorised potentiometers for load and permanent droop are disconnected from the RAISE and LOWER push buttons of the machine's remote control desk, and instead are controlled by the set-point tracking and follow-up circuit provided in the electronic governor. The set-point tracking & follow-up circuit tracks the positions of the load and permanent droop motorised potentiometers of joint control which are located in the joint control desk, and controls the corresponding individual motorised potentiometers of the governor to follow the joint control motorised potentiometers. The governor % control circuits are disconnected from the individual motorised potentiometers and are instead connected to the set-point signal generated by the joint control potentiometers.
When the machine is deselected from joint control, the individual motorised potentiometers for load and droop are disconnected from the tracking and follow-up circuit and reconnected back to the RAISE and LOWER push buttons of the individual remote control desk. Similarly, the governor's control circuits are also switched back from the joint control potentiometers to the individual potentiometers. Potential free contacts of relay are used to perform the required physical switching.
The joint control desk consists of two motorised potentiometers for generating load and permanent droop set-points. RAISE and LOWER push buttons, for each of the two motorised potentiometers is provided on the joint control desk. Additionally, the set point signals for load and droop generated by each governor is fed to the joint control desk. Joint control desk requires independent instrumentation to indicate the load set point, permanent droop set point, total MW generation of the utility, etc. To indicate total MW generated on the joint control desk, separate MW transducers will be required exclusively for this purpose, one for each machine. This instrumentation is useful as the command received from the bad dispatch center is for the total load generation of the utility. It will then become easy for the operator to observe the deviation from the given total demand requirement and give a corrective signal from the joint control desk. In the absence of this total generation feedback on the joint control desk, the operator will have to go to each remote control desk, note down the generation of each machine, sum them up manually, and then compare with the demand requirement. The MW transducers provided for each governor cannot be tapped for this purpose as they are 4 -20 mA current output signals.
Thus the existing method of realising joint control feature is by connecting the governors of the various machines to a separate joint control desk in a star configuration, i.e each machine is connected to a dedicated port on the joint control desk by means of a separate cable through which the joint control desk and the individual machine communicate with each other.
Joint control hardware provided in the joint control desk performs the joint control action based on the following algorithm :
Each machine is started independently, one at a time, and synchronised to the grid.
After all the machines are synchronised to the grid, each machine is initially in individual control, and the load and droop are controlled by the RAISE and LOWER push buttons provided on the individual! remote control desk of that machine.
The first machine is selected to be on joint control, manually by the operator by means of a switch provided for this purpose. After selection, the joint control hardware that is provided in the joint control desk makes the load and droop set point signals generated by the corresponding joint control motorised potentiometers match the load and droop set point signals generated by that machine % governor.
After the joint control motorised potentiometers generate the same signal as the individual motorised potentiometers of the first machine selected, the set point signals to the governor circuits are switched from the individual potentiometers to the joint control potentiometers. The joint control hardware provided in the governor
disconnects the individual motorized potentiometers from the RAISE and LOWER push buttons of the remote control desk, and connects them to the set point tracking and follow-up circuit. Now the machine responds to the raise /lower commands of the joint control desk.
When the second machine is selected to be on joint control, the joint control hardware in the joint control desk finds the average of the joint control settings and the second machine settings and makes the joint control settings equal to the average value. Then the set point signals to the second machine's governor are switched from the individual motorised potentiometers to the joint control potentiometers. Also the individual motorised potentiometers are disconnected from the raise/lower push buttons of the remote control desk, and are connected to the tracking and follow-up circuit. Now the second machine also responds to the joint control commands.
When any other machine (Nth machine) is selected to be on joint control, the joint control hardware calculates the new average for the joint control settings using the formula.
Where : 3C(n) = The new joint control setting
JC(n-l) = The present joint control setting when (n-1) machines are on
Nth = The setting of the Nth machine when it is selected to be on joint control
The joint control motorised potentiometers are made to match the new average values and then the set point signal to the governor control circuits are switched from the individual potentiometers to the joint control potentiometers. The individual potentiometers are disconnected from the raise/lower switches on the remote control desk and connected to the tracking and follow-up circuit. The Nth machine also now responds to the joint control commands.
When any machine is selected from joint control to individual control, the set point signals to the governor's control circuits are switched from joint control potentiometers to individual control potentiometers. The individual potentiometers are switched from tracking circuit to the raise/lower push buttons of the remote control desk. The machine is now on individual control and responds to commands from the individual remote control desk of the machine.
The existing method has the following disadvantages:
One disadvantage of the existing method is that in the event of failure of the joint control hardware in the joint control desk, joint control operation is not possible. The only way to overcome this problem is by having redundancy in the joint control desk.
Another disadvantage is that each machine has to be independently connected to the joint control desk. Increase in the number of machines will result in an increase in the interface hardware in the joint control desk. Cabling to the joint control desk also increases.
Yet another disadvantage is that the motorized potentiometers used are subject to wear and tear and will lead to unreliable operation over a period of usage. This calls for frequent maintenance.
A further disadvantage of the existing method is that the joint control desk requires additional independent instrumentation and exclusive MW transducers, one for each machine, and cabling for the same.
Summary of the Invention
The main object of the present invention is to implement the joint control feature using digital governors connected in a token ring or multi-drop configuration which permit communication between all governors connected to the ring.
Digital governors offer unique technical advantages which have been exploited in the present invention to significantly improve the technique of joint control.
Digital governor hardware is modular in construction, comprising a passive back plane, which supports the hardware modules of the governor such as central processing unit (CPU), analog input module (AIM), analog output module (AOM), digital input module (DOM), digital output module (DOM), etc. Each of these modules sits on the passive back plane and exchange data/control signals over a bus. The back plane consists of these bus signals, and can be extended to support more bus based modules if required. To implement joint control, a bus based serial interface module supporting RS485 interface, is the only extra hardware module required in the digital governor.
For joint control the digital governors implement is following algorithm:
Each machine is independently started and synchronized to the grid, one at a time.
The RS485 serial communication module in each digital governor is connected to the corresponding RS485 module in the next digital governor, in chain fashion. This single cable communication link between the governors allows any governor to interact with any other governor, not necessarily the next one in the chain, by assigning a unique address to each governor.
Any governor can be the sender, and it can send the information to the desired receiving governor by tagging the unique address of the receiver to the data packet. This data packet, along with the receiver address, is available to all the governors simultaneously, but is read and processed by the governor with the matching address. This type of networking is called multi-drop configuration.
When all the machines are on individual control, there is no need to communicate any information and hence no communication takes place. The RS485 communication module comes into picture only when joint control commences.
A machine is selected to be on joint control by means of a switch provided on the remote control desk of each machine. Two lamp indications are provided on each remote control desk, one to indicate that the machine is on joint control, and second to indicate that it is the Master of joint control. The first machine selected to be on joint control becomes the master automatically, and both lamps will glow, indicating that
the machine ie on joint control and also that it is the master. When the first selected machine becomes the master, it communicates this information to ail other machines. This remote control desk of the master serves the purpose of the joint control desk. The raise/lower push buttons of this remote control desk will now control the joint control load and permanent droop settings. The instrumentation of the remote desk of the master will now serve as the instrumentation for joint control. The present settings of the master will become the current settings of the joint control.
When any other machine is selected from individual control to joint control, the new machine selected has the information that a joint control master already exists, and hence only one lamp glows, indicating that it is selected to joint control, but the other lamp indicating master will not glow on the remote control desk of this machine.
The new machine selected on joint control will pass information regarding its present load and droop settings to the master. The master then calculates the average of the current joint control settings and the settings of the new machine. The master makes the joint control settings equal to the new average, and passes these new settings to all the machines on joint control, including the new machine. The load and droop settings of the new machine, which are used by the control software of the digital governor, are made equal to the joint control settings and the raise/lower keys on the remote control desk of the new machine are disabled. Thus the new machine responds to the commands from the master remote control desk, and not from its own remote control desk.
The governor of the new machine communicates the MW generated by the machine to the master, which the digital governor senses using the MW transducer meant for governor control. With this information the master is able to indicate the total MW generated by all the machines on joint control, without requiring any exclusive MW transducers.
In a digital governor all the set point values are digital in nature, and stored as variables. Hence motorised potentiometers are eliminated. The switching of the governor control signals from joint control to individual control and vice-versa is done in software thereby eliminating relays for this purpose. The tracking an d follow up circuits are eliminated as it is realized in software.
When the master remote control desk is not functioning, all the remaining machines can be deselected from joint control, so that all are on individual control. Then any healthy machine can be selected first to be on joint control, thereby becoming the new master. The remaining machines can be selected to be on joint control as described earlier.
One advantage of the present invention is that the hardware required to implement joint control in each governor is greatly reduced to only one RS485 module per governor. Joint control desk is totally eliminated, thereby eliminating the need for additional instrumentation and control hardware. The significant reduction in hardware and associated cabling automatically increases reliability.
Another advantage Is that the need for additional exclusive MW transducers, one per machine, is also eliminated.
Yet another advantage is that the redundancy to implement joint control increases with the number of machines, without requiring any additional hardware.
A further advantage of the present invention is that an increase in the number of machines does not result in increase of joint control hardware, as is the case with the existing method. Instead, redundancy for joint control increases.
Thus the present invention provides a joint control system of turbine generator sets in a power plant comprising digital governors of individual machines connected in a token ring or multi-drop configuration, thereby permitting any individual machine to be the master communicating with the other machines in the ring for joint control.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWISNGS Figure 1 shows the existing joint control desk in a star configuration Figure 2 shows the joint control system of the present invention in a token ring or multi-drop configuration.
In Fig. 1, the governors GOVi - GOVn of various machines are connected in star configuration by connecting each governor to a dedicated port PI - Pn on the joint control desk JCU. The connection between the ports and the governors is by means of separate cables C1 - Cn through which joint control desk JCU communicates with the individual machine and vice versa.
In the system of the present invention the governors GOV1 - GOVn of various machines are connected in a token ring or multi-drop configuration as shown in Fig.2. This arrangement allows any one of the governors GOV1 - GOVn to communicate with any other governor. A bus based serial interface module supporting RS485 interface is provided for implementing joint control. Each governor GOVI - GOV2 is connected to the next governor by means of RS485 module in the token ring.
1. A joint control device for turbine generator sets in a powder plant comprising digital governors (GOVi — GOV n) of individual machines connected in a token ring or multi-drop configuration, thereby permitting any individual machine to be the master communicating with the other machines in the ring for joint control.
2. The joint control device as claimed in claim 1, wherein each digital governor is connected to the next governor in the ring by means of an RS485 module.
3.A joint control device for turbine generator set in a power plant substantially as herein described and illustrated in the accompanying drawings.
|Indian Patent Application Number||1537/DEL/1999|
|PG Journal Number||12/2008|
|Date of Filing||14-Dec-1999|
|Name of Patentee||BHARAT HEAVY ELECTRICALS LTD.|
|Applicant Address||BHEL HOUSE, SIRI FORT, NEW DELHI-110049, INDIA.|
|PCT International Classification Number||F01D 17/00|
|PCT International Application Number||N/A|
|PCT International Filing date|