Proceedings of the ASME 2014 Gas Turbine India Conference GTINDIA2014 December 15-17, 2014, New Delhi, India
GTINDIA2014-8118 DEVELOPMENT OF A DAMPER CONTROL SYSTEM FOR COMBINED CYCLE THERMAL GAS POWER PLANT Amit Kumar Mondal Department of Electronics, Instrumentation & Control, University Of Petroleum and Energy Studies, Dehradun, India e-mail:
[email protected]
Vindhya Devalla Department of Aerospace Engineering, University Of Petroleum and Energy Studies, Dehradun, India e-mail:
[email protected]
Vivek Kaundal Department of Electronics, Instrumentation & Control, University Of Petroleum and Energy Studies, Dehradun, India e-mail:
[email protected]
Dr. Kamal Bansal Department of Electrical, Power and Energy, University Of Petroleum and Energy Studies, Dehradun, India e-mail:
[email protected]
Abstract— This paper addresses a technique to solve the problem of heat dissipation in solenoid coil of the solenoid valve which is controlling the hydraulic damper by using pulse width modulation (PWM) switching technique with low frequency. In addition to this damper controlling is achieved via wireless controlling. By using PWM based low frequency switching technique the gas turbine trip will be protected. PWM is achieved by microcontroller and wireless control is done by ZigBee.
a) The outlet is of the exhaust gas is allowed to escape directly into the atmosphere. b) The outlet is of the exhaust is sent through the heat exchanger to extract the heat energy for useful energy. The dampers should operate as per the system condition i.e. at the time of tripping the system and at the time of taking the combined cycle plant into service. Currently this process is achieved in semi autonomous way. In the proposed paper damper controlling is achieved via wireless controlling.
Keywords— Damper Controlling, USART, Analog to Digital Convertor, Pulse Width Modulation (PWM); Microcontroller; RF (ZigBee)
The conventional damper control system can be divided into two sub systems:
NOMENCLATURE L
Inductance
R
Resistance
f
Frequency (Crystal frequency coupled with Atmega 16)
τ
Time Constant
Ton
On Time
Toff
Off Time
TTotal
Total Time Period
Vo
Output Voltage
Vs
Supply voltage of Solenoid coil
a) Its control system in the plant control room so as to fulfill the control interlock system requirement. b) Its feedback system to the plant operator. Also, conventional damper control system faces problem of tripping due to (3, 4): a).The burning of solenoid coil. b).Fastening of solenoid valve of hydraulic damper. The control systems are extremely important the process requirement & feedback system are extremely essential in order to maintain the plant safety. In case of the auto control system failure, the operator has to take the control on manual and control the operations manually from control room or from the local. It is also important for the system calibration of servomotor and its transducers after unit over haul or any problem on the particular system is attended. The schematic diagram of the feedback system of damper control is as in fig. 1.
INTRODUCTION The existing combined cycle thermal power plant uses the exhaust gas exit from gas turbine in two modes (1, 2).
The mechanical linkage & transducers are installed at local and then through junction boxes and control wires, the signals are brought to the control room. Generally,
1
Copyright © 2014 by ASME
control room is at a distance from plant.. The length of the control wire may be from several meters to few kilometers in some cases. There are few disadvantages of wired route of control cables: a) Aging affect of wires. b) Laying of wires is costly. c) Fault detection is costly.
and another one is slave section. Different modules used in these sections are as follows: (i) Power supply: Our microcontroller is working on 5V/500mA so we have to design a power supply of this
Fault identification and replacement of such cables is one of the major problems in the maintenance departments. It takes more than normal time due to safety and site restrictions, adding the maintenance cost.
Fig.3: Flowchart for obtaining minimum voltage
Fig. 1: Damper Control feedback system
Fig. 2: Actuation using pulse width modulation
In the fig.2 it has been clearly described that how the controlling operation would be achieved. We are controlling the solenoid valve by PWM technique using OCRIA and OCRIB pins of Atmega 16 microcontroller marked as pin no. 18 and 19 respectively. We had initialized the timer register to control the electrical solenoid valve in which it is controlled by the analog manner.
Fig.4: MOSFET controlling using Atmega 16
rating. For this we are converting the AC supply using 90-9 transformer 1000uf/35V electrolytic capacitor, 1N4XXX series diode, 7805 regulated IC, 330Ω resistor, and 5mm red led. (ii) Display section (6): The lcd (liquid crystal display) jhd162A (16x2) is interfaced with AVR microcontroller to display the data information. The LCD data pins 11,12,13,14 are connected to port C (PC0 through PC3) of the AVR microcontroller. The control pins of LCD 4,5,6 Register-select (RS) , Read/write(R/W) and enable are interfaced with PD6, PD5 and PD7 of of Atmega 16 microcontroller.
Burning and fastening of solenoid valve produces a critical problem of system stability and also of availability. In past, service air method was used for cooling solenoid control valve (4). Generally for actuating the solenoid valves, it requires rated voltage supply. But we have to find out the minimum voltage that can hold the solenoid control valve, it can be achieved by adjusting the voltage from the rated voltage to zero voltage, on doing so we will get the minimum voltage required to hold the circuit.
(iii) Sensors: The temperature sensor (7) series are precision integrated circuit temperature sensor. It gives output in the form of analog voltage and its output voltage is linearly proportional to temperature. We have to use ADC (analog to digital) feature of controller in order to read its output. Limit switches are directly mechanically operated by the motion of the operating lever; it gives direct digital output which can readily be taken as an input to the microcontroller.
On getting the minimum voltage (5), we will follow the algorithm shown in fig. 3. The desired control mechanism can be achieved via microcontroller Atmega 16, using its OCR pins as a PWM input to the gate terminal of MOSFET as shown in fig. 4, also the controlling has been described in fig.3.
(iv) Relay: Relays are an electro-mechanical switches which is used to control AC devices. To turn ON a relay we have to give supply to the coil of relay, if we want to control relay through controller we have to use transistor as switch.
HARDWARE DEVELOPMENT We are here providing a wireless solution of the system so it contains two sections one is master section
2
Copyright © 2014 by ASME
(v) Microcontroller (8): There is a whole wide range of microcontroller available in the market. But this particular project is developed using AVR series of microcontroller (ATMEGA16) because of its inbuilt ADC port and its variable frequency.
SOFTWARE DEVELOPMENT Microcontroller, when it is used to operate as a wireless network, it involves few steps as shown in fig. 9. The
(vi) ZigBee Module (9): It is a low power and low cost 2.4 GHz transceiver, designed for wireless applications. ZigBee is designed for 2400- 2483.5 MHz ISM (Industrial, Scientific and Medical) and SRD (Short Range Device) frequency band. It provides extensive hardware support for packet handling, data buffering, burst transmissions, clear channel assessment, link quality indication, and wake-on-radio. The main operating parameters and the 64-byte transmit/receive FIFOs of CC2500 can be controlled via an SPI interface. In a typical system, the CC2500 will be used together with microcontroller and few additional passive components. Figure 5 and 6 are the block diagram of transmitting and receiving section of prototype and figure 7 and 8 are the proteus model of the same.
Fig. 8: Proteus (trial software) Simulation model for Receiver Side
software development of designed system is with the help of a high level language, AVR Studio 4 is a software for writing program for any AVR series of microcontroller‟s .After writing the program we have to compile it with the help compiler and debugger and if there is no error it converts it into machine level language and generates a asm (assembly) file as shown in fig. 10. Fig 5: Block diagram of Data transmitting section
Fig 6: Block diagram of parameter monitoring section (Receiving Section)
Fig 9: Steps for software development
This .asm file is used for programming the microcontroller memory with the help of a programmer. In order to Burn the program into program memory we can use serial programmer, parallel programmer or USB programmer, we are using Robokits AVR USB programmer (10) to burn the program. If the system performs as desired by the user and performs all the tasks efficiently and effectively the software development phase is over and the project is ready to be installed in any of the industrial sites otherwise we have to repeat this process in order to achieve desired output. While writing the program we are mainly using these features: Fig. 7: Proteus (trial software) Simulation model for Transmitter side
(i) USART (8): In this system we are using USART for serial communication so we are using only UBRR, UDR, and UCSCRA (for TX and RX enable only) registers only.
3
Copyright © 2014 by ASME
(ii) ADC (8): In this system we are using ADC only for converting Analog voltage of sensors into digital.
Fig. 11: Schematic diagram of Turbine exhaust to boiler Fig 10: Steps for dumping a program
In fig. 11, it has been clearly shown about the damper positions and its way of execution. Also, there are few other criteria‟s over which the opening and closing depends, although the algorithm of interlocking is been followed and they are as follows:
(iii) LCD (6): The functionality of the attached LCD module (jhd162A) is control using this file. This c file contain controls the initialization of the LCD code control the data (movement, characteristics and location of the cursor).
1. Both BID‟s & BYD‟s may remain open at the same time, but both BID‟s & BYD‟s should not remain close at the same instant.
CONTROL MECHANISM & SOFTWARE ALGORITHM Opening and closing of BID‟s (Boiler Inlet Damper) and BYD‟s (Boiler Bypass Damper) depends on few conditions as enlisted in table 1.
2. BID1&2 and BYD 1&2 not close – 2 out of 3 limit switches appears at 72% open status.(Taking 3 limit switch for open, 3 limit switch for close condition of any of the boiler damper)
Table.1: Damper Conditions
Sl. No. 1
2
3
4
5
6
Damper positions BID1 - OPEN, BID 2-CLOSE & BYD1&2CLOSE BID2OPEN,BID1CLOSE & BYD1&2CLOSE BID1&2OPEN& BYD1&2CLOSE BYD 1&2OPEN & BID1&2 CLOSE BID 1 &2CLOSE & BYD 1 &2 –CLOSE BID 1&2 difference >20 % position
WHRP
GT
Boiler Trip
GT on Load
Boiler Trip
GT on Load
Abnormal Condition
Boiler on Load
GT on Load
Final Condition
Boiler Trip
GT on Load
Starting condition
Boiler Trip
GT Trip
Boiler Trip
GT on load
Shutdown/ Unit Stand by Abnormal Condition
3. BID 1&2 and BYD 1&2 not open – 2 out of 3 limit switches appears at 12 - 14% open status.(vice versa of point 2, stated above)
Case Description Abnormal Condition
4. Whenever GT (Gas Turbine) tripsa. BYD‟s fast open & b. Then BID‟s get close.
4
5.
BID‟s full open & BYD‟s close status - i.e.GT & waste heat recovery boiler are in operation.
6.
Conditions for BID‟s opening: a. GT in service(GT breaker "ON")/ CC Flame” ON"/ GT load 200 Bar).
in solenoid coil of the solenoid valve is resolved properly. Current and voltage in terms of duty cycle has been shown in fig. 13 and snap shots of simulation results are shown in fig. 14, 15, 16 and 17 showing different percentages of opening under different percentages of duty cycles. The figures show the result of PWM output of damper in virtual environment of Proteus Software.
Algorithm for PWM for Damper Control using AVRStudio4 Algorithm shows only PWM technique in Atmega microcontroller. To make a wireless Control we have to initialize USART port of microcontroller and write the same algorithm for wireless control.
Initialize PWM timer1 of Atmega Void main () // initialize main program { LCD_Initialize 16 Bit initialization adc_values, error; 8 Bit initialization temporary value; Initialize i; ICR1=312; // top value for DC Motor Initialize ADC Port { adc_values=ReadADC Channel Zero; Error=adc_values; If (temporary value>512) { For (i=0; i
