Write Up On Aux Prds
Write Up On Aux Prds
Write Up On Aux Prds
3530-101-01-TR-PVI-T-006 / REV 00
PAGE 01 OF 06
DATE
DESCRIPTION
00
30/07/2008
Initial Release
PREPARED
CHECKED
APPROVED
CATII
SIMHADRI PRDS WRITEUP.DOC
3530-101-01-TR-PVI-T-006 / Rev 00
SHEET 02 OF 06
INTRODUCTION:
The purpose of the control system is to maintain the pressure and temperature of the PRDS header at the
values set by the set point stations, which is located in the control room console. The control system uses
microprocessor hardware design based on Max-DNA system, manufactured by Electronics Division / BHEL /
Bangalore. The control system comprises of basically eleven control loops, namely:1) High temperature (HT) PRDS header pressure control loop (Main steam)
2) High temperature PRDS header temperature control loops:a) Spray water pressure control loop (Normal line)
b) Spray water temperature control loop (Normal line)
c) Spray water pressure control loop (Bypass)
d) Spray water temperature control loop (Bypass)
3) Low temperature (LT) PRDS header pressure control loop (CRH steam)
4) Low temperature PRDS header temperature control loops:
a) Spray water pressure control loop (Normal line)
b) Spray water temperature control loop (Normal line)
c) Spray water pressure control loop (Bypass)
d) Spray water temperature control loop (Bypass)
5) Pressure control loop to plant station A/C equipment.
1) H.T PRDS HEADER PRESSURE CONTROL (Main steam/ CRH steam):
The PRDS header pressure is maintained at a pre-set level receiving steam from either main steam line or
CRH steam line. The pressure controller receives the set point signal from the set point station located at the
SG-MMI and compares it with the process feedback signals (4 to 20mA) received from the two pressure
transmitters located at the HT PRDS header. The deviation between the set point and the process feedback is
processed through a PI controller and the demand signal is fed to the control actuator through drive control
interface module and an electro-pneumatic converter. There are two independent pressure controllers, one for
taking steam from main steam and the other for taking steam from cold reheat line. Only one pressure
controller will be in operation at a time depending on the availability of steam in MS or in CRH header.
2) H.T PRDS HEADER TEMPERATURE CONTROL:
The temperature controller receives the set point signal from the set point station located at the SG-MMI and
compares it with the process feedback mill volts signals received from the temperature elements (redundant
duplex NiCr-NiAl thermocouples) located at the H.T PRDS header. The deviation between the set point and
the process feedback is processed through a PI controller and the demand signal is fed to the control actuator
through drive control interface module and an electro-pneumatic converter. The temperature controller
receives the (maximum of) feed forward signal from the MS pressure control valves (AS-22 (LBG10AA101))
position transmitter or from CRH PRDS pressure control valve AS-26 (LBG21AA101) position transmitter.
2.1) H.T PRDS SPRAY WATER PRESSURE CONTROL:
The spray water pressure controller receives the set point signal from the set point station located at the SGMMI and compares it with the process feedback signals received from the pressure transmitters (redundant)
located at the upstream of temperature control valve FD-31 (LAF20AA103). The deviation between the set
point and the process feedback is processed through a PI controller and the demand signal is fed to the
control actuator through drive control interface module and an electro-pneumatic converter. Spray water
pressure controller FD30 (LAF20AA102) receives a feed forward signal from HT temperature control valve
FD-31 (LAF20AA103).
Bypass temperature control valve FD28 (LAF21AA102) & spray water pressure control valve FD44
(LAF21AA101) is given in parallel to the above lines. Selection of by pass line will be decided by the operator
only upon failure of main line control valves and provisions shall be available in the MMI for selection of main /
bypass lines. Only one set of lines (i.e. FD28&FD44 or FD30&FD31) shall be opened at a time. Once bypass
line is opened by operator manually, main line shall be given a force close signal. Other operation and
interlocks shall be similar to that of main lines.
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3530-101-01-TR-PVI-T-006 / Rev 00
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e) FD-33 (LAF31AA201)
f)
FD-37 (LAF32AA201)
g) FD-43 (LAF10AA101)
h) FD-42 (LAF21AA201)
i)
AS-46 (LBG10AA202)
j)
k) AS-10 (LBG50AA202)
l)
AS-21 (LBG10AA211)
n) AS-18 (LBG90AA202)
o) AS-38
AS-181 (LBG40AA201)
m) AS-13 (LBG90AA201)
p) AS-39
3530-101-01-TR-PVI-T-006 / Rev 00
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7.2) The following block valve and motorised isolation valves are operable from SG-MMI which are applicable
for APRDS station headers (Controls for which are implemented unit -5 of SG-DDCMIS only and status
feedbacks will be given to unit-6 of SG-DDCMIS):
a) AS-12 (LBG50AA202)
b) AS-49 (LBG33AA201)
c) AS-03 (LBG91AA202)
d) AS-02 (LBG91AA201)
7.3) The following motorised inching (control) and pneumatic control valves are operable form SG-MMI
(applicable for each unit headers):
A) Control valves.
a) AS-22 (LBG10AA101)
b) AS-26 (LBG21AA101)
c) FD-30 (LAF20AA102)
d) FD-38 (LAF32AA101)
e) FD-35 (LAF31AA101)
f)
FD-46 (LAF31AA102)
g) FD-28 (LAF21AA102)
h) FD-44 (LAF21AA101)
i)
FD-47 (LAF32AA102)
j) FD-31 (LAF20AA103)
B) Inching valves.
a) AS-29 (LBG22AA202)
7.4) The following motorised inching and pneumatic control valves are operable form SG-MMI (applicable for
APRDS station headers - Controls for which are implemented unit-5 of SG-DDCMIS only and status
feedbacks will be given to unit-6 of SG-DDCMIS):
A) Control valves.
a) AS-04 (LBG91AA101)
B) Inching valves.
a) AS-05 (LBG91AA203)
7.5) All the above mentioned pneumatic / motorised (inching) control valves are operated through Drive
control Interface modules (DLI) located in the SG-MMI:
7.6) Opening of all the control valves are interlocked with its upstream motorised isolation valves so that when
the control valves are opened > 2%, isolation valves are to be fully opened automatically; and the isolation
valves will get a close command when the associated control valve is closed less that 2% with a time delay.
7.7) The valve FD-43 (LAF10AA101) shall close only when all the control valves namely AS-22
(LBG10AA101), AS-26 (LBG21AA101), AS-29 (LBG22AA202) are closed. FD-43 is a block valve, envisaged
with dual coil solenoid valve, each coil is rated for 24VDC.
7.8) The motorised inching valves AS-29 (LBG22AA202) need not be interlocked as they are normally closed
valves, opened only during initial start-up or after a long shutdown.
8) DETAILS OF SG-MMI:
The following facilities are available in the SG-MMI:
a) Auto / Manual station are available with open / close operation.
b) Set point station with indicators in engg. units.
c) Process value indicators with engg. units.
d) Position indication for motorised inching and control valves.
e) Open/ Close indication for motorised isolation valves.
f) Process signal selection from redundant process signals.
9) SYSTEM INTERLOCKS AND PROTECTION:
a) On MFT signal from FSSS system, HC and LC PRDS pressure control valves, temperature control valves
and spray water pressure control valves shall be closed.
b) Whenever the header temperature exceeds the too high set point the pressure control valves in operation
get a force close signal.
c) Whenever there is a failure of both process feedback signal which is used for control, the associated
control loop shall trip to manual mode.
d) Whenever the main valve is modulating in auto mode, if its bypass valves are opened manually, the main
valve will be given an auto-block signal.
3530-101-01-TR-PVI-T-006 / Rev 00
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e) When any control valves upstream and downstream isolation valves are closed, the control valve shall be
given a forced close signal, to prevent from drift opening.
10) SYSTEM SIGNAL INTERFACES:
a) This PRDS control system is implemented in SG-DDCMIS
b) The list of analogue and digital inputs/outputs of the system has been given in document ref. List of input
and output signals.
11) CONTROL INTERFACE FOR MOTORISED ACTUATORS:
a) Integral starters are used for motorised actuators and open/close commands (24V DC) are issued from
control panel and disturbance monitoring signals and open/close limit switch feedbacks will be provided
from integral starter.
b) For modulating drive the command to actuator shall be in the form of 4-20mA signal. The necessary
positioning circuit shall be provided.
c) The sequence of operation for integral bypass valve AS21 (LBG10AA211) is performed in the control
system itself. First, the integral bypass valve opens fully. The main valve is opened only after the bypass
valve is fully opened. On close command, both main and integral bypass valves shall close simultaneously.