17.Control Philosophy October 16, 2008

17.00.00    CONTROL   PHILOSOPHY

 

The control philosophy for different type of drives such as Bi-directional, unidirectional, solenoid operated, H.T .drives under C&I package  are detailed below :-

 

17.01.00   BI-DIRECTIONAL DRIVES ( INCHING OR    OTHERWISE )

 

(a)        All bi-directional drives shall be operable from remote i.e. from Central Control Room ( CCR ). Local operation of these drives is not envisaged.

 

(b)  Remote manual operation of all drives shall be done from Visual Display Unit / Monitor (VDU). Additionally back up remote operation through PB station mounted on Unit Control Panel (UCP) for some of the essential dives is provided. 

 

(c)   Remote control commands i.e. Open / close, generated from DCS shall be issued to MCC through interposing relays located in respective MCC.

 

(d)  Necessary electrical protections shall be realized at MCC, whereas process interlocks and protections shall be realized in DCS.

 

(e)   Following signal exchange shall take place between MCC & DCS.

 

-        Valve open & close command

-        MCC disturbance (when overload relay operates or MCC control power supply fails or MCC power supply is isolated ) for VDU alarm only.

 

(f)    Following signal exchange shall take place from valve actuator to DCS.

 

-        Valve status feed back by means of end position contact

( Open/Close )

-        Torque switch contacts ( Open / close )

-        Valve Position feed back ( 4-20 mA ) for inching duty drives.

-        Actuator Thermostat contact is wired directly to the MCC control circuit.

 

(g)   Emergency stop of the drive has been envisaged from the local push button

      provided near the drive.. Under locked position the drive operation is inhibited 

      from remote. The local emergency stop pushbutton shall be wired directly to MCC.

 

                   17.02.00     UNIDIRECTIONAL LT DRIVES

 

a)     Unidirectional LT drives shall be operable only from Remote i.e. 

      from CCR. Local operation of these drives is not envisaged except

      for LP dosing and Phosphate dosing system.

b)     Unidirectional LT drives shall be operable only from Remote i.e. from CCR. Local operation of these drives is not envisaged except for LP dosing and Phosphate dosing system.

 

c)     Remote/ Manual operation of all drives shall be done from VDU. Backup remote operation from PB station mounted on UCP is provided for some essential drives.

 

d)     Remote control commands i.e. start/stop, shall be generated from DCS and shall be issued to MCC through interposing relays located in respective MCC.

 

e)     Emergency stop of the drive has been envisaged from the local push button provided near the drive.. Under locked position the drive operation is inhibited from remote. The local emergency stop pushbutton shall be wired directly to MCC.

 

f)      Necessary electrical protections for the drive shall be realized at MCC, whereas process interlocks and protections are realized in DCS.

 

g)     Following signal exchange shall take place between MCC and DCS.

-        Drive start & Stop commands

-        Drive status feedback’s

-        MCC disturbance (when thermal overload relay operates, control power supply fails, Emergency local stop PB is pressed or MCC power supply is isolated ) for VDU alarm only.

 

h)      Suitable current transformer and transducer with two 4-20mA outputs shall be provided in MCC wherever drive rating is above 30KW and for a few essential drives below 30KW for remote monitoring in DCS and UCP. Auxiliary power supply to these transducers shall be from the control supply of the respective switchgears.

 

 

                   17.03.00   SOLENOID  OPERATED  DRIVES

 

a)     Solenoid operated drives shall be operated from remote from CCR. Local operation of these drives is not envisaged.

 

b)     Remote manual operation of all drives shall be done from VDU. However, backup remote operation from push button station mounted on UCP is provided for some essential drives.

 

c)      Remote control commands i.e. Open / Close, shall be generated from DCS and shall be issued to the solenoid through interposing relays located in the relay panel for the 240V AC / 24V DC operated solenoid drives.

 

d)     Necessary process interlocks shall be realized in DCS.

 

e)     The following signal exchange shall take place between solenoid operated drive and DCS for solenoids operating on 240V AC / 24V DC

 

-        Valve open/close command from DCS through interposing relay mounted in relay panel

-        Status feedback from the drive by means of limit switches.

 

 

17.04.00     H.T.DRIVES

 

a)     HT drives shall be operable only from remote i.e from CCR. However, the switchgear has two modes of operation i.e. Service and Test. Service mode is the normal mode of operation when the drive is operable from remote.

 

b)     The Test position is envisaged to test the switchgear, from switchgear as well as remote, during maintenance / commissioning.

 

c)      Remote manual operation of these drives shall be done from VDU. Backup e operation from UCP is provided for some essential drives.

 

d)     Remote control commands i.e. start/stop, shall be generated from DCS and shall be wired to switchgear through interposing relays housed in respective switchgear.

 

e)     Emergency stop of the drive has been envisaged from the local push button provided near the drive.,. Under locked position the drive operation is inhibited from remote. The local emergency stop pushbutton shall be wired directly to switchgear.

 

f)      Necessary electrical protection for drive shall be realized at switchgear, whereas process interlocks and protections are realized in DCS.

 

g)     Following signal exchange shall take place between switchgear and DCS.

-        Drive start & Stop commands

-        Drive status feedbacks by means of ON & OFF contacts ( in service/test position of switch gear)

-        Switch gear disturbance ( control power supply failure, trip coil supervision failure ).

-        switchgear available (Breaker spring charged, Breaker in service position and Switchgear selected in remote)

-        Master trip relay operated ( 86 Relay )  

-        Trip on overload

-        Alarm on overload

-        Emergency stop PB operated.

-         

h)     Current transducers with isolated two 4-20mA outputs shall be provided in the switchgear for monitoring the current in DCS and UCP. Auxiliary power supply to these transducers shall be from the control supply of the respective switchgears.