Interlock, Protection & Start Permissive of Aux.

Equipment

- :A Presentation: -

Nisith Kumar Roy, Sr. Mgr. (E).

What is Permissive ?• Permissive is nothing but certain

conditions which are to be fulfilled for safe start of the related Equipment / Machine. It is one kind of Interlock & Protection for starting.

• In older days, the task of Interlock and Protection were achieved by using some Sensor / Detector and Electromagnetic Relay. But now a day, due to advancement of Technology and introduction of Computer in Process Industry, Solid State Relay and / or PLC are widely used for the purpose of Interlock and Protection.

- :Boiler Feed Pump: -

Interlock, Protection and Permissive

Boiler Feed Pump (BFP):• There are three numbers BFP having

50% MCR capacity. • Normally two numbers BFP are running

and other one remains as Stand-by. • The Stand-by BFP can be selected for

Auto Standby mode of Operation.• Auto Start as well Remote Manual Start

of each BFP is permitted.• To Start BFP, either in Auto or Manual,

following conditions which are Known as Permissive, are to be fulfilled.

Start Permissive of BFP:

Interlock of BFP:Start (ON) of BFP will cause: -

• Auto Opening of Cooling Water Valve (DMCW-63 for BkTPP) to supply Cooling Water to Working Oil Cooler and Motor Winding Cooler.

• Auto cut-out of Auxiliary Lube Oil Pump will take place with a Time Delay of 30 Seconds if Lube oil Header Pressure rises above 2.8 Kg / Sq.cm.

Interlock for Aux. Lube Oil Pump of BFP:

Sequential Start of BFP [Auto ]:• To select Auto Sequence Start of BFP the

Group Sequence Control Selector Switch is to be placed at Unfulfillment Criteria position (Auto Mode) and Sequence Control Switch of the Pump is to be selected for Auto Operation.

• Then START Command is to be issued from Control Desk / Control Panel.

• Operation will take place in Step as detailed in next Slides.

Auto Start Sequence of BFP:

Auto Start Sequence of BFP:

Auto Standby Start of BFP:• The Auto Standby Mode Start of BFP will activate if

both the under mentioned conditions are satisfied. Otherwise, concerned BFP, though it is selected for Auto Standby mode of operation, will not take start automatically in the event of tripping of any running BFP.

1. Boiler Load must be more than 40% MCR. 2. Other Two BFP are in Running Condition.

Auto Standby Start Sequence of BFP:

Auto Standby Start Sequence of BFP:

Tripping Alarm of Boiler Feed Pump:

Protection Trip of BFP: