Sunday, May 3, 2020

Step by Step Flow of Point Machine Operation - Part 15

Step by Step Point Machine Operation

Let us assume that the point is in normal position so indication is also normal (NWKR  ) 

Relays WNR, WRR, WJR, XR, NWR/RWR etc. are normally de-energised relays. With SM’s key ‘IN’, SMCR is up and WLR is Normally up .
To operate the point from Normal to Reverse. 

Steps : -    

(a)  Press Button is turned from `N’ to `R’ position.       
(b)  Relay WRR picks up proving   RWKR()    WNR() 

(c)  Normal indication relay, NWKR drops (since,WRR drop is proved in NWKR)()

(d)  Point Time Relay WJR picks up with WRR() XR()NWKR()RWKR() & WLR()    
(e)  Special (pt. time control) Relay XR picks up through WJR()and disconnects feed to WJR. 

(f)  With WJR(), the direct feed to condenser through WJR drop contacts is also disconnected.  Now WJR remains up with condenser feed through its own front contact and drop contacts of NWKR, RWKR. The timing of  WJR(depends upon the capacity of condensers.  The time will be normally 3-4 times then the time required for operation of point under normal conditions. 

(g) With WJR(), XR() and through WRR() RWR will be energized proving Normal operation   relay NWR drop.  

(h)  With RWR, the DC110 feed for point operation is directly fed through a point contactor relay RWCR. If the point is far away, then a repeater of  RWR ie. RWPR is energized near the point location. Through RWPR , the point contactor relay RWCR is energised and 110 V DC extended to point for operation.  

(i)  The point operation to reverse completed ,  reverse detection contacts are made and the relay RWKR pick up at Relay Room with NWKR(), WNR()  

(j)  RWKR pick up causes WJR to drop immediately, and WRR, XR  relays also drop. 

(k)  With all the point controlling relays dropped, the feed to point is cut off.  

(l) For the operation of point from ‘R’ to ‘N’,  the point knob is turned from reverse to normal and the corresponding relays for normal operation at relay room and location pick up. 

Finally the point is set to normal and NWKR is picked up at relay room. 

In case, the point indication fails due to any obstruction, etc, the feed to point will extend only for a limited time till WJR remains up with condenser feed discharge path and subsequently WJR drops and cut off supply to point.  

This is to limit DC110 to point, to prevent excess drainage which may damage Battery, Motor, Charger, Cable, Relay Contacts etc., in case of point not setting in time due to any obstruction.       

But Relay XR remains up through WNR/WRR up (not dropped since no indication) and its own front contact.  It is a special relay controls WJR and feed to point. 

Now the point is turned once again to `N’ and then to `R’ to drop XR. Then allows WJR to pick up and try once again to set the point. The sequence of pick up of relays remains same. 


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