TPR Circuit and Concept of Cross protection- Part 26

TPR Circuit:

- TR is normally present at Location Box.
- TPR is placed at Relay Room.
- TR and TPR are connected by an underground signalling cable.
- Two front contacts of TR are used for double cutting and the back contact of
  TR is used for cross protection and TPR is picked up in the relay room.

CONCEPT OF CROSS PROTECTION

Cross protection is an arrangement by which any vital relay such as HR, WNR, WRR is prevented from picking up, in case a foreign feed appears on relay terminals when the conditions are not favorable for the relay to pick up.  

This is achieved by shunting the vital relay coils with the contacts of those relays, which are not favorable for the picking up of relay.

For example while ALSR is in pick up condition, the concerned HR should not pick up.   For this HR relay is shunted with ALSR front contact.

When 1 ALSR is picked up if feed appears on the HR coil, then it gets short circuited through 1ALSR front contact and HR cannot pickup.

Similarly, WNR/WRR should not pick up when WLR is dropped.  

The cross protection arrangements for WNR/WRR is: -

This wiring arrangement also ensures the integrity of cross protection loop i.e., if the cross protection loop get disconnected at either end of the cross protection contact, the circuit for the relay also gets disconnected.