TECHNICAL INFORMATION ABOUT THE NEUTRAL ZONE OPERATION

(kind courtesy Prakash Tendulkar. Contents reproduced here with his permission)

In the picture captioned   as "Instructions for driver to lower DC panto", the sign says "Open DS for speed below 40 kms." (picture # 1).

DS is an acronym for Disconnecting Switch. It is designed to ensure that switching of electrical power supply to the locomotive. It allows switching over from 25 KV AC catenary to 1500 V DC catenary and vice versa.

In fact, only 1500 V DC catenary supply transits via this switch; for 25 KV AC catenary supply does not transit via this switch.

This switch isolates 1500 V DC downstream circuits from 25 KV and connects them (DC circuits) to ground.

The purpose of this sign is, if the speed is less than 40 kms., the driver should keep on accelerating till the last moment and then isolate DC circuits on the fly. This is like emergancy shut down rather than normally smooth one.

For AC circuits, DJ performs the same function. Unlike DS which is inside the loco, DJ is on the roof. DS is a manual circuit breaker, DJ is pneumatically operated.

Someone had also asked earlier about minimum speed limit in neutral section. The neutral section is theoratically one OH structure long.However, if you look at cross overs, it becomes two structures long, half structure long DC + half structure neutral, one structure completely neutral followed by half section neutral + half section AC.

So the train needs enough momentum to overcome rail friction and travel little over two structures. Under normal circumstances, it is no big deal. Some brake binding should be okay too. But EC pull or parting of brake pipe can make the loco a dead duck.

I know a Parsi driver (who happens to be Viraf's relative) who faced this dead duck situation due to EC pull.

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Some addendum.

If driver throws off DS at the end of DC zone and does not lower DC panto, no harm is done even when he enters AC section. The moment AC supply enters the panto, it will energize the relays necessary to lower DC panto automatically. Same holds true for failure to lower AC panto while entering DC section.

BHEL does not cut corners on safety.

Both the pantos have same type of insulators, the only difference is # of blades. There is no restriction in using twin blade panto as "AC Alternate".

In DC section, the single bladed panto can be used as "DC Alternate" when twin bladed panto is inoperative. However, traction motors must be run in 6S (All six motors in series) only as against 6S and 2P-3S under normal circumstances to limit current drawn by panto.

Prakash

(SLIGHTLY MODIFIED TO ENSURE CONTINUITY)

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