AUTO SWITCHED NEUTRAL SECTION

AUTO SWITCHED NEUTRAL SECTION

This type of ASNS has been developed by M/s Arthur Flury.

In Australia, Taiwan, and China for 25 kV A.C.the ASNS works as a primary and has been functioning satisfactory.

The ASNS is nothing but a breaker with a load current-operated closing mechanism.

 Hence, this breaker has a minimum pick-up value (20 Amp.).

This makes limitations on the operation of the ASNS when EMU/ Loco current is less than 20 Amp.

As the current is interrupted by the pantograph in this case, a flashover will occur.

But the magnitude will be very less and the contact wire and the pantograph can withstand this flashover. Secondly, there is under-voltage trip protection on the EMU / Loco breaker.

When the incoming 25 kV supply is lost, it drops out after 660 ms. If EMU / Loco takes time more than 660 ms to travel the ASNS, the EMU / Loco breaker drops out and in such case, the motorman/driver has to reclose the breaker after entering the next live section.

OPERATION OF ASNS

Loco moves on the section X

1. At section insulator Point A, pantograph touches energized Skid Rod at point B.. A little further movement of Pantograph from point B  breaks contact from section insulator runners causing current to pass through HT coil 1.

2.The moment HT coil 1 gets energized, ( Minimum current required 20 Amps) VCB  closes in 15 Milli Sec. and energizes section DE at 25 kV AC from Phase 1 Supply.                

3.  At point C panto touches the trailing end of section insulator at point D which is already charged at 25 kV AC, from Phase 1 supply.

4. A little further movement of panto from point D results in breaking the panto contact from Skid Rod BC thus de-energising HT coil 1.

5. Within 15 Milli Sec of de-energization of HT coil 1, VCB 1 opens out and section  DE becomes neutral.

6 . As the panto is having solid contact with the contact wire in section DE at the time of opening out of VCB 1 resulting in switching off the 25kV power supply, there is no flashover on the pantograph, even though Loco might have been drawing full current. At this position, Loco DJ is in a closed position and the Master controller (MP) may be on any notch.

7. Loco travels in the neutral section between points  E F G & I a distance of 14.9 meters, which must be covered within 0.6 Sec. to avoid DJ opening through Q 44 relay. If the loco is with power ON & drawing current of more than 20 amps. then DE will remain energized otherwise not.

8. At Section insulator point I panto bridges Skid Rod at point J charged from phase 2 supply, resulting in the instant rushing of current through HT coil 2  thus closing VCB 2 in 15 milliseconds, which in turn charges the section H I at 25 kV AC from phase 2 supply.

9.At the point I & J there is a possibility of heavy flashover on the panto pan as it enters from the neutral section to the live 25 kV AC section through HT coil 2.This flashover will continue till the section HI gets charged at 25 KV from phase 2 supply after the closing of VCB 2.

10.Further at Skid Rod point K, panto bridges point L of section insulator which is charged at 25 kV AC supply from phase 2.

11.A little further movement of pantograph from point L results in panto leaving contact from Skid Rod J K, thus de-energizing HT coil 2.

12.Within 15 Milli Sec of de-energization of HT coil 2, VCB 2 opens out and section H I becomes neutral.

LIMITATIONS OF ASNS

ASNS can be operational only when EMU/ Loco current is more than 20 Amp.

The ASNS is not suitable for locomotives where the two consecutive pantographs are interconnected electrically.