IRSE Exam Forum

Nandhakumar · 29-09-2010, 04:58 AM

Hi PJW,

Could you explain about Multi relay track circuit and in which case it has to be used?

**PJW** · 29-09-2010, 07:24 AM

(29-09-2010 04:58 AM)Nandhakumar Wrote: Hi PJW,

Could you explain about Multi relay track circuit and in which case it has to be used?

Do you mean
a) a track circuit having a second relay at the feed end as well as the main relay at the other end, or
b) a long track circuit that is one section to the signaller but for functional reasons has to be composed of several separate ones actually trackside?

Nandhakumar · 29-09-2010, 09:22 AM

(29-09-2010 07:24 AM)PJW Wrote:
(29-09-2010 04:58 AM)Nandhakumar Wrote: Hi PJW,

Could you explain about Multi relay track circuit and in which case it has to be used?

Do you mean
a) a track circuit having a second relay at the feed end as well as the main relay at the other end, or
b) a long track circuit that is one section to the signaller but for functional reasons has to be composed of several separate ones actually trackside?

Yes, Please explain about item (a)

**Peter** · (This post was last modified: 29-09-2010 10:03 AM by Peter.)

Quote:
Quote:Do you mean
a) a track circuit having a second relay at the feed end as well as the main relay at the other end, or
Yes, Please explain about item (a)

Where there are problems which give poor shunting characteristics or leakage through the ballast from other track circuits give the risk that the relay could remain energised when a legitimate train shunt is at the opposite end of the track, a second relay is placed at the feed end as well and either TR down will occupy the section.

**PJW** · 29-09-2010, 02:44 PM

(29-09-2010 10:02 AM)Peter Wrote:
Quote:
Quote:Do you mean
a) a track circuit having a second relay at the feed end as well as the main relay at the other end, or
Yes, Please explain about item (a)
Where there are problems which give poor shunting characteristics or leakage through the ballast from other track circuits give the risk that the relay could remain energised when a legitimate train shunt is at the opposite end of the track, a second relay is placed at the feed end as well and either TR down will occupy the section.

The reason why the real TR could be invalidly up would be that not only is the rail insulation bad and there be some form of leakage / ballast battery affect, but also there could be a rail breal, high resisitance jumper within the track circuit bonding. Obviously for a plain line dc track there is practically no resistance along the length of the TC so that the rail volts at the real TR and the feed end TR will be practically identical- obviously if there is muchpointwork that has many intermediate jumpers to achieve series bonding, then this may not be the case as there could be high (or even infinite) resistance. In that scenario the train could be close to the feed end, a disconnection at an intermediate place in the track and the normal TR kept energised via extraneous leakage current from an adjacent track or elsewhere.