Arrangement for tapping line

GENERAL

Some times it may be necessary to construct a transmission line by tapping the existing transmission line to feed load of a nearby Sub-Station. The tapping is done by Loop-In-Loop-Out (LILO) arrangement by providing slack jumpers with the existing transmission line. the general arrangement is shown in the following sketch-

Fig. 6-1.

PRECAUTIONS

The following precautions are necessary while tapping any transmission line-

i. Solid Tee-off line from any existing transmission line is not allowed under any circumstances.

ii. The tapping is done from B or C-type angle tower only by Loop-In-Loop-Out arrangement. In case Suspension tower is provided at the location from where it is proposed to tap the line, then the suspension tower is replaced by B-type angle tower.

iii. Loop-In-Loop-Out arrangement is done either by providing Double circuit towers on the proposed tapping line or by providing Single circuit towers separately for Loop-In and separately for LILO line should terminate on towers designed for dead end conditions at both ends, i.e. at the tapping point as well as at Sub-Station end, so that  there is no problem of differential tension.

iv. ____________________________________________________ dead-end tower one circuit may be taken to the proposed Sub-Station end at right angle (Loop-In). The other circuit may be taken out from the S/S (Loop-Out) and should be connected square to this dead-end tower.

v. The tapping from the existing line is done by providing slack span jumpers, which should be connected with the existing line by means of PG Clamps (Parallel Groove Clamps). It is advisable to provide at least 3 Nos. PG Clamps at each connecting point to secure the jumpers safely from better reliability considerations.

SKETCH FOR LILO ARRANGEMENT

The typical arrangement for Loop-In-Loop-Out from existing Single circuit as well as Double Circuit transmission line are shown in the following diagrams as a guideline.

Fig. 6-II  

 Fig. 6-III

Note:

1. 1 No. Suspension disc for top conductor at location 123 and 124 'A' type tower shall be reduced only and suspension disc shall be reduced for top conductor to have proper clearance from tower body.

2. Compression should be used for taking out jumper at 'C' type tower introduced for Tee off.

3. Extension plate and extension link should be left for jumpring arrangement of bottom conductor through peak.

DOUBLE CIRCUIT TOWER

Fig. 6-IV.

FRONT & TOP VIEW OF A TYPICAL TAPPING OF 400KV SINGLE CKT. LINE BY DOUBLE CKT. TOWER