General

Power line crossing involved in the route of transmission line under construction are also very important. Adequate clearance is required to be maintained between bottom conductor of the line going above from top most conductor/earth wire of the line going below under maximum temperature conditions as given hereinafter.

Clearances Required

• The clearance required to be maintained between 132 KV, 220 KV & 400 KV lines from 66 KV, 33 KV & 11 KV going below are given hereunder

TABLE 8-I

• It is customary that line having higher voltage should pass above the line having lower voltage. In case the voltages of two lines are same then the line being constructed afterwards should cross the existing transmission line by providing necessary extensions 15/25m to normal towers so as to achieve necessary electrical clearances as illustrated above.

Arrangement of Crossing

• The power line crossing should be done at such a place where maximum clearance is obtained at the crossing point between the two lines. For this purpose tower of the higher voltage or the upper line should be as close as possible preferably about 50 meter or so, from the crossing point and _____ span or maximum sag point of the lower voltage or the line passing below should be at the crossing point.
• L.T. lines or secondary lines from which necessary clearance is not available may be got diverted at other suitable places so as to achieve proper clearance.

Typical Arrangements of Power Line Crossing

A typical arrangements of power line crossing done in the past are shown in the Figure no. 8-I as a guide line for carrying out power line crossings. In the sketch existing 400 KV lines has been crossed underneath by 220 KV line by providing gantries. In some cases crossing has been done by using 220 KV double Circuit Tower after removing first panel.

Fig. 8-I

• C dead end type tower are to be used on either side of the gantries -
• The end towers are to be placed square to the line i.e. no angle of deviation is to be permitted on line side. The entire angle on dead end tower is to be diverted on the gantry side.
• Maximum Tension of conductors and ground wire in the crossing spans between the dead end towers not to exceed 100 KV.
• Double tension insulator strings are to be used on the dead end tower sides over the gantries to avoid uplift.
• Minimum clearance of 6.1 meters has to be maintained at all points between 400 KV and 220 KV line conductors under worst condition.
• The earth wire of the dead end towers has to be lowered suitably along the towers before connecting it to the gantries as shown.