Bus Bar

Type: 

  1. Open Type: In telephone exchanges, 50 V battery room, power panel.

  2. Enclosed Type: Bus trunking

    1. Outdoor type - not in use in telecom.
    2. Indoor type – mostly used.
    3. Compound immersed.
    4. Gas immersed.
    5. Oil immersed.

Derating factor for enclosed type is as below:

Outdoor:0.85 - 0.95
Indoor (Good ventilation):0.6 - 0.8
Indoor (Poor ventilation):0.5 - 0.6
Black Painted:1.2

The bus bars are normally rectangular with long vertical side. The spacing/clearances between busbars are given in the tables below:

Spacing / clearance between bus bars / connectors (open and enclosed, indoor, air insulated)
Rated Voltage (kV)Minimum distance to earth (mm)Minimum clearance between phases (mm)
OpenEnclosedOpenEnclosed
0.41519162619
0.626193219
3.351515151
6.664648989
11.07777127127
15.0102102165165
22.0140140242242
33.0223223356356

Note: The above data is for altitude below 1000 m and shall be increased by 3 % for each 300 m higher altitude. Also for atmospheric pollution and electrically exposed installations, special consideration is to be given.

Note: Clearances shall not be less than the above unless the conductors are covered with solid insulation (additional to oil or compound) and are capable of withstanding the appropriate power frequency test voltage.

Spacing / clearance between busbars/connectors (immersed in oil or compound)
Rated Voltage (kV)Minimum clearance to earth (mm)Minimum clearance between phases (mm)
0.61313
3.31319
6.61926
11.02638
15.03245
22.04564
33.06489
Clearances and creepage distance as per IS 4821 : 1868 (all dimensions in mm)
No.DescriptionNomonal System Voltage (kV)
Up to 0.25Up to 0.65Up to 1.1Up to 3.3Up to 6.6Up to 11
In airIn oilIn airIn oilIn airIn oilIn airIn oilIn airIn oilIn airIn oil
A.Clearance phase to pase direct1013131913251951258938127
B.Clearance phase to earth direct101313191325135119642576
C.Creepage phase to phase over insulation13161925193238766414689216
D.Creepage phase to earth over insulation1316192519322551328944127
E.Creepage phase to earth over cable surface19252538255132764812773178
Clearance between open outdoor busbars for electrically exposed / un-exposed installations
Rated voltage (kV)Minimum clearance to earth (mm)Minimum clearance between phases (mm)Safety sectional clearance (mm)
0.61401402591
111781782591
15216216 
222793302743
333814322743
666867873048
1108649913353
132106712193505
220177820584267

Note

  1. Clearances shall not be less than the above. Also when the method of mounting of insulators is such that prevention of birds/vermin is not possible, larger clearances are required to be given.
  2. For rated voltage of 110 kV and above, the above clearances are applicable only to effectively earthed system.

Ratings: Following ratings are required for selection of busbar:

  1. RMS Current.
  2. Rated voltage.
  3. Frequency.
  4. Short time duration rating.

Factors for busbar design: 

  1. Material: Material for busbar should have low resistivity, good mechanical properties, high softening temperature and of course should be economical. Electrolytic grade copper or aluminium is used for bus bar (E41E-WP)
  2. Cross section of material.
  3. Temp rise during normal operation.
  4. Temp rise during short circuit, fault (for 1.3 s).
  5. Insulator height, strengthy and creep: The bending force experienced:

    F = 2.04 × Isp² × 10-02 × L / r kg⋅force, where r is gap between busbars and Isp is peak short circuit current.

    Factor of safety is considered to be 4, so F × H = Sk / 4, where Sk is the strength of insulator.

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