Open Type: In telephone exchanges, 50 V battery room, power panel.
Enclosed Type: Bus trunking
- Outdoor type - not in use in telecom.
- Indoor type – mostly used.
- Compound immersed.
- Gas immersed.
- 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|
The bus bars are normally rectangular with long vertical side. The spacing/clearances between busbars are given in the tables below:
|Rated Voltage (kV)||Minimum distance to earth (mm)||Minimum clearance between phases (mm)|
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.
|Rated Voltage (kV)||Minimum clearance to earth (mm)||Minimum clearance between phases (mm)|
|No.||Description||Nomonal System Voltage (kV)|
|Up to 0.25||Up to 0.65||Up to 1.1||Up to 3.3||Up to 6.6||Up to 11|
|In air||In oil||In air||In oil||In air||In oil||In air||In oil||In air||In oil||In air||In oil|
|A.||Clearance phase to pase direct||10||13||13||19||13||25||19||51||25||89||38||127|
|B.||Clearance phase to earth direct||10||13||13||19||13||25||13||51||19||64||25||76|
|C.||Creepage phase to phase over insulation||13||16||19||25||19||32||38||76||64||146||89||216|
|D.||Creepage phase to earth over insulation||13||16||19||25||19||32||25||51||32||89||44||127|
|E.||Creepage phase to earth over cable surface||19||25||25||38||25||51||32||76||48||127||73||178|
|Rated voltage (kV)||Minimum clearance to earth (mm)||Minimum clearance between phases (mm)||Safety sectional clearance (mm)|
- 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.
- 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:
- RMS Current.
- Rated voltage.
- Short time duration rating.
Factors for busbar design:
- 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)
- Cross section of material.
- Temp rise during normal operation.
- Temp rise during short circuit, fault (for 1.3 s).
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.