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What are bushings in transformers used for?
They are used to filter contaminants from the transformer oil.
They are used to cool the transformer oil.
They are used to connect the transformer to the power grid.
They are used to insulate the transformer leads as they come out through the tank.
They are used to insulate the transformer leads as they come out through the tank.
Transformer bushings are insulating devices that allow an energized conductor to pass through a grounded tank or barrier. Their primary function is to provide the necessary electrical insulation between the high-voltage conductor and the earthed metallic transformer tank.
IS 2099 / IEC 60137
Transformer bushings are insulating devices that allow an energized conductor to pass through a grounded tank or barrier. Their primary function is to provide the necessary electrical insulation between the high-voltage conductor and the earthed metallic transformer tank.
E=dVтАЛ тАФ Electric field intensity where V is voltage and d is the insulation distance.
C=ln(r2тАЛ/r1тАЛ)2╧А╧╡LтАЛ тАФ Capacitance per unit length of a cylindrical insulation system.
The bushing creates a capacitive stress grading system to manage the electric field. By employing layers of conductive inserts or capacitance graded insulation, it ensures that the potential gradient E=dVтАЛ does not exceed the dielectric strength of the insulating material (porcelain, resin, or oil-impregnated paper), preventing flashover at the point of penetration.
Prevents arcing between the conductor and the grounded transformer tank.
Acts as an electrical termination point for power lines.
Provides mechanical support for the transformer leads.
Can be classified as bulk type (porcelain) or condenser type (oil-impregnated paper).
High dielectric strength for extreme voltages.
Reliable isolation between metallic tank and HV leads.
Weatherproof design for outdoor operation.
Susceptible to moisture ingress if gaskets fail.
Porcelain components are prone to mechanical impact damage.
Power transformers for grid connectivity.
Distribution transformers.
High voltage switchgear.
Option A is incorrect because oil filtration is handled by the Oil Purification System or Buchholz relay.
Option B is incorrect because cooling is performed by radiators or cooling fans/pumps.
Bushings are designed to withstand impulse voltages defined in insulation coordination standards.
D is correct тАФ They are used to insulate the transformer leads as they come out through the tank.
Always remember that bushings are NOT cooling devices; confusion often arises because they are located near the cooling fins, but their primary design is dielectric insulation.
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