A high-energy capacitor consists of a pair of parallel metallic plates, separated by a paper layer, rolled up and immersed in a liquid dielectric. The dielectric is a mineral oil, and the combined paper-oil dielectric is found to have a dielectric strength of 6 x 107 V/m, relative permittivity 3.3 and volume resistivity 3 x 10⁹ m. (i) If the spacing between the plates is 0.6mm, determine the maximum theoretical operating voltage of this capacitor. Explain why you should avoid operating close to this voltage. (ii) The total capacitance is measured to be 58.4nF. Estimate the effective cross-sectional area of the plates. (iii) Assuming the relative permittivity of the dielectric remains unchanged, calculate its loss tangent at a frequency of 1MHz. (iv) Suggest two ways of increasing the energy storage capacity of this capacitor design and explain your reasoning.
A high-energy capacitor consists of a pair of parallel metallic plates, separated by a paper layer, rolled up and immersed in a liquid dielectric. The dielectric is a mineral oil, and the combined paper-oil dielectric is found to have a dielectric strength of 6 x 107 V/m, relative permittivity 3.3 and volume resistivity 3 x 10⁹ m. (i) If the spacing between the plates is 0.6mm, determine the maximum theoretical operating voltage of this capacitor. Explain why you should avoid operating close to this voltage. (ii) The total capacitance is measured to be 58.4nF. Estimate the effective cross-sectional area of the plates. (iii) Assuming the relative permittivity of the dielectric remains unchanged, calculate its loss tangent at a frequency of 1MHz. (iv) Suggest two ways of increasing the energy storage capacity of this capacitor design and explain your reasoning.
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Q3 Part b please
Transcribed Image Text:Q3.
a) Dielectrics are class of material, capable of storing energy by polarisation
in the presence of an applied electric field.
(i)
The relative permittivity (or dielectric constant) is a dimensionless
quantity relating the dielectric properties of a material to those of a
vacuum. Explain briefly why it is that polar dielectrics typically
exhibit higher relative permittivity than non-polar dielectrics.
(ii) With the aid of diagrams, describe any two of the principal
polarising mechanisms in a dielectric material,
(iii) Why does the relative permittivity and loss change with the
frequency of the applied electric field, and what is meant by the term
relaxation frequency? Can you suggest an application where a high
dielectric loss tangent might be desirable?
b) A high-energy capacitor consists of a pair of parallel metallic plates,
separated by a paper layer, rolled up and immersed in a liquid dielectric.
The dielectric is a mineral oil, and the combined paper-oil dielectric is
found to have a dielectric strength of 6 × 107 V/m, relative permittivity
3.3 and volume resistivity 3 × 10⁹ m.
(i)
If the spacing between the plates is 0.6mm, determine the maximum
theoretical operating voltage of this capacitor. Explain why you
should avoid operating close to this voltage.
(ii)
The total capacitance is measured to be 58.4nF. Estimate the
effective cross-sectional area of the plates.
(iii) Assuming the relative permittivity of the dielectric remains
unchanged, calculate its loss tangent at a frequency of 1MHz.
(iv) Suggest two ways of increasing the energy storage capacity of this
capacitor design and explain your reasoning.
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