Question 1: Explain how high currents and voltages are measured with the assist of instrument transformers. Draw diagrams to explain your answer. Explain the benefits of instrument transformers as regards extension of range of current and voltage on high voltage a.c. systems.
Question 2: Describe the drawbacks of shunts and amplifiers when used for extension of range. Describe how instrument transformers are a better replacement for shunts and multipliers especially for high range values.
Question 3: Define the given terms as used for instrument transformers:
a) Transformation ratio.
b) Nominal Ratio.
c) Terms Ratio.
d) Ratio correction factor.
e) Burden.
Use specific illustrations to exemplify your answer.
Question 4: Draw the equivalent circuit and phasor diagram of the current transformer. Derive the expressions for ratio and phase angle errors.
Question 5: Describe the effect of secondary burden on the ratio and phase errors of the current transformer.
Question 6: Describe the effect of the given on the performance of current transformers:
a) Change of primary winding current.
b) Change of secondary circuit burden and
c) Change of frequency.
Question 7: Describe the main sources of errors in current transformers. Explain the design and constructional features employed in current transformers to decrease the errors.
Question 8: Explain the constructional details of wound and bar type current transformers for reduction of the ratio and phase angle errors. Explain the features incorporated in the windings to lessen the leakage reactance.