1 PIN TYPE INSULATOR: Are made in piece up to 25KV and above for up to 50KV only. You can add up the voltage by adding one more piece, they become uneconomical for higher voltage.
2. SUSPENSION TYPE INSULATOR: Are made in form of disc and a number of them used in a flexible string for the voltage range desires with the conductor being attached to the lower end for 400KV lines, 19 discs of overall length 3.84m are used.
3 STRAIN TYPE INSULATOR: Are obtained often a string of suspension insulator is used in a horizontal position. They are mainly used in line terminal and crossed end roads.
An autotransformer is supplied at 240V. If the secondary is tapped to give 60V with a load current of 12A, calculate the other two circuit currents and show the direction of current and voltages (5 marks)
Solution
V1 = 240V, V2 = 60V, i1 = 12A
(I)THE OTHER TWO CIRCUIT CURRENTS
From transformer ratio K = V1/V2 = i2/i1
240/60 = 12/i1
i1 = 60 × 12/ 240
i1 = 3A
Recall,
i1 = i2 + i3, i3 = [i2 – i1]
i3 = 12-3
i3 = 9A