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Interview Question of Isolator

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1.What is an isolator and why is it used in the power system ?

Ans : An isolator is a disconnecting switch being operated under the condition of on load or negligible current. It is used in the power system for disconnecting the circuit breaker from the circuit at the time of repair and maintenance work.

2. Why are isolators provided on both sides of the circuit breakers ?

Ans : Isolators are provided on both sides of the circuit breakers for repairing work or replacement of breaker without any danger from the live circuit.

3. What interlocking arrangements are generally provided in the isolators ?

Ans : 1) Interlocking with circuit breaker is that the isolator can not be opened unless the circuit breaker is opened. The three poles of the isolator should be interlocked for simultaneous operation.

4.What are the types of O.H. isolators generally used ?

Ans : The types of isolators are as follows :-
Vertical break type single, double or triple pole isolator consisting mainly of fixed soiled core type insulator support with rigid contacts and moving copper blade supported by operating rod insulator. These are generally used in traction system of about 25 kV.
Horizontal two rotating post, center break type isolator consisting of two insulator stacks of post type insulator mounted on a bearing and also rotatable about its vertical axis through 90°. In this type one insulator stack swings in clockwise direction and other in opposite direction in such a way that the contact arms swings in horizontal plane isolating at the center. This is used at the voltage upto 220 kV.
Horizontal break center rotating double break isolator consisting of three insulator stacks per pole having two insulator stacks fixed on sides and center insulator stack rotating. Fixed contacts are mounted on the top of each of the insulator stacks on the side. It can be used in case of all outdoor isolation of circuit breaker, transformer banks, lightning arrestors and also for line sectionalization.
Extra high voltage column isolator consisting of a two part pantograph on the top, revolving drive insulator, solid core type porcelain insulator acting as the main supporting unit, the operating cubical provided with all necessary auxiliary contacts & other contacts for supervision & control and a vertically erected steel tube support anchored to the concrete plinth.

5. What are the advantages of extra high voltage column isolators ?

Ans : The advantages are as follows :-
i)It requires less ground area.
ii)It is clearly visible from a great distance.
iii)Keeping the fixed contacts alive the moving contacts can be inspected safely.

6. What material is used for making pantograph bar & why ?

Ans : An aluminium magnesium alloy is used for making pantograph bar for its high mechanical strength, light weight, good conductivity and more flexibility due to its high elasticity characteristics.

7. In which arrangement of busbar the bus coupler is very essential ?

Ans: Main and transfer bus arrangement.

8. What is meant by insulation co-ordination ?

Ans : Insulation co-ordination means the mutual relation between the insulation of the equipments and the overvoltage characteristics of the protective device the basis of which is that the withstand overvoltage characteristics of all the equipments should lie above the spar over characteristics of surge arrestor on worst on worst possible atmospheric condition.

9. What is the difference between an isolator and a circuit breaker ?

Ans : The difference between an isolator and a circuit breaker is that, an isolator is a mechanical device capable of opening or closing a circuit without any arc control device under conditions of no load or negligible current but a circuit breaker is a mechanical device for making and breaking a circuit with are control device under normal and abnormal conditions i.e. even when a heavy fault current is flowing.

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