Q. What are different insulators employed in substations?
Answer. Some of the insulators employed in substations are:
- Pin insulators
- Post insulators
- Strain insulators
- Suspension insulators
- Hallow apparatus insulators
- Dead-end insulators
- Solid core insulators
Q. What is creepage distance?
Answer. Creepage distance is the shortest distance between two conducting points along the surface of the insulating material.
Q. What is Basic Impulse Level (BIL)?
Answer. Basic Impulse Level (BIL) refers to the peak value of lightning impulse voltage withstand capability of the equipment.
Q. What is the significance of Corona rings in substations?
Answer. It is observed that corona discharge occurs mostly at sharp corners, edges near the conductor fixing points. Corona rings (also called grading rings) are hallowed metallic rings having a large diameter and will have a smooth surface. These corona rings are placed suitably to metal clamps, joints to encircle the conductors surface. This has the advantage of shifting of high-stress point shifted from the conductor surface to corona ring surface. As the diameter and surface area of the ring is higher than that of the conductor. This helps in:
- Field distribution is made uniform.
- Surface stress is reduced to a much lower value.
- Corona discharge is eliminated.
- Dust deposition is also minimized.
Q. What is the neutral point earthing and its advantages?
Answer. In a substation, all the neutrals of rotating machines, transformers, busbars and other equipment are connected to ground. Some of the advantages are
- Earth fault protection is based on the method of neutral grounding
- The system voltage during earth faults depends on the neutral grounding. During line to ground faults, grounding of neutral helps to reduce the over-voltages which occur on the one healthy phases.