High Voltage Fuses

Question 1

Define a High Voltage fuse

Answer 1

A fuse is an overcurrent protective device with a circuit-opening fusible part that is heated and severed by the passage of current through it. Fuses are single-pole devices, only the fuse(s) in the phase(s) with the overcurrent will open. After interruption, the complete fuse, the fuse-link, or the fuse-refill must be replaced, depending on the type of fuse.

Question 2

What are the two fuse category types

Answer 2

1. Distribution cutout - pole-top fuse used widely by power utilities to protect the pole transformers, lateral lines, etc
2. Power fuses - include current-limiting fuses, boric-acid fuses, and liquid fuses

Question 3

Fuses are rated for what three things?

Answer 3

1. Voltage - The higher its voltage rating, the longer the fuse must be in order to prevent flashover between its end-caps
2. Current - Is the magnitude of the current which the fuse link can carry continuously without blowing
3. Interrupting-current - Specifies the highest magnitude of current that the fuse link can interrupt without physical damage to the fuse

Question 4

What are the four most common fuse types?

Answer 4

1. Current-limiting - non-expulsion type, ability to limit fault current magnitudes by opening extremely fast under a short-circuit condition. (Arrow marking for pin direction)
2. Solid-materials (boric-acid fuse) - a fuse link in a solid-materials fuse is surrounded by a boric acid powder. When the link opens, heat from the arc reacts with the powder to produce a de-ionizing vapour that assists in quenching the arc. Expulsion type.
3. Liquid - the fuse link is inside a heat-resistant glass container filled with oil. The arc is quenched by the oil and the action of a spring that pulls the fuse link apart as it melts
4. Distribution cut-outs - are drop-out type fuses that are used widely by all power utilities on overhead lines in the distribution network for the protection of the pole mounted transformers, spur lines, and other equipment

Question 5

If you have a solid materials boric-acid fuse installed indoors what must you have to help control the expulsed material?

Answer 5

You must have a condenser, muffler, or snuffer

Question 6

How does a liquid filled fuse work?

Answer 6

A fuse link inside a heat-resistant glass container filled with oil is quenched by the oil when an arc is created and the action of a spring pulls the fuse link apart as it melts.

Question 7

When a distribution cutout fuse blows, the spring action allows the fuse tube to drop down, releasing it from its upper contact. The fuse holder then swings down a full 180º providing what two useful functions?

Answer 7

1. Easy visual inspection

2. Larger re-strike distance