Electrical Safety Rules Test (Part 4 Of 4)-electrical Person

Surge arresters are used for the protection of all components and switch gears in marine environments. This is because marine environments are prone to electrical surges and transient voltage spikes that can damage electrical equipment. By installing surge arresters, all components and switch gears are protected from these voltage surges, ensuring the safe and reliable operation of the electrical system on board marine vessels.

Surge voltage can originate in power systems due to various reasons, including lightning, switching operations, and faults. Lightning strikes can cause a sudden increase in voltage, leading to a surge. Switching operations, such as turning equipment on or off, can also result in voltage surges. Additionally, faults in the power system, such as short circuits or equipment malfunctions, can cause sudden voltage spikes. Therefore, surge voltage can occur due to any combination of these factors, represented by options A, B, and C.

Switching surge refers to a sudden and temporary increase in voltage that occurs when a switch or circuit is turned on or off. This surge can cause a short duration transient voltage, which is a brief and temporary fluctuation in voltage levels. It is not a high voltage dc or ac, nor is it hyperbolically dying voltage.

Sulphur hexafluoride is commonly used as an insulating medium in electrical appliances. It has excellent electrical insulation properties, high dielectric strength, and is chemically stable, making it ideal for use in high-voltage equipment. It is also non-toxic and non-flammable, making it a safe choice for electrical insulation.

SF6 (sulfur hexafluoride) is the medium employed for the extinction of an arc in an air circuit breaker. SF6 is a highly stable and non-flammable gas that has excellent electrical insulation properties. When an arc is formed in the circuit breaker, SF6 gas is released to extinguish the arc by rapidly cooling and suppressing the ionization. This allows for a quick and efficient interruption of the current flow. Compared to other mediums like oil, air, or water, SF6 is the most suitable choice for extinguishing arcs in air circuit breakers.

The minimum IR value recommended for MV (medium voltage) machines is typically calculated using the machine voltage (KV) plus 1M (megaohm). This value is important for determining the insulation resistance of the machine, which is necessary for ensuring the proper functioning and safety of the equipment.

Solid insulating materials can experience electro-mechanical breakdown when exposed to voltage fluctuations. These fluctuations create electrical stresses within the material, causing it to break down. This breakdown occurs due to the interaction between the electrical field and the mechanical stresses produced.

The minimum insulation resistance value recommended for LV machines is 1M Ohm/1000VAC. This is because a high insulation resistance is necessary to ensure the safety and proper functioning of the machine. Insulation resistance is a measure of how well the insulation material is able to resist the flow of electrical current. A higher resistance value indicates better insulation and reduces the risk of electrical leakage or short circuits. Therefore, a minimum value of 1M Ohm/1000VAC is recommended to ensure the machine's insulation is adequate. Option A and C both mention this correct value.

Connecting additional earthing local to work provides an extra layer of safety and confidence for the operator. This ensures that any potential electrical faults or accidents are properly grounded, reducing the risk of electric shock or other injuries. While it may not be a mandatory requirement in all cases, it is highly recommended for the protection of both the operator and the equipment being used.

The correct answer is "It provides off-line protection to 3.3 KV motor against ground fault." This means that ISAH3300M is a device that offers protection to a 3.3 KV motor when it is not in operation or offline, specifically against ground faults.