Fuse MCQ Quiz - Objective Question with Answer for Fuse - Download Free PDF

Concept:

Fusing current is proportional to the 3/2 power of the wire’s radius:

\( \frac{I_1}{I_2} = \left( \frac{r_1}{r_2} \right)^{3/2} \)

Substituting: \( \frac{16}{I_2} = (4)^{3/2} = 8 \Rightarrow I_2 = 2\ \text{A} \)

Fusing Factor

\(Fusing \space Factor={Minimum \space fusing \space current \over Current \space rating \space of \space fuse}\)

Minimum fusing current is the minimum value of current due to which the fuse melts.

It is always greater than 1. 

The small the value of the fusing factor, the greater is the chance of deterioration of the fusing element due to overheating and oxidation.

Explanation:

Rupturing Capacity of a Fuse

Definition: The rupturing capacity, also known as the breaking capacity or interrupting capacity, of a fuse is the maximum amount of fault current that a fuse can safely interrupt without causing an electric arc with unacceptable duration or causing damage to the electrical circuit or the fuse itself. It is a crucial parameter in ensuring the safety and reliability of electrical systems.

Working Principle: When an overcurrent or short-circuit condition occurs, the fuse element heats up due to the increased current flow, eventually melting and breaking the circuit. The rupturing capacity of the fuse ensures that this interruption occurs safely even at high current levels, preventing further damage or hazards.

Advantages:

• Provides protection against overcurrent and short-circuit conditions, ensuring the safety of electrical circuits and equipment.
• Prevents electrical fires and damage by safely interrupting excessive fault currents.
• Simple and cost-effective means of circuit protection.

Disadvantages:

• Once a fuse operates (blows), it must be replaced, unlike circuit breakers that can be reset.
• May not provide as precise protection as more sophisticated protection devices.

Applications: Fuses are widely used in various electrical and electronic systems, including residential wiring, industrial equipment, automotive applications, and consumer electronics, to protect against overcurrent conditions.

Correct Option Analysis:

The correct option is:

Option 1: MVA (Mega Volt Amperes)

This option correctly represents the rupturing capacity of a fuse. The rupturing capacity is expressed in terms of MVA, which stands for Mega Volt Amperes. MVA is a unit of apparent power, which combines both voltage and current. This unit is used because the rupturing capacity needs to account for both the voltage and the current that the fuse can interrupt safely during a fault condition. High fault currents can generate substantial energy, and the MVA rating ensures that the fuse can handle these conditions without causing damage or creating hazards.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 2: kVA (Kilo Volt Amperes)

This option is not correct for expressing the rupturing capacity of a fuse. While kVA is also a unit of apparent power, it is typically used for specifying the power capacity of transformers and generators rather than the rupturing capacity of fuses. The rupturing capacity usually involves higher power levels that are more suitably expressed in MVA.

Option 3: A (Amperes)

This option is incorrect as it only considers the current aspect of the fault condition. Although the current rating of a fuse is important, the rupturing capacity must also account for the voltage to ensure safe interruption. Therefore, using only Amperes (A) does not provide a complete measure of the rupturing capacity.

Option 4: kV (Kilo Volts)

Similar to Option 3, this option is also incorrect because it only considers the voltage aspect. The rupturing capacity needs to consider both the voltage and the current to ensure that the fuse can interrupt the fault condition safely. Using only Kilo Volts (kV) does not provide a comprehensive measure of the rupturing capacity.

Conclusion:

Understanding the rupturing capacity of a fuse is essential for ensuring the safe and reliable operation of electrical systems. The correct representation of the rupturing capacity is in terms of MVA (Mega Volt Amperes), as it combines both the voltage and current aspects of fault conditions. This comprehensive measure ensures that the fuse can interrupt high fault currents safely without causing damage or creating hazards. Evaluating the other options, it is clear that they do not provide a complete measure of the rupturing capacity, emphasizing the importance of using MVA for this parameter.

Explanation:

Fusing Factor Calculation

Definition: The fusing factor is the ratio of the minimum fusing current to the current rating of the fuse element. It indicates how much current the fuse can carry before it melts and breaks the circuit.

Given Data:

• Fuse constant (K) = 20
• Diameter of the round wire (d) = 0.5 mm
• Current rating of the fusing element (I) = 5 A

Formula: The fusing factor (F) can be calculated using the formula:

\(I_f = K \times d^{3/2}\)

Where,

• \(I_f\) = Minimum fusing current
• K = Fuse constant
• d = Diameter of the wire

First, we need to calculate the minimum fusing current \(I_f\).

\(I_f = 20 \times (0.5)^{3/2}\)

\(I_f = 20 \times (0.5)^{1.5}\)

\(I_f = 20 \times \sqrt{0.5}\)

Calculation:

\(\sqrt{0.5} \approx 0.7071\)

\(I_f = 20 \times 0.7071\)

\(I_f = 14.142\)

Now, the fusing factor (F) is given by:

\(F = \frac{I_f}{I}\)

\(F = \frac{14.142}{5}\)

\(F \approx 2.828\)

The correct option is:

Option 2: \(4 \times \sqrt{\frac{1}{2}}\)

This matches the calculated result, where the factor \(4 \times \sqrt{\frac{1}{2}}\) simplifies to approximately 2.828.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: \(4 \times \left(\frac{1}{2}\right)\)

This option is incorrect because it simplifies to 2, which is not the correct fusing factor for the given data.

Option 3: \(\frac{4}{3}\)

This option is also incorrect because it does not match the calculated fusing factor of approximately 2.828.

Option 4: 0

This option is incorrect as a fusing factor cannot be zero. A fusing factor of zero would imply that the fuse never melts, which is not possible.

Conclusion:

Understanding the calculation of the fusing factor is essential for ensuring the proper functioning of electrical circuits and protecting them from overcurrent conditions. The fusing factor helps in determining the appropriate fuse for a given application, ensuring safety and reliability in electrical systems.

H.R.C. Fuse:

• H.R.C. (High Rupturing Capacity) fuses are an essential component in electrical systems, designed to protect circuits from overcurrent conditions. They are known for their ability to safely interrupt high fault currents without causing damage to the circuit.

Construction of H.R.C. Fuse:

• **Ceramic Body**: The body of an H.R.C. fuse is made of a high-strength, heat-resistant ceramic material. This ceramic body provides excellent insulation and ensures that the fuse remains intact even under extreme conditions.
• **Metal End Caps**: The ceramic body is fitted with metal end caps at both ends. These end caps are typically made of brass or copper, which provide a reliable electrical connection to the fuse holder.
• **Fuse Element**: Inside the ceramic body, there is a carefully calibrated fuse element made of silver or copper. This fuse element is designed to melt when a specific overcurrent flows through it, thereby interrupting the circuit.
• **Filling Material**: The ceramic tube is often filled with a silica or quartz powder. This powder helps to quench the arc that forms when the fuse element melts, preventing the arc from causing further damage.

Operation of H.R.C. Fuse:

• **Normal Operation**: During normal operation, the current flowing through the fuse element is within the specified rating, and the fuse remains intact, allowing the circuit to function properly.
• **Overcurrent Condition**: When an overcurrent condition occurs, the excessive current generates heat, causing the fuse element to melt. This melting action breaks the circuit, effectively interrupting the current flow and protecting the equipment and wiring from damage.
• **Arc Quenching**: As the fuse element melts and an arc forms, the filling material inside the ceramic body absorbs the energy of the arc and extinguishes it quickly. This arc quenching action prevents the arc from causing further damage or reigniting.

Advantages of H.R.C. Fuse:

• **High Rupturing Capacity**: H.R.C. fuses can interrupt very high fault currents without causing damage to the surrounding equipment or circuit.
• **Reliable Protection**: They provide consistent and reliable protection for electrical systems, ensuring that overcurrent conditions are safely managed.
• **Durability**: The ceramic body and robust construction make H.R.C. fuses durable and long-lasting.
• **Arc Quenching**: The filling material inside the fuse ensures effective arc quenching, preventing further damage to the circuit.

In conclusion, H.R.C. fuses are a critical component in electrical systems, providing high-capacity protection and reliable operation. Their ceramic body with metal end caps, and the ability to interrupt high fault currents, make them an essential choice for safeguarding electrical circuits.

Concept:

Fusing factor: It is the ratio of minimum fusing current and current rating of the fuse. Minimum fusing current is the minimum value of current due to which fuse melts.

The current rating of fuse is the maximum value of current due to which fuse does not get melt.

Fusing factor = (Fusing current) / (Current rating of fuse)

Explanation:

• The value of fusing factor is always greater than 1.
• The small the value of fusing factor, greater is the chance of deterioration of fusing element due to overheating and oxidation.
• For a semi enclosed or rewirable fuse which employ copper as the fuse element, the value of fuse factor is usually 2.
• Lower values of fusing factor can be employed for enclosed type cartridge fuse which uses silver or bimetallic elements.

Fuses: A fuse is a short piece of metal, inserted in the circuit, which melts when excessive current flows through it and thus breaks the circuit.

DC Fuse:

• The DC fuse opens or breaks the circuit when the excessive current flow through it.
• It is very difficult to extinct because there are no zero current flows in the circuit.
• For the same current rating, the heat generated in a particular time period in the DC fuse is more than that of AC because the equivalent value of AC is 70.7% of the DC. Therefore it has larger in size as compared to any other AC fuses.

AC Fuses:

• The AC fuses are categorized into two types they are the low voltage fuses and high voltage fuses.
• Striker type fuses,  Cartridge type fuses, the rewirable fuses are considered as low voltage fuses.
• HV fuse, Expulsion type fuse, Liquid HV HRC fuses are considered as high voltage fuse.
• Thus, the arc extinction in the AC circuit can be done easily as compared to the DC circuit.

The correct answer is Iron.

The material used for fuse elements must have the following properties:

• Low melting point
• Low ohmic loss
• High conductivity (or low resistivity)
• Low cost
• Free from detraction

The materials used for fuse:

• The material mainly used as fuse elements are tin, lead, silver, copper, zinc, aluminium, and an alloy of lead and tin
• An alloy of lead and tin is used for small current rating fuses
• For current exceeding 15 A, this alloy is not used as the diameters of the wire will be larger and after fusing the metal released will be excessive.
• Beyond 15 A rating circuit, copper wire fuses are employed

Iron is not used as a fuse wire.

Residual Current Circuit Breaker (RCCB):

• It is a differential current sensing device used to protect a low voltage circuit in case of a leakage fault. It is sometimes also known as Residual Current Device (RCD).
• It contains a switch device that switches off (in a fraction of a second), whenever the current leaks out and does not return back through neutral.
• The RCCB provides protection from small current leakage arising due to accidental touch by human being or insulation failure, which is not possible by MCB or fuse alone.

Ratings of RCCB:

• 30 mA is recommended for residence for safety purpose
• 100 mA is recommended for industrial establishments

The fuse rating is basically dependent on current carrying to a particular connected load.

The order of the wring done for the consumer end connection is

1. From Secondary distribution transformers, power lines are sent to each pole present in the streets.
2. From the pole, each service main wire is connected to the energy meter of each house.
3. From the main meter, it is distributed to the main circuits of the building.
4. From the main circuit, it is then divided into sub-circuit connections.
   ​

The magnitude of current-carrying by the wries in the above process is given as

i_pole > i_meter  > i_{main circuit} > i_{sub circuit}

Hence pole caries more current of different service mains of houses, pole fuse has the highest fuse rating.

Additional Information

Fusing factor:

It is the ratio of minimum fusing current and current rating of the fuse. Minimum fusing current is the minimum value of current due to which fuse melts.

The current rating of fuse is the maximum value of current due to which fuse does not get melt.

Fusing factor = (Fusing current) / (Current rating of fuse)

• The current rating is the maximum current that a fuse will carry for an indefinite period without much deterioration of the fuse element.
• Any current higher than the current rating may cause the contacts of the switch for example to ‘melt’ or ‘weld’ together.
• The current rating of the cable is defined as the maximum current carrying capacity of the power cable under normal operating conditions.
• The current rating of power cable decided the upper limit of power transfer by a cable.
• It mostly depends on the insulation temperature and electrical resistance of the conductor.
• According to the question smallest cable means the shortest cable (length is small), if the length is small then resistance is also small/low because resistance is directly proportional to the length of the cable (R ∝ l).
• If resistance is small, then the maximum permissible current will pass through the cable and thus it will be the maximum current rating of the fuse for the particular distribution system.
• Thus the current rating of a fuse in the distribution system should not exceed the current rating of the smallest cable in the circuit.
• Current rating of a fuse ≤ current rating of smallest cable in the circuit

• The electric current flowing through the fuse wire is the same as the load current which is consumed by the electrical load
• That load current only decides the rating of the fuse
• Hence, the rating of the fuse is expressed in amperes

(HRC) High Rupturing Capacity fuse:

• It consists of a heat-resisting ceramic body having metal end-caps to which is welded silver current-carrying element
• The space within the body surrounding the element is completely packed with a filling powder
• The filling material may be chalk, plaster of paris, quartz or marble dust and acts as an arc quenching and cooling medium
• Under normal load conditions, the fuse element is at a temperature below its melting point. Therefore, it carries the normal current without overheating.
• When a fault occurs, the current increases and the fuse element melts before the fault current reaches its first peak. Hence it is used for overcurrent protection.

Important Point:

Advantages of HRC fuse:

• They can clear high as well as low fault currents
• They do not deteriorate with age
• They have a high speed of operation
• They provide reliable discrimination
• They require no maintenance
• They are cheaper than other circuit interrupting devices of equal breaking capacity
• They permit consistent performance

Disadvantages of HRC fuse:

• They must be replaced after each operation
• The heat produced by the arc may affect the associated switches

HRC fuse:

• HRC fuses are used for short circuit protection.
• It carries a heavy short circuit current for a known time period.
• HRC fuses on a transformer provided protection against external faults.

HRC fuses have various applications:

• Protection of radial lines
• Transformer protection (external fault only)
• It is also used for capacitor protection
• It also provides protection of the underground distribution system
• It is used in meter board in a residential application