In the realm of high voltage electrical systems, ensuring robust protection against faults is paramount. Expulsion fuse cutouts are vital for maintaining system integrity and safety among the protective devices available.
Why expulsion fuses are the backbone of high voltage protection？
What are expulsion fuses?
Expulsion fuses are a type of protective device used in high voltage systems to interrupt fault currents. They expel the arc created during a fault through a gas-producing mechanism, typically involving boric acid.
This process effectively extinguishes the arc and isolates the faulty section of the circuit. Expulsion fuses are known for their reliability and cost-effectiveness, making them popular in various applications, including utility poles, substations, and industrial plants.
Expulsion Fuses： How do high voltage fuse cutouts work?
The high voltage fuse cutout operates normally with the fuse tube closing position formed by the tension of the fuse wire.
When a fault occurs in the system, the fault current rapidly melts the fuse wire, forming an electric arc. The arc-extinguishing tube is heated by the arc, releasing a large amount of gas, which creates high pressure inside the tube and forms a longitudinal blowout along the tube. The electric arc is rapidly elongated and extinguished.
After the fuse wire melts, the lower moving contact loses tension and flips down, releasing the fuse tube from the lock, and causing the fuse tube to drop and form a clear open position. When disconnecting the load, the insulated rod is used to pull the moving contact.
At this point, the moving and static contacts are still in contact. Continuing to pull the moving contact with the insulated rod, the auxiliary contact rapidly separates, generating an electric arc between the auxiliary contacts. The electric arc is elongated in the arc extinguishing cover slot, while the arc extinguishing cover generates gas. When the current reaches zero, the electric arc is extinguished.
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What is the rating of an expulsion fuse?
The rating of a drop out fuse cutout refers to its ability to handle specific voltage and current levels. These ratings are crucial for ensuring that the fuse can effectively interrupt fault currents without damaging the electrical system. Typically, drop off fuse cutouts are available in various ratings to accommodate different applications.
Commonly, they range from a few kV to several tens of kV, with current ratings designed to match the specific requirements of the electrical system they protect.
DownLoad: Expulsion Fuse PDF
What are the technical requirements before installing a expulsion fuse?
Before installing a drop out fuse, several technical requirements must be met to ensure optimal performance and safety:
1、Site Assessment
Evaluate the installation site for environmental factors such as humidity, temperature, and exposure to contaminants. Ensure the site meets the necessary safety standards.
2、Correct Sizing
Select a fuse with the appropriate voltage and current ratings for the specific application. Using the wrong size can result in inadequate protection or unnecessary interruptions.
3、Secure Mounting
Ensure that the fuse holder is securely mounted to a stable structure. The holder should be easily accessible for maintenance and inspection.
4、Connection Integrity
Verify that all electrical connections are tight and secure to prevent loose connections, which could cause arcing or overheating.
5、Regular Inspections
Plan for periodic inspections of the fuse and its components to identify and address any signs of wear, damage, or environmental impact.
What is the difference between a current limiting fuse and an expulsion fuse?
1、Operation Mechanism
Expulsion Fuses: Use a gas-producing mechanism to extinguish the arc. They expel the arc and gases outside the fuse body.
Current Limiting Fuses: Contain the arc within the fuse body and limit the current by creating a high-resistance path. They operate faster and can interrupt higher fault currents with minimal energy let-through.
2、Applications
Expulsion Fuses: Ideal for outdoor and high voltage applications where visual indication of a blown fuse is beneficial.
Current Limiting Fuses: Commonly used in medium and low voltage systems where limiting the fault current is crucial to protect sensitive equipment.
3、Noise and Exhaust
Expulsion Fuses: Produce noise and exhaust gases during operation, which can be managed with exhaust control devices.
Current Limiting Fuses: Contain the arc and do not produce significant noise or exhaust, making them suitable for indoor applications.
What is the current limiting fuse?
Current-limiting fuses are essential components in electrical protection systems, designed to significantly reduce fault currents and prevent excessive damage to equipment. These fuses act rapidly, interrupting faults before they reach full intensity, thereby improving system reliability and minimizing downtime.
According to IEEE Standard C37.40, current-limiting fuses are categorized into three main types:
- Back-up Fuses
- General Purpose Fuses
- Full-Range Fuses
Each type effectively limits system fault currents, offering different levels of protection depending on the application.
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GRL backup current limiting fuses: XRNP1-12 and XRNT1-12
The XRNP1-12/(0.5~4)-50 high-voltage Backup current-limiting fuse is designed for indoor power systems operating at 50Hz, with a rated voltage of 12kV and a rated current of up to 4A. It serves as an overload and short-circuit protection device for voltage transformers and complies with GB/T 15166.2 and IEC 60282-1 standards.
Similarly, the XRNT1-12/(6.3~200)-50 high-voltage current-limiting fuse is designed for 12kV indoor power systems, supporting rated currents up to 200A. This fuse can reliably interrupt fault currents ranging from approximately (3.5~6) Into a rated breaking capacity of 50kA. It is widely used for protecting power transformers and other electrical equipment from overload and short-circuit conditions.
GRL Current-Limiting Fuses Key Features
- Reliable fault current interruption across a wide range
- High-breaking capacity with stable performance
- Low power loss, ensuring energy efficiency
- Compatible with other switchgear, such as load break switches and vacuum contactors
- Essential for high-voltage switchgear, ring main units, and pre-fabricated substations
These high-voltage fuses provide an essential layer of protection in modern electrical systems, preventing catastrophic failures and improving overall reliability. By selecting the appropriate type of current-limiting fuse, engineers can ensure the safe and efficient operation of power distribution networks.
Current-Limiting Fuses Key Advantages
- Rapid Fault Interruption – Clears faults almost instantly to prevent excessive energy transfer.
- Minimized Damage – Reduces burning at the fault point, limiting harm to connected equipment.
- Enhanced System Protection – Helps prevent extensive damage to power lines and other circuit components.
- Lower Energy Let-Through – Restricts the energy passing through the circuit during a fault, reducing wear and tear on electrical infrastructure.
Traditional fuses allow fault energy to complete a full cycle before activating, which increases potential damage. Current-limiting fuses, however, operate in a fraction of that time. As a result, these fuses are often referred to as “zero-forcing devices”, as they quickly bring the fault current back to zero, preventing further stress on the system.
Types of Current-Limiting Fuses
1. Back-Up Current-Limiting Fuses
Back-up fuses are engineered to clear only high fault currents, which typically result from internal failures within electrical equipment. While they are highly effective at reducing the stress of major faults, they must be used alongside a low-current interrupting device to provide comprehensive overcurrent protection.
Common Applications:
- Overhead distribution transformers
- Single-phase dead front pad-mounted transformers
- Three-phase dead front pad-mounted transformers
2. General-Purpose Current-Limiting Fuses
General purpose fuses protect a broader range of current levels, interrupting from maximum rated fault current down to the level that melts the fuse element within an hour. This range typically falls between 170% and 240% of the fuse’s rated current. However, these fuses may not always interrupt extremely low fault currents, requiring additional protective devices in some cases.
3. Full-Range Current-Limiting Fuses
Full-range fuses offer the most complete protection, capable of interrupting both high and low fault currents—from the fuse’s maximum rated fault current down to the lowest current that will melt the fuse element. Unlike general-purpose fuses, full-range fuses do not have a one-hour limitation and can interrupt any normal 60-cycle current that exceeds their melting threshold.
Benefits of Full-Range Fuses:
- Environmentally friendly operation
- Compatibility with interchangeable cutout mounts
- Reliable performance across a wide range of applications
Common Applications:
- Overhead cutouts
- Riser poles
- Three-phase dead front pad-mounted
- transformers
- Capacitor protection
| Type | Function | Current Interruption Range | Typical Applications | Additional Features |
| Back-up Fuse | Protects against high fault currents only | Can interrupt only high fault currents, requires a low-current protection device in series | Transformers, high-voltage power equipment | Needs to be used with a low-current fuse or circuit breaker for full protection |
| General Purpose Fuse | Protects against overloads and short circuits | Interrupts currents from maximum rating down to the current that melts the fuse in 1 hour (approximately 170%-240% of the rated current) | Transformers, power distribution systems, electrical equipment | May not clear very low fault currents, requiring additional protective devices |
| Full-Range Fuse | Provides complete overload and short-circuit protection | Can interrupt all currents from maximum rated fault current down to the minimum melting current, with no time limitations | Power transformers, ring main units, substations | Covers the full range of fault currents and can operate independently without additional breakers |
Understanding the role and specifications of expulsion fuses and Current-Limiting Fuses is essential for anyone involved in high-voltage electrical systems. These fuses offer reliable protection and clear fault indication, making them indispensable in maintaining system integrity.
By selecting the appropriate fuse ratings and adhering to technical requirements, you can ensure optimal performance and safety for your electrical infrastructure.
For more information on high-quality expulsion expulsion fuses, visit GRL Group.
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