The Bay-O-Net fuse holder is designed for use in pad-mounted or subsurface distribution transformer. It is used with fuse link to protective the secondary short circuit faulted of transformer, such as current sensing fuse link, dual sensing fuse link, dual element fuse link.
The fuse holder is with a flapper valve inside the housing which closes when it is removed. This results in minimal oil spillage from the transformer tank which increases safety to line personnel during fuse changeouts, reduces potential of environmental concerns with oil pillage, reduces potential of oil contamination on the molded rubber elbow connections.
How the Bay-O-Net fuse works
The core component of a fuse is the fuse. Its working principle can be simply summarized as:
Normal operation:
When the current in the circuit is within the design range, the fuse will not be blown, and the current can pass normally.
Current overload or short circuit:
When the current exceeds the set value, the fuse temperature rises rapidly.
The fuse material quickly fuses after reaching the melting point, cutting off the circuit and protecting the equipment from further damage.
State after fuse:
After the fuse is blown, the current in the circuit is interrupted to avoid overheating or burning of the device.
In this case, you need to replace the fuse in time to restore the normal operation of the device.
Plug-in fuses are usually also designed to prevent oil leakage, which can effectively avoid the leakage of insulating oil in the tank when the fuse is replaced.
Why do transformer fuses blow
• Cause:
When the current in the circuit exceeds the rated value of the fuse, the fuse gradually heats up due to prolonged overcurrent, eventually leading to the melting of the fuse element.
• Mechanism:
The overcurrent causes the fuse element to generate heat proportional to P=I2R. Once the heat exceeds the material’s thermal limit, the fuse element melts, interrupting the circuit.
• Common Scenarios:
• Increased load on the circuit, such as multiple high-power devices operating simultaneously.
• Devices running under overloaded conditions, causing the current to remain consistently above the rated level.
• Cause:
A short circuit occurs due to insulation failure, internal equipment faults, or improper circuit connections, causing the circuit resistance to drop to nearly zero and resulting in a surge of current.
• Mechanism:
Short-circuit currents are often several or even dozens of times the rated current, causing the fuse element to melt instantly due to the rapid heat generated.
• Common Scenarios:
• Aging or damaged cable insulation.
• Internal faults in electrical equipment.
• Loose wire connections creating arcs.
• Cause:
Devices such as transformers or motors generate significantly high inrush currents during startup or initial energization, potentially causing the fuse to blow if it cannot handle the surge.
• Mechanism:
The inrush current, often 6-10 times the rated current, causes a rapid temperature rise in the fuse element. Although the duration is short, it can still melt the element.
• Common Scenarios:
• Transformer magnetizing inrush current.
• High current during motor startup.
How to Choose the Size of a Fuse
The rated current (
) of a fuse is the maximum current it can handle continuously during normal operation.
Calculation Method:
• The fuse’s rated current should be slightly higher than the working current of the circuit, typically 1.25 times the maximum operating current.
Example:
• If the maximum operating current of the circuit is 80A, it is recommended to choose a fuse with a rated current of 80A×1.25=100A.
Devices like transformers or motors generate inrush currents during startup or initial energization. This is a short-term surge of current that can reach 6-10 times the rated current of the device.
Selection Recommendations:
• For devices with inrush current, use slow-blow fuses, which can tolerate short-term surges without unnecessary operation.
Example:
• If a transformer has a rated current of 50A and an inrush current of 300A lasting for a few milliseconds, select a fuse capable of withstanding such inrush currents.
The rated voltage of a fuse is the maximum voltage it can safely operate at.
Selection Recommendations:
• The fuse’s rated voltage must be greater than or equal to the operating voltage of the circuit. If the circuit voltage exceeds the fuse’s rating, insulation breakdown or fuse failure may occur.
Example:
• For a 23kV distribution system, select a fuse with a rated voltage of at least 23kV.
• In circuit design, it is recommended to set a 10%-20% safety margin for the rated current of the fuse to account for potential current fluctuations and equipment aging.
• Note: The safety margin should not be too large, as this could prevent the fuse from blowing during fault conditions, compromising its protective function.
Bay-O-Net in conjunction with isolation links
The Isolation Link is a device designed for transformer protection, intended to physically isolate the transformer during a fault by fusing and prevent accidental re-energization. Unlike traditional fuses, the Isolation Link does not have overcurrent protection or interrupting capabilities.
1.Fault Isolation:
• When a transformer experiences severe internal faults, the Isolation Link fuses and physically isolates the transformer from the grid, preventing the fault from propagating to other parts of the system.
2. Prevention of Accidental Re-Energization:
• After fusing, the Isolation Link completely disconnects the transformer from the system, ensuring that the equipment cannot be accidentally re-energized during maintenance or replacement.
3. Auxiliary Protection:
• It is not intended to protect equipment from overcurrent or short circuits but serves as the last line of fault isolation to ensure system safety and stability.
• When Isolation Link is used as a backup, the maximum fault current (Available Fault Current, AIC) of the transformer or equipment it is connected to must be less than or equal to the interrupting rating (IR) of the primary fuse (e.g., Expulsion Fuse).
• If the fault current exceeds the interrupting capability of the Expulsion Fuse, it will fail to safely interrupt the current. Since Isolation Link itself lacks the ability to interrupt fault currents, this could lead to protection failure or increased system risk.
