History of Blood and Tears in the Selection of Medium and High Voltage Fuses

2025-07-21 14:10:37

Last summer, Lao Zhang, the chief engineer of a chemical fiber factory in Zhejiang, received a phone call at 3am saying that the production line had collapsed again! He rushed to the scene and smelled a burnt smell - the newly replaced fuse had blown into pieces in the 10kV distribution cabinet. This is the third accident of the month, with production losses exceeding 600000 yuan. The root of the problem is actually that a parameter was overlooked during the initial selection process .."

1、 Rated voltage: It is not enough to meet the standard, sufficient "life margin" should be left

We have suffered losses: a certain photovoltaic project selected a 12kV fuse according to the "10kV system selection", but it continued to break down during the thunderstorm season. Later, we realized after flipping through the accident report of State Grid:

>Deadly detail: The maximum operating voltage of the system can reach 1.2 times the nominal voltage!   

>Practical formula: Rated voltage ≥ maximum system voltage × 1.15

>Example: 10kV system (actual peak 12kV) → rated voltage of fuse ≥ 13.8kV

Blood and tears case

A certain wind farm used a 12kV fuse and encountered a 14.3kV operating overvoltage → insulation breakdown causing a phase to phase short circuit. Now we all use K-type high-voltage Fuses (such as XRNP-12/16), with a measured withstand voltage value of 20kV.

2、 Rated current: Don't just look at numbers, temperature will 'steal' capacity

Common traps in the factory area:

-In summer, the temperature in the distribution room exceeds 45 ℃, and the actual current carrying capacity of the fuse decreases by 30%

-The instantaneous current during motor start-up is 6 times the rated value, and ordinary fast melting will explode

Practical reversal

A certain injection molding locomotive in Shandong frequently blows, and the original 125A fuse was used. We have found through actual testing that:

Environmental temperature 42 ℃ → 15% reduction in rating

Motor starting current 680A/0.6s → requires I 2 t value>200kA 2 s

Finally, we switched to a slow melting 160A fuse (model SDLAJ-160) with three years of zero malfunctions.

3、 Breaking ability: Life and death are within 16 milliseconds

The shocking truth: A steel plant's transformer outlet had a short-circuit current of 28kA, but it was equipped with a fuse with a breaking capacity of 25kA - the fuse tube exploded and ignited the cable trench. The iron law of selection:

>Breaking capacity ≥ expected short-circuit current × 1.3

Recommended for different scenarios:

Ultimate Pit Avoidance Guide (with Self Inspection Checklist)

The 3+2 inspection method privately passed down by veteran electricians:

1. Voltage: Use a multimeter to measure the peak voltage of the system

2. Current: Check the temperature rise at the connection point with an infrared thermal imager (danger of>65 ℃)

3. Breaking: Request the supplier to provide a test report

Two essential questions to ask:

??  Can you provide the I 2 t value curve of your company's fuse? "  

??  How much capacity reduction is required at an altitude of 2000 meters

(The models mentioned in the article are all real products, and the data is sourced from the State Grid's "High Voltage Fuse Fault Analysis Report 2023".)