Dead short fuse trip experiment using an MRBF fuse

[Johan]

Per request of @Pi Curio, 10 Heschen fuses (sourced on Amazon; HSPV-30; 32A; 1000VDC; I1 = 33kA) were blown while mounted in their DIN-rail fuse holders (sourced on Amazon) in the vertical position.


These fuses are filled with sand, similar to Class T fuses. The resulting current versus time plot is shown below. The legend shows the experiment number. Experiments 1 through 4 blow a single fuse. Experiment 5, 6, and 7 blow two fuses in series just to see if that makes any difference.

Here are all seven experiments on video ("Unlisted" on Youtube, so you need to use this link):

Notes:

• There was no sign of external damage for fuses and holders.
• Only experiment 5 has measurement data from both the Arduino and oscilloscope for comparison purposes.
• The negative 25000A "charge current" was completely unexpected and seemed to be artificial oscilloscope nonsense at first, but this current was later reproduced on the Arduino (not shown, separate experiment). This *may* be an effect or "ringing" due to parasitic capacitance in the circuit. Anybody comments on this?
• Scopes are generally very inaccurate for measuring voltages, so they are also inaccurate for measuring voltage drops across a shunt as was done here to calculate the current.
• I estimate the Arduino accuracy to be roughly +/- 160A based on specsheets data.
• The oscilloscope accuracy seems to be roughly +/- 1800A based on specsheets data.
• See also here if you want to read more about oscilloscope accuracy.
• When torquing the screws, the side panel of the thin plastic fuse holder housing can easily crack open.

 

[AntronX]

Try 50A/50mV shunt. It should give you 10x better signal to noise (10V signal instead of 1V). That -25kA peak could be due to magnetic field collapse but I doubt it would generate real current spike that high. Most likely that field is messing with your probes or scope.

 

[AntronX]

I would use precision current shunt instrumentation op amp fed to an ADC and microcontroller directly mounted to the shunt and powered by small onboard battery. This way you eliminate sense wires that can pick up collapsing magnetic field interference. Or if you want to use your scope you should be using true differential probe for this to cancel out magnetic field interference. Single ended (unbalanced) probes are not good.

 

[AntronX]

Can also use Rogowski coil as current sensor instead of shunt.

 

[Pi Curio]

@Johan

I can't thank you enough for doing the gPV fuse dead-short tests.

This is above and beyond my expectations! I did not expect I'd ever get to see this fuse being properly put to the test multiple times in different configurations by someone with the talent, knowledge, and skills to do this when I made my post a while back.

For me, this is an absolute game changer and makes all the difference for my project. I will in part try to replicate the test results here in Europe just to have no doubts left about the fuse quality available here, but 10 out of 10 fuses blown is very convincing.


Your work has helped give this curious soul an answer to the question

Much obliged.

 

[Hedges]

That -25kA peak could be due to magnetic field collapse but I doubt it would generate real current spike that high. Most likely that field is messing with your probes or scope.

Makes sense if there is a loop formed by ground lead of scope probe.

dI/dt through wires of circuit under test would induce current in that loop. Shunt holds low V = IR between probe tip and ground clip so voltage appears across scope input.

Different connection scheme like BNC connected to shunt with minimum loop area formed could help. Shunt and that little loop twisted right angles to loop formed by current carrying wires might help. Squeeze the air of loop formed by the wires, even twist them.

Can also use Rogowski coil as current sensor instead of shunt.

I got Fluke i2000 Rogowski coil.
It has 20 kHz bandwidth, better than the CT I have, makes a difference for inrush measurements (may want probe with DC response for that, but I was measuring AC circuits, transformer and SMPS inrush.)

I would think shunt would be good for these 10kA or 20A measurements.
The i2000 is rated 2kA or 3kA.