Magnetic Shielding with Mu-Metal: When and How?
How shielding with mu-metal and silicon steel against low-frequency magnetic fields works, with practical application examples.
3 min readOctober 25, 2026
What Is Partial Discharge?
Partial discharges are small electrical discharges in tiny voids within an insulating material, or on its surface, that don't fully break down the insulation. Though harmless on their own, they erode insulation over time and eventually cause failure.
That's why measuring the partial discharge level is mandatory in quality control of high-voltage equipment. IEC 60270 defines how this measurement is made.
How Small Is the Signal?
Partial discharge is measured as charge on the order of picocoulombs (pC). For some products acceptance limits are as low as a few pC. A signal this small is easily lost in the noise from a nearby radio transmitter, motor drive or fluorescent lamp.
When the noise level rises above the limit, the measurement can't be made or the result isn't reliable. This is the problem in many factory test halls: the product may be good, but the environment won't let it show.
What a Shielded Lab Contributes
A shielded high-voltage lab blocks radio-frequency noise from outside. Supply lines entering the room are filtered and the grounding system is designed not to create noise loops.
As a result, background noise drops below a few pC and the measurement becomes reliable. You'll find the design details on our high-voltage laboratory page.
Design Considerations
In high-voltage labs, shielding alone isn't enough. Safety clearances, doors for large equipment, corona-free fittings and dedicated grounding all need to be addressed together from the start.
We size the lab by assessing test voltage, equipment size and target noise level together. You can see similar applications in our energy sector solutions.
Frequently Asked Questions
Can an existing test hall be shielded?
In most cases, yes. Building height, floor and existing grounding are inspected during the survey.
What noise level can shielding achieve?
The target is set by the acceptance limit of the product to be tested; in well-designed labs the background drops below a few pC.
Do you also install the grounding system?
Yes. Grounding compatible with the shielding is designed and installed as part of the project.
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