VLF Test Voltage Calculator — IEEE 400.2-2024 by Cable Class
Choosing a VLF test voltage is a lookup, not a guess — provided you start from the right quantity and use the current edition of the standard. This page does the lookup for you. Pick the cable’s system voltage, the test class and the waveform, and it returns the test voltage, the hold time and the VA-TEK test set that reaches it, all drawn from the test-voltage table of IEEE 400.2-2024.
Key takeaways
- The test voltage is fixed by the standard you test to, expressed against the cable’s system voltage — not by the cable’s nominal rating alone.
- IEEE 400.2-2024 tabulates the VLF test voltage in kV rms; VA-TEK test sets are rated in kV peak. This tool shows both so the number and the equipment line up.
- Duration follows the test class: 60 min for installation and acceptance, 30 min for maintenance, at 0.1 Hz.
- A sinusoidal source is the reference waveform and the basis for tan delta and partial discharge; cosine-rectangular is a withstand-only waveform with its own, higher rms values.
- Above 66 kV the requirement moves past the 30–90 kV peak range — the tool says so plainly rather than rounding up.
1. What this calculator does — and what it does not
The calculator maps a cable class to the VLF withstand test voltage in IEEE 400.2-2024, then to the lowest VA-TEK test set whose rated output reaches that voltage. It covers the three test classes the standard distinguishes — installation, acceptance and maintenance — and the two waveforms a VLF set can produce.
It is a lookup, not a design tool. It does not decide whether a VLF test is appropriate for a given cable, does not cover damped AC (that is IEEE 400.4, a different guide), and does not override a utility’s own specification. Where a network operator or cable manufacturer specifies a test voltage, their specification governs.
2. VLF test voltage calculator
Test voltage: IEEE 400.2-2024, Table 3 (kV rms, phase to earth). Set ratings: VA-TEK VLF data sheets (kV peak). Confirm against the governing specification before issuing a procedure.
3. How to read the result
Three quantities drive everything downstream of the number the tool returns.
Voltage is expressed against U0, the phase-to-earth voltage
A cable is marked U / U0 — for example 8.7/15 kV. The test voltage is applied between conductor and screen, so it is the phase-to-earth stress that matters, and it is written as a multiple of U0. Enter the system voltage (phase to phase) above and the tool keyed the table row to it; conflating the two is the single most common arithmetic error in VLF records.
rms and peak are not the same number
IEEE 400.2-2024 tables the test voltage in kV rms. A VLF test set is rated, and displays, in kV peak. For a sinusoidal output the peak amplitude is the rms value times √2, so a 32 kV rms requirement lands on a 45 kV peak set. The tool shows both figures because an acceptance certificate and a purchase order speak in different units. A cosine-rectangular wave has a different rms-to-peak relationship, which is why the standard gives it its own, separately tabulated values.
Duration follows the class
Installation and acceptance holds run 60 minutes at 0.1 Hz. Maintenance holds run 30 minutes, and the standard notes that a stable 15-minute hold may be used on medium-voltage cable. A longer hold is not automatically safer — a VLF test deposits a small cumulative stress in the insulation, which is why duration is specified rather than maximised. The interaction is set out in VLF test duration and frequency.
4. IEEE 400.2-2024 test-voltage table (sinusoidal)
The values the calculator returns, for reference. All figures are kV rms, phase to earth. Installation and acceptance are the higher-stress columns; maintenance is the lower one.
| Cable system voltage (kV) | Installation | Acceptance | Maintenance |
|---|---|---|---|
| 5 | 9 | 10 | 7 |
| 8 | 11 | 13 | 10 |
| 11 | 14 | 16 | 13 |
| 15 | 19 | 21 | 16 |
| 20 | 24 | 26 | 20 |
| 22 | 26 | 28 | 22 |
| 25 | 29 | 32 | 24 |
| 28 | 32 | 36 | 27 |
| 30 | 34 | 38 | 29 |
| 33 | 37 | 42 | 31 |
| 35 | 39 | 44 | 33 |
| 46 | 51 | 57 | 43 |
| 66 | 72 | 80 | 60 |
| 69 | 75 | 84 | 63 |
| 90 | 98 | 110 | 82 |
Values transcribed from IEEE 400.2-2024 Table 3. The standard also notes that the test voltage may be reduced where the cable’s operating voltage is below its rating, and that the level is applied with the owner’s agreement. Different editions and different specifications — notably the 3U0 option in IEC 60502-2 and many utility standards — can call for higher levels, so treat this table as the IEEE basis and the governing specification as the final word.
5. Which VA-TEK test set reaches which class
VA-TEK builds two families, and the calculator picks from both.
| Test set | Output (peak) | Typical cable class | Standout capability |
|---|---|---|---|
| VLF-30-90 family (VLF-30 / 40 / 50 / 60 / 80 / 90) | 30–90 kV peak, sine, 0.1–0.01 Hz | MV through 46 kV | One split platform, six voltage ratings, withstand testing |
| VLF-34TD | 34 kV peak / 24 kV rms | 5–15 kV | Withstand + tan delta + DC + sheath test with fault location |
| VLF-45TD | 45 kV peak / 31.8 kV rms | 5–25 kV | Withstand + tan delta + DC + sheath test with fault location |
Where a monitored withstand or a diagnostic is required, the tan-delta and partial-discharge measurements are provided by the TD sets. On classes above the 45 kV peak range, a dielectric-loss diagnostic is not offered in the current line — a plain withstand with the appropriate family model is the configuration that fits. The full range is on the VA-TEK VLF test set page, and class-by-class selection is set out in choosing a VLF test set by voltage class.
6. Frequently asked questions
Is the test voltage based on the system voltage or on U0?
On U0, the phase-to-earth voltage — the stress the insulation actually sees between conductor and screen. IEEE 400.2-2024 tabulates the value against the cable’s system voltage; the tool resolves that to the phase-to-earth stress for you.
Why does the calculator show both rms and peak?
Because the standard and the equipment use different units. IEEE 400.2-2024 tables the test voltage in kV rms; VA-TEK sets are rated and display in kV peak. For a sine wave the peak is the rms value times √2, so both numbers describe the same test.
Is a higher test voltage better?
No. The test voltage is set by the standard and the test class, and a higher level is not automatically a better test. It applies more stress to the insulation, and on aged cable that stress is a real consideration. Use the level your specification calls for.
Can the same set test any cable class?
No — the voltage class of the set has to reach the test voltage of the cable class, and the load rating at 0.1 Hz has to reach the cable length. The VLF hipot tester buyer’s checklist sets out both, and the cost drivers are covered in what a VLF hipot test set costs.
Does this calculator cover damped AC (DAC / oscillating wave)?
No. This tool covers VLF under IEEE 400.2-2024. Damped AC is governed by IEEE 400.4, which is currently Inactive – Reserved. The two are compared in VLF versus DAC testing.
7. Where to go next
For how the test voltage is chosen end to end, see VLF test voltage selection. For the standard behind the table, see what IEEE 400.2-2024 requires. To size a set to your cable list, use selection by voltage class and the buyer’s checklist, or request a configuration quote.