Portable high-voltage VLF test sets generate a 0.1 Hz AC voltage to test cables without the size of a 60 Hz source. From b2 electronics, the HVA 68-2 delivers 68 kV peak with 2.0 µF; the HVA 68TD adds integrated tan delta and monitored withstand testing; the 14 kg HVA 28TD covers short and low-class cables. Kilovolt Prüftechnik Chemnitz offers the KPG series, with VLF and DC. The choice depends on the voltage class of the cable and its capacitance.
What a VLF hipot is
“Hipot” comes from high potential: a high-voltage test that verifies the insulation withstands. On medium-voltage cables, the DC hipot was the standard for decades. Today, for extruded-insulation cables (XLPE, PE, EPR), the recognized practice is very low frequency (VLF), a 0.1 Hz AC voltage that IEEE 400.2 describes for shielded cables from 5 kV upward (see VLF cable testing).
The reason is physical: the current that charges a cable grows with frequency. At 0.1 Hz the set needs a few hundred times less power than at 60 Hz. With a 1 µF cable at 44 kV rms, for example, the capacitive current is about 28 mA at 0.1 Hz and about 16.6 A at 60 Hz.
This guide describes three families of this type of equipment. The tests, with their voltages and times, are in power cable diagnostic tests.
The b2 electronics HVA family
The b2 electronics HVA sets share a design: dry construction with contacts that do not produce arcing (no oil to change) and a pure sinusoidal output independent of the load. They select the frequency automatically between 0.01 and 0.1 Hz depending on the load. They offer continuous operation, a screen that shows the waveform in real time and programmable test sequences. Two discharge systems, one electronic and one mechanical, and back-feed protection of 12 kV at 50 or 60 Hz.
| Model | Output | Load at 0.1 Hz | Weight | Diagnosis |
|---|---|---|---|---|
| HVA 28 | 29 kV peak, 21 kV rms | 0.5 µF at 20 kV rms | 14 kg | Expandable |
| HVA 28TD | 29 kV peak, 21 kV rms | 0.5 µF at 20 kV rms | 14 kg | Integrated tan delta |
| HVA 34-1 and 34TD-1 | 34 kV peak, 24 kV rms | 1.5 µF at 24 kV rms | 39 kg | TD version available |
| HVA 45 and 45TD | 45 kV peak, 32.3 kV rms | 0.9 µF at 32 kV rms | 39 kg | TD version available |
| HVA 60 | 62 kV peak, 44 kV rms | 1.0 µF at 44 kV rms | 57 kg | Expandable |
| HVA 68-2 | 68 kV peak, 48 kV rms | 2.0 µF at 44 kV rms | 57 kg | Expandable |
| HVA 68TD | 68 kV peak, 48 kV rms | 1.7 µF at 48 kV rms | 63 kg | Integrated tan delta |
The rated load depends on the voltage at which it is declared; do not compare a load at 20 kV with one at 48 kV.
HVA 28TD
It is the smallest: 14 kg, IP67 protection with the lid closed, a 4.3-inch color screen and a quick-change high-voltage cable. It performs VLF testing, DC and sheath testing with sheath fault location (the locator is not included). The TD version adds the tan delta unit and monitored withstand testing, which the manufacturer declares compliant with IEEE 400.2-2013. Its 0.5 µF limits it to cables of moderate length and low voltage classes.
HVA 68-2 and HVA 68TD
With 68 kV peak and 48 kV rms, they cover medium-voltage cables up to 46 kV according to the manufacturer, which cites IEEE 400.2-2013. The HVA 68TD measures 593 × 340 × 513 mm, weighs 63 kg and adds:
- Integrated tan delta diagnosis.
- Monitored withstand test (MWT) according to IEEE 400.2, which combines the withstand with the tan δ measurement.
- Arc Pre-Location (APL), which indicates the distance to the fault if the cable breaks down during the VLF test.
- Breakdown and charge voltage detection, sheath testing and sheath fault location with an external probe.
- Report download by USB or Bluetooth, with no computer on site, and reporting with b2 ControlCenter.
The HVA 68-2 weighs 57 kg and does not include integrated tan delta, although it can be expanded to a diagnostic system with the PD, TD or PDTD series.
Kilovolt KPG
Kilovolt Prüftechnik Chemnitz (Germany) makes the KPG series of portable test sets for medium-voltage cables, with VLF and DC. The designations KPG 24, 36, 44 and 54 kV correspond, according to the commercial information available, to the output voltage in rms. The commercial documentation cites IEC 60502-2, HD 620 and 621, DIN VDE 0276 and IEEE 400 for this series. Extruded-insulation and paper-insulated cables can be tested.
The load and weight of each model must be confirmed in the current manufacturer data sheet before choosing. A valid criterion for any VLF set: the load capacity at 0.1 Hz decreases as voltage rises, and a lower frequency, when the set offers it, allows testing more capacitive cables.
How to choose according to the cable
| Circuit data | What it decides |
|---|---|
| Voltage class (U0/U) | The test voltage set by the standard or the contract |
| Length and cross-section | The total capacitance, which must fit within the load of the set |
| Age and history | Whether diagnosis (tan delta) is advisable in addition to the withstand |
| Site accessibility | Weight and size; a 14 kg set fits where a 60 kg one does not |
To estimate the maximum length, b2 assumes 250 pF per meter of cable; the real value comes from the cable data sheet.
What sets it apart from a DC hipot
- Does the cable have extruded insulation (XLPE, PE, EPR)?
- Yes: Is it aged or an in-service cable?
- Yes: VLF at 0.1 Hz; avoid high DC
- No: VLF at 0.1 Hz according to the cable standard
- No: Is it paper-insulated (PILC)?
- Yes: VLF or DC, according to the standard and the contract
- No: Consult the cable standard
- Yes: Is it aged or an in-service cable?
Precautions that affect the result
- Load above the rated one. The circuit is divided or the frequency is lowered.
- Dirty terminations. They cause leakage that is mistaken for a defect.
- Connected equipment. Surge arresters and voltage transformers are isolated.
- Discharge and ground at the end. Always, even if the set discharges on its own.
Cable testing on request
Do you need this test? We run it for you: depending on your case we recommend the right test and equipment and include them in the quotation. That way you run the test your case really needs, without paying for extra ones.
See the scope in testing and commissioning (field work in Colombia, or elsewhere on request), in cable fault location, or ask for your quotation through the form.
Related guides
- Power cable diagnostic tests
- On-site withstand voltage test
- Power factor and tan delta test
- Power cables
- Medium-voltage splices and terminations
- b2 HVA 60: VLF test set for MV cable testing
- b2 TD60-MC: VLF tan delta for cable diagnosis
- VLF cable testing: withstand voltage and IEEE 400.2
References
- b2 electronics, product pages of the HVA series (b2hv.com/products/hva-series), HVA 68TD (b2hv.com/products/hva-series/hva68td) and HVA 28/28TD (b2hv.com/products/hva28-hva28td).
- Kilovolt Prüftechnik Chemnitz, KPG series: distributor commercial information; manufacturer data sheet pending confirmation.
- IEEE Std 400.2, guide for field testing of shielded power cable systems using VLF.
Frequently asked questions
What does TD mean in HVA 28TD and HVA 68TD?
It indicates that the set includes an integrated tan delta diagnostic unit, in addition to the VLF withstand test. Models without the suffix (HVA 68-2, HVA 60) generate the voltage and can later be expanded with diagnostic modules of the TD, PD or PDTD series.
What is the difference between a DC hipot and a VLF one?
A DC hipot applies a constant voltage; it is light but can leave trapped charge in aged extruded insulation, which is why IEEE 400 discourages high DC on those cables. VLF applies a 0.1 Hz AC voltage, closer to service conditions, with portable equipment. Many sets, among them the HVA and the KPG, do both.
What equipment is needed for a 15 kV or 34.5 kV cable?
It depends on the test voltage set by the standard or the contract for the cable class, on its total capacitance and on whether diagnosis is also wanted. It is not chosen by the cable rated voltage alone. That is why the recommendation is made from the circuit data: length, cross-section, insulation and age.