VA-TEK Engineering A VLF hipot test set is not a commodity with a list price. Two units that both say “60 kV” on the panel can differ several-fold in cost, and the difference is almost never in the label — it is in what the set can actually do to a real cable. This article explains the four parameters that set a VLF test set’s price, what usually sits outside the headline number, and how to compare two quotes on equal terms.
Key takeaways
- Price follows four parameters: voltage class, load rating at 0.1 Hz, waveform, and diagnostics (tan delta / partial discharge).
- The µF rating at 0.1 Hz decides how long a cable you can test, and it moves price more than the kV figure people quote.
- Sine output costs more than cosine-rectangular and is the only basis for tan delta and PD.
- Calibration, spares, training and freight are often outside the quoted equipment price — normalise before comparing.
- Compare quotes on the same voltage basis, the same frequency and the same load — not on a single headline number.
1. The four parameters that set the price
Every VLF hipot test set is specified by the same four things, and each one moves the cost:
| Parameter | What it decides | Effect on price |
|---|---|---|
| Voltage class | The highest cable class the set suits | Higher class → larger HV section, more cost |
| Load at 0.1 Hz (µF) | How long a cable one set can charge | The quiet driver: more µF → more power stage |
| Waveform | Sine or cosine-rectangular | Sine carries a cost premium and unlocks diagnostics |
| Diagnostics | Withstand only, or + tan delta / PD | Diagnostic options move price fastest |
If a quote only tells you one of these, it is not comparable yet. The rest of this article takes each in turn.
2. Voltage class — the headline number
Voltage class is the figure buyers quote first, and it is the easiest to compare — as long as the basis is the same. A VLF set is rated by the peak of its output sine wave. A “60 kV” sine set and a “60 kV” cosine-rectangular set do not stress a cable identically, so the same number on two datasheets can mean two different things. Always confirm the basis before comparing: kV is peak, and the measurement method must match the waveform.
Higher classes need a bigger high-voltage section, and cost climbs with it. But class alone rarely decides a purchase — a set that is one class too small cannot reach a long cable, and one that is two classes too big is paid for on every job. The class you need follows from the cable you test most often, which is set out in how to choose a VLF test set.
3. Load rating at 0.1 Hz — the number that decides reach
This is the parameter buyers most often under-weight, and it is where much of the price actually lives. A VLF set is limited by the capacitance it can drive at the working frequency. Cable is a large capacitive load, and the capacitance per metre is fixed by the cable, so the load rating at 0.1 Hz sets the maximum cable length a set can charge to the required voltage.
Two sets at the same voltage class but different µF ratings are different products. The lower-frequency modes (0.05, 0.02, 0.01 Hz) extend reach by trading test time for capacitance, but the 0.1 Hz figure is the one that matters most, because tan delta and partial discharge are run there. A set with a stronger 0.1 Hz rating effectively tests longer cable without dropping frequency — and that capability is priced in.
The practical rule: size on the longest circuit in your programme, then keep a margin, because voltage sags on a load at the edge of the rating.
4. Waveform — sine versus cosine-rectangular
Cosine-rectangular output is efficient for a withstand test and the electronics are simpler, which shows in the price. But the waveform also decides what else the set can do. A continuous sine wave is the basis for tan delta and partial discharge measurement, and it is the waveform most standards-based acceptance criteria are written against. If you might ever want diagnostics, the sine set is the one that keeps the door open — and it carries a premium for exactly that reason.
5. Diagnostics — where price moves fastest
Once you go beyond a plain withstand, price separates quickly. Adding tan delta turns a pass/fail test into an insulation-condition trend. Adding partial discharge adds detection — and possibly localisation — of a defect the withstand alone would miss. Each is a measurement system in its own right, and each adds cost.
Whether to buy them is a question about what you are testing for, not a question about budget alone: a routine acceptance programme on healthy cable may only need withstand, while an ageing network or a repair-verification job is where tan delta and PD earn their cost. The condition-testing use case is covered in VLF tan delta testing.
6. What is usually outside the headline price
The equipment figure on a quote is rarely the whole cost. Watch for whether each of these is included:
- Calibration certificate — an accredited or traceable certificate for the measurement chain, without which acceptance results are hard to defend.
- Spares and consumables — HV leads, connectors, and any items with a service life.
- Training and commissioning — especially for a first VLF set or a team moving from DC testing.
- Freight, duty and lead time — for a unit of this size these are not trivial and vary by destination.
- Service and repair turnaround — ask what happens when the set needs attention, and where.
Two quotes can look far apart until these are put on the same footing — and a cheaper headline can end up the more expensive unit.
7. How to compare two quotes
Put both on one line, with the same basis:
| Compare on | Ask for |
|---|---|
| Voltage basis | Peak kV, and the measurement method used for it |
| Load | µF rating at 0.1 Hz (not only at the lowest frequency) |
| Frequency range | Sweep available, and accuracy |
| Waveform | Sine (and its THD) or cosine-rectangular |
| Diagnostics | Tan delta? PD? Detection only, or localisation? |
| Protection | Flashover trip time, ground check, closed-loop regulation |
| Evidence | Calibration certificate, test reports, standard compliance |
A supplier who can answer all seven on paper, and back the numbers with documents rather than adjectives, is the one whose price you can actually trust. The same list, expanded, is in the VLF hipot tester buyer’s checklist.
8. Total cost of ownership, not just purchase price
Over a five- to ten-year life the purchase price is only the entry. Recalibration intervals, spares, repair logistics, and the cost of a set that is under-specified for a job you later win all accumulate. A set that is correctly sized on load and includes the diagnostics you will need is usually the cheaper unit by the time it has paid for itself — which is why the µF rating and the waveform deserve more attention than the headline kV.
9. Frequently asked questions
Is a higher kV rating always more expensive?
Generally yes — a higher voltage class means a larger high-voltage section. But the load rating at 0.1 Hz and the diagnostic options can move the price more than one step of voltage class, so never judge cost from the kV figure alone.
Why do two “60 kV” VLF sets cost very differently?
Usually because they differ in load rating at 0.1 Hz, in waveform (sine versus cosine-rectangular), or in diagnostics. Two sets at the same voltage class but different µF ratings are different products with different reach.
Is cosine-rectangular cheaper, and is it enough?
Cosine-rectangular is typically less expensive and adequate for a plain withstand test. It is not the usual basis for tan delta or partial discharge, so if diagnostics are on your roadmap, a sine set is the cheaper choice over its whole life.
Does the price include calibration?
Often not. Ask explicitly for the calibration certificate and whether it is accredited or traceable, because it is what makes an acceptance result defensible.
10. Where to go next
Start from the cable, not the price: how to choose a VLF test set covers voltage class and load sizing. For the test itself, see VLF test voltage selection and the wider VLF testing guide. The VLF hipot test set range lists the voltage classes and load ratings of the VA-TEK family from 30 to 90 kV peak, and you can request a configuration quote for the cables you actually test.
