VLF Tan Delta and Partial Discharge Tester
0.1 Hz Sine Wave · Up to 90 kV
Withstand + Tan-δ + Partial Discharge in one compact platform.
Trusted by power utilities across 100+ countries.
Direct manufacturer — factory lead time 2–3 weeks.
ZXVLF Series — Choose Your Voltage Range
All models feature 0.01 / 0.02 / 0.05 / 0.1 Hz quad-frequency, colour touchscreen, and IEC 60060-3 compliance. The YJS series adds integrated Tan-δ measurement.
0.02Hz ≤2.2µF · 0.01Hz ≤5.5µF
0.02Hz ≤2.2µF · 0.01Hz ≤5.5µF
0.02Hz ≤2.2µF · 0.01Hz ≤5.5µF
0.02Hz ≤2.2µF · 0.01Hz ≤5.5µF
0.02Hz ≤2.2µF · 0.01Hz ≤5.5µF
0.02Hz ≤2.2µF · 0.01Hz ≤5.5µF
- • Replaces Megger VLF Sine 37kV -- with onboard Tan-δ measurement included.
- • Covers 10 kV cable systems per IEEE 400.2 — higher voltage rating than Megger VLF 37kV, same 22 kg weight, integrated Tan-δ.
- • Full diagnostic suite: VLF withstand + Tan-δ condition assessment + PD localization — automated report generation with graphical visualization.
- • Automatic test data storage with Bluetooth + software remote communication for processing and analysis.
- • Full diagnostic suite: VLF withstand + Tan-δ condition assessment + PD localization — automated report generation with graphical visualization.
- • Automatic test data storage with Bluetooth + software remote communication for processing and analysis.
Which VLF Cable Test System Do You Need?
Answer two questions -- our system recommends the right model.
ZXVLF Series vs. Megger VLF Sine 37 kV — Full Technical Comparison
Two models, two configurations -- independently verified against Megger's published datasheets. Expand each panel to review the full parameter table.
VLF Main Unit Comparison
ZXVLF-YJS34 & ZXVLF-YJS45 vs. Megger VLF Sine 37 kV · Output voltage / current / capacitive load / tan-δ / general specs
34 kV / 45 kV peak
vs 37 kV peak
22 kg vs 29 kg
▼
| Parameter | ZXVLF-YJS34 Our Product — 34 kV peak |
ZXVLF-YJS45 Our Product — 45 kV peak |
Megger VLF Sine 37 kV Import Reference |
|---|---|---|---|
| Output Voltage | |||
| VLF Sine Output | max. 24 kVRMS (34 kVpeak) | max. 31.8 kVRMS (45 kVpeak) | 0 – 26 kVRMS (37 kVpeak) |
| DC Voltage | ± 1 – 34 kV | ± 1 – 45 kV | ± 0 – 37 kV |
| Rectangular Wave Voltage | — | — | 0 – 37 kV |
| Voltage Resolution | 0.001 kV | 0.001 kV | 0.1 kV |
| Accuracy | ± 1% | ± 1% | ± 1% |
| Output Current | |||
| Max. Output Current | 0 – 30 mA | 0 – 30 mA | 37 mA @ 37 kVpeak |
| Current Resolution | 1 μA | 1 μA | 1 μA |
| Accuracy | ± 1% | ± 1% | ± 1% |
| Maximum Capacitive Load | |||
| @ 0.1 Hz | 1.0 μF @ 24 kVRMS | 1.0 μF @ 31.8 kVRMS | 1.6 μF @ 26 kVRMS |
| @ 0.05 Hz | 2.0 μF @ 24 kVRMS | 2.0 μF @ 31.8 kVRMS | 2.3 μF @ 18 kVRMS |
| @ 0.01 Hz | 16.0 μF @ 18 kVRMS | 10.0 μF @ 22 kVRMS | — |
| Maximum Capacity | 16 μF | 10 μF | 10 μF |
| Dielectric Loss Factor — tan-δ (VLF TD) | |||
| VLF-Sine Measuring Range | 1 – 24 kVRMS | 1 – 31.8 kVRMS | Built-in optional 0.01 – 0.1 Hz |
| Load Range | 1 nF – 16 μF | 1 nF – 10 μF | Standard — built-in |
| Resolution | 1×10−5 | 1×10−5 | 10−5 or 10−6 |
| Accuracy | 1×10−4 | 1×10−4 | 10−4 |
| Measuring Range | 1×10−4 – 9999.9×10−4 | 1×10−4 – 9999.9×10−4 | 10−4 – 100 |
| tan-δ Test Frequency | 0.1 Hz | 0.1 Hz | 0.01 – 0.1 Hz |
| General Parameters | |||
| Power Consumption | max. 600 VA | max. 800 VA | 1,500 VA |
| Reverse Voltage Protection | 13 kV | 15 kV | Auto-discharge protection |
| Data Interface | USB 2.0 | USB 2.0 | USB + LAN + Wireless |
| Display | — | — | 7" Colour Touchscreen |
| Internal Memory | — | — | ≥ 1,000 datasets |
| Sheath Testing | ✗ | ✗ | ✓ 0 – −20 kV DC |
| Dimensions (W × H × D) | Peli Case 1430 — 430 × 240 × 340 mm (shared) | 529 × 478 × 380 mm | |
| Weight | 22 kg (shared housing) | 29 kg | |
| Operating Temperature | −10°C to +50°C | −20°C to +55°C | |
| Storage Temperature | −20°C to +60°C | −20°C to +70°C | |
| Safety & EMC | CE — 2014/35/EC, 2014/30/EC, EN 60068-2 | ISO 9001, CE | |
| UI Languages | EN / ZH / RU / ES and more | 10+ languages | |
* Megger specifications sourced from VLFSinus37KV_DS_EN_V01. ZXVLF specs from factory documentation.
PD Module Comparison
ZXVLF-YJS34 + PD & ZXVLF-YJS45 + PD vs. Megger VLF Sine 37 + PDS 62-SIN · Resolution / localisation / signal separation / data & comms
0.1 pC | 0.1 m resolution
T-Fmap + Spectrum
IP67 protection
▼
| Parameter | ZXVLF-YJS34 + PD Our Product — Combined Set |
ZXVLF-YJS45 + PD Our Product — Combined Set |
VLF Sine 37 + PDS 62-SIN Import Reference |
|---|---|---|---|
| PD Measurement Parameters | |||
| PD Localisation Accuracy | 1% | 1% | 1% of cable length |
| PD Resolution | 0.1 pC | 0.1 m | 0.1 pC | 0.1 m | ± 1 pC | ± 1 m |
| Sensitivity Range | — | — | 2 pC – >100 nC |
| Self-Noise Level | — | — | < 2 pC |
| Sampling Precision | 14 bit | 14 bit | 125 MHz (8 ns) |
| Signal Separation Method | T-Fmap + Spectrum Filtering | T-Fmap + Spectrum Filtering | PRPD (Phase-Resolved PD Pattern) |
| Measuring Range | Full cable length | Full cable length | 0 – 16,000 m (v/2 = 80 m/μs) |
| Pulse Repetition Rate | — | — | 100 kHz |
| Bandwidth | — | — | 3 / 20 MHz (switchable) |
| HV Coupling Capacitor | — | — | 25 nF |
| Compatible Voltage | Matched to ZXVLF unit | Matched to ZXVLF unit | All VLF sine testers up to 62 kVpeak |
| Data & Communication | |||
| Data Interface | Ethernet + Bluetooth | PC software + USB (3 hardware keys) | |
| Test Report | Auto-generated on host unit — graphical display | MeggerBook Lite software — one-click report | |
| Data Processing | Bluetooth + software sync; browse & analyse on PC | Real-time evaluation — no post-processing required | |
| PD Calibrator | — | — | Included (100 pC – 100 nC) |
| Mechanical & General | |||
| UI Language | English | Multi-language incl. | |
| PD Module Weight | ≤ 15 kg (host unit) | 15 kg (incl. laptop, cables, calibrator) | |
| Protection Class (PD) | ✓ IP67 (with protective case) | Standard enclosure (optional IP67 transport case) | |
| Compliance Standard | — | IEC 60270 | |
* Megger PD specifications sourced from PDS62-SIN_DS_EN_V04a.
VLF vs. Power Frequency vs. Series Resonance — One Table, Full Picture
Three methods, one job. "Why not just use power-frequency transformers?" · "When do I actually need series resonance?" -- Engineering answers from first principles to field selection.
| Dimension | VLF 0.1 Hz Sine Wave | Power Frequency AC 50/60 Hz | Variable-Frequency Series Resonance |
|---|---|---|---|
| Voltage Nature | AC sine wave at 0.1 Hz; one cycle every 10 s | AC sine wave at service frequency, 50/60 Hz | AC sine wave, typically 20–300 Hz, close to service-frequency stress |
| Main Application | MV cable field withstand test, maintenance test and Tan Delta diagnosis | Factory/laboratory AC withstand test; suitable for short test objects | AC withstand testing for cables and other capacitive test objects during commissioning and maintenance |
| Typical Cable Range | Distribution cables below 35 kV class; higher application depends on project specification | Technically valid for many voltage classes, but field use is limited by cable capacitance | Not limited to a specific cable voltage class; configuration depends on test voltage, load capacitance and site conditions |
| Standard Reference | IEEE 400.2; IEC 60060-3; IEC 60502-2 where applicable | IEC 60060-1 / IEC 60060-3; relevant cable product standards define test level | IEC 60060-3; IEC 60840; IEC 62067; relevant project or equipment test standards |
| Field Practicality | Portable, low input power, suitable for field teams and mobile testing | Requires large transformer and high charging current; usually impractical for long field cables | Requires resonant reactor system, control unit, voltage divider and experienced operators |
| XLPE Cable Suitability | Good for field withstand and Tan Delta diagnosis; avoids DC space-charge issues | Closest to actual service-frequency stress, but not practical for most long field cable tests | Suitable for AC withstand testing of XLPE cable systems; especially useful when high test capacity is required |
| Diagnostic Capability | Can support Tan Delta and monitored withstand test; PD depends on system configuration | PD measurement possible in factory or controlled laboratory environment | Can be combined with PD measurement depending on system configuration and site noise conditions |
| Power Supply Requirement | Low input power; often suitable for single-phase supply or small generator, depending on load capacitance | Very high input power required due to cable charging current | Resonance reduces required supply capacity compared with direct power-frequency AC testing |
| Equipment Weight | Compact and portable; suitable for site movement | Heavy equipment; usually requires lifting and transport vehicle | Modular system; reactor, divider, control unit and accessories may require vehicle transport |
| Relative Cost Level | Low to medium | High | Medium to very high, depending on voltage level and system capacity |
| Best Fit | Commissioning and maintenance tests for distribution cables below 35 kV class | Factory routine/type test or very short cable sections | Various acceptance tests and preventive maintenance tests; not limited to a specific cable voltage class |
| Main Limitation | Not identical to 50/60 Hz service frequency; acceptance depends on project standard and local utility practice | Heavy, costly and difficult for field use on long cables | Requires proper reactor configuration, capacitance matching and skilled setup |
| Procurement Focus | Output voltage, load capacitance, test frequency, Tan Delta function, test duration, cable length | Transformer capacity, PD level, insulation level, laboratory conditions | Rated voltage/current, reactor configuration, frequency range, load capacitance, PD noise level and site logistics |
| Industry Use Trend | Widely used for MV distribution cable field testing and maintenance | Mainly used in factory or laboratory testing | Widely used for AC withstand tests where high test capacity is required, especially for field acceptance and preventive testing |
Please send us your cable rated voltage U0/U, cable length, cable type, applicable test standard and test purpose. Our engineers will calculate the required output voltage, load capacitance, test frequency and recommend a suitable equipment configuration.
Engineering Scenarios
How utilities and contractors use ZXVLF systems in the field -- with quantified outcomes.
Underground Cable Acceptance Test After New Installation
A city utility needs to perform acceptance testing on 3.2 km of newly installed 10 kV XLPE cable (3×185 mm²) before energization. The manholes are accessible only by narrow access shafts — equipment weight is critical.
Using ZXVLF-30kVB: Full withstand test at 3U₀ for 60 minutes completed in under 3 hours. Single technician operable. IEC 60502-4 compliant test report generated automatically.
Condition Assessment — 8-Year-Old XLPE Cable Before Refurbishment Decision
A 110 kV substation feeder (35 kV, 1.2 km, 3×300 mm²) shows elevated dielectric loss after 8 years in service. The asset manager needs data to decide: repair, replace, or continue operation.
Using ZXVLF-YJS45: Combined withstand + Tan-δ measurement identifies three sections with Tan-δ > 0.4 × 10⁻³ (IEEE 400.2 alarm threshold). PD not yet detectable. Targeted joint replacement recommended.
Cable Repair Verification After Fault Location and Joint Repair
Following a cable fault on a 20 kV feeder (0.8 km), the repair crew has replaced the damaged joint. Before re-energization, a withstand test is required to verify the repair quality per IEC 60060-3.
Using ZXVLF-40kVB: 5-minute withstand at 2U₀ confirms repair integrity. Test result archived with GPS location and timestamp for asset management records.
30 Years of Power Test Expertise
WUHAN GDZX POWER EQUIPMENT CO., LTD. is a professional manufacturer of high-voltage electrical testing equipment, providing reliable testing solutions for power utilities, electrical contractors, cable manufacturers, substations, and high-voltage laboratories.
Our products cover VLF cable test sets, AC resonant test systems, transformer test equipment, relay protection test sets, insulation resistance testers, and other high-voltage testing instruments. With practical engineering experience in power system maintenance and high-voltage testing applications, GDZX supports customers in field testing, commissioning, routine maintenance, and laboratory testing.
We understand that voltage levels and testing requirements differ from country to country. GDZX can customize equipment according to local voltage standards, grid requirements, site conditions, and specific project needs, helping customers choose suitable solutions for their power systems.
Before shipment, each unit is factory-tested to verify performance, safety, and operating stability. A factory inspection and test report is provided with the equipment, giving customers clear documentation before delivery.
GDZX exports to 100+ countries and maintains regional technical support partnerships in Southeast Asia, the Middle East, Africa, and other key markets. We support international customers with product selection, technical communication, documentation, training guidance, and after-sales service for high-voltage testing projects.
Facility photos available on request -- contact us for a virtual factory tour.
Our Team
Building a strong team culture through shared experiences, annual meetings, and collaborative activities.
Our overseas on-site project case studies
On-site case study for an overseas client; images provided by the client.
Standards & Certifications
All ZXVLF products are designed and tested to meet the following international standards.
Frequently Asked Questions
Answers to the most common technical and procurement questions from engineers and procurement managers.
What is the difference between VLF withstand testing and power-frequency withstand testing? +
VLF (Very Low Frequency) testing uses a 0.1 Hz sine wave instead of the standard 50/60 Hz power frequency. For cable testing, this is significant because the reactive charging current of a cable is proportional to frequency — at 0.1 Hz, the required current (and therefore the generator power) is 500–600× lower than at 50 Hz. This means a VLF unit weighing 25 kg can test cables that would require a 500 kVA power-frequency test set. VLF is now the international standard method for field cable testing per IEC 60060-3 and IEEE 400.2.
What does Tan-δ (Tan delta / dissipation factor) measurement tell me about my cable? +
Tan-δ is the ratio of the resistive (lossy) current to the capacitive (charging) current in the cable insulation. A healthy XLPE cable has Tan-δ below 1 × 10⁻³. Values above 3 × 10⁻³ (IEEE 400.2 warning level) indicate moisture ingress, electrochemical treeing, or thermal degradation. The ZXVLF-YJS series measures Tan-δ at three voltage levels simultaneously, producing a "Tan-δ vs voltage" curve — a rising curve indicates water treeing, while a flat elevated baseline suggests uniform insulation degradation. This data allows asset managers to make evidence-based decisions on repair vs. replacement.
Can a single ZXVLF-YJS45 unit replace both the Megger VLF Sine 37kV and the PDS 62 SIN? +
For withstand testing and Tan-δ measurement: yes, completely. The ZXVLF-YJS45 integrates both functions in a single 22 kg unit, with a higher peak voltage (45 kV vs. 37 kV) and higher cable capacitance rating (12 µF vs. 10 µF). The Megger PDS 62 SIN also adds partial discharge (PD) detection capability, which the YJS series does not include. If your test programme requires PD location , you would need a separate PD detector. For the large majority of 6–35 kV cable testing requirements — acceptance testing, Tan-δ condition assessment, and post-fault verification — the ZXVLF-YJS45 is a complete solution.
Which model should I choose for a 35 kV cable system? +
For a 35 kV cable system, the required withstand test voltage per IEC 60502-4 is typically 2U₀ to 3U₀, where U₀ = 20.2 kV (35/√3). This gives a test voltage of 40.4 kV to 60.6 kV peak. For acceptance withstand only: the ZXVLF-50kVB (50 kV peak) or ZXVLF-60kVB (60 kV peak) are appropriate. For condition assessment with Tan-δ (the more informative test): the ZXVLF-YJS45 (45 kV peak, 31.8 kV RMS) covers the Tan-δ measurement range at 1.5U₀ and 2U₀, which is the standard IEEE 400.2 test protocol — this is the most commonly specified configuration for 35 kV cable maintenance programmes.
What is your lead time and what does the delivery include? +
Standard lead time is 2–3 weeks from order confirmation and receipt of advance payment. Each shipment includes: the main VLF unit, HV output cable (standard 5 m, extension available), earthing leads, operating manual (English), factory test report with calibration certificate, and a transport case. Optional accessories include: extension HV cables, additional earthing sets, and a second calibration certificate from an accredited third-party lab. We ship under FCA, FOB Wuhan, or CIF as preferred. DDP to select countries is available — enquire for details.
Do you support FAT (Factory Acceptance Test) and SAT (Site Acceptance Test)? +
Yes. Factory Acceptance Testing is available for all orders — customers or their appointed inspectors are welcome at our facility in Wuhan. We can prepare a FAT procedure document aligned to your project specification in advance. For Site Acceptance Testing, we provide commissioning support documentation and can arrange on-site technical assistance in most regions — contact us for availability in your country. For large project orders (typically 3+ units), we can include on-site commissioning in the contract price.
How does your warranty and after-sales service work? +
All ZXVLF products carry a 12-month warranty covering manufacturing defects. Technical support is available by email and WhatsApp in English and Chinese. For most fault scenarios, remote diagnosis resolves the issue within 48 hours. If a hardware repair is required, we provide a repair service at our factory with a typical turnaround of 2–3 weeks including return shipping. Extended warranty and preventive maintenance contracts are available — please enquire when placing your order.
Request a Quotation or Spec Sheet
Our engineers respond within 24 hours. Tell us your cable parameters and we'll recommend the exact model, include a compliance checklist, and provide pricing for your project.
- ✓ Detailed technical specification sheet (PDF)
- ✓ Compliance matrix vs. IEC 60060-3 / IEEE 400.2
- ✓ FOB / CIF pricing with Incoterms
- ✓ FAT/SAT test programme outline
- ✓ 1-year warranty, 3-year repair service.
Send an Inquiry
Fill in the form -- we respond within 24 hours.