VLF Tan Delta Test System

The durable VLF Tan Delta Test System offered by Weshine, a professional manufacturer in China, is designed for insulation diagnosis and withstand testing of medium-voltage power cables. It integrates VLF AC voltage withstand and dielectric loss measurement into one compact unit. The equipment complies with CENELEC standards HD 620 S1:1996 and HD 621 S1:1996, applicable to PE, XLPE and paper-insulated cables.

During routine cable maintenance, invisible insulation defects including water tree aging, contamination, mechanical damage and partial deterioration cannot be detected by simple visual inspection. The 0.1 Hz VLF sine wave test applies AC stress to cable insulation while requiring far less power capacity than traditional 50 Hz test equipment, making field testing of long medium-voltage cables much easier.

This VLF Tan Delta Test System delivers VLF sine wave output for withstand tests and direct tan delta measurement. Tan delta reading reflects cable insulation’s dielectric loss factor, which judges aging and deterioration degrees. The unit automatically runs loss tests under multiple voltage levels following a fixed procedure: 0.5 U0 cycles, U0 cycles and 1.5 U0 cycles. After finishing all rounds, test data is saved and the cable is fully discharged.

Two standard configurations are available: 34 kV and 45 kV peak models. The 34 kV unit generates sine wave up to 24 kV RMS (34 kV peak); the 45 kV unit reaches 31.8 kV RMS (45 kV peak). DC voltage output is also built-in, ranging ±1~34 kV for the 34 kV version and ±1~45 kV for the 45 kV version. Rectangular wave and DC test modes are supported as well.

For cable sheath upkeep, the test machine supports sheath inspection and fault locating with maximum 10 kV output. Leakage current measurement under DC mode helps assess overall cable insulation quality. Built-in breakdown detection instantly cuts off high voltage once flashover or cable failure occurs, offering full protection.

The complete set includes main test host, high-voltage cable, grounding wire, power cord, USB flash drive and accessory bag. USB 2.0 port enables data export and firmware upgrade. All test logs are stored locally and can be exported to USB for report generation on PC. Matching software supports simultaneous opening of phase A/B/C data files and outputs detailed reports with test figures and dielectric loss curves.

Safety is the top priority. High voltage will be generated during operation, so only professionally trained technicians are allowed to operate. Operators must strictly follow five core safety rules: cut off power, lock out re-energization, verify zero voltage, ground and short-circuit, isolate adjacent live components. High-voltage testing needs two or more staff on site for supervision.

Product Guide

The integrated cable tester works by applying controllable 0.1 Hz sine voltage on tested cables. Compared with conventional 50 Hz AC testing, ultra-low frequency technology greatly lowers current demand for capacitive cable loads, enabling portable field inspection of medium-voltage cables.

Before cable connection, follow the five high-voltage safety rules strictly. Ensure the test cable is power-off, isolated, voltage-verified, grounded and short-circuited. All nearby live parts must be covered or separated. Only trained operators can run the equipment with at least one supervisor present.

Connect accessories in fixed order: link ground cable to the host grounding terminal first, then connect to station protective ground; attach high-voltage cable to the high-voltage output port; connect the high-voltage cable’s inner conductor to cable phase or sheath via matched fittings; fix the high-voltage cable shield to a nearby grounding bar; finally plug in the power cord.

For VLF withstand tests, select waveform, rated voltage, frequency and test duration. Real-time peak voltage, current, output waveform, set frequency and RMS values are displayed on screen. The timer starts automatically once voltage hits the preset value.

For tan delta diagnosis, activate the dielectric loss function and input the cable’s rated phase voltage U0. The machine will launch automatic test cycles, and each full measurement takes roughly 3 minutes 30 seconds. It records cable capacitance, resistance, average dielectric loss and real-time loss values under 0.5 U0, 1.0 U0 and 1.5 U0.

Once testing finishes, data auto-saves and the cable discharges completely. Users can browse historical records, export single or multiple logs to USB 2.0, and generate printable reports via supporting software. The tool displays loss curves and independent data for three cable phases.

When running sheath testing or fault pinpointing, confirm the cable sheath is not grounded at both ends, with no indirect ground through joints or attachments. The maximum output for sheath inspection and fault tracing is 10 kV.

Features

1．Supports VLF sine wave AC withstand testing

2．All-in-one dielectric loss tan delta measurement function

3．Two peak voltage options: 34 kV and 45 kV

4．Sine wave output: max 24 kV RMS or 31.8 kV RMS

5．Built-in DC voltage output for extra insulation tests

6．Rectangular wave voltage test mode available

7．DC mode leakage current measuring function

8．Max 10 kV output for sheath test and sheath fault pinpointing

9．Auto dielectric loss test sequences at 0.5 U0, U0 and 1.5 U0

10．Real-time peak voltage & current display during operation

11．On-screen real-time output waveform visualization

12．Automatic high-voltage cut-off upon voltage breakdown

13．Local internal storage for all test logs

14．Test data export via USB 2.0 interface

15．Supporting software for customized test report output

16．Firmware upgrade function via USB drive

17．Multi-language interface (English & Simplified Chinese)

18．Equipped with emergency stop button and high-voltage output lock

19．Reverse voltage protection design

20．Portable protective case design for outdoor field cable testing

Application Scenarios

Power Utilities

Grid operators adopt the test unit for medium-voltage cable commissioning, regular maintenance, tan delta diagnosis, sheath inspection and insulation evaluation on distribution networks and substations.

Transformer Manufacturers

Transformer and electrical equipment factories utilize the tester for cable and component insulation tests requiring VLF voltage and dielectric loss measurement.

Power Plants

Power stations rely on the equipment for station cable inspection, auxiliary generator cable maintenance, sheath testing and insulation diagnosis during maintenance outages.

Railways

Railway power supply networks lay medium-voltage cables in traction substations and transmission lines. The machine supports cable withstand tests and tan delta analysis during maintenance windows.

Industrial Plants

Mining, petrochemical, steel and manufacturing workshops use it for new cable acceptance tests, periodic maintenance and sheath fault investigation.

Universities

Colleges and research institutes apply the test device for teaching VLF cable testing theories, dielectric loss calculation, insulation aging analysis and high-voltage safety operation standards.

Testing Laboratories

Professional high-voltage and cable labs adopt this VLF Tan Delta Test System to conduct VLF withstand tests, tan delta measurement, sheath inspection and third-party cable diagnostic services.

Cable Maintenance

Cable service crews use the equipment for XLPE, PE and paper-insulated cable inspection, water tree aging diagnosis, sheath fault locating and test report making.

Applicable Test Items

1．VLF sine wave cable withstand testing

2．Medium-voltage cable tan delta dielectric loss testing

3．XLPE cable insulation aging diagnosis

4．PE cable withstand voltage inspection

5．Paper-insulated cable performance testing

6．Cable water tree deterioration assessment

7．Up-to-10kV cable sheath testing

8．Cable sheath fault pinpointing

9．DC voltage withstand testing

10．Rectangular wave voltage testing

11．DC mode leakage current measurement

12．New cable handover acceptance tests

13．Cable routine preventive maintenance tests

14．Three-phase integrated test report generation

15．Local log storage & USB data export

Customer Case

Industry Field: Medium-voltage cable maintenance service

Project Trouble

A power grid maintenance team needed to evaluate multiple aged XLPE cable feeders. Simple withstand tests could only check breakdown resistance, while the team also required dielectric loss data to judge insulation aging and identify cables with potential water tree defects.

Test Operation Flow

Technicians isolated the target cable, followed five safety specifications, grounded the whole set, connected high-voltage cable and shielding wire as instructed, then powered on the test unit. They selected tan delta test mode, filled in cable rated phase voltage U0, released emergency stop and high-voltage lock, then started automatic testing. The unit measured dielectric loss under 0.5 U0, U0 and 1.5 U0, stored data and discharged the cable after completion.

Test Outcome

Staff checked historical records and exported all data to a USB drive. Matching software generated phase comparison reports with dielectric loss values and trend curves. Cables with normal loss indicators remained in service, while severely deteriorated ones were scheduled for follow-up monitoring.

Application Advantages

The team finished both withstand voltage inspection and aging diagnosis with one portable device. Automatic test cycles, USB export and report generation greatly improve data traceability and cut manual paperwork workload.

FAQ

Q:What functions does this test equipment realize?

A:It completes medium-voltage cable VLF withstand testing, tan delta dielectric loss measurement, sheath inspection, sheath fault pinpointing, DC withstand testing, rectangular wave testing and leakage current detection.

Q:What is the difference between VLF withstand test and tan delta test?

A:VLF withstand test verifies whether cable insulation can bear specified AC voltage; tan delta test measures dielectric loss factor to judge insulation aging and deterioration degree.

Q:What voltage configurations are optional?

A:Two models: 34 kV peak and 45 kV peak. The 34 kV model outputs sine wave up to 24 kV RMS / 34 kV peak; the 45 kV model reaches 31.8 kV RMS / 45 kV peak.

Q:At what frequency is tan delta measured?

A:Tan delta measurement is performed under 0.1 Hz ultra-low frequency.

Q:What cable capacitance range supports tan delta testing?

A:34 kV model: 1 nF ~ 8 μF; 45 kV model: 1 nF ~ 5 μF.

Q:Can the equipment export test records?

A:Yes. Test logs are stored internally and exportable via USB 2.0. Exported files can be opened with dedicated software to generate formal test reports.

Q:Does it support sheath fault pinpointing?

A:Yes, the test machine supports sheath inspection and fault locating with maximum 10 kV output.

Q:Key safety notes during operation?

A:Only trained professionals can operate the unit. The test cable must be power-off, grounded and fully isolated before wiring. High-voltage testing requires on-site supervision, and emergency stop & high-voltage lock should be used correctly.

Weshine Advantages

Weshine Electric supplies professional electrical testing instruments for power grid operators, cable maintenance teams, engineering contractors, testing labs and all types of industrial users. For VLF and tan delta cable diagnosis, we focus on easy field operation, stable high-voltage output, precise loss measurement, complete data storage and report supporting functions. We provide one-stop service including model selection guidance, cable test scheme matching, safety operation training and customized testing solutions. With abundant engineering experience, strict quality control, full technical support, mature testing solutions and global after-sales service, we help clients finish cable withstand inspection and insulation diagnosis with clear, traceable test data. If you need reliable all-in-one cable diagnostic equipment, our VLF Tan Delta Test System can fully meet your on-site testing demands.

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