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HF-TC-649 Transformer Core Grounding Current Tester
This Transformer Core Grounding Current Tester adopts clamp-on measurement to detect transformer core grounding current. It judges multi-point grounding faults online without power cut, widely used in daily substation inspection.
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This tester is specially developed for on-site measurement of transformer core grounding current and leakage current in power systems. It consists of main unit, current clamp, monitoring software and communication cable.
Transformers normally adopt single-point core grounding. If two or more grounding points appear, a closed current loop will form between the core and ground. The current may reach tens of amperes, leading to local overheating or burnout of the core and severe consequences for the power grid. This instrument can detect latent faults of transformers at an early stage and serves as essential equipment for safe operation and routine maintenance.
It is widely used in substations and power plants to test leakage current on transformer and reactor cores and clamping parts. It can also conduct leakage & current tests for power, communication, meteorology, railway, oilfield, construction, metering, scientific research, mining enterprises and other overhead lines & equipment.
The main unit is equipped with a high-speed processor and a 3.5-inch color touch LCD screen for intuitive touch operation. It can display real-time current values and waveforms. Adopting FFT transformation and digital filtering, it delivers highly accurate test data. Built-in functions include alarm threshold setting, date clock, auto power-off, test serial number configuration and USB data export to PC. The instrument can store up to 200 groups of data and waveforms.
The current clamp is made of special alloy with magnetic shielding technology. It has strong anti-interference capability and minimal impact from external magnetic fields, ensuring long-term stable, high-precision and reliable measurement.
Clamp inner size: 80mm×80mm, suitable for cables ≤Φ80mm or flat steel grounding strips 96mm×4mm. The portable clamp design enables non-contact measurement without disconnecting conductors, safe and efficient.
Clamp inner size: 80mm×80mm, suitable for cables ≤Φ80mm or flat steel grounding strips 96mm×4mm. The portable clamp design enables non-contact measurement without disconnecting conductors, safe and efficient.
The supporting monitoring software supports real-time online monitoring and history query, dynamic waveform display, alarm threshold configuration, as well as reading, saving and printing historical data.
Technical Specifications
| Item | Specification |
|---|---|
| Function | Transformer core grounding current test; AC leakage current & online current measurement |
| Power Supply | DC 9V alkaline battery (LR6 1.5V ×6) |
| Measuring Method | Clamp-on CT |
| Clamp Opening Size | 80mm×80mm (fits cables Φ≤80mm or flat steel 96mm×4mm) |
| Measurement Range | AC 0.00mA ~ 1000A Frequency: 10Hz ~ 1000Hz |
| Resolution | AC 0.01mA |
| Accuracy | ±1.5% ±3 digits |
| Display | 3.5-inch color touch LCD (3200×240 dots) |
| Operation | Touch screen + physical keys |
| Main Unit Dimensions | 198mm×100mm×45mm |
| Current Clamp Dimensions | 194mm×145mm×40mm |
| Weight | Main unit: 450g (including batteries); Clamp: 780g |
| LCD Display Area | 71mm×53mm |
| Electric Field Interference | Approx.10mA with external 100A electric field at 10mm distance |
| Sampling Rate | 2 times/second |
| Data Storage | 200 groups (data will not be lost after power-off or battery replacement) |
| Date Clock | Built-in clock with setting function |
| Test Numbering | Support test point serial number setting |
| Auto Power-off | Configurable; default auto power-off after 5 minutes startup |
| Touch Screen Calibration | Available |
| USB Interface | Export stored data to computer |
| Alarm Setting | Threshold adjustable: 10mA ~ 99.99A |
| Alarm Indication | LCD flashing + buzzer when exceeding threshold |
| Rated Circuit Voltage | Suitable for circuits below AC 600V |
| Over-range Display | “OL” symbol |
| Low Battery Reminder | Low battery icon appears at 7.2V±0.1V; measurement remains accurate |
| Maximum Operating Current | 180mA |
| Clamp Cable Length | 2 meters |
| Operating Temperature & Humidity | -10℃ ~ 40℃; ≤80%RH |
| Storage Temperature & Humidity | -10℃ ~ 60℃; ≤70%RH |
| Dielectric Strength | AC 2kV (rms) between screws and housing for 1 min |
| Safety Standard | IEC1010-1, IEC1010-2-032, Pollution Degree 2, CAT III 600V, IEC61326 (EMC) |
| Standard Accessories | Main unit ×1; current clamp ×1; USB cable ×1; software CD ×1; LR6 batteries ×6; carrying bag ×1 |
Field Application of Transformer Core Grounding Current Tester

Packing List
| No. | Description | Qty | Unit | Remarks |
|---|---|---|---|---|
| 1 | Main Tester Unit | 1 | Set | HF-TC-649 host |
| 2 | 80×80mm Clamp-on Current Probe | 1 | Pcs | 2m cable |
| 3 | USB Communication Cable | 1 | Pcs | Data transmission |
| 4 | Software CD | 1 | Pcs | PC monitoring software |
| 5 | LR6 Alkaline Batteries | 6 | Pcs | 1.5V |
| 6 | Portable Carry Bag | 1 | Pcs | Shockproof storage |
| 7 | Operation Manual (English & Chinese) | 1 | Copy | |
| 8 | Calibration Certificate | 1 | Copy | |
| 9 | Warranty Card | 1 | Copy |
FAQ
Q1: What is the main application of this tester?
A1: It measures transformer core grounding current online to diagnose multi-point core grounding faults. It can also test leakage current of reactors and substation equipment.
Q2: Is power cut required during measurement?
A2: No. Adopting clamp CT design, you can measure directly on live grounding wire without disconnecting any circuit.
Q3: What size conductor can the current clamp measure?
A3: Clamp opening 80mm×80mm, applicable for cables below Φ80mm or flat steel grounding strip 96mm×4mm.
Q4: What is the measuring range and resolution?
A4: AC range: 0.00mA ~ 1000A; resolution 0.01mA, suitable for capturing tiny abnormal grounding current.
Q5: Can the instrument store test data?
A5: It can save up to 200 groups of data and waveforms. Data will not be lost when replacing batteries. Data can be exported to PC via USB.
Q6: Does it support alarm function?
A6: Yes. Users can set alarm threshold from 10mA to 99.99A. The screen flashes and buzzer activates once exceeding the limit.
Q7: What frequency signals can it detect?
A7: Measuring frequency range covers 10Hz ~ 1000Hz, able to monitor fundamental wave and harmonic components of grounding current.
Q8: Is the instrument resistant to external magnetic interference?
A8: The clamp adopts special alloy and magnetic shielding technology to reduce interference from surrounding magnetic fields and guarantee stable readings on site.
Q9: Can I view real-time current waveform?
A9: Yes. The 3.5-inch touch LCD displays real-time waveform, helping engineers analyze abnormal current characteristics.






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