Characteristics and Usage of Transformer Core Ground Current Tester

I. Instrument Overview
The transformer core grounding current tester is a specialized instrument designed for detecting the grounding current of the transformer core and its accessories. It is an important detection device for ensuring the safe operation of the transformer and preventing multi-point grounding faults.
II. Detection Necessity
When the transformer is operating normally, the core must meet the requirement of one-point grounding. If there are two or more points of grounding, a closed circuit will be formed and a circulating current will be generated, which will lead to a series of problems:
Local overheating, burning of the core insulation
Causing the action of the gas relay
Causing oil decomposition, seriously affecting the service life and operational safety of the transformer
The transformer core grounding current tester can accurately capture the aforementioned tiny and dangerous electrical parameter changes.
III. Main Functions and Features
1. High-precision micro-current measurement
During normal operation of the transformer, the grounding current of the core is at the milliampere level, generally less than 0.1A; when there is multi-point grounding fault, the current will significantly increase. The instrument has high resolution and can effectively distinguish between normal operation and fault conditions.
2. Strong anti-interference ability
Suitable for the complex electromagnetic environment of substations, it has strong suppression ability against industrial frequency interference and can accurately extract the real leakage current value from strong electric field interference.
3. Wide range automatic switching
The measurement range covers the weak current of milliamps in normal conditions and the large current of amperes in fault conditions. The measurement process does not require manual switching of gears.
4. Online testing function
It can conduct detection work while the transformer is operating normally, without power outage, and does not affect the normal power supply of the power grid.
5. Data storage and transmission
It has the functions of data storage, waveform display, and data transmission, facilitating the recording of on-site detection data and the generation of inspection reports.
IV. Typical Technical Parameters
Measurement range: 0.1mA～10A (AC)
Measurement accuracy: ±(0.5% + 3 digits) and above
Frequency response: 45Hz～65Hz (applicable to industrial frequency)
Display mode: LCD color screen, capable of displaying real-time current values and waveforms
Clamp specifications: Can clamp the thicker grounding lead-down line of the transformer core, meeting the requirements of on-site wiring detection
V. On-site Operation Method
Connection operation
Open the instrument clamp, clamp it on the grounding lead-down line of the transformer core, ensuring that the entire grounding line is clamped, not including branch lines, to ensure that the measurement result is the total grounding current.
Measurement operation
In the operating state of the transformer, directly read the current value displayed by the instrument.
VI. Detection Result Judgment Criteria
Less than 100mA: Grounding current is within the normal range
100mA～1A: There is suspected multi-point grounding or insulation deterioration, and it needs to be continuously tracked and monitored
Greater than 1A: It is determined to be a serious multi-point grounding fault, and an immediate power outage treatment should be arranged