Ultra-Low Frequency/Extremely Low Frequency Generator | Test Precautions?

Ultra-Low Frequency/Very Low Frequency Generator (VLF) Generator - Testing Precautions and Features? The testing precautions and core features of the ultra-low frequency (VLF) high-voltage tester are as follows:

I. Testing Precautions

1. Safety Grounding and Monitoring: Before testing, ensure that both ends of the cable are completely isolated from other equipment and reliably grounded. The VLF equipment casing and grounding terminal must be firmly grounded. Operation requires dedicated supervision, maintaining a safe distance.

2. Correct Connection and Inspection: Confirm that the high-voltage lead connection is secure and points to an open area. Check that the cable termination is intact, without cracks or dirt. Before testing, be sure to remove all external cable connections, leaving only a single grounding point for testing.

3. Standardized Voltage Increase and Monitoring: Strictly follow the specifications (e.g., 0.1Hz cosine square wave) to set the voltage value (usually 1.5-3 times U₀) and time. Increase the voltage at a uniform rate, closely monitoring the voltage and current waveforms throughout the process. If the current increases abnormally or the waveform is distorted, it may indicate an insulation defect; immediately reduce the voltage and stop the machine.

4. Thorough Discharge: After the test, the cable must be completely discharged using the built-in discharge rod or a dedicated discharge rod (VLF capacitors store significant energy). Sufficient discharge time is required, and contact should only be made after confirming there is no residual charge.

II. Core Features

1. Portability and Capacity Advantage: Due to the extremely low output frequency (0.01-0.1Hz), the charging current for capacitive test samples such as cables is significantly reduced (only 1/100-1/1000 of that at power frequency), making the power supply equipment small and lightweight, ideal for mobile field use.

2. Effective Diagnosis of Insulation Defects: The electric field distribution generated inside the insulation by the VLF AC voltage is similar to that of power frequency AC, effectively detecting insulation defects such as water treeing and aging that cannot be detected by DC testing. The diagnostic accuracy is far higher than that of DC withstand voltage testing.

3. Minimal Insulation Damage: Compared to DC testing, which easily causes space charge accumulation and damages insulation, VLF AC testing causes less damage to insulation, making it a gentler and more effective condition assessment method.

In summary, the VLF generator is an ideal device for field testing of medium and high voltage cable insulation. Its core value lies in combining the effectiveness of AC testing with the portability of DC equipment, enabling safe and accurate assessment of cable insulation condition. Proper operation and discharge are crucial for safety. The MSVLF-80kV 1.1uF (VLF) generator is particularly suitable for withstand voltage testing of electrical equipment with large insulation equivalent capacitance (e.g., power cables, power capacitors, large and medium-sized generators and motors).

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