Very Low Frequency Voltage Withstand Test Set For Generator , Diagnosing Stator End Insulation Defects

I. Product Description and Why select the test device :

In fact, the withstand voltage test with very low frequency is a substitute for withstand voltage test with power frequency. As we all know, it needs a large-capacity test transformer or resonant transformer to do withstand voltage test for large generators due to great capacity in their insulation layer. This huge equipment is not only heavy and expensive but also inconvenient. In order to resolve the problem, the power sector reduces the test frequency to lessen the capacity of test power. From many years of theory and practice at home and abroad show that compared with power frequency, the very low frequency with 0.1Hz has more advantages such as small size, light weight, 1/500 capacity that of power frequency in theory, and easy-operating with the same equivalence. That is why developed countries adopt this approach in general. National Development and Reform Committee has drawn up relative industry standards. China is promoting this approach and this instrument is developed based on the needs. It can be widely used in AC voltage withstand test for cables, and large-scale high-pressure rotary motor.The very low frequency test device can effectively find the insulation defect at the end of the stator than traditional power frequency test method.

II. Technical Features

It performs step-up, step-down, measurement and protection automatically by using computer control with joining modern digital conversion of advanced technology. It not only owns small size, light weight, large-screen liquid crystal display with clear and intuitive but also displays output waveform and prints test reports. It is designed in full compliance with the industry standard, easy to use. Both at home and abroad, there are many disadvantages in current equipment, such as wrong sine waveform, large measurement error, spark discharge, high power consumption and so on.This instrument can overcome these disadvantages. Besides, it has the following features:

• The data is accurate because that current, voltage, waveform data are sampled directly from the high voltage side.
• It has overvoltage protection function. If the output voltage exceeds the set limit value, the instrument will shutdown with an action time less than 20ms.
• It has over current protection function. It will shutdown if current exceeds the set value in high voltage side with action time less than 20ms. And it will shutdown if current exceeds rated current in low voltage side with action time less than 20ms.
• A built-in protection resistor and so no need other outside resistor.
• It adopts high and low voltage closed-loop negative feedback control circuit, and so voltage will not go up due to an inherent capacitance.

IV. Ground capacitance of single-phase for different generators

Note: Utest＝√2×1.2×1.5×Un Un = rated voltage of generator

HV test current to tested stator =2πfCUtest

V. Universal Technical Parameters

• Output voltage ratings: See Details of Table 1
• Output frequency: 0.1Hz, 0.05Hz, 0.02Hz
• Measurement accuracy: 3%
• Positive and negative voltage peak errors: ≤ 3％
• Voltage wave form distortion: ≤ 5％
• Use condition: indoor and outdoor; temperature: -10℃∽+40℃; Humidity: ≤ 85％RH
• Power: AC50Hz, 220V ±5%

VI. Schematic and description of the display

P.S. F=Freqency, T=Timing, V=Voltage, I=Current

VII. Test Connection Figure

VIII. Supply List

• One Control host
• One HV booster(60KV and below Model)
• Two HV booster(80KV and above model)
• One special high-voltage connecting cable
• One special low-voltage connecting cable
• One power cable
• Ten power supply fuse tubes
• One discharging rod