Technical Analysis: Capacitor Leakage Current Tester and What is the Current Leakage of a Capacitor

Leakage in insulation is related to the material structure, defects and electric field strength of the insulating material, which can be weakened and reduced. Generally speaking, electromagnetic sealing is an effective way to enhance the leakage current of the insulating material, and increasing the thickness of the insulating material and the quality of the insulating material can improve the leakage current. Leakage current refers to the current formed between multiple metal components with mutual insulation and between energized components and grounding components through their surrounding medium or insulation surface when no fault voltage is applied in the electrical, such current is called leakage current, which is one of the most important parameters in the test of electrical appliances.

According to the UL standard, leakage current refers to the current that is conducted from the accessible parts of household appliances, including capacitively coupled current. It is mainly composed of two parts: the conductive current I1 through the insulation resistance and the displacement current I2 through the distributed capacitance, and the coupling standing wave ratio varies with the frequency, thus resulting in the change of leakage current. If it involves the assessment of the insulation performance of a circuit or a system, in addition to all current flowing into the ground through insulating materials, it shall also include the current flowing into the ground caused by capacitive components (including distributed capacitance) in the circuit or system. And, longer wiring will form larger distributed capacitance, thus increasing leakage current, which should pay more attention to in the ungrounded system.

Capacitors are indispensable parts in circuits or power equipment, one of which is ceramic capacitor, then how will current leakage occur in capacitors? The dielectric medium between the two poles of the capacitor is not absolutely insulated, but relative insulation, so there will be current leakage in the capacitor. Leakage current will have a limited damage to the capacitor, and should be paid attention to under normal use conditions, so as not to affect its life and normal work. So Capacitor Leakage Current Tester plays an important role in power testing.

What is the current leakage of a capacitor?
Capacitor leakage current refers to the current leaking out from the circuit when the rated DC voltage related to capacity is applied. Capacitor leakage current is the current leaked out from the capacitor after applying the rated DC voltage. Its main sources come from electrolyte medium and conduction performance of components in the capacitor. With the increase of time, leakage current will reach a stable value. It is related to temperature, size of capacitor and characteristic of dielectric medium.

There are many types of capacitors, but not all capacitors have the same leakage current characteristics. Especially the film capacitor, the use of high-quality film capacitor can ensure low leakage current, provide guarantee for the safety of the circuit, reduce circuit interference.

LS6586_Capacitor Leakage Current Tester

What factors are correlated to the size of capacitor leakage current:
The size of capacitor leakage current is generally affected by many factors, mainly are applied DC voltage, time and capacitor capacity. Applied DC voltage is directly related to leakage current, the higher the applied voltage, the greater the leakage current; Applied voltage time will also affect leakage current, with the increase of time, leakage current will decrease. In addition, the capacity of the capacitor will also affect leakage current, the bigger the capacity, the bigger the leakage current.

Now, in China, the neutral point of power supply in distribution system is generally not directly grounded. If the line is grounded in single phase, according to statistics, the culprit of fault is likely to be too large grounding capacitance, thus can not be self-extinguish. Therefore, the state has separately specified that when the capacitive current exceeds 30A and 10A for 10kV and 35kV systems respectively, arc suppression should be installed to compensate capacitive current. But to determine whether such problem exists, it’s necessary to accurately measure whether the grounding capacitance value of the distribution network and parameters of PT will lead to PT magnetism resonance overvoltage, so as to take corresponding measures.

The traditional measurement methods of distribution network capacitive current, such as the direct method of single phase metal grounding and the indirect measurement method of external capacitance, all require contact with secondary equipment, and there are safety hazards, cumbersome operations and low efficiency. Thus, it’s necessary to improve this measurement method.

The core technology of modern capacitor leakage current tester is the capacitive measuring technology designed by advanced design. Due to the elimination of connection to the secondary side, the use of the instrument can significantly improve the safety and measurement efficiency both. By the instrument inputting weak alternating frequency signal from the secondary side of the PT, it can withstand 100V AC voltage, without the need of cumbersome safety measures and waiting for long scheduling commands, making the operation safer, simpler and faster.

At the same time, capacitor leakage current tester can measure the capacitive current of the distribution network accurately and stably, and reliably. In addition, if there is single-phase grounding fault in the system, it will not damage the measuring instrument and PT equipment, achieving practical effect. Therefore, the use of capacitive leakage current tester in actual operation will bring significant practicality to the inspection of power system.

Using capacitor leakage current tester with LCD display and Chinese menu operation can effectively solve the problems of inconvenience in carrying, cumbersome wiring, slow testing speed and low work efficiency. The instrument is small in size and light in weight, and easy to operate. When used for outdoor work and long-term testing, it can reduce the labor intensity of the operators greatly, and the data is accurate and reliable, and can also improve the speed of testing and work efficiency.

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