Regularly inspect the capacitor and inductor tester for verification.

发布时间：2022-11-16

Regularly inspecting and calibrating capacitance‑inductance testers to promptly identify capacitor defects and prevent the escalation of common faults is of great importance. However, capacitors on site are typically connected in parallel, and conventional capacitance meters require disconnecting the leads before measurement, which is labor‑intensive and can easily lead to wiring errors or damage to the capacitors.

The flame‑retardant performance of generator rotor windings encompasses the following aspects: electrical properties, referring to the dielectric strength and overvoltage‑withstand capability of the insulation; thermal properties, meaning that at operating temperatures the insulation should not release impregnating varnishes or adhesives and must maintain adequate heat‑resistance; physical properties, including resistance to thermal expansion and dimensional changes under various insulation materials, as well as the alternating electrodynamic forces experienced during normal operation and after sudden short‑circuit faults; and chemical characteristics, namely the ability to withstand the corrosive and erosive effects of active oxygen generated by severe corona discharge and of various sulfur oxides on the insulating materials.

The insulation structure of generator rotor windings primarily comprises three types: mica tape impregnated with asphalt, baked rolled black mica, and epoxy‑resin‑filled black mica. These are classified as composite interlayer insulations. Among them, the epoxy‑resin‑filled black mica exhibits superior electrical strength, high‑temperature resistance, and overall physical properties compared to the other two, while also being more cost‑effective. Consequently, this type of insulation is now predominantly used in high‑current generators.

Its core handover test items include:

Use an insulation resistance tester to measure the rotor winding’s ground resistance and its absorption ratio or polarization index.

The equivalent circuit of the generator set’s insulation layer is as follows: (diagram omitted); when an AC voltage is applied,

The current measured by a capacitance–inductance tester is the capacitor current, which decays rapidly according to an exponential curve over time. Its decay characteristics depend on the motor’s structural dimensions, winding connection configuration, insulation thickness, and the magnitude of the applied test voltage.

The parameter being measured is the transmission current, which includes both volume resistivity and surface resistivity. These properties are relatively stable and do not degrade over time. They are influenced by the insulating layer’s electrical conductivity, operating temperature, manufacturing process, and the series loops of the winding. Additionally, moisture, contamination, and certain defects can increase its electrical conductivity.

To dissipate and absorb current, the generator set employs a composite insulation layer; its polarization process is essentially a time‑dependent decay of the current Ia. Moreover, large‑capacity generator sets exhibit relatively long dissipation and absorption times, thereby enabling a clear determination of the dielectric polarization index.

In addition, there is a magnetic‑field‑intensity loop; during testing, if you observe fluctuations in the grounding megger or microammeter, this is usually due to severe partial discharges within the instrument.

Typically, a 2500 V megger is used for testing. Before testing, ensure the power is off, verify with a voltage detector, and fully charge and discharge the device. During measurement, regularly check the megger, maintain a stable speed, and carefully control the test duration. Common precautions include disconnecting the test leads prior to measurement and only stopping the megger after completing the test. When comparing results with the manufacturer’s rated values, apply appropriate temperature‑correction formulas and perform calculations accordingly.

Capacitance and Inductance Tester

A three-phase, heterofrequency capacitance and inductance tester has been developed.

Applications of Capacitance and Inductance Meters

A three-phase, heterofrequency capacitance and inductance tester has been developed.

Applications of Capacitance and Inductance Meters