Product Details

   This product is designed to meet the requirements of the triple frequency induced withstand voltage test and partial discharge test in the "Regulations for Preventive Tests of Electrical Equipment".

The induced withstand voltage test for transformers and instrument transformers is an important test to verify whether the product meets national standards. The longitudinal insulation induction test of interlayer, inter-turn, segment, and phase-to-phase insulation of windings is an important item to assess whether the windings meet requirements. In order to increase the test voltage of the winding without causing excessive saturation of the transformer or instrument transformer core and excessive excitation current, the test frequency needs to be increased, generally to 100Hz-400Hz.

There are several ways to obtain a 100Hz-400Hz power supply, among which the more applicable ones are: ① Combination of three variable frequency generators (100Hz-400Hz); ② Combination of three single-phase transformers (150Hz), and the most convenient is the second method.

Combination of three single-phase transformers: The primary side is star-connected, and the secondary side is open-delta connected. When the core is not saturated, the main magnetic flux it produces must be a flat-topped wave. Since the flat-topped main magnetic flux contains a large component of third harmonic magnetic energy Φ3, and the frequency of the third harmonic magnetic flux is f3=3f1, the main magnetic flux induces a third harmonic phase electromotive force.

Since the primary side is star-connected and the secondary side is open-delta connected, the core operates in a saturated state, and the no-load current I presents a peaked wave. In addition to the fundamental wave, it also contains higher harmonics. Among the higher harmonics, the amplitude of I is relatively large. Due to the open secondary, the three-phase fundamental components cancel each other out, leaving only the third harmonic output.

SFQThe triple frequency test transformer utilizes the saturation characteristics of the magnetic circuit to extract the third harmonic voltage, which has the largest component among harmonics, as the power source for the generator. It is used for inter-turn, inter-segment, and interlayer frequency multiplication and voltage multiplication tests on inductive coil electrical products such as transformers and instrument transformers, to assess the insulation strength and withstand voltage level of the coils.

  Principle

According to national test standards, the induced test voltage for power transformers and voltage transformers is generally considered to be 2-3 times the maximum working phase voltage. As is well known, under rated frequency and rated voltage, the core of a transformer is close to saturation. If a power frequency power supply is used to apply a test voltage greater than the rated voltage across the winding of the transformer under test, the no-load excitation current will increase sharply to an unacceptable level. From the relationship of induced electromotive force, it can be seen that in order to apply a test voltage greater than the rated voltage without saturating the core, the method of increasing the power supply frequency must be adopted, and a power generator with a frequency greater than the multiple frequency must be used.

   Characteristics

Technical Parameters