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I. Brief Introduction
This product is a lightweight testing device based on the principle of utilizing the saturation characteristics of the magnetization curve of silicon steel sheet cores to induce zero-sequence third harmonic electromotive force in the open-delta connected secondary windings of a three-phase transformer bank.
The lightweight triple frequency generator produced by our factory can be supplied as a complete set including control equipment and chassis. This generator is one of the basic equipment for performing frequency-doubled induction high-voltage tests on series-connected high-voltage potential transformers and small-capacity power transformers in power systems, power plants, substations, and power supply and distribution networks. It can also be used for frequency-doubled and voltage-doubled tests on various low-voltage electronic and instrument power transformers, inductor coils, and electrical appliance coils. Additionally, it can serve as a frequency-doubled power source with a power not exceeding 1 kilowatt for the power supply or testing of certain special electrical equipment.
This product is a static frequency conversion device with low noise and small size, which can completely replace traditional frequency conversion motor-generator sets in high-voltage testing.
II. Basic Working Principle of the Triple Frequency Generator
The primary sides of three single-phase transformers are connected in a Y configuration, and the secondary sides are connected in an open delta. When a three-phase 50 Hz sinusoidal AC power is applied to the primary side, the induced electromotive force on the secondary side is a flat-topped wave containing zero-sequence harmonics. The vector sum of the three-phase fundamental (positive sequence) electromotive forces and the fifth harmonic (negative sequence) electromotive forces is zero, while the three-phase vector sum of the third harmonic (zero sequence) electromotive forces adds in phase. Therefore, among the zero-sequence harmonics, the third harmonic component is the largest.
The 150 Hz (triple power frequency) induced voltage output from the secondary side of the open-delta connected generator serves as the triple frequency test power supply voltage. To obtain a larger 150 Hz induced voltage output, the generator operates at a high working magnetic flux density, and the magnetic flux tends to saturate (i.e., the over-excitation multiple is large), making the waveform of the induced voltage on the secondary side flatter at the top, and the amplitude of the decomposed 150 Hz electromotive force is also larger. Therefore, the leakage reactance of the triple frequency generator is relatively large, and its variation pattern is nonlinear, meaning the output impedance of the generator is relatively large.
When the triple frequency generator is loaded with a capacitive load (e.g., JCC—220 type high-voltage series-connected potential transformer), due to the low power factor, the efficiency of the generator is relatively low, generally only about 20%. During loaded operation, a reactor can be connected to a certain idle winding of the test object on the secondary side of the generator for current compensation to improve the power factor of the entire test circuit.
III. Equipment Structure and Technical Parameters
The SBF（Q）-I type portable triple frequency generator consists of three single-phase transformers forming a transformer bank, each single-phase transformer being a core-type double-coil structure. The iron core is laminated with high-quality cold-rolled silicon steel sheets, and the coils are wound with high-strength polyester enameled copper wire and Class E insulation materials into cylindrical windings.
In addition to the transformer bank, the generator is equipped with a compensation reactor. The structure of the reactor is similar to that of a single-phase transformer, but the iron core has an air gap (working air gap), and the coil parameters are also different (there is no secondary winding).
The transformer bank can be assembled together according to user requirements, while the control box and reactor are of independent structures.
The main technical parameters are shown in the table below.
I. Triple Frequency Power Generator Technical Specifications
Input Voltage 380V 50Hz Sine Wave
Output Voltage 250V- 1000V 150Hz Waveform Distortion ≤5%
Output Capacity 3kVA, 5kVA, 10kVA, 20kVA, 50kVA
No-load Operation Time ≤5 minutes
Load Operation Time 40～60s
