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I. Overview
This product is a lightweight test 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 casing. This generator is one of the basic equipment for performing frequency doubling induction high voltage tests on cascade 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 doubling and voltage doubling tests on various low-voltage electronic, instrument power transformers, and inductive coils of electrical appliances. Additionally, it can serve as a frequency doubling power source with a power not exceeding 1 kilowatt for 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 force and the fifth harmonic (negative sequence) electromotive force is zero, while the three-phase vector sum of the third harmonic (zero sequence) electromotive force is in-phase addition. Therefore, the third harmonic component in the zero-sequence harmonics is the largest.
The 150 Hz (triple power frequency) induced voltage output from the secondary side of the open-delta 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 magnetic flux density, and the flux tends to saturate (i.e., the over-excitation multiple is large), making the top of the induced voltage waveform on the secondary side flatter, and the amplitude of the decomposed 150 Hz electromotive force larger. Therefore, the leakage reactance of the triple frequency generator is large and its variation is nonlinear, meaning the output impedance of the generator is relatively high.
When the triple frequency generator is loaded with a capacitive load (e.g., JCC-220 type high-voltage cascade potential transformer), due to the low power factor, the efficiency of the generator is low, generally only about 20%. When operating with a load, a reactor can be connected to an 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 portable triple frequency generator consists of three single-phase transformers forming a transformer bank, each single-phase transformer being a core-type double-winding structure. The iron core is laminated with high-quality cold-rolled silicon steel sheets, and the windings are made of high-strength polyester enameled copper wire and Class E insulation materials processed 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 winding parameters are different (no secondary winding).
The transformer bank can be assembled together according to user requirements, while the control box and reactor are 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
