Overview
The LXQ Ⅱ and LXQ (D) Ⅱ type harmonic eliminators (referred to as L Ⅱ type) installed between the neutral point of the primary winding of the voltage transformer and the ground in the Y0 junction line have been in operation in the power grid for many years. Experience has shown that L Ⅱ type has good functions of eliminating the ferromagnetic resonance of the voltage transformer and preventing the melting of single-phase high-voltage fuses. It also has the advantages of adapting to weak insulation coordination of the voltage transformer neutral point, being compact and easy to install. The accessory "Third Harmonic Voltage Limiter" installed at both ends of the open triangle of the residual voltage winding of the voltage transformer (hereinafter referred to as the open triangle) can reduce the voltage drop of the third harmonic current and the unbalanced current of the fundamental wave of the voltage transformer on the harmonic eliminator, and limit it to the satisfaction of the user.
In recent years, due to the adoption of harmonic elimination measures by most transformers, cases of transformer burnout caused by ferromagnetic resonance have become rare. However, an accident caused by incorrect wiring leading to the simultaneous burning of multiphase voltage transformers is frequently seen in 6-35kV power grids. This mistake short circuits the two ends of the voltage transformer's open triangle (in fact, both ends of the open triangle are grounded), and when the single-phase grounding of the power grid is slightly longer, the multiphase voltage transformers will burn out simultaneously. The most effective way to prevent such accidents is to determine whether the voltage transformer delta is short circuited during normal operation of the power grid. Based on years of operation and manufacturing experience, our company has added an open triangle short circuit alarm function to the improved L III type harmonic eliminator accessory (LXQ-F type) to prevent such accidents from happening again. In addition, the L III type harmonic eliminator and its accessories (LXQ-F type) have undergone multiple improvements, and the improved product has more functions in protecting the safe operation of the transformer.

Installing the accessory (LXQ-F type) "Voltage Limit and Short Circuit Alarm" at both ends of the voltage converter delta not only reduces the third harmonic voltage and unbalanced fundamental voltage at both ends of the delta during normal operation of the power grid, but also lowers the voltage at both ends of the harmonic elimination resistor in the primary winding. Tests have shown that the voltage on the harmonic elimination device can be reduced to less than a quarter of its original value. This is more beneficial for voltage transformers with low insulation at the neutral point to operate at low voltage (less than 100 volts) for a long time.

3、 Electrical wiring
The electrical wiring diagram of L III type resistor and its accessories is shown in Figure 1. The resistor is connected between the neutral point of the primary winding of the transformer and the ground; The attachment is connected to both ends of the voltage converter delta, and the AC100V power supply is provided by the secondary winding voltage of the voltage converter. The required power is not greater than 5VA. If a simple attachment is used, only the two supporting wires of the simple attachment need to be directly screwed onto the da and dn ends of the terminal block.

2、 Outline dimension diagram

RXQ, FXQ, DXQ, LXQ series harmonic eliminators