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LXQ Series Harmonic Eliminator

The LXQ, LXQIII, and LXQ(D)III 6~35kV voltage transformers use neutral point harmonic suppression resistors (called harmonic suppressors). These are nonlinear damping resistors installed between the neutral point of the primary winding of the Y0 connection and the ground, serving to provide damping and current limiting. The resistor body is made of SiC, the connectors are often made of die-cast aluminum, and the overall design is attractive, compact, lightweight, strong, easy to dissipate heat, and simple to install. These have been used in power grids for many years, and experience shows that this harmonic suppressor effectively eliminates transformer ferroresonance and prevents fuses from blowing on single-phase high-voltage lines. It also adapts well to transformers with weakly insulated neutral points and is compact and easy to install. The product with the (D) model is usually used with semi-insulated or fully insulated transformers, while other models can only be used with fully insulated transformers.
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Product Overview

The harmonic-suppression resistor (hereinafter referred to as the “harmonic suppressor”) for the neutral point of LXQ, LXQIII, and LXQ(D)III type 6–35 kV voltage transformers is a nonlinear damping resistor installed between the neutral point of the primary winding of the Y0-connected transformer and ground, serving to damp oscillations and limit current. The resistive element of the harmonic suppressor is made of SiC as the base material, while the connecting parts are die-cast aluminum. The overall design is aesthetically pleasing, with a compact footprint, light weight, high mechanical strength, excellent heat dissipation, and easy installation. Having been in service in power grids for many years, practical experience has demonstrated that this harmonic suppressor effectively eliminates ferroresonance in voltage transformers and prevents single-phase high-voltage fuse blowout. It also features good compatibility with weak insulation at the transformer neutral point and a compact, easy-to-install configuration. Products designated with the “(D)” suffix are typically paired with semi-insulated or fully insulated voltage transformers, whereas other models can only be used with fully insulated transformers.


Implementation Standard

JB/T8459


Technical Specifications

Main electrical parameters of resistors: The main electrical parameters of the resistor body are listed in Table 1. Since resistors are made of nonlinear materials, accurate characterization of the resistance value requires measurement with a peak meter.

Project

LXQ Type III-6 
LXQ(D)III-6 Type

Model LXQ III-10 
LXQ(D)III-10 Type

LXQ Type III-35 
LXQ(D)III-35 Type

Through communication 
at 10 mA (peak/)

Voltage (V) peak / √2

480~600

800~1000

2100~2625

Resistance (kΩ)

>48

>80

>210

Through communication 
at 1 mA (peak/)

Voltage (V) peak / √2

170~210

280~350

840~1050

Resistance (kΩ)

>170

>280

>840

Variation of power-frequency voltage across the terminals of a resistor with type (D)

At 3 kV (peak/√2), 
The resistance value decreases by more than half.

The resistance value decreases at 3 kV (peak/√2). 
More than half less

The resistance value decreases at 5 kV (peak/√2). 
More than half less

Power (W) tolerated for 2 hours

>800

>800

>800

Thermal capacity for passing a 500 mA (RMS) current for 10 minutes

① No obvious damage 
② Before and after the heat capacity test, under cold conditions, the electrical parameters shall not vary by more than ±10%.

If the X terminal of the primary winding of the voltage transformer is internally connected to the core and the enclosure, with no insulated lead wire for the X terminal, then when installing a harmonic eliminator on such a transformer, insulation treatment must be applied to the enclosure and the mounting bolts. The procedure is as follows: install an insulating plate at least 5 mm thick between the metal enclosure of the voltage transformer and the grounded metal frame; the metal bolts used for fastening must be fitted with insulating sleeves and insulating washers, or secured using screws made of insulating material, thereby transforming the originally directly grounded enclosure into one with a specified insulation strength. The now-insulated enclosure may be paralleled to form a neutral point, which is then grounded through a harmonic-eliminating resistor. The insulation strength of the transformed insulated enclosure shall not be lower than that of the secondary winding leads, and a harmonic-eliminating resistor model designated with (D) must be selected.


Outline Dimension Drawing (mm)

The external dimensions of the ultra-compact 6 kV and 10 kV resistors are shown in the figure below; for the standard models, the heights for 6 kV, 10 kV, and 35 kV are all 147 mm, with all other dimensions remaining identical.

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