NDXL-110B Transmission Line Heterodyne Parameter Testing System

Product Introduction

        Before a newly constructed high-voltage transmission line is put into operation, in addition to checking the line insulation and verifying the phase sequence, various power frequency parameter values should be measured. These serve as the actual basis for calculating system short-circuit currents, setting relay protections, estimating power flow distribution, and selecting reasonable operating modes. The parameters that generally need to be measured include DC resistance R, positive sequence impedance Z1, zero sequence impedance Z0, positive sequence capacitance C1, zero sequence capacitance C0, and inter-phase capacitance C12.

       For multi-circuit lines erected on the same tower or lines with long parallel sections, and for lines that are close to each other, it is also necessary to measure the coupling capacitance Cm and mutual impedance Zm. Before measuring the parameters, relevant design data of the line should be recorded, such as the line name, voltage level, line length, tower type, conductor model and cross-section, etc. Based on this data and the on-site conditions, a testing plan should be developed.

       In traditional power frequency parameter testing of transmission lines, a three-phase autotransformer and a high-capacity isolation transformer are used to provide the test power supply. Electrical signal conversion is done using CTs and PTs for power metering, and various electrical parameters are measured using high-precision analog voltmeters, ammeters, and wattmeters to calculate the power frequency parameters of the transmission line. This makes the entire test equipment large in volume and heavy in weight, requiring crane assistance for operation, which is very inconvenient for on-site measurements. Moreover, since the test power supply is at power frequency, it is highly susceptible to mixing with coupled power frequency interference signals, leading to significant measurement errors. This necessitates a substantial increase in the signal-to-noise ratio, which further increases the requirements for the power supply's capacity and size.

       This instrument can accurately measure various power frequency parameters (positive sequence capacitance, zero sequence capacitance, positive sequence impedance, zero sequence impedance, mutual inductance and coupling capacitance, inter-phase capacitance, etc.) of high-voltage transmission lines (overhead lines, cables, mixed overhead-cable lines, and multi-circuit lines on the same tower).

       The instrument complies with the requirements of the "Start-up Acceptance Regulations for 110 kV and Above Power Transmission and Transformation Basic Construction Projects", DL/T559-94 "Operating Setting Regulations for Relay Protection Devices in 220-500 kV Power Grids", and "GB50150-2016".

       The instrument adopts an integrated structure with a built-in variable frequency power supply module, capable of outputting a variable frequency and voltage power supply. It uses digital filtering technology to avoid interference from power frequency electric fields, fundamentally solving the problem of accurate measurement under strong electric field interference.

Product Features

☆ Quickly and accurately complete the measurement of parameters such as positive sequence capacitance, zero sequence capacitance, positive sequence impedance, and zero sequence impedance of the line; it can also measure mutual inductive reactance, coupling capacitance, and inter-phase capacitance between lines;
☆ Strong anti-interference ability, capable of accurate measurement even when the ratio of heterodyne signal to power frequency signal is 1:10;
☆ Simple external wiring; only one connection to the leads of the line under test is needed to complete all line parameter measurements; thoroughly solves the problems of cumbersome wiring changes, interference, stability, and accuracy existing in current testing methods.
☆ The instrument uses a high-speed microcontroller as its core, integrating the test power supply, meters, and calculation models into one unit, condensing a truckload of equipment into a single instrument.
☆ The instrument features an 8-inch color touch screen for display and an embedded Chinese character micro printer for printing results;
☆ The testing process is fast; the instrument automatically completes the tests, finishing the measurement of one sequence parameter in about one minute, significantly reducing testing time; it can complete the workload of traditional methods in one day within 20 minutes;
☆ High measurement accuracy; 47.5Hz/52.5Hz easily separates power frequency and noise interference, effectively achieving high-precision measurement of small signals;

Technical Parameters

Accurately measures various parameters of high-voltage transmission lines:

Positive sequence capacitance, zero sequence capacitance, positive sequence impedance, zero sequence impedance, mutual inductance and coupling capacitance, inter-phase capacitance, etc.

Input power: Three-phase AC380V±10%, 50HZ
Maximum output voltage: AC 200V Accuracy: 1%
Maximum output current: 5A
Output signal frequency: 47.5HZ/52.5HZ; 50HZ/50HZ
Measurement range: Positive sequence capacitance, zero sequence capacitance, coupling capacitance 0.1~50uF  Measurement resolution: 0.01uF  Measurement accuracy: ±3%±0.05uF for 0.2uF~1uF
Measurement range: Positive sequence impedance, zero sequence impedance, mutual inductive reactance 0.5~400Ω  Measurement resolution: 0.01Ω Measurement accuracy: ±1.5%±0.03uF for 1uF~50uF
Measurement range: Impedance angle 0~360°     Measurement resolution: 0.01° Measurement accuracy: ±0.2° (voltage > 1.0V) ±0.3° (voltage > 0.2~1.0V)
Dimensions: 535×435×360mm³ (excluding wheels)
Weight: 61kg
Explanation of measurement results in this instrument:
Positive sequence impedance: Already converted to per-phase per-kilometer positive sequence parameters.
Zero sequence impedance: Already converted to per-phase per-kilometer zero sequence parameters.
Positive sequence capacitance: Already converted to per-phase per-kilometer line-to-ground positive sequence parameters.
Zero sequence capacitance: Already converted to per-phase per-kilometer average line-to-ground zero sequence parameters.
Coupling capacitance: Actual measured value, not converted.
Mutual impedance: Actual measured value, not converted.
Inter-phase capacitance: Actual measured value, not converted.
Line-to-ground capacitance: Actual measured value, not converted.
Line-to-ground impedance: Actual measured value, not converted.