Pilihan sa Primero nga Veripikasyon Circuit ug Pag-sukod sa mga Parametro alang sa UHV GIS Current Transformers

Sa UHV GIS, ang mga current transformers mao ang kritikal sa pagsukod sa electric energy. Ang ilang accuracy nagdetermina sa power trade settlements, kaya ang on - site error verification batasan sa JJG1021 - 2007 gikinahanglan. On - site, gamiton ang mga power supplies, voltage regulators, ug current boosters. Tungod sa encapsulation sa GIS, pagbuhat og test circuits pinaagi sa exposed grounding knives, bushings, ug return conductors; ang tama nga circuits mosimplify ang wiring ug moaumento ang accuracy.

Ang mga hamubo sama sa large test current, long circuits, ug high impedance adunay, apan ang reactive compensation (paggamit sa mas taas nga inductive reactance sa GIS primary circuits) mogamay sa equipment capacity needs. Ang accurate primary circuit parameter measurement mao ang key para sa compensation. Ang existing methods dili maayo para sa GIS primary circuits, kaya ang paper na: sorts UHV GIS current transformer primary circuit structures/features aron mapili ania ang verification circuits; develops intelligent methods aron mapataas ang parameter measurement intelligence/automation.

1 Primary Circuit Selection for UHV GIS Current Transformers
1.1 Structure & Features

Ang GIS nagintegro sa substation primary equipment (wala ang transformers) ngadto sa walo ka komponente (e.g., CB, DS). Encapsulated sa metal shells, ang GIS naghandog: miniaturization (pinaagi sa SF₆), gamay nga espasyo); high reliability (sealed live parts resist environment/earthquakes); safety (wala electric shock/fire risks); superior performance (shields EM/static, wala interference); short installation (factory assembly cuts on - site time); easy maintenance & long inspection (good structure, advanced arc extinction).

1.2 Circuit Selection

Ang mga circuit breakers nahimutang mid - GIS pipelines, uban ang current transformers sa duha ka bahin. Ang mga disconnectors naghulagway sa wala, plus ang grounding switches alang sa proteksyon. Ang pipelines gamiton ang (SF₆), ug ang transformers adunay epoxy resin semi - casting. Tungod sa enclosure, gamiton ang exposed grounding switches/bushings + return conductors. Adunay apat ka option: grounding switches sa breaker ends, GIS pipeline shells, large - current conductors, o adjacent GIS busbars isip return. Pagkahuman sa pag solve sa reactive compensation, ang adjacent GIS busbars (safe, simple, operable) napili alang sa on - site verification.

2 Research on GIS Primary Circuit Intelligent Measurement Systems
2.1 Parameter Measurement Method Analysis

Ang GIS primary circuits adunay equivalent resistance R ug inductive reactance (Z_L). Ang conventional methods (measure R, apply AC, calculate complex impedance Z then (Z_L) gikinahanglan og daghan nga devices, complex ops, ug heavy calculations. Ang paper na develop intelligent systems. Key tasks: system design (component matching, process planning); determine signal collection (points, methods, circuits for voltage/current); find voltage - current phase difference calculation; select line parameter methods (from amplitude/phase difference, get equivalent resistance/inductive reactance); overcome harmonics/interference for accuracy.

2.2 Overall Design of the Intelligent Measurement System

Ang intelligent measurement system nakentro sa microcontroller - based computer system, equipped with buttons, a display, a printer, ug uban pang peripherals. Ang voltage ug current signals gikapture sa signal acquisition system, then processed through a filter, multiplexer switch, automatic signal gain amplifier, ug analog - to - digital (A/D) converter before reaching the microcontroller for signal processing. The hardware principle is illustrated in Figure 1.

System Components

• Signal Acquisition System: Captures voltage ug current signals from the circuit.

• Filter: Eliminates interference signals.

• Multiplexer Switch: Enables voltage ug current signals to share one A/D converter, reducing hardware costs.

• Automatic Signal Gain Amplifier: Adjusts amplification automatically based on signal strength to ensure stable output.

• A/D Converter: Transforms analog signals into digital format for microcontroller processing.

• Display: Utilizes a direct - read digital screen for easy data viewing.

• Buttons: Simplifies system operation with user - friendly controls.

• Printer: Outputs measurement results on demand.

Operational Process

The acquired signals are processed and transmitted to the microcontroller, which runs pre - installed signal processing programs. The system analyzes the data via dedicated software, computes the results, and displays them on the screen.

2.3 Design of the Signal Acquisition Circuit

Given that measuring primary circuit parameters doesn’t require high currents, the system uses a regulated power supply with a 200A output. After passing through a current booster, the induced current on the line side is significantly lower than the GIS rated current, minimizing the need for large - capacity equipment. This setup keeps the current within the safe operating range of the GIS enclosure and grounding switches.

Circuit Options

The signal acquisition circuit can adopt any of the three test circuits discussed earlier (excluding the grounding - switch - based circuit, which doesn’t cover the entire GIS line). Using multiple methods simultaneously can enhance measurement accuracy. During testing, voltage and current transformers are installed to convert high primary - side values into manageable secondary - side signals for the acquisition system.

Circuit Design for Adjacent GIS Busbar Return Conductor

When using an adjacent GIS high - current busbar as the return conductor:

• Connect a voltage transformer in parallel on the current - booster line side.

• Install a current transformer in series between the current - booster line side and a GIS inlet bushing.

• Feed the secondary - side voltage and current signals into the acquisition system.

The designed signal acquisition circuit is shown in Figure 2. The collected voltage and current data correspond to the total values of the circuit.

2.4 Selection of Calculation Method for Voltage and Current Phase Difference

This measurement system uses the zero - crossing phase angle method to measure the phase difference between voltage and current. The so - called zero - crossing phase angle method is to shape the fundamental wave components of the collected voltage and current signals into square waves, obtain their respective zero - crossing pulses through a differential circuit, measure the time difference between the two pulses, and then calculate the phase difference between the voltage and current.

Assume that the time of the rising edge of the voltage square wave is τ₁ and the time of the rising edge of the current square wave is τ₂. Then, the calculation formula for the phase difference φ between the two signals is as follows:

Among them: T is the period of voltage and current. Since the frequency of voltage and current is 50 Hz, its period is 0.02 s. The calculation formula for the phase difference of voltage and current can be simplified as：

2.5 Calculation Method for Line Parameters

These calculation processes have been programmed into the microcontroller's memory. Specialized signal - processing software is used to automatically handle the data, and the results are displayed on the device's monitor. For the convenience of analysis, the voltage and current mentioned below are by default considered to have been converted to the voltage and current of the primary side.

Assume that the amplitude of the total line voltage collected by the signal acquisition system is U, and the amplitude of the line current is I. Then, the total line resistance R₁ and inductance L₁ can be obtained from the following formulas

If the resistivity of the connecting conductor between the busbars of the GIS outgoing line bushing is measured as ρ, the effective cross - sectional area is s, and the length of the conductor is measured as l, then the impedance calculation formula for this connecting conductor is as follows

Neglecting other connecting conductors, the equivalent resistance R and equivalent inductance L of the primary circuit of the GIS pipeline can be obtained from the following formulas.

Error Control & Optimization

Each measurement method should be repeated 3 times at different intervals to reduce errors. If feasible, use all 3 methods simultaneously and compare results:

• Consistent results: Average the values.

• One outlier: Check for loose connections or wiring errors; discard the outlier if issues persist.

• Inconsistent results: Recheck for interference. Modify the circuit if necessary; revise theoretical parameters if discrepancies remain.

To mitigate interference and harmonics:

• Install hardware filters in the signal acquisition circuit.

• Apply FFT software to extract fundamental wave components for calculation.

3. Conclusion

UHV GIS integrates primary equipment in sealed metal tanks, offering immunity to environmental factors, high reliability, and minimal footprint. For current transformer verification, using adjacent GIS busbars as return conductors simplifies wiring and ensures safety, making it ideal for primary detection circuits.

This study introduces an intelligent measurement system for GIS primary circuits, enabling precise measurement of equivalent resistance and inductance. The system's user - friendly interface, high accuracy, and robust anti - interference capabilities advance automation in GIS verification. Further field testing is recommended for validation and refinement.