Three-Phase 35kV 1000A Instrument Transformer Calibration Test System CT PT Error Test Bench

This system is applicable to three-phase combined current transformers with a rated current of up to 1000 A and a voltage level of up to 10 kV. This system can be used for three-phase voltage transformers with a voltage rating of 35 kV and below.

This high-tech three-phase combined current transformer calibration system enables simultaneous error calibration of three-phase combined current transformers. It aligns with the actual field operating conditions of combined current transformers, facilitates streamlined calibration procedures, and eliminates the need for multiple wiring tests required by conventional single-phase calibration methods. Consequently, this system reduces labor and material costs, enhances operational efficiency, and accurately performs error testing on three-phase voltage transformers with Y/YO wiring configurations, thereby ensuring measurement accuracy and reliability. The three-phase calibration methodology employed in this system will drive advancements in the design and manufacturing quality of combined current transformers. It enables more precise characterization of the performance characteristics of these transformers under operational conditions and provides a comprehensive identification of potential issues encountered during practical application, thereby ensuring the fairness and impartiality of electrical energy measurement.

• Ambient temperature: -20 °C to 45 °C
• Relative humidity: not exceeding 85%
• Elevation: Not exceeding 1,000 m
• Operating environment: Indoor
• Test power supply: single-phase power supply, voltage 230 V ± 15%, frequency 45–65 Hz, current not less than 100 A
• Grounding resistance: multi-point grounding, with a grounding resistance of less than 0.5 Ω
• Other requirements: The installation site must be free from severe gas or steam exposure, chemical deposits of dust or grime, or other explosive media, as well as severe vibration.

The design, manufacture, installation, and operation of all equipment in this system comply with the requirements of the following standards (current versions). In the event of any discrepancies between these standards, the more stringent requirements shall prevail.

• GB 20840.1-2010 Instrument transformers — Part 1: General technical requirements
• GB 20840.2-2014 "Current transformers — Part 2: Supplementary technical requirements for current transformers"
• GB 20840.3-2013 "Instrument transformers — Part 3: Supplementary technical requirements for electromagnetic voltage transformers"
• GB 20840.4-2015 "Current transformers — Part 4: Supplementary technical requirements for combined transformers"
• JBT 10432-2016 Three-phase combined current transformers
• JBT 10433-2015 Three-phase Voltage Transformers
• JJF 1701.6-2019 Outline for Type Evaluation of Instrument Transformers for Measurement – Part 6: Three-phase combined instrument transformers
• JJG 1165-2019 Verification Standard for Three-Phase Combined Current Transformers

• Accuracy Testing of Three-Phase Combined Current Transformers and Three-Phase Voltage Transformers

• Manually adjust the voltage and load of the voltage regulator
• Automatically record test data
• Analysis of Visualization Test Results
• Automatically generate test records
• Historical Data Query
• Anomaly data alert
• Supports remote access control
• Supports gated power-off system
• Supports extended network data communication
• Siemens industrial PLC
• Manual switching of primary and secondary terminals of current transformers via wiring devices
• Automatic alarm for abnormal test status
• The test data supports communication via serial port RS-485 and TCP network interface.

Regulator section

• Input voltage: 380 ± 5%
• Rated power: 5 kVA × 3 phases
• Output voltage: 0–400 V
• Output current: 0–12.5 A
• Output frequency: 45–55 Hz
• Pressure-adjustable resolution: 0.1 V
• Ripple factor <3%
• Stable output for over 10 hours

• Input voltage: 380 ± 5%
• Rated power: 5 kVA
• Output voltage: 0–400 V
• Output current: 0–12.5 A
• Output frequency: 45–55 Hz
• Pressure-adjustable resolution: 0.1 V
• Ripple factor <3%
• Stable output for over 10 hours

• Input voltage: 0–400 V
• Maximum output voltage: 42 kV
• Stable output for over 10 hours

Precision voltage transformer

• Voltage: 35 kV, 35/√3kV
• Secondary voltage: 100 V, 100/√3V
• Measurement accuracy class 0.05
• Rated load: 0.25,0.07 VA; power factor φ = 1.0
• Double-end ground withstand voltage test at power frequency: 1.3Un

• Input voltage: 0–400 V
• Ground-frequency withstand voltage: 1.3Un

Precision current transformer

• Single-phase current: 5–600 A
• Secondary current: 5 A, 1 A
• Measurement accuracy: Class 0.05S
• Rated load: 5 VA, cosφ = 1.0
• Ground-frequency withstand voltage: 1.3Un
• Withstand voltage: 42 kV for 5 min

• measuring range
• In-phase component (%): 0.0001–200.0; Resolution: 0.0001;
• Orthogonal components: 0.001–700.0; Resolution: 0.001;
• Impedance (Ω): 0.0001–60.0; Resolution: 0.0001; Impedance (Ω): 0.0001–60.0; Resolution: 0.0001;
• Admittance (mS): 0.0001–60.0; Resolution: 0.0001; Admittance (mS): 0.0001–60.0; Resolution: 0.0001;
• Current measurement range: 0–7.5 A
• Voltage measurement range: 0–150 V
• Measurement accuracy: Class 2

The three-phase verification instrument can simultaneously connect to the current and voltage circuits of both the test object and the reference standard for all three phases (A, B, and C) — supporting both three-wire and four-wire three-phase configurations. The current and voltage signals from both the test object and the reference standard are fed into the instrument for differential comparison, and the results are displayed in real time on the instrument's 5.8-inch large LCD screen according to the specified operating points, while also being transmitted to a computer and printing devices. A key feature of this instrument is its ability to display the mutual sensor error data for all three phases on a single interface, facilitating the observation of mutual influences between the three-phase sensors caused by magnetic and electric fields. DSP technology is employed in this design: compared to traditional microcontrollers, DSP chips abandon the von Neumann architecture in favor of a Harvard architecture—where program and data are separated—thereby significantly enhancing processing speed. The instruction cycles are typically in the nanosecond range, whereas those of conventional microcontrollers are usually in the millisecond range, representing a three-order-of-magnitude improvement. This capability enables the system to handle large volumes of real-time data in three-phase devices. FFT technology has been adopted: unlike existing single-phase calibrators, this approach utilizes FFT to compute phase difference and angular difference, thereby eliminating the impact of hardware circuits on data due to variations in frequency, temperature, time, and humidity. Notably, while many current calibrators employ RC phase-shifting to measure angular difference—a method where the capacitance is significantly affected by temperature and frequency—using a pure software-based FFT algorithm can circumvent these issues, thereby enhancing test stability and accuracy. By employing high-speed, high-precision A/D sampling, the instrument can not only simultaneously input and compare the errors of three mutual sensors, but also conveniently observe the mutual influence between the voltage unit and the current unit, thereby accurately reproducing the errors of the three mutual sensors under actual operating conditions.

• Rated current: 5 A
• Measuring range: 1%–120% (5A)
• Rated output (5A)
• Cos=0.8 2.5VA,3.75VA,5VA,7.5VA,10VA,15VA,20VA,25VA,30VA,40VA,60VA,80VA Cos=0.8 2.5VA,3.75VA,5VA,7.5VA,10VA,15VA,20VA,25VA,30VA,40VA,60VA,80VA
• Cosφ=1 2.5VA,5VA Cosφ=1 2.5VA,5VA
• Measurement accuracy: Class 3
• Supports online remote measurement control
• Supports manual testing
• Phase separation: Three-phase

• Rated current: 1 A
• Measuring range: 5%–120% (1A)
• Rated output (1A)
• Cos=0.8 2.5VA,3.75VA,5VA,7.5VA,10VA,15VA,20VA,25VA,30VA,40VA,60VA,80VA Cos=0.8 2.5VA,3.75VA,5VA,7.5VA,10VA,15VA,20VA,25VA,30VA,40VA,60VA,80VA
• Cosφ=1 2.5VA,5VA Cosφ=1 2.5VA,5VA
• Measurement accuracy: Class 3
• Supports online remote measurement control
• Supports manual testing
• Phase separation: Three-phase

• Rated voltage: 100 V, 100/√3V
• Measurement range: 20%–120%
• Rated output: 1.25VA–158.75VA; adjustment granularity: 1.25VA
• Power factor: 0.8, 1.0
• Measurement accuracy: Class 3
• Supports online remote measurement control
• Supports manual testing
• Phase separation: Three-phase

• Supporting secondary test line
• One set of high-current conductors
• One wrench and one screwdriver.

Figure 1: Block diagram of the principle of verifying three-phase combined current transformers using the three-phase method Figure 1: Block diagram of the principle of verifying three-phase combined current transformers using the three-phase method

Strictly follow the wiring diagram provided below. Since three-phase verification differs from single-phase verification—owing to its greater wiring complexity and the availability of standardized equipment for three-phase applications—special attention must be paid to safety during the test procedure. Pay particular attention to the insulation clearance in high-voltage environments to prevent secondary open circuits in the current transformers (TA), thereby avoiding accidents that could cause injury to personnel or damage to the verification equipment. Subsequently, in accordance with the requirements indicated on the nameplate of the combined current transformer, position each load on the test platform located on the right side of the test frame to the corresponding rated position.

Figure 2: Current transformer error wiring diagram for a three-phase, two-element combined transformer Figure 2: Current transformer error wiring diagram for a three-phase, two-element combined transformer

Figure 3: Wiring diagram of the current transformer for a three-phase, three-element combined transformer Figure 3: Wiring diagram of the current transformer for a three-phase, three-element combined transformer

During TV testing, the principle of "listen first, observe second, and do not touch third" should be followed. Strictly follow the correct wiring instructions shown below (for the V-type connection, refer to the V-type wiring diagram; for the Y-type connection, refer to the Y-type wiring diagram; the wiring methods for 10 kV and 35 kV are identical). Ensure proper grounding in accordance with the requirements.

Figure 5: Error calibration wiring diagram for a three-phase, two-element voltage transformer Figure 5: Error calibration wiring diagram for a three-phase, two-element voltage transformer

Figure 6: Error calibration wiring diagram for a three-phase, three-element voltage transformer Figure 6: Error calibration wiring diagram for a three-phase, three-element voltage transformer

Figure 7: TV Test V-Type Wiring Diagram Figure 7: TV Test V-Type Wiring Diagram

Figure 8: Y-connection diagram for the TV test Figure 8: Y-connection diagram for the TV test