ZXHQ‑T: Automatic Verification for Current and Voltage Transformers

Abstract

Transformer performance directly determines measurement accuracy and operational safety within power grids. Conventional manual transformer verification workflows suffer from heavy labour workload, low test efficiency and poor data traceability. This article introduces the ZXHQT highspeed multitransformer verification device, a virtualinstrumentbased automatic calibration platform for current transformers (CT) and voltage transformers (VT). The paper covers working principle, core features, critical technical specifications and field application notes, for reference by metrology and testing technicians.

1. Introduction

Current transformers and voltage transformers are key metering components widely deployed in power generation, transmission and distribution systems. Their ratio error and phase displacement must be periodically verified to guarantee reliable energy metering and relayprotection operation. Traditional verification relies heavily on manual recording and calculation, which brings humanintroduced error and limits testing throughput.

The ZXHQT highspeed multitransformer verification device is newly developed to realise fullyautomatic CT & VT verification. Built upon virtualinstrument architecture, the system completes parameter input, automatic testing, result computation, database management and report output under computer control, greatly improving the automation level of transformer calibration laboratories.

2. Working Principle

Adopting virtualinstrument design ideology, the hardware measurementcontrol unit is built around singlechip microcomputer to realise signal acquisition, control logic and status display. Technicians operate graphical virtualinstrument interfaces via mouse and keyboard. Operators input transformer metadata including transformer type, rated range, accuracy class, capacity and power factor.

After parameter configuration, the platform automatically executes tests for current transformers and voltage transformers. It implements automatic switching of current and voltage load boxes during test sequences. Measured raw data is processed automatically: error calculation, data storage and database archiving are completed inside the system. Test records and calibration certificates can be printed on demand.

Notably, the platform supports nonidentical transformation ratios between standard transformers under reference and units under test. Verification can proceed as long as the standard transformer’s rated primary voltage or primary current is greater than or equal to that of the device under test. This relaxes fieldsite preparation requirements.

3. Main Technical Features

Integrated singlechip hardware platform: The automatic mutualinductor calibration platform uses singlechip microcomputer to unify measurement, control and display functions, ensuring realtime response during test cycles.

PCconnected architecture: Equipped with computer communication interface. It promotes office automation and effectively reduces manual labour intensity for metrology staff.

Userfriendly manmachine interaction: Largescreen display delivers abundant realtime measurement information, simplifying onsite operation.

Full automatic measurement flow: It completes transformer measurement autonomously and realises automatic switching for current and voltageload boxes without manual rewiring.

Abnormal diagnosis and prompt: Equipped with reliable faultcapture mechanisms. It timely outputs warning messages for abnormal working conditions.

Measurement accuracy: The automatic transformer calibration station achieves Class 2 performance index.

Flexible standardtransformer matching: Standard transformer and tested transformer do not require matching transformation ratios, improving adaptability for onsite verification work.

4. Key Technical Indicators

4.1 Ambient Operating Conditions

Operating temperature: 5 ℃ ~ 40 ℃

Relative humidity: less than 80 % (at 25 ℃)

Altitude: below 2500 m

Powergrid frequency: 50 Hz ±0.5 Hz

Supply voltage: 220 V ±5 V

4.2 Measurement Ranges & Resolution

Inphase component: 0.0001 % ~ 200.0 %, resolution 0.0001 %

Orthogonal component: 0.001 ~ 999.9 minutes, resolution 0.001 minutes

Impedance: 0.0001 W ~ 60.0 W, resolution 0.0001 W

Admittance: 0.0001 ms ~ 60.0 ms, resolution 0.0001 ms

4.3 Basic Error

Inphase component: DX = ±(X × 2 % + Y × 2 % ± 2 words)

Quadrature component: DY = ±(X × 2 % + Y × 2 % ± 5 characters)

Note: X, Y stand for instrument display value; “words / characters” represent instrument quantization error.

Dialindicator accuracy class: Level 1

4.4 Working Current Range

For In = 5 A: 1 %149 % rated current

For In = 1 A: 5 %149 % rated current

4.5 Warning & Protection Functions

Polarity error indication: Polarity warning triggers when operating current exceeds 5 % rated value and measured error surpasses 180 %.

Important caution: If polarity indication appears above 10 % rated working current, software malfunction is suspected. Do NOT raise test current further to avoid instrument burnout.

Variableratio error indication: Ratioerror alert activates when working current >5 % rated and error sits between 30 % ~ 180 %.

4.6 Insulation & Withstand Voltage

Terminal Tx connects to ground terminal; terminals K and D shall be isolated from ground.

Mains power socket endures 1.5 kV, 1minute withstand voltage versus instrument shell.

5. Practical Application Considerations

Technicians must observe environmental limits before test execution. Operating beyond temperature, humidity or altitude specifications may degrade actual measurement precision. Operators should doublecheck wiring of Tx, K and D terminals. When polarityerror or ratioerror alarms popup, operators must interpret alarm thresholds strictly following specification notes. Special attention should be paid to the abnormal condition: polarity alert triggered above 10 % rated working current. Under this fault condition, increasing excitation current will cause permanent hardware damage.

When selecting reference standard transformers, users only need to guarantee standardtransformer rated primary voltage / current meets or exceeds that of equipmentundertest, without strict ratio matching. This characteristic reduces sparepart inventory burden for testing organisations. After measurement completion, technicians can export test data to local database and generate standard calibration certificates for filing.

6. Conclusion

ZXHQT highspeed multitransformer verification device combines virtualinstrument technology with singlechip control hardware, solving multiple painpoints of traditional transformer verification. Automatic testing, loadbox autoswitching, builtin abnormal alarm and flexible standardtransformer matching optimise calibration efficiency for CT and VT. Its complete set of protection and insulation indexes ensures instrument stability for laboratory and field metrology work. For powergrid metrology teams, this equipment provides an effective solution to realise highautomation transformer verification.

GDZX is a manufacturer of power detection equipment, offering a diverse range of products with comprehensive models and providing professional technical support. Contact us at +86-27-6552607 or +86-17396104357.Website: http://en.gdzxdl.com/