Secondary Load Test Instrument

Introduction to the Two-Time Load Tester

The total error of an electric energy metering device is the comprehensive error of electric energy metering, which consists of the errors from the electric meter, the composite error of voltage transformers, the composite error of current transformers, and the metering error caused by the voltage drop of the secondary winding of voltage transformers, and can be expressed by the following formula:

    ε=εw＋εTA＋εTV＋εr

εw — Energy meter error %

ETA — Current Transformer Synthetic Error %

εTV — Voltage Transformer Synthetic Error %

εr — Metering Error (%) Caused by Voltage Transformer Secondary Wire Voltage Drop

In power plants and substation electrical energy measurement loops, the outdoor voltage transformers are relatively far from the electrical meters installed on the distribution panels in the control room, generally around 200 to 400 meters. The entire loop includes terminal blocks, switches, fuses, and wires, which necessarily involve contact resistance, wire resistance, and distributed parameters, thereby creating a certain loop impedance. This results in voltage drops across the secondary loop between the voltage transformers and the electrical meters. The total voltage drop in the secondary voltage transformer loop includes the sum of voltage drops from cables, terminal contact resistance, fuse wires, intermediate relay contacts, and air switches. The error caused by the voltage drop in the secondary voltage transformer refers to the percentage difference in voltage amplitude between the secondary terminal and the load terminal relative to the actual secondary voltage, as well as the total phase difference between the two voltages.

The new "On-site Inspection Operation Manual for Electric Energy Measurement Devices" issued by the Production and Operation Department of State Grid Corporation explicitly stipulates the measurement of the actual secondary load of current transformers and voltage transformers.

Secondary Actual Load of Voltage Transformer:

In actual operation, the total admittance is composed of the capacitance between the measuring instruments connected to the secondary of the voltage transformer, the secondary cables, and the ground wire.

Secondary Actual Load of Current Transformers:

In actual operation, the total effective impedance consists of the impedance of the measuring instruments connected to the secondary side, the secondary cable, and the junction resistance.

The dual-load tester features the following functions:

⑴. Achieves fully automatic measurement.

Utilizing engineering plastic enclosures, the product offers durability and effectively ensures the safety of both test personnel and the system.

The instrument features an automatic range switching function, ensuring testing accuracy.

The integration of electronic principle circuitry with DSP technology ensures excellent test stability and strong anti-interference capabilities.

After measurement, automatic calculation of various parameters is provided for customer analysis and testing.

⑥. Featuring large-screen Chinese LCD display, all operations are prompted by Chinese menu options; data has the capability for power-off storage and browsing, and can be connected to a computer for data transmission.

The product is powered by a high-capacity 7.2V 11Ah lithium battery, which has no impact on the test circuit and prevents the system from entering protective mode. Additionally, it can be used in the field without access to a power supply.

⑻. The secondary load test utilizes a clamp-on current meter for current sampling, eliminating the need to disconnect the secondary circuit. This enables continuous online measurement without power interruption. Automatic range switching: During the measurement process, the meter can automatically switch to different positions based on the test object's values, ensuring measurement accuracy and display precision.

⑼. Work hours can last up to 24 hours (long), and can be measured while charged.

⑽. Equipped with a compact charger, it is convenient for measurement and can be used with an external charger for testing when the battery is low.

The instrument is compact and lightweight.

Can store 480 sets of measurement data and retain them for ten years after power failure.

⒀. Large-screen Chinese interface display with RS-232 communication interface

Key Technical Indicators

1. Environmental Conditions

——Temperature: -5°C to 40°C

—— Relative Humidity: <95% (25°C)

—— Altitude: <2500m

—— External Interference: No Severe Vibration, No Severe Electromagnetic Field

2. PT Secondary Load Tester's Key Technical Specifications

⊙ Accuracy of admittance measurement:

X = (X * 2% + Y * 2%) squared

Y = (Y * 2% + X * 2% * 34.38) squared

Two Words – Quantitative Error of the Instrument

Voltage Meter Head: 0.5%

○ Resistance measurement range: 0.1Ω - 50.0Ω

⊙ Accuracy in Impedance Measurement:

X = (X * 2% + Y * 2%) squared

Y = (Y * 2% + X * 2% * 34.38) squared

Two Words – Quantitative Error of the Instrument

Current Meter Head: 1%

3. CT Secondary Load Test Instrument's Main Technical Specifications

——Impedance Measurement Range: 0.1Ω – 50.0Ω

—— Impedance Measurement Accuracy:

X = (2% × X + 2% × Y) squared

Y = (2% of X + 2% of Y) squared

Two Words — Quantitative Error of the Instrument

Ammeter Head: 1%