The error of the electric energy metering device is the integrated error of electric energy measurement, which is composed of the error of the electric energy meter, the composite error of the voltage transformer, the composite error of the current transformer and the measurement error caused by the voltage drop of the secondary conductor of the voltage transformer. The following formula represents:

ε=εw＋εTA＋εTV＋εr

In the formula: εw-energy meter error%

εTA—Combined error of current transformer%

εTV—Composite error of voltage transformer%

εr—The measurement error caused by the voltage drop of the secondary conductor of the voltage transformer%

In the electric energy metering circuit of power plants and substations, the outdoor voltage transformer is far away from the electric energy meter installed on the switchboard in the control room, generally about 200-400m. The entire circuit has terminal blocks, switches, fuses and Wires must have contact resistance, wire resistance, and distribution parameters, so there is a certain loop impedance, which causes a voltage drop on the secondary loop between the voltage transformer and the electric energy meter. The voltage drop of the secondary circuit of the voltage transformer includes the sum of the voltage drop of the cable, terminal contact resistance, fuse, intermediate relay contact, and air switch. The error caused by the secondary voltage drop of the voltage transformer refers to the percentage of the voltage amplitude difference between the secondary terminal and the load terminal of the voltage transformer relative to the actual secondary voltage, and the general term for the phase difference between the two voltages.

The State Grid Corporation’s Production and Operations Department’s "Electric Energy Metering Device Site Inspection Operation Guide" clearly stipulates that the actual secondary load of current transformers and voltage transformers should be measured.

The secondary actual load of the voltage transformer:

In the actual operation of the voltage transformer, the total admittance between the measuring instrument connected to the secondary and the capacitance between the secondary cable and the ground wire is formed.

The secondary actual load of the current transformer:

In the actual operation of the current transformer, the impedance of the measuring instrument connected to the secondary, the total effective impedance of the secondary cable and the contact resistance.

1. It can realize three-phase three-wire, three-phase four-wire, single-phase automatic measurement;

2. The use of engineering plastic chassis is durable, and effectively guarantees the safety of testers and the system;

3. The instrument has automatic range switching function to ensure test accuracy;

4. The use of electronic principle circuit combined with DSP technology makes the test stable and strong anti-interference ability;

5. After the measurement is completed, various parameters related to the load are automatically calculated, which is convenient for customers to analyze and test.

6. The large-screen Chinese character LCD display is adopted, and all operations are prompted by the Chinese character menu; the data has the functions of power-off storage and browsing, and can transmit data online with the computer.

7. Use large-capacity 7.2V11Ah lithium battery to supply power, which will not have any impact on the test circuit and avoid the protection of the system. At the same time, it is used when there is no power supply on site.

8. Load test uses clamp-type ammeter to sample current without disconnecting the secondary circuit. Can realize on-line measurement without power failure. Automatic range switching: During the measurement process, it can be switched to different positions according to the value of the test object, so that the measurement accuracy and display digits are guaranteed.

9. The working time can be as long as 24 hours.

10. It is equipped with a lightweight charger, which is convenient for measurement. When the battery power is insufficient, the external charger can be used for measurement.

11. The instrument is small in size and light in weight.

12. Very wide secondary working current/voltage range. Under a working current of 50mA, it can distinguish resistance and reactance of 1mΩ, and can test the actual online load of an S-class current transformer with a secondary rated current of 5A; under a working voltage of 5V, it can distinguish conductance and susceptance of 0.001mS

13. It can store 480 sets of measurement data, which can be maintained for ten years after power failure

14. Large screen display with Chinese interface, with RS-232 communication interface

1. Environmental conditions

——Temperature: -10°C～40°C

——Relative humidity: <85% (25°C)

——Altitude: <2500m

——External interference: no strong vibration, no strong electromagnetic field

2. The main technical indicators of the instrument during the secondary pressure drop test

⑴. Measuring range: ratio difference: 0.001%～19.99% angle difference: 0.01’～599’

⑵. Resolution rate: ratio difference: 0.001% angle difference: 0.01’

⑶. Basic error of the instrument

——DX=±(2%×X+2%×Y)±2 words;

——DY=±(Y×2%+ X×2%×34.38)±2 words.

2 words-quantization error of the instrument

⑷. Accuracy of voltmeter head: 0.5%

⑸. Scope of work

——Voltage: (50～120)V

⑹. The instrument indicates the action value (prompt error)

——Error: the ratio difference is greater than 20% or the angle difference is greater than 600'.

——Voltage: Voltage <2.0V.

3. The main technical indicators of the instrument during the PT secondary load test

⑴.PT secondary load test

——Admittance measurement range: 0.1ms-50.0ms

——Admittance measurement accuracy:

——Secondary voltage (50V－120V)

DX=±(2%×X+2%×Y)±2 words

DY=±(2%×X+2%×Y)±2 words

2 words-quantization error of the instrument

Note: When the measured value is below 0.2mS, the test voltage should be kept above 50V, and at the same time, pay attention to keeping the core wire of the clamp meter in the middle. At this time, the quantization error of the instrument is 5 words

⑵.Voltage meter head: 0.5%

4. The main technical indicators of the instrument during the secondary load test of CT

——Impedance measurement range: 0.1Ω—50.0Ω

——Accuracy of impedance measurement:

DX=±(2%×X+2%×Y)±2 words

DY=±(2%×X+2%×Y)±2 words

2 words-quantization error of the instrument

Current meter head: 1%