3　Electrical Measuring Devices

3.1　General Requirements

3.1.1　The electrical measuring devices shall be configured to correctly show the electrical operating parameters and insulation of power devices.

3.1.2　Electrical measuring devices should incorporate measuring components of computer supervisory systems，general electrical measuring meters and measuring components of other integrated devices.

3.1.3　Electrical measuring devices may measure by using instruments directly or indirectly through primary instruments or secondary instruments.

3.1.4　It is required that the accuracy of electrical measuring devices shall not be lower than the values specified in Table 3.1.4.

3.1.5　The total accuracy of AC circuit indicating instruments shall not be lower than class 2.5，and the total accuracy of DC circuit indicating instruments shall not be lower than class 1.5.The accuracy of instruments connected to the secondary side of electrical measuring transducers shall not be lower than class 1.0.The accuracy of current and voltage transformers，accessories and fittings for electrical measuring devices shall not be lower than the values specified in Table 3.1.5.

3.1.6　The measuring range of pointer-type meters should be selected such that the rated value of power equipment is at 2/3 of the full scale.Overload meters should be used for power equipment and circuits that may be overloaded.

3.1.7　The electrical measurement of several power equipment and circuits of the same type may be performed in a selective manner.

3.1.8　In case of secondary measurement made via transducers，the full scale value of secondary measuring meters shall match with the calibration value of transducers and can be calculated as per Appendix A and B to this code.

3.1.9　For bidirectional-current DC circuits and bidirectional-power AC circuits，ammeters and wattmeters/varmeters with bidirectional scales shall be used.Polar meters shall be employed for polar DC current and voltage circuits.

3.1.10　Ammeters with overload scales should be used for heavy-duty start motors and power equipment and circuits potentially subjected to short-time impulse current.

3.1.11　In power plants and substations deployed with remote telemetry and computer supervisory systems（DC sampling applied），secondary measuring meters，computer and remote telemetry systems should share one set of transducers.

3.1.12　The upper limit of meters in excitation circuits shall not be lower than 1.3 times the value for rated conditions，and the total error of meters shall not exceed 1.5%.

3.1.13　The measuring range of meters for reactive power compensators shall be selected such that it can accommodate the maximum current and voltage that may occur at the devices.The current measuring device for shunt capacitor banks shall be designed assuming that the continuous current flowing through the shunt capacitor bank is 1.35 times the rated current.

3.1.14　The measuring components in both computer supervisory systems and integrated devices may substitute the corresponding general electrical measuring meters provided that their accuracies are acceptable.

3.1.15　The electrical measuring devices adopted in direct instrument measurements shall meet the requirements on dynamic and thermal stability of primary circuits.