Accounting with the use of measuring transformers

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Section 1 General Rules

Accounting for electricity. Accounting with the use of measuring transformers

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Encyclopedia of radio electronics and electrical engineering / Rules for the installation of electrical installations (PUE)

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1.5.16. Accuracy class of current transformers and voltage for connection of calculated electricity meters should be no more than 0,5. It is allowed to use voltage transformers of accuracy class 1,0 to turn on settlement meters of accuracy class 2,0.

To connect technical accounting meters, it is allowed to use current transformers of accuracy class 1,0, as well as built-in current transformers of accuracy class below 1,0, if additional sets of current transformers are required to obtain accuracy class 1,0.

Voltage transformers used to connect technical meters may have an accuracy class below 1,0.

1.5.17. It is allowed to use current transformers with an overestimated transformation ratio (according to the conditions of electrodynamic and thermal resistance or busbar protection), if, at the maximum load of the connection, the current in the secondary winding of the current transformer will be at least 40% of the meter's rated current, and at the minimum working load - at least 5 %.

1.5.18. The connection of the current windings of meters to the secondary windings of current transformers should be carried out, as a rule, separately from the protection circuits and together with electrical measuring instruments.

It is allowed to jointly connect current circuits if their separate connection requires the installation of additional current transformers, and joint connection does not lead to a decrease in the accuracy and reliability class of current transformer circuits used for accounting, and provides the necessary characteristics of relay protection devices.

The use of intermediate current transformers to turn on settlement meters is prohibited (for an exception, see 1.5.21).

1.5.19. The load of the secondary windings of the measuring transformers to which the meters are connected must not exceed the nominal values.

The cross section and length of wires and cables in the voltage circuits of settlement meters should be chosen so that the voltage losses in these circuits are not more than 0,25% of the rated voltage when powered by voltage transformers of accuracy class 0,5 and not more than 0,5% when powered by voltage transformers of accuracy class 1,0. To ensure this requirement, it is allowed to use separate cables from voltage transformers to meters.

Voltage losses from voltage transformers to technical accounting meters should not exceed 1,5% of the rated voltage.

1.5.20. To connect calculated meters on power lines of 110 kV and above, it is allowed to install additional current transformers (in the absence of secondary windings for connecting meters, to ensure the operation of the meter in the required accuracy class, according to the load conditions on the secondary windings, etc.). See also 1.5.18.

1.5.21. For 110 and 220 kV bypass switches with built-in current transformers, it is allowed to reduce the accuracy class of these current transformers by one step in relation to that specified in 1.5.16. For a 110 kV bypass switch and a 110 kV bus-connecting (intersectional) switch used as a bypass, with separate current transformers (having no more than three secondary windings), it is allowed to turn on the current circuits of the meter together with the protection circuits when using intermediate current transformers of an accuracy class of not more than 0,5; in this case, it is allowed to reduce the accuracy class of current transformers by one step.

The same inclusion of meters and a decrease in the accuracy class of current transformers is allowed for a bus-connecting (intersectional) switch for a voltage of 220 kV, used as a bypass switch, with separate current transformers and for a voltage of 110-220 kV with built-in current transformers.

1.5.22. To power the meter circuits, both single-phase and three-phase voltage transformers, including four- and five-rod ones used for insulation control, can be used.

1.5.23. Metering circuits should be led to independent terminal assemblies or sections in the general row of terminals. In the absence of assemblies with clamps, test blocks must be installed.

The clamps must ensure the shorting of the secondary circuits of the current transformers, the disconnection of the current circuits of the meter and the voltage circuits in each phase of the meters when they are replaced or checked, and also the inclusion of the exemplary meter without disconnecting the wires and cables.

The design of assemblies and terminal boxes of settlement meters should ensure the possibility of their sealing.

1.5.24. Voltage transformers used only for metering and protected on the higher voltage side by fuses must have fuse integrity monitoring.

1.5.25. With several bus systems and each voltage transformer is connected only to its own bus system, a device must be provided for switching the meter circuits of each connection to the voltage transformers of the corresponding bus systems.

1.5.26. At consumer substations, the design of grilles and doors of chambers in which fuses are installed on the higher voltage side of voltage transformers used for settlement accounting should ensure the possibility of sealing them.

The handles of the drives of disconnectors of voltage transformers used for settlement accounting must have devices for their sealing.

See other articles Section Rules for the installation of electrical installations (PUE).

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