Precautions For The Installation Of Dc Energy Meters And Transformers

Precautions for the installation of DC watt-hour meters and transformers, including the wiring process of the wiring terminals of DC watt-hour meters and current transformers, whether the selection of secondary wires is appropriate, the protection measures for the voltage position of the secondary wires, and the current transformer conversion Than parameters etc.

In the measurement, people attach great importance to the calibration and testing of DC energy meters and transformers, but they often overlook the installation details of DC energy meters and transformers. These details will affect the metering accuracy, so they should not be ignored.

1. Wiring process of terminal block

The connection parts such as gaskets and fastening screws at the connection terminals of DC energy meters and current transformers are prone to poor contact when they are rusted or loosened by moisture, resulting in increased contact resistance.

2. Improper selection of secondary wires

The secondary wire connected to the DC electric energy meter through the transformer should be a single-strand hard copper wire as required. However, although some people choose copper wire, they choose soft copper wire for the convenience of wiring. In fact, the soft copper wire presses the bolt at the connection point. Strand breakage is easy to occur under pressure, which reduces the effective cross-sectional area of ​​the wire, thereby increasing the loop resistance and increasing the measurement error; From: Home of Electrical Engineering Technology

In addition, when high-voltage measurement is used, the cross-sectional area and length of the secondary leads of the current transformer and voltage transformer will also have an impact, because the cross-sectional area of ​​the wire and the length of the wire are directly related to the loop resistance. If single-strand hard copper is used The wire cross-sectional area is small or the wire length is too long. Will increase the loss and affect the accuracy of measurement.

3. No corresponding measures have been taken to obtain the voltage position of the secondary wire

In the voltage circuit of the low-voltage metering device of rural distribution transformers, if the voltage metering is used for the convenience of the diagram, the voltage metering method is directly from the low-voltage pillar of the transformer to the nearest break T-connection method, because the low-voltage outgoing lines of the transformers generally use aluminum wires, while the metering voltage leads are copper wires. , To form a copper-aluminum connection, and the running time is long, a layer of oxide film will be formed on the copper-aluminum connection part, which increases the loop resistance, increases the voltage loss, and affects the accuracy of the measurement.

4. Conversion ratio of current transformer

The accuracy of a current transformer is related to the current it passes. If the primary current is too large or too small, the ratio of the output secondary current to the primary current will increase the error.

In order to ensure the accuracy of measurement and reduce unnecessary power loss, in addition to the normal calibration of meters and transformers, the details that affect the measurement should also be incorporated into the measurement system for management.

Strengthen the inspection of the wiring terminal technology, timely replace and deal with the corroded wiring terminals, avoid direct connection of copper and aluminum wires in the connecting wires, and tin enamel the wire ends if necessary; choose a suitable converter ratio to make the current The primary current of the transformer should be about 30% to 120% of the actual load current in normal operation.

It is best to reach about 60%; the secondary wire of the metering loop should be a single-strand hard copper wire, and the cross-sectional area of ​​the secondary wire must meet the requirements to reduce the voltage loss and current loss on the wire.

According to requirements, the measuring voltage lead adopts 2.5 square millimeter single-strand hard copper wire, and the current lead is not less than 4 square millimeter single-strand hard copper wire; the length of the secondary loop wire is generally required to be horizontal and vertical, as short as possible, and best The use of colored phase wires not only facilitates installation and reduces wiring errors, but also facilitates the usual measurement safety survey to prevent errors.

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