As an electric energy metering device, the electric energy meter is the "scale" of electric energy trading, which is valued by both the supply and consumption parties. Whether the multi-function meter is accurate or not, in addition to the accuracy of the device, is also closely related to whether the metering loop is wired correctly.
The accuracy error of the electric energy meter itself is within the accuracy level, and the conventional accuracy level is 0.5S, 1, and 2, and the error of the regular factory meter is generally less than the accuracy level. However, if there is a problem of voltage and current wiring, then the metered electric energy is wrong, and the error can even reach more than 100 times, which brings trouble to users and power supply enterprises, and leads to electricity disputes.
Because there are a large number of meters that need to be wired and installed at the project site, it is easy to have miswiring errors in the meters and are not easy to be found during installation, which leads to inaccurate metering in the power monitoring or billing system, resulting in disputes between the supply and consumption parties.
1. Common meter wiring methods
The common wiring methods of electric energy metering devices are as follows:
(1) The electric energy metering device connected to the neutral point insulation system shall use a three-phase three-wire active and reactive energy meter. If it is connected to the non-neutral point insulation system, a three-phase four-wire active and reactive energy meter or three induction non-stop single-phase energy meters shall be used.
(2) 2 voltage transformers connected to the neutral point insulation system, 35kV and below should be wired in VN mode, 3 voltage transformers connected to the non-neutral point insulation system, and 35kV and above should be wired in Y0/y0 mode. The primary side wiring method is consistent with the system grounding method.
(3) When the load current is 80A and below for low-voltage power supply, it is advisable to use a direct-access electric energy meter; If the load current is more than 80A, it is advisable to use the wiring method connected through the transformer.
(4) For the three-phase three-wire wiring electric energy metering device, the secondary winding of the two current transformers and the electric energy meter should be connected by four-wire. For the three-phase four-wire wiring electric energy metering device, the secondary winding of the three current transformers is connected with the electric energy meter by six wires.
3. Wrong wiring type
The wrong wiring of any component of the meter, voltage transformer, and current transformer will cause the meter to be omitted, undercounted, or overcharged. The amount of electric energy measured by an energy metering device depends on the product of voltage, current and power factor and time, and as long as any one of the three elements is changed, it will cause measurement errors.
The three-phase three-wire TATV is used to analyze the miswiring of the electricity meter, and the wiring error of the voltage part can be attributed to the following two situations when the TV is wired correctly at the first time. One is the reverse polarity and phase disconnection of the secondary output terminal of TV, and the other is voltage misphase.
When the three-phase three-wire system is wiring, there are 2 TVs, and there are 3 possibilities for the secondary wiring of each TV: correct wiring, reverse polarity and phase break, so there are 3x3=9 wiring possibilities. There are 6 possible voltage misphases. In the case of correct TA primary wiring, the wiring error of the current part can be attributed to three situations, the first is the reverse polarity and short circuit of the TA secondary input terminal, and the second is the current misphase, similarly, in the three-phase three-wire wiring, there are 2 TAs, and the secondary wiring of each TA has 3 possibilities: correct wiring, reverse polarity and short circuit, so there are 3x3=9 kinds of wiring possibilities, and there are 6 possibilities of current misphase. There are four types of reverse connection of current in and out of the electric energy meter: 1 type of correct wiring, 1 type of reverse connection, and 2 types of reverse connection of 1 component. From the above analysis, it can be seen that there are two cases of voltage wiring and three cases of current wiring, and these five situations can be randomly combined, therefore, there are a total of 9x6x9x6x4 = 11664 kinds of wiring. Strictly speaking, among so many wiring combinations, only one of them conforms to the national standard wiring, and the rest are incorrect wiring.
Figure CT reversed
4. The wiring diagnosis function of the multi-function meter of CET CLP technology
CET's metering device supports wiring diagnostics to alert the user of possible wiring errors when installing the meter, such as phase sequence errors, CT polarity reversal, TC disconnection, etc. Avoid power supply disputes and economic problems caused by miswiring.
Wiring diagnostics detects the following:
- Frequency out-of-limit monitoring: When the frequency measurement value is not in the range of 45Hz~65Hz, the frequency error is prompted.
- The logic diagram of voltage phase loss diagnosis is as follows:
Voltage phase loss logic diagram
- Current phase loss diagnosis: When the maximum current of the three-phase ≥ 0.1%Ie, and the minimum current of the three-phase is 0, the current phase is missing. When the current phase is missing, the current phase sequence diagnosis is invalid.
- Voltage/current phase sequence diagnosis: When the voltage and current phase sequence is inconsistent with the normal phase sequence, the phase sequence is incorrect. If the default normal phase sequence is ABC, if the access phase sequence is CBA, the phase sequence diagnosis will prompt a phase sequence error.
- Three-phase and total active power direction diagnosis: When the measured value of active power is negative, it will indicate that the direction of active power is abnormal.
- CT polarity monitoring: If the voltage phase sequence is normal and the active power is negative, it indicates that the CT polarity may be wrong, and it is necessary to check and confirm whether the wiring is normal, if the wiring is normal, it can be ignored. Some loads have current direction changes during no-load, start-stop, etc., which will also cause this state to be set.
The following is an introduction to the selection of some of CET's multi-function meters with wiring diagnostics function.
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