- Accuracy class concept
- A little about the device and how it works
- Meter malfunctions
- Consumer responsibility area
- How to replace the meter
- If the energy consumption has not decreased
“I’m being deceived!” – this phrase periodically sweeps through the thoughts of many users of municipal power grids. But can faulty meters really be the reason for the round sums in electricity bills and how to get out of the situation if this turns out to be true? Let’s find out how to check the electricity meter.
Accuracy class concept
All electricity metering devices adopted for settlements between the supplier and the consumer must have a number of criteria. The main one is compliance with the accuracy class, expressed as a percentage, by which a deviation of the meter readings from the actual values of energy consumption is possible.
According to the current legislation on the regulation of retail trade in electricity, for individual consumers the minimum acceptable accuracy class is 2.0, for consumer groups – 1.0. If the meter must also take into account the reactive energy component or register the return transmission to the network, the accuracy class should not be lower than 1.0 in all cases..
1 – induction (disk) electric meter; 2 – electronic electricity meter
Specifically, the required accuracy class of metering devices is indicated in the technical conditions for the connection. Higher accuracy may be required at the discretion of the electricity supplier, which may well be disputed. You need to understand that the accuracy tolerance implies deviations in the direction of both “recalculation” and “defect”.
However, in general, among, say, a hundred consumers, all these deviations compensate for each other, and therefore one or two differences in excess of the norm for the supplier is practically irrelevant, but for the consumer this can result in tens of kilowatts of overruns monthly.
A little about the device and how it works
So, all the counters lie: in one direction or another, weaker or stronger. However, over time, deviations in readings can become much stronger than the original ones. Let’s try to figure out why this is happening.
At the moment, induction-type meters (disk) are not used in ASKUE systems mainly due to design flaws that do not allow to provide an accuracy class higher than 2.5. They were replaced by electronic meters, which have a smaller error, but are also characterized by high sensitivity..
Block diagram of an electronic meter
In an electronic electricity meter, the current in the secondary winding of current transformers is converted by a frequency generator into a series of pulses proportionally to the high frequency. Such measuring circuits include a large number of high-precision electronic components, while the instrument does not have built-in protection against dust, moisture and vibration..
Due to the high sensitivity of the electronics, there is a high probability of failures, the cause of which is the inconsistency of the conditions for placing the meter. The most vulnerable point is the group of measuring circuits, which are characterized by:
- clogging of radioelements with a violation of normal conductivity;
- reducing the thickness of the conductive paths due to corrosion;
- deviation of the values of trimmers and passive elements from vibration.
Another common category of breakdowns is caused by degradation of electronic components. This includes:
- malfunctions of the frequency generator;
- breakdown of the ADC;
- violations in the microcontroller program.
All these malfunctions can be eliminated only by servicing the meter and repairing it in a specialized laboratory. Each metering device has a verification stamp and an energy supervision seal that restricts access to its insides. Their presence means that a new or repaired meter has passed bench tests and its readings correspond to the indicated accuracy class. The subtotal is as follows: the probability of breakdowns causing deviations in readings increases in proportion to the period that has passed since the meter was checked.
Consumer responsibility area
It would seem that the more often the meter is checked, the lower the possibility of incorrect data and the less their potential economic harm. This is true, but after all, verification is not performed for free: someone must dismantle, temporarily install a replacement for the verified meter, and then return everything to its place.
Usually, the person who maintains metering devices on the balance sheet of the power grid pays for this. The line of delimitation of areas of responsibility is indicated in the contract for the supply of electricity, usually it is the ASU, which is located on the chain before the meter. Suppliers are not stupid enough to commit to measuring instrument error control.
Perhaps, having studied your own contract, you will see a different situation: as a rule, the owners of distribution networks of new housing estates and cottage settlements take responsibility for the state of metering devices. In this case, you can demand an extra verification of the meter without hitting your own wallet. One way or another, such a requirement requires good reasons..
The only way to personally identify the presence of an error is to install a control metering unit in the consumer’s area of responsibility immediately after the current meter. An attempt to calculate the consumption by the pulsed blinking of the LED is not an accurate method, moreover, with different loads, the meter can give different errors. When installing a control meter, the discrepancy in the readings should not be more than the sums of the two accuracy classes (after all, the readings can deviate in both directions), in this case there is every reason for checking or replacing the metering unit.
How to replace the meter
The feasibility of carrying out repairs and verification at its own expense is determined by two factors: the technical condition of the metering unit and the size of the error. If there really is such a meter and the meter shows an overrun, for example, about 100 kW / year, then the payback period for an extraordinary verification will be 2 years: 500 rubles for a check and the same for removal / installation. In about the same time, the control counter will pay off. With the error value described above, the installation of a new meter will pay off from 3 to 7 years, depending on the cost of the meter, which is approximately equal to the calibration period for most metering devices.
To perform a replacement or extraordinary withdrawal for verification at your own expense, you must contact the office of the energy supplying organization for working with consumers. There, a statement is written to the name of the head of energy supervision at a certain area, after which an inspector and an electrician leave for the facility. For convenience, it is recommended to personally agree with the site foreman about the time of work to be able to sign the current documentation (acts of removal, installation, sealing and work performed) at the place.
If the energy consumption has not decreased
Usually, a conclusion about a high error is made on the basis of calculating the power of existing consumers and their operating time. Unlike popular belief, the meter will not calculate the consumer when operating at the lower limit of the permissible voltage, for example, at 170 V. Overvoltage is a possible, but not the main reason for high errors, but the increased consumption of the household appliances themselves at low voltage in networks are a separate topic. We will only mention that it is possible to appeal the problem of low or too high voltage only by removing telemetry from the general house meter and only if the deviations are significantly greater than the tolerances specified in the contract.
If, even after replacing the meter, the monthly consumption significantly differs from the calculated one, you should pay attention to the quality of the consumer wiring. Transient resistances at the connections, insufficient cable conductivity, a significant line length from the metering unit to the pantographs – all this generates an active load on the heating of cable and wire products. In especially advanced cases, the own consumption of wiring can be up to 25-30% of the total.
As a conclusion, consider the opposite situation: when, as a result of measurements, it turns out that the device accepted for accounting does not count the consumed energy. No matter how great the temptation to take advantage of this error, perhaps the reason is a serious breakdown of the meter. In this case, the supplier may ascribe to the consumer intentional damage to the device and recover a round sum for this..