§ 11 Theory of the method of unwinding an induction electric meter by the "transformer" method.
As we found out from the previous paragraphs, an electric meter is an asynchronous squirrel-cage electric motor. In this case, the role of the squirrel-cage rotor is performed by the disk of the electric meter. And the windings form Wi (current winding of the meter) and Wu ( voltage winding of the meter). Figure 1 shows a simplified electrical diagram of an electric meter. The remaining additions are aimed at increasing the accuracy of the counter and they are not listed here. And Since this is an electric motor, it obeys two basic laws of electromechanics:
1. Any electric motor can operate as an electric power generator and vice versa. (In this case, this law is not useful to us)
2. Any electric motor rotating in one direction can rotate in the other.
This means that there are no theoretical obstacles to making the counter rotate backwards.
In order for the motor to begin to rotate in the opposite direction, it is necessary to change the direction of the current in one of the windings of the electric motor (of course for an alternating current motor it would be more correct to say that it is necessary to change the phase angle of the current, but we will not go into the theoretical subtleties, and under the direction of the current we will understand the phase angle). That is, if we manage to change the direction of the current in the current winding of the meter, then it will begin to rotate backward.
Now let's look at Figure 2. Suppose that we found an AC source Uobr that gives current in the opposite direction (out of phase), connected it to points E1 and E2 (or terminals 1 and 2 of the electric meter).
The current through the winding Wi, will be equal to the sum of all currents through the winding (Kirchhoff law), that is, Iwi = In-Iob.
What follows from this formula? If In = Iob, then the counter will stop, although the load R will consume power. If In <Iob the meter will go back, and the load Rn will continue to consume power.
The most interesting thing is that in order to stop the counter, the voltage Uobr should be about 2-3 V, since the resistance of the current winding of the counter Rwi is quite small, about 0.2 - 0.3 Ohm. Accordingly, according to Ohm's law, Iobr = Uobr / Rwi and even 3 V create a current of the order of 10 A.
Now you need to find a device with an output voltage of 2-3 V, and it issued it in antiphase to the main load current. Fortunately, there is such a device and it is not difficult to find it - it is called an ordinary step-down transformer for 2-3 V and a power of about 100 watts.
Let's look at Figure 3 - if everything is clear by the magnitude of the secondary voltage, it is elementarily measured by a tester, then with the phase everything is a little more complicated. In order for the transformer to give out current in antiphase, it is enough to simply turn the secondary winding. Now we have everything to make the counter spin back.
Now, if we substitute new elements in Figure 2 and bring it a little closer to reality, we get the circuit shown in Figure 4. This is already a real device with which you can make the counter rotate either forward or backward (just turn the plug in the socket for this). But this option is full of significant drawbacks:
1. The step-down transformer is located in the shield, and this is an obvious fuse.
2. It is necessary to pull an additional two wires in the electrical panel, which is quite problematic, and also a fuse.
Let's try to solve the first problem, that is, move the transformer to the apartment. Partially, you can solve the second. Pay attention to fig. 4 point E2, L2 and the upper pin on the socket are connected, so you can use one wire from the wiring to power the primary winding of the transformer Tr1.
Now let's look at fig. 5. This is a modified diagram of Fig. 4, but now some of the problems have already been solved - now the transformer is already in the apartment and it is easy to hide it, one wire from the apartment to the shield disappeared. But still I want no snot to stretch from the apartment to the shield. That is, it remains only to find a free bypass wire from point E1 to terminal 1 of the meter. There are no extra wires in the apartment and it would seem that the problem is insoluble. But fortunately for us in the apartments we have networks with earthed neutral. What does it mean ? In the power shield, the neutral wire is electrically connected to ground. And in our apartment, grounding is present everywhere - these are central water supply pipes.
That is, we got the same missing third wire, but it cannot be used in the form shown in Figure 6, because the current winding of the electric meter is included in the phase wire and the neutral wire is grounded. So you need to make sure that the current winding of the electric meter is not included in the phase circuit, but zero. To do this, change the incoming wires to the counter, that is, going to the terminals 1 and 3. (See Fig. 7)
And now this bypass wire can be used. Instead of a dashed bypass wire, we use grounding. (see Fig. 8) What we get - all that is needed is in the apartment, it remains to perform only a few shamanistic actions.
So what needs to be done so that the counter starts spinning backwards:
You need to find a step-down transformer 220/4 V with a capacity of at least 100 watts.
Need a socket next to the water pipe.
It is necessary to change the incoming wires on the counter, so that the phase wire comes to the third terminal of the counter, and zero to the first.
Strip the heating pipe to metal.
Assemble the circuit shown in Figure 8.
In the winding up of electricity meters, the main sense of proportion. If it turns out that for half a year you have not consumed a kilowatt - wait for the energy inspection with all the consequences. That is, you still need to pay for electricity, preferably regularly and not less than 100 kW. And the rest can be slightly reduced. If you follow these simple rules and not be impudent, then the flight is almost impossible.
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