Why is there a self-propelled counter

When the load is turned off, the counter sometimes continues to rotate, that is, self-motion is observed.

Why does the disk spin? The fact is that special compensating devices are provided in the counter to compensate for the frictional moment. For example, in the path of the working magnetic flux, either a special plate or a short-circuit coil is installed, or a compensating screw is installed. In this case, the working flux Ф is divided into fluxes Ф'p and f»p, between which a certain phase shift angle appears due to different magnetic resistance along the flux path.

Thus, an additional moment Mk = kF’rf»p sin ψ appears in the rotating disc of the electricity meter, which compensates for the frictional moment in the meter.

Usually, full compensation of the frictional moment occurs when the load on the meter is more than 100% and the rated supply voltage in the network. Therefore, at idle speed, that is, when the measuring device works without load, the compensation moment becomes greater than the friction moment, and the disk, under the influence of the difference in these moments, begins to move, i.e. is driven arises.

Especially the influence of self-propelled power in an electricity meter is manifested when the voltage in the network rises, for example at night. In this case, the compensation moment Mk increases because it depends on the square of the applied voltage:'p = k1U, F»p = k2U and Mk = k1 NS k2 NS U2 = kU2.

In order to eliminate self-running, a special device is provided in the measuring devices, which creates an additional braking moment.