A simple phase indicator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology
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For proper operation, three-phase electrical equipment must be connected to the network, observing a certain phase sequence. If the network wires are not marked, a special device, a phase indicator, will help to do this.
Industrially produced phase indicators of the induction type I-517 or FU-2 operate similarly to asynchronous electric motors. However, the presence of rotating parts makes them complex in design and inconvenient to use. There are known phase indicators based on other principles.
A diagram of a simple phase indicator is shown in fig. 1. It allows you to determine the order of the phases in three-phase power networks with a neutral wire, to which the terminal XT3 of the device is connected, and the terminals XT1 and XT2 are connected to two of the three phase wires.
Assume that the voltage applied to terminal XT1 is 120° out of phase with the voltage applied to terminal XT2. This situation corresponds to the graphs in Fig. 2.
Thanks to the diode VD1, the current Iue in the control electrode circuit of the thyristor VS1 flows only during positive half-cycles of the voltage at the XT2 terminal. At the moment t1, when the voltage at the terminal XT1 and the anode of the thyristor becomes positive, the latter opens and remains open until the end of the half-cycle (time t2). The value of the resistor R1 is chosen in such a way that the lamp HL1 glows in full heat, signaling that the phase order corresponds to the marking of the terminals (XT2 - "A", XT1 - "B", the phase remaining unconnected is "C").
If the phase wires are connected to the device in the reverse order ("A" - to XT1, "B" - to XT2), the current phase of the thyristor control electrode lags 120 ° from the phase of the anode voltage (Fig. 3). Now the thyristor opens at time t3 and closes at time t4. The average value of the current flowing through the HL1 lamp is much less than in the previous case, so it glows very weakly or does not glow at all. The intervals during which current flows through the lamp HL1, in fig. 2 and 3 are shaded.
As VS1, in addition to those indicated in the diagram, thyristors T112-10-5, KU202N are suitable. The KD105V diode can be replaced by any of the KD209 series. HL1 is a 26 V, 0,12 A incandescent lamp, however, another one with a rated current of at least the holding current of the used thyristor is also suitable. It is only necessary to select a resistor R1 of the appropriate rating and power. Resistor selection will also be required if the nominal line voltage in the network differs from 220 V.
Parts of the phase indicator are mounted in a housing made of insulating material of suitable dimensions, on the front panel of which terminals XT1-XT3 and a lampholder HL1 are installed.
Author: N. Safonkin, Bryansk
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