Phase sequence indicator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / electrician's tool
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The article describes a device for determining the order of phase rotation in a three-phase 380 V AC network.
Recently, a number of notes on the design of this indicator have appeared in popular journals [1, 2]. These simple and useful devices are not mass-produced and are not available where they are needed. Known devices are physically and morally obsolete.
Figure 1 shows a diagram of a device that does not require a power source and scarce parts.
The indicator is assembled using the well-known four-layer pnpn controlled structure, formed by turning on two complementary transistors VT1, VT2 - an analogue of a thyristor. The control electrode of this structure through the resistor R2 is briefly connected to one of the phases of the three-phase AC network, and its anode through the HL1 LED and the limiting resistor R1 is also briefly connected to any of the two remaining phases. Transistor VT2 shunts the thyristor input depending on the voltage at the collector of transistor VT3 through the feedback circuit: collector VT3, resistor R3, base VT2. The VD2 zener diode limits the forward and reverse voltages on the thyristor, and the VD1 diode removes only the reverse voltage from its input.
The indicator works like this. If a positive half-wave of the leading phase voltage first arrives at the input of the device (let's call it phase A for definiteness), and a positive half-wave of the lagging voltage of phase B arrives at the anode of the thyristor through the resistor R1 and LED HL1, then at which the voltage in the feedback circuit is zero, the transistor VT2 closed, the thyristor is on. Otherwise (phase B at the input, phase A at the anode) by the voltage of the leading phase A, by the time the voltage of the lagging phase B arrives, the transistor VT2 is open in the feedback circuit, i.e. the control signal is shunted, the thyristor is closed and the LED is off. For this case, the voltage supply transistor VT2 does not allow false illumination of the LED, allowing you to get unambiguous information: there is a glow, there is no indicator glow. In the absence of one of the different voltages, the LED does not light up.
Design. The device is assembled on a board made of foil fiberglass with a thickness of 1,0 mm and dimensions of 35x35 mm (Fig. 2).
Three double-insulated conductors are soldered to the structure, withstanding alternating voltages up to 1000 V (for example, MGShV-0,35): a neutral wire with a crocodile clip at its second end; wire from terminal A, the second end of which is soldered to the probe with the inscription "Phase A"; wire from terminal B, also with a probe at the end and the inscription "Phase B".
Working with the device. Connect the crocodile clip to the zero point of the three-phase network. Then they take the probe in both hands and briefly touch any selected phases. If the LED is lit, then the phase sequence corresponds to that indicated on the probes. If the LED does not light up, then change the probes at the same network points so that the LED lights up. At the same time, the health of the LED is checked, which may not work for various reasons. The remaining third phase of the network is C.
On the board, the LED is turned so that it looks from the side of the upper end of the board, three conductors are also directed to the upper end, after which the board is filled with sealant, leaving the LED lens open.
Probes can be made from durable cases of ballpoint pens by placing a steel wire electrode in the case, which must be additionally insulated inside with a cambric and fixed in the case from swinging.
Transistors, if necessary, can be replaced by transistors of the KT342, KT352 or KT502, KT503 types. The LED can be anything.
References:
- Safonkin N. A simple phase indicator//Radio. - 2002. No. 9. - P.40.
- Samelyuk V. Know-how of electrician Maxim // Electrician. 2002. - No. 9. - P.15.
Author: V.A. Ermolov
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