Phase presence indicator. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Phase presence indicator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / electrician's tool

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Those who work with three-phase electric motors know how dangerous it is for a motor to lose one phase. Only a specialist can immediately notice this, since the engine continues to work, only the sound changes slightly. And the engine in this mode quickly overheats and burns out. In a noisy room, anyone can miss a phase loss, which will inevitably lead to an accident.

There are special starters that turn off the motor when one phase fails, but in private practice it is difficult and expensive to find such devices, although a three-phase network in the private sector is widespread. The quality of our electrical networks leaves much to be desired, and the absence of one phase is a fairly common phenomenon.

To prevent an accident, it is recommended to include a phase presence indicator in a three-phase network. In the simplest case, you can turn on a neon bulb in each phase (through a resistor), but the attention of a person working at any machine is mainly focused on work and you can miss the extinction of one of the indicators, besides, a neon bulb sometimes blinking, which can be confusing. Therefore, in addition to light indicators, it is desirable to have a sound signal.

The device indicates the presence of three phases with the help of LEDs and, in the event of a phase failure, in addition to the extinction of one of the LEDs, it gives an intermittent sound signal. The device also has a redundant power supply (in case of loss of its supplying phase), is assembled according to a transformerless circuit, does not require configuration and is made of the most common parts.

The schematic diagram of the device is shown in Fig.1.

(click to enlarge)

All three phases through diodes VD1-VD3 are fed to resistive voltage dividers, ripples are smoothed out by capacitors C1-C3, then a constant voltage is applied to the "3I-NOT" element DD1.1, at the output of which a log "0" is set. This "0" blocks the operation of the generators on the DD2 chip, and the ZP1 tweeter is silent. Three LEDs are lit through the corresponding elements DD1.2, DD1.3 and transistor VT1. Zener diodes VD6-VD8 protect the inputs of the microcircuit from breakdown during voltage surges.

When one of the phases disappears, the corresponding LED goes out, a log "1.1" appears at the output of DD1, and the generator on the elements DD2.1, DD2.2 begins to generate pulses with a frequency of about 2 ... 3 Hz, which, in turn, run the multivibrator on the elements DD2.3, DD2.4. As a result, an intermittent sound signal is heard in the ZP1 tweeter. The device is powered by two identical circuits (C4, R7, VD4, VD9 and C5, R8, VD5, VD10) included in two different phases, only the stabilization voltages of the zener diodes VD9 and VD10 are different.

Therefore, if all three phases are present, the VD5 diode will be closed, and the voltage will come from the VD9 zener diode through the VD4 diode. If the voltage disappears in one of the phases, then the backup remains, the microcircuits are powered by the voltage taken from the VD11 zener diode.

The printed circuit board of the device is shown in Fig.2.

Phase presence indicator

The circuit uses resistors MLT-0,5 (R1, R3, R5, R15), MLT0,125 (R7, R8, R10), the rest are planar type R1206, electrolytic capacitors K50-35 or similar for a voltage of 16 V, non-electrolytic capacitors of the type C1206, except for C4, C5 (type K73-17 with a voltage of at least 250 V) and C8 (type K10-17). Microcircuits of the K561 series can be replaced without changes in the circuit with microcircuits of the K176 series. KT3102 transistors (with any letter index) can be replaced with any npn structures, for example, KT315, KT3117, etc. Instead of the VD6-VD8, VD11 zener diodes indicated in the circuits, you can use any voltage of 7 ... 9 V (KS175, D818), and instead of zener diodes VD9, VD10 - any for a voltage of 10 ... 15 V (KS515, D814D). Diodes KD209 can be replaced by KD105 or KD102B. Instead of AL307 LEDs, you can use any LEDs, it is advisable to take well-marked ones. As a "tweeter" use a piezoceramic emitter ZP-1 or similar.

The device does not need adjustment and starts working immediately after switching on. If necessary, you can adjust the frequency of the audio signal using resistor R14 or capacitor C9.

Author: I.A. Korotkov

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