Phase detector for a wide voltage range. Encyclopedia of radio electronics and electrical engineering

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

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This development is a simple and easily repeatable phase detector, an instrument often needed by an electrician. Its advantages: a wide range of voltages in the network (from 9 to 400 V), low energy consumption, simplicity of design and availability of components (microcircuits of the K561 series, KT315 transistors, AL307 LEDs), the ability to work in networks with or without "zero" (with "zero" the third phase can not be connected). The revision of the circuit for its power supply from the mains (without battery) is given. A printed circuit board has been developed.

When installing electrical installations, it often becomes necessary to connect the phases in a three-phase network in the desired sequence. The developed phase detector allows you to determine the phase sequence in networks with or without a neutral wire. In this case, the line voltage in the network can be from 9 to 400 V (phase from 5 to 230 V). At a supply voltage of 9 V, the device consumes a current of 20...25 mA.

The electrical circuit of the device is shown in Fig.1.

(click to enlarge)

The sensor is formed by elements R1-R3, VD1-VD3. Phases A, B, C are connected to terminals X1, X2, X3, respectively. Zener diodes limit the voltage to the level of log. "1" (8 ... 9 V). As a result, we obtain trapezoidal signals. These signals are fed to the shapers of rectangular signals on the elements "NOT" DD1.1-DD1.6. At the outputs of the elements DD1.4-DD1.6, rectangular signals are generated with a phase difference of 120°. The C1R7 circuit generates a short-term pulse along the edge of the X2 phase signal (Fig. 2b). These pulses are fed to the inputs of the triggers DD2. The waveforms at the inputs of the triggers are shown in Fig. 2, a, c, and at the outputs of the triggers - in Fig. 2, d, e.

If the phases on X1, X2, X3 are connected correctly (X1-A, X2-B, X3-C), then the location of the signals at the inputs and outputs of the triggers corresponds to Fig.2. If the phase order is reversed, then a "1" log will appear at the output of Q2. The signals from the trigger outputs are fed to amplifiers based on transistors VT1, VT2, in the collector circuits of which LEDs VD4, VD6 are turned on. If the VD4 LED is on, then the phase sequence is correct, if VD6, then it is incorrect.

The VD5 LED is a power-on indicator. The device is powered by a 9 V battery. The power is turned on with the SB1 button only for the time of phase sequence control (1 ... 3 s), which significantly increases the battery life.

It was possible to reduce the current consumed by the device and expand the range of supply voltages through the use of CMOS microcircuits. Resistors R4-R6 prevent the failure of the elements DD1.1-DD1.3 due to the internal diodes of the elements.

The lower voltage limit in this circuit is limited by the level of log. "1" (4,5 V). Given the voltage drop across the resistors, the lower limit will be slightly higher. The upper limit is determined by the sensor details. To expand it to 660 V, it is enough to increase the power of the resistors R1-R3 to 2 W, and to 1000 V - up to 4 W.

If there is a neutral wire at the measuring point, then it can be connected to terminal X4, and the third phase should not be connected at all.

The power supply of the circuit can be taken directly from the network. Part of the circuit of the device with mains power is shown in Fig.3. Diodes VD7-VD9 play the role of a rectifier, capacitor C3 is a ripple filter. The power button is not needed. The mains voltage must be 350...400 V.

Construction and details. All elements of the circuit are assembled on a printed circuit board (Fig. 4) with dimensions of 45×60 from foiled one-sided textolite. The housing is made of insulating material in accordance with safety regulations. Holes are cut opposite the LEDs. The circuit details are shown in Fig.1 and Fig.3. Schema adjustments are not required.

The phase detector can be improved by using a seven-segment liquid crystal indicator as an indicator. Amplifiers are not needed. I leave this work to amateurs who like to improve devices.

Attention! The device does not have galvanic isolation and operates with high voltage, so you need to be careful when installing and checking the device.

Author: S.P. Stepanchuk

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