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Device for measuring three-phased voltage

IPC classes for russian patent Device for measuring three-phased voltage (RU 2314630):

H02M7 - Conversion of ac power input into dc power output; Conversion of dc power input into ac power output

G01R29/16 - Measuring asymmetry of polyphase networks

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FIELD: transformation equipment engineering, possible use for engineering indicators of three-phased voltage.

SUBSTANCE: device contains three-phased bridge rectifier, made on diodes (1-6). Output contacts of rectifier, being output contacts of indicator, are meant for connecting load circuit (7). Resistors (8-10) are introduced into input circuits of alternating current, connected to corresponding phases of voltage supply being measured. Resistance value of each resistor (8-10) equals to (0,5÷0,7) of value of active resistance of constant current load chain (7).

EFFECT: increased precision of measurements due to improved dynamic characteristics of measuring device.

2 dwg

The invention relates to the field of electrical engineering and can be used in the design of automatic control systems as sensor three-phase voltage.

When building systems of automatic control of three-phase voltage dynamoelectric generators or static converters are used schema converting three-phase voltage to DC. Known measuring sensors three-phase voltage, made on the basis of diagrams three phase bridge rectifiers, such as (1). A disadvantage of the known circuit is the high level of pulsations of the rectified voltage, which reduces the measurement accuracy. To reduce ripple, you can use RC filter, which has inertia, leading to the delay of the control loop and, consequently, deterioration of the dynamic properties of the system automatic voltage regulation.

The closest to this invention is a device for measuring three-phase voltage (2)containing a three-phase bridge rectifier, the input alternating-current circuit which is connected to the phase terminals of the source of the measured voltage and the output circuits of direct current through RC filter connected to the DC load. A known solution is characterized by a lower level of output ripple voltage the I and doubling their frequency compared with (1). However, pulsations occur, which requires the introduction of the RC smoothing filter, which reduces the dynamic properties of the measuring body and, therefore, the whole automatic control system as a whole. Relatively high inertia of the sensor leads to less accurate measurements.

The technical result, which can be achieved with the use of this invention is to improve the measurement accuracy by improving the dynamic characteristics of measuring devices.

The technical result is achieved due to the fact that the device for measuring three-phase voltage containing a three-phase bridge rectifier, the input circuit of AC which are intended for connection to the corresponding phases of the source of the measured voltage, the output of the conclusions of the bridge rectifier, which is output by the output device, are used for connection to the load circuit DC (2), in the input circuit of AC three-phase bridge rectifier introduced the resistors, the resistance of each of which is (0,5÷0,7) on the value of the resistance of the load circuit DC.

Figure 1 shows a schematic electrical diagram of the device.

Figure 2 presents the timing diagram of operation of the circuit (corresponding to each of the phases a, b, C).

The device is IG) contains a three-phase bridge rectifier performed on diodes 1-6. The alternating-current circuit of the rectifier is connected to the input pins on the device, intended for connection to the respective phases (a, b, C) source of the measured voltage. The output terminals of the rectifier connected to the output pins, which serves for connection to a load circuit DC 7. In the input circuit of AC bridge rectifier included resistors 8-10 with the same resistance r, the value of which is (0,5÷0,7)R, where R is the resistance of the load circuit DC 7.

Figure 2 shows:

e_ande_ine_withphase and e_ABe_sune_CA- line voltage of the AC power (mains);

i_and, i_in, i_c- phase currents;

u_ABu_sunu_ca- line voltage at the input of the bridge;

u_d- voltage on output pins DC bridge (load).

The device operates as follows.

When connected to a source of three-phase voltage in known circuits of three-phase rectifiers (1, 2) with almost zero resistance of the alternating current in each moment of time, there are two valve at the output is formed of a unipolar testpulse voltage.

In this device, due to the presence of the resistor in each of the phases of the output circuit of the rectifier, there is a redistribution of currents, resulting in the intervals t₁-t₂(2) simultaneously in a conducting state, there are three diode (1-5-4). The sum of the currents of two phases (a and C) equal to a current of the third phase (C): I_and+I_with=I_in.

On the interval t₁-t₂(switching) current phase smoothly into phase A.

On the interval t₁-t₃(mostly) open the diodes 1 and 4. Current flows in only two phases - a and B.

When this ratio of the input and output impedances of the bridge (r/R=0,5-0,7) duration and levels of pulses of voltage on the load 7 on the primary and the switching intervals are equal (Figure 2).

PulseNet rectified voltage determined by the ratio of the frequency of pulsations of the rectified voltage to the frequency of the AC voltage at the input of the bridge is equal to 12, i.e. in comparison with the prototype 2 times larger, and the amplitude of the pulsations is reduced almost in 4 times.

Assuming ideal diodes, when the voltage drop across them is equal to 0, dvenadtsatiosnye mode rectifier is provided with r=0,57735 R.

When real diodes depending on their type and level of the measured voltage at the input device, the ratio between g and R may be in the range from 0.5 to 0.7.

This scheme retains its properties when connecting receivers with the AK large input impedance (>100 kω), for example amplifiers or Comparators, and relatively low (less than 100 Ohms). For matching impedance of the input and output circuits of the rectifier bridge load circuit may include additional resistors in series with the receiver input signal or parallel to it.

In the real circuit for easy adjustment for different values of load resistors 8-11 can be performed adjustable.

To pair a high level of the measured voltage low-level control devices, performed on the elements of information electronics, can be used transformers.

The absence of inertial RC filter at the output of the rectifier increases the dynamic properties of the device, making it the most preferred for use in low-power devices, information electronics, where important performance measure of the average or maximum values of three phase voltage, and the efficiency principle irrelevant.

The source of information

1. The Handbook of transformative technology. /Ed Imirek, Kiev, Tekhnika, 1978, p.30.

2. Ibid, s.

Device for measuring three-phase voltage containing a three-phase bridge rectifier, alternating-current circuit which is connected to the input pins, designed to establish what Uchenie to the corresponding phases of the source of the measured voltage, weekend conclusions three-phase bridge rectifier, which is output by the output device, are used for connection to the load circuit DC, characterized in that in the circuit of AC three-phase bridge rectifier introduced the resistors, the resistance of each of which is 0.5÷0.7 magnitude of the resistance of the load circuit DC.