SU676948A1 - Arrangement for measuring symmetrical components of three-phase ac voltage system - Google Patents

Description

the device and the code setter, as well as the polarity discriminator whose input is connected to the output of the reversible counter, and the output to the input of the scaling unit, the input terminal of the devices through the converter and the "code-code connected to the input of the multiplying device, and and phase shifting device - with the setting unit of the codes, the second input of the recalculating unit is connected to the output of the reversible counter and the input of the recording device, its output - with the input of the setting unit of the codes, the output of the setting unit - with the second input of the multiplying device, and the second output of the threshold device - with the second input of the phase-shifting device. Consider the construction principle of the proposed device for measuring the symmetrical components of a three-phase system of alternating voltages. Let us write the values for the instantaneous values of forward U, inverse Hz and zero f / o sequence: u, 1 / l, „sin (--t + А) + Uv: n sin XX (c ,: + 45 + 120) + V, sinX X (“+ FC -120 °), and, WASH sin (o t + T) + Vb, g sin X XH + 5-120) + V." sinX X (i + s + 120 °), and, 1 / Lt sin (i + T) + 1 / I. sin (c: + c) + + l /, sin (.c). (3) Multiply the instantaneous value of phase A by the normalized harmonic 51n (a) / + fl, where fl is the initial phase of the normalized harmonic. blog V UA, P sin (. g + l) X (1 Xsin (a - /; 4-9l), l / lmSin (f + l) X XC08 (a); + srl), SAY is the projection of the Ult vector on imaginary axis of the complex plane; projection of the vector onto the real axis of the complex plane; - moment of signal sampling; n is the number of sampling points. Under the condition of flA FA, we have 5 lk - d / LmSin2 () l “ω82 (“), + l), (6) SAX -V Ult sin (ω, + l) Xn XcosK-lh l) - sin2 (o , + T) (7) Since cos2 (“., + L) 0 and 2 si2 (u / +) is 0, i l THAT 1 / L„ r - 6lH. The amplitude and phase values of phases B and C are determined similarly. From the equations () it can be seen that if the conditions are met (equality of the initial phases of the system of voltages under study and normalized harmonics), then the amplitude of the fundamental harmonic of each phase voltage is equal to the imaginary part of the amplitude vector. The principle of operation of the proposed device is based on this. The drawing shows a block diagram of a device for measuring the symmetrical components of a three-phase peremegny voltage system. It consists of a scaling unit 1, a dial of codes 2, a multiplying device 3, a 4 analog-code converter (PAK), a reversible counter 5, a threshold device 6, a phase shifter 7, a polarity divider 8, a switch D phases, a registering device 10. V the initial state in the scaling block I recorded the value of the angle pho, from which the search for the angle begins. The analog-code converter 4 converts the voltage V at measurement time ii into numeric codes. Setpoint code 2 sets the values of cos (co / i + + f) in a digital code, and sets the value of sin ((,) ti + f) or sin (co / i + ф 120 °) in response to a command from threshold device 6. The multiplier device 3 at the moments of measurement ti multiplies the voltage values received from PAK 4 and the values of orthogonal functions received from the setter of codes 2. The polarity distinguisher 8 determines the sign of the phase increment of the normalized harmonic. The phase switch 9 establishes the order of connection of the measured phases and the measured sequence. A phase switch 9 controls the operation mode of the phase shifter 7, which shifts the phase by i 120 °. The device works as follows.

Phase switch 9 set the phase measurement mode A.

From the scaling unit 1, the code proportional to the first value of the initial phase fAo of the normalized main harmonic is fed to the setpoint generator code 2, and from it the code proportional to the value cos (- | fAo) goes to one of the inputs of the multiplying device 3, where it multiplies with the instantaneous the value of the input signal at the measurement point ti, which is supplied from the output of the analog-code converter 4. As a result, in the reversing counter 5, the value SAX is written for n measurement points according to expression (5).

After this, the second measurement cycle begins, in which in the scaling unit 1, the command angle from FAO + AFA1 is set instead of the FAO angle from the reversing counter 5. At the end of the second cycle, in the reversible counter 5, a new value fl will be recorded.

The change in the FA angle continues until the SAX 0 condition is met. At this time, the threshold device 6 is triggered and issues a signal to the setpoint code 2, from which the value of sm (+ PLL) arrives at the multiplying device 3, resulting in a reversible counter 5 The component consists of the phase A, which is equal to the amplitude value of the phase of the ULT (6), and in the conversion unit 1, the initial phase.

Similarly, the amplitude and phase values of phases B and C are

When determining the direct (reverse) sequence in phases B and C, it is necessary to shift the phase by an angle of ± 120 °, according to expressions (1) and (2). A shift of an angle of ± 120 ° is performed by the phase shifter 7, and an angle code of 120 ° is entered into the setpoint codes 2. The sign of this code is determined by the phase switch 9.

The proposed design principle of the instrument allows one to measure the amplitude and phase of the symmetric components, their bringing a sinusoidal input signal with high accuracy and in a wide frequency range.

Claims (3)

Invention Formula A device for measuring symmetrical components of a gosh, their three-phase system of alternating voltages, containing an analog-code converter, a phase switch, a phase-shifting device, a scaler, and a recording device that differs in that, in order to improve the measurement accuracy, serially connected a multiplying device, a reversible counter, a threshold device and a setter of codes, as well as a polarity discriminator whose input is connected to the output of the reversible counter, and the output to the input of a counting Lok, wherein the input device through the clamp analog converter connected to the code the input of the multiplying device, and through series-connected phase switch and phase-shifting device - with the setting unit, the second input of the counting unit is connected to the output of the reversing counter and the input of the recording device, its output - with the setting input of the codes, the output of the setting unit - with the second input of the multiplying device and the second output of the threshold device - with the second input of the phase-shifting device Sources of information taken into account in the examination 1. USSR author's certificate 473126, cl. G 01R 29/16, 1975. 2. USSR author's certificate No. 432542, cl. G 06G 7/62, 1974. 3. USSR author's certificate D 374557, cl. G 01R 29/16, 1973.