SU1453334A1 - Device for measuring power in three-wire symmetric networks - Google Patents

Abstract

The invention relates to electrical measuring equipment and can be used to measure the active and reactive power of three-phase power consumers of dispersed objects. The purpose of the invention is to expand the functionality due to the possibility of measuring reactive power. This is achieved by introducing a current conversion channel 2 and an phase adapter-adapter 9, which, depending on the task, produce a signal proportional to cos or sin. The device also comprises a channel 1 of a voltage converter, a pulse-width modulator 3, an amplitude-pulse modulator 4, a low-pass filter 5, a voltage-to-frequency converter 6, an indication unit 7, and a current converter 8. 1 il. S (l

Description

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with so with so

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The invention relates to electrical measuring equipment and can be used to measure the active and reactive power of three - phase power consumers of dispersed objects.

The purpose of the invention is to expand the functionality of the device due to the possibility of measuring the re-Q active power.

The drawing shows a structural-functional diagram of a device for measuring power in three-phase three-wire symmetric networks. | 5

The device comprises a voltage conversion unit 1, a current conversion unit 2, a pulse-width modulator 3, an amplitude-pulse modulator 4, a low-frequency filter 5, 20 a voltage-to-frequency converter 6, an indication unit 7, a current converter 8 and a phase shifter adapter 9, the voltage inputs of the voltage conversion unit 1 are connected to two 25 phases of the monitored network, and the output through the pulse-width modulator 3 to the first input of the amplitude-im- pulse: modulator 4, the output of which is through the filter 5 low frequency zo is connected to transform a voltage to frequency converter 6 and an indication unit 7, and a second input through a current conversion unit 2 to a current converter 8 included in the third phase of the monitored network, outputs of the voltage conversion unit 1 and a current converter 8 through a phase shifter-adapter 9 are connected to the second inlet. do block 2 current conversion. dd

The device works as follows.

Pulse width modulator 3,

Amplitude pulse modulator 4, dd

the low-pass filter 5 and the voltage-to-frequency converter 6 are a signal multiplier with a digital output. The input of the pulse-width modulator 3, being the first input of the multiplier, receives a signal proportional to the average value over the half-period of the output voltage of the voltage conversion unit 1. The signal of the current converter 8 converted by the current conversion unit 2 is fed to the second multiplier input (the second input of the amplitude-pulse modulator 4).

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d

d

0

The functional relationship of the output and input signals of the current conversion unit 2 is determined by the expression

I; IcosCf, (1)

where Cf is the phase angle of the signal

and a control demodulator signal.

Consequently, the frequency at the output of the voltage-to-frequency converter 6 is determined by the expression

f | kUIcos (f /, (2)

where k is the proportionality coefficient; and - the average value of voltage

for the half period; I - the average current for

half period.

The shift angle if the signal and control signals of the current conversion unit 2 is determined by the nature of the load of the three-phase circuit and the operating mode of the phase shifter of the adapter 9. When measuring the reactive power, the phase shifter adapter 9 generates square frequency pulses in phase or anti-phase with respect to the output signal of the block 1 voltage conversion.

Expression (2) takes the form of an active-inductive load.

f | kUIcos (Cf + | 7) kUIsinCp /, (3) for active-capacitive load

f kUIcos (| S - tp) | -kUIsinCf /. (four)

Thus, the device produces pulses whose frequency is proportional to the reactive power consumed by the three-phase load. The display unit 7 gives information about the sign of the output signal of the multiplier, i.e. indicates the nature of the load - inductive or capacitive.

When measuring active power, the phase shifter-adapter 9 generates signals shifted by an if / 2 angle with active-inductive load, and an active-capacitive load causes an additional shift by an angle if.

When measuring active power, the control signal of the current conversion unit 2 is additionally shifted by an angle with active-inductive 37G

load or angle with active-capacitive load. Expression (2)

takes the form of active-inductive load

f | kyicoslf (if + | J- + |) / / kUIcos (f /, (5) for active-capacitive load

f / KUIcos (| ir-q | t) | / -kUIcos (.

(6)

Thus, the device produces pulses whose frequency is proportional to the active power, re. required t1) phase load. The display unit 7 uniquely identifies the nature of the load.

Claims (1)

The invention of the device for measuring power in a three-phase three-wire symmetric-20 second input of a thin network converting unit, comprising a 1-converter conversion unit, a pulse-width modulator, an amplitude-pulse modulator, a low-pass filter, a voltage-to-frequency converter, a display unit, and a current converter, the inputs the voltage conversion unit is connected to two phases of the network, and the output is through a pulse-width modulator to the first input of the amplitude-pulse modulator, the low-pass filter is connected to input voltage transformer in the frequency and display unit, characterized in that, in order to extend the functionality, in it. Neither the current nor the phase shifter-adapter, the output of the current converter through the first input of the current conversion unit is connected to the second input of the amplitude-pulse modulator. It is connected to the output of the phase shifter adapter, whose inputs are connected to the outputs of the current converter and the voltage conversion unit.