RU1786447C - System for measuring phase-shift angles of current transformers - Google Patents

Abstract

Usage: in electrical engineering, in phase meters designed to measure the phase angle in current measuring transformers, used, in particular, in wattmeters and varmeters, where the permissible phase angle can be less than 0.1 °. SUMMARY OF THE INVENTION: in order to improve measurement accuracy at small phase angle, the device comprises a current source 1 / connected to the input terminal of the measured transformer 2 of the trunk and shunt 3, the output of the last connection is not & with Чх бд б m phase-shifting integrator 4, the output of which is connected to the input of the comparator 5, the output of the comparator 5 is connected to the input of the inverter 6 and the control input, key 7, the output terminal of the current transformer 2 is connected to the input of the first key 7, the output of the shunt 3 is connected to the input of the key 8, the outputs of the keys 7 and 8 are connected to the input of the amplifier 9, the output of the amplifier 9 is connected to the indicator 10. 1 ill.

Description

.... The invention relates to electrical engineering and can be used in phase meters designed to measure the angle of phase shift. In current measuring transformers used in particular in wattmeters and varmeters, where the value of the phase angle may be less than 0.1 ° depending from the accuracy class of a wattmeter or varmeter.

A device is known for measuring the phase characteristics of a four-terminal network. However, it does not make it possible to measure with small accuracy small angle of phase shift (p41 °), in particular between currents, -. ,

Closest to the claimed device is a device for measuring the phase angle in power plants. However, this device allows one to determine the phase shift of current transformers only indirectly, with low accuracy not exceeding 5 ° ...

An object of the invention is to improve measurement accuracy at low phase angles.

This goal is achieved by the fact that in the device for measuring the phase angle of the current transformers, consisting of the input of the device connected to the input of the transformer, the phase shifting device, the output of which is connected to the input of the comparator and the amplifier connected to the indicator, additionally introduced: a shunt, an inverter, the first and second keys, and the input of the device is connected to the shunt, the output of the transformer is connected to the input of the first key, the output of the shunt is connected to the input of the second key and the input of the phase shifting device, the output of the computer Ator connected to

00

about

1

Xi

the inverter input and the control input of the first key, the inverter output is connected to the control input of the second key, the key outputs are connected to the amplifier input.

Comparative analysis with the prototype shows that the claimed device is characterized in that it is equipped with a shunt, inverter, first and second keys, the input of the device being connected to the shunt, the transformer output connected to the input of the first key, and the output of the shunt connected to the input of the second of the key and the input of the phase shifting device, the comparator output is connected to the inverter input and the control input of the first key, the key inverter output is connected to the amplifier input.

Thus, the claimed device meets the criteria of the invention of novelty. Comparison of the claimed solution not only with the prototype, but also with other technical solutions in the art did not allow them to identify features that distinguish the claimed solution from the prototype, which allows us to conclude that the criterion meets significant differences.

 Figure 1 shows a functional diagram of a device containing 1 current source, a current transformer 2, in which the phase angle is measured (not included in the inventive device), shunt 3, phase-shifting device 4, comparator 5, inverter 6 , the first and second keys 7 and 8, amplifier 9, indicator 10.

The current source 1 is connected to the inputs of the tested transformer 2 and shunt 3, the output of the transformer 2 is connected to the input of the first key 7, the output of the shunt 3 is connected to the input of the key 8 and the input of the phase shifter 4, the output of the phase shifter 4 is connected to the input of the comparator 5, the output the comparator 5 is connected to the input of the inverter 6 and the control input of the key 7, the output of the inverter 6 is connected to the control input of the key 8, the outputs of the keys 7 and 8 are connected to the input of the amplifier 9, the output of the amplifier is connected to the indicator 10.

The device operates as follows.

the shunt 3 travels to a phase shifter 4 providing a 90 ° shift. Using a comparator 5, a rectangular pulse is generated, which is supplied to the control input of the key 7. The signal from the output of the transformer 2 is fed to the input of the key 7 .:

In the absence of a shift in the transformer 2, the constant component of the signal at the output of the switch 7 will be zero. With the phase shift of the transformer 2, the average component at the output of the key 7 will be equal to:

.p

ABOUT)

where Lh is the voltage amplitude obtained at. the output of the transformer 2. The signal received at the output of the switch 7 is amplified by the amplifier and displayed on the indicator 10. Thus, a value proportional to the phase shift will be displayed on the indicator.

In the event of an error of 90 ° in the integrator 4, a measurement error appears.

To improve the accuracy of measurement of the device, the signal received at the shunt is used. It is supplied to the key 8, which is controlled by the inverter 6 in antiphase with respect to the key 7. In this case, the value of the signal U2 supplied to the amplifier 9 will be equal to :. .

About I I Sin (if))

2 Us.

-jrsm

(2)

where Us is the amplitude of the sinusoidal voltage obtained at the output of the shunt. The minus of the second element of the right-hand side of formula (2) is obtained due to the out-of-phase operation of keys 7 and 8. From the expression (2) it follows that for y and (small quantities less than 2 °, we have

U2

2ui

l

sin p cos f +

+ sin ip

 2ui

l

(4)

A calibrated AC value is supplied from the input of current source 1. At the output of the shunt, we obtain a voltage proportional to the magnitude of the calibrated current. As a shunt 3, a non-reactive shunt is used. The phase shift introduced by the non-reactive shunt depending on the design of the shunt may vary from tenths to units of minutes and does not affect the measurement accuracy. Signal from vy2 2 2 s1 +. (5)

Therefore, with Ui Us, we get error compensation arising from the work of the integrator. Thus, the use of the signal of the shunt 3 of the inverter 6 and the key 8 can improve the accuracy of measuring the phase angle of the current transformer.

At p 2 ° (the measuring range of the device to be connected) and the difference between lh and Uz no more than 1.0%, the error determined by the difference in expressions (1) and (3) will not exceed 0.1%.

The use of the claimed technical solution allows the introduction of technological control of current measuring transformers before assembling the devices, which reduces the complexity and also increases the reliability of the device.

Claims (1)

The claims A device for measuring the phase angle of current transformers, comprising terminals for connecting the primary and secondary windings of the current transformer, series-connected phase shifting integrator and comparator, an amplifier and an indicator connected in series, characterized in that, in order to increase the accuracy of measuring small phase shift angles of current transformers, a power source, a shunt, an inverter and two switches are additionally introduced into it, the first terminal of the current source being connected to the first terminal of the primary winding of the current transformer, the second terminal of the aforementioned 0 windings are connected to the input of the phase-shifting integrator and through a shunt to the second grounded terminal of the current source, the comparator output is connected to the control input of the first key and the inverter input, 5, the output of which is connected to the control input of the second key, the input of which is connected to the input of the phase-shifting integrator, and the output to the input of the amplifier and the output of the first key, the input of which is connected to 0 terminal for connecting the secondary winding of a current transformer.