RU2248003C2 - Device for calibrating instrument current transformers - Google Patents

Abstract

FIELD: radio and electric measurement technology.

SUBSTANCE: device for calibrating instrument current transformers has shunts disposed in primary and secondary windings of instrument current transformer. Shunt disposed in the first winding of instrument current transformer is made in form of two imitators of resistors and one resistor with non-standardized error; all the resistors are connected in parallel. Current resistor imitators have to be current dividers which have primary windings connected in series with primary winding of instrument current transformer; secondary windings are connected with current terminals of resistors. Circuit for measurement of current and angular error of instrument current transformers is made in form of electromagnet current comparator. First shoulder of the comparator is connected with potential terminals of shunt through variable resistor in the second winding of instrument current transformer. The second shoulder is connected through resistor with potential terminals of shunt in the circuit of secondary winding of instrument current transformer. Winding intended for measuring angular error of instrument current transformer is connected with the secondary winding of auxiliary current transformer through phase-shifting capacitor. Indicator winding is connected with null indicator.

EFFECT: widened range of calibration.

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Description

The present invention relates to electrical engineering and is intended for calibration of measuring current transformers in an extended range of measured values.

A device for calibrating measuring current transformers containing an alternating current source, shunts in the circuit of the primary and secondary windings of the calibrated measuring current transformer, resistance stores, capacity stores and a zero indicator [1].

The disadvantage of this device is the complexity of manufacturing shunts of high accuracy, as well as a limited range of measured values.

A device (prototype) for checking measuring current transformers, containing an AC source, a shunt in the primary circuit of the measuring current transformer, made in the form of three parallel-connected resistors, a shunt in the secondary circuit of the measuring current transformer, an auxiliary current transformer, an electromagnetic current comparator and zero indicator [2].

A disadvantage of the known device (prototype) is the limited range of calibration of measuring current transformers.

The problem to which the invention is directed is to develop a technical solution that provides an extension of the calibration range of measuring current transformers.

This problem is solved as a result of the fact that in the device for checking measuring current transformers containing an AC source, a shunt in the primary circuit of the measuring current transformer, made in the form of three parallel connected resistors, a shunt in the secondary circuit of the measuring current transformer, an auxiliary current transformer , electromagnetic current comparator and zero indicator, the shunt in the primary circuit of the measuring current transformer is made in the form of two connected in parallel resistors and resistors with non-standard error with the possibility of disconnecting them from the primary winding of the measuring current transformer and changing the shunt conversion coefficient, while their current and potential clamps are connected separately. Resistor simulators are current dividers, the primary windings of which are connected in series with the primary winding of the measuring current transformer, and the secondary windings are connected to the terminals of the resistors.

The ability to verify measuring current transformers in an extended range of measured values is provided by the fact that the device uses a composite shunt, which includes simulators of resistors designed for high currents.

Figure 1 shows a diagram of a device for checking measuring current transformers when determining ρ ₁ and ρ ₂ ;

figure 2 shows a diagram of a device for checking measuring current transformers when balancing the shoulders of the current comparator and when determining ρ ₃ .

A device for checking measuring current transformers (FIGS. 1, 2) contains an AC source 1, shunts 2, 3 in the circuit of the primary and secondary windings of the measuring current transformer, an electromagnetic current comparator 4, an auxiliary current transformer 5, and a calibrated current measuring transformer 6 with a resistive -inductive load 7 in the secondary circuit of the measuring current transformer and zero indicator 8. The shunt 2 in the primary circuit of the measuring current transformer 6 is made in the form of parallel connected two simulators ditch of resistors 9, 10 and resistor 11 with a non-standard error with the possibility of disconnecting them from the primary circuit of the measuring current transformer and changing the shunt conversion coefficient by means of connectors designed for high currents, while the current and potential terminals of the simulators of resistors 9, 10 and resistor 11 are connected apart. The simulators of resistors 9, 10 are current dividers 12, 13, the secondary windings of which are connected to the current terminals of resistors 14, 15, and the primary windings are connected in series with the primary winding of the measuring current transformer 6. It should be noted that the division factors of the current dividers 12, 13 are interconnected in a ratio of 10: 1, and the resistors 14, 15 are nominally equal. The nominal value of the resistance of the shunt 3 in the secondary circuit of the measuring current transformer 6 is equal to the nominal value of the resistance of the resistor 11 of the shunt 2 in the primary circuit of the measuring current transformer 6.

The electromagnetic current comparator 4 is made with an adjustable conversion coefficient; the first arm 16 is made in one decade and connected to the potential terminals of the shunt 2 through the variable resistor 17, the second arm 18 is made in multi-decade and connected to the potential terminals of the shunt 3 in the secondary circuit of the measuring current transformer 6 through the resistor 19. Winding 20 for determining the angular error of the current measuring transformer connected to the secondary winding of the auxiliary current transformer 5 through a phase-shifting capacitor 21, and the primary winding of the auxiliary current transformer 5 is connected to This is the case with the primary winding of the measuring current transformer 6. The indicator winding 22 is connected to the zero indicator 8.

The operation of the device for checking measuring current transformers is as follows.

Before the verification operation of measuring current transformers, the current comparator arms 4 are balanced in the following sequence. Assembled circuit in accordance with figure 2. In this case, the resistance value of the shunt 2 in the primary circuit of the measuring current transformer 6 is equal to the resistance value of the resistor 11. In the secondary circuit of the measuring current transformer 6, the nominal current value is set, for example, I ₂ = 5 (A). On the shoulders of the current comparator 16, 18, values equal to one are set (readings on the scales of the first arm 16 and the second arm 18 of the current comparator 4 are respectively equal: δ = 1, ρ = 1). Then, using a variable resistor 17 in the first arm 16 of the current comparator (for example, a resistance store), the magnetic flux in the core of the current comparator 4 is equal to zero, which is indicated by the zero (minimum) reading of the zero indicator 8.

After the balancing of the shoulders of the current comparator is completed, the transformation coefficient of the measuring current transformer is determined and the following operations are performed. At the first measurement stage, the circuit in accordance with FIG. 1 is assembled. In this case, the shunt 2 in the primary winding of the measuring current transformer 6 is composed of two parallel simulators of resistors 9, 10 and resistor 11. The circuit is balanced by adjusting the ampere turns in the arms 16, 18 and winding 20 of the current comparator 4. The equality

where R ₉ , R ₁₀ are the equivalent resistance values of simulated resistors 9, 10;

R ₁₁ is the resistance value of the resistor 11;

To ₆ - the transformation coefficient of the measuring current transformer 6;

ρ ₁ - readout on a scale of the second shoulder 18 of the current comparator 4.

At the second stage of measurements, the shunt 2 is composed of parallel connected simulator resistor 9 and resistor 11. The circuit is balanced and a new equality is made:

In the third measurement step, the circuit in accordance with FIG. 2 is assembled. In this case, the shunt 2 is composed of parallel connected simulator resistor 10 and resistor 11. Then the circuit is balanced, which corresponds to the new equality

Solving equations (1), (2), (3) together, we find the transformation coefficient K _{6 of the} measuring current transformer from the obtained values of ρ ₁ , ρ ₂ , ρ ₃

то выражение (4) принимает видIn the event that when balancing the shoulders of the current comparator, the ratio of the shoulders

then expression (4) takes the form

Since the equivalent resistance of the resistor simulator is equal to the resistance of the resistor connected to the secondary winding of the current divider multiplied by the conversion factor of the current divider, the heat loss power in the resistor in this case decreases in proportion to the square of the conversion factor of the current divider.

Thus, the proposed technical solution allows us to expand the range of currents when determining the transformation coefficient of measuring current transformers, which is ensured by the use of resistor simulators designed for high currents in the device.

Sources of information

1. Lyubimov L.I. Questions of verification and certification of large-scale AC converters / L.I. Lyubimov, I.D. Forsilova, E.Z. Shapiro. - M.: Mechanical Engineering, 1984. - S.4-13, 21-27.

2. Nefediev D.I. Device for checking measuring current transformers. Patent No. 2192020 for an invention (Russia). Published in BI, 2002, No. 30.

Claims (1)

A device for checking measuring current transformers containing an AC source, a shunt in the primary winding circuit of the measuring current transformer, made in the form of three parallel-connected resistors, a shunt in the secondary winding circuit of the measuring current transformer, an auxiliary current transformer, an electromagnetic current comparator and a zero indicator, different the fact that the shunt in the primary circuit of the measuring current transformer is made in the form of two resistor simulators connected in parallel resistors with non-standard error with the possibility of disconnecting them from the primary winding of the measuring current transformer and changing the shunt conversion coefficient, while their current and potential clamps are connected separately, and the resistor simulators are current dividers whose primary windings are connected in series with the primary winding of the current measuring transformer and the secondary windings are connected to the current terminals of the resistors.

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