RU2244319C1 - Device for calibration testing instrument current transformer - Google Patents

Abstract

FIELD: measurement engineering; electrical engineering.

SUBSTANCE: device has ac source, inductive current divider installed in primary winding circuit of instrument current transformer, shunt installed in secondary winding of inductive current divider which shunt is made of three resistors connected in parallel which resistors have non-normalized error, and shunt mounted in secondary winding circuit of instrument current transformer. Measuring circuit for defining current and angular error of instrument current transformer is made in form of electromagnetic current comparator. First shoulder of comparator is connected with potential terminals of shunt in secondary winding circuit of inductive current divider through variable resistor. Second shoulder is connected to potential terminals through resistor with potential terminals of shunt mounted in secondary winding circuit of instrument current transformer. Winding for measuring angular error of instrument current conductor is connected to secondary winding of ancillary current transformer through phase-shifting capacitor. Indicator winding is connected with null indicator.

EFFECT: widened range of calibration testing.

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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 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 , an electromagnetic current comparator and a zero indicator, an inductive current divider with a known division coefficient is introduced, the primary winding of which is connected to In particular, with the primary winding of the measuring current transformer, the secondary winding is connected to the current terminals of the shunt, made in the form of three parallel-connected resistors with an irregular error with the possibility of disconnecting them from the secondary winding of the inductive current divider and changing the conversion coefficient of the shunt, while their current and potential terminals are connected separately, and the nominal value of the resistance of the third resistor with a large shunt resistance in the secondary circuit of the inductive divide current I is equal to the nominal value of the resistance in the shunt circuit of the secondary winding of current transformer multiplied by the division factor of the inductive current divider.

The ability to verify measuring current transformers in an extended range of measured values is ensured by the fact that the device uses an inductive current divider included in the primary circuit of the measuring current transformer.

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 alternating current source 1, an inductive current divider 2 in the primary circuit of the measuring current transformer, a shunt 3 in the secondary circuit of the inductive current divider 2, a shunt 4 in the secondary circuit of the measuring transformer current, electromagnetic current comparator 5, auxiliary current transformer 6, verifiable measuring current transformer 7 with resistive-inductive load 8 in the secondary circuit of the measuring current transformer and zeros minutes indicator 9. Inductive current divider 2 comprises a primary 10 and secondary 11 windings. The shunt 3 in the circuit of the secondary winding 11 of the inductive current divider 2 is made in the form of three parallel-connected resistors 12, 13, 14 with an unnormal error with the possibility of disconnecting them from the secondary winding of the inductive current divider and changing the conversion coefficient of the shunt by means of connectors designed for high currents while the current and potential clamps of the resistors 12, 13, 14 are connected separately. It should be noted that the nominal values of the resistance of the resistors 12, 13 are in a ratio of 1:10, and the nominal value of the resistance of the resistor 14 of the shunt 3 in the secondary circuit of the inductive current divider 2 is equal to the nominal value of the resistance of the shunt 4 in the secondary circuit of the measuring current transformer 7 times the division coefficient of the inductive current divider 2.

The electromagnetic current comparator 5 is made with an adjustable conversion coefficient; the first arm 15 is made in one decade and connected to the potential terminals of the shunt 3 of the secondary circuit of the inductive current divider 2 through the variable resistor 16, the second arm 17 is made in multi-decade and is connected through the resistor 18 to the potential clamps of the shunt 4 in the secondary circuit of the measuring current transformer 7. Winding 19 to determine the angular error of the measuring current transformer is connected to the secondary winding of the auxiliary current transformer 6 through the phase-shifting capacitor 20, the primary winding of the cat cerned is connected in series with the primary winding a measuring current transformer winding 7. The indicator 21 is connected to a zero indicator 9.

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

Before the verification operation of the measuring current transformers, the shoulders of the electromagnetic current comparator 5 are balanced in the following sequence. Assembled circuit in accordance with figure 2. In this case, the resistance value of the shunt 3 in the secondary circuit 11 of the inductive current divider 2 is equal to the resistance value of the resistor 14. In the secondary circuit of the measuring current transformer 7, the nominal current value is set, for example, I ₂ = 5 (A). Values equal to unity are set on the shoulders of the current comparator 15, 17 (readings on the scales of the first arm 15 and the second arm 17 of the electromagnetic current comparator 4 are respectively equal to δ = 1, ρ = 1. Then, using a variable resistor 16 in the first arm 15 of the electromagnetic current comparator (for example, a resistance store), the magnetic flux in the core of the electromagnetic current comparator 5 is equal to zero, which is noted by the zero (minimum) reading of the zero indicator 9.

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. The shunt 3 in the circuit of the secondary winding 11 of the inductive current divider 2 is composed of three parallel-connected resistors 12, 13, 14. The circuit is balanced by regulating the ampere turns in the arms 15, 17 and the winding 19 of the electromagnetic current comparator 5. The equality

Where

R ₁₂ , R ₁₃ , R ₁₄ - resistance values, respectively, of resistors 12, 13, 14;

R ₄ is the resistance value of the shunt 4;

K ₂ is the division coefficient of the inductive current divider 2;

K ₇ - transformation coefficient of the measuring current transformer 7;

ρ ₁ - readout on a scale of the second shoulder 15 of the electromagnetic current comparator 5.

Provided that R ₁₄ = K ₂ R ₄ , equation (1) takes the form

At the second stage of measurements, the shunt 3 is made up of resistors 12, 14 connected in parallel. The circuit is balanced and a new equality is made:

or:

In the third measurement step, the circuit in accordance with FIG. 2 is assembled. In this case, the shunt 3 is composed of parallel-connected resistors 13, 14. Then, the circuit is balanced, which corresponds to the new equality:

or:

Solving equations (2), (4), (6) together, we determine the transformation coefficient k _{7 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

Thus, the proposed technical solution allows to expand the range of currents when determining the coefficient of transformation of measuring current transformers, which is achieved through the use of an inductive current divider designed for large primary currents.

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 B.I. No. 30, 2002.

Claims (1)

A device for calibrating measuring current transformers, containing an AC source, a shunt in the primary winding circuit of the verified measuring current transformer, made in the form of three parallel-connected resistors, a shunt in the secondary winding circuit of the measuring current transformer, auxiliary current transformer, electromagnetic current comparator and zero indicator, characterized in that an inductive current divider with a known division coefficient is introduced into the device, the primary winding of which is connected to therefore, with the primary winding of the measuring current transformer, the secondary winding is connected to the current terminals of the shunt, made in the form of three parallel-connected resistors with an irregular error with the possibility of disconnecting them from the secondary winding of the inductive current divider and changing the conversion coefficient of the shunt, while their current and potential clamps are connected separately, and the nominal value of the resistance of the third resistor with a large shunt resistance in the secondary circuit of the inductive d current divisor equal to the nominal value of the resistance in the shunt circuit of the secondary current transformer windings multiplied by the division factor of the inductive current divider.

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