CN203164408U - Current transformer error testing circuit - Google Patents

Abstract

The utility model relates to a current transformer error test circuit, comprising a test current transformer, a test main circuit, a DC excitation winding and a load winding, the test current transformer is connected in series in the test main circuit, and the DC excitation The winding and the load winding are respectively connected to the test current transformer. Compared with the prior art, the utility model has the advantages of simple structure and high test precision.

Description

A current transformer error test circuit

technical field

The utility model relates to the technical field of transformer testing, in particular to a current transformer error testing circuit.

Background technique

The principle of current transformer is based on the principle of electromagnetic induction. A current transformer consists of a closed core and windings. Its primary winding has few turns and is connected in series with the current line that needs to be measured, so it often has all the current of the line flowing, and the secondary winding has more turns and is connected in series in the measuring instrument and protection circuit. With the continuous expansion of power system transmission capacity, new current sensors are more and more widely used in medium and high voltage power grids. As an important part of electric energy metering devices, current sensors are directly related to the accuracy and rationality of converted data. The calculation of the comprehensive error of electric energy measurement, so the accuracy test of the current sensor must be carried out. For example, the utility model patent application 03271777.6 discloses a current sensor error inspection platform, which is mainly connected by a circuit consisting of a voltage regulator, a current booster, a standard current transformer, a current-voltage converter and a transformer calibrator. Suitable for medium voltage grid testing.

Contents of the invention

The purpose of this utility model is to provide a current transformer error test circuit with simple structure and high test precision in order to overcome the above-mentioned defects in the prior art.

The purpose of this utility model can be achieved through the following technical solutions:

A current transformer error test circuit, including a test current transformer, a test main circuit, a DC excitation winding and a load winding, the test current transformer is connected in series in the test main circuit, and the DC excitation winding and the load winding Connect with the test current transformer respectively.

The test main circuit includes a current booster, a switch, a second ammeter and a grounding resistor connected in sequence, the test current transformer is connected in series between the second ammeter and the grounding resistor, and the current booster and the grounding resistor ground respectively.

The DC excitation winding includes a DC power supply, an adjustable resistor and a first ammeter connected in sequence, and the first ammeter is connected to the DC power supply.

The load winding includes an induction coil, a third ammeter and a load resistor. The induction coil is wound on the test current transformer. Both ends of the induction coil are respectively connected to the third ammeter and the load resistor, and the load resistor is grounded.

The test current transformer is a current transformer for measurement.

Compared with the prior art, the utility model adds a DC excitation winding to the test circuit, controls the DC current flowing into the transformer through the adjustable resistance connected in series in the DC excitation winding, and observes the load end induction under different DC biases. The degree of distortion of the current and the change of the transmission characteristics are used to detect the error of the current transformer, which has the advantages of simple structure and high test accuracy.

Description of drawings

Fig. 1 is the structural representation of the utility model.

Detailed ways

The utility model will be described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is carried out on the premise of the technical solution of the utility model, and the detailed implementation and specific operation process are given, but the protection scope of the utility model is not limited to the following examples.

As shown in Figure 1, a current transformer error test circuit includes a test current transformer CT, a test main circuit, a DC excitation winding and a load winding, and the test current transformer CT is connected in series in the test main circuit. The above-mentioned DC excitation winding and load winding are respectively connected with the test current transformer. The test current transformer is a current transformer for measurement.

The test main circuit includes a current booster I, a switch K, a second ammeter A2 and a grounding resistor Z connected in sequence, and the test current transformer CT is connected in series between the second ammeter A2 and the grounding resistor Z. The current booster I and the grounding resistor Z are grounded respectively. The DC excitation winding includes a DC power supply E, an adjustable resistor R and a first ammeter A1 connected in sequence, the first ammeter A1 is connected to the DC power supply E, and the adjustable resistor R is connected to the first ammeter through a wire L. The ammeter A1 is connected, and the wire L bypasses the test current transformer CT. The load winding includes an induction coil, a third ammeter A3 and a load resistance _RL , the induction coil is wound on the test current transformer CT, and the two ends of the induction coil are respectively connected to the third ammeter A3 and the load resistance _RL , The load resistor _RL is grounded.

When using the above-mentioned current transformer error test circuit for testing, the DC current flowing into the transformer is controlled through the adjustable resistor connected in series in the DC excitation winding, and the distortion degree and transmission characteristics of the induced current at the load end are observed under different DC biases. Changes, so as to detect the error of the current transformer.

According to the test results, the influence of the DC bias current on the angle difference of the measuring current transformer is small. When the DC ampere-turn reaches 9NI, the critical error is at 5% of the rated primary current; only when the primary current reaches 20%, the angle difference is 13 points, which exceeds the angle of 3 points in the national standard. Compared with the error limit of the national standard 0.5S-level measurement CT, using the CT under 9NI DC bias as the 0.5s-level measurement CT can meet the error range.

The influence of DC bias current on the ratio difference of measuring CT is obvious. When the DC ampere-turn reaches 5NI, 50%, and 80% of the rated primary current, the error is divided into -0.22 and -0.24 respectively, and the error range has exceeded the 0.2S level error stipulated by the national standard, reaching 1.1 to 1.2 times. When the DC ampere-turn reaches 9NI, the error of the rated primary current of more than 20% has far exceeded the error value specified in the national standard, reaching 1.6 to 2.5 times. Similarly, when the DC ampere-turns is above 5NI, using a 0.2S-level measurement CT as a 0.5S-level measurement CT can satisfy the measurement error.

Claims (5)

1. current transformer error hookup, it is characterized in that, comprise test current mutual inductor, test major loop, DC excitation winding and load winding, described test current mutual inductor is serially connected in the test major loop, and described DC excitation winding is connected with the test current mutual inductor respectively with the load winding.

2. a kind of current transformer error hookup according to claim 1, it is characterized in that, described test major loop comprises current lifting device, switch, second reometer and the stake resistance that connects successively, described test current mutual inductor is serially connected between second reometer and stake resistance, and described current lifting device and stake resistance be ground connection respectively.

3. a kind of current transformer error hookup according to claim 1 is characterized in that, described DC excitation winding comprises direct supply, adjustable resistance and first reometer that connects successively, and described first reometer is connected with direct supply.

4. a kind of current transformer error hookup according to claim 1, it is characterized in that, described load winding comprises inductive coil, the 3rd reometer and pull-up resistor, described inductive coil winding is on the test current mutual inductor, the inductive coil two ends connect the 3rd reometer and pull-up resistor respectively, described pull-up resistor ground connection.

5. a kind of current transformer error hookup according to claim 1 is characterized in that, described test current mutual inductor is Verification of Measuring Current Transformer.