Application

Used as a standard to calibrate current transformer whose accuracy class is two or more lower than itself.

 

Structure

CT is made up with primary winding and secondary winding, with the principle shown in Figure 2.

Wiring must strictly follow the current ratio given by wiring nameplate. L1 and K1 are the polar terminals of primary winding and secondary winding respectively, and La is the polar terminal when it is needed to cross the core.

 

Technical Parameters

1. Temperature: -5℃～40℃

2. Relative humidity: ＜80%

3.Capacity:5VA,1VA COSφ=1

4.Primary Current :1-2000A

5.Secondary Current:5A,1A

6.Accuracy Class:0.05S

7.Rated Voltage:500V

8.Frequency:50Hz

9. Allow long-term work under the rated current; More than 500A across the core.

 

Self-calibration

When the current ratio of CT is 5/5 or 1/1,it could often perform self- calibration to assess its accuracy. Wiring diagram for self- calibration is shown in Figure 3.

In this figure,Tx is current transformer,Z is load box.

 

Calibrating

When it is used as a standard to calibrate current transformer whose accuracy class is two or more lower than itself.The wiring diagram is shown in Figure 4. In this figure,T0 is the standard CT; Tx is the tested CT; Z is load box of the tested CT

 

Precautions

1. The current of standard CT and tested CT must be the same in CT calibration.

2. Follow the given wiring diagram strictly.

3. Test whether the load box is accurate or not before calibrating the transformer.

4. Forbid secondary winding opening during the calibration.

5. Select demagnetization before calibration.The wiring diagram is shown in figure 5.

Short out the secondary winding before cutting off the power when the demagnetization is finished.

6.Principle wiring diagram of CT with large current generator is similar to above diagram. They are the same except the output winding of large current generator and primary winding of transformer are the same one.

 

Figure

1. Structural principle diagram of large current generator

2. Structural principle diagram of CT