SU1195315A1 - Apparatus for determining error of current transformers - Google Patents

Abstract

THE DEVICE OF THE DAY DETERMINATION OF THE CURRENT ACCEPTANCE OF THE CURRENT TRANSFORMERS, containing an AC source, terminals for connecting the secondary winding of the test person, the current transformer whose primary winding is open, millivoltmeter, load resistor, and additional resistor, which is used by the current flow, in order to improve the current flow ratio, to get the current position. power supply with adjustable amplitude and voltage phase, a current comparison device and an isolation transformer, the first output of the current comparison device being connected through the load resistor with the first. the output of the auxiliary power source, which through an additional resistor is connected to the first outputs of a millivoltmeter and an alternating current source, the second output of which is connected to the second output of the device and compares the currents through the primary winding of the isolation transformer (L transformer connected to the secondary - with the red leads of the auxiliary power source and millivoltmeter, the third and fourth terminals of the current comparison instrument are connected to the secondary, o test current transformer coils.

Description

The invention relates to measurement technology and can be used for testing transformers,

The purpose of the invention is to improve the accuracy achieved by using a differential null method.

The drawing shows a block diagram of the proposed device.

The device contains an AC source 1, the terminals 2 for connecting the secondary winding of the current transformer 3 under test, the primary winding of which is open, the first output of the device 4 current comparison is connected through a load resistor 5 to the first output of the auxiliary power source 6 and through an additional resistor 7 to the first terminals millivoltmeter 8 and source 1 whose second output through the primary winding of the current transformer 9 is Oredinen with the second output of device 4 and through terminals 2 is connected to the second output of ffl millivoltmeter 8 and source 6, the third and fourth terminals of the device 4 are connected to the transformer secondary winding vshodami- 9.

The device works as follows.

Through the resistor 7, determined by the leakage inductance and the active resistance of the secondary winding of the current transformer 9 under test, a current flows through which is equal to the ratio of the primary current of the current transformer under test to its nominal transformation ratio. The current and error angles of the current transformer 9 being tested are measured with a device 4 comparison with a zero reading of millivoltmeter 8, which is established by adjusting the amplitude and phase of the voltage of the auxiliary power supply 6. In this case, the magnetic flux in the magnetic core and the current in the resistor 5 of the current transformer under test are the same. values, as in the direct test method. This is explained as follows. The magnetizing current I and the secondary current Ij in a complex form are determined from the expressions

.

 Yo

0)

4-.g:

2 "tZ Z,

 - the value of the primary current reduced to the secondary windingJ

Zp is the resistance of the magnetizing branch;

2- resistance determined by the dissipation inductance and the active resistance of the secondary winding of the current transformer;

2c - load resistance. Equations for currents of the proposed triple have the form

i fZH-UBc

(

((2)

one,. ,

and

- and auxiliary power supply;

1 g, .- 1e currents flowing in the secondary winding and in the load, respectively. After a number of transformations, the system equations (2) give

I and ,,,, g,

7

2 "+, Z.

Oh, then UBC r 2,

equations (3) take z,

(M 2 „

HI ,.

Thus, according to (l), the currents C and C are equal to the magnetizing current and the secondary current in the current transformer, respectively.

Using the proposed device, when testing current transformers in a lightweight mode, one can determine the angular error and improve the accuracy in measuring the current error due to the use of the differential zero method in the proposed device.

3P95315

implemented using the device, it is determined indirectly, while in the prototype, based on the measured values of currents.

Claims (1)

DEVICE FOR DETERMINING ERRORS OF CURRENT TRANSFORMERS, containing an alternating current source, terminals for connecting the secondary winding of the test, a current transformer, the primary winding of which is open, a millivoltmeter, a load resistor and an additional resistor, characterized in that, in order to increase accuracy, an auxiliary circuit is introduced into it a power supply with adjustable amplitude and phase of voltage, a current comparison device and an isolation transformer, the first output of the current comparison device being connected via load resistor with the first output of the auxiliary power supply, which is connected through the additional resistor to the first terminals of the millivoltmeter and the alternating current source, the second output of which is connected through the primary winding of the isolation transformer to the second output of the current comparison device and is connected to the WTO through the terminals for connecting the secondary winding of the tested transformer - ·. With the findings of the auxiliary power supply and the millivoltmeter, the third and fourth conclusions of the current comparison device are connected to the terminals of the secondary winding of the current transformer under test.