JPH11142459A - Transformer error testing device with zero load function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a testing device capable of accurately measuring various types of loads ranging from a designated load to zero load in the error tests of a current transformer and a potential transformer for an instrument. SOLUTION: For a current transformer test, a voltage feedback transformer T2 and a current detector CTd are connected in series in a connection circuit 6 between a device to be tested CTx and a measuring circuit 2 of a tester 1, a voltage es with the same phase as a circuit current Ix and a 90 deg. phase voltage ej added, with the detection voltage of the CTd taken as a reference voltage, to a feedback voltage control circuit 15 with a voltage (e) corresponding to the terminal voltage of the CTx taken as an input signal, and its output is fed back to the transformer T2 to reduce the amount of voltage drop in the connection circuit 6 to zero.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for comparing and measuring the ratio error and the phase angle error of an instrumentation transformer (VT) or a current transformer (CT) so that the VT and CT burdens become zero. The present invention relates to a device having a function of manually or automatically controlling the internal impedance of a vessel.

[0002]

2. Description of the Related Art When measuring CT errors by a comparison method, as shown in FIG. 1, a standard current transformer CT _S is directly connected to an error measuring circuit 2 of a measuring device 1 and a device under test CT _X is designated and charged. connected via a Z _i, I _S-phase component I _R and regulator 4a the 90 ° component I _j in unbalanced current I _g flowing through the detection coil N _g of the current comparator transformer 3 in the meter, 4b seeking specific error ε and the phase angle error θ as an index the galvanometer D in addition to the feedback winding n _n via the amplifier 4c by. 5 is a standard current transformer circuit, and 6 is a device-under-test connection circuit. In this measurement, the load (unit [VA]) of CT _X is V ₂ · I _X , but the connecting wire 7 of CT _X and other lead resistance R _r and the N _X winding winding resistance is that a voltage drop of V _m + V _r to V ₂ due to the presence as the internal resistance R _m, the error factor for a given load Z _i of. This effect increases as Z _i decreases. However, recently, a measuring instrument connected to the secondary side of the CT has a low burden, and a specified burden 0 [VA] (V ₂ =
0) may be required, and in the above conventional circuit, Z _i =
Even if it is 0, it is impossible to make V _m + V _r ≠ 0, so that the zero burden test cannot be realized. Transformer V
If the error test T, then a standard transformer in front of the measuring circuit 2 of the tester 1 as illustrated in FIG. 4 VT _S and secondary rated voltage (typically 63.5V～220V) is different under test transformer V
Rated voltage switching precision transformer T _D in order to correspond to the T _X
Is inserted. The burden of VT _X in this circuit is V _X
· I ₂ is a [VA], the current I _2, in addition to the current I ₂ 'flowing to the load impedance Z _T, the exciting current I _O of the transformer T _D
Error increases increases relatively is I _m If the small designation burden for containing the sum I _m of the current I _m 'flowing through the measuring circuit 2 as a measurement current. If the burden is to be reduced to zero, that is, even if Z _T is released, it is impossible to set I ₂ = 0 because of _Im , so that zero burden cannot be realized.

[0003]

[Problems that the Invention is to Solve The present invention, the secondary terminal voltage V ₂ of the test current transformer in the case of current transformer to the state of 0, the measurement of the device under test connection circuit in the case of a transformer It is an object of the present invention to provide an error test apparatus which can set a current _Im to 0 and can perform stable measurement without causing oscillation or the like regardless of the use of an amplifier circuit in each case.

[0004]

According to the present invention, there is provided a current transformer testing apparatus comprising a current detecting current transformer and a voltage feedback transformer inserted into a connection circuit between a current transformer under test and an error measuring circuit. Using the output of the current transformer for detection as a reference voltage vector, an in-phase voltage and a 90 ° phase voltage are obtained, and these are connected via an amplifier so that the output of the voltage detector connected between the secondary terminals of the current transformer to be measured becomes zero. The negative feedback to the transformer. Further, in the above device, between the feedback transformer and the voltage detector connected between the terminals of the current transformer under test, the output of the detector is used as an input signal, and the common mode voltage having the output of the current detection current transformer as a reference vector and 90%. ° An automatic feedback voltage control circuit using a phase voltage as a reference signal is connected so that the output of the control circuit is fed back to the feedback transformer. Further, the transformer test apparatus of the present invention uses a rated voltage switching transformer interposed between the measurement circuit and the transformer under test, and the reference voltage vector generating winding and the feedback winding are provided on the transformer. And a control circuit similar to the automatic control circuit in the current transformer test device is connected to the feedback winding, and the conversion voltage from the current detector connected in series to the transformer connection circuit under test is connected to this control circuit. Is supplied to the feedback winding to supply the sum current of the exciting current of the rated voltage switching transformer and the inflow current of the measurement circuit flowing through the secondary winding, that is, the measurement current, thereby eliminating the measurement current flowing through the connection circuit. Things.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 2, the configuration of a measuring circuit 2 is the same as that of FIG. Transformer for voltage feedback to the connecting circuit 6 (trans) T ₂ and the current I _X detecting current transformer CT _d are connected in series, the secondary terminal u of the test current transformer CT _X, v connection circuit voltage detection transformer in parallel to 6 (trans) T ₁ is connected. G is a galvanometer which is connected to the secondary side of the transformer T _1. Reference numeral 8 denotes a connection cable. 10
The integral output current I _X connect 'circuit current I _X and phase of the voltage vector e _S and 90 ° phase voltage vector e _j inverting amplifier circuit 9a a reference vector generation circuit for generating a current detection current transformer And a circuit 9b.
R _S and R _j are the respective variable resistors for adjustment, and AK is an amplifier having a relatively small amplification factor (1 ≧ amplification factor). The output of the amplifier is applied to the transformer T ₂ so that the negative feedback with respect to load voltage V ₂ of the test current transformer CT _X. In this circuit, the state where the deflection of the galvanometer G becomes zero by adjusting the variable resistors R _S and R _j is when the output voltage V ₀ of the transformer T ₂ becomes − (V _m + V _r ). From V ₂ = 0. Conductor resistance R _{r of} connection circuit
_Includes the resistance of CT _d and also includes the resistance of the connection cable 8 between CT _X and the measuring instrument 1. Therefore, even if the connection cable is extended, the secondary circuit of the device under test CT _X , that is, The voltage drop of the entire connection circuit can be canceled. In this circuit, the voltage V ₂ , which is a burden element of the device under test CT _X , is set to CT _X
Are directly detected between the terminals, controlling the V ₂ = 0 I _T
= 0 since the error of the error component or CT _X of do not affect the measurement current I _X in I _X can be accurately measured. In this circuit, the amplification factor of the amplifier AK is 1
Therefore, there is no possibility of oscillation.

In the circuit of FIG. 2, the variable resistor R_SPassing
And R_jNeed to be adjusted manually. FIG. 3 illustrates this operation.
This is a circuit that can perform measurement automatically without making it unnecessary.
You. Circuit elements indicated by the same symbols as those in FIG. 2 are the same.
Therefore, the description is omitted. 15 is a feedback voltage automatic control circuit
Road, M₁, M_TwoIs a multiplying synchronous rectifier, Q_S, Q_jIs
Multiplying variable resistance element, A₁, A_TwoIs a high gain amplifier, AK is
This is an amplifier with a small amplification factor. Transformer T₁Output voltage e
= KV_Two(Where K is T₁Turns ratio). Synchronous rectifier M
₁Output E_S′ Is the input voltage e E_SIs proportional to the in-phase component
DC voltage, and M_TwoOutput E_j'Is e E_jSame phase
DC voltage in proportion to minutes₁, A_TwoBy
Is amplified. In this circuit, A₁, A_TwoAmplification factor
E for infinity_S'= 0, E_j'= 0, and as a result
e = 0, ie, V_Two= 0. Real amplifier
A₁, A_TwoHas a finite amplification factor, so a control deviation close to 0
It remains but can be measured with sufficient accuracy for practical use. Also, Q_S, Q_j
Output E_S, E_jIs a DC signal, so amplifier A₁, A_Twoof
Current transformer CT even if the amplification factor is increased_d→ Amplifier AK → Metamorphosis
Bowl T_TwoBecause the amplification of the AC circuit is small,
Absent.

FIG. 5 is a circuit diagram corresponding to FIG. 3 of the transformer error measuring device. In the figure, CT _P is the transformer under test VT _X
Is inserted into the connecting circuit 6 in series, current transformer for detecting the measurement current I _m, N _f is the feedback winding which is added to the rated voltage switching transformer T _D, N _d is the reference voltage detector Winding. Detection current of the current transformer CT _P i _X is a current - voltage converter 14
Is converted into a voltage e by the feedback voltage automatic control circuit 15.
Is input to The voltage e ₂ generated in the detection winding N _d is supplied to the reference vector generation circuit 10 by the reference voltage vector e _S ,
Multiplying synchronous rectifier M ₁ of the control circuit 15 is a e _j, M ₂
Is input to The configuration of the control circuit 15 is the same as that of FIG. 3, and the output voltage is applied to the feedback winding. Feedback winding N _f
Current generated the excitation current I _O of the transformer T _D and current I _m 'flowing into the measuring circuit 2 is fed back to thereby primary winding of the measuring current I _m That rated switching transformer T _D of the connection circuit 6 the current flowing through the line N _P can be made zero. Measurement current _Im
Voltage drop and tested transformer VT rated voltage even the voltage drop due to the resistance of the connecting cable from _X to meter switching transformer input terminal voltage due but 0 a is because current detecting current transformer CT _P The condition of V _X ′ = V _X is maintained, and the zero burden test can be performed.

[0008]

According to the error test apparatus of the present invention, a relatively simple circuit including a feedback transformer is connected in a connection circuit between the device under test and the measurement circuit, and an amplifier is connected to the feedback winding. Since the low gain amplifier has an amplification factor close to 1, the zero load test can be realized without fear of oscillation. In the case of performing the specified load test in the present device, for example in the case of a current transformer test can be performed accurately specified load test by inserting as shown in FIG. 2 the specified load Z _i.

[Brief description of the drawings]

FIG. 1 is a main part circuit diagram of a conventional error measuring device for a current transformer.

FIG. 2 is a circuit diagram of a zero-burden error test apparatus for a current transformer according to the present invention.

FIG. 3 is a circuit diagram of an automatic zero load error test apparatus for a current transformer according to the present invention.

FIG. 4 is a main part circuit diagram of a conventional error test apparatus for a transformer.

FIG. 5 is a circuit diagram of an automatic zero load error test apparatus for a transformer according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Measuring instrument 2 Error measuring circuit 3 Current comparison transformer 4c Amplifier 5 Standard circuit 6 Connection circuit 7 Conductor 8 Connection cable 9a Inverting amplifier circuit 9b Integration circuit 10 Reference vector generator 14 Current-voltage conversion circuit 15 Automatic feedback voltage control circuit T ₁ the voltage detection transformer T ₂ voltage feedback transformer CT _d current detecting current transformer T _D rated switching transformer N _f feedback winding N _d reference voltage detection winding

Claims (3)

[Claims] 1. A in said connecting circuit with a voltage detection transformer T ₁ between the secondary terminals of the CT _X in parallel with the connection circuit for connecting the tested current transformer CT _X and the error measurement circuit is connected current detecting current transformer CT _d and voltage feedback transformer T ₂ are connected in series, the detection voltage of the current transformer CT _d as the reference voltage vector in-phase voltage e _S and 90 ° phase voltages e _j and the voltage detection current transformer error test and wherein the feeding back said feedback transformer T ₂ via the low-gain amplifier so that the detection voltage of the transformer T ₁ is zero. Wherein in said connection circuit with a voltage detection transformer T ₁ between the secondary terminals of the in parallel to the connection circuit which connects the DUT current transformer CT _X and error measuring circuit and the CT _X is connected current detecting current transformer CT _d and voltage feedback transformer T ₂ are connected in series, the voltage detection transformer T ₁ and the feedback voltage automatic control circuit between the other terminal of the voltage feedback transformer T ₂ is connected to the the current transformer CT _d of the detection voltage current transformer error tester reference vector generating circuit is connected to a reference voltage to the control circuit. 3. A transformer feedback winding with a reference voltage detecting winding N _d the rated switching transformer T _D which is interposed between the tested transformer VT _X and the measurement circuit in the error tester the provided with a N _f VT _X and the T current transformer for current detection to connect the circuit between _D CT _P is connected, the conversion voltage of the detected current by the current detecting current transformer in the feedback winding the reference voltage detection winding N instrumentation transformer error tester feedback voltage automatic control circuit is a voltage vector is input which are connected from the connected reference vector generator to _d.