JPH0980097A - Instrument for measuring tan delta without any influence of outside induced voltage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an instrument for measuring tanδ wherein tanδ of various electric devices connected to a single phase cable or a three-phase cable can be accurately measured in a hot line state or a non hot line state. SOLUTION: Accurate tanδ is found without any influence of an alternating component as a voltage signal ei proportional to leakage current I of an electric device to be measured H, direct current component output ED having multiplied a signal ev proportional to applied voltage of the device H and other direct current component output EDT obtained to multiply a signal eVT in which the signals ei and ev are 90-degree phase-shifted are made an input signal of a division circuit 14.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to tan δ of various electric devices.
The present invention relates to a device for measuring.

[0002]

2. Description of the Related Art Generally, a commercially available measuring instrument as a tan δ meter is 1000 Hz built in an LCR meter.
Tanδ meter of tanδ≈s in the range of small δ
Since inδ is established, sinδ is obtained, and it is impossible to accurately measure δ in a wide range. The Applicant has a bridge type t using a standard capacitor.
An an δ measuring device has been proposed (JP-A-7-98347).
However, the circuit becomes complicated and expensive for high precision.

[0003]

DISCLOSURE OF THE INVENTION The present invention has a simple circuit configuration and is small in size, and moreover, is accurate t without being affected by the frequency due to the distortion current of the device under test and the induction frequency from the outside.
an δ can be measured, and the device under test is single phase or 3
The present invention provides a tan δ measuring device that can be measured even in a live line state connected to a phase power supply and can be applied to an insulation monitoring and alarm device.

[0004]

The apparatus of the present invention comprises a first multiplication circuit for multiplying a voltage signal e _v proportional to a voltage applied to an electric device under test by a voltage signal e _i proportional to a leakage current of the device, and A second multiplication circuit for multiplying a phase- _shifted voltage signal e _vT obtained by phase-shifting the voltage signal e _i and the e _v by 90 °, and the first and second
It is configured by including a selection circuit that selects each DC component from each of the multiplied outputs and an arithmetic circuit that divides the selected output, and each circuit is simply configured by an IC. The same applies when the multiplication circuit is a synchronous rectification circuit.

[0005]

1 is a circuit diagram illustrating the basics of the present invention. Test voltage V (0.3V, 200Hz) is applied to the multiplier 1.
Signal e proportional to leakage current I from device under test H due to
e _V proportional to _i and V are respectively inputted through the buffer amplifier, and K · V · I {cos (2ωt−θ) + cos θ} (K: proportional constant, θ: phase angle between V and I, The same shall apply hereinafter). When this output Q is applied to the selection circuits 2 and 3, respectively, the effective component E _A ∝V · I / √2 of the AC component of the first term and the DC component E _D ∝V · I · cos θ of the second item can be obtained. Can, co
S.theta = cos can be determined (90 ° -δ) ≒ sinδ ≒ because a tan [delta √2Tanderuta by computing E _D / E _A them in divider 4 (δ = 90 ° -θ) as a tan [delta. However, in this case, if the leakage current I has a frequency component that does not exist in the test voltage V, such as a frequency due to a distortion current from the device under test or an external induction frequency, the DC component of the multiplier output has no effect, but the AC component has a range. Since it is affected by the modulation, an error occurs in tan δ. FIG. 2 is a circuit diagram of the present invention in which this drawback is improved. The input signal to the first multiplier 11 is the same as in the case of FIG.
The second multiplier 12 passes e _i and e _v through the phase shift circuit 13
The 0 ° phase _shifted e _vT is input. The output signal E _D of the selection circuit 2 is similar to that of FIG.
_DT becomes K, V, I, sin θ. Therefore, the division circuit 14
In the case of K · V · I · cos θ /
K · V · I · sin θ = tan (90 ° −θ) = tan
An accurate tan δ can be obtained as δ. FIG. 3 shows the case where the measuring instrument A of the present invention is applied to a single-phase circuit, and the signal e is obtained from the leakage current I flowing in the secondary winding of the zero-phase current transformer ZCT.
A circuit that obtains _i and monitors the insulation of the motor H, for example.
Figure 4 is a case of applying to a 3-phase circuit, the second ZCT ₁
A test voltage for the next coil is an integral multiple of the power supply voltage, for example, 10
A leakage current I is injected by ZCT ₂ by injecting an AC voltage of 0 Hz.
Is getting

[0006]

The device of the present invention is capable of accurately measuring tan δ regardless of the simple circuit configuration, and the multipliers 11 and 12, the DC selection circuits 2 and 2a, and all other circuit elements are configured by IC. It can be manufactured economically, is easy to adjust, is small and mechanically strong, and is easy to carry. Moreover, there is an advantage that there is no restriction on the installation location because it is not affected by external guidance. Further, since it is possible to accurately measure tan δ even in a live state, it is effective for an insulation monitoring system of equipment.

[Brief description of drawings]

FIG. 1 is a circuit diagram illustrating the present invention.

FIG. 2 is a circuit diagram of the measuring device of the present invention.

FIG. 3 is a connection diagram when the device of the present invention is applied to a single-phase circuit.

FIG. 4 is a connection diagram when the device of the present invention is applied to a three-phase circuit.

[Explanation of symbols]

 H device under test I leakage current 11 multiplication circuit 2, 2a DC component selection circuit 14 division circuit

Claims (2)

[Claims] 1. A first multiplication circuit for multiplying a voltage signal e _v proportional to a voltage applied to an electric device under test by a voltage signal e _i proportional to a leakage current of the device, the voltage signal e _i and the e signal. Second multiplication of the phase- _shifted voltage signal e _vT obtained by phase-shifting _v by 90 °
A tan δ measuring device comprising a multiplication circuit, a selection circuit for selecting a direct current component from each of the first and second multiplication outputs, and an arithmetic circuit for dividing the selection output. 2. The apparatus according to claim 1, wherein each of the first and second multiplication circuits is a synchronous rectification circuit.