DE2021029B2 - METHOD OF MEASURING THE INDUCTIVITY OF ELECTRIC COILS WITH AN IRON CORE AND DEVICE FOR CARRYING OUT THIS METHOD - Google Patents

Description

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The invention relates to a method for measuring the inductance of electrical coils with an iron core. In particular, it deals with a method of measuring inductance of direct current biased inductors or windings of electrical machines.

It is used for operational measurement of the inductance of commutating reactors for inverters known to connect the DUT to the series connection or to a decoupled parallel connection of a DC and an alternator and after setting the bias, the drop to measure the alternating voltage and to calculate the inductance from this measured value.

This process is cumbersome and correspondingly expensive. The one necessary to carry out these measurements Effort is considerable, so that the need for an operational, simple and cheap Measurement method exists.

From the German Auslegeschrift 1 093 904 a method for measuring the inductance of Choke coils known, according to which the inductance to be measured is via a glow discharge path, whose contacts are initially bridged, is connected to a DC voltage source. After this If a steady current has been established in the circuit with the throttle, the contact is closed the discharge path interrupted so that the glow discharge begins, and with a time measuring device the time is determined during which the glow discharge persists. With otherwise constant The measured time is then directly proportional to the size of the inductance.

In this method, however, the mean value of the inductance during the time of the glow discharge becomes measured because the current in the inductor differs from that at the onset of the glow discharge existing value drops to zero. For the measurement, the current feeding the choke coil must first be used can be set to a stationary value. A power source of the appropriate power is required for this. If the task is the inductance of an operating condition with premagnetization operated choke at the current intensity to measure the magnitude of the bias direct current occurring during operation corresponds, then a current of this size must be stationary for the measurement Current can be adjusted. Even in this case, only the mean value of the inductance is used in the interval the glow discharge measured.

The task is to measure the value of the inductance at the pre-magnetization current that occurs in practice is available. In addition, a DC voltage source should have a low yield to be worked.

This object is achieved according to the invention in that a capacitive charge storage device is known The capacity is charged to a defined DC voltage, the storage device from the charging current source is separated and connected to the coil via a switch, and in that the maximum through Discharge direct current flowing through the coil is measured.

The drawing explains a measuring device for implementation on the basis of an exemplary embodiment of the measuring method according to the invention.

In the drawing, 1 denotes a housing containing an adjustable direct current source 2 and a capacitor 3 with a given capacity.

The capacitor 3 can be connected to the output terminals of the direct current source 2 via a switch 4 and the connecting lines 5 and 6. 7 with a Gleichstrommeßinstrument is designated with high internal resistance, which is connectable via a switch 7 A to the terminals of the capacitor. 3

The terminals of the capacitor are also connected via lines 8 and 9 to a socket pair 11 accessible on the outer wall of the housing 1. A resistor 10 is switched on in line 9. The line 8 contains a switch AA. A second pair of connection sockets is denoted by 13, which is accessible on the outer wall of the housing 1 and is connected to the two terminals of the resistor 10 via lines 14 and 15.

An inductive resistor, whose inductance is measured, can be connected to the pair of connection sockets 11 shall be. In the drawing is an exemplary embodiment of the pair of connection sockets Armature winding of a direct current shunt motor 16 connected.

A DC voltage measuring instrument with a high internal resistance can be connected to the socket pair 13. The drawing shows an electron beam oscilloscope 17 with capacitive control of the Electron beam. The y-deflection plates of the oscilloscope are connected to the connection sockets 13.

The time deflection takes place in the ΛΤ direction using a sawtooth generator with adjustable frequency.

Reference numeral 12 designates a diode which is connected in parallel to the connection sockets 12.

The measuring device described works as follows: When switches 4 A and 7 A are open, switch 4 is closed and capacitor 3 is charged to a corresponding voltage. Then the switch 4 is opened and the switch 7 A is closed and the voltage at the terminals of the capacitor 3 is measured by means of the calibrated measuring instrument 7.

After opening the switch TA , the switch 4 A is closed and the time course of the discharge current through the armature winding of the DC shunt motor 16 is tracked on the screen of the oscilloscope 17, which is provided with a measuring graduation, and the maximum flowing DC charging current is tracked on the basis of the measuring graduation of the screen determined.

Since (apart from ohmic losses) the maximum energy content of the inductance during the Discharge process equal to the energy content of the capacitor 3 at the beginning of the discharge process is, the inductance to be measured results from the relationship

L sä,

Γ- 5

where L is the desired inductance, C the known. Capacity of the capacitor 3, U denote the voltage on the terminals of the capacitor 3 at the beginning of the discharge process and / the maximum discharge current through the inductance.

The above relationship can, if necessary, with sufficient accuracy in practical cases with regard to the ohmic losses that occur during discharge in the inductance and those associated with it Leads occur, are corrected.

The diode 12 serves to prevent electrical oscillation processes in the course of the discharge of the capacitor 3.

In particular, the method explained allows the inductance of direct-current biased To measure choke coils in a simple way. It is therefore preferred to the operational one Used to measure the inductance of such reactors.

1 sheet of drawings

Claims (2)

Patent claims: 1. A method for measuring the inductance of electrical coils with an iron core, in particular for measuring the inductance of direct current biased choke coils, dadurchgek e η η ζ eich η et that a capacitive charge storage (3) of known capacity is charged to a defined DC voltage, the storage of the Charging current source (2) is separated and connected to the coil (16) via a switch (4A) , and in that the maximum DC discharge current of the store flowing through the coil is measured. 2. Measuring device for carrying out the measuring method according to claim 1, characterized in that in a housing (1) a charging direct current source (2) with a capacitor (3) of known capacity combined and the terminals of the capacitor via a switching device (4A) with a The pair of connection sockets (11) of the housing can be connected and also in that the terminals of the capacitor can be connected to the output terminals of the charging direct current source via a second switching device (4) and a measuring device suitable for measuring the maximum of the discharging direct current of the capacitor (3), preferably an electron beam oscilloscope is provided.