DE1796791U - DEVICE FOR DEMAGNETIZING PRECISION CURRENT CONVERTERS WITH INACCESSIBLE SECONDARY CIRCUIT. - Google Patents

Description

Device for demagnetizing precision current transformers with inaccessible secondary circuit. = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = t- It is often important to be able to demagnetize a precision current transformer SU, aa due to an erroneous direct current load or a high short-circuit alternating current, a residual magnetism remains in the iron core of the transformer, which results in a large current and angle error of the transformer which is disruptive in subsequent precision measurements. For example, in the case of a transformer of class 0.1, the current error can be increased by 0.05% and the error angle by 3 ', so that the current transformer is then no longer within the error limits of its class.

It is known to demagnetize a precision current transformer in such a way that that one increases the applied alternating current in its amplitude until the converter comes into the state of saturation, whereupon by steadily decreasing the amplitude of the alternating current, the residual magnetism is destroyed down to zero. To the current transformer To bring into the state of saturation, the following known measures have been used : On the one hand, you have the converter in the idle state, for example through Interruption of its secondary circuit, magnetized with nominal current of normal frequency (50 Hz), the supplied current due to the lack of a secondary current for magnetization alone serves. With a relatively small current, a high induction is obtained, from which then the demagnetization can be carried out. Furthermore, you already have the converter with a load connected on the secondary side, with a nominal current on the primary side, such a smaller one Frequency (about 10 Hz) charged until saturation occurs.

The converter was also connected to the secondary side at normal frequency connected load supplied such a large current, z. B. five times the nominal current, until saturation occurred.

The subject matter of the utility model relates in particular to a device for demagnetizing precision current transformers with inaccessible secondary circuit, so with a permanently attached burden.

It is assumed that of the three possibilities mentioned above to bring the current transformer into saturation, the former is made usable, because with this saturation is achieved at nominal current and normal frequency, while the other two possibilities have the disadvantage that they either require the use of an unusual frequency (10 Hz) or a considerable overload of the windings and load dimensioned for the nominal current. In order to be able to use current transformers with unacceptable to bring the converter into saturation in the idle state, it is proposed according to the innovation to provide a switch in the secondary circuit of the current converter, which in the "demagnetize" position increases the burden of the converter, be it by interrupting the secondary circuit or by Switching on resistors in these so that the converter already saturates with the nominal current fed in at the nominal frequency. The demagnetization is then brought about in the usual way by reducing the current to zero.

As is well known, when demagnetization occurs, sinusoidal currents occur as a result of the flattened field that occurs here Voltage peaks, which are especially dangerous, when it comes to converters with large iron cores or with high ones Turns numbers. A remedy can be found in this case according to a further proposal to achieve the innovation in that voltage-dependent resistors are provided in the secondary circuit of the current transformer, which become effective after opening the switch and limit the level of voltage peaks that occur.

An embodiment of the subject of the innovation is on hand the schematic illustration explained in more detail.

The precision current transformer 1 to be demagnetized feeds with its Secondary side 2 the burden 3 via a switch 4, the terminals of which are a high resistance Resistor 5 is connected in parallel.

In the normal operating state, the switch 4 is closed, so that the operating burden 3 is traversed by the secondary current of the converter. To make the demagnetization the switch 4 is opened, so that in series with the burden 3 the resistance 5 lies, which increases the amount of the band in the desired manner enlarged.

Should the aforementioned voltage peaks during demagnetization are weakened, a voltage-dependent resistor 6, 7 or 8 can be parallel to the primary side, to the secondary side of the converter or to the additional burden 5.

Claims (2)

Protection claims: ----- m-- 1. Device for demagnetizing precision current transformers with inaccessible secondary circuit from the state of saturation, characterized in that a switch is provided in the secondary circuit of the precision current transformer, which in the "demagnetize" position increases the burden of the current transformer, be it by interrupting the secondary circuit or by Switching on resistors in these so that the converter already saturates with the nominal current fed in at the nominal frequency. 2 Apparatus according to claim 1, characterized in that in the Secondary circuit of the current transformer voltage-dependent resistors are provided, which take effect after opening the switch and the level of voltage peaks that occur limit.