DE2051836C2 - Insulation resistance monitoring circuit for DC power network - uses measured value transformer with variable response earth excitation winding - Google Patents

Abstract

The circuit for monitoring the insulation resistance between the conductors of a d.c. power distribution network, as is the main patent uses a switch which is periodically operated to connect the lines to the measuring circuit. This uses a measured value transformer with an earth excitation winding through which a constant d.c. passes. This is incorporated with a primary winding connected to the switch and a secondary winding with a field monitoring device formed by a variable resistance corresponding to the field strength. The earth excitation winding can be adjusted to regulate its response.

Description

The invention relates to a device for monitoring the insulation of ungrounded direct current networks, especially for higher operating voltages, alternating with one in the operating state A winding that can be switched between the mains poles and earth as a primary part, furthermore with a galvanic separate secondary part, which is electromagnetically influenced by the winding, in an evaluation circuit and with one to compensate for fluctuations in response sensitivity due to line voltage changes Serving, mains voltage-controlled, electromagnetic compensation device with a further winding connected between the network poles.

Such a device is known from DE-AS 10 160 and has a relatively complex structure. It two separate control chokes are required, each with three windings and a total of four places are to be connected to the evaluation circuit. While one control throttle is secondary to one earth-fault-dependent change of the alternating current resistance in the evaluation circuit, forms the other Secondary control throttle one connected in parallel to the evaluation circuit and controlled depending on the mains voltage AC resistance, the primary windings depending on the earth fault or mains voltage cause a more or less strong magnetic saturation of the control chokes. It is further a transformer for coupling a measuring alternating voltage into the evaluation circuit is available.

The present invention is based on the object of providing a device of the type mentioned in the preamble Kind to simplify with respect to the electromagnetic part and get along with fewer components.

A device of the type mentioned in the preamble is characterized according to the invention in order to achieve the object set characterized in that the secondary part is designed as a field probe or Hall generator that the primary-side winding, the secondary part and the further winding to a transducer electromagnetic are combined and that the further winding in the transducer is a counter-excitation winding forms.

This device is therefore an electromagnetically integrated, simple transducer with only two windings and a field probe or a Hall generator. The transducer is secondary with the field probe or the Hall generator only to be connected to the evaluation circuit at two points. Since the further winding is only used to generate a mains voltage-dependent counter-excitation, the galvanic isolation of the device is retained.

In a further embodiment, it is preferred that the field probe is a field strength-dependent resistor

Furthermore, it is preferred that the transducer additionally has a basic excitation winding which is preferably traversed by a constant direct current. In a further embodiment, the Basic excitation adjustable to change the response sensitivity. In this way, the Basic magnetization of the transducer or the response sensitivity can be set, with the Counter-excitation ensures that the response sensitivity is independent of changes in the mains voltage.

The device described is particularly advantageous for monitoring the insulation of direct current networks with variable operating voltage, such as with Leonard drives as well as with forming and Electrolysis systems.

The invention is explained in more detail below using an exemplary embodiment shown in the drawing.

To monitor the insulation resistances Ren and Rep of the direct current network with its network poles P, N and its grounded protective conductor SL , the network poles P, N are alternately temporarily connected to a measuring circuit 2 by a switch 1, which is preferably operated periodically. A measuring circuit current, which is dependent on the insulation resistance of the respective mains pole not switched on by switch 1, flows in this. When the network pole P is switched on , a measuring circuit current Ϊεν flows through the insulation resistance Ren, while when the network pole N is switched on, a measuring circuit current i'ep flows through the insulation resistance Rep . As the driving voltage in the measuring circuit 2, the supply voltage acts U. In this case, the current flowing in the measuring circuit current depending on the internal resistance of the measuring circuit and hereby in series lying insulation resistance Ren or Rep. Once the Meßkreisstrom i'en ΪΕΡ or exceeds a predetermined threshold, a display is triggered by means of an evaluation circuit or a shutdown of the network is prepared or brought about.

In the embodiment shown, an electromagnetic transducer 8 is the primary part a primary-side winding 8.1, which in the present case is connected to the DC voltage connections

a diode bridge rectifier located in the measuring circuit 2 is connected. A secondary part 8.2 of the transducer 8, which is electromagnetically coupled to the primary part 8.1 and galvanically separated from the mains voltage U, is designed as a field probe in the form of a field strength-dependent variable resistor. Instead, a Hall generator can also be used as the secondary part 8.2.

A basic excitation winding 8.0, which is connected to a power supply unit 9 via a resistor Po and through which a preferably constant direct current flows, is used for the basic magnetization of the transducer 8. This basic excitation can also be adjustable to change the response sensitivity.

In order to make the response sensitivity independent of changes in the mains voltage U , the transducer 8 has a further winding 8.3, which works as a counter-excitation winding and is to be connected to the mains circuit P, N via Zener diodes Z and a preferably adjustable resistor R. Accordingly, an excitation current that is dependent on the mains voltage U flows through the counter-excitation winding.

The transducer 8 is designed in the manner of an electromagnet, the primary-side winding 8.1, the secondary part! 8.2, the further winding 83 and, in the present case, the additional basic excitation winding 8.0 are electromagnetically coupled.
The switch 1 is periodically switched back and forth between the network poles P and N via a pulse generator 10 connected to the power pack 9, for example every 4 seconds. The pulse generator 10 contains a 2 stable. Multivibrator

ίο 10.1, a power level 10.2 and a relay 10.3.

The secondary part 8.2, which is designed here as a field probe the transducer 8 is connected to an evaluation circuit in the form of a response element 3, the For example, there is a Schmitt trigger 3.1, a power stage 3.2 and a signal relay 3.3.

The latter can trigger an alarm or shutdown the network as soon as the power is on exceeds a certain threshold in measuring circuit 2.

The present device with galvanic isolation between the secondary part and the primary-side winding is used for direct current networks with a particularly high constant and variable voltages advantageous / ationsüberwachungseinrichtungen particular also at Iso.

1 sheet of drawings

Claims (4)

Patent claims: 1. Device for insulation monitoring of ungrounded direct current networks, especially for higher operating voltages, with a winding that can be switched on alternately between the mains poles and earth as the primary part, further with a galvanically separated secondary part, which is electromagnetically influenced by the winding, in an evaluation circuit and with one for compensation of fluctuations in response sensitivity as a result of line voltage changes serving, line voltage-dependent, electromagnetic compensation device with a further winding connected between the network poles, characterized in that the secondary part (8.2) is designed as a field probe or Hall ^ enerator, that the primary-side winding (8.1), the Secondary part (8.2) and the further winding (83) are combined electromagnetically to form a measuring transducer (8.0) and that the further winding (83) forms a counter-excitation winding in the measuring transducer. 2. Device according to claim 1, characterized in that the field probe (8.2) is a field strength-dependent Resistance is. 3. Device according to claim 1 or 2, characterized in that the transducer (8) additionally has a basic excitation winding (8.0), which is preferably of a constant Direct current flows through it. 4. Device according to claim 3, characterized in that the basic excitation to change the response sensitivity is adjustable. 35