DE1763249C3 - Monitoring device for the insulation status of non-earthed direct current systems - Google Patents

Description

The invention relates to a monitoring device for the insulation resistance of ungrounded equals; "romnetzen with several main distributions which are each connected through reverse-flow preventing valves with multiple sub-distributions and those practicing an AC voltage is superimposed ^r by each main distribution is connected via an own capacitive coupling unit to a common alternating voltage source.

Unearthed electrical direct current networks cause difficulties in monitoring. So long If an insulation fault occurs only in one pole, there are no immediate consequences. There is a short circuit, if a fault also occurs in the other pole, and it is therefore necessary to identify the source of the fault identify them as quickly as possible and take measures to eliminate them.

Monitoring devices are known which deal with this problem. It is known to superimpose an alternating voltage on the direct current network and to use alternating currents as a criterion for the insulation resistance of the lines. The AC voltage source is single-pole grounded, so that an alternating current flows through a display device whenever there is an insulation fault. The alternating voltage is applied to the distributions via capacitive coupling units, with each main distribution being connected to a common alternating voltage source via its own constant capacitive coupling unit, in particular according to German patent specification 742 359 . This method of insulation fault location only gives unambiguous results in systems that can be viewed as radial networks without parallel branches. If, on the other hand, the direct current system is designed in such a way that several main distributions are each connected to several sub-distributions, then an unambiguous determination of _% sub-distributions with insulation faults is no longer easily possible. In such systems, the sub-distributions are connected several times via non-return valves.

The reverse flow blocking valves are used for alternating current but meaningless if a direct current flows through them. The direct current, which can be regarded as a bias current in this case, removes the blocking effect for the alternating current on. However, since there is always a current flowing in such systems, in the event of a fault in any one of the sub-distributions for the superimposed alternating current a current branch over all connected Lines of the main and sub-distributions, so that the selective fault detection extremely

ίο becomes difficult. So even if the coupling switch that connects the main distribution with each other is opened, the uncontrollable flow of electricity remains exist via the valves that have been lifted in their blocking effect. It has been suggested that that to connect both main distributions by a coupling condenser, however, by the Capacitive asymmetries in the structure, especially in the case of larger DC systems, the desired success \ says, because also in the earth fault condition

ao of the direct current system capacitive earth currents (let.

It is now an object of the invention for several

Main distributions, which are each connected to several sub-distributions via non-return valves are, return flows and undefined distributions of both the capacitive earth currents and the ohnic To avoid insulation fault currents.

According to the invention, this object is achieved in that all coupling units, except for one, are changeable Have capacities such that capacities

se several times in succession in the earth fault-free state are balanced according to the number of sub-distributions so that the capacitive earth currents are the same in the outlets of the individual main distributions to one sub-distribution.

The invention is explained in more detail with reference to the drawing: A direct current system is shown there, specifically for two main distributions I and II. Each of these main distributions is fed _{via its own direct voltage source G 1} and G _11.

Both main distributions are each connected to a common AC voltage source G _u via a coupling capacitor Q and Q _11. The two main distributors feed jointly to sub-distributors A. B, C. Any number of consumers can be connected to these sub-distributions. The individual line sections naturally have given capacitances to earth, which are collectively designated by C ₁ . The individual outputs are separated from one another by diodes D.

The mode of operation of the system is as follows: When there is no earth fault, the capacitive earth currents are in the outlets of the individual sections I and II of the main distribution to one sub-distribution each determined and compared with each other.

By balancing the coupling capacitance Q ₁₁ , the two capacitive earth currents I ₁ ^ and I | _{M brought} to the same value.

This measured value is noted. _{Now the two capacitive earth currents I 1 H} and I ₁ , _{B are brought} to the same value by a new adjustment of the coupling capacitance Qn. This measured value is noted again. Then the two capacitive earth currents I ₁ , - and I _{nc are brought} to the same value by a renewed adjustment of the coupling capacitance Q _11. This measured value is also noted. These measured values serve as the basis for the determination of earth faults.

On the basis of the changes that occur when

If measurements are taken, the insulation status of the individual lines can be determined. Tends the Isolation at any point for an early breakdown and increased currents flow at this point, this will be determined immediately and the error can be eliminated before it actually occurs.

The comparison method can of course also be used for more than two main distributions, whereby then two or more coupling units are matched, while a coupling unit with a fixed The reference value remains unchanged. As a rule, you will be in the outlets of the main distributors Sub-distributions that do not yet have a low-resistance insulation fault only measure small currents that caused by the high-resistance discharges in the direct current system. It becomes appropriate the measured values together with the information about the switching status of the DC system to be entered in logs, which will later be used as the basis for regular monitoring of the insulation status serve the direct current system. It ίο can thus by comparing the setting and Fixed values also insulation faults with medium-ohmic leakage values can be recorded.

1 sheet of drawings

Claims (1)

Claim: Monitoring device for the insulation resistance of ungrounded direct current networks with several main distributions, which are each connected to several sub-distributions via non-return valves and on which an alternating voltage is superimposed, in that each main distribution is connected to a common alternating voltage source via its own capacitive coupling unit, characterized in that all coupling units ( Qn), with the exception of one (C _A1 ), have variable capacities such that the capacities in the earth fault-free state are adjusted several times one after the other according to the number of sub-distributions so that the capacitive earth currents (I _{1 A} , I ₁₁₄ ; I, ", I _{n ö} ; I _n . I ,,,) are the same in the outputs of the individual main distributions (I, II) to one sub-distribution (A: B: C) .