DE4322944C2 - Current transformer of an electrical switchgear filled with protective gas - Google Patents

Description

The invention relates to a current transformer with a protective gas filled electrical switchgear according to the preamble of claim 1.

Such a current transformer is from DE-GM 70 17 125 known. The known current transformer has a rectilinear, high-voltage conductor on the coaxial in tubular Encapsulation parts is arranged. The encapsulation parts are at least partially pushed into each other and by one Annular gap, which is filled with insulating material, from each other Cut. In this way, the Encapsulation parts formed a capacity. On the outside of the both encapsulation parts are toroidal cores with secondary windings appropriate. The annular gap is intended to ensure that no backflow through the ring cores Cross-sectional area flows back. Such a backflow would Amount of current induced in the secondary windings reduce and thus falsify the measurement result.

A measure for the management of flowing at operating frequency Reverse current through one installed outside the toroidal cores Current supply equipment is not guaranteed. On the problem the disruptive influence of high-frequency - especially at Switching occurring - traveling waves will not received.

DE 32 47 383 C2 describes one of conductive encapsulation parts enclosed current transformer known, the one inside contains tubular shielding. The shield coaxially surrounds one serving as the primary winding for the current transformer high-voltage conductor. On the tubular Shielding are toroidal cores with secondary windings. The shielding and the encapsulation parts are over metal bars conductively connected. The metal bars have one small wave resistance for high frequency, when propagating currents flowing from traveling waves.  

The shield and the conductor together form a capacitance. It is in the design of the shield as Capacitor electrode not possible from traveling waves resulting high-frequency currents across the shield due to the cross-sectional area limited by the toroidal cores to let it flow back so that it can flow through the conductor and the Shielding flowing high-frequency electricity components in total cancel each other out and consequently in the secondary windings do not induce interfering currents.

Outside the ring cores are two encapsulation parts over flanges screwed together. A measure that is largely prevents reverse currents of high frequency only within the Toroids and not (additionally) outside by the Flowing encapsulation parts is not mentioned.

When switching on and off occur in the switchgear Traveling waves that are between the conductor and him Spread out the surrounding encapsulation parts. The one of these Traveling waves originating from (high-frequency) magnetic fields should not cause currents in the secondary windings. These currents would be the result of measuring the through the Falsify the current flowing considerably. Furthermore can the induced currents and voltages - as a result lack of electromagnetic compatibility - interference in the electronics belonging to the relevant switchgear cause.

The invention has for its object a current transformer to create an electrical switchgear filled with protective gas, in which No interference voltages even when switching on and off are caused, which the functionality of the Current transformer endanger electronics.

This task is solved by a single-phase current transformer an electrical switchgear filled with protective gas according to claim 1.

In this current transformer, the section of the carrier on which the ring cores are seated in normal operation at mains frequency practically not flowed through by a backflow.  

At the mains frequency, the capacitor acts as a current block (Insulation). At the same time, it is outside the ring cores current carrying device located at network frequency particularly good conduct. The reverse current therefore takes the path at the mains frequency via the current carrying device (outside the toroidal cores); therefore, the magnetic field from that flowing in the conductor Current is caused, not by the reverse current canceled or diminished; the one in the secondary windings induced current is proportional to the current in the conductor.

Only high-frequency electricity components, which of fast Wandering waves originate, flow through the section of the Carrier located between the conductor and the toroidal cores located.  

Such fast traveling waves occur in the switchgear at and shutdowns.

Because the section of the carrier is conductive for the high-frequency current components, the traveling waves pass through the area of the current transformer, without interference voltages in the secondary windings to evoke. The high-frequency current components on the carrier and conductor flow in the opposite direction and rise with respect to the cross-sectional area limited by the ring cores practically each other; the high-frequency components therefore do not call Currents emerge in the secondary windings; the measurement result is thus not distorted by the traveling waves.

So that the high-frequency current components as completely as possible on the The back flow under the toroidal cores is outside of the Ring cores located in the way frequency-dependent designed that at high frequencies that of Traveling waves come from, practically blocks.

As a capacitor that is integrated in the carrier and only for high-frequency current components that occur during switching operations is permeable, a capacitor according to claim 2 is suitable consists of two concentric tubular electrodes and thereby has only a very low inductance.

Since in an embodiment according to claim 5 in the amount of Current transformer - because of the constant geometry in the Inside - no significant, sudden change in the Characteristic impedance to adjacent sections of the Switchgear occurs, unwanted reflections in the area of Current transformer largely prevented.

Further advantageous configurations are the others See subclaims.

The invention is described below using an exemplary embodiment, from which further features, details and advantages result, described in more detail.

It shows the figure in longitudinal section in a fully insulated Switchgear integrated current transformer.

Inside a conductive encapsulation part ( 1 ), which is part of a switchgear with an integrated current transformer, there is a cylindrical conductor ( 3 ), which is arranged coaxially in the tubular encapsulation part ( 1 ) and is carried by the insulation support (not shown) and carries the current of one phase and forms the primary winding for the current transformer.

The conductor ( 3 ) is surrounded in the area of the current transformer by another electrically conductive tubular encapsulation part, which serves as a carrier ( 4 ). The carrier ( 4 ) shields high voltage and holds - arranged on it on the outside - toroidal cores ( 5 ) with secondary windings ( 6 ). Further encapsulation parts ( 1 ) adjoin the carrier ( 4 ) along the longitudinal axis of the conductor ( 3 ), only one of which is shown.

The conductor ( 3 ) is held coaxially by the insulating supports in the carrier ( 4 ), which is tubular on the inside. There is only a conductive connection between the support ( 4 ) and the encapsulation part ( 1 ), which is at ground potential, via four metal rods, which form a current-carrying device ( 2 ); the current carrying device ( 2 ) is mounted outside the carrier ( 4 ) and outside the toroidal cores ( 5 ); it bridges the ring cores ( 5 ) from a flange of the carrier ( 4 ) and is guided to a flange of the encapsulation part ( 1 ). It represents the only conductive connection between the carrier ( 4 ) and the encapsulation part ( 1 ), since the carrier ( 4 ) and the encapsulation part ( 1 ) are arranged adjacent to one another, but they are at the point at which they are directly adjacent to one another isolated.

The current carrying device ( 2 ) conducts poorly at high frequencies than at low ones; so it has inductive behavior.

The four metal rods of the current-carrying device ( 2 ) are distributed uniformly over the circumference of the carrier ( 4 ) and are arranged at a distance from the latter and from the ring cores ( 5 ).

Operating frequencies, ground-side return currents flow through the current carrying device ( 2 ), which conducts very well at the mains frequency.

At this frequency, no current flows over the section of the carrier ( 4 ) that lies below the ring cores ( 5 ), which will be discussed in more detail below.

When the conductor (3) is flowed through by alternating current, are then formed around the conductor (3) circular magnetic field lines, and the ring cores (5) are penetrated by an alternating magnetic flux that in the secondary windings (6) wound around the toroidal cores (5 ) induced a current. Protective gas, for example sulfur hexafluoride (SF ₆ ), is located within the encapsulation parts ( 1 , carrier 4 ). The conductor ( 3 ) serves as the primary winding. The current intensity in the conductor ( 3 ) can be measured via the current induced in the secondary windings ( 6 ).

The encapsulation part ( 1 ) and the carrier ( 4 ) placed next to it are insulated from one another at the point at which they are arranged next to one another with a cast resin layer ( 7 ), so that during normal operation - that is to say continuous operation at mains frequency - no (reverse) current flows through the section of the carrier ( 4 ) which is surrounded by the ring cores ( 5 ). Only the current flowing through the conductor ( 3 ) passes through a cross-sectional area delimited by the ring cores ( 5 ). The location at which the encapsulation ( 1 ) and carrier ( 4 ) are insulated from one another is spatially configured as a capacitor arranged concentrically around the conductor ( 3 ); in electrical terms, this capacitor is connected between the carrier and the encapsulation part ( 1 ). As a result, electrical traveling waves can pass this point largely unhindered, as will be explained further below.

The capacitor with a capacitance of approx. 1 nF is implemented by two tubular capacitor electrodes lying one inside the other, which are insulated from one another with casting resin ( 7 ). One capacitor electrode is formed by a circumferential step ( 8 ) on the outer surface of the carrier ( 4 ) and the other by an electrically conductive band ( 9 ) which is electrically connected to the encapsulation ( 1 ) and which is separated by casting resin ( 7 ) its broad side is arranged opposite the step ( 8 ) and is guided around it. The distance between the step ( 8 ) and the belt ( 9 ) may only be a few millimeters so that a sufficiently large capacity is created.

The inside diameter of the carrier ( 4 ) is exactly the same size as the inside diameter of the encapsulation ( 1 ) in the area next to the current transformer, which prevents reflections in the area of the current transformer.

If a traveling wave passing through the switchgear between the conductor ( 3 ) and the encapsulation part ( 1 ) hits the current transformer, it continues to run practically unhindered between the carrier ( 4 ) and the conductor ( 3 ), without significant voltage and current at the secondary windings ( 6 ) to influence. The consequence of this is that no interference voltages are also coupled out via the connections of the secondary windings ( 6 ) which could interfere with the function of downstream electronic devices, ie a better electromagnetic compatibility (EMC) of the switchgear is achieved.

Claims (6)

1.Current converter of an electrical switchgear filled with protective gas with a continuous conductor which is at high voltage potential and serves as a primary winding and which is surrounded by gas-tight, tubular encapsulation parts, with between two encapsulation parts, one of which serves as a carrier for at least one ring core attached to it on the outside secondary windings is used, circumferentially a gas-tight electrically insulating intermediate layer is provided, this insulating layer forming an electrical capacitor with the adjacent Kapselungsteilen and the capacitor a between the / the toroidal core (s) and the conductor portion located connects the support with the immediately adjacent enclosing member, characterized characterized in that the capacitor is dimensioned such that the mentioned section of the carrier ( 4 ) is only current-carrying for a high-frequency reverse current far above the operating frequency, which is between the durc outgoing conductor ( 3 ) and the encapsulation parts ( 1 , carrier 4 ) resulting in fast traveling waves, and that outside of the toroidal core (s) ( 5 ) the encapsulation part ( 1 ) immediately adjacent to the carrier ( 4 ) via a current carrying device ( 2 ) with the carrier ( 4 ) is electrically conductively connected, which is designed frequency-dependent in such a way that it conducts poorly with increasing frequency. 2. Current transformer according to claim 1, characterized in that the first electrode of the capacitor is formed by an outer circumferential step ( 8 ) of the carrier ( 4 ) and the second by a distance surrounding the first capacitor electrode with the immediately adjacent encapsulation part ( 1 ) electrically connected electrically conductive tape ( 9 ). 3. Current transformer according to claim 2, characterized in that the insulating intermediate layer of the capacitor electrodes consists of cast resin ( 7 ). 4. Current transformer according to one of the preceding claims, characterized in that the current carrying device ( 2 ) has a plurality of rods made of electrically conductive material. 5. Current transformer according to one of the preceding claims, characterized in that the inner diameter of the carrier ( 4 ) is the same size as the inner diameter of the encapsulation parts ( 1 ) located next to the current transformer. 6. Current transformer according to one of the preceding claims, characterized, that the capacitor has a capacitance of approximately 0.5 to 2 nF.