EP1022753A1 - Contact device for current limiting switch - Google Patents

Abstract

The contact arrangement is axially symmetrical and comprises a fixed switch section in the form of two coaxial cylinders (1,2) and a bridge switch section in the form of a contact ring (4) which is placed, in the switched on state, at the free end of the cylinders in the annular space (3). A coil (5) is arranged in a section of the annular space adjoining a space that receives the contact ring.

Description

TECHNICAL AREA

The invention is based on a contact arrangement for a nominal current-carrying switching point of a current-limiting high or Medium voltage switch according to the preamble of claim 1. In the field high powers and thus high rated currents are used in electrical Energy technology today almost without exception purely mechanical contact systems for construction used by switches because it achieves the lowest nominal current losses can be. The typical idle times (time from the switching command to Contact separation or power interruption) today's circuit breakers are in Time range of a few 10 ms. Such idle times do not allow these switches to be used for the construction of current-limiting switching systems. Semiconductor switch, like e.g. GTO's (Gate Turn-Off Thyristors) are three orders of magnitude smaller Own times, but inadmissibly high losses in nominal operation. Through the Combination of a very fast mechanical switch with High-performance semiconductors, a hybrid switching system is created, which current-limiting switching is suitable.

STATE OF THE ART

The invention relates to a prior art of contact arrangements as described in EP 0 275 857 A1. The known contact arrangement is Part of a current-limiting device that is preferably used in traction technology Switch and serves to carry nominal currents during the operation of the Switch. Parallel to the contact arrangement is an auxiliary circuit with switching thyristors and Diodes as well as switched with a charging capacitor and with a coil. At the If a short-circuit current occurs, the switching thyristors are switched on and the charging capacitor is then discharged via the coil. The magnetic field of the Discharge current from the coil induces in a with a bridge contact the contact arrangement connected disc flowing in opposite directions Short-circuit current. The electrodynamic forces generated here push the Disc and thus also the bridge contact from the coil and thus cause very quick opening of the contact arrangement. The one when opening the contact assembly Short-circuit current commutating in the auxiliary circuit is achieved by reloading the Charging capacitor interrupted.

SUMMARY OF THE INVENTION

The object of the invention is as set out in the claims to create a contact arrangement of the type mentioned, which enables a particularly safe operation of the current-limiting switch.

The contact arrangement according to the invention is constructed axially symmetrically. Unwanted leakage inductances are largely avoided and it is so an extremely rapid commutation of short-circuit currents into one Achieved parallel current path containing semiconductor switch. At the same time it becomes Formation of the forces of an electrodynamic contact drive necessary Induction current generated in the moving bridge contact piece carrying the nominal current, whereby an otherwise usually provided disc-shaped part for guidance the induction current and thus additional mass to be accelerated can be. This will help you achieve a specific one Opening speed of the contact arrangement necessary drive energy minimized. When opening, there are also two contact gaps, each of one of two partial arcs connected in series are bridged. Through this Series connection of partial arcs increases that at the contact arrangement falling arc voltage, which makes the short-circuit current particularly fast and can be effectively commutated in the parallel current path.

BRIEF DESCRIPTION OF THE DRAWING

Fig.1

eine einphasige Grundschaltung einer ein Mittelspannungsnetz nachbildenden Prüfvorrichtung mit einem eine Kontaktanordnung nach der Erfindung enthaltenden strombegrenzenden Schalter,

Fig.2

die Kontaktanordnung gemäss Fig.1 im Einschaltzustand, und

Fig.3

die Kontaktanordnung gemäss Fig.1 im Ausschaltzustand.

Preferred exemplary embodiments of the invention and the further advantages which can be achieved thereby are explained in more detail below with reference to drawings. Here shows:

Fig. 1

a single-phase basic circuit of a test device emulating a medium-voltage network with a current-limiting switch containing a contact arrangement according to the invention,

Fig. 2

the contact arrangement according to Figure 1 in the on state, and

Fig. 3

the contact arrangement according to Figure 1 in the off state.

WAY OF CARRYING OUT THE INVENTION

In all figures, the same reference numerals refer to parts having the same effect. The circuit shown in FIG. 1 is a single-phase basic circuit of a test device emulating a medium-voltage network with a current-limiting switch S. The test device contains a generator G which simulates a mains voltage u _N of typically a few 10 kV, for example 20 kV, which via the current-limiting switch feed simulated by an ohmic resistor R _L and an inductance L _L. A short-circuit detection unit KSE arranged between generator G and switch S and acting on switch S has a measuring and evaluation part for the very rapid detection of short-circuit currents i _N. The short-circuit currents are typically around 10 kA, for example 20 kA. In the current path from the generator to the load, the switch S has an arc-proof rated current-carrying switching point S ₁ , which typically opens within 100 to 500 μs, for example 250 μs, and a disconnector S _S connected in series with it.

Two commutation paths K ₁ and K _{2 are} connected in parallel with switching point S ₁ . The commutation path K ₁ contains an electrically controllable switching device T and, in series with the switching device T, a rapidly opening isolating switching point S _T (opening time typically a few 100 microseconds) with contacts that can be mechanically separated from one another. The switching device T is advantageously a semiconductor switch T ₁ that can be switched off, for example a thyristor, such as, in particular, a GTO. The switching device T can also contain a plurality of semiconductor switches connected in parallel instead of one semiconductor switch T ₁ for the purpose of high current carrying capacity. In order to achieve a rapid response of the switching device T in the case of an alternating current with both negative and positive polarity, the switching device has one or more further semiconductor switches T ₂ , which are connected antiparallel to the one or more further semiconductor switches T ₁ .

The commutation path K ₂ is connected in parallel to the switching point S ₁ and the commutation path K ₁ and has a current limiter R _B and a switching device T _P connected in series with the current limiter. The current limiter R _B responds to a commutation current with a delay and is advantageously designed as a PTC resistor. The switching device T _P contains at least one, but advantageously at least two, semiconductor switches connected antiparallel to one another, which need not necessarily be designed to be disconnectable, but can delete an alternating current carried by them in the zero current crossing, such as, in particular, thyristors or triacs. By arranging further such semiconductor switches in series, the dielectric strength of the switching device T _{P can be} increased.

When the short-circuit current occurs, the detection unit KSE triggers a switch-off process at the current-limiting switch S within approximately 100 μs. The switching devices T and T _P located in the two commutation paths K ₁ and K ₂ are immediately made conductive. At the same time, the nominal current contact arrangement S _{1 is} opened. As a result of two arcs formed in this way and connected in series, the still increasing short-circuit current commutates into the commutation path K ₁ within approximately 250 microseconds. This remains conductive until a dielectric strength is reached above the nominal current contact arrangement S ₁ , which is somewhat greater than that of T. The short-circuit current to be switched off then commutates into the commutation path K ₂ . This creates both a transient overvoltage due to the leakage inductances and an ohmic voltage drop at the current limiter R _B. The current limiter R _B limits with a delay of a few 100 µs. This time delay is sufficient to open the nominal current contact arrangement S ₁ and the isolating contact arrangement S _T practically without power. After opening the isolating contact arrangement S _T , virtually all of the voltage U _s present at the switch S drops across this isolating contact arrangement in the commutation path K ₁ . Since the current limiter R _B responds with a delay, the limitation of the short-circuit current now flowing in the commutation path K ₂ only begins after the opening of S ₁ and S _T. The limited short-circuit current can be switched off in the following current zero crossing, for example after 5 to 6 ms, by the switching device T _P with a very low overvoltage. Then a galvanic isolating path is created by opening the isolating switch S _s .

The structure and the mode of operation of the contact arrangement of the fast switching point S ₁ can be seen from FIGS. 2 and 3:
The contact arrangement is axially symmetrical and has two fixed contact pieces and a movable bridge contact piece. The two fixed contact pieces are designed as coaxially arranged cylinders 1, 2 and delimit an annular space 3. The bridge contact piece is designed as a contact ring 4 made of an electrically highly conductive material, such as preferably aluminum or an aluminum-based alloy, and is in the switched-on state at free ends of the Cylinder 1, 2 guided into the annular space 3. It then short-circuits the two cylinders 1, 2 acting as fixed contact pieces. In a section of the annular space 3, which adjoins a section of the annular space receiving the contact ring 4, a cylindrical coil 5 is arranged coaxially, which forms an electrodynamic drive with the contact ring 4. The coil 5 is fixed in the annular space 3 with the aid of a mechanically and dielectrically high-quality insulating material and has two connections, one of which is connected directly to one connection of a capacitor 6 and the other via a switching thyristor 7 to the other connection of the capacitor 6. A free-wheeling diode 8 is connected in parallel with the series connection of capacitor 6 and switching thyristor 7 and thus also with the two connections of the coil 5.

The cylinder 1 has axially guided, finger-shaped contact elements 10, which are bent outwards at their free ends facing away from the coil 5 to form a conical widening of the annular space 3. The cylinder 2 has axially guided, finger-shaped contact elements 20. These contact elements are bent inwards at their free ends facing away from the coil 5 to form a conical widening of the annular space 3. Contact surfaces made of erosion-resistant material are formed on the contact elements 10 and 20 in the annular space 3 and, in the switched-on state shown in FIG. 2, interact with contact surfaces of the contact ring 4 which also consist of erosion-resistant material. The short-circuit current i _N led to the switching point S ₁ then flows from the contact elements 10 via the contact ring 4 in the radial direction to the contact elements 20. The contact ring 4 therefore acts as a movable bridge contact.

The detection unit KSE which triggers the switch-off process when the short-circuit current occurs at the current-limiting switch S causes the switching thyristor 7 to be switched on. The capacitor 6 is now discharged via the coil 5. The magnetic field of the coil current i _P induces in the contact ring 4 a secondary current i _{S out of} phase by approximately 180 °. A Lorentz force F, which is proportional to the two currents and acts axially upward, acts on the contact ring, which overcomes the adhesive forces between the contact surfaces of the contact elements 10, 20 and the contact ring 4 and at the same time applies the required acceleration of the contact ring 4. Since the contact ring 4 combines the function of the bridge contact and the secondary coil of the electrodynamic drive, the mass to be accelerated is extremely low and is typically 0.05 kg in the case of the aforementioned performance data of the switch S. Even with a small-sized capacitor 6, a sufficiently high dielectric strength can be achieved in less than 1 ms after the switch-off command has been issued by the detection unit, via the annular space 3 which represents the open switching distance of switching point S ₁ (switch-off position according to FIG. 3).

The movement of the contact ring 4 triggered when the Lorentz force occurs made possible by a guide, not shown, only in the axial direction. When switched on, the conical widenings of the annular space 3 the insertion of the contact ring 4 into the annular space 3.

Further favorable properties of the switching point according to the invention can be seen in the fact that the stray inductance is minimized by the coaxial structure and thus a particularly fast commutation of the short-circuit current in the commutation paths connected in parallel is ensured. In addition, when the contact ring 4 is separated from the contact elements 10 and 20, two arcs connected in series occur. This increases the commutation voltage and the short-circuit current commutates particularly quickly into the two parallel paths K ₁ and K ₂ .

Reference list

K ₁ , K ₂

Commutation paths

KES

Short circuit detection unit

L _L

Inductance

R _L

ohmic resistance

R _B

Current limiter

S

current limiting switch

S ₁

Nominal current contact arrangement

S _S

Disconnector

S _T

Isolating contact arrangement

T ₁ , T ₂

Semiconductor switch

T, T _P , T _S

Switching devices

i _N

Short-circuit current

u _N

Mains voltage

i _P

Primary current

i _p

Secondary current

u _p

voltage present at switch S.

1, 2

cylinder

3rd

Annulus

4th

Contact ring

5

Kitchen sink

6

capacitor

7

Switching thyristor

8th

Free-wheeling diode

10, 20

Contact elements

Claims (4)

Contact arrangement for a nominal current-carrying switching point (S ₁ ) of a current-limiting high or medium voltage switch (S), in which a current path (K ₁ ) with a semiconductor switch (T) is connected in parallel with the nominal current-carrying switching point (S ₁ ), containing a movable bridge contact, two from the bridge contact in the switched-on state of the contact arrangement, short-circuited, fixed contact pieces and a drive acting on the movable bridge contact piece with electrodynamic force and having a coil (5), characterized in that the contact arrangement is axially symmetrical and as fixed contact pieces two coaxial to form an annular space (3) one inside the cylinder (1, 2) and as a bridge switching element has a contact ring (4) which is guided into the annular space (3) at the free ends of the cylinders (1, 2) when switched on. Contact arrangement according to claim 1, characterized in that the coil (5) is arranged in a section of the annular space (3) which is connected to a connects the contact ring (4) receiving portion of the annular space (3). Contact arrangement according to claim 1 or 2, characterized in that the cylinders (1, 2) each have axially guided, finger-shaped contact elements (10, 20) have contact surfaces delimiting the annular space (3). Contact arrangement according to claim 3, characterized in that the Contact elements (10, 20) at their open ends to form a conical widening of the annular space (3) are curved.

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