Interface circuit for surge impedance

p0001description

p0002Matching for impedances

p0003The invention relates to a matching circuit for characteristic impedances for use in data transmission on power lines.

p0004The data transmission on power lines, which is referred to in the trade as far PLC (Power Line Communication) increasingly contains practical significance. To date signals in the audio frequency range and in the carrier frequency range are used to approximately 200 kHz for PLC. In this area, the coupling circuits for connecting the transmitter and receiver to the network in terms of adjusting the impedances are relatively uncritical, since these signal frequencies the reflections at the transition points do not have any significant meaning. In this area, the connection lines for the transmitter and receiver are still substantially shorter than the wavelength of the signal. In this regard coupling circuits for a parallel capacitive coupling are known. There is here a transformer signal transmission, which serves mainly the potential separation of transmitter and receiver. Such transformational Ankopplungsschaltun- gen are described for example in US 4,437,817 A.

p0005Furthermore, from US 4,686,382 A discloses a bypass circuit for the PLC transmission, especially in the kHz range at which a switch is bridged via two transformers, in which a transmitter / receiver is switched on. For simultaneous connection of a signal at all three phase conductors of a three phase power conductors with a neutral conductor, a circuit with a group of three same low voltage windings and a group of three identical high-voltage windings is described in DE 29 33 473 AI, said magnetic coupling each winding group takes place with a corresponding winding of the other group. This in the power line coupled in signal is applied to the unconnected ends of the two windings of the first group of windings.

p0006Especially for data transfers in the MHz range, however, signal reflections can lead to the crossing points to problems. It should therefore be taken at those locations on an adaptation of the characteristic impedances. while an average value is to be set for the partially fluctuating impedance of the power network. In a corresponding matching circuit for the MHz range, therefore, the signal transmitter must be fitted with the corresponding coupling capacitors very close to the respective power lines.

p0007Essentially the same problems as for bridging

p0008Transformers resulting in bridging of switches. In both cases, the respective signal damped during the transmission of signals on network lines through the transformers or interrupted by the switch. In order to secure the signal transmission in such places, these elements have to be bridged.

p0009When working in the audio frequency and carrier frequency range up to approximately 200 kHz, there is no problem. As already mentioned the problems occur in the MHz range due to the signal reflections at the crossing points on account of the different impedances of power lines. This is especially true during the transition from insulated power cables on overhead lines.

p0010Object of the invention is in contrast to establish appropriate matching circuits specifically for the MHz range.

p0011The object is achieved by the features of the patent claim. 1 Further developments are indicated in the dependent claims. In the invention, signal transformer converters are provided in a cascade circuit for use in the MHz range. The transducers are coupled to the power lines, wherein the data transmission via the signal converters takes place. Preferably two transducers are available transformer and a coaxial line is used for connecting the two signal converter transformer. In this case, the data transmission between the transducers is carried out on the coaxial line.

p0012In the invention, a bypass circuit can therefore by the cascade circuit, preferably in connection with the coaxial line to be realized, which, for example, alternatively ausleg- for transformers as well as for switch bar. a suitable solution for the transition from or on overhead lines can thus be created in particular cables.

p0013Further details and advantages of the invention will become apparent from the following description of embodiments with reference to the drawing. Show it

p00141 shows a circuit arrangement with two Signalübertragern in cascade as a coaxial bypass for use in transformers, Figure 2 shows a modification of Figure 1 for use with shielded cables and plastic

p0015Figure 3 shows a circuit with two Signalübertragern in cascade as a coaxial bypass for use in switches.

p0016Same units have the same reference numerals in the figures.

p0017The figures are partially described jointly.

p0018In each of the figures, the coupling point of networks of multi-phase conductors 1 and 2 with each phase Ll to L3 and a respective neutral N is displayed. In such conductors, apart from the energy transfer data transfer achieved consequences. For this, the characteristic impedances'll have each adapted.

p0019Especially in Figures 1 and 2, the coupling point between the line sections 1 and 2, includes a transformation medium voltage to low voltage, a transformer 3 with the medium-voltage side of the transformer coils 31 to 33 and the low voltage side of the transformer coils 31 ^λ are to 33 'available. Figure 3, however, contains ing a switch 5 with individual switches 51 to 53 for the power lines.

p0020In Figures 1 to 3 each two transformer signal transmitter 10 and 20, the signal transformers are connected in cascade available to re- duce to a minimum the unavoidable signal reflections. 10 and 20 each consist of the Teilübertragern 11, 12 and 21, 22 and have associated coupling capacitors Cl and C2. The associated protective circuit is not shown in detail.

p0021It is essential that the signal transmitter 10 and 20 are mounted very close to the respective power lines. The compound of the signal transmitter 10 and 20 is effected by a coaxial cable 30th

p0022The two transformers 10 and 20 with the respective transformer transmission between the units 11 and 12 or 21 and 22 are used for electrical isolation and the adaptation of the characteristic impedance of the power networks to the coaxial cable 30. For this, the signal transmitter 10 and 20 themselves also constructively largely constructed coaxially.

p0023The arrangement specifically in Figure 1 with the transformer bypass for the MHz range and parallel capacitive coupling on both sides is particularly suitable for the connection of cables or lead-sheathed cables in the medium voltage side and any lines on the low voltage side. 2 shows the arrangement of Figure 1 is modified to the extent that on the medium voltage side, a plastic cable for use is, in which a shield 4 is present. The shield 4 is connected via the sub-transmitter 11 of the first Ü bert ragers 10 to ground potential. Otherwise the serial inductive coupling is constructed in accordance with FIG. 1

p0024In Figure 3, a switch 5 for individual switches 51, 52 and 53 for the phases Ll to L3 is present between the lines 1 and 2 instead of the transformer 3rd In other respects, the

p0025The circuit configuration of Figure 1. With the coaxial bypass for the MHz range can be effected in this case, the bridging of a network switch.

p0026It is essential in all of the examples described with reference to Figures 1 to 3, that a data transmission on the low-frequency networks, also in the MHz range is possible. The outgoing signal reflections problems are eliminated.