SK68097A3 - Power line signalling system - Google Patents

Abstract

A 3-phase overhead distribution network operates at intermediate voltage (e.g. 11 kV to 33 kV), between a high voltage supply network (at e.g. 110 kV or 275 kV) and a consumer mains system (at e.g. 110 V or 230 V). A signalling system uses signals at frequencies preferably in the region of 10 kHz to 100 kHz for signalling over the network, the signals being coupled inductively to and from the network. The signals are coupled to different phases at different points in the network cross-coupling between the phases ensures that signals coupled onto the system on one phase give adequate signal strength for detection at other points in the system regardless of which phase the detector is coupled to.

Description

Signaling system

Technical field

The present invention relates to power line signaling, and the present invention relates in particular to low or medium voltage overhead power line signaling.

BACKGROUND OF THE INVENTION

Network distribution - general

In most larger countries, electricity is supplied on a large scale through companies producing and distributing electricity (electricity services). The distribution network usually consists of a large number of low-voltage networks (often called supply networks or lines) to which home and retail consumers are connected, and these low-voltage networks are fed through a distribution system or a higher-voltage network. Low voltage networks (for consumers) can operate, for example, at 110 or 230 V (or 440 V 3-phase).

The distribution network will usually operate with more than one voltage. There is a long distance distribution operating at voltages, for example 132 kV or 275 kV, which are reduced (preferably in two or more steps) to a voltage, for example 11 kV or 33 kV, which will be referred to as medium voltage. The first mentioned voltage (i.e. the voltage used for the long-distance distribution) will be referred to as the high voltage and the latter voltage (i.e. the voltage relatively close to the final line voltage) will be referred to as the medium voltage.

Network signaling - general

The use of a power supply network for signaling is often suggested. Systems are available to communicate between rooms in residential buildings (typically for baby alarms), to connect to a telephone system and to transfer data between computer units. Many suggestions have also been made to use network signaling for remote measurements (primarily for electricity meters; although gas meters and other meters can be connected to the network for this purpose, preferably by means of electrical meters).

There is already an international standard for such signaling that uses a frequency generally in the range of 3 to 150 kHz. This standard is CENELEC EN50065.1, which specifies which frequencies from 3 kHz to 148.5 kHz are achievable for signaling on low-voltage electrical systems. This bandwidth is subdivided into several smaller bands with different uses and with different constraints associated with these bands. For example, the 9 kHz to 95 kHz band is reserved for electricity suppliers and their concessionaires.

Signaling, which is provided by electricity suppliers, will usually very likely relate to measurement and, more generally, system and load management. Thus, such signaling will usually be performed on low-voltage parts of the grid. However, as mentioned above, the distribution network will normally include medium and high voltage levels connected through power transformers. Thus, it will often be desirable for the measurement information collected on the low-voltage portions of the network to pass on the portions of the medium-voltage network and / or portions of the high-voltage network and similarly to pass the control information in the opposite direction. This control information may include information to be passed to consumers connected to the low voltage level as well as signals to control the actual electrical distribution system.

- 3 Connection to medium voltage networks

Thus, for the above reasons, techniques are required to connect signals to medium voltage networks. These signals may be generated or used at junction points, i.e. auxiliary substations, in which the medium voltage networks are connected to either the high voltage or low voltage networks, or these signals may pass between the medium voltage network and the low voltage network connected thereto.

It should be noted that signaling frequency signals generally do not pass effectively through power transformers. If effective signaling is to be achieved between the low and medium voltage parts of the network, it is necessary to use some means to connect the PLC signals around these transformers. This usually involves receiving and retransmitting signals. Thus, the signals are connected separately to two sides of the transformer and pass around the transformer between its two sides, which signals are processed to remove noise. It may also be desirable to use different frequency bands on two sides of the transformer. (This has the advantage that any signal passing through power transformers will not be meaningful.)

Signaling on the grid - the importance of the grid voltage level

Signal transmission and reception techniques are relatively simple for low voltage power grids. The signal transmitting and receiving device can be connected directly to the grid.

However, medium-voltage networks present greater difficulties than for electrical or mechanical reasons. Medium voltage networks require physically robust insulation that is largely incompatible with direct connection to medium voltage. Also, much finer and sensitive electronic devices are largely incompatible with direct connection to medium voltage (the term medium voltage is used here, but in conjunction with power grids; but 11 kV is excessively large for most electronic devices).

Air and underground networks

The grids may be airborne, underground or both. High-voltage sections are usually routed suspended in the air, as they usually cross very large distances in a relatively open country and the cost of digging them underground would be disproportionately high. In many countries, low voltage parts are usually underground, as they are routed in densely populated areas where suspended wires would be inappropriate and potentially dangerous. The medium voltage parts may be guided by air or underground; and, like low-voltage parts, are usually routed underground in urban and suburban areas. In this description, the interest will be focused primarily on air-guided, suspended medium voltage networks.

For network signaling over suspended medium-voltage medium-voltage networks, it is obvious to connect the signal to the network at one point and be able to obtain the signal from the network at another point. Various methods of attaching signals to overhead networks have been proposed, including inductive coupling. For this technique, a transducer comprising a magnetic core is arranged around one of the conductors to form a transformer. The core has a signal winding wound around it as a primary winding, and the conductor itself effectively forms a single-winding secondary winding (for transmitting; for receiving the driver is a single-winding primary winding and the signal winding is a multi-winding secondary winding). In this description we will deal with such inductive coupling.

3-phase systems

Distribution systems are generally 3-phase at medium (and high) voltages and often also at low voltages. Thus, the distribution system generally consists of 3 live supply conductors and usually also a neutral (earth) conductor. The lead wires are commonly referred to as R, Y, and B (red, yellow, and blue) and form a star connection along with the neutral wire.

Large consumers are often supplied through a 3-phase supply. Small-scale consumers (such as household users) are normally supplied through a single-phase supply. Utilities are trying to organize the connection of (single-phase) consumers so that the loads on the three phases are almost equal or balanced. In particular, suspended 3-phase medium voltage networks may have different single-phase taps or branches, since the cost of installing such a tap is considerably less than installing a 3-phase tap. (In principle, single-phase taps are also possible for underground networks, but are rarely used in practice for a variety of reasons).

A true single-phase tap would use only one of the 3 phases (R, Y and B) together with the ground or neutral wire, but for various reasons this is generally undesirable. Thus, so-called single-phase taps typically utilize 2 of the 3 phases at medium voltage, whereby the transformer at the end of the low voltage reduces the voltage between the 2 phases to a common mains voltage (e.g. 110 or 230 V).

With a three-phase system and inductive coupling, the signals are carried on any phase to which the input transducer is connected, and the detection transducer detects signals on any phase to which it is connected. This indicated that one phase was used for signaling and all transducers were connected to that phase. (It is preferable to describe the phase to which the transducers are attached as the primary phase and the other two phases as the secondary phases). This required that the primary phase be identified at all points in the system where transducers were coupled. This also meant that signaling could be performed on single-phase taps only when the taps contained the primary phase.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a signaling system for signaling at a 3-phase substation, the principle being that the signals are coupled inductively to and from the network and are bound to different phases at different points in the network. The signal frequency is preferably in the range from 10 kHz to 100 kHz.

The present invention resides in detecting or realizing this fact that the primary phase is bound to the secondary phases (at the signal frequency) sufficiently well so that the signal indicated on the primary phases is satisfactorily detectable on the secondary phases as well as on the primary phase. Of course, the primary phase is now defined with reference to a certain signal input transducer; however, if another input transducer is contemplated, its primary phase may be different.

The signals will usually be coupled to a system in the vicinity of the transformer, and the binding to the secondary phase is predominantly capacitive in that transformer. We will further assume that the transformer is a 3-phase transformer that is connected to a triangle (if this transformer is actually connected to a star, we will further consider its equivalent connection to a triangle). The winding of such a transformer represents a high impedance at the signal frequency, but there are effective leakage capacities on the windings from the primary phase to each of the two secondary phases, and these capacities bind the signal from the primary phase to the two secondary phases. (If there is a true transformer configuration in a triangle, then there is no real neutral point. If there is a real configuration in a star, then there is a true neutral point that may or may not have a neutral conductor attached to each other; with the same voltage as the ground, but is usually not grounded.

The capacities between each of the three points of the winding triangle and the ground are also effective here. The two capacities between the cundary phases and the ground will act, in conjunction with the capacities between the primary and secondary windings, as signal passages; also the capacity of the primary phase to ground will tend to drive the signal to the primary phase to ground. However, although these effects reduce the signal strength on the secondary phases, they do not limit it to an unacceptable degree.

There is also capacity on the winding between the two secondary phases. Under balanced load conditions, the two secondary phases receive the same signals, so this capacity is meaningless, but if the load conditions are unbalanced, then this capacity will help balance the signals on the two secondary phases.

At the 3-phase termination and reception point, the signal binding can be coupled to any of the three phases. If it is bound to the primary phase, the signal on the primary phase will of course be sensed. If bound to either of the two secondary phases, it will sense a secondary phase signal that is less than the primary phase signal but still has an acceptable strength. Similarly, at a single-phase tap and receive point (ie a single 2-phase medium supply), the signal coupling will sense either the primary or secondary phase signal, depending on which 2 phases are used at the tap and to which of the two phases a signal coupling is attached. Since in the 3-phase terminations the line signal current is zero to the end, then there may also be a ground current.

In the case of signals fed to a single-phase tap, one of the 2 phases of the medium voltage will necessarily be the primary phase for the signals fed here by the transducer. It is likely that there will be an imbalance between the secondary tap phase and the remaining secondary phase, but at the 3-phase termination, the signals on the primary phase will be split between the two secondary phases so that they can be received on any of the secondary phases , of course), although the signals on the two secondary phases will erase different forces. Similar mechanisms will usually also ensure that the signals supplied at the single-phase tap are received at the other single-phase taps.

The medium-voltage 3-phase power distribution network comprising a signaling system according to the present invention will be described in the following description by way of example with reference to the accompanying drawings.

Overview of the figures in the drawing

Fig. 1 is a general circuit diagram of a system incorporating the present invention.

Fig. 2 is a much more detailed circuit diagram of a substation with the system of the invention.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, the system is fed from a transformer station 10, which is fed from a high voltage grid via a 3-phase transformer that drives a 3-phase medium voltage power distribution system having 3 phases R, Y and B. These 3 phases are fed to 3 a phase auxiliary substation 11 in which the energy is transformed down by a low voltage via a 3-phase transformer. Two single-phase taps are also discharged from the system, a tap consisting of R and Y phases fed to the auxiliary substation 12 and a tap consisting of phases Y and B fed to the auxiliary substation 13 ,. Obviously, the system may have additional 3-phase extensions and additional single-phase taps.

For the sake of simplicity, only the transformer medium voltage windings are shown, leaving out the high voltage windings (for transformer 10 and low voltage windings (for transformers 11 and 13).). connected to a star that provides 3 separate low-voltage phases, and the secondary winding of the low-voltage transformers 12 and 13 will usually be each one winding, providing one low-voltage phase.

The transformer station 10 has a phase T transducer 10T; the transducer comprises a magnetic core through which the phase R of the power line passes (thereby forming a single-winding winding) and a (multi-threaded) excitation and sensing winding bound to the core (symbolically indicated by the U-mark). The 3-phase substation 11 has a transducer 11T coupled to its phase B power line; the single-phase substation 12 has a transducer 12T coupled to its phase Y power line; and the single-phase substation 13 has a transducer 13T coupled to its phase Y power line.

The excitation transducer 10T is bound to phase R, so that this phase is the primary phase and phases Y and B are secondary phases. In the present system, the 11T to 13T receiving transducers may each be bound to any phase, and in particular may be bound to the secondary phases as shown. So far, it has been reported that it is mandatory or necessary for receiving transducers to be coupled to the primary phase, so that transducers at sub-stations 11 and 12 should be located as indicated by 11T 'and 12T'; it was also not conceivable in the past to connect the transducer to the auxiliary substation 13, since this auxiliary substation is not fed via the primary phase.

It should be understood, of course, that while the 10T transducer acts as an excitation transducer and the 11T and 13T transducers act as receiving transducers for signals fed from the transformer station 10, any of the transducers may act as a transducer for signals from its own substation, then the other transducers work as receiving transducers. Phase R is, by definition, the primary phase for the signals from the 10T transducer, but the other phases may be the primary phases for the signals delivered through the transducers.

Fig. 2 shows the operating circuit of the system in the transformer 10 in greater detail. The transformer has three medium voltage windings V1, V2 and V3 arranged in a triangle. (If the transformer windings are actually arranged in a star, this arrangement can be converted to an equivalent arrangement by means of a standard transform.) Each winding is, at the signal frequency, bridged by a leakage capacity, indicated by the reference numerals C1. C2 and C3. Each point of the triangle is also bound to the ground by means of the ground capacity, which is designated herein by reference numerals C4, C5 and C6.

In analyzing the system in relation to the voltages, the 10T transducer induces voltage to the R phases of the power line. This voltage is coupled to ground through 3 parallel paths: capacitances C1 and C6 connected in series, capacitances C3 and C4 connected in series and capacitance C5. Two paths in a series of connected capacities C1 - C6 and C3 - C4 result in voltages that are induced on the phases Y and B of the power line. thus, all three phases of the power line have induced voltages thereon; the primary voltage on the primary phase R and two equal and slightly smaller voltages, with the opposite phase, on the phases Y and B of the power line.

When analyzing the system in relation to currents, the primary current Ir is induced in phase R of the power line, two equal and slightly smaller secondary reverse currents 1γ and Ι_β, with the opposite phase, induced in the phases Y and B of the power line and ground return Ιβ, also with the opposite phase with respect to the primary current, is induced in the ground G of the transformer 10 ,. Obviously, Ir = ly + 1β + 1β · The primary current passes along the primary phase of the power line to the various auxiliary substations and passes to the secondary phases and ground in these auxiliary substations. At signal frequencies, power lines act as transmission lines between auxiliary substations and switching points where the power distribution system branches (into 2-phase or 3-phase branches).

Obviously, each of the two secondary phase reverse currents is effectively divided between different substations, but that each of the auxiliary substations will generally receive significant portions of the two total secondary phase reverse currents. Specifically, the substation 11 will receive a significant portion of the phase B reverse current, and the substations 12 and 13 will each receive substantial portions of the phase Y reverse current. Receiving transducers 11T, 12T and 13T will all receive significant signals from the driver 10T transducer.

At signal frequencies, the windings of the transformers in the substations are each effectively bridged by capacities, and also each is effectively coupled to ground through capacitances to ground. The currents in the power lines to which the transducers are coupled find their return paths through these capacities. (This action can of course also be explained in relation to tensions).

The present invention may advantageously utilize a power line signaling device as described in the co-pending patent application of the same Applicant which has been filed with the present application and which bears the name of the power line signaling device.

Claims (6)

PATENT CLAIMS PV58O-47 Signaling system for signaling on a 3-phase grid, characterized in that the signals are coupled inductively to and from the grid and are coupled to different phases (R, Y, B) at different points in the grid (10T to R, 11T) to B, 12T to R, 13T to Y). 2. Signaling by 10 kHz to 100 kHz. The system of claim 1, wherein the signal frequency is in a range from a system according to any of the features 3. Signaling claims, the system operates at a voltage between 11 kV and 33 kV. from the previous, that Signaling system according to any one of the preceding claims, characterized in that the system comprises at least one branch having only one of the preceding phases. Signaling system according to any one of the preceding claims, characterized in that the system comprises at least one branch (12, 13) having only two phases. 6. Any new and inventive feature or combination of features described in this description within the meaning of Article 4H of the International Agreement (Paris Agreement).