GB2267971A

GB2267971A - Determining cable phase

Info

Publication number: GB2267971A
Application number: GB9227071A
Authority: GB
Inventors: Keith John Roy; John Lucas Howard
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-12-24
Filing date: 1992-12-24
Publication date: 1993-12-22
Also published as: GB9227071D0

Abstract

An apparatus for determining to which phase an electricity power distribution cable belongs comprises a detector 11 for coupling to a selected outgoing distribution cable 8 from a sub-station or distribution centre 10 and a radio transmitter 12 for transmitting a phase-identifying signal modulated with the signal detected on the cable B. At a point 20 remote from the sub- station or distribution centre a detector 21 is coupled to the distribution cable X, and a radio receiver 22 receives and demodulates the radio signal. The receiver 22 includes a comparator which compares the demodulated signal with the signal carried by the distributor cable X to provide an indication of the difference in phase between the two signals. In an alternative arrangement, differently coded signals are injected onto the respective cables at the sub-station and a decoder at a remote point processes the signals from a detector to determine which of the coded signals are present on a cable. <IMAGE>

Description

Phase Detecting This invention relates to electricity distribution and more particularly to a method and apparatus for determining to which of several phases a particular distribution cable belongs.

Electrical power is generated as three phases and usually all three phases are distributed to local sub-stations.

Typically, three separate cables, one for each phase, run from each sub-station to the consumers; usually each consumer (e.g.

a house) is connected to one of these three separate cables, whilst large consumers (e.g. factories) are often connected to all three phases. In general, no record is made of which consumer is connected to which individual phase. We have found, therefore, that the three phases running from a particular sub-station can have substantially different numbers of consumers connected to them. Similarly in factories and other large premises receiving all three phases, no attempt is made to balance the loads between the phases.

We have now devised a method and apparatus for determining to which of the three phases a particular distribution cable belongs. In using this method and apparatus, then when connecting new consumers (or new loads) to the electrical supply, an effort can be made to balance the loading between the three phases, and so maximise the efficiency of the electrical supply system. In the case of a large consumer using all three phases, by maximising the efficiency of the electrical distribution within his premises, he will minimise his electricity usage.

In accordance with this invention, there is provided a method of determining to which phase an electricity power distribution cable belongs, comprising accessing the distribution cables running from a sub-station or other distribution centre, to generate and transmit a phase identifying signal, accessing a distribution cable at a point remote from the sub-station or other distribution centre, and receiving and processing said phase-identifying signal at said point to determine the phase of the latter cable.

In one embodiment of this method, a radio signal is derived and transmitted from the sub-station or other distribution centre, the radio signal representing the phase of one of the cables accessed at the sub-station or other distribution centre: at the remote point where the phase of a cable is to be determined, a signal is derived from that cable representing the phase of the electrical power which it carries, and processed with the received radio signal to determine if the cable at the remote point corresponds in phase with the cable represented by the radio signal. The radio signal may have a waveform synchronised with the waveform carried by the cable selected at the sub-station or other distribution centre, and the signal derived from the cable at the remote point is synchronised which the waveform carried by that cable at that point: the relative phases of the two waveforms are then compared.

In another embodiment of the method, a distinctive signal is injected onto one of the cables running from the substation or other distribution centre: preferably differentlycoded signals are injected onto the different cables: at the remote point where the phase of a cable is to be determined, a signal is derived from the cable and processed to determine if it is the distinctive signal (or which coded signal it is).

Also in accordance with this invention, there is provided an apparatus for determining to which phase an electricity power distribution cable belongs, comprising means for use at a sub-station or other distribution centre to generate and transmit a phase-identifying signal, and means for coupling to a distribution cable at a point remote from the sub-station or other distribution centre and for receiving and processing said phase-identifying signal to determine the phase of the latter cable.

Embodiments of this invention will now be described by way of examples only and with reference to the accompanying drawings, in which: FIGURE 1 is a schematic diagram to explain the principles of a first embodiment of the method and apparatus in accordance with the invention; and FIGURE 2 is a similar schematic diagram to explain the principles of a second embodiment of the method and apparatus in accordance with the invention.

Referring to Figure 1, an electricity distribution substation 10 receives a three-phase supply, and the individual phases are connected to three out-going cables R, Y, B. A number of consumers are connected to each of the distribution cables R, Y, B, but there is no record of which consumer is connected to which cable, or how many consumers are connected to each cable. However, the method and apparatus which will now be described enables a determination to be made, at a remote point along any one of the cables R, Y, B, to which of the three phases that cable belongs. In the example shown, it is desired to determine the phase of the distribution cable X to which a consumer's premises 20 are connected.

At the sub-station, a detector 11 is coupled to any selected one of the three outgoing cables R, Y, B to form an alternating signal synchronised with the waveform of the electrical power carried by that cable. This signal is modulated onto a radio frequency carrier and transmitted by a radio transmitter 12. The detector 11 may comprises a coil for inductively coupling with the live conductor of the selected outgoing distribution cable: alternatively the detector may comprise a transformer the primary of which connects between the live and neutral conductors of the outgoing distribution drawing negligible current.

At the consumer's premises 20, a detector 21 is coupled to the distribution cable X. In particular, the detector 21 may be coupled either to the cable X, running from the distribution cable X into the premises 20, or to a cable within the premises 20. The detector 21 may comprise a coil for inductively coupling with the cable (or the live conductor of the cable), or it may comprise a transformer the primary of which connects between live and neutral, drawing negligible current: in this case the detector may plug into a mains supply socket within the premises 20. The detector 21 provides an alternating signal synchronised with the waveform of the power carried by the cable X, and this signal is passed to a receiver 22 which receives and demodulates the radio signal from the transmitter 12. The receiver 22 includes a phase comparator which compares the phase of the demodulated radio signal with the phase of the signal from detector 21. The phase comparator is arranged to determine whether the phases of the two signals correspond, or whether cable X is 120" leading or 1200 lagging relative to the outgoing cable R,Y or B to which the detector 11 is applied. Preferably the phase comparator gives a numerical output of the difference in phase between the two waveforms.

Referring to Figure 2, in another embodiment of the method and apparatus of this invention, a coded-signals generator 30 is used at the sub-station 10 to inject differently-coded signals onto the respective outgoing cables R, Y, B. The coded signals may be injected onto the cables R, Y, B for example via coils 31,32,33 inductively coupled with the live conductors of the respective cables. At the premises 40 of a consumer, where the phase of the distribution cable X is to be determined, a detector 41 is used, as described with reference to Figure 1, to provide a signal including the coded signal carried on the cable X. A decoder 44 processes the signal from detector 41 to determine which of the three coded signals are present in cable X, thus indicating the phase of cable X.

In place of the types of detectors 11, 21 and 41 which have been described, use may be made of an optical sensor directed at a filament lamp powered from the phase being examined: the optical sensor gives an electrical output signal which includes an alternating component synchronised with the waveform of the current passing through the lamp.

In the above description, the method and apparatus of the invention are used to determine to which phase the distribution cable for a consumer's premises belongs. However, the method and apparatus can equally be used to determine the phase of individual distribution cables within factories or other premises which use more than one phase.

Claims

1) A method of determining to which phase an electricity power distribution cable belongs, comprising accessing the distribution cables running from a sub-station or other distribution centre, to generate and transmit a phase identifying signal, accessing a distribution cable at a point remote from the sub-station or other distribution centre, and receiving and processing said phase-identifying signal at said point to determine the phase of the latter cable.

2) A method as claimed in claim 1 comprising generating and transmitting a phase-identifying radio signal deriving a signal from the distribution cable at said remote point, and comparing the derived signal with the radio signal received at said remote point.

3) A method as claimed in claim 1 comprising generating and transmitting a distinctive signal onto one of said distribution cables running from the sub-station or other distribution centre, deriving a signal from the distribution cable at said remote point and determining whether said derived signal is said distinctive signal.

4) A method as claimed in claim 3 comprising generating and transmitting differently-coded signals onto different ones of said distribution cables.

5) A method substantially as herein described with reference to the accompanying drawings.

6) An apparatus for determining to which phase an electricity power distribution cable belongs, comprising means for use at a sub-station or other distribution centre to generate and transmit a phase-identifying signal, and means for coupling to a distribution cable at a point remote from the sub-station or other distribution centre and for receiving and processing said phase-identifying signal to determine the phase of the latter cable.

7) An apparatus as claimed in claim 6 in which the means for use at the sub-station or other distribution centre comprises a radio transmitter for transmitting a phaseidentifying radio signal, the means for coupling to the distribution cable at said remote point comprising a radio receiver for receiving said radio signal and a phase comparator which compares the phase of the demodulated radio signal with a signal carried by the distribution cable at said remote point.

8) An apparatus as claimed in claim 7 in which the phase comparator gives a numerical output of the difference in phase between the two signals.

9) An apparatus as claimed in any of claims 6 to 8 which the means for use at the sub-station or other distribution centre comprises a coil for inductively coupling with a live conductor of the outgoing power distribution cable.

10) An apparatus as claimed in any of claims 6 to 8 which the means for use at the sub-station or other distribution centre comprises a transformer having its primary windings connected between live and neutral conductors of the outgoing power distribution cable.

11) An apparatus as claimed in any of claims 6 to 10 in which the means for coupling to the distribution cable at the remote point comprises detector having a coil for inductively coupling with the cable.

12) An apparatus as claimed in any of claims 6 to 10 in which the means for coupling to the distribution cable at the remote point comprises detector having a transformer having its primary winding connected between live and neutral conductors of said cable.

13) An apparatus as claimed in claim 12 comprising a plug for connecting to a mains supply socket at said remote point.

14) An apparatus as claimed in any of claims 6 to 10 in which the means for coupling to the distribution cable at the remote point comprises an optical sensor for directing at a filament lamp connected to the cable, the sensor giving an electrical output signal which includes an alternating component synchronised with the current passing through the lamp.

15) An apparatus as claimed in claim 6 in which the means for use at the sub-station or other distribution centre comprises a generator for injecting differently-coded signals onto respective outgoing distribution cables, the means for coupling to the distribution cable at said remote point comprising a decoder for determining which of the coded signals are present on the cable.

16) An apparatus substantially as herein described with reference to the accompanying drawings.