Power line communication system

Abstract

This invention relates to a power line communication (PLC) system wherein the power supply line supplies power and also acts as a communications supply line. A receiver is able to detect small changes in the modulated transmitted information and thereby shut down the circuit. The invention is particularly suitable for use where the IEL is remote from the power supply such as, for example, in down hole oil production situations where very long power cables are used.

1 . A power line communications (PLC) system, comprising:
 an electric motor having a neutral point and plurality of phases,   a power line having conductors for connection to the respective phases,   a power supply for connection to the conductors and operable to supply a polyphase power signal to the motor,   a transmitter for connection to the neutral point and one of the motor phase conductors and operable to transmit information to the receiver by adding modulation to the respective phase conductor of the power signal, and   a receiver for connection to the conductor of the respective phase.   
     
     
         2 . A PLC system according to  claim 1 , wherein the transmitter is operable to add modulation to the power signal phase by modulating a current flow through a winding of the respective motor phase conductor. 
     
     
         3 . A PLC system according to  claim 2 , wherein the modulation is effected by an amplitude modulation technique. 
     
     
         4 . A PLC system according to  claim 2 , wherein the transmitter is operable not to rectify the current flow to provide modulated power flow in both positive and negative half-cycles in the power signal phase conductor. 
     
     
         5 . A PLC system according to  claim 2 , wherein the transmitter is operable to rectify the current flow to only provide modulated power flow in one half-cycle of the power signal phase conductor. 
     
     
         6 . A PLC system according to  claim 1 , wherein the receiver is operable to filter out and recover the transmitted information. 
     
     
         7 . A PLC system according to  claim 1 , wherein the transmitter is operable to transmit the information within a sequence of modulations. 
     
     
         8 . A PLC system according to  claim 7 , wherein multiple consecutive or concurrent modulations occur in the same positive or negative half-cycle of the power signal waveform. 
     
     
         9 . A PLC system according to  claim 1 , wherein the transmitter includes a current detection circuit operable to determine a zero crossing in the power signal phase conductor in order that the modulation is activated only at pre-determined points of current flow. 
     
     
         10 . A PLC system according to  claim 1 , wherein the transmitter includes a voltage detection circuit to determine a zero crossing in the power signal phase conductor in order that modulations are activated only at fixed periods on a voltage waveform. 
     
     
         11 . A PLC system according to  claim 1 , wherein the transmitter is operable to transmit the information within a pre-set time period to reduce power loss within the motor phase conductor. 
     
     
         12 . A PLC system according to  claim 1 , wherein the transmitter is operable to schedule the transmission at times of reduced power flow through the motor phase conductor. 
     
     
         13 . A PLC system according to  claim 1 , wherein:
 the transmitter includes a circuit to provide feedback on background noise at a mode of the modulation, and   the transmitter is operable to actively alter the modulation mode or a technique of the modulation.   
     
     
         14 . A PLC system according to  claim 13 , wherein the receiver includes a circuit to sweep modulation modes in order to detect if the transmitter has modified the modulation mode in order to increase signal to noise ratio. 
     
     
         15 . A system for mine, sump, and quarry dewatering or oil production, comprising:
 a PLC system according to  claim 1 , wherein the motor, the transmitter, and the power line are submersible, and   a submersible pump coupled to the motor for being driven thereby.   
     
     
         16 . A PLC system according to  claim 1 , further comprising a thermistor in communication with the motor. 
     
     
         17 . A PLC system according to  claim 16 , wherein the thermistor is operable to activate the transmitter in response to overheating of the motor.