Power supply monitoring system

Abstract

A method for detecting predetermined fault conditions associated with the supply of AC electrical power to a consumer, the supply having an active conductor and a neutral conductor with the neutral conductor being connected to earth. The method comprises providing a first current detector associated with the active conductor; providing a second current detector associated with the neutral conductor; providing a voltage detector to detect voltage between the active conductor and the neutral conductor; and checking a current ratio of neutral current to active current whereby the current ratio is indicative of a predetermined fault condition. Also disclosed is a method of checking the condition of supply line active and neutral conductors in a consumer's supplied premises including determining the impedance of the active conductor and the impedance of the neutral conductor to indicate the condition of each of the active and neutral conductors.

1 . A method for detecting predetermined fault conditions associated with the supply of AC electrical power to a consumer, the supply having an active conductor and a neutral conductor, the neutral conductor being connected to earth, the method comprising the steps of:
 providing a first current detector associated with the active conductor;   providing a second current detector associated with the neutral conductor;   providing a voltage detector to detect voltage between the active conductor and the neutral conductor;   checking a current ratio of neutral current to active current whereby the current ratio is indicative of a predetermined fault condition.   
     
     
         2 . A method according to  claim 1  wherein a normal connection without any faults is indicated by the current ratio being less than 1 as the neutral current will always be less than the active current. 
     
     
         3 . A method according to  claim 1  wherein the predetermined fault condition is a reverse polarity connection indicated by the current ratio being greater than 1. 
     
     
         4 . A method according to  claim 1  wherein the predetermined fault condition is a broken neutral indicated by the current ratio being equal to zero as all incoming current on the active conductor exits through earth so that zero current appears on the neutral conductor. 
     
     
         5 . A method according to  claim 1  wherein the predetermined fault condition is a broken customer earth with a normal polarity indicated by the current ratio being equal to 1. 
     
     
         6 . A method according to  claim 1  wherein the predetermined fault condition is a broken customer earth with a reverse polarity indicated by the current ratio being equal to 1. 
     
     
         7 . A method according to  claim 1  wherein the predetermined fault condition is a short circuit present between the active conductor and the neutral conductor indicated by the current ratio being equal to minus infinity. 
     
     
         8 . A method according to  claim 1  wherein the predetermined fault condition is a short circuit present between the active conductor and earth indicated by the current ratio being equal to infinity. 
     
     
         9 . A method according to  claim 1  further comprising providing a contactor switch in the active conductor to and providing a second contactor switch in the neutral conductor to enable remote disconnection of the consumer by the supply authority. 
     
     
         10 . A system for detecting one or more predetermined fault conditions associated with the supply of AC electrical power to a consumer, the supply having an active conductor and a neutral conductor, the neutral conductor being connected to earth, the system comprising:
 a first current detector associated with the active conductor;   a second current detector associated with the neutral conductor;   a voltage detector to detect voltage between the active conductor and the neutral conductor; and   a contactor switch in the active conductor.   
     
     
         11 . A system according to  claim 10  wherein the one or more predetermined fault conditions includes reverse polarity whereby the contactor switch in the active conductor is opened and any current detected on the neutral connection indicates a said reverse polarity. 
     
     
         12 . A system according to  claim 11  further comprising a second contactor switch in the neutral conductor to enable the neutral conductor to be disconnected from the supply by opening the second contactor in the event that a reverse polarity is detected. 
     
     
         13 . A system according to  claim 12  wherein the contactor switch in either or both of the active conductor and the neutral conductor is controlled by the supplier of the AC electrical power. 
     
     
         14 . A system according to  claim 10  in which the one or more predetermined fault conditions include any of a broken neutral conductor, a broken customer earth connection, a short circuit between the active conductor and neutral conductor in the low voltage supply line, and a short circuit between the active conductor and the consumer earth connection. 
     
     
         15 . A system according to  claim 14  where the predetermined fault condition is a broken neutral conductor, all incoming current on the active conductor exits the through the earth connection and zero current exist through the neutral conductor, such that the second current detector shows a zero current flow. 
     
     
         16 . A system according to  claim 14  where the predetermined fault condition is a broken customer earth that is detected by measuring the current on each of the active conductor and the neutral conductor. 
     
     
         17 . A system according to  claim 16  where the predetermined fault condition is a broken customer earth and the connection is normal polarity, detection of the broken customer earth occurs when the current on the active conductor exits through the neutral conductor and therefore is of the same magnitude as the active conductor current. 
     
     
         18 . A system according to  claim 16  where the predetermined fault condition is a broken customer earth and the connection is reverse polarity, detection of the broken customer earth occurs when the current on the neutral conductor exits through the active conductor and therefore is of the same magnitude as the neutral conductor current. 
     
     
         19 . A system according to  claim 14  where the predetermined fault condition is a short circuit between the active conductor and neutral conductor, the detection of which occurs when the second current detector detects current flowing through the neutral conductor and the consumer's meter in a reverse direction and when the first current detector does not detect any current in the active conductor. 
     
     
         20 . A system according to  claim 14  where the predetermined fault condition is a short circuit between the active conductor and earth, the detection of which occurs when the second current detector detects current flowing through the neutral conductor and the consumer's meter in a forward or positive direction and when the first current detector does not detect any current in the active conductor.