Monitoring device for a medium voltage overhead line

• US 20060187074A1
• Filed: 01/31/2003
• Published: 08/24/2006
• Est. Priority Date: 01/31/2003
• Status: Active Grant

• Current Assignee: FMC Tech Limited (GE Aerospace)
• Original Assignee: FMC Tech Limited (GE Aerospace)
• Inventors: O'Sullivan, Charles Brendan, Quinlan, Michael Martin
• Granted Patent: US 7,518,529 B2
• Time in Patent Office: Days
• US Class Current: 340/660
• CPC Class Codes: G01R 15/142 Arrangements for simultaneous measurements of several parameters employing techniques covered by groups G01R15/14 - G01R15/26

Abstract

A monitoring device (1) for monitoring the electrical properties of a medium voltage overhead line (3) in a medium voltage network comprises three separate measurement sensors (2a, 2b, 2c), each being adapted for direct connection onto a medium voltage overhead line. Each of the measurement sensors has means to draw operating power from the medium voltage overhead line. The measurement sensors measured results may be combined for accurate measurement analysis.

Claims

1-52. -52. (canceled)

53. A monitoring device (1) for monitoring the electrical properties of a medium voltage overhead line (3) in a medium voltage network, the monitoring device comprising means to measure the electrical properties of the medium voltage line and means to communicate the measured electrical properties to a control centre computer of the medium voltage network;

the monitoring device comprises three separate measurement sensors (2a, 2b, 2c), each measurement sensor being adapted for direct and electrically insulated connection onto a separate medium voltage overhead line (3a, 3b, 3c);

each measurement sensor having means to measure (4) the electrical properties of its respective medium voltage overhead line;

each measurement sensor having means to communicate (6) with at least one of the control centre computer and another measurement sensor, at least one of the measurement sensors having means to communicate with the control centre computer; and

in which the three measurement sensors further comprise a master sensor and two slave sensors, each of the slave sensors having means to communicate data to and from the master sensor and the master sensor having means to communicate with the control centre computer.

54. A monitoring device (1) as claimed in claim 53, in which the master sensor further comprises a processor (5) for processing data received from each of the slave sensors before transmitting electrical properties data onwards to the control centre computer.

55. A monitoring device (1) as claimed in claim 53, in which each measurement sensor has a processor for processing the measured electrical properties of its respective medium voltage overhead line.

56. A monitoring device (1) as claimed in claim 53, in which there is provided means to synchronise the three measurement sensors (2a, 2b, 2c).

57. A monitoring device (1) as claimed in claim 53, in which each monitoring device has means to draw operating power directly from the magnetic field of the medium voltage overhead line.

58. A monitoring device (1) as claimed in claim 57 in which each measurement sensor has the means to draw operating power directly from the magnetic field of the medium voltage overhead line.

59. A monitoring device (1) as claimed in claim 58 in which the means to draw operating power directly from the magnetic field of the medium voltage overhead line comprises a magnetic field pick up coil.

60. A monitoring device (1) as claimed in claim 53 in which each measurement sensor has means to draw operating power directly from the electric field of the medium voltage overhead line.

61. A monitoring device (1) as claimed in claim 60 in which the means to draw operating power directly from the electric field of the medium voltage overhead line comprises foil plates for electric field pickup.

62. A monitoring device (1) as claimed in claim 53 in which each measurement sensor'"'"'s means to measure the electrical properties of its associated medium voltage line further comprises a current measurement device.

63. A monitoring device (1) as claimed in claim 62 in which the current measurement device comprises a Rogowski coil.

64. A monitoring device (1) as claimed in claim 62 in which the current measurement device comprises a Hall effect device.

65. A monitoring device (1) as claimed in claim 62 in which the current measurement device comprises a current transformer constructed from a magnetically soft material.

66. A monitoring device (1) as claimed in claim 65 in which the current transformer further comprises means to draw operating power directly from the magnetic field of the medium voltage overhead line.

67. A monitoring device (1) as claimed in claim 53 in which each measurement sensor has means to measure one or more of the instantaneous current, (I_C), the peak current, (I_Pk), the root-mean square (RMS) current, (I_RMS), the harmonic content of the current, and the phase of the current in its associated medium voltage overhead line.

68. A monitoring device (1) as claimed in claim 67, in which each measurement sensor has means to calculate the phase element of the peak current using the formula:

$I_p=\frac{1}{N}·<br><br>\underset{0}{\overset{N}{\sum <br><br>}}<br><br>f<br><br>\left(n\right)·<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\left({\mathrm{\omega <br><br>}}_0<br><br>n\right)$

69. A monitoring device (1) as claimed in claim 67, in which each measurement sensor has means to calculate the quadrature element of the peak current using the formula:

$I_q=\frac{1}{N}·<br><br>\underset{0}{\overset{N}{\sum <br><br>}}<br><br>f<br><br>\left(n\right)·<br><br>\sin <br><br>\left({\mathrm{\omega <br><br>}}_0<br><br>n\right)$

70. A monitoring device (1) as claimed in claim 53, in which any three adjacent measurement sensors may be combined to form arbitrary triplets to form a monitoring device.

71. A monitoring device (1) as claimed in claim 67, in which each measurement sensor has means to filter instantaneous current values and compare the instantaneous current values with peak current values for re-striking earth fault detection.

72. A monitoring device (1) as claimed in claim 67 in which each measurement sensor has means to compare the output of the sine/cosine functional block on a cycle by cycle basis with averaged values from the same source for detection of re-striking earth faults.

73. A monitoring device (1) as claimed in claim 67 in which one of the measurement sensors has means to receive the measurements from the other two measurement sensors and based on the received measurements and its own measured values has means to calculate one or more of the instantaneous balance current, I_B, the zero sequence current, I_Oo, and the ground current I_G.

74. A monitoring device (1) as claimed in claim 73 in which the measurement device that has a means to receive the measurements from the other two devices further comprises means to perform one or more of the following operations:

(a) measure the RMS value of I_G,

(b) measure the amplitude and phase of I_G,

(c) measure the harmonic content of I_G,

(d) filter the I_G signal,

(e) compare I_G to a predetermined set of thresholds,

(f) determine the duration of an over-threshold condition and

(g) generate and transmit a status report to the control centre.

75. A monitoring device (1) as claimed in claim 53 in which each measurement sensor is provided with a slow discharge high capacitance capacitor to act as a temporary power supply.

76. A monitoring device (1) as claimed in claim 53 in which the means to communicate with the control centre computer comprises a radio transmitter/receiver.

77. A monitoring device (1) as claimed in claim 53 in which the three measurement sensors further comprise a master sensor and two slave sensors, the master sensor having means to communicate with the control centre, means to receive measurements from the slave sensors and a processor to process the measurements prior to transmission to the control centre.

78. A monitoring device (1) as claimed in claim 53 in which the monitoring device is provided with means to operate remote switch gear.

79. A monitoring device (1) as claimed in claim 57 in which the power supply of each of the measurement sensors is provided with a low loss full wave rectifier consisting of four transistors.

80. A monitoring device (1) as claimed in claim 57 in which each measurement sensor is provided with a shunt circuit to control the power being transferred to the measurement sensor.

81. A monitoring device (1) as claimed in claim 80 in which the shunt circuit further comprises an auxiliary winding to facilitate shunting.

82. A monitoring device (1) as claimed in claim 53 in which each measurement sensor samples the current flowing in its associated medium voltage line at a predetermined rate and there is provided means to synchronise the sampling rate of each of the three measurement sensors.

83. A monitoring device (1) as claimed in claim 82 in which the means to synchronise the sampling rate with the other measurement sensors comprises an analogue phase locked loop circuit.

84. A monitoring device (1) as claimed in claim 82 in which the means to synchronise the sampling rate with the other measurement sensors comprises a digital phase locked loop circuit.

85. A monitoring device (1) as claimed in claim 82 in which the means to synchronise the sampling rate with the other measurement sensors comprises a radio borne time signal.

86. A monitoring device (1) as claimed in claim 82 in which the means to synchronise the sampling rate with the other measurement sensors comprises a receiver on each of a pair of the measurement sensors to receive a transmitted synchronisation signal from the third measurement sensor.

87. A monitoring device (1) as claimed in claim 57 in which there is provided a boost regulator to provide adequate power supply integrity for circuitry of each measurement sensor.

97. A monitoring device (1) as claimed in claim 53 in which each measurement sensor has means to measure one or more of the instantaneous current, (I_C), the peak current, (I_Pk), the root-mean square (RMS) current, (I_RMS), the harmonic content of the current, and the phase of the current in its associated medium voltage overhead line.

99. A monitoring device (1) as claimed in claim 97 in which one of the measurement sensors has means to receive the measurements from the other two measurement sensors and based on the received measurements and its own measured values has means to calculate one or more of the instantaneous balance current, I_B, the zero sequence current, I_O, and the ground current I_G.

100. A monitoring device (1) as claimed in claim 99 in which the measurement device that has a means to receive the measurements from the other two devices further comprises means to perform one or more of the following operations:

(a) measure the RMS value of I_G,

(b) measure the amplitude and phase of I_G,

(c) measure the harmonic content of I_G,

(d) filter the I_G signal,

(e) compare I_G to a predetermined set of thresholds,

(f) determine the duration of an over-threshold condition and

(g) generate and transmit a status report to the control centre.

88. A monitoring device (1) for monitoring the electrical properties of a medium voltage overhead line (3) in a medium voltage network, the monitoring device comprising means to measure the electrical properties of the medium voltage line and means to communicate the measured electrical properties to a control centre computer of the medium voltage network;

the monitoring device comprises three separate measurement sensors (2a, 2b, 2c), each measurement sensor being adapted for direct and electrically insulated connection onto a separate medium voltage overhead line (3a, 3b, 3c);

each measurement sensor having means to measure (4) the electrical properties of its respective medium voltage overhead line;

each measurement sensor having means to communicate (6) with at least one of the control centre computer and another measurement sensor, at least one of the measurement sensors having means to communicate with the control centre computer;

the three measurement sensors further comprise a master sensor and two slave sensors, each of the slave sensors having means to communicate data to and from the master sensor and the master sensor having means to communicate with the control centre computer; and

in which the master sensor further comprises a processor (5) for processing data received from each of the slave sensors before transmitting electrical properties data onwards to the control centre computer.

89. A monitoring device (1) as claimed in claim 88, in which each measurement sensor has a processor for processing the measured electrical properties of its respective medium voltage overhead line.

90. A monitoring device (1) as claimed in claim 88, in which there is provided means to synchronise the three measurement sensors (2a, 2b, 2c).

91. A monitoring device (1) as claimed in claim 88, in which each monitoring device has means to draw operating power directly from the magnetic field of the medium voltage overhead line.

92. A monitoring device (1) as claimed in claim 91 in which each measurement sensor has the means to draw operating power directly from the magnetic field of the medium voltage overhead line.

93. A monitoring device (1) as claimed in claim 92 in which the means to draw operating power directly from the magnetic field of the medium voltage overhead line comprises a magnetic field pick up coil.

94. A monitoring device (1) as claimed in claim 91 in which each measurement sensor has means to draw operating power directly from the electric field of the medium voltage overhead line.

95. A monitoring device (1) as claimed in claim 94 in which the means to draw operating power directly from the electric field of the medium voltage overhead line comprises foil plates for electric field pickup.

96. A monitoring device (1) as claimed in claim 88 in which each measurement sensor'"'"'s means to measure the electrical properties of its associated medium voltage line further comprises a current measurement device.

98. A monitoring device (1) as claimed in claim 88, in which any three adjacent measurement sensors may be combined to form arbitrary triplets to form a monitoring device.

101. A monitoring device (1) as claimed in claim 88 in which the three measurement sensors further comprise a master sensor and two slave sensors, the master sensor having means to communicate with the control centre, means to receive measurements from the slave sensors and a processor to process the measurements prior to transmission to the control centre.

102. A monitoring device (1) as claimed in claim 88 in which each measurement sensor samples the current flowing in its associated medium voltage line at a predetermined rate and there is provided means to synchronise the sampling rate of each of the three measurement sensors.

103. A monitoring device (1) as claimed in claim 102 in which the means to synchronise the sampling rate with the other measurement sensors comprises a receiver on each of a pair of the measurement sensors to receive a transmitted synchronisation signal from the third measurement sensor.

104. A monitoring device (1) for monitoring the electrical properties of a medium voltage overhead line (3) in a medium voltage network, the monitoring device comprising means to measure the electrical properties of the medium voltage line and means to communicate the measured electrical properties to a control centre computer of the medium voltage network,

the monitoring device comprises three separate measurement sensors (2a, 2b, 2c), each measurement sensor being adapted for direct and electrically insulated connection onto a separate medium voltage overhead line (3a, 3b, 3c);

each measurement sensor having means to measure (4) the electrical properties of its respective medium voltage overhead line;

each measurement sensor having means to communicate (6) with at least one of the control centre computer and another measurement sensor, at least one of the measurement sensors having means to communicate with the control centre computer;

the three measurement sensors further comprise a master sensor and two slave sensors, each of the slave sensors having means to communicate data to and from the master sensor and the master sensor having means to communicate with the control centre computer;

each monitoring device has means to draw operating power directly from the magnetic field of the medium voltage overhead line; and

each measurement sensor has means to draw operating power directly from the electric field of the medium voltage overhead line.

105. A monitoring device (1) as claimed in claim 104, in which the master sensor further comprises a processor (5) for processing data received from each of the slave sensors before transmitting electrical properties data onwards to the control centre computer.

106. A monitoring device (1) as claimed in claim 104, in which each measurement sensor has a processor for processing the measured electrical properties of its respective medium voltage overhead line.

107. A monitoring device (1) as claimed in claim 104, in which there is provided means to synchronise the three measurement sensors (2a, 2b, 2c).

108. A monitoring device (1) as claimed in claim 104 in which each measurement sensor has the means to draw operating power directly from the magnetic field of the medium voltage overhead line.

109. A monitoring device (1) as claimed in claim 104 in which the means to draw operating power directly from the electric field of the medium voltage overhead line comprises foil plates for electric field pickup.

110. A monitoring device (1) as claimed in claim 104 in which each measurement sensor has means to measure one or more of the instantaneous current, (I_C), the peak current, (I_Pk), the root-mean square (RMS) current, (I_RMS), the harmonic content of the current, and the phase of the current in its associated medium voltage overhead line.

111. A monitoring device (1) as claimed in claim 104, in which any three adjacent measurement sensors may be combined to form arbitrary triplets to form a monitoring device.

112. A monitoring device (1) as claimed in claim 110 in which one of the measurement sensors has means to receive the measurements from the other two measurement sensors and based on the received measurements and its own measured values has means to calculate one or more of the instantaneous balance current, I_B, the zero sequence current, I_O, and the ground current I_G.

113. A monitoring device (1) as claimed in claim 112 in which the measurement device that has a means to receive the measurements from the other two devices further comprises means to perform one or more of the following operations:

(a) measure the RMS value of I_G,

(b) measure the amplitude and phase of I_G,

(c) measure the harmonic content of I_G,

(d) filter the I_G signal,

(e) compare I_G to a predetermined set of thresholds,

(f) determine the duration of an over-threshold condition and

(g) generate and transmit a status report to the control centre.

114. A monitoring device (1) as claimed in claim 104 in which each measurement sensor samples the current flowing in its associated medium voltage line at a predetermined rate and there is provided means to synchronise the sampling rate of each of the three measurement sensors.

115. A monitoring device (1) as claimed in claim 114 in which the means to synchronise the sampling rate with the other measurement sensors comprises a receiver on each of a pair of the measurement sensors to receive a transmitted synchronisation signal from the third measurement sensor.

116. A monitoring device (1) for monitoring the electrical properties of a medium voltage overhead line (3) in a medium voltage network, the monitoring device comprising means to measure the electrical properties of the medium voltage line and means to communicate the measured electrical properties to a control centre computer of the medium voltage network,

the monitoring device comprises three separate measurement sensors (2a, 2b, 2c), each measurement sensor being adapted for direct and electrically insulated connection onto a separate medium voltage overhead line (3a, 3b, 3c);

each measurement sensor having means to measure (4) the electrical properties of its respective medium voltage overhead line;

each measurement sensor having means to communicate (6) with at least one of the control centre computer and another measurement sensor, at least one of the measurement sensors having means to communicate with the control centre computer;

the three measurement sensors further comprise a master sensor and two slave sensors, each of the slave sensors having means to communicate data to and from the master sensor and the master sensor having means to communicate with the control centre computer; and

each measurement sensor has means to measure one or more of the instantaneous current, (I_C), the peak current, (I_Pk), the root-mean square (RMS) current, (I_RMS), the harmonic content of the current, and the phase of the current in its associated medium voltage overhead line.

117. A monitoring device (1) as claimed in claim 116, in which the master sensor further comprises a processor (5) for processing data received from each of the slave sensors before transmitting electrical properties data onwards to the control centre computer.

118. A monitoring device (1) as claimed in claim 116, in which each measurement sensor has a processor for processing the measured electrical properties of its respective medium voltage overhead line.

119. A monitoring device (1) as claimed in claim 116, in which there is provided means to synchronise the three measurement sensors (2a, 2b, 2c).

120. A monitoring device (1) as claimed in claim 116 in which each measurement sensor has the means to draw operating power directly from the magnetic field of the medium voltage overhead line.

121. A monitoring device (1) as claimed in claim 116 in which each measurement sensor has means to draw operating power directly from the electric field of the medium voltage overhead line.

122. A monitoring device (1) as claimed in claim 116, in which each measurement sensor has means to calculate the phase element of the peak current using the formula:

$I_p=\frac{1}{N}·<br><br>\underset{0}{\overset{N}{\sum <br><br>}}<br><br>f<br><br>\left(n\right)·<br><br>\cos <br><br>\left({\mathrm{\omega <br><br>}}_0<br><br>n\right)$

123. A monitoring device (1) as claimed in claim 116, in which each measurement sensor has means to calculate the quadrature element of the peak current using the formula:

$I_q=\frac{1}{N}·<br><br>\underset{0}{\overset{N}{\sum <br><br>}}<br><br>f<br><br>\left(n\right)·<br><br>\sin <br><br>\left({\mathrm{\omega <br><br>}}_0<br><br>n\right)$

124. A monitoring device (1) as claimed in claim 116, in which each measurement sensor has means to filter instantaneous current values and compare the instantaneous current values with peak current values for re-striking earth fault detection.

125. A monitoring device (1) as claimed in claim 116, in which each measurement sensor has means to compare the output of the sine/cosine functional block on a cycle by cycle basis with averaged values from the same source for detection of re-striking earth faults.

126. A monitoring device (1) as claimed in claim 116 in which one of the measurement sensors has means to receive the measurements from the other two measurement sensors and based on the received measurements and its own measured values has means to calculate one or more of the instantaneous balance current, I_B, the zero sequence current, I_O, and the ground current I_G.

127. A monitoring device (1) as claimed in claim 126 in which the measurement device that has a means to receive the measurements from the other two devices further comprises means to perform one or more of the following operations:

(a) measure the RMS value of I_G,

(b) measure the amplitude and phase of I_G,

(c) measure the harmonic content of I_G,

(d) filter the I_G signal,

(e) compare I_G to a predetermined set of thresholds,

(f) determine the duration of an over-threshold condition and

(g) generate and transmit a status report to the control centre.

128. A monitoring device (1) as claimed claim 116 in which each measurement sensor samples the current flowing in its associated medium voltage line at a predetermined rate and there is provided means to synchronise the sampling rate of each of the three measurement sensors.

129. A monitoring device (1) as claimed in claim 128 in which the means to synchronise the sampling rate with the other measurement sensors comprises a receiver on each of a pair of the measurement sensors to receive a transmitted synchronisation signal from the third measurement sensor.

130. A monitoring device (1) for monitoring the electrical properties of a medium voltage overhead line (3) in a medium voltage network, the monitoring device comprising means to measure the electrical properties of the medium voltage line and means to communicate the measured electrical properties to a control centre computer of the medium voltage network;

the monitoring device comprises three separate measurement sensors (2a, 2b, 2c), each measurement sensor being adapted for direct and electrically insulated connection onto a separate medium voltage overhead line (3a, 3b, 3c);

each measurement sensor having means to measure (4) the electrical properties of its respective medium voltage overhead line;

each measurement sensor having means to communicate (6) with at least one of the control centre computer and another measurement sensor, at least one of the measurement sensors having means to communicate with the control centre computer;

the three measurement sensors further comprise a master sensor and two slave sensors, each of the slave sensors having means to communicate data to and from the master sensor and the master sensor having means to communicate with the control centre computer;

and in which any three adjacent measurement sensors may be combined to form arbitrary triplets to form a monitoring device.

131. A monitoring device (1) as claimed in claim 130, in which the master sensor further comprises a processor (5) for processing data received from each of the slave sensors before transmitting electrical properties data onwards to the control centre computer.

132. A monitoring device (1) as claimed in claim 130, in which each measurement sensor has a processor for processing the measured electrical properties of its respective medium voltage overhead line.

133. A monitoring device (1) as claimed in claim 130, in which there is provided means to synchronise the three measurement sensors (2a, 2b, 2c).

134. A monitoring device (1) as claimed in claim 130, in which each measurement sensor has means to filter instantaneous current values and compare the instantaneous current values with peak current values for re-striking earth fault detection.

135. A monitoring device (1) as claimed in claim 130 in which one of the measurement sensors has means to receive the measurements from the other two measurement sensors and based on the received measurements and its own measured values has means to calculate one or more of the instantaneous balance current, I_B, the zero sequence current, I_O, and the ground current I_G.

136. A monitoring device (1) as claimed in claim 135 in which the measurement device that has a means to receive the measurements from the other two devices further comprises means to perform one or more of the following operations:

(a) measure the RMS value of I_G,

(b) measure the amplitude and phase of I_G,

(c) measure the harmonic content of I_G,

(d) filter the I_G signal,

(e) compare I_G to a predetermined set of thresholds,

(f) determine the duration of an over-threshold condition and

(g) generate and transmit a status report to the control centre.

137. A monitoring device (1) as claimed in claim 130 in which the three measurement sensors further comprise a master sensor and two slave sensors, the master sensor having means to communicate with the control centre, means to receive measurements from the slave sensors and a processor to process the measurements prior to transmission to the control centre.

138. A monitoring device (1) as claimed in claim 130 in which each measurement sensor samples the current flowing in its associated medium voltage line at a predetermined rate and there is provided means to synchronise the sampling rate of each of the three measurement sensors.

139. A monitoring device (1) as claimed in claim 138 in which the means to synchronise the sampling rate with the other measurement sensors comprises a receiver on each of a pair of the measurement sensors to receive a transmitted synchronisation signal from the third measurement sensor.

140. A monitoring device (1) for monitoring the electrical properties of a medium voltage overhead line (3) in a medium voltage network, the monitoring device comprising means to measure the electrical properties of the medium voltage line and means to communicate the measured electrical properties to a control centre computer of the medium voltage network;

the monitoring device comprises three separate measurement sensors (2a, 2b, 2c), each measurement sensor being adapted for direct and electrically insulated connection onto a separate medium voltage overhead line (3a, 3b, 3c);

each measurement sensor having means to measure (4) the electrical properties of its respective medium voltage overhead line;

each measurement sensor having means to communicate (6) with at least one of the control centre computer and another measurement sensor, at least one of the measurement sensors having means to communicate with the control centre computer;

the three measurement sensors further comprise a master sensor and two slave sensors, each of the slave sensors having means to communicate data to and from the master sensor and the master sensor having means to communicate with the control centre computer;

each measurement sensor has means to measure one or more of the instantaneous current, (I_C), the peak current, (I_Pk), the root-mean square (RMS) current, (I_RMS), the harmonic content of the current, and the phase of the current in its associated medium voltage overhead line; and

in which one of the measurement sensors has means to receive the measurements from the other two measurement sensors and based on the received measurements and its own measured values has means to calculate one or more of the instantaneous balance current, I_B, the zero sequence current, I_O, and the ground current I_G.

141. A monitoring device (1) as claimed in claim 140, in which the master sensor further comprises a processor (5) for processing data received from each of the slave sensors before transmitting electrical properties data onwards to the control centre computer.

142. A monitoring device (1) as claimed in claim 140, in which each measurement sensor has a processor for processing the measured electrical properties of its respective medium voltage overhead line.

143. A monitoring device (1) as claimed in claim 140, in which there is provided means to synchronise the three measurement sensors (2a, 2b, 2c).

144. A monitoring device (1) as claimed in claim 140, in which each measurement sensor has means to calculate the phase element of the peak current using the formula:

$I_p=\frac{1}{N}·<br><br>\underset{0}{\overset{N}{\sum <br><br>}}<br><br>f<br><br>\left(n\right)·<br><br>\cos <br><br>\left({\mathrm{\omega <br><br>}}_0<br><br>n\right)$

145. A monitoring device (1) as claimed in claim 140, in which each measurement sensor has means to calculate the quadrature element of the peak current using the formula:

$I_q=\frac{1}{N}·<br><br>\underset{0}{\overset{N}{\sum <br><br>}}<br><br>f<br><br>\left(n\right)·<br><br>\sin <br><br>\left({\mathrm{\omega <br><br>}}_0<br><br>n\right)$

146. A monitoring device (1) as claimed in claim 140, in which any three adjacent measurement sensors may be combined to form arbitrary triplets to form a monitoring device.

147. A monitoring device (1) as claimed in claim 140, in which each measurement sensor has means to filter instantaneous current values and compare the instantaneous current values with peak current values for re-striking earth fault detection.

148. A monitoring device (1) as claimed in claim 140 in which each measurement sensor has means to compare the output of the sine/cosine functional block on a cycle by cycle basis with averaged values from the same source for detection of re-striking earth faults.

149. A monitoring device (1) as claimed in claim 140 in which the measurement device that has a means to receive the measurements from the other two devices further comprises means to perform one or more of the following operations:

(a) measure the RMS value of I_G,

(b) measure the amplitude and phase of I_G,

(c) measure the harmonic content of I_G,

(d) filter the I_G signal,

(e) compare I_G to a predetermined set of thresholds,

(f) determine the duration of an over-threshold condition and

(g) generate and transmit a status report to the control centre.

150. A monitoring device (1) as claimed in claim 140 in which the three measurement sensors further comprise a master sensor and two slave sensors, the master sensor having means to communicate with the control centre, means to receive measurements from the slave sensors and a processor to process the measurements prior to transmission to the control centre.

151. A monitoring device (1) as claimed in claim 140 in which each measurement sensor samples the current flowing in its associated medium voltage line at a predetermined rate and there is provided means to synchronise the sampling rate of each of the three measurement sensors.

152. A monitoring device (1) as claimed in claim 151 in which the means to synchronise the sampling rate with the other measurement sensors comprises a receiver on each of a pair of the measurement sensors to receive a transmitted synchronisation signal from the third measurement sensor.

153. A monitoring device (1) for monitoring the electrical properties of a medium voltage overhead line (3) in a medium voltage network, the monitoring device comprising means to measure the electrical properties of the medium voltage line and means to communicate the measured electrical properties to a control centre computer of the medium voltage network;

the monitoring device comprises three separate measurement sensors (2a, 2b, 2c), each measurement sensor being adapted for direct and electrically insulated connection onto a separate medium voltage overhead line (3a, 3b, 3c);

each measurement sensor having means to measure (4) the electrical properties of its respective medium voltage overhead line;

each measurement sensor having means to communicate (6) with at least one of the control centre computer and another measurement sensor, at least one of the measurement sensors having means to communicate with the control centre computer;

in which the three measurement sensors further comprise a master sensor and two slave sensors, the master sensor having means to communicate with the control centre, means to receive measurements from the slave sensors and a processor to process the measurements prior to transmission to the control centre.

154. A monitoring device (1) as claimed in claim 153, in which each measurement sensor has a processor for processing the measured electrical properties of its respective medium voltage overhead line.

155. A monitoring device (1) as claimed in claim 153, in which there is provided means to synchronise the three measurement sensors (2a, 2b, 2c).

156. A monitoring device (1) as claimed in claim 153 in which each measurement sensor has the means to draw operating power directly from the magnetic field of the medium voltage overhead line.

157. A monitoring device (1) as claimed in claim 153 in which each measurement sensor has means to draw operating power directly from the electric field of the medium voltage overhead line.

158. A monitoring device (1) as claimed in claim 153 in which each measurement sensor has means to measure one or more of the instantaneous current, (I_C), the peak current, (I_Pk), the root-mean square (RMS) current, (I_RMS), the harmonic content of the current, and the phase of the current in its associated medium voltage overhead line.

159. A monitoring device (1) as claimed in claim 153, in which any three adjacent measurement sensors may be combined to form arbitrary triplets to form a monitoring device.

160. A monitoring device (1) as claimed in claim 158 in which one of the measurement sensors has means to receive the measurements from the other two measurement sensors and based on the received measurements and its own measured values has means to calculate one or more of the instantaneous balance current, I_B, the zero sequence current, I_O, and the ground current I_G.

161. A monitoring device (1) as claimed in claim 160 in which the measurement device that has a means to receive the measurements from the other two devices further comprises means to perform one or more of the following operations:

(a) measure the RMS value of I_G,

(b) measure the amplitude and phase of I_G,

(c) measure the harmonic content of I_G,

(d) filter the I_G signal,

(e) compare I_G to a predetermined set of thresholds,

(f) determine the duration of an over-threshold condition and

(g) generate and transmit a status report to the control centre.

162. A monitoring device (1) as claimed in claim 153 in which each measurement sensor samples the current flowing in its associated medium voltage line at a predetermined rate and there is provided means to synchronise the sampling rate of each of the three measurement sensors.

163. A monitoring device (1) as claimed in claim 162 in which the means to synchronise the sampling rate with the other measurement sensors comprises a receiver on each of a pair of the measurement sensors to receive a transmitted synchronisation signal from the third measurement sensor.

164. A system for monitoring a medium voltage network comprising a plurality of medium voltage overhead lines, the system comprising a control centre computer (24) and a plurality of remote monitoring devices (1) distributed throughout the medium voltage network, each of the monitoring devices having means to measure the electrical properties of a medium voltage overhead line and means to communicate the measured electrical properties to the control centre computer, each monitoring device further comprises three measurement sensors (2a, 2b, 2c), each measurement sensor being mounted directly on a separate medium voltage overhead line (3a, 3b, 3c) to the other two measurement sensors and each measurement sensor having means to measure the electrical properties of its respective medium voltage line, each measurement sensor has communication means for communication with at least one of the control centre computer (24) and another measurement sensor, at least one of the measurement sensors having means to communicate with the control centre computer and in which the three measurement sensors further comprise a master sensor and two slave sensors, each of the slave sensors having means to communicate data to and from the master sensor and the master sensor having means to communicate with the control centre computer.

165. A system as claimed in claim 164 in which there are provided a plurality of Data Acquisition Communicators (DACs) (22) intermediate the control centre computer and the plurality of monitoring devices, each Data Acquisition Communicator having a plurality of monitoring devices associated therewith so that electrical properties data sent from a monitoring device to the control centre computer is sent to the relevant DAC (22) before being transferred from the relevant DAC to the control centre computer.

166. A system as claimed in claim 164 in which one of the measurement sensors further comprises a processor for processing the measured electrical signals from all three measurement sensors before transmitting the processed data to the control centre computer.

167. A system as claimed in claim 165, in which the DAC'"'"'s are further provided with a processor to process the electrical properties data, prior to transmitting the data onwards to the control centre computer.

168. A system as claimed in claim 165 in which electrical properties data is sent from the DAC to the control centre computer over a GSM link.

169. A system as claimed in claim 165 in which there are provided repeaters intermediate a DAC and one or more of it'"'"'s associated monitoring devices to amplify any communications to and from the DAC and the monitoring device.

170. A system as claimed in claim 167 in which each monitoring device may act as a repeater for another monitoring device in the system.

171. A system as claimed in claim 164 in which each of the measurement sensors is powered directly from the medium voltage line upon which it is mounted.

172. A system as claimed in claim 171 in which each measurement sensor has means to draw operating power directly from the magnetic field of the medium voltage overhead line.

173. A system as claimed in claim 171 in which the measurement sensors has means to draw operating power directly from the electrical field of the medium voltage overhead line.

174. A system as claimed in claim 164 in which the measured electrical signals are processed and in which the phase element of the peak current is calculated using the formula:

$I_p=\frac{1}{N}·<br><br>\underset{0}{\overset{N}{\sum <br><br>}}<br><br>f<br><br>\left(n\right)·<br><br>\cos <br><br>\left({\mathrm{\omega <br><br>}}_0<br><br>n\right)$

175. A system as claimed in claim 164, in which the measured electrical signals are processed and in which the quadrature element of the peak current is calculated using the formula:

$I_q=\frac{1}{N}·<br><br>\underset{0}{\overset{N}{\sum <br><br>}}<br><br>f<br><br>\left(n\right)·<br><br>\sin <br><br>\left({\mathrm{\omega <br><br>}}_0<br><br>n\right)$

176. A system as claimed in claim 164, in which any three adjacent measurement sensors may be combined to form arbitrary triplets to form a variety of detectors.

177. A system as claimed in claim 164, in which instantaneous current values are filtered and compared with typical peak values of current and these values are transmitted to the DAC for re-striking earth fault detection.

178. A system as claimed in claim 164, in which the output of the sine/cosine functional block is compared on a cycle by cycle basis with averaged values from the same source and the results of the comparison are transmitted to the DAC for detection of re-striking earth faults.