CDR – High Voltage Cables Defects Monitoring and Diagnostic System
Introduction of cables with rated voltage 110 kV and more is need in operative condition diagnostics especially online monitoring.
There are two types of monitoring systems of high voltage cables: on the basis of thermal monitoring or PD measuring and analyzing in the insulation. The first way is more useful for cables thermal load monitoring; the second way has maximal sensitivity for defect diagnostics. Using complex monitoring system with two these ways is optimal.
Device «CDR» (Cables Diagnostics Relay) produced by DIMRUS Company is matched to these demands. This device is used for creation monitoring system of condition and search defects of high voltage cables insulation.
The «CDR» system makes:
- Continuous monitoring of high voltage cables insulation condition on the basis of measuring and analyzing PD level and distribution; detecting type of defect in the insulation and its development level.
- Automatic location of defect location in the insulation measured by system in the joints and cables. It is in cables with rated voltage.
- Online temperature measurements of the cable terminations.
- Monitoring value of phase shield current passed on cables shield by supplementary current sensor. Appearance of cross current is negative for cables load because of temperature load on insulation.
Two types of sensors can be used with "CDR" system in dependence of cables construction and its mounting
1. «CDR-S» sensors. This is PD and joint temperature sensors mounted on surface of cables. «CDR-S» sensor is flexible metalize ring with width up to 200 mm. Surface of cable near joints and terminal joints is wrapped by these rings. Thanks to it mounting of cable is simple.
Sensor has maximal sensitivity to near locating defects because it operates in UHF frequency range. It will measure PD in joint correctly, but has low sensitivity to remote defects. It is because of intensive damping of high-frequency pulses in the cables.
2. «RFCT-7» sensors. This is current transformer for measuring high-frequency pulses in grounded cables wires. Construction of «RFCT-7» sensor is consisted of two parts easy mounted on conductors of cable screen ground or body of joint. «RFCT-7» sensor is mounted without breaks of grounded circuit.
Sensor operates in HF frequency range because it is sensitive to far defects up to several kilometers. «RFCT-7» sensor has low sensitivity to near defects than «CDR-S» sensor.
Features of PD pulses measuring and analyzing cables in «CDR» system
«CDR» system has 6-channel device for measuring and analyzing cables parameters. It is modern and effective device for PD measuring.
The features are:
- PD pulse measuring in wide frequency range – from 50 kHz to 1 GHz because of PD pulses are reduced by amplitude and degreased by length moved on cables. If pulse is near sensor, its frequency will be high up to several hundred MHz. Frequency of remote pulse can be several hundred kHz. The longer are the cables; the lower is the frequency of measured PD.
- «CDR» system has two modern methods of defects location in the cables insulation. One method is on the basis of reflectogramm analyzing of PD pulses distribution in cables; the second method of analyzing difference between arrival times of high frequency pulse from defect to the ends of monitored cables.
- «CDR» system has expert diagnostics system «PD-Expert». It allows detecting type of defect and stage of its developing. «CDR» system has specific solutions:
At first, PD pulses measuring are made synchronically in 6 measuring channels of «CDR» device. At this case all diagnostic algorithms are used.
At second, if there is need to use monitoring system for several cables, should be used several «CDR» devices. PD measuring synchronization task becomes global.
This synchronization can be made by 2 ways. Synchronization is made by optical line at distance up to 2 km. There will be synchronization pulses sending and information exchanging by this line. If cables length is more than 2 km or there is no possibility for fiber optic, measurements can be synchronized by GPS/GLONASS. Devices have built-in GPS receivers.
Cables monitoring systems with synchronization by optical line
There is circuit of cables monitoring system with two joints in every phase. Monitoring system is consisted of 4 «CDR» devices and computer with special software. Because of not far distance and possibility to optical line, it is used for measuring synchronization.
Cables monitoring system with synchronization by GPS
System with global synchronization is used for long cables condition monitoring. Information transmission is made by usual information channels shown on figure. These are available local network, global network and any alternative channels for information transmission.
Connection of «CDR» system to SCADA system can be made by ways:
- By fiber optic.
- By RS-485 interface.
Software «iNVA» is for monitoring and diagnostics of one or several lines.
Protocol ModBus RTU or IEC 61850 is used for information transmission from monitoring system to the SCADA system.
Specifications of «CDR» system
|Rated voltage of monitored cable line, kV||10 ÷ 500|
|Insulation condition monitoring mode||PD|
|Cables temperature monitoring mode||Pt100|
|Type of cross currents monitoring in cable shield||CT|
|Quantity of cables (phases) monitored by one system||Up to 6|
|Length of monitored cables by one device, m||Up to 6000|
|PD measuring range, MHz||0,1 ÷ 1000,0|
|SCADA connection||RS-485 interface, Optical fiber|
|Synchronization of several devices||GPS, optical fiber|
|Temperature range without heating, °C||-40 ÷ +60|
|System supply voltage, V||AC/DC 120 ÷ 260|
|Device dimensions, mm||400 * 230 * 110|