Cable control system

Monitoring principle is based on measurement of voltage to earth on cable screen and comparison of this potential to the standard one. Standard voltage is set by resistances built into module.

Internal and external cable insulation resistances are resistive bridge arm. Second arm consists of built-in resistors with preliminarily rated values.

Values of voltage in bridge arms are converted into resistances by the module. If calculated values drop below set ones, insulation resistance reduction signal is initiated.

Data transfer between cable monitoring system and SMTN-3 system central unit is performed via optical fiber. Besides, optical fiber provides galvanic isolation between systems modules for safe device application.

Interface output is applied for serial asynchronous data transfer via fiber optic cable into SMTN-3 system central processing module. Fiber-optic communication components are designed for 1mm fiber optic cable with data transmission rate min. 40 kBaud. Data transmission rate: 38400 Bit/s, 8 Bit, parity checking: 1 stop bit.

Data exchange with SMTN-3 system additionally provides full module state monitoring, measured values transfer, monitoring of measured values in long-term dynamics, providing power cable insulation characteristics degradation monitoring for a long period, allowing to foresee critical cable insulation resistance reduction.

NC/NO relay contacts are used as output signals. Contacts parameters are listed in table. Module involves three contact pairs for signaling:

• voltage availability (at network voltage from +430 V up to +1000 V);
• external insulation fault;
• internal insulation fault;
• cable insulation calculated resistance reduction below setting.

Cables monitoring system module doesn’t require additional external power supply sources, power circuits galvanic isolation, providing therefore more efficient safety.