Several issues should be noted when choosing to use control cables

In order to ensure the control cable in the event of insulation breakdown, mechanical damage, or fire, and reduce the scope of the spread, the national standard GB50217-91 "Power Engineering Cable Design Specification" stipulates: dual protection current, voltage, and DC power supply and trip control loop, etc. 

Two systems that require enhanced reliability should use separate control cables.

After the control cable is put into operation, there is a problem of electrical interference between the different cores of the same cable and between the cables laid in parallel. 

The main causes of electrical interference are: 

(1)Due to the externally applied voltage, the core-to-core capacitive coupling Electrostatic interference is generated under the action.

(2)Electromagnetic induction interference due to the energization current. When there is a high-voltage, high-current interference source nearby, the electrical interference is more serious. 

Because the distance between the cores of the same cable is small, the degree of interference is much greater than that of the parallel line.

For example, the control circuit of a phase-division operated circuit breaker of an ultra-high voltage substation, a three-phase combined cable, has had such an accident, the pulse of the phase separation operation causes the thyristors of other phases to be triggered, and the three-phase linkage is caused by mistake. 

With separate cables, no accidents occurred. Another example is the computer monitoring system of a power plant. 

Since a four-core cable is used to mix the analog low-level signal line with the power line of the transmitter, it has caused a 70V interference voltage on the signal line, which is in millivolts. 

The low-level signal loop will obviously affect regular operation.