To comprehend cables system difficulties, you must understand cable construction, properties, and ratings. However, more knowledge is necessary to choose a cable system and ensure its satisfactory operation.
This information could include things like service conditions, the sort of load served, the operation mode and maintenance, and so on.
The key to a cable system’s successful operation is to install it correctly and conduct the necessary maintenance.
The focus of this technical article is on the proper cable selection and use for power distribution and usage.
Importance of choosing the correct control cables
It’s critical to not only choose the right cable for the work but also to grasp the surroundings and the cable’s ampacity. A lack of awareness might lead your cables to fail, bringing your overall structure to a standstill and costing you cash in disruption.
The total pressure, in amperes, that a conductor can carry continually under normal operating conditions without exceeding its temperature rating is ampacity.
Current-carrying capacity is another term for it. A correction factor is a multiplier calculated and used to alter the amount of energy delivered through a cable depending on the quantity of heat emitted while the cable is conducting energy.
How to choose the correct cables?
To apply proper correction factors to a cable’s ampacity value, you must first understand the application for which you can use. This will assist you in determining the correct ampacity correction factor. Select your cable through the following factors:
Cables installation
Depending on the distribution network and the load served, you can employ cables for both outdoor and indoor installations.
A thorough awareness of local circumstances, installation workers, and maintenance workers are necessary. Many times, inappropriate pulling pressures cause cable insulation to damage or deteriorate during installation.
Not only should the number of duct bends and lengths between manholes minimize, but the pulling tensions should also be specified.
Cable construction
The type of cable construction required for a specific installation is part of the selection and implementation of cable. Conductors, cord arrangement, insulation, and final covering are all part of cable construction.
Conductors
Consider all, including Construction quality, ambient conditions, and maintenance, when using conductor materials. Aluminum conductors must meet more severe standards than copper conductors in certain areas.
Cable arrangements
The arrangement of conductors can be in a variety of ways. All types of arrangements have their pros and disadvantages. However, a single conductor is easier to install, and join, and allows multiple-cable circuits to form.
Protected single conductors carry large shield currents, hence take care to avoid the cable overheating.
Insulation
Insulation is usually determined by the type of installation, atmospheric operating temperature, service circumstances, weight served, and other factors. A corrosive atmosphere, insect and rodent threat, availability of oil and solvents, existence of ozone, and freezing weather may all be present in various installations.
Cable operation
The cable’s insulation must be able to withstand both regular and abnormal operation circumstances. As a result, the cable insulation should be set based on the appropriate phase-to-phase voltage and the overall system category, which can divide into three degrees of insulation: 100 percent, 133 percent, and 173 percent.
100 percent
When the system equips with relay protection, which generally clears ground faults within a minute, cables in this category are useful. The grounded systems are the most common name for this category.
133 percent
When the system equips with relay protection, which generally clears ground faults within one hour, cables in this category can be useful. Low resistance ground, or ungrounded systems, are the most common names for this type of system.
173 percent
This category of cables is essential where the necessary time is indefinite. For both ungrounded and resonant grounded systems, this level is suggestive.
Cable size
Concerns with voltage regulation and circuit breaker ratings are commonly overlooked. This error could endanger property and workers, as well as cause the cable to be destroyed. The selection of cable size depends on the following factors:
Current carrying capacity
The thermal heating of a cable determines its current carrying capacity. Tables of current capacity for list cables are available. The current rating of the cable is a specific spacing that allows for thermal transfer. If the spacing where the cable is to be put is smaller, cable de-rating is necessary.
Voltage regulation
Voltage regulation is usually not an issue in properly designed electrical power systems. Properly examine excessive voltage drops to confirm that the load voltage is correct. Check both steady-state voltage regulation and starting voltage regulation in spinning loads.
Short circuit rating
The cable size you select depends on the circuit recovery time in the event of a short circuit. In other words, until the fault could rectify by the switching device, such as a power switch or fuse, the cable should hold without thermal damage.
Shielding
A crucial aspect in the selection and application of medium voltage cables is whether the cable needs protection or not. The following discussion explains the conditions within which you can select shield cables.
Consider the following factors:
- Insulation system type.
- If the neutral system is in-ground or not.
- System criteria for safety and reliability.
When there is no shield or metallic covering on a power system, an electric field is vulnerable partly to air and rest in the insulation system. Surface discharges occur when the electric field is powerful, as it happens in the case of high and medium voltage.
Ozone production takes place when air ionizes, which can degrade some insulations and finish coverings. The external electric lead-in duct-type systems using non-shielded, nonmetallic cable may be high enough to constitute a safety threat to workers working on a single wire in multi-circuit installations.
In situations where people may handle portable cables, wire assemblies, or exposed overhead cable installations.
Conclusion
To conclude, it’s critical to understand the ampacity, application, and purpose of a conversion factor for your cable. It can assist you in selecting the appropriate conductor size for your application and decrease the time and expenses involved with unneeded cord and cable repairs or replacement.
