Skip to main content

ADVANTAGES OF SHIELDED CABLES


ADVANTAGES OF SHIELDED CABLES
What are the known advantages of using shielded cables?

Electrical insulation surrounding a conductor creates a capacitor when the conductor is electrically energized. Thus, all insulated conductors are capacitors.

In the majority of non-shielded cable systems, thecable surface makes intermittent contact with an electrical ground. Where intimate contact with this ground is not made, the intervening air spaces also act primarily as capacitors in ac circuits and as resistors in dc circuits. This forms a series of cable dielectric and air dielectric. Voltage across this circuit varies along the length of the cable depending on the voltage across the air gap. The cable surface becomes a floating voltage point in a voltage divider. This floating point voltage can vary considerably, depending on the cable design and the characteristics of the air gap. If the voltage is high enough, the cable surface can experience detrimental surface tracking of arcing discharges to electrical ground. The cable surface can also become potentially hazardous causing an electrical shock if contacted by field personnel.

Shielding the cable insulation surface and grounding of this shielding eliminates tracking and arcing discharges. The grounding of this shield prevents the accumulation of an electrical potential on the surface of the cable that could be hazardous to any individual that comes into contact with the cable surface.

Comments

Popular posts from this blog

PARTS OF A POWER TRANSFORMER

What are the name of the basic parts of a Power Transformer? We can not deny the fact that only a handful of electrical engineering students are presently familiar with power transformers especially on what it looks like. Unlike a transformer we found in our homes, a power transformer’s appearance and construction is somewhat more complicated. It is not just a simple winding with a primary and secondary terminal although basically any transformer has one. The function that a power transformer plays in an electrical system is very important that an electric utility can not afford to loss it during its operation. Our discussion here will focus more on the basic parts and functions of a power transformer that are usually tangible whenever you go to a substation . Although not all power transformers are identical, nonetheless they all have the following listed parts in which the way of construction may differ.

ELECTRIC MOTOR FRAME SIZE STANDARD SPECIFICATIONS

ELECTRIC MOTOR FRAME SIZE STANDARD SPECIFICATIONS How is electric motor frame size being specified? Motor frame dimensions have been standardized with a uniform frame size numbering system. This system was developed by NEMA and specific frame sizes have been assigned to standard motor ratings based on enclosure, horsepower and speed. The current standardized frames for integral horsepower induction motors ranges from 143T to 445T. These standards cover most motors in the range of one through two hundred horsepower. Typical example of where you can locate the frame is shown in Fig 1.2.D – Frame No. The numbers used to designate frame sizes have specific meanings based on the physical size of the motor. Some digits are related to the motor shaft height and the remaining digit or digits relate to the length of the motor. The rerate, or frame size reduction programs were brought about by advancements in motor technology relating mainly to higher temperature ratings of insulating mate

ELECTRIC MOTOR NAMEPLATE SPECIFICATIONS

How do we interpret an electric motor nameplate? Motor standards are established on a country by country basis.Fortunately though, the standards can be grouped into two major categories: NEMA and IEC (and its derivatives). In North America, the National Electric Manufacturers Association (NEMA) sets motor standards, including what should go on the nameplate (NEMA Standard MG 1-10.40 "Nameplate Marking for Medium Single-Phase and Polyphase Induction Motors").