Cable Sleeves-An overview

Cable Sleeves are used to enclose a single wire or a group of wires.  Cable sleeves are used to arrange a set of wires going through a panel or to an equipment like a motor.  Cable sleeves are made of different materials from braided metals to rubber and even kevlar. 

Sleeves serve to protect the wires and their insulation from sharp edges.  They can protect wires from UV radiation, moisture, oil and temperature. 

In automobiles, special heat resistant sleeves are used to protect the wires from hot surfaces. 

Teflon sleeves have great cut resistance.  Nylon sleeves have great abrasion resistance. 

Sleeves are available in two broad categories depending on the method of installation. 

The first is the slit sleeve which is cut and the wires are inserted into the sleeve.  The second is the wrap-around, side entry type of sleeve. 

Heat Shrinkable Sleeves

Some sleeves are heat shrinkable.  Heat shrinkable sleeves are made of a polymer which contracts when heat is applied. A stream of hot air from a blower is passed on the sleeve.  This results in the sleeves shrinking and wrapping the wires.  

Electrical Safety Mats

Electrical Safety Mats are important safety equipment.  Safety mats protect personnel from electric shock by providing an insulated surface to work on.  If the worker comes in contact with a live conductor by mistake, he will not get an electric shock as his feet are insulated from the ground by the safety mat.

Safety mats come in different colours.  They are usually made of rubber.  The surface of the mats is ribbed to provide an anti-slip surface to workers. 

Safety mats are also designed to resist aging and ozone. 

Safety mats should also be age and fire resistant.

Safety mats come in different voltage ratings.   They should also be resistant to acids and oils. 

The following is the list of mats and their working voltages

 

Class of Mats	Working Voltage	Colour
0	1000	Red
1	7500	White
2	17000	Yellow
3	26500	Green
4	36000	Orange

 

The most common class of safety mats is the type 0 which is rated for a working voltage of 1000 V.

What is a Synchronous Phase Modifier

A synchronous phase modifier is a synchronous motor which is not connected to any load.  The motor can be made to behave like an inductor or a capacitor by decreasing or increasing the excitation. 

Synchronous Phase modifiers are used to regulate the voltage in transmission lines.

Comparison of Series and Shunt Capacitors

Series Capacitors	Shunt Capacitors
Used to reduce the line reactance	Has no impact on the line reactance
Voltage rise only occurs across terminals.	Can be used to raise the line voltage
No effect on system stability	Improves system stability
Does not affect the power factor	Used to improve power factor

What is percentage compensation in Transmission Lines

The ratio of capacitive reactance to the inductive reactance in a transmission line is called the percentage compensation of the Transmission Line.  The inductive reactance is mainly caused by the nature of the load.  The capacitive reactance is caused by the line capacitances and by series capacitors, if any.

Submarine Power Cables

Submarine Power Cables are used to carry power underwater.  They are used to connect small islands with the mainland.  Sometimes, the route through the water is shorter than through land.  Submarine Cables are used for both AC as well as DC transmission. 

AC is used up to 80 km while DC is used for long distance transmission.  Submarine cables are mostly gas filled cables.  The cable laying is done by special ships.  XLPE cables fpr submarine transmission are also available.

AC cables can be laid as three separate cables or as a single 3 phase cable.

Offshore wind farms are connected to the mainland by submarine cables.   

Damage to these cables by shipping is a matter of concern.  The routes which contain submarine cables are specially marked in nautical maps.

Gas Filled Cables

Gas filled cables are used in many applications.  In these cables, the insulation is filled with gas, usually nitrogen.  The inert gas fills up the voids which may form in the insulation.  There are low pressure and high pressure variants in this type of cable. 

The gas is filled in the insulation and is enclosed by means of a sheath.  Since Nitrogen is easily available, any losses can be easily replaced during installation. 

However, the gas has a low dielectric strength.  It cannot be used at very high voltages.  Gas filled cables can be used up to 275 kV.

Oil Filled cables have almost replaced Gas filled cables in recent times.  However, there are situations where oil filled cables cannot be used such as undersea applications and in hilly terrain.