As the electric infrastructures evolved, the wire and cable industry evolved too and the wire and cables were categorized into 3 categories: low, medium, and high voltage with different specifications. Because homes, businesses, and industries all over the world are becoming more reliant on energy to power their operations, there is an increasing demand for power infrastructure that is dependable and effective. This calls for innovative systems that can manage bigger loads while maintaining acceptable levels of safety. Cables that operate at medium voltage (MV) are one possible answer. 
The transmission of electrical energy at voltages ranging from 3 kV to 36 kV requires a specific kind of power cable known as a medium voltage cable. High-voltage cables, in contrast to low-voltage cables, are not intended to be erected by private individuals or commercial enterprises. Instead, only licensed electricians and other appropriately trained specialists should be allowed to install them in your home. As an electrician, one of the most important parts of your job is to select the appropriate cable for medium voltage. Power cords that are damaged in any way, shape, or form can result in malfunctioning equipment, fire, and other potentially disastrous consequences. In this piece, we are going to go over the many kinds of high voltage cables as well as the applications for each one. We will also go over some of the fundamental considerations that need to be made when selecting the appropriate cable for your next project from the most reputable suppliers of medium voltage cables. Cables with medium voltage can be used for grounding successfully. Because of the outstanding insulating qualities of the material made of cross-linked polyethylene and the fact that it is firmly bound to both the conductor of the semiconductor material and the insulating shielding layer, the cable has a high level of dependability. 
It is appropriate for use in power plants, industrial plants, and substations. High voltage cables that operate in the voltage range from 3 kV to 36 kV are referred to as having a "medium voltage," and the phrase "medium voltage" defines these cables. Cables that operate at medium voltage are frequently utilized in a variety of applications, including those in the commercial and industrial sectors as well as those in the utility sector. Insulation for medium voltage cables can be produced from a variety of materials, such as paper, oil-filled cables, and cross-linked polyethylene (XLPE). The XLPE cable is the most prevalent variety of medium voltage cable, and it accounts for around 85% of the market share. There are various applications for which high voltage cables are utilized. Cables operating at medium voltage are intended to be installed only by licensed electricians or other appropriately trained specialists. These cables are not designed for usage in either business or domestic settings. There is a wide variety of conductor sizes and insulation classes available for use in medium voltage cables (5 kV, 11kv, 15 kV, 25 kV, and 35 kV). In addition, there are three primary varieties of cables used to carry medium voltage. Each type of cable used for medium voltage has a set of benefits and applications that are exclusively its own. Medium voltage cables with a single conductor or three conductors are two examples of this type of cable. Copper and aluminum are the most common metals used in the construction of conductors. For further strength, the cables are reinforced with steel strips and wires. 
Medium voltage wire specifications
The specifications of each medium rate voltage cable and wire can be affected by some factors which make them suitable for different applications. According to national and international standards, one of the ways to distinguish different types of cables is according to rated voltage and working voltage. According to the requirements of Iranian National Standard No. 3569 or its international equivalent IEC 60502, cables are divided into the following groups according to voltage: Low-voltage cables - voltage range up to 1 kV Medium voltage cables - voltage range up to 30 kV High-voltage cables - Voltage category Above 30 kV There is no doubt that the structure of the cable and the number of layers used varies at different levels and levels, but generally the following layers are observed in the structure of the product: Conductor Semiconductor layer Insulation, mainly XLPE or XLPE type Semiconductor layer on the insulator Graphite paper Copper shield Mechanical protection layer Cover over 
The main difference between medium voltage cable construction and low voltage cable construction is the presence of inner and outer semiconducting layers and the semiconducting ribbons in the medium voltage cable. As the voltage level increases, the electric field also increases. If the insulation is placed on an uneven surface (such as a stranded conductor), the depression of the conductor wires in the insulation can increase the electric field stress in the insulation. Furthermore, the electric field distribution around the conductor will not be uniform. In fact, the semiconducting layer in this type of cable is used to prevent partial discharges from occurring at the interface between the insulating layer and the conductor and between the insulating layer and the shielding layer. This layer also regulates electrical voltage in the insulating surfaces and prevents partial discharge (corona) in the conductors and the insulating surfaces by maintaining close contact between the inner and outer surfaces of the insulation. In addition, the semiconductor layer also has a protective effect against damage caused by the heating of the conductor during a short circuit. The voltage range for medium voltage cables is 6 kV to 30 kV. Such cables are manufactured in copper and aluminum types in single and triple strands. Medium voltage cables are used to power commercial or residential buildings and industrial distribution circuits. These cables are for indoor use, installed in buildings in accordance with relevant regulations, can be used in channels or trenches, buried directly in dry or wet soil and used in cable trays in industrial buildings, switchboards and power plants. Also suitable for mounting in an open place. Medium voltage cables are designed and manufactured to IEC or BS standards with copper or aluminum conductors and are available in single or triple core types. These cables are produced with XLPE or TR-XLPE insulation. As can be seen in the picture of a single strand medium voltage cable, this cable consists of several layers, which will be examined in detail below. Cable conductors are made of annealed copper or aluminium. In general, various designs are used in the construction of conductors, the most common of which are conventional compact irradiated conductors and multi-component conductors (Milliken). According to the diagram above, the conductor in a twisted circular or regularly twisted construction consists of a set of round wires twisted together, usually with one wire in the middle, and six wires twisted around it in the first layer, the larger part being twelve wires, which is radiated to the first layer and this structure is repeated in the same way in the next layer. To eliminate the gap between wires that causes discharge and reduce cable life, and to minimize the materials used in the cable, they compress the conductors. 
In a Milliken or multi-component leadership structure, the leaders in each layer are regularly arranged in each sector according to the diagram above. The distance between the strands causes their distance to the center to vary along the length of the conductor. Reduction of the skin effect is one of the advantages of this conductor structure. Conductor shielding is also a semi-conductive compound extruded onto the conductor, which reduces the electric field strength between the XLPE insulation and the conductor. Medium voltage cable insulation is made of XLPE of suitable thickness to meet the electrical and physical requirements specified by IEC, BS and other cable design standards. The insulation must be of high quality and resistant to heat and moisture, and the cable insulation must be installed in wet and dry locations with temperatures above 90°C under normal conditions and 130°C and 250°C under emergency overload conditions. Grade must be suitable for short circuit conditions. At the next level, there is an insulating screen that works in the same way as a conductive screen. The insulating shield must be applied directly to the insulating layer and consists of a semiconducting composition extruded onto the insulating layer. When the voltage reaches tens of thousands or even hundreds of kilovolts, a metal shield is required to neutralize the electric field outside the cable. Shielding is located in the cable structure and its purposes include returning capacitor charging currents, conducting ground fault currents in the event of a fault until the system shuts down, reducing electrical effects in the surrounding cable during ground faults, and protecting against accidental contact.
Medium voltage cable specifications
Medium rate voltage wire and cable are used in a variety of applications with different specifications, including industrial and commercial environments and the utility sector. Industrial use: Medium voltage cables are commonly used in industrial applications such as manufacturing plants and oil refineries. These cables are designed to withstand harsh conditions, including exposure to chemicals and high temperatures. Medium voltage cables are also often used in industrial environments where there is a risk of physical damage. In particular, tray cables are often used in these applications. Commercial application: Medium voltage cables are also used in commercial applications such as office buildings and retail stores. These cables are typically used for lighting and power distribution. Flexible medium voltage cables are often used in these applications to facilitate installation. The supply sector: Applications in the utility sector, such as power transmission and distribution, constitute the largest market for medium voltage cables. These cables carry electricity from power plants to homes and businesses. When selecting medium voltage cables for these applications, the capacity of the medium voltage cable must be carefully considered. 
Medium voltage cables are also used in a number of other applications, including renewable energy and the military. Renewable energy: Medium voltage cables are used in various renewable energy applications such as solar and wind energy. These cables are designed to withstand exposure to the elements and provide reliable power transmission. Army: Medium voltage cables are also used in military applications. These cables must be able to withstand harsh conditions, including exposure to extreme temperatures and physical damage. Dimensioning of medium voltage cables is essential to ensure that the cable can safely transmit the required current. When calculating the size of medium voltage cables, the following points must be taken into account: Data Collection: The first step in calculating MV sizing is to collect all relevant data such as cable length and rating, ambient conditions, required load, voltage type, power factor and required conductor type. Determine the current-carrying capacity of the cable: The next step is to determine the current-carrying capacity of the cable. This can be done by determining the voltage drop and cable reactance, which gives you the required current carrying capacity of the cable. Choose a cable with a larger cross-sectional area for minimal resistive losses. Determination of the voltage drop: Once the current carrying capacity has been determined, the voltage drop can be calculated using the following equation: V = I × R where V is the voltage drop, I is the current value of the cable, and R is the resistance per length unit. Current and resistance are the two main causes of voltage drop. 
Calculate the cable size: After determining the current carrying capacity and voltage drop, the next step is to select the appropriate cable size. The most important factor to consider when choosing a high voltage power cable size is the current carrying capacity of the 5kv cable or the current carrying capacity of the cable. The minimum size of the cable under short-circuit conditions can be calculated using the following formula: A = √(i2t) / k Where A is the minimum size of the cable, i is the short-circuit current, t is the short-circuit time in seconds, and k is the short-circuit temperature constant. Ground fault loop impedance: The ground fault loop impedance should also be taken into account when sizing medium voltage cables. Earth fault protection is important to trip to avoid any accident. It can be calculated using the following equation: IA = V0/Z0 By taking all of the above into consideration, you can calculate exactly the size of medium voltage cable you will need for your project.