If you can't explain it simply, then you don't know it well enough. — Albert Einstein

Watch Out! Kitchen Appliances Can Be Dangerous If Misused

More than half of the accidental house fires start in the kitchen. Most often homeowners don’t put much thought into how to use their major kitchen appliances on a day-to-day basis. Using them in the right way is necessary to avoid mishaps and accidents. According to the statistics of a survey, an electrical incident kills around 16 Australians every week. So you should always put safety first to avoid any accident that can turn out to be a fatal one. Government records show that the largest number of accidents reported are caused by electricity flaws in homes due to people misusing electrical cooking appliances, including food processors, microwaves, electric stoves, ovens, etc.
In case you need 24/7 emergency electrician to fix any type of electrical defect in your home, you will be contented to know that there are various experts who can help you in this task. Here are certain aspects that can help you for sure to avoid the chances of an accident taking place due to mishandling of electrical appliances.

Hot Heat

Appliances that generate heat must be handled with caution, especially the oven and stove that are frequently used in the kitchen. One among all safety rules that need to be followed in a kitchen is to always be prepared to put out a fire. This means that fire extinguisher should be handy for out-of-control blazes. Keep the baking soda to extinguish grease fires. Remember that using water will only cause a grease fire to spread.
Contact burn is the most common injury linked to the oven and stove, so keeping a first aid kit nearby is always advisable. Moreover, using thick and dry potholders to handle hot items and exercising extra care when children are around is a sound and safe decision. Turing the handles of pots and pans toward the centre of a stove, since children can pull them down if handles face outward.

[Also read: Benifits of upgrading your home HVAC system]

Steam

Dishwashers are considered as a significant appliance used to simplify day-to-day tasks. They also produce a good amount of heat, albeit no flames. The most important safety risk associated with them is the steam that escaped at the time of the heat dry cycle. Yes! Steam can be more dangerous than flames, as it can lead to severe injuries. Furthermore, delicate and stemware glass dishes should be used carefully because they can break inside the machine.
You may cut yourself if you don’t pay attention the time you unload the unit, it can be really dangerous. And if you are unloading a machine after a heat dry cycle, some of them may be too hot to handle specially, if they are made of metals.

Cook or Bake Safely

Using microwave for cooking or banking includes certain key safety precautions, so you need to pay extra attention to avoid any kind of accident. You should only use microwave-safe dishes and containers than metal dishes. Nowadays, these machines are designed to prevent radiation leaks, damage to doors and seals may make this possible. Inspecting microwave timely can be a great way to avoid accidents in a kitchen.
You should be extra careful while heating liquids. If you overheat a liquid, these super-heated ones can explode out of their containers, leading to a scalding spray.
It’s not only the electrical appliances that can be dangerous, even the sockets or wire can also be the reason behind an accident. So, you can’t miss other aspects such as faulty wiring or other problem delivering power to your kitchen. You can contact an experienced and skilled electrician offering after-hours electrical services. Just look for the best one to offer an extra protection to your home.
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Skin effect and Proximity effect

What is skin effect?

When an Alternating Current flows through a conductor, it is not distributed uniformly throughout the conductor cross-section. AC current has a tendency to concentrate near the surface of the conductor. This phenomenon in alternating currents is called as the skin effect. Due to the skin effect, current is concentrated between the outer surface of the conductor and a level called as the skin depth (skin depth is shown by ẟ in the following figure). If the frequency of AC current is very high, the current is restricted to a very thin layer near the conductor surface. Skin effect increases with increase in the frequency.
Due to skin effect, the effective cross-section of the conductor through which the current flows is reduced. Consequently, the effective resistance of the conductor is slightly increased.

skin effect

The cause of skin effect

Imagine a solid conductor split into a large number of strands, each strand carrying a small part of current. The inductance of each strand will vary according to its position. Strands located at the center would be surrounded by a greater magnetic flux and, therefore, will have a larger inductance than those near the surface. Higher inductance (and hence, higher reactance) of the inner strands causes the alternating current to flow through the strands having lower reactance, i.e. near the surface.
The skin effect depends upon the following factors:
  • Conductor material: Better conductors and ferromagnetic materials experience higher skin effect
  • Cross-sectional area of the conductor: skin effect increases with increase in the cross-sectional area
  • Frequency: increases with increase in the frequency
  • Shape of the conductor: skin effect is lesser for stranded conductors than solid conductors

Proximity effect

When two or more conductors carrying alternating current are close to each other, then distribution of current in each conductor is affected due to the varying magnetic field of each other. The varying magnetic field produced by alternating current induces eddy currents in the adjacent conductors. Due to this, when the nearby conductors carrying current in the same direction, the current is concentrated at the farthest side of the conductors. When the nearby conductors are carrying current in opposite direction to each other, the current is concentrated at the nearest parts of the conductors. This effect is called as Proximity effect. The proximity effect also increases with increase in the frequency. Effective resistance of the conductor is increased due to the proximity effect.

proximity effect
Skin effect and proximity effect both are absent in case of DC currents, as frequency of DC current is zero.
[Also read: Corona effect]
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Corona discharge - its effects and methods of reducing it

Electrical power transmission generally deals with very high voltages as a bulk amount of electrical energy has to be transmitted from generating stations to load centers. At this much high voltages, an effect called as corona effect is introduced. As this corona effect results in loss of electrical energy, it is also called as corona discharge.

What is Corona effect in transmission line?

Have you ever heard a hissing noise when standing below a high voltage transmission line? That hissing noise is due to the corona discharge. Corona discharge is usually accompanied by a hissing or cracking audible noise, visual violet glow, production of ozone gas around the conductor, power loss and radio interference.
When a potential difference is applied between two conductors, a potential gradient (or electric field) is set up in the air. This potential gradient is maximum at the surfaces of the conductors. Under the influence of this potential gradient, existing free electrons in the air acquire greater velocities. Some free electrons are always present in the air due to cosmic rays, UV radiations etc.. Greater the applied voltage, greater the potential gradient and, hence, greater the velocity of free electrons.
When the potential gradient at conductor surfaces is large enough (about 30 kV/cm), existing free electrons strike neutral air molecules with enough velocity to dislodge one or more electrons from it. Hence, cumulative ionization of the air near the conductor surfaces occurs. Ionized air is partially conductive. Electric discharge occurs due to the ionized air which results in corona. And if the conductors are close enough to each other, the air insulation breaks down and electric discharge occurs through a spark.
The minimum phase-neutral voltage at which corona starts to occur is called as critical disruptive voltage. And, the minimum phase-neutral voltage at which visual corona glow appears all along the conductors is called as visual critical voltage.

Factors affecting corona

  • Atmosphere: As it is already explained that the corona forms due to ionization of the air. There are always some free electrons in the air (which means air is pre-ionized to a little extent). However, in stormy weather, the number of free electrons is more than that in normal conditions. In such case, corona occurs at much lesser voltage.
  • Conductor size: Corona discharge also depends on the shape and size of the conductors. Irregularities on the conductor surface concentrate the electric field at locations, resulting in corona at these spots. Thus, a stranded conductor gives rise to more corona than a solid conductor with a smooth surface. Also, conductors having large diameter have lower electric field gradient at the surface. Hence, conductors having large diameter produce lower corona than small-diameter conductors.
  • Spacing between the conductors: Larger distance between the conductors reduces the electric stresses between them. And, hence, larger the distance between conductors, lesser the corona formation.
  • Line voltage: As it is already explained, lesser the line voltage, lesser the ionization of surrounding air. Corona discharge starts to occur when the voltage becomes greater than a minimum critical voltage called as critical disruptive voltage.

How to reduce the corona discharge?

Corona discharge is always accompanied by power loss (which is dissipated in the form of sound, light, heat and chemical action). Though it accounts for a small percentage of total losses, power loss due to corona becomes significant in foul or wet weather conditions. Corona discharge can be reduced by the following methods:
  • By increasing the conductor size: As explained above, larger the diameter of the conductor, lesser the corona discharge.
  • By increasing the distance between conductors: Larger the conductor spacing, lesser the corona.
  • Using bundled conductors: Using a bundled conductor increases the effective diameter of the conductor. This results in reduction of the corona discharge.
  • Using corona rings: The electric field is greater where the conductor curvature is sharp. Therefore, corona discharge occurs first at the sharp points, edges and corners. To mitigate this, corona rings are employed at the terminals of very high voltage equipments such as at the bushings of a very high voltage transformer (Corona discharge also occurs in high voltage equipment). A corona ring is electrically connected to the high voltage conductor, encircling the points where corona discharge may occur. This significantly reduces the potential gradient at the surface of the conductor, as the ring distributes the charge across a wider area due to its smooth round shape. Corona rings are employed at the top and bottom of the string insulators of a high voltage transmission line.
corona rings to reduce corona discharge
Corona Rings
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Types of Conductors used in Overhead Power Lines

A conductor is one of the most important components of overhead lines. Selecting a proper type of conductor for overhead lines is as important as selecting economic conductor size and economic transmission voltage. A good conductor should have the following properties:
  • high electrical conductivity
  • high tensile strength in order to withstand mechanical stresses
  • relatively lower cost without compromising much of other properties
  • lower weight per unit volume

Conductor Materials

Copper was the preferred material for overhead conductors in earlier days, but, aluminium has replaced copper because of the much lower cost and lighter weight of the aluminium conductor compared with a copper conductor of the same resistance. Following are some materials that are considered to be good conductors.
  • Copper: Copper has a high conductivity and greater tensile strength. So, copper in hard drawn stranded form is a great option for overhead lines. Copper has a high current density which means more current carrying capacity per unit cross-sectional area. Therefore, copper conductors have relatively smaller cross-sectional area. Also, copper is durable and has high scrap value. However, due to its higher cost and non-availability, copper is rarely used for overhead power lines.
  • Aluminium: Aluminium has about 60% of the conductivity of copper; that means, for the same resistance, the diameter of an aluminium conductor is about 1.26 times than that of a copper conductor. However, an aluminium conductor has almost half the weight of an equivalent copper conductor. Also, tensile strength of aluminium is less than that of copper. Considering combined factors of cost, conductivity, tensile strength, weight etc., aluminium has an edge over copper. Therefore, aluminium is being widely used for overhead conductors.
  • Cadmium-copper: Cadmium-copper alloys contain approximately 98 to 99% of copper and up to 1.5% of cadmium. Addition of about 1% of cadmium to copper increases the tensile strength by up to 50% and the conductivity is reduced only by about 15%. Therefore, cadmium-copper conductors can be useful for exceptionally long spans. However, due to high cost of cadmium, such conductors may be uneconomical in many cases.
  • Other materials: There are many other metals and alloys that conduct electricity. Silver is more conductive than copper, but due to its high cost, it is not practical in most of the cases. Galvanised steel may also be used as a conductor. Although steel has very high tensile strength, steel conductors are not suitable for transmitting power efficiently due to the poor conductivity and high resistance of steel. High strength alloys such as phosphor-bronze may also be used sometimes at extreme conditions.

Types of Conductors

As it is already mentioned above, aluminium conductors have an edge over copper conductors considering combined factors of cost, conductivity, tensile strength, weight etc. Aluminium conductors have completely replaced copper conductors in overhead power lines because of their lower cost and lower weight. Though an aluminium conductor has larger diameter than that of a copper conductor of same resistance, this is actually an advantage when 'Corona' is taken into consideration. Corona reduces considerably with increase in the conductor diameter. Following are four common types of overhead conductors that are used for overhead transmission and distribution to carry generated power from generating stations to the end users.
Generally, all types of conductors are in stranded form in order to increase the flexibility. Solid wires, except for very small cross sectional area, are very difficult to handle and, also, they tend to crystallize at the point of support because of swinging in winds.
  1. AAC : All Aluminium Conductor
  2. AAAC : All Aluminium Alloy Conductor
  3. ACSR : Aluminium Conductor, Steel Reinforced
  4. ACAR : Aluminium Conductor, Alloy Reinforced

AAC : All Aluminium Conductor

This type is sometimes also referred as ASC (Aluminium Stranded Conductor). It is made up of strands of EC grade or Electrical Conductor grade aluminium. AAC conductor has conductivity about 61% IACS (International Annealed Copper Standard). Despite having a good conductivity, because of its relatively poor strength, AAC has limited use in transmission and rural distribution lines. However, AAC can be seen in urban areas for distribution where spans are usually short but higher conductivity is required.

AAAC : All Aluminium Alloy Conductor

These conductors are made from aluminium alloy 6201 which is a high strength Aluminium-Magnesium-Silicon alloy. This alloy conductor offers good electrical conductivity (about 52.5% IACS) with better mechanical strength. Because of AAAC's lighter weight as compared to ACSR of equal strength and current capacity, AAAC may be used for distribution purposes. However, it is not usually preferred for transmission. Also, AAAC conductors can be employed in coastal areas because of their excellent corrosion resistance.

ACSR : Aluminium Conductor, Steel Reinforced

ACSR conductor (Aluminium Conductor Steel Reinforced)
ACSR consists of a solid or stranded steel core with one or more layers of high purity aluminium (aluminium 1350) wires wrapped in spiral. The core wires may be zinc coated (galvanized) steel or aluminium coated (aluminized) steel. Galvanization or aluminization coatings are thin and are applied to protect the steel from corrosion. The central steel core provides additional mechanical strength and, hence, sag is significantly less than all other aluminium conductors. ACSR conductors are available in a wide range of steel content - from 6% to 40%. ACSR with higher steel content is selected where higher mechanical strength is required, such as river crossing. ASCR conductors are very widely used for all transmission and distribution purposes.

Aluminium Conductor, Alloy Reinforced

ACAR conductor is formed by wrapping strands of high purity aluminium (aluminium 1350) on high strength Aluminum-Magnesium-Silicon alloy (6201 aluminium alloy) core. ACAR has better electrical as well as mechanical properties than equivalent ACSR conductors. ACAR conductors may be used in overhead transmission as well as distribution lines.

Bundled Conductors

Bundled Conductors
Transmission at extra high voltages (say above 220 kV) poses some problems such as significant corona loss and excessive interference with nearby communication lines when only one conductor per phase is used. This is because, at EHV level, the electric field gradient at the surface of a single conductor is high enough to ionize the surrounding air which causes corona loss and interference problems. The electric field gradient can be reduced significantly by employing two or more conductors per phase in close proximity. Two or more conductors per phase are connected at intervals by spacers and are called as bundled conductors. The image at right shows two conductors in bundled form per phase. Number of conductors in a bundled conductor is greater for higher voltages.
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Types of Electrical Loads

An electrical load is a device or an electrical component that consumes electrical energy and convert it into another form of energy. Electric lamps, air conditioners, motors, resistors etc. are some of the examples of electrical loads. They can be classified according to various different factors. Some popular classifications of electrical loads are as follows.

Resistive, Capacitive, Inductive

Electrical loads can be classified according to their nature as Resistive, Capacitive, Inductive and combinations of these.

Resistive Load

  • Two common examples of resistive loads are incandescent lamps and electric heaters.
  • Resistive loads consume electrical power in such a manner that the current wave remains in phase with the voltage wave. That means, power factor for a resistive load is unity.

Capacitive Load

  • A capacitive load causes the current wave to lead the voltage wave. Thus, power factor of a capacitive load is leading.
  • Examples of capacitive loads are: capacitor banks, buried cables, capacitors used in various circuits such as motor starters etc.

Inductive Load

  • An inductive load causes the current wave to lag the voltage wave. Thus, power factor of an inductive load is lagging.
  • Examples of inductive load include transformers, motors, coils etc.

Combination Loads

  • Most of the loads are not purely resistive or purely capacitive or purely inductive. Many practical loads make use of various combinations of resistors, capacitors and inductors. Power factor of such loads is less than unity and either lagging or leading.
  • Examples: Single phase motors often use capacitors to aid the motor during starting and running, tuning circuits or filter circuits etc.

Types of loads in power system

Domestic load / residential load

Domestic load consists of lights, fans, home electric appliances (including TV, AC, refrigerators, heaters etc.), small motors for pumping water etc. Most of the domestic loads are connected for only some hours during a day. For example, lighting load is connected for few hours during night time.

Commercial load

Commercial load consists of electrical loads that are meant to be used commercially, such as in restaurants, shops, malls etc. This type of load occurs for more hours during the day as compared to the domestic load.

Industrial load

Industrial load consists of load demand by various industries. It includes all electrical loads used in industries along with the employed machinery. Industrial loads may be connected during the whole day.

Municipal load

This type of load consists of street lighting, water supply and drainage systems etc. Street lighting is practically constant during the night hours. Water may be pumped to overhead storage tanks during the off-peak hours to improve the load factor of the system.

Irrigation load

Motors and pumps used in irrigation systems to supply the water for farming come under this category. Generally, irrigation loads are supplied during off-peak or night hours.

Traction load

Electric railways, tram cars etc. come under traction loads. This type of loads reaches its peak during morning and evening hours.

Some other classifications of electrical loads

According to load nature

  • Linear loads
  • Non-linear loads

According to phases

  • Single phase loads
  • Three phase loads

According to importance

  • Vital electrical loads (e.g. required for life safety)
  • Essential electrical loads
  • Non-essential / normal electrical loads
Electrical loads may also be classified in may different manners, such as according to their functions.
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