Thursday, 27 September 2018

Impact of Voltage Dip on Power Quality

A voltage sag or voltage dip is a short duration reduction in rms voltage which can be caused by a short circuit, overload or starting of electric motors. A voltage sag happens when the rms voltage decreases between 10 and 90 percent of nominal voltage for one-half cycle to one minute.

Its also explained as short, temporary drop in the voltage magnitude in the distribution or customer's electrical system. It may be caused by various faults in the transmission and distribution networks, faults in the connected equipment or high inrush and switching currents in the customer's installation.

What is causing voltage dips?

Figure 1 shows the sketch of a voltage dip, together with the associated definitions. The major cause of voltage dips on a supply system is a fault on the system, that is sufficiently remote electrically that a voltage interruption does not occur.

Other sources are the starting of large loads (especially common in industrial systems), and, occasionally, the supply of large inductive loads.
Figure 1 - Voltage dip sketch

Voltage dips due to the latter are usually due to poor design of the network feeding the consumer. A voltage dip is the most common supply disturbance causing interruption of production in an industrial plant.

Faults on a supply network will always occur, and in industrial systems, it is often practice to specify equipment to ride-through voltage dips of up to 0.2s. The most common exception is contractors, which may well drop out if the voltage dips below 80% of rated voltage for more than 50-100ms.

Motor protection relays that have an under voltage element setting that is too sensitive is another cause. Since contactors are commonly used in circuits supplying motors, the impact of voltage dips on motor drives, and hence the process concerned, requires consideration.

Figure 2: multiple-voltage-dip emerich

Other network-related fault causes are weather–related (such as snow, ice, wind, salt spray, dust) causing insulator flash over, collisions due to birds, and excavations damaging cables. Multiple voltage dips, as illustrated in Figure 2, cause more problems for equipment than a single isolated dip.

The impact on consumers may range from the annoying (non-periodic light flicker) to the serious (tripping of sensitive loads and stalling of motors). Where repeated dips occur over a period of several hours, the repeated shutdowns of equipment can give rise to serious production problems.

Figure 3 shows an actual voltage dip, as captured by a Power Quality recorder.

Figure 3 - Recording of a voltage dip

Typical data for under voltage disturbances on power systems during evolving faults are shown in Figure 4.

Figure 4 - Under voltage disturbance histogram

Disturbances that lie in the front right-hand portion of the histogram are the ones that cause most problems

Wednesday, 26 September 2018

Electrical Load & Types

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. 

Classifications of electrical loads:

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:  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.
Example: 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: 

It 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.

HVDC Technology for Transmitting Electricity

High Voltage direct current (HVDC) technology

An alternate means of transmitting electricity is to use high-voltage direct current (HVDC) technology. As the name implies, HVDC uses direct current to transmit power. Direct current facilities are connected to HVAC systems by means of rectifiers, which convert alternating current to direct current, and inverters, which convert direct current to alternating current.

"Early applications used mercury arc valves for the rectifiers and inverters but, starting in the 1970s, thyristors became the valve type of choice"

Thyristors are controllable semiconductors that can carry very high currents and can block very high voltages. They are connected is series to form a thyristor valve, which allows electricity to flow during the positive half of the alternating current voltage cycle but not during the negative half.

"Since all three phases of the HVAC system are connected to the valves, the resultant voltage is unidirectional but with some residual oscillation. Smoothing reactors are provided to dampen this oscillation"

🔺 HVDC transmission lines can either be single pole or bipolar, although most are bipolar, that is, they use two conductors operating at different polarities such as +/-500 kV.

HVDC submarine cables are either of the solid type with oil-impregnated paper insulation or of the self-contained oil-filled type. New applications also use cables with extruded insulation, cross-linked polyethylene. Although synchronous HVAC transmission is normally preferred because of its flexibility, historically there have been a number of applications where HVDC technology has advantages:

1 The need to transmit large amounts of power (>500 mW) over very long distances ( >500 km), where the large electrical angle across long HVAC transmission lines (due to their impedances) would result in an unstable system.

🔺 Examples of this application are the 1,800 mW ABC Project, where the transmission delivers the power to approximately 930 km away; the 3,000 mW system from the Three Gorges project to Shanghai in China, approximately 1,000 km distant; and the 1,456 km long, 1,920 mW line from the Cabora Bassa project in Mozambique to Apollo, in South Africa. In the United States the 3,100 mW Pacific HVDC Intertie (PDCI) connects the Pacific Northwest (Celilo Converter Station) with the Los Angeles area (Sylmar Converter Station) by a 1,361 km line.

2. The need to transmit power across long distances of water, where there is no method of providing the intermediate voltage compensation that HVAC requires. 

3. When HVAC interties would not have enough capacity to withstand the electrical swings that would occur between two systems. 

4. The need to connect two existing systems in an asynchronous manner to prevent losses of a block of generation in one system from causing transmission overloads in the other system if connected with HVAC. 

5.  Connection of electrical systems that operate at different frequencies. These applications are referred to as back-to-back ties. An example is HVDC ties between England and France.

6 Provision of isolation from short-circuit contributors from adjacent systems since dc does not transmit short-circuit currents from one system to another.

There is increasing interest in the use of HVDC technology to facilitate the new markets.

HVDC provides direct control of the power flow and is there-fore a better way for providing contractual transmission services. Some have suggested that dividing the large synchronous areas in the United States into smaller areas interconnected by HVDC will eliminate coordination problems between regions, will provide better local control, and will reduce short-circuit duties, significantly reducing costs.

Monday, 24 September 2018

Emerich Motivation - Change your mind and the rest will follow!

All change starts with a change of mind. You have to start by changing your thoughts about want you want to change. 

"Progress is impossible without change, and those who cannot change their minds cannot change anything. - GEORGE BERNARD SHAW 

Change has a very negative connotation for most people. On a deep emotional level we are creatures of comfort and we automatically seek out that which feels good in the moment. We long for comfort and this usually comes from that which we know; that which is familiar to us. Once we can comfortably deal with and "know" all the "unknowns" we can "relax" –because your nervous system and your mind is designed to find and attach a meaning(s) to everything and therefore something new is always a confrontation between that which is and that which will be in your mind. 

The unknown is always something that your mind and your nervous system has to "unravel" afresh and this very process feels uncomfortable on many levels. When something becomes comfortable you get used to it as you remove all the "unknowns" and your automatic behaviour can take over again. 

Our nervous system works primarily by conditioning and by repetition we notice and assume patterns that are consistent. This system is really there to serve us in helping us being more efficient and to be able to do more, more efficiently. Your mind is designed to always look for the best way. Through repetition we learn certain orders and sequences in which things happen and we learn to
recognise and respond according to these sequences.

Every emotion you experience, for instance, is nothing but the result of a sequence of events and reactions triggered by your unconscious awareness that generates and creates the actual feeling which is nothing but a sensation in your nervous system.

To change anything you must first of all become aware of these patterns. You must become aware of what goes on under the surface of your conscious awareness. This is not difficult and everybody can do this. You need not understand everything about the human nervous system to use it. Simply be
aware of the fact that there is a part of you that responds and acts "automatically" based on your past experiences and associations. 

The challenge is to go from one pattern, one that does not serve you, to one which does. You quite literally would have to change your mind in that you have to change the way you perceive yourself and your life. Doing things differently will feel uncomfortable at first, but you can rest assured that the "uncomfortable" will become "comfortable" as you start to form new associations and new patterns of association. 

The process of making the "uncomfortable" comfortable or making the "unknown" known is the way we grow as human beings. What you are comfortable with represents your comfort zone which includes all the experiences that you can comfortably deal with. If you don't expand this "zone" then you simply won't expand yourself as a person. The need to grow and become more as a person, is a deep emotional need that all humans have. Without growth you simply won't be happy. 

All growth, although it feels uncomfortable in the moment always feels immensely fulfilling in the long term and it is this feeling that we all really crave for; the feeling that we call "good". You can do something that feels comfortable and "good" in the moment by staying with what you know, but true fulfilment
comes from pushing beyond your comfort zone and creating a sense of pride in yourself. Growth means change and change involves risk and risk is the process of stepping from the known to the unknown. The truth is that all of life is constantly in a process of change. Nothing ever stays the same.

It is the nature of all of life, including you! Even if you do nothing life will still change. For you to progress, you have to decide to consciously initiate and create the change. You have to consciously put yourself in the uncomfortable place where you can grow and as you do this you progress. Progress is by choice while change is automatic. To be in control of your life you have to consciously choose to change and to keep changing yourself to become the person you want to be. All change starts with a change of mind. You have to start by changing your thoughts about want you want to change. 

In changing the way you think about something you immediately change your perception and consequently the way you feel about it. When you change the way you feel you change your behaviour and that is how you progress. Constantly trying to change behaviour will rarely create long term and lasting change. Change your mind and the rest will follow! If you don't change then you simply won't grow and if you don't grow you are not really living.

Electric Potential and Potential Difference

Potential difference is the term used to describe how large the electrostatic force is between two charged objects. If a charged body is placed between two objects with a potential difference, the charged body will try to move in one direction, depending upon the polarity of the object.

If an electron is placed between a negatively-charged body and a positively-charged body, the action due to the potential difference is to push the electron toward the positively-charged object.

The electron, being negatively charged, will be repelled from the negatively-charged object and attracted by the positively-charged object, as shown in Figure 1.
Fig-1: potential difference between two charged objects

Due to the force of its electrostatic field, these electrical charges have the ability to do work by moving another charged particle by attraction and/or repulsion.

This ability to do work is called “potential”; therefore, if one charge is different from another, there is a potential difference between them. The sum of the potential differences of all charged particles in the electrostatic field is referred to as electromotive force (EMF).

The basic unit of measure of potential difference is the “volt“. The symbol for potential difference is “V” indicating the ability to do the work of forcing electrons to move.

Because the volt unit is used, potential difference is also called “voltage”


The basic unit of measure for potential difference is the volt (symbol V), and, because the volt unit is used, potential difference is called voltage . An object’s electrical charge is determined by the number of electrons that the object has gained or lost. Because such a large number of electrons move, a unit called the “coulomb” is used to indicate the charge. One coulomb is equal to 6.28 x 1018 (billion, billion) electrons.

For example, if an object gains one coulomb of negative charge, it has gained 6,280,000,000,000,000,000 extra electrons. A volt is defined as a difference of potential causing one coulomb of current to do one joule of work.

A volt is also defined as that amount of force required to force one ampere of current through one ohm of resistance. The latter is the definition with which we will be most concerned in this module.

Source: Web based Article about Electric Potential

Friday, 21 September 2018

Sources of Sound / Noise in Transformers

Humming and buzzing noises are a common complaint with electrical transformers, which are a common sight in both industrial and residential areas. Even though a transformer has no moving parts, these vibration-like sounds are quite similar to those produced by generators and motors.

The main cause of transformer noise is the Magnetostriction Effect. This is where the dimensions of ferromagnetic materials change upon contact with a magnetic field. The alternation current that flows through an electrical transformer’s coils has a magnetic effect on its iron core. It causes the core to expand and contract, resulting in a humming sound.

Low Frequencies

Unlike cooling-fan or pump noise, the sound radiated from a transformer is tonal in nature, consisting of even harmonics of the power frequency. It is generally recognised that the predominant source of transformer noise is the core.

The low frequency, tonal nature of this noise or buzzing makes it harder to mitigate than the broadband higher frequency noise that comes from the other sources.

🔺 This is because low frequencies propagate farther with less attenuation. Also, tonal noise can be perceived more acutely than broadband levels, even with high background noise levels. This combination of low attenuation and high perception makes tonal noise the dominant problem in the neighbouring communities around transformers.

To address this problem, most noise ordinances impose penalties or stricter requirements for tonal noise.

Even though the core is the principal noise source in transformers, the load noise, which is primarily caused by the electromagnetic forces in the windings, can also be a significant influence in low-sound-level transformers. The cooling equipment (fans and pumps) noise typically dominates the very low-and very high-frequency ends of the sound spectrum, whereas the core noise dominates in the intermediate range of frequencies between 100 and 600 Hz.

These sound-producing mechanisms can be further characterised as follows.

Core Noise

When a strip of iron is magnetized, it undergoes a very small change in its dimensions (usually only a few parts in a million).

🔺 This phenomenon is called magnetostriction.

The change in dimension is independent of the direction of magnetic flux; therefore, it occurs at twice the line frequency. Because the magnetostriction curve is nonlinear, higher harmonics of even order also appear in the resulting core vibration at higher induction levels (above 1.4 T).

Flux density, core material, core geometry, and the wave form of the excitation voltage are the factors that influence the magnitude and frequency components of the transformer core sound levels. The mechanical resonance in transformer mounting structure as well as in core and tank walls can also have a significant influence on the magnitude of transformer vibrations and, consequently, on the acoustic noise generated.

Load Noise

Load noise is caused by vibrations in tank walls, magnetic shields, and transformer windings due to the electromagnetic forces resulting from leakage fields produced by load currents. These electromagnetic forces are proportional to the square of the load currents.

🔺 The load noise is predominantly produced by axial and radial vibration of transformer windings.

However, marginally designed magnetic shielding can also be a significant source of sound in transformers. A rigid design for laminated magnetic shields with firm anchoring to the tank walls can greatly reduce their influence on the overall load sound levels.

The frequency of load noise is usually twice the power frequency. An appropriate mechanical design for laminated magnetic shields can be helpful in avoiding resonance in the tank walls. The design of the magnetic shields should take into account the effects of overloads to avoid saturation, which would cause higher sound levels during such operating conditions.

Studies have shown that except in very large coils, radial vibrations do not make any significant contribution to the winding noise.

The compressive electromagnetic forces produce axial vibrations and thus can be a major source of sound in poorly supported windings. In some cases, the natural mechanical frequency of winding clamping systems may tend to resonate with electromagnetic forces, thereby severely intensifying the load noise. In such cases, damping of the winding system may be required to minimize this effect. The presence of harmonics in load current and voltage, most especially in rectifier transformers, can produce vibrations at twice the harmonic frequencies and thus a sizeable increase in the overall sound level of a transformer.

Through several decades, the contribution of the load noise to the total transformer noise has remained moderate.

However, in transformers designed with low induction levels and improved core designs for complying with low sound-level specifications, the load-dependent winding noise of electromagnetic origin can become a significant contributor to the overall sound level of the transformer.

In many such cases, the sound power of the winding noise is only a few dB below that of the core noise.

Fan and Pump Sound

Power transformers generate considerable heat because of the losses in the core, coils, and other metallic structural components of the transformer. This heat is removed by fans that blow air over radiators or coolers. Noise produced by the cooling fans is usually broadband in nature.

🔺 Cooling fans usually contribute more to the total noise for transformers of smaller ratings and for transformers that are operated at lower levels of core induction.

Factors that affect the total fan noise output include tip speed, blade design, number of fans, and the arrangement of the radiators.

Resistors in detail

Resistors are one of the simplest varieties of electronic components. A resistor is a two-terminal device that has a fixed relationship between the current passing through the device and the voltage drop across the device.

This relationship is described in Ohm’s law, which states that “the strength of a direct current is directly proportional to the potential difference and inversely proportional to the resistance of the circuit” (Merriam-Webster).

This relationship is illustrated by the following equation:

Resistance formula


I = current in amps (A)
V = voltage in volts (V)
R = resistance in ohms (Ω)

Although resistors are very common and simple devices, the different composition types of resistors are often misunderstood.

There are three common resistor composition types:

Carbon resistors
Film resistors
Wirewound resistors

Carbon Resistors

Carbon resistors are the most common type of composition resistors. They are inexpensive, and serve a general purpose in electronic circuits.

Consisting of carbon particles mixed with a binder, carbon resistors are molded into a cylinder and baked. The carbon particles mixed with the binder (usually ceramic) are the resistive element, accompanied by embedded wire leads or metal end caps to which the lead wires are attached 

Carbon Film Resistors

A film resistor uses a film of carbon that is deposited (either sprayed or coated) onto a substrate, which forms the resistive element. The resistance is adjusted by cutting or shaping the film.

Wirewound Resistors

Wirewound resistors are made up of metal resistance wire (usually nichrome), and are made by winding the wire around the insulated core of the resistor. Wirewound resistors have a poor frequency response and are typically only used in low frequency applications.

Thursday, 20 September 2018

LED light - Technical analysis

A Light Emitting Diode (LED) is a semiconductor device which converts electricity into light. Each diode is about 1/4 inch in diameter and uses about ten milliamps to operate at about a tenth of a watt. LEDs are small in size, but can be grouped together for higher intensity applications.

LED fixtures require a driver which is analogous to the ballast in fluorescent fixtures. The drivers are typically built into the fixture (like fluorescent ballasts) or they are a plug transformer for portable (plug‐in) fixtures. The plug‐in transformers allow the fixture to run on standard 120 volt alternating current (AC), with a modest (about 15 to 20 percent) power loss.

The efficacy of a typical residential application LED is approximately 20 lumens per watt (LPW). Incandescent bulbs have an efficacy of about 15 LPW and compact fluorescent (Energy saver Bulbs) are about 60 LPW, depending on the wattage and lamp type. LEDs are better at placing light in a single direction than incandescent or fluorescent bulbs.

Because of their directional output, they have unique design features that can be exploited by clever designs. LED strip lights can be installed under counters, in hallways, and in staircases; concentrated arrays can be used for room lighting.

Waterproof, outdoor fixtures are also available. Some manufacturers consider applications such as gardens, walkways, and decorative fixtures outside garage doors to be the most cost‐efficient. LED lights are more rugged and damage‐resistant than compact fluorescents and incandescent bulbs. LED lights don’t flicker.

They are very heat sensitive; excessive heat or inappropriate applications dramatically reduce both light output and lifetime. 
Uses include:

Task and reading lamps
Linear strip lighting (under kitchen cabinets)
Recessed lighting/ceiling cans
Porch/outdoor/landscaping lighting
Art lighting
Architectural lighting
Night lights
Stair and walkway lighting
Pendants and overhead
Retrofit bulbs for lamps


Individual LEDs are considerably more efficient; however, the lamp or fixture design is reduced by the driver and electronics. In addition, LEDs do not produce heat like incandescent bulbs.

LEDs last considerably longer than incandescent or fluorescent lighting. LEDs don’t typically burn out like traditional lighting, but rather gradually decrease in light output. Their “useful life” is defined by the Alliance for Solid‐State Illumination Systems and Technologies (ASSIST) as the time it takes until 70% of initial light output is reached, often 50,000 hours.

They are resistant to thermal and vibrational shocks and perform well when subjected to frequent on‐off cycling.

Initial Cost

The biggest limitation to LED for common residential use is the cost of manufacturing due to still‐limited production runs. Manufacturers claim production will increase considerably in the near future, further lowering prices. Currently, there is a limited number of LED fixture manufactures, but this is changing.

Retrofit bulbs range from Rs. 500/= to Rs. 2000/= for night lights and small lamps.

Operational Cost

The cost savings of LEDs can be found in smaller wattage lamps or for applications that take advantage of their longevity, such as difficult to reach places. They are also advantageous for dimmable fixtures, since dimmable fluorescents are expensive.


The small size of LED lights encourages a variety of design options. White LED lamps are available with Edison (screw‐in type) bases to retrofit existing fixtures. There are LED strips that can be used under cabinets. In addition, outdoor landscaping fixtures are available.

Cons and Pros of LED

LED lamps have many advantages over traditional lighting methods. These include:

  • Low energy consumption – retrofit bulbs range from 0.83 to 7.3 Watts
  • Long service life – LED bulbs can last up to 80,000 hours
  • Durable – LED bulbs are resistant to thermal and vibrational shocks and turn on instantly from ‐ 40C° to 185C°, making them ideal for applications subject to frequent on‐off cycling, such as garages and basements
  • Directional distribution of light – good for interior task lighting
  • No infrared or ultraviolet radiation – excellent for outdoor use because UV light attracts bugs
  • Safety and environmentally conscious – LEDs contain no mercury and remain cool to the touch
  • Fully dimmable – LEDs do not change their color tint when dimmed unlike incandescent lamps that turn yellow
  • No frequency interference – no ballast to interfere with radio and television signals
  • Range of color – LEDs can be manufactured produce all colors of the spectrum without filters, they can also produce white light in a variety of color temperatures

Some disadvantages to LED lighting:

  • LEDs are currently more expensive than more conventional lighting technologies, and may be hard to locate
  • LED is very heat sensitive. Excessive heat or inappropriate applications dramatically reduce both light output and lifespan & create Harmonics
  • LEDs typically cast light in one direction at a narrow angle compared to incandescent or fluorescent lamps so lenses or reflectors are needed in fixtures to broaden the beam (if desired)

How & Why Electro Static Discharge? (ESD)

An increasing problem today with the use of more and more electronic equipment in our systems is the Electro Static Discharge(ESD).The main source of the problem is the wrong handling of electronic components, printed circuit boards, etc.

A component damaged by ESD has been exposed to a too high voltage level and today the components are much more sensitive depending on integration, which means more functions in the same capsule. The distances between the conductors are decreased and therefore the insulation distance will be at a minimum.

A value of 0.002 mm is common in modern integrated circuits.

Electro static charge is caused in three different ways:
  1. Rubbing of two surfaces to each other.
  2. Separation of two surfaces from each other, for example when removing a plastic cover from its contents.
  3. Induction caused by static electricity without any contact of the material.

Two type of faults and different circuits

  1. The ESD damages are divided into two groups of faults: direct fault and latent defect. The direct faults are quite easy to detect since the component will not work at all and this is very often discovered at the factory before shipping.
  2. The latent defects can be very difficult to identify since the component is not working in a reliable way and the life length of the device may be reduced dramatically.

Fault generated by ESD Digital circuits:

  • ”Ones” becomes ”zeros” and ”zeros” becomes ”ones” for no reason.
  • No ”ones” or ”zeros” at all ( the circuit is dead).
Analogue circuits:
  • Worsening accuracy of measuring
  • Wrong voltage levels that require adjustments
  • Malfunction
Electro static voltage levels:

A voltage level of between 100-500 V can destroy any electronic components in principle. The most sensitive components can only withstand voltages between 25-170 V.

Sometimes it is possible to hear a ”click” sound when touching an object and that is typical ESD phenomena. When it is possible to hear that ”click” sound the voltage level is already at least 3,5 kV. Sometimes it is also possible to see a spark when touching an object and the voltage level is then at least 10 kV.

Below some values are given for typical Electro static charge:

  • Walking on a wall-to-wall carpet: 10 – 20 kV
  • Walking on a plastic floor (PVC): 2 – 5 kV
  • Walking on an anti-static floor: 0 – 2 kV
  • Lifting paper from a table: 5 – 35 kV
  • Rising from a chair: 10 -25 kV
  • Protection against ESD damages
  • It is possible to reduce the risk of ESD to a minimum for the equipment.
  • This is very important to remember when making service and/or repair with electronic components for example the printed circuit board on a soft starter.

Actions to prevent damages:
  • Avoid charge if possible
  • Always use a wrist strap or similar connected to ground potential when working with electrical components
  • Always use the right type of package (ESD protected bags, etc.)
  • Connect all machines and apparatus to ground potential
  • High humidity

Wednesday, 19 September 2018

Explanation of IP Protection standard.

IP interpreted as Ingress Protection Marking, classifies and rates the degree of protection provided against intrusion (body parts such as hands and fingers), dust, accidental contact, and water by mechanical casings and electrical enclosures.

The protection of enclosures against ingress of dirt or against the ingress of water is defined in IEC60529 (BSEN60529:1991). Conversely, an enclosure which protects equipment against ingress of particles will also protect a person from potential hazards within that enclosure, and this degree of protection is also defined as a standard.

The degrees of protection are most commonly expressed as ‘IP’ followed by two numbers, e.g. IP65, where the numbers define the degree of protection. The first digit shows the extent to which the equipment is protected against particles, or to which persons are protected from enclosed hazards. The second digit indicates the extent of protection against water.

The wording in the table is not exactly as used in the standards document, but the dimensions are accurate.

IP Degree of Protection according to EN/IEC 60529

Power quality improvement with harmonic filters

In electrical plants the loads draw from the network electric power (active) as power supply source (e.g. personal computers, printers, diagnostic equipment, etc.) or convert it into another form of energy (e.g. electrical lamps or stoves) or into mechanical output (e.g. electrical motors). To get this, it is often necessary that the load exchanges with the network (with net null consumption) the reactive energy, mainly of inductive type.

This energy, even if not immediately converted into other forms, contributes to increase the total power flowing through in the electrical network, from the generators, all along the conductors, to the users. To smooth such negative effect, the power factor correction of the electrical plants is carried out.

The power factor correction obtained by using capacitor banks to generate locally the reactive energy necessary for the transfer of electrical useful power, allows a better and more rational technical-economical management of the plants.

Passive Filter

Capacitor banks can be used combined with inductors in order to limit the effects of the harmonics on a network. Actually, the combination capacitor-inductor constitutes a filter for harmonics.

To avoid the negative effects of resonance, it is necessary to insert an inductor in series with a capacitor. By applying an analogous reasoning, it is possible to think of placing in a point of the network a combination of an inductor and a capacitor properly dimensioned in order to get the same resonance frequency of the order of the current harmonic to be eliminated.

In this way, the assembly inductor-capacitor presents a very low reactance in correspondence with the harmonic to be eliminated which shall circulate in the assembly without affecting the whole network.

Therefore this filter, called passive filter, consists in a capacitor connected in series with an inductor so that the resonance frequency is altogether equal to the frequency of the harmonic to be eliminated. Passive filters, which are defined on a case by case basis, according to a particular harmonic to be filtered, are cost-effective and easy to be connected and put into function.

Active Filter

Active filters instead can automatically eliminate the current harmonics present in a network in a wide range of frequencies. Exploiting power electronic technology, they can inject a system of harmonics able to neutralise those present in the network.

The active filter has the advantage of filtering simultaneously dozens of harmonics and does not involve design costs for dimensioning.


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