Transformers Fire Protection System – Causes, Types & Requirements

Basic Requirements for Transformers Fire Protection System

By: Manuel Bolotinha

Causes of Fire in Transformers

Excessive overheating, extremely severe short circuits, faults in the oil and lightning strokes may cause a fire on transformers.

Transformer fires are rare but the impact is great. Even though a transformer involved in a fire likely will be destroyed almost immediately, as seen in the figure below, the fire’s effect on adjacent equipment and structures can be mitigated and therefore must be considered.

Transformers Fire Protection System – Causes, Types & Requirements

An uncontained fire can do a significant amount of damage and result in a prolonged and unscheduled outage.

For transformers of high rated power and voltages above 123 kV is usual to provide a fire protection system, using water spray fixed systems, commonly called transformer “deluge” or “fire water” systems, as shown in Figure 1Transformers Fire Protection system

Figure 1 – Transformer fire protection system

This system is activated through flame detectors if the transformer is installed outdoors, or by smoke detectors, if the transformer is installed indoors.

Types of Fire Protection System of a Transformer

Fire protection system of a transformer may be divided into:

  • Water Based and Mist Systems: fire pumps; water spray fixed system/nozzles; valves; valves components; piping.
  • Fire Detection System: fire detectors; control panel; cabling.

Also read: TRANSFORMER NAMEPLATE (GENERAL REQUIREMENTS).

Fire suppression requirement may be mitigated when the transformer is located remotely from the structure and other equipment, or the burning oil can be contained.

Protection of the plant structure and adjacent equipment, as well as reducing hazards to personnel, warrants fire suppression in most cases.

In some cases, use of less-flammable insulating fluids may mitigate the need for fire suppression and should be considered as an alternative.

In common practice that industry standards and insurance requirements include fire suppression and fire walls (Figure 2) for transformers containing as little as about 1,900 l of combustible oil where acceptable separation/barriers from buildings and other equipment cannot be achieved.

Transformers Fire Protection System - Causes, Types & Requirements

Figure 2 – Fire walls

Requirements for Transformer Fire Protection

Summarizing, the basic principles are:

  • New facilities with large, mineral-oil-filled transformers located near the plant structure or other equipment should include active transformer fire suppression systems to protect the structure and adjacent equipment and properly designed containment systems to protect the environment.
  • For new facilities, and where justified at existing plants, serious consideration should be given to locating mineral-oil-filled transformers away from the plant, other equipment, and waterways as a way of reducing fire and environmental risks. In these cases, active fire suppression may not be necessary if other considerations allow.
  • Existing, functional fire suppression systems should continue to be used to protect plant structure and other equipment but should be reviewed for adequacy and compliance with current codes and standards.
  • Inactive fire suppression systems should be reviewed for adequacy and compliance with current codes and standards and restored to service.
  • Fire suppression systems should be added to existing facilities (where none currently exist) and where required to protect the plant structure or other equipment.
  • Transformers should have periodic condition assessments in addition to routine inspection, testing, and maintenance. Transformers with low condition indices should be programmed for rehabilitation or replacement.
  • Fire walls between adjacent transformers, between transformers and the plant structure, between single-phase transformers, or between transformers and other equipment should be added where feasible and appropriate to contain a fire and explosion, thus reducing collateral damage.
  • Fire suppression systems must be adequately operated, maintained, and tested.
  • Containment and oil-water separation structures must comply with all applicable laws, regulations, and standards.
  • Access to transformers will be limited only to those having official business in the area. Proximity of the public to transformers will be restricted.
  • Applicable environmental laws must be accommodated.

Also read: Transformers MCQs With Explanatory Answers

Download Project Report on Transformer Fire Protection

  • Title:
  • Format:
  • Size:
  • Pages:
  • Download:
GUIDE FOR TRANSFORMER FIRE SAFETY PRACTICES
PDF
4MB
139

About the Author: Manuel Bolotinha

-Licentiate Degree in Electrical Engineering – Energy and Power Systems (1974 – Instituto Superior Técnico/University of Lisbon)
– Master Degree in Electrical and Computers Engineering (2017 – Faculdade de Ciências e Tecnologia/Nova University of Lisbon)
– Senior Consultant in Substations and Power Systems; Professional Instructor

You may also read:

The post Transformers Fire Protection System – Causes, Types & Requirements appeared first on Electrical Technology.



February 28, 2018 at 06:22AM by Department of EEE, ADBU: http://ift.tt/2AyIRVT

Submarine Cables – Construction, Characteristics, Cables Laying & Joints

An Introduction to Submarine Cables & Subsea Power Cables

Introduction to Submarine Cables

The development of offshore wind farms and oil and gas offshore platforms requires the installation of power, control and monitoring and communications cables between the platforms and the main land.

For this purpose submarine cables are installed, which are also used for power and/or communications between islands and the main land, between countries and even between continents.

Submarine Cables – Construction, Characteristics, Cables Laying & Joints

Characteristic of Submarine Cables

Submarine cables, that must comply with IEC Standard 60288[1], are specifically designed and manufactured to be installed underwater, laid at seabed, taking into account that seabed is rugged and rocky, that there are marine animals, which can damage the cables, and that is mandatory that cables must withstand tsunamis and volcanic activity, as well as trawls used by fishermen, that are more hazardous than the fish itself.

To establish the characteristics of a submarine cable is necessary to consider the following parameters:

  • Ambient temperature (seabed and land).
  • Burial depth.
  • Particular burial/protection requirement at shore approach (deeper burial, directional drill pipe…).
  • Axial spacing of cables.
  • Thermal resistivity of seabed and land.
  • Length of submarine cable.
  • Water depths.

Typical rated voltages of power submarine cables are 3.6/6(7.2) kV to 290/500(525) kV, in AC systems, and higher in DC systems.

Depending of rated voltage and of the cross section (for DC systems manufacturers construct these cables with cross sections up to 2500 mm2 and for network rated voltage up to 725 kV) they may be multicore or single core.

Characteristics of Power Submarine Cables

Main characteristics of power submarine cables are:

  • Conductor: Copper or aluminum. In case that the conductors are going to be used in long depths and if requested the conductor is sealed with special material which prevents the water penetration in case of cable damage.
  • Insulation: XLPE, EPR or MIND (mass impregnated paper).
  • Screening: Copper wires or tapes and lead sheath where required.
  • Armoring: The protection of the cable from mechanical stresses is achieved by the armoring consisted of steel wires (for single core cables armoring must be of non-magnetic material – usually aluminum – to avoid overheating of armoring due to Foucault currents[2]Joule effect), which provide also to the cables the required mechanical strength which during laying or pulling. The steel wires are of different categories of breaking load and they are heavily galvanized.
  • Outer protection: The outer protection of the cable, according to the conditions and requirements of the installation, is achieved by PVC or PE sheath and layers of polypropylene yarns or jute.

Also read: Types Of Cables Used In Internal Wiring

Three-core power cables may also have optic fiber cables for communications, as shown in Figure 1

Figure 1 – Construction of Three-phase submarine cable

When single core power cables are used usually they do not include the optical fibers and in this situation is necessary to install also optical fiber submarine cables like the one shown in Figure 3.Optical fiber submarine cable

Figure 2 – Optical fiber submarine cable

Some manufacturers include in the same submarine cable communications (optical fiber) and controls to subsea processing and boosting systems, whether requirements are for low voltage, medium voltage or high voltage power supply – umbilical cables (see Figure 3).

Umbilical cables may also include low and high pressure lines (steel tube) used for fluids.Umbilical cable

Figure 3 – Umbilical cable

Basic Procedure for Submarine Cables laying

Laying a submarine cable is a remarkably complex, hazardous and expensive business.

Routes need to be surveyed, technology developed, the cable needs to be laid without being lost, broken or damaged.

Prior to install a submarine cable is necessary to undertake a series of actions:

  • Choose the routing, using updated nautical maps.
  • Evaluate the geological conditions of the chosen routing.
  • Proceed to seabed identification, namely in what concerns bathymetry (depth), slope, existence of topographic incidents, lithology (seabed nature), environment conditions, such as saltiness, temperature and pH, and the dynamic movements that may exist at seabed (waves, sea currents, etc.) or that may affect it (tsunamis, volcanic activity, sludge currents, etc.).

Once the routing is chosen and all studies of seabed are completed, it is necessary to find if there any stretches were the cable needs to be buried (using a hydro jet burial machine) and to develop specific technologies to constantly survey the place where the cable is installed to avoid damages or cable loose.

Submarine cables is generally done by a cable laying ship, as seen in Figures 4 and 5, and robots may be used to control cable laying (see Figure 6).

Cable laying ship

Figure 4 – Cable laying ship

Submarine cable laying

Figure 5 – Submarine cable laying

Cable laying robot

Figure 6 – Cable laying robot

Submarine Cable Joints

When submarine cable run is very long or if damage occurs in the cable it is necessary to install cable joints.

These cable joints, that are subjected to high pressures, are executed prior the cable installation in seabed (whenever possible at the manufacturer facilities), must be submitted to insulation and dielectric tests and also to ultrasonic and radiographic tests, in order to assure the reliability of the installation.

Figure 7 shows a phase of submarine cable joints.

Execution of submarine cable joint

Figure 7 – Execution of submarine cable joint

Good to know:

[1] IEC: International Electrotechnical Comission.

[2] Foucault currents are induced currents (magnetic induction phenomenon).

Gallery of Submarine / Subsea & Power Submarine Cables

About the Author: Manuel Bolotinha

-Licentiate Degree in Electrical Engineering – Energy and Power Systems (1974 – Instituto Superior Técnico/University of Lisbon)
– Master Degree in Electrical and Computers Engineering (2017 – Faculdade de Ciências e Tecnologia/Nova University of Lisbon)
– Senior Consultant in Substations and Power Systems; Professional Instructor

You may also read:

The post Submarine Cables – Construction, Characteristics, Cables Laying & Joints appeared first on Electrical Technology.



February 27, 2018 at 06:12AM by Department of EEE, ADBU: http://ift.tt/2AyIRVT

Design of Grounding / Earthing System in a Substation Grid

Design of Earthing / Grounding System in a Substation Grid

By: Manuel Bolotinha

Introduction to Substation Earthing Grid

In high and medium voltage[1]Air Insulated Substations (AIS) the electromagnetic field, which causes are the static charges of bare cable and conductors and by the atmospheric conditions (surges), induce voltages at no-live parts of the installation that create potential differences between metallic parts and ground and also between different points of the ground.

Similar situations can occur when there are faults between live parts of the installation and no-live parts, for example in phase-to-earth short circuit.

Design of Grounding Earthing System in a Substation Grid - Substation earthing grid

These potential differences give origin to step potential and touch potential, or a combination of both, that can lead to circulation of an electric current through the human body, that can cause hazardous to people.

Touch voltage (Et) can be defined as the maximum potential difference that exists between an earthed metallic structure capable to be touched by the hand and any point of the ground, when a fault current flows.

It is usual to consider a distance of 1 m between the metallic structure and the point on the ground.

Step voltage (Es) is defined as the maximum potential difference that exists between the feet when a fault current flows.

It is usual to consider a distance of 1 m between the feet.

A particular case of step voltage is the Transferred voltage (Etrrd): where a voltage is transferred into or out of the substation from or to a remote point external to the substation site.

Other concepts are:

  • Ground potential rise (GPR): The maximum electrical potential that a substation grounding grid may attain relative to a distant grounding point assumed to be at the potential of remote earth. This voltage, GPR, is equal to the maximum grid current times the grid resistance.
  • Mesh voltage (Em): The maximum touch voltage within a mesh of a ground grid.
  • Metal-to-metal touch voltage (Emm): The difference in potential between metallic objects or structures within the substation site that may be bridged by direct hand-to-hand or hand-to-feet contact.

The diagram in Figure 1 shows the phenomena referred above.Touch, step and transferred voltages - Design of Earthing / Grounding System in a Substation Grid

Figure 1 – Touch, step and transferred voltages

In order to minimize to acceptable values of the currents through the human body, to ensure electrical safety for people working within or near the installation, and also to limit any eventual electrical interference with third-party equipment, AIS must be provided with an earthing (or grounding) system, to which all metallic non-live parts of the installation must be connected, such as metallic structures, earthing switches, surge arresters, enclosures of switchboards and motors, transformers rails and metallic fences.

Since earthing has an influence on the levels of power system overvoltages and fault current, and the definition of protection systems, earthing system must be designed to ensure that there is proper operation of the protective devices such as protective relaying and surge arresters.

Design and construction of earthing system must assure that system performs for the expected life of the installation and it must therefore take into account future additions and the maximum fault current for the ultimate configuration.

Earthing system is made of a mesh of buried bare copper cable, with additional earth rods, and shall be calculated, being recommended to use IEEE Std. 80-2000.

Important formulas for Designing a Substation Grid Earthing System

The cross section of the buried cable should calculated in accordance with the value of the phase-to-earth short circuit current, but it is common to use the three phase short-circuit current for this purpose.

For this calculation the following formula must be used:Where:

  • I”K1 is the phase-to-earth short-circuit current [A]
  • ts is the duration of the fault [s]
  • Δθ is the maximum admissible temperature rise [°C] – for bare copper Δθ = 150 °C

According to the referred IEEE Standard maximum tolerable step and touch potential and maximum tolerable current through the human body (Ihb) and the resistance of the earth grid (Rg) are calculated by the formulas:

Maximum tolerable step potential

Maximum tolerable touch potential

Maximum tolerable current through the human body

Resistance of the Earth GridResistance of the earth grid

Where:

  • Cs is the surface layer derating factor and is calculated by the formula:
  • ts is the duration of the fault [s]
  • ρs is the surface material resistivity [Ω.m] typical value for wet crushed rock/gravel: 2,500 Ω.m
  • ρ is the resistivity of the earth beneath the surface material [Ω.m]
  • hs is the thickness of the surface material [m]
  • A is the area occupied by the ground grid [m2]
  • lT is the total buried length of conductor, including the earth rods [m]

If no protective surface layer is used, then Cs =1 and ρs = ρ

These calculations are usually done using specific software.

Substation Earthing Grid

Figure 2 shows an example of the earth grid.Earth grid

Figure 2 – Earth grid

The most suitable methods for the connection of the earth grid connections are:

a.) Exothermic welding

Exothermic welding

Figure 3 – Exothermic welding

Exothermic welding is conductors’ permanent connection process that uses molten metal and molds, which is based in a chemical reaction between metal oxides (the conductor) and ignited aluminium powder, which acts as fuel, with heat energy release. This chemical reaction is a pyrotechnic composition known as thermite.

It must be assured that the number of exothermic welding done with each mold will not exceed the indications of the manufacturer.

b.) C connector:

using a hydraulic crimping tool and matrixes with a size suitable for the size of the connectors.C connector and crimping tool

Figure 4 – C connector and crimping tool

Close to the control boxes of circuit breakers, switches and isolators it must be installed a metallic equipotential mat, connected to the earth system, similar to the one shown in Figure 5.

Figure 5 – Metallic equipotential mat

Good to know:

[1] Being Un the rated voltage of the network: HVUn ≥ 60 kV; MV1 kV < Un ≤ 49.5 kV.

About the Author: Manuel Bolotinha

-Licentiate Degree in Electrical Engineering – Energy and Power Systems (1974 – Instituto Superior Técnico/University of Lisbon)
– Master Degree in Electrical and Computers Engineering (2017 – Faculdade de Ciências e Tecnologia/Nova University of Lisbon)
– Senior Consultant in Substations and Power Systems; Professional Instructor

You may also read:

The post Design of Grounding / Earthing System in a Substation Grid appeared first on Electrical Technology.



February 25, 2018 at 04:08AM by Department of EEE, ADBU: http://ift.tt/2AyIRVT

Introduction to Harmonics – Effect of Harmonics on Power System

What are Harmonics and How to Filter and Eliminate it.

(Manuel Bolotinha)

Introduction to Harmonics

The quality of electrical power supply is an important issue both for utility companies and users, but that quality may affected by electromagnetic disturbances.

Among these disturbances it must be highlighted harmonics that happens in all voltage levels and whose study, calculation of acceptable values and correction methods are defined in IEC[1] Standard 61000-2-4: Electromagnetic compatibility (EMC)[2] – Environment – Compatibility levels in industrial plants for low-frequency conducted disturbances.

Introduction to Harmonics

What are Harmonics?

Alternators produce alternated voltages (V) and currents (I) with a sinusoidal wave form and a frequency (f) of 50 Hz or 60 Hz (this frequency, the first harmonic, is usually designated by industrial frequency or fundamental), what can be observed in Figure 1.Sinusoidal alternated voltage

Figure 1 – Sinusoidal alternated voltage

However, due to some equipments characteristics, which are installed in the network, voltages and/or currents with different frequencies, odd integral multiples of industrial frequency, may be induced in the network, the harmonics, i. e.: 3th harmonic150 Hz or 180 Hz; 5th harmonic250 Hz or 300 Hz; 7th harmonic350 Hz or 420 Hz; etc.

We can say then that harmonics are continuous (steady-state) disturbances or distortions on the electrical network and are a completely different subject or problem from line spikes, surges, sags, impulses, etc., which are categorized as transient disturbances.

Figure 2 shows examples of 1st harmonic, 3th harmonic and 5th harmonic.Fundamental, 3th harmonic and 5th harmonic waves

Figure 2 – Fundamental, 3th harmonic and 5th harmonic waves

The presence of harmonics gives origin to a distorted wave of voltage (or current) that may be observed in Figure 3, taking into account that all complex waveforms can be resolved into a series of sinusoidal waves of various frequencies, therefore any complex waveform is the sum of a number of harmonics of lesser or greater value.

Fourier series[3] expresses the instantaneous value of that sumu(t) – by the equation:EquationWhere:

  • t is the time [s]
  • ω = 2πf [s-1]
  • T is the period [s]
  • f0 is the fundamental frequency [Hz]
  • s(t) is a periodic function integrable in the interval [0, T]

Harmonic distortion

Figure 3 – Harmonic distortion

Usually 3th harmonic is the most harmful, but in certain conditions, 5th and 7th harmonics cannot be overlooked.

Harmonic Distortion

According to IEC Standard 61000-2-4 harmonic distortion is characterized by the parameter THDTotal Harmonic Distortion – calculated by the equation:

Where Q1 represents the rms value of the voltage or of the current at industrial frequency and Qi the harmonic wave of order i (2nd harmonici=2; 3th harmonic i=3; etc.) of the voltage or of the current.

The same IEC Standard defines also the following parameters:

  • TDC (Total Harmonic Content), which rms value is calculated by the equation:equation

Where Q1 represents the rms value of the voltage or of the current at industrial frequency and Q the rms value of the voltage or of the current.

  • TDR (Total Harmonic Ratio) – relation between the rms value of TDC and the rms value of the voltage or of the current at industrial frequency (Q1), which is calculated by the equation:equation

Usually calculations are made for the voltage, considering minimum three-phase short-circuit power (S”K) of the network and maximum values (in Ω) of short-circuit impedance in the points where THD is calculated (ZK; RK; XK[4]); a specific software is required to do these calculations.

The above referred IEC Standard defines 3 classes for electromagnetic environment[5]:

  1. Class 1: This class applies to protected supplies and has compatibility levels lower than those on public networks. It relates to the use of equipment very sensitive to disturbances in the power supply, for instance electrical instrumentation in laboratories, some automation and protection equipment, some computers, etc.
  2. Class 2: This class applies generally to PCC[6] and to IPC[7] in the environments of industrial and other non-public power supplies. The compatibility levels of this class are generally identical to those of public networks. Therefore, components designed for supply from public networks may be used in this class of industrial environment.
  3. Class 3: This class applies only to IPC in industrial environments. It has higher compatibility levels than those of class 2 for some disturbance phenomena. For instance, this class should be considered when any of the following conditions are met: a major part of the load is fed through converters; welding machines are present; large motors are frequently started; loads vary rapidly.

Harmonic compatibility levels[8] (Uh [%]) for odd frequencies multiples of 3 are indicated in Table 1and for odd frequencies not multiples of 3 are indicated in Table 2.

Table 1 – Levels of harmonic compatibility for odd frequencies multiples of 3

Levels of harmonic compatibility for odd frequencies multiples of 3

Table 2 – Levels of harmonic compatibility for odd frequencies multiples of 3

Levels of harmonic compatibility for odd frequencies multiples of 3

Compatibility levels of THD for each of the classes are:

  • Class 1 – 5%.
  • Class 2 – 8%.
  • Class 3 – 10%.

Sources and Effects of Harmonics

Harmonics are a permanent source of problems in electrical equipments and systems.

The following types of loads (non-linear loads [9]) are the main sources of harmonics:

  • Power electronic equipment (example: rectifiers – namely those used in electrical traction systems – and static converters).
  • Arcing equipment (example: arc furnaces, AC or DC, arcing welding machines).
  • Saturable devices (example: off-load current wave absorbed by a transformer with an insufficiently large power rating).

To minimize harmonics generation rectifier units are preferably six-pulse and these type of units for electrical traction systems typically generate current harmonics of 5th, 7th, 17th and 19th order, resulting from diodes unbalancing and from network impedance.

Although of a lower magnitude, under normal working conditions of equipments and of network, it must be taken into account the risk of resonance for those frequencies.

Switching operations of capacitor banks and power transformers with a permanent overload are also an important harmonics source.

Power transformers for voltages above 60 kV with star-star connection (Yy) are equally a harmonic source. To compensate those harmonics, the referred power transformers must have a tertiary winding, delta connected.

Apart from the distortion of voltage wave, harmonics are an origin of erroneous operation of control and protection systems, due to electromagnetic interferences, increase skin effect [10], cause mechanical oscillation and vibrations of electrical machines, namely power transformers and rotating machines, decrease power factor (cos Φ), conduce to premature ageing of insulation materials, leading to the lost of their dielectric characteristics, origin overheating and losses increasing, namely power transformers and cables, and decrease useful life of equipments.

Harmonics, which are the cause of voltage wave distortion, circulating in non-linear loads, like motors, when subjected to a variable magnetic flux, induce circulating currents (Foucault currents) in conducting materials, what decrease torque.

In unbalanced systems, harmonics may cause a neutral current higher than the vectorial sum of phase currents at fundamental frequency, leading to an overload in the neutral conductor.

Skin effect increases conductors’ resistance and therefore voltage drop and losses by Joule effect. This issue is particularly sensitive in overhead lines with a voltage above 150 kV and a length of 800 km and above. Common solution to solve this problem is to use DC overhead lines, in which skin effect does not exists.

Mechanical oscillation and vibrations of rotating electrical machines may origin shaft misalignment and destruction of stator, rotor and bearings.

Losses increase in power transformers, happens in iron losses, due to Foucault currents and hysteresis[11], which are proportional to the frequency and in copper losses, due to skin effect.

Harmonics Compensation & Types of Filters

When capacitor banks are used for power factor correction, a significant harmonics component flows into the capacitor bank; in these situations is necessary to temporarily switch-off the capacitor bank to allow an accurate location of harmonics sources.

In such an installation it is crucial to verify if there is any risk of harmonic resonance caused by the specific capacitor bank harmonics. This is the first step to define the correct solution for harmonic compensation.

Once confirmed the existence of harmonics and that THD value exceeds the limit defined by IEC Standard 61000-2-4 and/or established by the utility company it is mandatory proceed to harmonic compensation; the solution to be implemented depends on the installation characteristics.

The simplest solution, used in low voltage (V ≤ 1 kV) installations, is the use of copper coils (see Figure 4) that act as high frequency filter, limit the starting current of rectifiers and restrain mutual interference.Reactance for harmonic compensation

Figure 4 – Reactance for harmonic compensation

The inductance (L) of each phase is calculated by the equation:equationWhere:

  • ΔVL is the internal voltage drop of the reactance [%]
  • Vn is phase-to-phase voltage of the network [V]
  • fn is the industrial frequency of the network [Hz]
  • In is the current [A]

In networks and installations with a strong electrical pollution (higher harmonics level), where Gh/Sn > 60% (Gh is the apparent power of all non-linear loads responsible for harmonics production and Sn is the apparent power of all upstream transformers connected to the same bus bar where loads are connected) is recommended to install harmonics filters, like the one shown in Figure 5).Harmonics filter

Figure 5 – Harmonics filter

Harmonics compensation may be centralized, with harmonic filters connected in the main incoming switchboard, or de-centralized or local, installing the harmonic filters close to the equipments that are the main sources of harmonics. Both solutions are shown in Figure 6.Location of harmonic filters

Figure 6 – Location of harmonic filters

Harmonic filters are classified into three categories:

Passive filters

These are constituted by LC series association circuits, tuned for each one of the frequencies that they are designed to compensate, usually 5th, 7th and 11th harmonics. Their main characteristics are:

  • There is no limit to harmonic to current to be eliminated.
  • They perform power factor correction.
  • They risk amplifying harmonics when there are network modifications.
  • There is an overload risk, caused by external electromagnetic pollution.

Active filters

These are constituted by electronic and micro-processed units, controlling harmonics within a range between 2nd to 50th orders; for each range of frequency it is generated a current, which has a phase shift of 180° and the same value of the harmonic current to be compensated.

This type of filters is well adapted to modifications of the network, of the loads and of the harmonic range, being particularly suitable for de-centralized or local compensation.

Hybrid filters

These are a combination of active and passive filters, controlling harmonics within a range between 2nd to 25th orders, doing also power factor correction.

Good to know:

Good to know:

[1] IEC: International Electrotechnical Comission.

[2] Electromagnetic compatibility is defined as the capability of electrical equipments to worker properly in a “electromagnetic environment” without introducing any type of electromagnetic disturbances in other equipments and systems that may exist in that environment.

[3] Fourier series are converging trigonometric series used to represent the sum of sinusoidal functions.

[4] If the values of RK e XK of the network it is usual to consider, as an approximation, RK/XK = 0.1 and the equation

ZK = √(RK2+XK2).

[5] The definition of the classes is a transcription of IEC Standard 61000-2-4.

[6] PCC: Point on a public power supply network, electrically nearest to a particular load, at which other loads are, or could be, connected.

[7] IPC: Point on a network inside a system or an installation, electrically nearest to a particular load, at which other loads are, or could be, connected.

[8] Compatibility level defines the specified electromagnetic disturbance level used as a reference level in a specified environment for coordination in the setting of emission and immunity limits.

[9] A load is said non-linear if its impedance vary with applied voltage.

[10] Skin effect is a phenomenon that can be characterized by the repulsion of electromagnetic current lines, which consequence is a tendency for AC current to flow only at the surface of conductors.

[11] Hysteresis is the by which, when magnetic field is applied to a ferromagnetic material, as the core of the transformers, the material stays permanently magnetized, even if the magnetic field is not present.

About the Author: Manuel Bolotinha

-Licentiate Degree in Electrical Engineering – Energy and Power Systems (1974 – Instituto Superior Técnico/University of Lisbon)
– Master Degree in Electrical and Computers Engineering (2017 – Faculdade de Ciências e Tecnologia/Nova University of Lisbon)
– Senior Consultant in Substations and Power Systems; Professional Instructor

The post Introduction to Harmonics – Effect of Harmonics on Power System appeared first on Electrical Technology.



February 24, 2018 at 01:45AM by Department of EEE, ADBU: http://ift.tt/2AyIRVT