The effects of three-phase harmonics

The effects of three-phase harmonics on circuits are similar to the effects of stress

and high blood pressure on the human body. High levels of stress or harmonic distortion can lead to problems for the utility's distribution system, plant distribution

system and any other equipment serviced by that distribution system. Effects can

range from spurious operation of equipment to a shutdown of important plant

equipment, such as machines or assembly lines.

Harmonics can lead to power system inefficiency. Some of the negative ways that

harmonics may affect plant equipment are listed below:

❏ Conductor Overheating: a function of the square rms current per unit volume of the conductor. Harmonic currents on undersized conductors or cables

can cause a "skin effect", which increases with frequency and is similar to a

centrifugal force.

❏ Capacitors: can be affected by heat rise increases due to power loss and reduced life on the capacitors. If a capacitor is tuned to one of the characteristic

harmonics such as the 5th or 7th, overvoltage and resonance can cause dielectric failure or rupture the capacitor.

❏ Fuses and Circuit Breakers: harmonics can cause false or spurious operations and trips, damaging or blowing components for no apparent reason.

❏ Transformers: have increased iron and copper losses or eddy currents due

to stray flux losses. This causes excessive overheating in the transformer

windings. Typically, the use of appropriate "K factor" rated units are recommended for non-linear loads.

❏ Generators: have similar problems to transformers. Sizing and coordination is critical to the operation of the voltage regulator and controls. Excessive harmonic voltage distortion will cause multiple zero crossings of the

current waveform. Multiple zero crossings affect the timing of the voltage

regulator, causing interference and operation instability.

❏ Utility Meters: may record measurements incorrectly, resulting in higher

billings to consumers.

❏ Drives/Power Supplies: can be affected by misoperation due to multiple

zero crossings. Harmonics can cause failure of the commutation circuits,

found in DC drives and AC drives with silicon controlled rectifiers (SCRs).

❏ Computers/Telephones: may experience interference or failures.

HIGH-VOLTAGE (HV) TRANSMISSION LINE PROTECTION SCHEMES

Most transmission lines are protected by directional distance relays. These may serve as backup protection to other schemes in service, or these may be the sensing components in various forms of differential protection.

Figure below shows the basic elements of a PLC (power line carrier) system extensively used for protection of HV transmission lines.

 

An HV transmission line is capable of simultaneous functions of communications and electrical energy transmission. PLC equipment consists of three distinct parts: terminal assemblies consisting of transmitters, receivers, and protective relays; the coupling and tuning equipment, which connects the terminals to selected points on the transmission line; and the transmission line itself, which provides a suitable channel for the transmission of carrier energy in PLC bands of frequencies between terminals.

 

Coupling to lines is accomplished by means of high-voltage capacitors, which provide a low-loss path to carrier signals and block 60 Hz power frequency energy from the carrier equipment. Line traps minimize the loss of carrier power into adjacent lines and prevent external ground fault currents from short-circuiting the carrier signal of the unfaulted line.

 

Carrier Frequencies.

Frequencies in the range of 30 kHz to 500 kHz have been employed for PLC relaying and other communication purposes. The range is high enough to be isolated from the transmission line and the noise it creates and yet not so high as to give rise to excessive attenuation.

 

There are two basic types of signals used for teleprotection channels. Keyed carriers are sometimes referred to as AM, amplitude modulation: It is normally off and intelligence is transmitted by turning the carrier on and off.

 

This type of signal is normally used in blocking-type relaying systems. The frequency may be in range from 29 kHz to 31 kHz, and the signal could be applied to a single sideband (SSB) PLC channel.

 

Frequency Shift Keyed Carrier.

This signal is always on, which provides a means of continuously monitoring the channel. The frequency shift keyed (FSK) carrier is less susceptible to noise and has a greater operating range. FSK channels have been available with two-frequency operations, high and low shift frequencies for additional security.

 

Blocking Schemes.

Transmission line faults are detected using either high-speed phase comparison, in which the phase of the currents at the two terminals are compared, or direction comparison relaying. The scheme operates in a trip permissive mode.

 

A received signal is used to block tripping of the protected line for external faults. The blocking scheme is biased toward dependability because channel or remote relay failure will result in operation of the local blocking relay.

 

Tripping Schemes.

A phase comparison tripping scheme channel is keyed to the trip condition every half cycle during the fault. The scheme is biased toward security so that a failure of the channels or relays would result in non operation of the local relay for external and internal faults. Directional distance relays can be used both for phase as well as ground fault conditions.

-Power system protection blog

String Effeciency and methods to improve String Effeciency

The ratio of voltage across the whole string to the product of number of discs and the voltage across the disc nearest to the conductor is known as string efficiency i.e.,

 

String efficiency is an important consideration since it decides the potential distribution along the string. The greater the string efficiency, the more uniform is the voltage distribution. Thus 100% string efficiency is an ideal case for which the voltage across each disc will be exactly the same. Although it is impossible to achieve 100% string efficiency, yet efforts should be made to improve it

as close to this value as possible.

 

Methods of Improving String Efficiency

The maximum voltage appears across the insulator nearest to the line conductor and decreases progressively as the cross arm is approached. If the insulation of the highest stressed insulator (i.e. nearest to conductor) breaks down or flash over takes place, the breakdown of other units will take place in succession. This necessitates to equalize the potential across the various units of the string i.e. to improve the string efficiency.

The various methods for this purpose are :

 

By using longer cross-arms. The value of string efficiency depends upon the value of K i.e., ratio of shunt capacitance to mutual capacitance. The lesser the value of K, the greater is the string efficiency and more uniform is the voltage distribution. The value of K

can be decreased by reducing the shunt capacitance. In order to reduce shunt capacitance, the distance of conductor from tower must be increased i.e., longer cross-arms should be used. However, limitations of cost and strength of tower do not allow the use of very long cross-arms. In practice, K = 0·1 is the limit that can be achieved by this method.

 

By grading the insulators. In this method, insulators of different dimensions are so chosen that each has a different capacitance. The insulators are capacitance graded i.e. they are assembled in the string in such a way that the top unit has the minimum capacitance, increasing progressively as the bottom unit (i.e., nearest to conductor) is reached. Since voltage is inversely proportional to capacitance, this method tends to equalize the potential distribution across the units in the string. This method has the disadvantage that a large number of different-sized insulators are required. However, good results can be obtained by using standard insulators for most of the string and larger units for that near to the line conductor.

By using a guard ring. The potential across each unit in a string can be equalized by using a guard ring which is a metal ring electrically connected to the conductor and surrounding the bottom insulator. The guard ring introduces capacitance between metal fittings and the line conductor. The guard ring is contoured in such a way that shunt capacitance currents i1, i2 etc. are equal to metal fitting line capacitance currents i′1, i′2 etc. The result is that same charging current I flows through each unit of string. Consequently, there will be uniform potential distribution across the units.

Voltage ranges

Synchronization process

There are five conditions that must be met before the synchronization process takes place. The source

(generator or sub-network) must have equal line voltage, frequency, phase sequence, phase angle, and

waveform to that of the system to which it is being synchronized.

 

Waveform and phase sequence are fixed by the construction of the generator and its connections to the system.

During installation of a generator, careful checks are made to ensure the generator terminals and all control

wiring are correct so that the order of phases (phase sequence) matches the system. Connecting a generator

with the wrong phase sequence will result in a short circuit as the system voltages are opposite to those of the

generator terminal voltages.

 

The voltage, frequency and phase angle must be controlled each time a generator is to be connected to a grid.

Generating units for connection to a power grid have an inherent droop speed control that allows them to share

load proportional to their rating. Some generator units, especially in isolated systems, operate with isochronous

frequency control, maintaining constant system frequency independent of load.

Sizing of protective earthing conductor

Below is based on IEC 60364-5-54. This table provides two methods of determining the appropriate c.s.a. for both PE or PEN conductors.

 

 

	c.s.a. of phase conductors Sph (mm2)	Minimum c.s.a. of PE conductor (mm2)	Minimum c.s.a. of PEN conductor (mm2)
			Cu                       AI
Simplified method (1)	Sph≤ 16	Sph(2)	Sph(3)	Sph(3)
	16 < Sph ≤ 25	16	16
	25 < Sph ≤ 35			25
	35 < Sph ≤ 50	Sph/2	Sph/2
	Sph > 50			Sph/2
Adiabatic method	Any size	(3)  (4)

(1) Data valid if the prospective conductor is of the same material as the line conductor. Otherwise, a correction factor must be applied.
(2) When the PE conductor is separated from the circuit phase conductors, the following minimum values must be respected:

§  2.5 mm² if the PE is mechanically protected

§  4 mm² if the PE is not mechanically protected

(3) For mechanical reasons, a PEN conductor, shall have a cross-sectional area not less than 10 mm² in copper or 16 mm² in aluminium.
(4) Refer to table G53 for the application of this formula.

Wikipedia

Earthing Systems

Panel boards are selling several Countries then earthing systems and main Bus bar arrangement are changed each country.

Type of System Earthing

01.  TN system:

TN power system have one point directly earthed, the exposed conductive parts of the installation being connected to that point by protective conductors. Three types of TN systems are recognized, according to the arrangement of neutral and protective conductors,

(a)    TN-S System – A system having separate neutral and protective conductors throughout

(b)   TN-C-S System – A system in which neutral and protective function are combined in a single conductor in a part of system.

(c)    TN-C system - A system in which neutral and protective functions are combined in a single conductor throughout.

02. TT System -

The TT power system has one point directly earthed, the exposed conductive parts of the installation being connected to earth electrodes electrically independent of the earth electrodes of the power system,

03. IT System  -

The IT power system has no direct connection between live parts and earth, the exposed conductive parts of the electrical installation being earthed.

 

DOL starter

Commercial and Industrial Power distribution systems

Power distribution systems used in multi-family, commercial, and industrial facilities are more complex. A power distribution system consists of metering devices to measure power consumption, main and branch disconnects, protective devices, switching devices to start and stop power flow, conductors, and transformers. Power may be distributed through various switchboards, transformers, and panel boards.

Good distribution systems don’t just happen. Careful engineering is required so that the distribution system safely and efficiently supplies adequate electric service to existing loads and has expansion capacity for possible future loads.

-          siemens

Power outage

A power outage (also power cut, blackout, brownout, or power failure) is a short- or long-term loss of the electric power to an area.

There are many causes of power failures in an electricity network. Examples of these causes include faults at power stations, damage to electric transmission lines, substations or other parts of the distribution system, a short circuit, or the overloading of electricity mains.

Power failures are particularly critical at sites where the environment and public safety are at risk. Institutions such as hospitals, sewage treatment plants, mines, and the like will usually have backup power sources such as standby generators, which will automatically start up when electrical power is lost. Other critical systems, such as telecommunications, are also required to have emergency power. Telephone exchange rooms usually have arrays of lead-acid batteries for backup and also a socket for connecting a generator during extended periods of outage.

 

Types of power outage

 

Power outages are categorized into three different phenomena, relating to the duration and effect of the outage:

A transient fault is a momentary (a few seconds) loss of power typically caused by a temporary fault on a power line. Power is automatically restored once the fault is cleared.

A brownout or sag is a drop in voltage in an electrical power supply. The term brownout comes from the dimming experienced by lighting when the voltage sags. Brownouts can cause poor performance of equipment or even incorrect operation.

A blackout refers to the total loss of power to an area and is the most severe form of power outage that can occur. Blackouts which result from or result in power stations tripping are particularly difficult to recover from quickly. Outages may last from a few minutes to a few weeks depending on the nature of the blackout and the configuration of the electrical network.

 

Protecting the power system from outages

 

In power supply networks, the power generation and the electrical load (demand) must be very close to equal every second to avoid overloading of network components, which can severely damage them. Protective relays and fuses are used to automatically detect overloads and to disconnect circuits at risk of damage.

Under certain conditions, a network component shutting down can cause current fluctuations in neighboring segments of the network leading to a cascading failure of a larger section of the network. This may range from a building, to a block, to an entire city, to an entire electrical grid.

Modern power systems are designed to be resistant to this sort of cascading failure, but it may be unavoidable (see below). Moreover, since there is no short-term economic benefit to preventing rare large-scale failures, some observers[who?] have expressed concern that there is a tendency to erode the resilience of the network over time, which is only corrected after a major failure occurs. It has been claimed[who?] that reducing the likelihood of small outages only increases the likelihood of larger ones. In that case, the short-term economic benefit of keeping the individual customer happy increases the likelihood of large-scale blackouts.

Brownout

A brownout is an intentional or unintentional drop in voltage in an electrical power supply system. Intentional brownouts are used for load reduction in an emergency.[1] The reduction lasts for minutes or hours, as opposed to short-term voltage sag or dip. The term brownout comes from the dimming experienced by lighting when the voltage sags. A voltage reduction may be an effect of disruption of an electrical grid, or may occasionally be imposed in an effort to reduce load and prevent a power outage, known as a blackout.

In the Philippines the term brownout refers to an intentional or unintentional power outage or blackout and there is no apparent word in Philippine English to refer to a drop in voltage.

 

Effects

 

Different types of electrical apparatus will react in different ways to a sag. Some devices will be severely affected, while others may not be affected at all.

The heat output of any resistance device, such as an electric space heater, is equal to the true power consumption, which is an increasing function of the applied voltage. If the resistance stays constant, power consumption is proportional to the square of the applied voltage. Therefore, a significant loss of heat output will occur with a relatively small reduction in voltage. An incandescent lamp will dim due to lower heat creation in the filament, as well as lower conversion of heat to light. Generally speaking, no damage will occur but functionality will be impaired.

Commutated electric motors, such as universal motors will run at reduced speed or reduced torque. Depending on the motor design, no harm may occur. However, under load, the motor may draw more current due to the reduced back-EMF developed at the lower armature speed. Unless the motor has ample cooling capacity, it may eventually overheat and burn out.

An induction motor will draw more current to compensate for the decreased voltage, which may lead to overheating and burnout. If a substantial part of a grid's load is electric motors, attempting to reduce an overload by voltage reduction may not decrease load and can result in damage to customer's equipment.

An unregulated direct current supply will produce a lower output voltage for electronic circuits. The output ripple voltage will decrease in line with the usually reduced load current. In a CRT television, the reduced output voltage can be seen as the screen image shrinking in size and becoming dim and fuzzy.

A linear direct current regulated supply will maintain the output voltage unless the brownout is severe and the input voltage drops below the drop out voltage for the regulator, at which point the output voltage will fall and high levels of ripple from the rectifier/reservoir capacitor will appear on the output.

A switched-mode power supply which has a regulated output will be affected. As the input voltage falls, the current draw will increase to maintain the same output voltage and current, until such a point that the power supply malfunctions.

Brownouts can cause unexpected behavior in systems with digital control circuits. Reduced voltages can bring control signals below the threshold at which logic circuits can reliably detect which state is being represented. As the voltage returns to normal levels the logic can latch at an incorrect state; even can't happen states become possible. The seriousness of this effect and whether steps need to be taken by the designer to prevent it depends on the nature of the equipment being controlled; for instance a brownout may cause a motor to begin running backwards.

SF6 gas & advantages

SF6 Advantages

 

The electric power industry has been using Sulfur Hexafluoride (SF6) gas as a dielectric and

insulating material for many years. Its popularity is mainly due to its unique physical and electrical

properties including:

1) Dielectric strength twice that of air.

2) Nontoxic, nonflammable and noncorrosive.

3) Chemically stable with high breakdown strength. SF6 molecules provide excellent arc extinction

during electrical operations which minimizes contact wear and maintenance.

4) Excellent thermal conductivity. High heat transfer permits lower operating temperatures.

5) Readily available in many commercial locations.

For distribution voltage switchgear, SF6 provides these important advantages:

1) Size reduction

2) Weight reduction

3) Reliable operation

4) Ease of installation

5) Ease of handling

6) Ease and reduction of maintenance

 

Common Applications

Electrical uses include high voltage circuit breakers, high voltage transformers, distribution voltage

switchgear, gas insulated power substations, gas insulated transmission lines, radar equipment, linear

particle accelerators and generators.

Approximately 80% of the annual consumption of SF6 is used for gas insulated substation (GlS)

equipment and medium voltage switchgear including circuit breakers and load break switches. Of the

80%, medium voltage switchgear accounts for approximately 10%. In both electrical applications, the equipment is designed to contain the gas in sealed pressure systems which are assembled, filled

and tested in a controlled environment.

Nonelectrical uses include molten magnesium and aluminum protection and purification, leak

detection, tracer gas studies, propellants, insulating windows, shock absorbers, lasers and in the

electronics industry as a plasma etchant gas. The other 20% of the annual consumption of SF6 is

used in these applications which typically require release of the gas into the atmosphere.

Load shedding (rolling blackout)

Load shedding is an intentionally engineered electrical power shutdown where electricity delivery is stopped for non-overlapping periods of time over different parts of the distribution region. Rolling blackouts are a last-resort measure used by an electric utility company to avoid a total blackout of the power system. They are a type of demand response for a situation where the demand for electricity exceeds the power supply capability of the network. Rolling blackouts may be localised to a specific part of the electricity network or may be more widespread and affect entire countries and continents. Rolling blackouts generally result from two causes: insufficient generation capacity or inadequate transmission infrastructure to deliver sufficient power to the area where it is needed.

Rolling blackouts are a common or even a normal daily event in many developing countries where electricity generation capacity is underfunded or infrastructure is poorly managed. Rolling blackouts in developed countries are rare because demand is accurately forecasted, adequate infrastructure investment is scheduled and networks are well managed; such events are considered an unacceptable failure of planning and can cause significant political damage to responsible governments. In well managed under-capacity systems blackouts are scheduled in advance and advertised to allow people to work around them but in most cases they happen without warning, typically whenever the transmission frequency falls below the 'safe' limit.

Base current rating table

Residual-current device

RCDs are designed to disconnect the circuit if there is a leakage current. By detecting small leakage currents (typically 5–30 milliamperes) and disconnecting quickly enough (<30 ms), they may prevent electrocution. There are also RCDs with intentionally slower responses and lower sensitivities, designed to protect equipment or avoid starting electrical fires, but not disconnect unnecessarily for equipment which has greater leakage currents in normal operation. To prevent electrocution, RCDs should operate within 25-40 milliseconds at leakage currents (through a person) of 30 milliamperes, before electric shock can drive the heart into ventricular fibrillation, the most common cause of death through electric shock. By contrast, conventional circuit breakers or fuses only break the circuit when the total current is excessive (which may be thousands of times the leakage current an RCD responds to). A small leakage current, such as through a person, can be a very serious fault, but would not cause the total current to become high enough for a fuse or circuit breaker to break the circuit, let alone do so fast enough to save a life.

RCDs operate by measuring the current balance between two conductors using a differential current transformer. This measures the difference between the current flowing through the live conductor and that returning through the neutral conductor. If these do not sum to zero, there is a leakage of current to somewhere else (to earth/ground, or to another circuit), and the device will open its contacts.

Residual current detection is complementary to over-current detection. Residual current detection cannot provide protection for overload or short-circuit currents, except for the special case of a short circuit from live to ground (not live to neutral).

Animated 3-phase RCD schematic.

 

For a RCD used with three-phase power, all live conductors and the neutral must pass through the current transformer.

FACTORS GOVERNING THE CURRENT RATING

The current rating of a cable or wire indicates the current capacity that the wire or cable can safely carry continuously. If this limit, or current rating, is exceeded for a length of time, the heat generated may burn the insulation. The current rating of a wire is used to determine what size is needed for a given load, or current drain. The factors that determine the current rating of a wire are the conductor size, the location of the wire in a circuit, the type of insulation, and the safe current rating. Another factor that will be discussed later in this chapter is the material the wire is made of. As you have already seen, these factors also affect the resistance in ohms of a wire-carrying current.

CONDUCTOR SIZE

An increase in the diameter, or cross section, of a wire conductor decreases its resistance and increases its capacity to carry current. An increase in the specific resistance of a conductor increases its resistance and decreases its capacity to carry current.

WIRE LOCATION

The location of a wire in a circuit determines the temperature under which it operates. A wire may be located in a conduit or laced with other wires in a cable. Because it is confined, the wire operates at a higher temperature than if it were open to the free air. The higher the temperature under which a wire is operating, the greater will be its resistance. Its capacity to carry current is also lowered. Note that, in each case, the resistance of a wire determines its current-carrying capacity. The greater the resistance, the more power it dissipates in the form of heat energy. Conductors may also be installed in locations where the ambient (surrounding) temperature is relatively high. When this is the case, the heat generated by external sources is an important part of the total conductor heating. This heating factor will be explained further when we discuss temperature coefficient. We must understand how external heating influences how much current a conductor can carry. Each case has its own specific limitations. The maximum allowable operating temperature of insulated conductors is specified in tables. It varies with the type of conductor insulation being used.

INSULATION

The insulation of a wire does not affect the resistance of the wire. Resistance does, however, determine how much heat is needed to burn the insulation. As current flows through an insulated conductor, the limit of current that the conductor can withstand depends on how hot the conductor can get before it burns the insulation. Different types of insulation will burn at different temperatures. Therefore, the type of insulation used is the third factor that determines the current rating of a conductor

Types of Hydropower Turbines

There are two main types of hydro turbines: impulse and reaction. The type of hydropower turbine selected for a project is based on the height of standing water—referred to as "head"—and the flow, or volume of water, at the site. Other deciding factors include how deep the turbine must be set, efficiency, and cost.

Terms used on this page are defined in the glossary.

Impulse Turbine

The impulse turbine generally uses the velocity of the water to move the runner and discharges to atmospheric pressure. The water stream hits each bucket on the runner. There is no suction on the down side of the turbine, and the water flows out the bottom of the turbine housing after hitting the runner. An impulse turbine is generally suitable for high head, low flow applications.

Pelton hydropower turbine
Credit: GE Energy

·         Pelton

A pelton wheel has one or more free jets discharging water into an aerated space and impinging on the buckets of a runner. Draft tubes are not required for impulse turbine since the runner must be located above the maximum tailwater to permit operation at atmospheric pressure.

A Turgo Wheel is a variation on the Pelton and is made exclusively by Gilkes in England. The Turgo runner is a cast wheel whose shape generally resembles a fan blade that is closed on the outer edges. The water stream is applied on one side, goes across the blades and exits on the other side.

·         Cross-Flow

A cross-flow turbine is drum-shaped and uses an elongated, rectangular-section nozzle directed against curved vanes on a cylindrically shaped runner. It resembles a "squirrel cage" blower. The cross-flow turbine allows the water to flow through the blades twice. The first pass is when the water flows from the outside of the blades to the inside; the second pass is from the inside back out. A guide vane at the entrance to the turbine directs the flow to a limited portion of the runner. The cross-flow was developed to accommodate larger water flows and lower heads than the Pelton.

Reaction Turbine

A reaction turbine develops power from the combined action of pressure and moving water. The runner is placed directly in the water stream flowing over the blades rather than striking each individually. Reaction turbines are generally used for sites with lower head and higher flows than compared with the impulse turbines.

Propeller hydropower turbine
Credit: GE Energy

·         Propeller

A propeller turbine generally has a runner with three to six blades in which the water contacts all of the blades constantly. Picture a boat propeller running in a pipe. Through the pipe, the pressure is constant; if it isn't, the runner would be out of balance. The pitch of the blades may be fixed or adjustable. The major components besides the runner are a scroll case, wicket gates, and a draft tube. There are several different types of propeller turbines:

Bulb hydropower turbine
Credit: GE Energy

·         Bulb turbine

The turbine and generator are a sealed unit placed directly in the water stream.

·         Straflo

The generator is attached directly to the perimeter of the turbine.

·         Tube turbine

The penstock bends just before or after the runner, allowing a straight line connection to the generator.

·         Kaplan

Kaplan hydropower turbine
Credit: GE Energy

Both the blades and the wicket gates are adjustable, allowing for a wider range of operation.

·         Francis

Francis hydropower turbine
Credit: GE Energy

A Francis turbine has a runner with fixed buckets (vanes), usually nine or more. Water is introduced just above the runner and all around it and then falls through, causing it to spin. Besides the runner, the other major components are the scroll case, wicket gates, and draft tube.

·         Kinetic

Kinetic energy turbines, also called free-flow turbines, generate electricity from the kinetic energy present in flowing water rather than the potential energy from the head. The systems may operate in rivers, man-made channels, tidal waters, or ocean currents. Kinetic systems utilize the water stream's natural pathway. They do not require the diversion of water through manmade channels, riverbeds, or pipes, although they might have applications in such conduits. Kinetic systems do not require large civil works; however, they can use existing structures such as bridges, tailraces and channels.

 

Busbars And Their Uses

Used in electrical power distribution, busbars are usually made out of aluminium or copper and they are able to conduct electricity to transmit power from the source of electric power to the load. They are usually supported by insulators and conduct electricity within switchboards, substations or other electric apparatus. Some typical applications of these devices can be to form the interconnectedness of the incoming and outgoing electrical transmission lines and transformers at an electrical substation; supplying huge amounts of amperes to the electrolytic process in an aluminium smelter by using large busbars and also interconnecting generators to the main transformers in a power plant.

 

The size of the busbar determines its application and the amount of current that it can carry safely. They can be tubular, solid or flat depending on the application and to serve different needs. A tubular busbar is hollow and this shape allows it to dissipate heat more efficiently as it has a high surface area. Hollow or flat shaped bus bars are prevalent in high current applications. Also, the hollow section of a busbar is generally stiffer as compared to a solid rod, thus this allows a greater span between busbar support in outdoor switchyards. The smallest cross-sectional area of a busbar can be as little as 10mm2, but electrical substations would make use of busbars with a diameter of more than 50 mm as they carry great amounts of amperes. Aluminium smelters would make use of these large busbars to carry tens of thousands of amperes to the electrochemical cells that produce aluminium from molten salts.

 

As they carry large amount of electricity, it is important to support the busbars with insulation to prevent any accidents from happening whereby someone may accidentally touch the bus bar. Insulation can either support the busbar or completely surround it. They can be prevented from accidental touch by placing the bus bars at an elevated height so it would not be easily accessible or by a metal earth enclosure. Some bus bars such as the earth bus bar can be bolted directly into the housing chassis of their enclosure. This prevents unwanted touch and also saves the bus bar from any damage it may incur when left exposed. There are several other ways that busbars can be connected to one another or the electrical apparatus with which they would be used with such as by bolting, clamping or welding connections. Switchgears, panelboards or busways usually contain the busbars and the electrical supply is split by the distribution boards into different circuits. Busways are a type of busbars that have a protective cover and are long in shape. Also referred to as bus ducts, these devices allow the electricity to branch out to different circuits at any point along its surface; unlike regular busbars that allow branching of the main supply only at one location.

 

The most common types of busbars present in the industry today are rigid busbars, strain busbars and insulated phase busbars. Each of these different types of busbars has different applications and uses. The rigid busbars are used in low, medium or high voltage applications, constructed with aluminium or copper bars and they make use of porcelain to insulate them. As for the strain busbars, they are mostly used in high voltage applications and are usually strung between the metal structures of a substation. They are held in place by suspension-type insulators. Lastly, as for the insulated-phase bus bars, they are used at medium voltage and similar to the rigid bus bars, they are rigid bars that are supported by insulators. These busbars are able to eliminate short circuits between adjacent phases.

 

Busbars And Their Uses

Used in electrical power distribution, busbars are usually made out of aluminium or copper and they are able to conduct electricity to transmit power from the source of electric power to the load. They are usually supported by insulators and conduct electricity within switchboards, substations or other electric apparatus. Some typical applications of these devices can be to form the interconnectedness of the incoming and outgoing electrical transmission lines and transformers at an electrical substation; supplying huge amounts of amperes to the electrolytic process in an aluminium smelter by using large busbars and also interconnecting generators to the main transformers in a power plant.

 

The size of the busbar determines its application and the amount of current that it can carry safely. They can be tubular, solid or flat depending on the application and to serve different needs. A tubular busbar is hollow and this shape allows it to dissipate heat more efficiently as it has a high surface area. Hollow or flat shaped bus bars are prevalent in high current applications. Also, the hollow section of a busbar is generally stiffer as compared to a solid rod, thus this allows a greater span between busbar support in outdoor switchyards. The smallest cross-sectional area of a busbar can be as little as 10mm2, but electrical substations would make use of busbars with a diameter of more than 50 mm as they carry great amounts of amperes. Aluminium smelters would make use of these large busbars to carry tens of thousands of amperes to the electrochemical cells that produce aluminium from molten salts.

 

As they carry large amount of electricity, it is important to support the busbars with insulation to prevent any accidents from happening whereby someone may accidentally touch the bus bar. Insulation can either support the busbar or completely surround it. They can be prevented from accidental touch by placing the bus bars at an elevated height so it would not be easily accessible or by a metal earth enclosure. Some bus bars such as the earth bus bar can be bolted directly into the housing chassis of their enclosure. This prevents unwanted touch and also saves the bus bar from any damage it may incur when left exposed. There are several other ways that busbars can be connected to one another or the electrical apparatus with which they would be used with such as by bolting, clamping or welding connections. Switchgears, panelboards or busways usually contain the busbars and the electrical supply is split by the distribution boards into different circuits. Busways are a type of busbars that have a protective cover and are long in shape. Also referred to as bus ducts, these devices allow the electricity to branch out to different circuits at any point along its surface; unlike regular busbars that allow branching of the main supply only at one location.

 

The most common types of busbars present in the industry today are rigid busbars, strain busbars and insulated phase busbars. Each of these different types of busbars has different applications and uses. The rigid busbars are used in low, medium or high voltage applications, constructed with aluminium or copper bars and they make use of porcelain to insulate them. As for the strain busbars, they are mostly used in high voltage applications and are usually strung between the metal structures of a substation. They are held in place by suspension-type insulators. Lastly, as for the insulated-phase bus bars, they are used at medium voltage and similar to the rigid bus bars, they are rigid bars that are supported by insulators. These busbars are able to eliminate short circuits between adjacent phases.

 

DC motor types

Advantages & disadvantages of energy saving bulbs

Energy saver light bulbs are highly energy efficient. You can find a wide range of energy efficient products in the market. However during the time when they were introduced in the market they were available in big sizes and did not have unique designs. Moreover they were costly and took a considerable time to reach full brightness. With the advanced technology the energy light bulbs available today are much more superior to their old models. After improvisation the energy saver bulbs are available in several sizes, designs and are cost effective.

Below are some of the advantages and disadvantages discussed

 

1.       The Advantages of energy saver Bulb are many.

2.       They are environmental friendly

3.       Help in saving your electricity bills;

4.       Serve the households with 4 times better energy efficiency than the incandescent lamps

5.       Prevent carbon emissions to a large extent.

6.       Are durable and long lasting than the filament lamps.

 

Disadvantages:

 

1.       They are expensive but by considering the best eco-friendly features the price really does not matter.

2.       The Compact fluorescent light also known as CFLs are available in only white or colored lights

3.       The size of the CFLs is bigger as compared to the conventional bulbs.

4.       These cannot be used with dimmer switches.

Thus summing up briefly we can come up to a conclusion that the disadvantages of CFLs are ignorable as they have numerous solutions available. Ignoring the drawbacks which are too minute we can say that CFLs are the highly energy efficient lights.

DIFFERENTIAL PROTECTION

Differential protection is a very reliable method of protecting generators, transformers, buses, and transmission lines from the effects of internal faults.

Figure: Differential Protection of a Generator

In a differential protection scheme in the above figure, currents on both sides of the equipment are compared. The figure shows the connection only for one phase, but a similar connection is usually used in each phase of the protected equipment. Under normal conditions, or for a fault outside of the protected zone, current I₁ is equal to current I₂ . Therefore the currents in the current transformers secondaries are also equal, i.e. i₁ = i₂ and no current flows through the current relay. 

If a fault develops inside of the protected zone, currents I₁ and I₂ are no longer equal, therefore i₁ and i₂ are not equal and there is  a current flowing through the current relay.

 

Differential Protection of a Station Bus

The principle of the differential protection of a station bus is the same as for generators.

The sum of all currents entering and leaving the bus must be equal to zero under normal conditions or if the fault is outside of the protected zone. If there is a fault on the bus, there will be a net flow of current to the bus and the differential relay will operate.

 

Figure: Single Line Diagram of Bus Differential Protection

 

Hybrid cars

Hybrid cars are considered as major breakthrough in the vehicle technology progress. For long, vehicles that use gasoline or some other fossil fuels have been running on the road. People have been familiar with such kind of vehicle, but more of them are aware with such fossil fuel engine performance effects to environment condition. Pollutions that are provided by combustion process of the engine can bring bad effects. Therefore, hybrid technology is considered as the most reasoned solution to correct the failure of usual car engine, but still maintain or even improve the performance.

 

Hybrid cars technology combines two or more different power sources to make the car moving. Actually, this technology is not a new one. There have been some kinds of vehicle applying hybrid technology long time ago, such as the WWII submarine that used diesel-electric engine as its mover engine. Usual locomotive also applies such diesel –electric engine and it is considered as a hybrid engine. Any car that uses two or more power sources is recognized as hybrid car. The main benefit of such hybrid car technology types is the lower consumption of the fuel and surely lower emission rate as well. With the latest improvement of the technology, such hybrid system can also provide better performance.

 

Hybrid cars are also categorized into several types. People who want to purchase a new hybrid car should also understand the types of hybrid car so they can try choosing one that suits their need.

 

Basically, there are three types of hybrid car: full hybrid, parallel hybrid and series hybrid car. The first type is the full hybrid car. The obvious characteristic of such type of hybrid car is it still can propel the car forward when it runs slowly without any gasoline intake. The other type is parallel hybrid car. This type applies two motors that work together. The first motor is powered by gasoline and the other is powered by electrical battery. Other hybrid cars type is the series hybrid car. In this type, fuel is mainly only used to ignite the engine, while the power source is the generator. Generator has main function as the battery charger. It can charge batteries, which later provide powers to such car electric motor that drives the transmission and moves the car. The main benefit of such type of hybrid car is that it does not require fuel engine to obtain the energy; at least not immediately. Hybrid car type that is offered mostly today is the parallel type.

 

The progress of hybrid technology has been passing long timeline, from just several military vehicles to current common vehicles. Hybrid vehicles have been known by many people for about two decades. Its main concept is to combine fuel engine system and the electrical motor system that has been invented previously. The electrical engine seemed more environmental friendly, but it was only capable for short distance use, while common gasoline car provides emission. Hybrid cars battery provide energy to the electric motor until such car reaches specific speed then gas engine will take the main role. The gas engine also has function to charge the battery while it propels the car. This combined system provides benefit in the fuel intake rate as such type of car can save more fuel when the electrical motor system works.

 

Previously, the battery that provided power to the motor took pretty wide space and provided energy for short time and took pretty long time for charging, but the technology progress of hybrid car battery provides better quality battery, which is smaller, but can provide power for longer last and takes fewer times for charging. The next step in hybrid car progress is the availability of plug-in car. People can charge their hybrid car in a charging station while they get rest.

Voltage sags

Voltage sags -- or dips typically lasting from a cycle to a second or so, or tens of milliseconds to hundreds of milliseconds. Voltage swells are brief increases in voltage over the same time range.

(Longer periods of low or high voltage are referred to as "undervoltage" or "overvoltage".)

Voltage sags are caused by abrupt increases in loads such as short circuits or faults, motors starting, or electric heaters turning on, or they are caused by abrupt increases in source impedance, typically caused by a loose connection. Voltage swells are almost always caused by an abrupt reduction in load on a circuit with a poor or damaged voltage regulator, although they can also be caused by a damaged or loose neutral connection.

 

A typical voltage sag.

Voltage sags are the most common power disturbance. At a typical industrial site, it is not unusual to see several sags per year at the service entrance, and far more at equipment terminals.

Power system protection

Types of protection

 

Generator sets – In a power plant, the protective relays are intended to prevent damage to alternators or to the transformers in case of abnormal conditions of operation, due to internal failures, as well as insulating failures or regulation malfunctions. Such failures are unusual, so the protective relays have to operate very rarely. If a protective relay fails to detect a fault, the resulting damage to the alternator or to the transformer might require costly equipment repairs or replacement, as well as income loss from the inability to produce and sell energy.

 

High voltage transmission network

Protection on the transmission and distribution serves two functions: Protection of plant and protection of the public (including employees). At a basic level, protection looks to disconnect equipment which experience an overload or a short to earth. Some items in substations such as transformers might require additional protection based on temperature or gas pressure, among others.

 

Overload & Back-up for Distance (Overcurrent)

Overload protection requires a current transformer which simply measures the current in a circuit. There are two types of overload protection: instantaneous overcurrent and time overcurrent (TOC). Instantaneous overcurrent requires that the current exceeds a pre-determined level for the circuit breaker to operate. TOC protection operates based on a current vs time curve. Based on this curve if the measured current exceeds a given level for the preset amount of time, the circuit breaker or fuse will operate.

 

Earth fault

Earth fault protection again requires current transformers and senses an imbalance in a three-phase circuit. Normally the three phase currents are in balance, i.e. roughly equal in magnitude. If one or two phases become connected to earth via a low impedance path, their magnitudes will increase dramatically, as will current imbalance. If this imbalance exceeds a pre-determined value, a circuit breaker should operate.

 

Distance (Impedance Relay)

Distance protection detects both voltage and current. A fault on a circuit will generally create a sag in the voltage level. If the ratio of voltage to current measured at the relay terminals, which equates to an impedance, lands within a pre-determined level the circuit breaker will operate. This is useful for reasonable length lines, lines longer than 10 miles, because its operating characteristics are based on the line characteristics. This means that when a fault appears on the line the impedance setting in the relay is compared to the apparent impedance of the line from the relay terminals to the fault. If the relay setting is determined to be below the apparent impedance it is determined that the fault is within the zone of protection. When the transmission line length is too short, less than 10 miles, distance protection becomes more difficult to coordinate. In these instances the best choice of protection is current differential protection.

 

Back-up

The objective of protection is to remove only the affected portion of plant and nothing else. A circuit breaker or protection relay may fail to operate. In important systems, a failure of primary protection will usually result in the operation of back-up protection. Remote back-up protection will generally remove both the affected and unaffected items of plant to clear the fault. Local back-up protection will remove the affected items of the plant to clear the fault.

Low-voltage networks – The low voltage network generally relies upon fuses or low-voltage circuit breakers to remove both overload and earth faults.