How reactive power is helpful to maintain a system healthy

How reactive power is helpful to maintain a systemhealthy

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How reactive power is helpful to maintain a system healthy

We always in practice to reduce reactive power to improve system efficiency. This are acceptable atsome level, if system is purely resistively or capacitance it make cause some problem in Electricalsystem. AC systems supply or consume two kind of power: real power and reactive power.

Real power accomplishes useful work while reactive power supports the voltage that must becontrolled for system reliability. Reactive power has a profound effect on the security of power systemsbecause it affects voltages throughout the system.

Find important discussion regarding importance about Reactive Power and how it is useful to maintainSystem voltage healthy.

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Need of Reactive PowerVoltage control in an electrical power system is important for proper operation for electricalpower equipment to prevent damage such as overheating of generators and motors, to reducetransmission losses and to maintain the ability of the system to withstand and prevent voltagecollapse. In general terms, decreasing reactive power causing voltage to fall while increasing itcausing voltage to rise. A voltage collapse occurs when the system try to serve much more loadthan the voltage can support..When reactive power supply lower voltage, as voltage drops current must increase tomaintain power supplied, causing system to consume more reactive power and the voltagedrops further . If the current increase too much, transmission lines go off line, overloading otherlines and potentially causing cascading failures..If the voltage drops too low, some generators will disconnect automatically to protectthemselves. Voltage collapse occurs when an increase in load or less generation ortransmission facilities causes dropping voltage, which causes a further reduction in reactivepower from capacitor and line charging, and still there further voltage reductions. If voltagereduction continues, these will cause additional elements to trip, leading further reduction involtage and loss of the load. The result in these entire progressive and uncontrollable declinesin voltage is that the system unable to provide the reactive power required supplying thereactive power demands.

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Importance of Present of Reactive Power Voltage control and reactive-power management are two aspects of a single activity that bothsupports reliability and facilitates commercial transactions across transmission networks..On an alternating-current (AC) power system, voltage is controlled by managing production andabsorption of reactive power. There are three reasons why it is necessary to manage reactivepower and control voltage..First, both customer and power-system equipment are designed to operate within a range ofvoltages, usually within5% of the nominal voltage. At low voltages, many types of equipmentperform poorly; light bulbs provide less illumination, induction motors can overheat and bedamaged, and some electronic equipment will not operate at. High voltages can damageequipment and shorten their lifetimes..Second, reactive power consumes transmission and generation resources. To maximize theamount of real power that can be transferred across a congested transmission interface,reactive-power flows must be minimized. Similarly, reactive-power production can limit agenerators real-power capability..Third, moving reactive power on the transmission system incurs real-power losses. Bothcapacity and energy must be supplied to replace these losses..Voltage control is complicated by two additional factors..First, the transmission system itself is a nonlinear consumer of reactive power, depending on

system loading. At very light loading the system generates reactive power that must beabsorbed, while at heavy loading the system consumes a large amount of reactive power thatmust be replaced. The systems reactive-power requirements also depend on the generationand transmission configuration..Consequently, system reactive requirements vary in time as load levels and load and generationpatterns change. The bulk-power system is composed of many pieces of equipment, any one ofwhich can fail at any time. Therefore, the system is designed to withstand the loss of any singlepiece of equipment and to continue operating without impacting any customers. That is, thesystem is designed to withstand a single contingency. Taken together, these two factors result ina dynamic reactive-power requirement. The loss of a generator or a major transmission line canhave the compounding effect of reducing the reactive supply and, at the same time,reconfiguring flows such that the system is consuming additional reactive power..At least a portion of the reactive supply must be capable of responding quickly to changingreactive-power demands and to maintain acceptable voltages throughout the system. Thus, justas an electrical system requires real-power reserves to respond to contingencies, so too it mustmaintain reactive-power reserves..Loads can also be both real and reactive. The reactive portion of the load could be served fromthe transmission system. Reactive loads incur more voltage drop and reactive losses in thetransmission system than do similar-size (MVA) real loads..Vertically integrated utilities often include charges for provision of reactive power to loads in theirrates. With restructuring, the trend is to restrict loads to operation at near zero reactive powerdemand (a 1.0 power factor). The system operator proposal limits loads to power factorsbetween 0.97 lagging (absorbing reactive power) and 0.99 leading. This would help to maintainreliability of the system and avoid the problems of market power in which a company could useits transmission lines to limit competition for generation and increase its prices.

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Purpose of Reactive PowerSynchronous generators, SVC and various types of other DER (Distributed energy resource)equipment are used to maintain voltages throughout the transmission system. Injecting reactivepower into the system raises voltages, and absorbing reactive power lowers voltages..Voltage-support requirements are a function of the locations and magnitudes of generatoroutputs and customer loads and of the configuration of the DER transmission system..These requirements can differ substantially from location to location and can change rapidly asthe location and magnitude of generation and load change. At very low levels of system load,transmission lines act as capacitors and increase voltages. At high levels of load, however,transmission lines absorb reactive power and thereby lower voltages. Most transmission-systemequipment (e.g., capacitors, inductors, and tap-changing transformers) is static but can beswitched to respond to changes in voltage-support requirements.System operation has three objectives when managing reactive power and voltages..First, it must maintain adequate voltages throughout the transmission and distribution system for

both current and contingency conditions..Second, it seeks to minimize congestion of real-power flows..Third, it seeks to minimize real-power losses..However, the mechanisms that system operators use to acquire and deploy reactive-powerresources are changing .These mechanisms must be fair to all parties as well as effective.Further, they must be demonstrably fair.

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What is Reactive Power?While active power is the energy supplied to run a motor, heat a home, or illuminate an electriclight bulb, reactive power provides the important function of regulating voltage.If voltage on the system is not high enough, active power cannot be supplied.Reactive power is used to provide the voltage levels necessary for active power to do usefulwork.Reactive power is essential to move active power through the transmission and distributionsystem to the customer.

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Why Do We Need Reactive Power?Reactive power (VARS) is required to maintain the voltage to deliver active power (watts)through transmission lines.Motor loads and other loads require reactive power to convert the flow of electrons into usefulwork.When there is not enough reactive power, the voltage sags down and it is not possible to pushthe power demanded by loads through the lines.

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Reactive Power is a Byproduct of Alternating Current (AC) SystemsTransformers, transmission lines, and motors require reactive powerTransformers and transmission lines introduce inductance as well as resistance:

1. Both oppose the flow of current2. Must raise the voltage higher to push the power through the inductance of the lines3. Unless capacitance is introduced to offset inductance

The farther the transmission of power, the higher the voltage needs to be raisedElectric motors need reactive power to produce magnetic fields for their operation

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How Are Voltages Controlled?

Voltages are controlled by providing sufficient reactive power control margin to modulate andsupply needs through:

1. Shunt capacitor and reactor compensations2. Dynamic compensation3. Proper voltage schedule of generation.

Voltages are controlled by predicting and correcting reactive power demand from loads

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Voltage must be maintained within Acceptable LevelsUnder normal system conditions, both peak or off peak load conditions, the voltages need to bemaintained between 95% and 105% of the nominal.Low voltage conditions could result in equipment malfunctions:

1. Motor will stall, overheat or damage2. Reactive power output of capacitors will be reduced exponentially3. Generating units may trip.

High voltage conditions may:

1. Damage major equipment insulation failure2. Automatically trip major transmission equipment

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Voltage and Reactive PowerVoltage and reactive power must be properly managed and controlled to:

1. Provide adequate service quality2. Maintain proper stability of the power system.

Reactive Power and Power FactorReactive power is present when the voltage and current are not in phase:

1. One waveform leads the other2. Phase angle not equal to 0o3. Power factor less than unity

Measured in volt-ampere reactive (VAR)Produced when the current waveform leads voltage waveform (Leading power factor)Vice versa, consumed when the current waveform lags voltage (lagging power factor)

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Reactive Power LimitationsReactive power does not travel very far.

Power Triangle

Usually necessary to produce it close to the location where it is neededA supplier/source close to the location of the need is in a much better position to providereactive power versus one that is located far from the location of the needReactive power supplies are closely tied to the ability to deliver real or active power.

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Reactive power caused absence of electrical supply in country-A blackout

The quality of the electrical energysupply can be evaluated basing on anumber of parameters. However, themost important will be always thepresence of electrical energy and thenumber and duration of interrupts..If there is no voltage in the socketnobody will care about harmonics,sags or surges..A long term, wide-spread interrupt ablackout leads usually to catastrophiclosses. It is difficult to imagine that inall the country there is no electricalsupply..In reality such things have already happened a number of times. One of the reasons leading to ablackout is reactive power that went out of the control..When consumption of electrical energy is high, the demand on inductive reactive powerincreases usually at the same proportion. In this moment, the transmission lines (that are wellloaded) introduce an extra inductive reactive power..The local sources of capacitive reactive power become insufficient. It is necessary to delivermore of the reactive power from generators in power plants..It might happen that they are already fully loaded and the reactive power will have to bedelivered from more distant places or from abroad. Transmission of reactive power will loadmore the lines, which in turn will introduce more reactive power. The voltage on customer sidewill decrease further. Local control of voltage by means of autotransformers will lead to increaseof current (to get the same power) and this in turn will increase voltage drops in lines. In onemoment this process can go like avalanche reducing voltage to zero. In mean time most of thegenerators in power plants will switch off due to unacceptably low voltage what of course willdeteriorate the situation..In continental Europe most of the power plant is based on heat and steam turbines. If ageneration unit in such power plant is stopped and cool down it requires time and electricalenergy to start operation again. If the other power plants are also off -the blackout is permanent..

Insufficient reactive power leading to voltage collapse has been a causal factor in majorblackouts in the worldwide. Voltage collapse occurred in United States in the blackout of July 2,1996, and August10, 1996 on the West Coast..While August 14, 2003, blackout in the United States and Canada was not due to a voltagecollapse as that term has traditionally used by power system engineers, the task force finalreport said that Insufficient reactive power was an issue in the blackout and the reportalso overestimation of dynamics reactive output of system generation as common factoramong major outages in the United States..Demand for reactive power was unusually high because of a large volume of long-distance transmissions streaming through Ohio to areas, including Canada, than neededto import power to meet local demand. But the supply of reactive power was low becausesome plants were out of service and, possibly, because other plants were not producingenough of it.

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Problems of reactive powerThough reactive power is needed to run many electrical devices, it can cause harmful effects onyour appliances and other motorized loads, as well as your electrical infrastructure. Since thecurrent flowing through your electrical system is higher than that necessary to do the requiredwork, excess power dissipates in the form of heat as the reactive current flows through resistivecomponents like wires, switches and transformers. Keep in mind that whenever energy isexpended, you pay. It makes no difference whether the energy is expended in the form of heator useful work..We can determine how much reactive power your electrical devices use by measuring theirpower factor, the ratio between real power and true power. A power factor of 1 (i.e. 100%) ideallymeans that all electrical power is applied towards real work. Homes typically have overall powerfactors in the range of 70% to 85%, depending upon which appliances may be running. Newerhomes with the latest in energy efficient appliances can have an overall power factor in thenineties..The typical residential power meter only reads real power, i.e. what you would have with apower factor of 100%. While most electric companies do not charge residences directly forreactive power, its a common misconception to say that reactive power correction has noeconomic benefit. To begin with, electric companies correct for power factor around industrialcomplexes, or they will request the offending customer to do so at his expense, or they willcharge more for reactive power. Clearly electric companies benefit from power factor correction,since transmission lines carrying the additional (reactive) current to heavily industrialized areascosts them money. Many people overlook the benefits that power factor correction can offer thetypical home in comparison to the savings and other benefits that businesses with largeinductive loads can expect..Most importantly, you pay for reactive power in the form of energy losses created by the reactivecurrent flowing in your home. These losses are in the form of heat and cannot be returned to thegrid. Hence you pay. The fewer kilowatts expended in the home, whether from heat dissipationor not, the lower the electric bill. Since power factor correction reduces the energy losses, yousave..

As stated earlier, electric companies correct for power factor around industrial complexes, orthey will request the offending customer to do so, or they will charge for reactive power. Theyrenot worried about residential service because the impact on their distribution grid is not assevere as in heavily industrialized areas. However, it is true that power factor correction assiststhe electric company by reducing demand for electricity, thereby allowing them to satisfy serviceneeds elsewhere. But who cares? Power factor correction lowers your electric bill by reducingthe number of kilowatts expended, and without it your electric bill will be higher, guaranteed..Weve encountered this with other electric companies and have been successful in getting eachof them to issue a retraction. Electric companies do vary greatly and many show no interest indeviating from their standard marketing strategy by acknowledging proven energy savingproducts. Keep in mind that promoting REAL energy savings to all their customers woulddevastate their bottom line..Power factor correction will not raise your electric bill or do harm to your electrical devices. Thetechnology has been successfully applied throughout industry for years. When sized properly,power factor correction will enhance the electrical efficiency and longevity of inductive loads.Power factor correction can have adverse side effects (e.g. harmonics) on sensitiveindustrialized equipment if not handled by knowledgeable, experienced professionals. Powerfactor correction on residential dwellings is limited to the capacity of the electrical panel (200amp max) and does not over compensate household inductive loads. By increasing theefficiency of electrical systems, energy demand and its environmental impact is lessened.

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Profound effects of Reactive Power in Various elements of Power System:Generation

An electric-power generators primary function is to convert fuel (or other energy resource) intoelectric power. Almost all generators* also have considerable control over their terminal voltageand reactive-power output..Payment for the use of this resource is the specific focus of voltage control from generationservice. The ability of generator to provide reactive support depends on its real-powerproduction. Like most electric equipment, generators are limited by their current-carryingcapability. Near rated voltage, this capability becomes an MVA limit for the armature of thegenerator rather than a MW limitation..Production of reactive power involves increasing the magnetic field to raise the generatorsterminal voltage. Increasing the magnetic field requires increasing the current in the rotating fieldwinding. Absorption of reactive power is limited by the magnetic-flux pattern in the stator, whichresults in excessive heating of the stator-end iron, the core-end heating limit..The synchronizing torque is also reduced when absorbing large amounts of reactive power,which can also limit generator capability to reduce the chance of losing synchronism with thesystem..The generator prime mover (e.g., the steam turbine) is usually designed with less capacity thanthe electric generator, resulting in the prime-mover limit. The designers recognize that thegenerator will be producing reactive power and supporting system voltage most of the time.Providing a prime mover capable of delivering all the mechanical power the generator can

convert to electricity when it is neither producing nor absorbing reactive power would result inunderutilization of the prime mover..To produce or absorb additional VARs beyond these limits would require a reduction in the real-power output of the unit. Control over the reactive output and the terminal voltage of thegenerator is provided by adjusting the DC current in the generators rotating field .Control can beautomatic, continuous, and fast..The inherent characteristics of the generator help maintain system voltage. At any given fieldsetting, the generator has a specific terminal voltage it is attempting to hold. If the systemvoltage declines, the generator will inject reactive power into the power system, tending to raisesystem voltage. If the system voltage rises, the reactive output of the generator will drop, andultimately reactive power will flow into the generator, tending to lower system voltage. Thevoltage regulator will accentuate this behavior by driving the field current in the appropriatedirection to obtain the desired system voltage.

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Synchronous condesersEvery synchronous machine (motor or generator) with a controllable field has the reactive-powercapabilities discussed above..Synchronous motors are occasionally used to provide dynamic voltage support to the powersystem as they provide mechanical power to their load. Some combustion turbines and hydrounits are designed to allow the generator to operate without its mechanical power source simplyto provide the reactive-power capability to the power system when the real-power generation isunavailable or not needed..Synchronous machines that are designed exclusively to provide reactive support are calledsynchronous condensers..Synchronous condensers have all of the response speed and controllability advantages ofgenerators without the need to construct the rest of the power plant (e.g., fuel-handlingequipment and boilers). Because they are rotating machines with moving parts and auxiliarysystems, they may require significantly more maintenance than static alternatives. They alsoconsume real power equal to about 3% of the machines reactive-power rating.

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Capacitors and inductorsCapacitors and inductors (which are sometimes called reactors) are passive devices thatgenerate or absorb reactive power. They accomplish this without significant real-power losses oroperating expense. The output of capacitors and inductors is proportional to the square of thevoltage. Thus, a capacitor bank (or inductor) rated at 100 MVAR will produce (or absorb) only 90MVAR when the voltage dips to 0.95 pu but it will produce (or absorb) 110 MVAR when thevoltage rises to 1.05 pu. This relationship is helpful when inductors are employed to holdvoltages down..The inductor absorbs more when voltages are highest and the device is needed most. Therelationship is unfortunate for the more common case where capacitors are employed to support

voltages. In the extreme case, voltages fall, and capacitors contribute less, resulting in a furtherdegradation in voltage and even less support from the capacitors; ultimately, voltage collapsesand outages occur..Inductors are discrete devices designed to absorb a specific amount of reactive power at aspecific voltage. They can be switched on or off but offer no variable control..Capacitor banks are composed of individual capacitor cans, typically 200 kVAR or less each.The cans are connected in series and parallel to obtain the desired capacitor-bank voltage andcapacity rating. Like inductors, capacitor banks are discrete devices but they are oftenconfigured with several steps to provide a limited amount of variable control which makes it adisadvantage compared to synchronous motor.

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Static VAR compensators (SVCs) An SVC combines conventional capacitors and inductors with fast switching capability.Switching takes place in the sub cycle time frame (i.e., in less than 1/60 of a second), providinga continuous range of control. The range can be designed to span from absorbing to generatingreactive power. Consequently, the controls can be designed to provide very fast and effectivereactive support and voltage control. Because SVCs use capacitors, they suffer from the samedegradation in reactive capability as voltage drops. They also do not have the short-termoverload capability of generators and synchronous condensers. SVC applications usuallyrequire harmonic filters to reduce the amount of harmonics injected into the power system.

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Static synchronous compensators (STATCOMs)The STATCOM is a solid-state shunt device that generates or absorbs reactive power and isone member of a family of devices known as flexible AC transmission system (FACTS).The STATCOM is similar to the SVC in response speed, control capabilities, and the use ofpower electronics. Rather than using conventional capacitors and inductors combined with fastswitches, however, the STATCOM uses power electronics to synthesize the reactive poweroutput. Consequently, output capability is generally symmetric, providing as much capability forproduction as absorption. The solid-state nature of the STATCOM means that, similar to the SVC, the controls can bedesigned to provide very fast and effective voltage control. While not having the short-termoverload capability of generators and synchronous condensers, STATCOM capacity does notsuffer as seriously as SVCs and capacitors do from degraded voltage.STATCOMs are current limited so their MVAR capability responds linearly to voltage as opposedto the voltage squared relationship of SVCs and capacitors. This attribute greatly increases theusefulness of STATCOMs in preventing voltage collapse.

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Distributed generationDistributing generation resources throughout the power system can have a beneficial effect ifthe generation has the ability to supply reactive power. Without this ability to control reactive-power output, performance of the transmission and distribution system can be degraded.Induction generators were an attractive choice for small, grid-connected generation, primarily

because they are relatively inexpensive. They do not require synchronizing and havemechanical characteristics that are appealing for some applications (wind, for example). Theyalso absorb reactive power rather than generate it, and are not controllable. If the output fromthe generator fluctuates (as wind does), the reactive demand of the generator fluctuates as well,compounding voltage-control problems for the transmission system. Induction generators canbe compensated with static capacitors, but this strategy does not address the fluctuationproblem or provide controlled voltage support. Many distributed generation resources are nowbeing coupled to the grid through solid-state power electronics to allow the prime movers speedto vary independently of the power-system frequency. For wind, this use of solid-stateelectronics can improve the energy capture..For gas-fired micro turbines, power electronics equipment allows them to operate at very highspeeds. Photovoltaics generate direct current and require inverters to couple them to the powersystem. Energy-storage devices (e.g., batteries, flywheels, and superconducting magnetic-energy storage devices) are often distributed as well and require solid-state inverters to interfacewith the grid. This increased use of a solid-state interface between the devices and the powersystem has the added benefit of providing full reactive-power control, similar to that of aSTATCOM..In fact, most devices do not have to be providing active power for the full range of reactivecontrol to be available. The generation prime mover, e.g. turbine, can be out of service while thereactive component is fully functional. This technological development (solid-state powerelectronics) has turned a potential problem into a benefit, allowing distributed resources tocontribute to voltage control.

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Transmission sideUnavoidable consequence of loads operation is presence of reactive power, associated withphase shifting between voltage and current..Some portion of this power is compensated on customer side, while the rest is loading thenetwork. The supply contracts do not require a cos equal to one. The reactive power is alsoused by the transmission lines owner for controlling the voltages..Reactive component of current adds to the loads current and increases the voltage drops acrossnetwork impedances. Adjusting the reactive power flow the operator change voltage drops inlines and in this way the voltage at customer connection point. The voltage on customer sidedepends on everything what happens on the way from generator to customer loads. All nodes,connation points of other transmission lines, distribution station and other equipment contributeto reactive power flow..A transmission line itself is also a source of reactive power. A line that is open on the other end(without load) is like a capacitor and is a source of capacitive (leading) reactive power. Thelengthwise inductances without current are not magnetized and do not introduce any reactivecomponents..On the other hand, when a line is conducting high current, the contribution of the lengthwiseinductances is prevalent and the line itself becomes a source of inductive (lagging) reactivepower. For each line can be calculated a characteristic value of power flow Sk..

If the transmitted power is above Sk, the line will introduce additionally inductive reactive power,and if it is below Sk, the line will introduce capacitive reactive power. The value of Sk dependson the voltage: for 400 kV line is about 32% of the nominal transmission power, for 220 kV line isabout 28% and for 110 kV line is about 22%. The percentage will vary accordingly toconstruction parameters..The reactive power introduced by the lines themselves is really a nuisance for the transmissionsystem operator. In the night, when the demand is low it is necessary to connect parallelreactors for consuming the additional capacitive reactive power of the lines. Sometimes it isnecessary to switch off a low-loaded line (what definitely affect the system reliability). In peakhours not only the customer loads cause big voltage drops but also the inductive reactive powerof the lines adds to the total power flow and causes further voltage drops..The voltage and reactive power control has some limitations. A big part of reactive power isgenerated in power plant unites. The generators can deliver smoothly adjustable leading andlagging reactive power without any fuel costs..However, the reactive power occupies the generation capacity and reduces the active powerproduction. Furthermore, it is not worth to transmit reactive power for long distance (because ofactive power losses). Control provided on the way in transmission line, connation nodes,distribution station and other points requires installation of capacitors or\and reactors..They are often used with transformer tap changing system. The range of voltage controldepends on their size. The control may consist e.g. in setting the transformer voltage higher andthen reducing it by reactive currents flow.. If the transformer voltage reaches the highest value and all capacitors are in operation, thevoltage on customer side cannot be further increase. On the other hand when a reduction isrequired the limit is set by maximal reactive power of reactors and the lowest tap of transformer.

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Voltage and reactive power planning and assessment practices

(1) Key Principles:

Reactive power cannot be transmitted over a long distance or through power transformers dueto excessive reactive power losses.Reactive power supply should be located in close proximity to its consumption.Sufficient static and dynamic voltage support is needed to maintain voltage levels within anacceptable range.Sufficient reactive power reserves must be available to regulate voltage at all time

(2) Key Implications:

Metering must be in place and maintained to capture actual reactive consumption at variouspoints.Transmission and Distribution planners must determine in advance the required type andlocation of reactive correction.

Reactive power devices must be maintained and functioning properly to ensure the correctamount of reactive compensation.Distribution reactive loads must be fully compensated before transmission reactivecompensation is considered.

(3) Transmitting Reactive Power

Reactive power cannot be effectively transmitted across long distances or through powertransformers due to high I2X lossesReactive power should be located in close proximity to its consumption.

(4) Static vs. Dynamic Voltage Support

The type of reactive compensation required is based on the time needed for voltage recovery.Static Compensation is ideal for second and minute responses. (Capacitors, reactors, tapchanges).Dynamic Compensation is ideal for instantaneous responses. (condensers, generators)A proper balance of static and dynamic voltage support is needed to maintain voltage levelswithin an acceptable range.

(5) Reactive Reserves during Varying Operating Conditions

Ideally, the system capacitors, reactors, and condensers should be operated to supply thenormal reactive load.As the load increases or following a contingency, additional capacitors should be switched on orreactors removed to maintain acceptable system voltages.The reactive capability of the generators should be largely reserved for contingencies on theEHV system or to support voltages during extreme system operating conditions.Load shedding schemes must be implemented if a desired voltage is unattainable thru reactivepower reserves.

(6) Voltage Coordination

The reactive sources must be coordinated to ensure that adequate voltages are maintainedeverywhere on the interconnected system during all possible system conditions.Maintaining acceptable system voltages involves the coordination of sources and sinks whichinclude:

1. Plant voltage schedules2. Transformer tap settings3. Reactive device settings4. Load shedding schemes.

The consequences of uncoordinated operations would include:

1. Increased reactive power losses2. A reduction in reactive margin available for contingencies and extreme light load

conditions

3. Excessive switching of shunt capacitors or reactors4. Increased probability of voltage collapse conditions.

(7) Voltage Schedule

Each power plant is requested to maintain a particular voltage on the system bus to which theplant is connected.The assigned schedule will permit the generating unit to typically operate:

1. In the middle of its reactive capability range during normal conditions2. At the high end of its reactive capability range during contingencies3. Under excited or absorb reactive power under extreme light load conditions.

(8) Transformer Tap Settings

Transformer taps must be coordinated with each other and with nearby generating stationvoltage schedules.The transformer taps should be selected so that secondary voltages remain below equipmentlimits during light load conditions.

(9) Reactive Device Settings

Capacitors on the low voltage networks should be set to switch on to maintain voltages duringpeak and contingency conditions. AndOff when no longer required supporting voltage levels.

(10) Load Shedding Schemes

Load shedding schemes must be implemented as a last resort to maintain acceptablevoltages.

(11) Voltage and Reactive Power Control

Requires the coordination work of all Transmission and Distribution disciplines.Transmission needs to:

1. Forecast the reactive demand and required reserve margin2. Plan, engineer, and install the required type and location of reactive correction3. Maintain reactive devices for proper compensation4. Maintain meters to ensure accurate data5. Recommend the proper load shedding scheme if necessary.

Distribution needs to:

1. Fully compensate distribution loads before Transmission reactive compensation isconsidered

2. Maintain reactive devices for proper compensation3. Maintain meters to ensure accurate data

4. Install and test automatic under voltage load shedding schemes

References:1. Samir Aganovi,2. Zoran Gaji,3. Grzegorz Blajszczak- Warsaw, Poland,4. Gianfranco Chicco5. Robert P. OConnell-Williams Power Company6. Harry L. Terhune-American Transmission Company,7. Abraham Lomi, Fernando Alvarado, Blagoy Borissov, Laurence D. Kirsch8. Robert Thomas,9. OAK RIDGE NATIONAL LABORATORY

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About Author //Jignesh Parmar

jiguparmar - Jignesh Parmar has completed his B.E(Electrical) from GujaratUniversity. He is member of Institution of Engineers (MIE),India. MembershipNo:M-1473586.He has more than 12 years experience in Transmission -Distribution-Electrical Energy theft detection-Electrical Maintenance-Electrical Projects (Planning-Designing-Technical Review-coordination -Execution). He is Presently associate with one of the leading business groupas a Assistant Manager at Ahmedabad,India. He has published numbers ofTechnical Articles in "Electrical Mirror", "Electrical India", "Lighting India","Industrial Electrix"(Australian Power Publications) Magazines. He is Freelancer Programmer ofAdvance Excel and design useful Excel base Electrical Programs as per IS, NEC, IEC,IEEE codes. Heis Technical Blogger and Familiar with English, Hindi, Gujarati, French languages. He wants to Sharehis experience & Knowledge and help technical enthusiasts to find suitable solutions and updatingthemselves on various Engineering Topics.

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19 Comments1.

raju

Feb 12, 2015

The information provided is so much useful..Landed in a best place after manytrailsKeep doing good..:)

(reply)

2. Satish Kr. Barnwal

Nov 21, 2014

Very useful & interesting

(reply)3.

rohit

Oct 16, 2014

too good.

(reply)4.

Legalectric Blog Archive Transmission for us in Delaware? NOT!

Aug 23, 2014

[] One of these is the necessity of reactive power that needs to be supplied along with activepower. Reactive power can be leading or lagging.While it is the active power that contributes tothe energy consumed, or []

(reply)5.

Dr Sanjay R Joshi

Jun 24, 2014

Following can said in the answer to the question What is reactive power?It is power associated with the net zero energy transfer over a integer multiple of cycles ofsupply.

Also following is worth to note :

In case of say, induction machine, the reactive power is responsible for the magnetic field, whichis the,a must medium for energy transfer. Now this field strength has to be constant so that themachine magnetic circuit do not saturate. So the magnetic field must not get any amount energyonce it is fully developed. At the same time, a continuous flow of current has to be there in orderto have the flux. The flux is there as long as the current flows in the stator winding. These bothcan happen only if the current responsible for machine magnetization, over a cycle (to be morespecific even a half cycle) , do not become a tool for transfer of energy from source to machinemagnetic field. So, here there is the role of reactive power.Therefore. we can state that the machine operation is possible only if it draws reactive powerfrom the source.

(reply)6.

Arifa

Feb 24, 2014

Very informative. I have some queries pls,1. Reactive power is required by some loads, so does the utility specifically generate reactive

power for that purpose? i know S=P+jQ, Does generating station produce S or P?

(reply)

Oc

Jun 25, 2014

It produces S, wich include P and Q.

(reply)

7. sewar

Feb 07, 2014

Fine.thanks.

(reply)

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How reactive power is helpful to maintain a system healthyCOVERED TOPICS:Need of Reactive PowerImportance of Present of Reactive PowerPurpose of Reactive PowerWhat is Reactive Power?Why Do We Need Reactive Power?Reactive Power is a Byproduct of Alternating Current (AC) SystemsHow Are Voltages Controlled?Voltage must be maintained within Acceptable LevelsVoltage and Reactive PowerReactive Power and Power FactorReactive Power LimitationsReactive power caused absence of electrical supply in country-A blackoutProblems of reactive powerProfound effects of Reactive Power in Various elements of Power System:GenerationSynchronous condesersCapacitors and inductorsStatic VAR compensators (SVCs)Static synchronous compensators (STATCOMs)Distributed generationTransmission side

Voltage and reactive power planning and assessment practices(1) Key Principles:(2) Key Implications:(3) Transmitting Reactive Power(4) Static vs. Dynamic Voltage Support(5) Reactive Reserves during Varying Operating Conditions(6) Voltage Coordination(7) Voltage Schedule(8) Transformer Tap Settings(9) Reactive Device Settings(10) Load Shedding Schemes(11) Voltage and Reactive Power Control

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