3 phase distribution

8/4/2019 3 Phase Distribution

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3 Phase Distribution To Buy 3 Phase Distribution Transformers

We Recommend TEMCo Brand.

Call 1-510-490-2187Web Link: Distribution Transformers

3 Phase Power Distribution and Transmission 3 phase electricity distribution is the process in the delivery of 3 phase power from thegeneration equipment to the business or location for use. This include the transmission overpower lines, possibly through electrical substations and pole-mounted transformers , and theappropriate distribution 3 phase wiring and sometimes electricity meters.
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3 Phase Power Distribution Transformer After numerous further conversions in the transmission and distribution network the 3phase power is finally transformed to the standard mains voltage (the voltage of "house" or"household" current in American English). The power may already have been split intosingle phase at this point or it may still be 3 phase. Where the step-down is 3 phase , theoutput of this power transformer is usually star connected with the standard mains voltage(120V in North America and 230V in Europe) being the phase-neutral voltage.

Another system commonly seen in the USA is to have a delta connected secondary on thestep down transformer with a center tap on one of the windings supplying the ground andneutral. This allows for 240V 3 phase as well as three different single phase voltages (120Vbetween two of the phases and the neutral, 208V between the third phase (sometimesknown as a wild leg) and neutral and 240V between any two phases) to be made availablefrom the same supply.

Generating 3 Phase Power From Single Phase When single phase power is readily available but 3-phase power is not already allocated,there is an easy way to generate 3 phase power with a 3 phase power generating RotaryPhase Converter or with a modern Motor Generator Set. Today these are a super efficientmethod to get 3 phase power anywhere single phase is already available. Read more aboutsuper efficient 3 phase generating Rotary Phase Converters here.

Electric Power Distribution HistoryIn the early days of electricity generation, direct current (DC) generators would beconnected to loads at the same voltage. The generation, transmission and loads all neededto be of the same voltage because, at the time, there was not a common way of doing DCvoltage conversion (other than motor-generator sets which today have became superefficient). The voltages usually had to be fairly low with old generation systems due to thedifficulty and danger of distributing high voltages to small loads. The losses in a linetransmission cable are proportional to the square of the current, the length of the cable, andthe resistive nature of the conductor line wire material, and are inversely proportional tocross-sectional area. Early power transmission networks were already using copper, which isone of the best conductors that is also very economically feasible for this application. Toreduce the current while keeping power transmission constant requires increasing the
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voltage which, as previously mentioned, was, at that time, problematic. This meant in orderto keep losses to a reasonable level the (DC) Edison power transmission system neededthick cables and local power generators.

Alternating Current (AC) Becomes Most Common StandardSoon, the adoption of alternating current (AC) for electricity generation dramaticallychanged the situation. Power transformers , installed at power substations, could be used toraise the voltage from the generators and reduce it to supply loads. Increasing the voltagereduced the current in the power transmission and distribution lines. Thus the size of conductors required and distribution losses incurred were also reduced. This made it moreeconomic to distribute power over long distances. The ability to transform to extra-highvoltages enabled power generators to be located far from loads with transmission systemsto interconnect generating stations and distribution networks.

Though due to power line losses, it is still often valuable to locate the power generatorsnearby the actual power load.

In North America, the early power distribution systems used a voltage of 2200 volts corner-

grounded delta. Over time, this was gradually increased to 2400 volts. As cities grew, most2400 volt systems were upgraded to 2400/4160 Y three-phase systems, which alsobenefited from better surge suppression due to the grounded neutral. Some city andsuburban power distribution systems continue to use this range of voltages, but most havebeen converted to 7200/12470Y.

European systems used higher voltages, generally 3300 volts to ground, in support of the220/380Y volt power systems used in those countries. In the UK, urban power generationand transmission systems progressed to 6.6 kV and then upgraded to 11 kV (phase tophase), the most common power distribution voltage.

North American and European power distribution systems also differ in that North American

power distribution systems tend to have a greater number of low-voltage step-downtransformers located closer to customers' premises. For example, in the US a pole-mountedtransformer in a suburban area may supply only one or a very few houses or smallbusinesses, whereas in the UK a typical urban or suburban low-voltage substation might berated at 2MW of power and supply a whole neighborhood. This is because the higher voltageused in Europe (230V vs 120V) may be carried over a greater distance without anunacceptable power loss. An advantage of the North American setup is that failure ormaintenance on a single power transformer will only affect a few customers. Advantages of the UK setup are that fewer transformers are required; larger and more efficienttransformers are used, and due to diversity there need be less spare capacity in thetransformers, reducing power wastage.

Rural power electrification systems, in contrast to urban power systems, tend to use highervoltages because of the longer distances covered by those power distribution lines. 7200volts is commonly used in the United States; 11kV and 33kV are common in the UK, NewZealand and Australia; 11kV and 22kV are common in South Africa. Other voltages areoccasionally used in unusual situations or where a local utility simply has engineeringpractices that differ from the normal practices

Power Distribution Network Layout Power distribution networks are typically arranged out in one of two types, radial or
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interconnected. A radial network leaves the station and passes through the network areawith no connection to any other supply. This is typical of long rural lines with isolated loadareas. An interconnected network is generally found in more urban areas and will havemultiple connections to other points of supply.

These points of connection are normally open but allow various configurations by closing

and opening switches. The benefit of the interconnected model is that in the event of a faultor required maintenance a small area of network can be isolated and the remainder kept onsupply. The only downside to this design occurs when there is a major power outage thatcauses a domino effect damaging the power supply systems from the whole network leavingmore customers without power. There are protections in place to keep this from happeningthough it still occurs every few years in places where this method of power distribution andtransmission is used.

Characteristics of the supply given to customers are generally mandated by law and bycontract between the electric power supplier and customer. Variables include: AC or DC -Virtually all public electricity supplies are AC today. Users of large amounts of DC powersuch as some electric railways, telephone exchanges and industrial processes such as

aluminum smelting either operate their own generating equipment or have equipment toderive DC from the public AC supply).

Phase and Frequency Converters There are several instances where the equipment may need not only the phase changedfrom 1-phase, or the rare 2-phase (in the US this is mostly used in Chicago) to 3 phasepower, but also the frequency converted from 50Hz to 60Hz or 400Hz (400Hz is mostly usedin ships and aircraft). Click here to read more about 3 phase frequency converters .

Volume 2 No.2 March 1999

AUTOMATION IN POWER DISTRIBUTION

The demand for electrical energy is ever increasing. Today over 21% (theft apart!!) of the totalelectrical energy generated in India is lost in transmission (4-6%) and distribution (15-18%). Theelectrical power deficit in the country is currently about 18%. Clearly, reduction in distributionlosses can reduce this deficit significantly. It is possible to bring down the distribution losses to a6-8 % level in India with the help of newer technological options (including informationtechnology) in the electrical power distribution sector which will enable better monitoring and

control.

How does Power reach us?

Electric power is normally generated at 11-25kV in a power station. To transmit over longdistances, it is then stepped-up to 400kV, 220kV or 132kV as necessary. Power is carriedthrough a transmission network of high voltage lines. Usually, these lines run into hundreds of kilometres and deliver the power into a common power pool called the grid. The grid is
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connected to load centres (cities) through a sub-transmission network of normally 33kV (orsometimes 66kV) lines. These lines terminate into a 33kV (or 66kV) substation, where thevoltage is stepped-down to 11kV for power distribution to load points through a distributionnetwork of lines at 11kV and lower.

The power network, which generally concerns the common man, is the distribution network of 11kV lines or feeders downstream of the 33kV substation. Each 11kV feeder which emanatesfrom the 33kV substation branches further into several subsidiary 11kV feeders to carry powerclose to the load points (localities, industrial areas, villages, etc.,). At these load points, atransformer further reduces the voltage from 11kV to 415V to provide the last-mile connectionthrough 415V feeders (also called as Low Tension (LT) feeders) to individual customers, eitherat 240V (as single-phase supply) or at 415V (as three-phase supply). A feeder could be either anoverhead line or an underground cable. In urban areas, owing to the density of customers, thelength of an 11kV feeder is generally up to 3 km. On the other hand, in rural areas, the feederlength is much larger (up to 20 km). A 415V feeder should normally be restricted to about 0.5-1.0 km. Unduly long feeders lead to low voltage at the consumer end.

Bottlenecks in Ensuring Reliable Power

Lack of information at the base station (33kV sub-station) on the loading and health status of the11kV/415V transformer and associated feeders is one primary cause of inefficient powerdistribution. Due to absence of monitoring, overloading occurs, which results in low voltage atthe customer end and increases the risk of frequent breakdowns of transformers and feeders. Infact, the transformer breakdown rate in India is as high as around 20%, in contrast to less than2% in some advanced countries.

In the absence of switches at different points in the distribution network, it is not possible to

isolate certain loads for load shedding as and when required. The only option available in thepresent distribution network is the circuit breaker (one each for every main 11kV feeder) at the33kV substation. However, these circuit breakers are actually provided as a means of protectionto completely isolate the downstream network in the event of a fault. Using this as a tool for loadmanagement is not desirable, as it disconnects the power supply to a very large segment of consumers. Clearly, there is a need to put in place a system that can achieve a finer resolution inload management.

In the event of a fault on any feeder section downstream, the circuit breaker at the 33kVsubstation trips (opens). As a result, there is a blackout over a large section of the distributionnetwork. If the faulty feeder segment could be precisely identified, it would be possible tosubstantially reduce the blackout area, by re-routing the power to the healthy feeder segmentsthrough the operation of switches (of the same type as those for load management) placed atstrategic locations in various feeder segments.


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Typical Power Transmission and Distribution Scenario with DA components

The Technology Development Mission

A Technology Development Mission on Communication, Networking and IntelligentAutomation, was jointly taken up by IIT Kharagpur and IIT Kanpur. While the mission focus atIIT Kharagpur is to develop technology for industrial automation, IIT Kanpur embarked upon thedevelopment of an integrated technology for power distribution automation system.

In a distribution automation (DA) system, the various quantities (e.g., voltage, current, switchstatus, temperature, and oil level) are recorded in the field at the distribution transformers andfeeders, using a data acquisition device called Remote Terminal Units (RTU). These systemquantities are transmitted on-line to the base station (33kV substation) through a variety of communication media. The media could be either wireless (e.g., radio, and pager) or wired (e.g.,


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Dial-up telephone, RS-485 multi-drop, and Ethernet). The measured field data are processed atthe base station for display of any operator selected system quantity through Graphic UserInterface (GUI). In the event of a system quantity crossing a pre-defined threshold, an alarm isautomatically generated for operator intervention. Any control action (for opening or closing of the switch or circuit breaker) is initiated by the operator and transmitted from the 33kV base

station through the communication channel to the remote terminal unit associated with thecorresponding switch or circuit breaker. The desired switching action then takes place and theaction is acknowledged back to operator for information.

DA systems are being adopted by utilities in some developed countries in a phased manner,primarily for reliability evaluation in a field environment. In India too, a small beginning hasbeen made by a few state utilities (Andhra Pradesh, Assam, Kerala and Rajasthan), which areconfining themselves initially to the automation of 33kV substations. Electronics Research andDevelopment Centre, Trivandrum, and Computer Maintenance Corporation, Hyderabad, areinvolved in these early experiments, the main objective being the development of know-how anda better understanding of the issues involved in implementing DA systems indigenously. The

utility environment in India is far different from that in most of the developed countries, becauseof the existing social scenario. Hence, technological solutions available for DA in developedcountries cannot be directly implanted in India. Also, the cost of importing a DA systemtechnology is prohibitive.

The Mission Activities at IIT Kanpur

IIT Kanpur has embarked on an effort to develop indigenous technology for an integrated powerdistribution automation system in collaboration with four industry partners (Secure MetersLimited, Udaipur; Indian Telephone Industries, Raebareli; DataPro Electronics Private Limited,Pune; and Danke Switchgears, Vadodara). This effort includes development of

(a) communication and networking technology using wired and wireless media,

(b) micro-controller based remote terminal unit (RTU),

(c) remotely operable switch for 11kV and 415V feeders,

(d) application Specific Integrated Circuit (ASIC) for electrical instrumentation,

(e) DA software to enable remote monitoring, alarm generation and remote control, and

(f) distribution network simulator (a scaled down model of a real-life distribution network) toprovide a test bed for a comprehensive testing of the developed technology, components andsoftware.

Some of the developments noted above are being implemented in the IIT Kanpur distributionnetwork as a pilot level installation for field reliability evaluation.

Salient Contributions


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The technology development mission at the Institute has made the following contributions:

Communication and Networking Technology

This enables distributed data acquisition, monitoring and control system functions. Unlike

traditional communication solutions, the approach here is to have a core communicationcontroller in the base station that can support diverse choices of communication media (dial-up,RS485, Ethernet, and radio). This open approach facilitates cost effective implementation. Thebase station communication controller has cross-platform portability, supports functions forcommunications network management, and permits LAN, Internet, and Intranet connectivitythrough Ethernet. All command communication functions are invoked through GUI of automation software. Data transfer from/to RTUs supports industry standard data links.

Remote Terminal Unit

The micro-controller based pole-top RTU has 32 analog and 16 digital channels, and affords

RS232 full duplex asynchronous communication. The acquired data (voltage and current) isprocessed for rms and power factor calculations. Some design goals focus at low cost, flexibilityand expandability, modularity at signal conditioning level, and communication interface.

Remotely Operable Switch

A load break switch (LBS) for 11kV operation and a moulded case circuit breaker (MCCB) unitfor 415V operation have been developed and tested as per available specifications. The three-pole 11kV LBS opens in 80 milliseconds at the rated current of 80 A. While this switch isprimarily meant for breaking load current, it can sustain 16 kA of fault current for one secondand can also close on fault. The remote operation is through a three-phase induction motor

coupled with gear mechanism. The 415V MCCB unit, on the other hand, has an isolator on theincoming circuit and two MCCBs for two outgoing feeders. Flexibility exists to choose theMCCB of appropriate rating corresponding to the rated feeder current. The remote operation isthrough solenoid-plunger arrangement.

Application Specific Integrated Circuit (ASIC)

ASIC supports up to four-phase analog inputs (four voltage and four current) for applicationssuch as tri-vectormetre, RTU, and single-phase meter. It has an option for frequency selection(50/60 Hz) and is of 0.2 class accuracy with 16 bit A/D converter. Sampling rate is 5000 samplesper second per channel. It calculates quantities like rms values of voltage and current (both actual

and fundamental), power, power factor, total harmonic distortion, frequency, and energy. TheASIC design is verified using Verilog HDL simulation. While the ASIC fabrication is beingfinalised, the ASIC-based metering applications have been validated using the hardwarebehavioural simulation of ASIC.

DA software


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The DA software has the following components: (i) Distribution network software with attributeslike graphical representation of network, cross-platform portability (Windows NT, Linux,Solaris), editing features, customizing, network validation, system topological information,component specification, and billboard printing; (ii) Set-up utilities for installation on differentplatforms; (iii) Automation software having real-time features, cross-platform portability, alarm

generation (audio/video), system monitoring (of system quantities, equipment health and switchstatus), switch control commands, control interlocks and event log report; (iv) Database withreal-time attributes that conforms to DNP3.0 library format, uses shared memory approach,provides SQL interface for backup in standard databases for all off-line applications, permitssharing of data in multiple processes, and has registry access for security and RTU identification;and (v) Application software which includes packages for network re-configuration, loadshedding, volt-var control through capacitor switching, and fault detection and isolation.

Distribution Network Simulator

It is a scaled-down model of the actual IIT Kanpur distribution network, having suitably scaled-

down versions of fourteen transformers, thirty 11 kV feeders, forty one circuit breakersrepresented by four-pole controllable relays (with selection for remote/local operation), LT loadswhich can be varied from 0-150% in steps of 25%, communication linkage (for Ethernet, dial-up,RS485 and radio), single generic RTU (96 digital and 128 analog channels) covering alltransformers. The simulator applications include testing of various communication systems andprotocols, testing of DA software, fine tuning of RTU and LBS control prior to field installation,and integration and testing of application software. As the simulator provides a feel of actualphysical system, it can serve as a training tool for operators of DA system.

Closure

Most of the developments undertaken as part of the mission have been completed over the lastthree years. Some of these developments have already been implemented in the 33kV substationof IIT Kanpur. Implementation at five 11kV substations in IIT Kanpur is currently in progress,and is expected to be completed by the end of 1999. Based on this field experience, the necessaryfine tuning of the technology will be done for increased reliability. It is expected that thetechnology for DA system developed through this mission, will be marketed by the four industrypartners, not just within India, but also in the other developing countries

Electrical Distribution System Overview

Modern power grids are extremely complex and widespread.

Surges in power lines can cause massive network failures andpermanent damage to multimillion-dollar equipment in powergeneration plants. After electricity is produced at power plantsit has to get to the customers that use the electricity. Asgenerators spin, they produce electricity with a voltage of about 25,000 volts [a volt is a measurement of electromotiveforce in electricity, the electric force that pushes electrons
http://www.globalsecurity.org/security/intro/images/transformer.gif


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around a circuit]. The transmission and distribution system delivers electricity from thegenerating site (electric power plant) to residential, commercial, and industrial facilities.

The electricity first goes to a transformer at the power plant that boosts the voltage up to 400,000volts for distribution through extra-high voltage (EHV) transmission lines. When electricity

travels long distances it is better to have it at higher voltages since the electricity can betransferred more efficiently at high voltages. High voltage transmission lines carry electricitylong distances to a substation. At transmission substations a reduction in voltage occurs fordistribution to other points in the system through high voltage (HV) transmission lines. Furthervoltage reductions for commercial and residential customers take place at distributionsubstations, which connect to the primary distribution network.

Utility transmission and distribution systems [T&D] systems link electric generators with endusers through a network of power lines and associated components. In the United States typicallythe transmission portion of the system is designated as operating at 69 kilovolts (kV) and above,while the distribution portion operates between 110 volts and 35 kV. A further distinction is

often made between primary distribution (voltages between 2.4 and 35 kV) and secondarydistribution (110 to 600 volt) systems. Industrial and commercial customers with large powerdemands often receive service directly from theprimary distribution system.

Transformers are a crucial link in the electricpower distribution system. Utility transformersare high-voltage distribution transformerstypically used by utilities to step down the voltageof electricity going into their customers'buildings. Distribution transformers are one of the

most widely used elements in the electricdistribution system. They convert electricity fromthe high voltage levels in utility transmission systems to voltages that can safely be used inbusinesses and homes. Distribution transformers are either mounted on an overhead pole or on aconcrete pad. Most commercial and industrial buildings require several low-voltage transformersto decrease the voltage of electricity received from the utility to the levels used to power lights,computers, and other electric-operated equipment.

Transformers consist of two primary components: a core made of magnetically permeablematerial; and a conductor, or winding, typically made of a low resistance material such as copperor aluminum. The conductors are wound around a magnetic core to transform current from onevoltage to another. Liquid insulation material or air surrounds the transformer core andconductors to cool and electrically insulate the transformer. Many different distributiontransformer designs are available to utilities, depending on the loading patterns and needs of theend-user. Transformer engineers modify transformer design and vary material depending uponthe needs of a particular utility (cost of energy, capacity, etc.).

A blackout is a condition where a major portion or all of an electrical network is de-energizedwith much of the system tied together through closed breakers. Any area whose tie-lines to the


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high voltage grid cannot support reasonable contingencies is a candidate for a blackout. Systemseparations are possible at all loading levels and all times in the year. Changing generationpatterns, scheduled transmission outages, and rapid weather changes among other reasons can alllead to blackouts. Separations due to dynamic instability are typically initiated by multiplecontingencies such as loss of corridors, several transmission circuits, several generating units, or

delayed fault clearing.

The system just prior to a blackout may not be dynamically unstable but in an overloadedcondition. At such loadings, the collapse may come about due to damage to thermally overloadedfacilities, or circuits contacting underlying facilities or vegetation. When an overloaded facilitytrips, other facilities will increase their loadings and may approach their thermal capabilities orrelay trip settings.

Voltage collapse is the process by which voltage instability leads to the loss of voltage in asignificant part of the system. This condition results from reactive losses significantly exceedingthe reactive resources available to supply them. Circuits loaded above surge impedance loadings

and reduced output of shunt capacitors as voltages decline can lead to accelerating voltage drops.Voltage collapse can look like both a steady-state problem with time to react and a problemwhere no effective operator intervention is possible. It is very hard to predict the area that will beaffected or electrically isolated from the grid.

Voltage collapse is an event that occurs when an electric system does not have adequate reactive support to maintain voltage stability in which the sustained voltage level is controllable andwithin predetermined limits. Voltage Collapse may result in outage of system elements and mayinclude interruption in service to customers. Apparent Power, the product of the volts andamperes, comprises both real and reactive power, usually expressed in kilovoltamperes (kVA) ormegavoltamperes (MVA). Real Power is the rate of producing, transferring, or using electrical

energy, usually expressed in kilowatts (kW) or megawatts (MW). Reactive power is the portionof electricity that establishes and sustains the electric and magnetic fields of alternating-currentequipment. Reactive power must be supplied to most types of magnetic equipment, such asmotors and transformers. It also must supply the reactive losses on transmission facilities.Reactive power is provided by generators, synchronous condensers, or electrostatic equipmentsuch as capacitors and directly influences electric system voltage. It is usually expressed inkilovars (kvar) or megavars (Mvar).

The system restoration sequence and timing will be directly impacted by the various sizes, types,and state of operation of the system generating units prior to the blackout. After a system hasblacked out, the system operators perform a survey of the system status. Circuit breaker positionswill not provide a reliable indication of faulted versus non-faulted equipment. Breakers can befound in the closed position, but the associated transmission facility is faulted. If the systemblackout is storm-initiated, this condition is quite possible. The storm can continue to damageequipment after the system is de-energized. Also, equipment with neutral connections, such asreactors, transformers, and capacitors, may be locked out from the neutral overcurrent conditionsduring system shutdown. These facilities may be in perfectly serviceable condition. Most relaysystems will remain reliable and secure during restoration, provided there is adequate fault


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current available to activate the relaying. The most questionable relay reliability issues comefrom reclosing relays.

A power generating unit separated from the may have islanded and continue to generate powerfor its station auxiliary load. With no system load on the generators, the station auxiliary demand

will be quite small, and the steam generators output may be difficult to control. Immediate loadaddition may be required to keep the steam generator from tripping or having the steam turbinetrip out on overspeed. Other units may be able to operate indefinitely on their auxiliary load.

An electrical utility which experiences an operating capacity emergency seeks to balance itsgeneration to its load to avoid prolonged outages of service. The emergency reserve inherent infrequency deviation may be used as a temporary source of emergency energy. A utility unable tobalance its generation to its load removes sufficient load to permit correction of the outage. Inthe event of a capacity deficiency, generation and transmission facilities are used to the fullestextent practicable to promptly restore normal system frequency and voltage. If all other stepsprove inadequate to relieve the capacity emergency, the system may take immediate action

which includes but is not limited to manual load shedding. Unilateral adjustment of generation toreturn frequency to normal may jeopardize overloaded transmission facilities. Voltage reductionfor load relief is made on the distribution system. Voltage reduction on the subtransmission ortransmission system may effective in reducing load; however, voltage reduction would not bemade on the transmission system unless the system has been isolated from other interconnectedsystems. If the overload on a transmission facility or abnormal voltage/reactive condition persistsand equipment is endangered, the affected system or pool may disconnect the affected facility.shutdown. If abnormal levels of frequency or voltage resulting from an area disturbance make itunsafe to operate the generators or their support equipment in parallel with the system, theirseparation or shutdown would be accomplished in a manner to minimize the time required to re-parallel and restore the system to normal.

After a system collapse restoration begins when it can proceed in an orderly and secure manner.Restoration priority is normally given to the station supply of power plants and the transmissionsystem. Even though restoration is intended to be expeditious, system operators seek to avoidpremature action to prevent a re-collapse of the system. Customer load is normally restored asgeneration and transmission equipment becomes available, since load and generation mustremain in balance at normal frequency as the system is restored. When voltage, frequency andphase angle permit, the system operator may resynchronize the isolated area with thesurrounding area. In order to systematically restore loads without overloading the remainingsystem, opening circuit breakers may isolate loads in blacked-out areas. Reenergizing oil-filledpipe-type cables must be given special consideration, especially if loss of oil pumps could causegas pockets to form in pipes or potheads.

After determining the extent of the blackout and assessing the status of system equipment, theswitching operations necessary for system reintegration represent a significant portion of therestoration process. Depending on the specific utility's requirements, there are two generalswitching strategies which may be used to sectionalize the transmission system for restoration.The first is the "all open" approach where all circuit breakers at affected (blacked out)


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substations are opened. The second strategy is the "controlled operation" where only thosebreakers necessary to allow system restoration to proceed are opened.

3 phase distribution

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