186-Intelligent LV Switchboards

8/11/2019 186-Intelligent LV Switchboards

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Antoine Jammes

Received his engineering degree from ENSEM (Ecole NationaleSuprieure d'Electricit et de Mcanique de Nancy) in 1979. JoinedSchneider (Merlin Gerin) in 1980 and participated in the developmentof protection software in the Dependability Systems and ElectronicsDepartment (SES). In 1991, he moved to the Low Voltage PowerDistribution SBU where he has played a major role in the developmentof intelligent LV switchboards.

n186

Intelligent LV switchboards

E/CT 186first issued, june 1997


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Cahier Technique Schneider n186 / p.3

Intelligent LV switchboards

In all buildings, regardless of the activity carried out inside, the distribution

of electrical power must today satisfy ever-increasing needs for

dependability and efficiency.

Energy must be available not only to ensure the comfort and safety of

users, but also to avoid the costs incurred by power failures.

Electrical installations must therefore be monitored and be capable of

reacting automatically to optimise power distribution. Information

processing makes this possible.

Already used in medium-voltage industrial and public-distribution

applications, digital control and monitoring is now becoming a reality for

low-voltage installations as well.

Starting with an analysis of needs, this Cahier Technique takes a close

look at how LV power distribution can be managed. Particular emphasis isplaced on decentralising and distributing intelligence in and around the LV

switchboard. Several examples of such installations are also provided.

Contents

1 Control and monitoring needs 1.1 Introduction p. 4

1.2 Needs p. 4

1.3 Functions p. 7

2 Current solutions 2.1 Currently used solutions p. 9

2.2 Advantages and disavantages of these solutions p. 10

3 Intelligent switchboards 3.1 Dfinitions - decentralised architecture and distributedintelligence p. 12

3.2 Decentralisation of functions in an electrical installation p. 13

3.3 Advantages of decentralised architecture and distributedprocessing p. 17

3.4 Conclusion on decentralised processing in a LV switchboard p. 18

3.5 A switchboard bus suited to electrical applications p. 20

4 Implementation examples 4.1 Computer centre p. 23

4.2 Hospital p. 24

5 Conclusion and prospects for the future p. 27

Bibliography p. 28


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Cahier Technique Schneider n186/ p.4

1 Control and monitoring needs

1.1 Introduction

For whatever type of application, whether inoffice buildings, banks, hospitals, supermarkets,airports, tunnels or industrial sites, the need tomonitor and control electrical installations isincreasingly prevalent, to ensure the following:csafety,cavailability of power,coptimisation of energy consumption and costs(depending on the energy supplier's tariffschedules),creduction in operating and maintenance costs;

cease of operation,cmaintainability and upgradeability of theelectrical installation.

Power management can today be implemented

by a Digital Control System (DCS) designed tomeet all the above needs.

Power management may be combined with the

management of other facilities:

cbuilding management (access control, air-conditioning and heating, anti-intrusion systems,

lighting ),

cdigital control and monitoring of industrialprocesses.

Due to the wide range of needs and significant

technological progress over the last few years, a

number of solutions are today available when

designing systems to monitor and control

electrical installations. It is now possible to arrive

at a judicious balance between needs and the

corresponding solutions through the use of

digital communications buses and the

integration of microprocessors in electrical

equipment.

Cahier Technique n156 explains how to

design the power section of an electrical

switchboard so that it satisfies needs concerning

dependability.

The goal of this document is to discuss the

optimised design of power-management systems

in LV electrical installations.

The first step is to review the needs expressedby users and operators.

1.2 Needs

The needs of users and operators of electricalinstallations are different, depending on whetherthe building is intended for commercial, industrialor infrastructural purposes. A hierarchy of needsmay be established (see fig. 1 ).

For example, in a small office building, the costof energy and ease of use of systems by non-specialists are the foremost criteria. On the other

Comfort

Costs

Availability

Safety

Source management

Tariff schedule management

Automatic source changeover

Protection of persons

Examples:

hand, in a hospital or a factory implementing anindustrial process, the most important need iscontinuity of service.

Safety of life and property

An electrical installation must distribute electricalpower while ensuring the safety of life and property.A power-management system does not replace theprimary protective functions (reflex-type devices).

fig. 1: hierarchy of needs in LV electrical.


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Insulationresistance

Time

InterventionPeriodic drop in insulation,steadily worsening.

First fault alarm threshold

Given its capacity to communicate as well as storeand process data, it simply assists the operator byindicating the settings of protective devices, thetype of fault that caused a device to trip and thestatus of the installation prior to the incident, etc.

Power management can, however, include overallprotective functions. For example, on IT systems,insulation-monitoring may be implemented towarn the operator of a first fault. It is then possibleto identify and clear the fault without any break inthe continuity of service (see fig. 2 ).

Technological advances have made it possible foroperators to reduce the duration of a fault in aninstallation, thus reducing the probability of asecond fault occurring. Operators can check atany time the insulation measurements at differentpoints in the installation and even the evolution ofthe insulation measurements over time. Preventivemaintenance therefore becomes a real possibility.The insulation monitoring function is autonomousand may be considered a decentralised function inthe framework of a power-management system.

Availability

Each field of activity has its own requirementsconcerning continuity of service:cin hospitals, operating rooms and reanimationcentres are designed to provide a high level ofdependability,cin commercial buildings, the widespread use ofcomputer systems has led many people to useuninterruptible power supplies (UPS) installedeither locally for individual machines or more

centrally for the supply of entire installations withhigh-quality power,

cin industry, power failures result in productionlosses. For example, a ten-minute power outagein a Danone factory results in a production lossof 20 000 cups of yoghurt.

The need to ensure the availability of power hasled to a number of technological choices forequipment (withdrawable or disconnectabledevices or switchboard units, switchboard forms,etc.) and to the distinction in electricalinstallations between uninterruptible, high priorityand low priority circuits, with different choices forthe system earthing arrangement.

In this context, the job of a LV electricalswitchboard is to manage the sources. To beeffective, action taken when a problem occursmust be automatic and immediate.

Managing power failures is one function ofpower-management systems.

Energy costsA constant concern for all companies is the needto reduce the cost of energy. Reductions may beachieved by working on two different factors, thelevel of consumption and the pricing system of theenergy supplier. To that end, in-depth knowledgeis required on daily and seasonal fluctuations, aswell as on power and consumption levels.A measuring system providing digital data foruse on a supervision screen is required tomonitor and analyse the above elements.

It is then possible to:vundertake action to improve the situation,vcheck the effects of the action taken,

vdetermine energy costs per workshop,department, etc.

fig. 2: insulation monitoring for an outgoing circuit (IT systems).


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cReduce consumptionThere are numerous possibilities, depending onthe type of application:v turn off lighting and reduce heating inunoccupied rooms,vuse motors equipped with variable-speed

drives for industrial applications,vuse conditioners and/or filters to reduce lossesdue to harmonic and capacitive currents incables and transformers.

cReduce costs related to the terms of thecontract with the energy suppliervuse capacitor banks to avoid being billed forreactive power,vsmoothing peaks in consumption to reduce thesubscribed power and avoid overrun penalties.An intelligent system is capable of makingoptimum use of the subscribed power byshedding certain loads, smoothing peaks andalternating the supply of power to high-inertia

loads.vSelect the best available contract and programproduction cycles requiring particularly highquantities of electrical power for periods whenthe cost of power is low. These periods may be apart of the day, the season or the year. Forexample, certain contracts offer attractive pricesif the subscriber accepts to reduce hisconsumption on a certain number of peak daysper year.vUse replacement sources. This solution makesits possible not only to have a backup source ofpower in the event of a failure, but also tosmooth peaks in consumption and to avoid

moments when the power costs are highest.Managing consumption and energy costs isanother function of power-management systems.

Operating ease

Certain installations are managed remotely,either from a control and monitoring stationinside the building or from a centre coveringseveral sites (remote supervision).

Centralisation of management functions is ameans to optimise human resources and improvethe working conditions for personnel through theuse of ergonomic computerised systems andautomatic execution of repetitive tasks(programmed operating times for air-conditioning

or heating of offices, etc.).

Another consideration is the fact that in officebuildings and on small industrial sites, thepersonnel in charge of the installation isincreasingly a non-specialist. The electricalswitchboard is commonly under the responsibility ofthe building watchman or a receptionist. To ensureeffective operation as well as for safety reasons,the information presented to these persons mustbe in the form of a man/switchboard interface thatis as ergonomic and simple as possible.

Operating ease is achieved by an electricalinstallation that is as autonomous as possible

(self managed).

Maintainability

The primary mission of the electricalmaintenance department in a company is to keepthe electrical installation up and running.

There are two types of servicing:ccorrective action following an operating fault;cperiodic preventive action.

Maintenance may be enhanced in two ways:cby stressing preventive rather than correctiveaction to avoid breaks in the continuity of service,cfor preventive level, by stressing conditional

maintenance, i.e. action taking into accountmonitored data, rather than systematicmaintenance. The more maintenance is preventiveand based on monitored information, the higherthe availability of the installation (seefig. 3 ).

Depending on the type of application, the timerequired to begin servicing and the duration maybe very different. They may be very short forindustrial processes if there is on-site

Corrective

Systematicpreventive

Conditional

preventive

Type of maintenance

Availability

fig. 3: operational availability as a function of the type of maintenance.


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maintenance personnel and a stock of spareparts. On the other hand, they may be muchlonger in office buildings if an outside companymust be called in and the spare parts ordered.

The time required to service an installationalways depends on the information available:cwhen troubleshooting, precise and rapidlyavailable information on the problem and data oninstallation operating parameters prior to the faultare critical to making the right analysis andpreparing the subsequent work (new parts),cwhen undertaking preventive maintenance, in-depth information on the installation statusmakes it possible to intelligently select thoseelements most requiring servicing.

To carry out effective maintenance, personnelmust have relevant information concerning theinstallation status.

Providing information for maintenance is one ofthe advantages of power-management systems.

Upgradeability

The points in an electrical installation that are

most subject to change are those closest to the

final loads. In a factory, the electrical

switchboard may be upgraded to keep pace with

changes in production facilities. In officebuildings, changes in how rooms are used,

increasing use of microcomputers, installation of

air-conditioning, etc., all result in modifications to

the electrical installation.

Improvements in availability and reductions in

the cost of the power consumed are also

reasons for modifying electrical installations.

To correctly manage these changes, in-depth

knowledge of the installation and operating

parameters is required.

Power-management systems contribute to easy

and effective installation upgrades.

1.3 Functions

Satisfaction of all the above needs by a power-management system requires that a number ofdevices be installed in the electrical system,generally speaking in order to:ccarry out a number of automatic actions,cprovide the operator, either locally or remotely,with the informationneeded to plan ahead andcarry outthe required work on the installation.

These devices provide a number of functions,

not all of which are required in a giveninstallation.

Automatic-control functions

cSource management. Loads are supplieddepending on the availability of power on thedifferent incomers (source changeover systems,normal and replacement sources, engine-generator sets, etc.).cLoad shedding. Only priority loads are suppliedwith power when demand exceeds the availablelevel of power on the incomers (for example, whenpower is supplied by an engine-generator set).cTime management. To reduce consumption.

cTariff schedule management. Installationoperation is organised to respect the terms of thecontract signed with the power distributor(smoothing of peak power levels, special tariffs,etc.).cProtection of the electrical distribution system.In large industrial installations, systemdisturbances (transient voltage drops) may, dueto the presence of large motors, provoke transientinstability phenomena. This function ensures thenecessary load shedding to avoid collapse of theentire electrical distribution system.cPower-factor correction. This functionmanages the switching of capacitor banks.

cSwitchboard safety (over-temperature, internalarcing, etc.).

cInsulation monitoring and fault locating for ITsystems.

Information to plan and take action

The purpose of the functions presented above isto make the main LV switchboard autonomous. Itis then capable of reacting to various situationsto ensure continuity of service and optimaloperating conditions.

The second major type of function in anintelligent switchboard is the capacity tocommunicate information for planning and takingaction.Information includes:cthe status of breaking devices (open orclosed),cmeasurements (U, I, P, cos ),cthe settings of protective devices.

These functions require links to:ca power-management system at a higher level,in charge of managing the entire LV or MVinstallation,ca local or remote control and monitoringstation,cwhere applicable, secondary switchboards,cwhere applicable, a process-control system.

Before the operator can be informed and takeaction (manually reconfigure the distributionsystem, maintenance, comfort), the electricalswitchboard must first communicate with ahigher-level system that can be consulted by theelectrician and the person in charge of monitoringoperation of facilities in the building or factory.

During normal operation, an intelligent(i.e. communicating) LV switchboard is useful inpiloting and managing the electrical installation,

but it is all the more so when planning andaction are required in a fault situation.


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This is because corrective maintenanceismore effective if each of the persons involved israpidly provided with the relevant information.Below is an example of a circuit breaker,communicating via the intelligentLV switchboard, in the event of a fault:con the circuit breaker, the information isprovided by an mechanical indicator.cnear the circuit breaker, a red light identifiesthe device that has tripped.con a screen at the head of the switchboard, amessage in clear text is displayed 10:32:23 -outgoer to Lift 2 - section B - position 12b -tripping due to short-circuit.con the supervisor screen of the electricalmanager, the same message.

con the main supervisor screen (e.g. in thesecurity room), a message in clear text is displayed10:32:23 - Lift 2 out of order due to an electricalfault - call the electrical department on line 347.

Note that planning and taking action also relate

to preventive maintenance if the following areavailable:cinformation on the protection and controlswitchgear in the LV switchboards. Thisinformation may be provided by a counter for thenumber of times a device has opened or closed,a maintenance indicator derived from data suchas the sum total of currents interrupted, etccinformation on the electrical installation, forexample, the number of hours the supplied loadsoperate, drops in insulation


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2 Current solutions

2.1 Currently used solutions

The functions presented in chapter 1 are alreadyavailable, either in whole or in part, using anumber of different technical solutions:cin industry, by adding electrical managementto the facilities already implemented forindustrial-process control,cin commercial buildings, by including electrical-distribution management systems in the existingbuilding-management systems.

Consider the solutions implemented for a motorcontrol centre (MCC) or a main low-voltage

switchboard (MLVS).

Solution implementing PLCs

cPLCs and wired connections

The first step toward an intelligent switchboardinvolved the use of industrial PLCs(Programmable Logic Controllers) near theswitchboard.The PLCs serve as interfaces between theswitchboard and the technical managementsystem and are capable of carrying out certainautomatic-control functions.Made up of racks filled with input/output boards,the PLCs are wired to the various sensors and

actuators of an electrical switchboard.A specialist is required to program the PLCs andeach application is the result of a specificdevelopment.

This type of solution is subject to the followinglimits and constraints:vgreat quantities of control wires between theswitchboard and the PLC, with the followingdisadvantages:- very high wiring costs;- a large number of terminal blocks whichincrease the volume and notably the footprint ofthe switchboard;- high risk of latent defects due to the many

connection points;- risk of malfunction due to the very strongmagnetic field created by a short-circuit on anoutgoer;vsignificantly reduced capacity for installationupgrading, due to the very specific nature ofthe PLC programming which can rarely bemodified by the in-house electrical department,va data-processing system poorly suited to thegiven applications in that the main task of a PLCis to continuously poll the status of devices whichin this case often remain in the same positionyear round.

cPLCs and remote input/outputs

In the past few years, PLC manufacturers havetaken advantage of dropping costs in

microelectronics and communications buses anddeveloped remote input/output modules, thusmaking it possible to reduce the quantity andcost of wiring.

This solution has been put to very little use in thefield of electrical switchboards because it ispoorly suited to the constraints inherent in thefield, notably the thermal environment, electro-magnetic disturbances, the need to controlswitchgear locally, etc.

Solution implementing automatedswitchboards

In the 1980's, a number of offerings weredeveloped by the major panel builders forapplications in continuous-process industries orin large commercial buildings.

These offerings differ from the solutionspresented above in two aspects:cthe development of specialised modules wiredto the switchgear components andcommunicating via a parallel link or a serial buswith a PLC installed at the head of theswitchboard. These modules, designed for use

exclusively in switchboards produced by specificpanel builders, are installed on the front panel ofthe switchboard and include built-in local controland status-indication functions.cthe development of repetitive functions for theelectrical automatic-control systems. Forexample, source changeover systems with loadshedding and reconnection of outgoers.

These systems are characterised bydecentralised data processing in the switchboardand the fact that the functions can be handled byelectricians. What is more, they contribute to themassive reduction in the quantity of wiring inside

the switchboard.

The limited success of this type of system is dueto the fact that these modules were specific tothe different panel builders.

Communicating components

Microprocessors are now used by manufacturersof electrical equipment to:cimprove the performance of their products. Agood example is the widespread use ofelectronic trip units in circuit breakers. The latterare increasingly capable of communicating thedata they process via digital buses.

cenhance their offering with new functions, forexample, power and energy measurements at a


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given point in an installation, with the capacity tocommunicate the data.In parallel, automatic-control functions such assource changeovers or reactive power regulationcontinue with their own developments.

The increasing use of such products andmodules in electrical switchboards has resultedin a considerable increase in the quantity ofinformation that can be transmitted to a

centralised supervision system. In large-scale

applications, the engineering firm in charge of

the entire installation is still obliged to

implement a complex communications

architecture with intermediate levels fulfilling a

dual mission:

csorting and analysing the available information,

cproviding communications gateways between

different buses.

2.2 Advantages and disadvantages of these solutions

The three types of solution presented abovewere developed over the last ten years to satisfysome of the needs listed in chapter 1.Their advantages and disadvantages aresummed up in figure 4.

In conclusion, the following may be observedconcerning the currently implemented solutions:ca tendency, well underway, towarddecentralisation of automatic-control functionsand data processing for electrical switchboards,ca hierarchical structure for data flow,cthe need for specific development work and,consequently, for specialists.

In the electrical-switchboard field,decentralisation of data processing has beenmade possible by digital communications buses.This is the case for:cindustrial-process control and monitoring.PLCs with hundreds of input/outputs first gave

way to PLCs with remote input/outputs and arenow gradually being replaced by networksof PLCs and micro-PLCs positioned as close aspossible to the controlled sensors or actuators.The near future will see networks comprisingintelligent sensors and actuators,

cbuilding management. Functions have nowbeen standardised and are carried out byspecific products well suited to needs. Solutionsproviding industrial-process management,building management and electrical-distributionmanagement are now dedicated systems built

around decentralised architectures thatincreasingly incorporate distributed intelligence(see fig. 5 ).

A notable aspect of low-voltage electricalswitchboards is their great diversity and the widerange of functions that they must provide. On thebasis of existing solutions described in thischapter and that have already been put to use, itis today possible to determine a number ofprinciples that define and specify what isunderstood by the term intelligent switchboardand the corresponding control and monitoringsystem.cAn intelligent switchboard is defined by its

capacity to autonomously carry out the functionsassigned to it and to fit into the control system ofan electrical installation.cTo handle the wide variety of installations, thedesign of the switchboard must be based on thefollowing principles:

fig. 4: advantages and disadvantages of traditional solutions in meeting control and monitoring needs.

PLC-based Automated Communicatingsolutions switchboards components

Weak points Specific to each application, Solution available only Single-function solutionslittle capacity for upgrading to large panel builders

Large quantity of wiring Requires PLC specialists Increase in the numberof modules

Requires PLC specialists Requires electriciansspecialised incommunications

Strong points Reliable equipment, Implementation of the Reliable field-busused on large decentralisation concept technologyindustrial sites

Solutions perfectly Functions may be mastered Industrial productstailored to the by an electrician capable of withstandinginitial needs of each EMC constraints incustomer switchboards

Functions standardisedwith progression ofprojects


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3 Intelligent switchboards

3.1 Definitions - decentralised architecture and distributed intelligence

cAn analogy based on how companies areorganised may be useful in understanding these

two terms.In centralised organisations, all decisions aremade by the boss. Subordinates provide himwith all information and wait for orders.In an effectively decentralised organisation, amajority of decisions are delegated by the bossto the subordinates. Each person, within thelimits of the delegated powers, actsautonomously and reports only the necessaryinformation back to the boss. Only thosefunctions concerning the entire company are

centralised, for example, the payroll.

possible manner, whether for an entire installation(power management), for a low-voltageswitchboard or for a given outgoing circuit.

Then the criteria determining the selection of aninternal communications bus forthe LV switchboard, suited to the given needs,will be examined.

Finally, a given function may be distributed

between a number of subordinates. This form of

organisation implies information exchange and a

certain degree of autonomy for the team in

charge of the function.

cFigure 6 shows how a function may be:vtotally decentralised,

vpartially decentralised, whereby execution of

the function is decentralised, but parameter

settings remain centralised and common to a

number of functions,

vdistributed among equipment on the same

hierarchical level.

fig. 6: possibilities ranging from a fully centralised to a decentralised system with distributed intelligence.

Intelligent switchboards, as defined in thepreceding chapter, are based on the concept ofdecentralised architecture with distributedintelligence.

After defining these terms, we will go into how thevarious functions of an electrical installation maybe decentralised and distributed in the best

Solution 2.Centralised processing,decentralised acquisition.

F1 F2

F4 F5

F3

Solution 3.Function F3 and F4decentralised.

F1 F2

F5

F4F3

Solution 4.Distributed processingof functions F2 and F5.

F4 F5F3

F1

F2

Solution 1.Centralised system(acquisition and processing).

F1 F2

F4 F5

F3


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3.2 Decentralisation of functions in an electrical installation

Energy contract management

This type of function requires an overall view ofthe installation.

In many cases (small and mid-sized installations),the LV switchboard is the central element in theinstallation. If this is the case, the contract-

management function is handled by the LVswitchboard central unit, with either local or

remote (from a supervision station) parameter

settings. On a large site (medium-voltage

distribution system), switchboards receive

operating orders from a higher-level system.

Time management of outgoers

In centralised systems, this function is traditionallyassigned to the supervision station which can be

cDecentralisation as implemented in a company

may be applied in a similar manner to the control

and monitoring system of an electrical

installation. The Centralised Technical-

Management (CTM) concept is now giving way

to the decentralised power-management concept

with distributed processing.

Note that high-power distribution systems

(architecture and protection) follows the

same principles, thus ensuring coherence

between high- and low-current systems

(see fig. 7 ).Below are examples of these concepts applied

to different electrical functions.

Power-supply substation

Operatorcan monitor,issue ordersand set parameters

Switchboard control

and monitoring

Autonomous functionsfor measurements andcontrol and monitoringof outgoers

Configurationconsole

MLVS

central unit

LV switchboard

G

VAR

VAR

Supervisionstation

fig. 7: small to mid-sized installation with a control and monitoring system (power management), of which the major part is located in the MLVS.


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Outgoer 1 Outgoer 2

Q1 Q2

MLVS 1

Non-intelligent outgoers

Outgoer 4Outgoer 3

Q3 Q4

MLVS 2

Intelligent outgoers(equipped with internal clockand memory), capable ofhandling part of the function

Operating-time parametersset by operator

Execute orders

Transmit parameters

Store parametersIssue and execute orders

Power-management systemCentralised system

Set operating-time parametersStore parametersIssue orders

Transmit orders andacknowledgements

used to set operating-time parameters for outgoersand to issue opening and closing orders for devices.On the other hand, in a decentralised power-management system, these commands areexecuted at the level of the switchboard centralunit or even at each device. A device must

simply receive the operating set-points and beequipped with an internal clock that is regularlysynchronised by the supervisor.

In figure 8, the information flow is shown for atraditional centralised solution and adecentralised solution. It is clear that thepermanent information flow is reduced asdecentralisation is increased. On the other hand,new data exchanges, much more limited in

scope, are required to periodically synchronisethe various internal clocks and transmit newoperating set-points.

fig. 8: time management of outgoers, in a centralised system (CTM) and in a decentralised and distributed system (power management).


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Source management

This function opens or closes the incoming

circuit breakers in the switchboard, depending onthe data processed either in the switchboard orin the immediate proximity. It is therefore

perfectly logical that the operations required forthis function be carried out in the electricalswitchboard. Note that in relay-based systems,the relay sub-assemblies were installed in theswitchboard and the diagrams were drawn up bythe panel builders. It was only when a newtechnique arrived, one that most panel builderscould not handle, that this processing wasremoted to a centralised PLC.

If the incoming diagram is simple, for examplewith a normal and replacement source, thisfunction is totally decentralised and is carried outby an autonomous standard product. If theincoming diagram is more complex or requires

programmable shedding of outgoers, thefunction is located at the level of the switchboardcentral unit:cif the replacement source supplies the main LVswitchboard alone, a switchboard central unit willcarry out the function autonomously (see fig. 9 ),con the other hand, if the replacement source

supplies the MV system and/or several MLVSs,

GE

Presence Un

Presence Ur

Generator-start order

main LVswitchboardcentral unit

this function is distributed between

the MV switchboard central unit and the central

units of the various LV switchboards.

Reactive power regulation

Power-factor correction using capacitor banks isan independent automatic-control function built

into a product called a reactive power regulator.

This type of regulator must operate

autonomously in over 90% of all installations.

A communicating reactive power regulator can

be built into a power-management system to

provide the following additional useful functions:

csetting of parameters from a supervisionstation,

caction on alarms processed by the switchboard

central unit,caction on maintenance information in the

framework of overall switchboard maintenance,

ccoordination of the reactive power regulationfunction with other switchboard functions. Forexample, during operation on an engine-

generator set, the capacitors must be

disconnected. This can be carried out by

opening a circuit breaker upstream from thecapacitor banks or by transmitting a shutdown

order to the regulator if it is connected by bus to

fig. 9: example of source management. With this solution, the switchboard central unit manages the outgoers. Priority outgoers are

progressively reconnected during operation on an engine-generator set. Definition of outgoers as priority or non-priority is adjustable. Note that it

is not necessary to separate the busbars into two parts, thus eliminating the coupling device. Finally, this solution makes it possible to handle

multiple-incomer diagrams with great ease.


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the switchboard central unit managing or

monitoring source changeovers.

Threshold-initiated load shedding

In certain situations (voltage drop due to a

problem on the distribution system, failure of asource, demand exceeding the available power

from a source supplying the switchboard, etc.), it

may be necessary to rapidly shed a group of

non-priority outgoers, for example to avoid

transient-stability problems.

Figure 10shows how shedding of non-priorityoutgoers is processed in a decentralised

manner, following an overload on themain LV switchboard.

This example shows that the amount ofinformation exchanged is very small. The centralunit receives a signal, issues an order via the busand the concerned circuit breakers carry out the

order.

Switchboard

central unit

Q2Q1 Q3

M

Parameter setting of threshold and priority (P)non-priority (NP) status for each outgoer

Store threshold parameterDecide: if measured power > threshold,send load-shedding order

Measure power

Store P/NP parameterDecide: if parameter = NP, open outgoeron receiving load-shedding orderControl the circuit breakers

Management of an incomer or an outgoer

Management of an incomer (or an outgoer)may include some or all of the followingfunctions:ccontrol and monitoring (control of the device

and monitoring of its status),cmeasurements (currents, power levels, energydrawn, etc. ),clocal or remote operator interface,ccommunication with the switchboard centralunit.By distributing these functions among differentmodules (see fig. 11 ), it is possible to solvecertain problems:cnot all the outgoers require all the functions

listed above,

cthe operator interface can be remoted,

cthe interface must be adaptable to the

various users (language, level of competence,

etc.).

fig. 10: example of decentralised processing of a load-shedding order.


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3.3 Advantages of decentralised architecture and distributed processing

Mastering complexityA complex problem can often be broken down intoa set of simple basic problems. Similarly,controlling an electrical installation may prove verycomplicated given the size of the installation andthe number of functions that must be processed.By decentralising a majority of the functions, mostof the processing can be carried out by smallerunits. The processing is then easier to handle andcan be standardised. The concept of type-testedassemblies, already used for the power part ofelectrical switchboards, can now be expanded toinclude power-management functions. The loadon the higher-level processing unit is significantly

lightened and it can devote its processing powerto the tasks for which it is specifically intended.

Technical and economical constraintsAs already mentioned in the preceding chapter,the considerable increase in the quantity ofinformation to be transmitted has led to thedevelopment of hierarchical architectures. Justas in large installations where there are levels inthe power-distribution structure (main andsecondary LV switchboards, final distributionenclosures, etc.), the creation of levels for theprocessing of information is the best solution:cconstraints (response times, environment,throughputs, etc.) are not the same inside aswitchboard and throughout an entireinstallation,

call the information that is useful for a functionat a given level is not necessarily relevant on a

Module M1 controls the device and reads its status conditions.

Module M2 measures the currents and voltages and prepares the power and energy information.

Module M3 displays the status and measurement information for the outgoer on the front panel of the switchboard. It can

also control the outgoer.

Module M4, identical to module M3, is a display remoted to a point outside the electrical room. The information may be

displayed in a manner different than on M3

Control &

Monitoring

M1

Measurement

M2

Localdisplay

M3

Outgoer 3 closed

I1 = 125 A E = 327 kVAh

M4

Switchboard

centralunit

fig. 11: example of distributed processing for outgoer management.


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3.4 Conclusion on decentralised processing in a LV switchboard

higher level, for example, all the information

available locally on each device is not

necessarily of great use to the operator:

vsome information is intended strictly for

maintenance purposes,

v

other information must be summarised to avoidsubmerging the operator (see fig. 12 ),

vthe cost of programming is reduced by using

standard codes for a vast majority of the

functions.

Continuity of service

In a centralised system, a breakdown results in

an interruption of service for the entire

installation. In a decentralised system, however,

the same breakdown can be limited to the single

subsystem where it occurred, thus enabling therest of the installation to continue operating,though perhaps in a downgraded operatingmode. For example, if maintenance is requiredon the switchboard central unit, local functionsinside the switchboard remain operational, giventhe decentralised nature of the installation.

Maintainability

A decentralised system implements a largenumber of processing units, however, theirfailure rate is not cumulative.

The limited number of connection points reducesthe number of breakdowns.

The self-test system on the digital products andthe communications buses can detect nearly100% of possible breakdowns.

Flexible implementation

cSetting up a new site often takes place overrelatively long periods. It is not uncommon thatfor budgetary reasons, the remote supervisionstation is installed one or two years aftercommissioning of the switchboards. The lattercan, nonetheless, operate autonomously oversuch long periods if decentralised processing iscarried out locally.cWhen existing installations must be renovated,upgrading can be spread out over several years.Decentralisation makes the replacement of aswitchboard simpler. The new switchboard canbe factory tested and a single serial link is all thatis required to connect the new switchboard to the

control system.

The examples presented in chapter 3 show thatthe functions managed by an intelligentLV switchboard can be distributed to varyingdegrees among different processing units.cCertain functions are handled by theswitchboard central unit when:vthe processing is complex and cannot becarried out by a standard autonomous module.

For example, source management when thereare multiple incomers,vthe functions call on processing that iscommon to other functions. For example, asource changeover can be caused by the failureof the normal source or by an order issued by acontract-management function,vthe functions must be coordinated with otherequipment. For example, when management ofreplacement sources brings MV equipment intoplay.cCertain autonomous functions can be carriedout by dedicated products that have beenoptimised for the given function. This is the case

for reactive power regulators and sourcechangeover units.

When these autonomous products areincorporated in an intelligent switchboard, they canbe connected via a bus to the switchboard centralunit which provides additional functions such as:vsetting of parameters for the products by amore user-friendly device that is common to allthe functions carried out in the switchboard,vminimum management during downgraded

operating modes,vincorporation of the products in predictive- andcorrective-maintenance functions.

The various functions mentioned in thisdocument may be included in the architecturepresented in figure 13:cThe switchboard central unit is in charge of:vprocessing the general switchboard functionsand the interdependent functions,vcoordinating the functions managed by lower-level modules,vintegrating in a higher-level control system,vcommunicating with a terminal intended for theelectrician in charge of implementation and

maintenance operations. During servicing, thisterminal is connected locally in front of the

fig. 12: example of sorting information to be made

available to different users.

Information User

Maintenance Supervision

room station

Device position X X

Faulty outgoer X X

Energy measurement X

Outgoer not available (summary) X

vDisconnected/locked out X

vNot supplied X

Trip unit setting X

Load shedding in progress X X


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switchboard. In no way does it replace the

centralised supervision station from which the

operator manages the installation.

cCertain modules are in charge of processing

autonomous functions (reactive power

regulation, insulation monitoring, etc.).cOther modules are in charge of managing an

incomer or an outgoer.

Modularity makes it possible to:

vintegrate control and monitoring in the concept

of tested, standardised functional units,

vstandardise connections between the module

and the switchgear, thus reducing the risks of

breakdowns due to faulty connections,

vtake action on a given outgoer without shutting

down other elements in the switchboard, in the

event of a breakdown or installation upgrading.

The modules and the switchboard central unitare connected via a digital bus. Note that use of

this type of bus offers a wide range of

advantages:

cmassive reductions in the quantity of control

wires in the switchboard and consequently in the

cost of wiring and the space required,creduced risks of breakdowns due to faulty

connectionscless design and wiring time for the panel

builder,

cgreater installation upgradeability, for example,

the addition of outgoers or functions in anexisting installation.

The next chapter describes the types of buses

best suited to power management

applications.

Switchboardcentral

unit

Centralfunctions

Autonomousfunctions

Localfunctions

Installationsupervisionstation

Source managementwith load shedding/ reconnection

Generator managementReactive powerregulationUPSsInsulation monitoring

Outgoer control andmonitoring andmeasurements

Secondaryswitchboards

Configuration

fig. 13: distribution of functions in the architecture of a switchboard.


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3.5 A switchboard bus suited to electrical applications

Before selecting a suitable field bus, it is essentialto fully comprehend the constraints weighing on

an electrical application, notably the informationflow, response times, the environment, etc.

Characteristics of an electrical application

cA naturally stable and continuous applicationThe purpose of an electrical installation is todistribute power to each load. The purpose ofan LV switchboard is therefore to permanentlymaintain the operational status of outgoers.Opening of a device may be related to one of thefollowing events:vreaction of a protective device to an electricalfault,voperator intervention to isolate a circuit (for

servicing, to turn off the lights on a floor at theend of the day, etc.),vintervention of an automatic-control function toshed non-priority loads, for example, followingthe failure of the normal source.The change in status of a device is therefore anexceptional event. An electrical switchboard iscontinuously in a naturally stable state. Note thatcircuit breakers are by nature bistable devices.

cCertain situations cause an informationavalancheOn the other hand, certain situations may resultin an avalanche of information over very shorttime periods. For example, following the failure

of the source supplying the switchboard, mono-stable devices such as contactorssimultaneously open and the automatic sourcechangeover and load-shedding functions issueorders to the circuit breakers.

cLimited real-time constraintsIn an electrical installation, the response time ofthe system to an event depends on the nature ofthe event:vwhen the operator issues an order from thesupervision station, the system must respondwithin an time delay that is acceptable to theoperator, i.e. one or two seconds betweenconfirmation of the order by the operator and thechange in status of the device displayed on thescreen,vfor source-changeover automatic-controlfunctions, no specific constraints concerning theresponse time weigh on the application. The goalis simply to reduce to the strict minimum the timethat the loads are not supplied with power.Response times of several hundred millisecondsare perfectly reasonablevif, during operation on an engine-generator set,the rated output of the set is overrun, certainnon-priority loads must be shed. The authorisedoverload time is indicated by the manufacturer ofthe engine-generator set and depends on thelevel of the overload.

In complex installations where local powergeneration facilities are coupled with the power

supplied by the utility, in the event of a utilityfailure, certain loads must be shed in a fraction

of a second, before the engine-generator setprotective functions can react.

cData flow capacity sized for the number ofmeasurementsElectrical measurements may result is a constantflow of information on the switchboard bus. Themost common measurements concern voltages,currents, power levels and quantities of energy.Sizing of the bus therefore depends not only onthe quantity of information that must betransmitted, but above all on how often theinformation must be transmitted:vmeasurement values for currents or powerlevels may be used by the operator to monitor

the distribution system in real time and thevalues may therefore have to be transmittedevery few seconds,vvalues concerning the quantity of energyconsumed are required only every few minutes,at most, i.e. the frequency of transmission forthese values is very low.

cImplementation constraints in an electricalswitchboardInstallation of a bus inside an electricalswitchboard must take into account the followingconstraints:vthe bus must not be sensitive to the majorelectromagnetic disturbances that exist in a low-voltage switchboard,vit must be easy to install during wiring of theswitchboard and be easily modified duringswitchboard upgrades,vthe cost of each connection point, which is adecisive element in selecting a bus in that a low-voltage switchboard comprises great numbers ofconnection points.

Master/slave protocols are inadequate

For the solutions discussed in chapter 2, master/slave protocols are commonly used. An exampleis ModBus (for further information, see CahierTechnique n147).

For a basic automated switchboard, i.e. one thatmanages only orders and acknowledgements, amaster/slave protocol is sufficient to satisfy therequired functions. For example, given aswitchboard with 50 incomers and outgoers anda polling time of 20 milliseconds for each one,approximately one second is required to poll allthe incomers and outgoers. When an eventoccurs (order from the supervisor or interventionof an automatic-control function in theswitchboard central unit), polling of the status ofeach incomer or outgoer can be interrupted tosend the necessary orders.

But when the system functions require thetransmission of measurement values, the


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weaknesses of master/slave protocols, i.e. the

increased time required for each polling cycle,

rapidly become apparent.

What is more, when a device-status change

occurs following tripping, the information is made

available to the switchboard central unit onlyduring the next polling cycle.

Finally, this type of protocol is inadequate for

distributed processing because the central unit

can act as the master only if all the information

runs through it.

CSMA protocols

Contrary to protocols using the master/slave

access method, CSMA (Carrier Sense Multiple

Access) protocols allow the various stations

connected to the bus to spontaneously transmit

data only when there is a real need.

cCSMA constraintsRandom access to the bus creates three

constraints that do not exist in master/slave

systems which are, by definition, centralised.Solutions for these difficulties are easy toimplement.

vRisk of collision. Several connected stationsmay transmit data simultaneously. Rules are setup to avoid collision between the differentmessages.Two different solutions exist:- CSMA-CD (Collision Detection). Using this

technique, the stations detect the interference on

Station 1

Station 2

Line status

Line monitoringby station 1

Line monitoringby station 2

15 V

0 V

OK OKOKOKOKOKOKOK

1 111 10 00

1 0 0 Stop transmitting

_ ErrorOK OK_ _

Station 1 pinches the lineand short-circuits it.

Stations 1 and2 pinches the line.

Station 1 pinches the line.Station 2 leaves the line at rest.It detects the short-circuit onthe line, analyses a collision andstops transmitting.

Stations 1 and2 leave the lineat rest.

Station 1 leavesthe line at rest.

Station 1 did not detecta collision and continuestransmitting its message.

fig. 14: collision analysis in the BatiBus system.

the bus due to the two simultaneous messagesand stop transmitting. Each station will thenattempt to retransmit its message as some latertime. This is the solution used by Ethernet- CSMA-CA (Collision Analysis). Using thistechnique, the station transmitting the message

with the lowest priority level stops, thus allowingthe higher-priority level message continue.Management of priorities is based the coding ofthe frames transmitted. This is the solution usedby BatiBus (see fig. 14 ).

vNon-deterministic response times. Dependingon the information load on the bus, thetransmission time for a frame is not constant. It istherefore not possible to guarantee a maximumtransmission time using a protocol implementingthis type of access to the bus. However, acertain number of devices and design rulesmake it possible to ensure maximumtransmission times that are nearly 100% certain.For example, in the BatiBus system, commandsare priority messages. This is a means to avoidthe response-time constraint.

vDetection of faulty stations.In a system using the master/slave method ofaccess to the bus, the breakdown of a slave isdetected by the master during the next pollingcycle. But for protocols in which messages aretransmitted only when necessary, a faultymodule is not detected. Each application musttherefore develop and implement the necessarymonitoring devices required to periodically checkthe status of each module.


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cAdvantages of a CSMA bus for an electrical

installationIn the preceding paragraphs, it was shown howthe constraints specific to CSMA buses may beavoided.The main advantages that may be gained from

this type of bus are listed below:

vOptimised data exchange: a CSMA protocoloptimises data exchange because the bus is notclogged with continuous polling operations.Consequently, for a stable application, which isgenerally the case for an electrical installation,with the same transmission speeds as a master/slave protocol, the quantity of useful informationtransmitted is significantly increased andresponse times can even be shorter.

vReduced costs: the greater the transmissionspeed on the bus, the greater the systemconstraints concerning protection against

electromagnetic disturbances and, consequently,the greater the costs. A CSMA protocol makes itpossible to select slower transmission speedsand thus reduce transmission-related costs.

vDecentralised processing: a protocol offeringthis type of access to the bus makes foroptimised processing of decentralised and/ordistributed operations. The example in figure 15(decentralisation) shows how data exchange canbe simplified (opening orders to non-prioritycircuits) with respect to a centralised master/slave system.Note that for distributed processing, it is themeasurement module which directly transmits

the opening order to the non-priority loads.Consequently, even if the switchboard centralunit has failed, load shedding remains possible.

Using FIP for MCC applications

Certain industrial applications impose verysevere demands in terms of continuity of serviceand performance levels. For example, aguaranteed response time (deterministic) may berequired for an order issued by an automatic-control function managing the industrial process.This is the case for certain MCC (Motor ControlCentre) switchboards. Contrary to a mainLV switchboard, opening and closing orders fordevices are by no means exceptional.

In this case, the performance levels offered bybuses implementing master/slave protocols arenot sufficient, unless very high transmissionspeeds are used, with the corresponding highcosts. Buses implementing random-accessprotocols are not up to the job either.

It was for this type of application that the FIP buswas designed by industrial companies andmanufacturers. It is not within the scope of thisdocument to present the FIP bus in detail,however, it should be noted that it combines theadvantages of both master/slave and random-access protocols:caccess to the bus is controlled by a bus

manager located in the switchboard central unit(LV switchboards),

Time

0 ms

10 ms

20 ms

30 ms

40 ms

Status

Status

Status

Status

Status

Commands

Commands

Commands

cStatusinformation is sentas periodic

variables every 10milliseconds.

cCommands aresent as periodicmessages every 20milliseconds.

cThe remainingavailable time(shown in grey) canbe used to transmitparameters,measurements,diagnosticsinformation, etc., asnon-periodic

messages.

fig. 15: time diagram for an MCC implementing FIP.

cdata may be periodically transmitted over the

bus (orders and status information, for example),

cstations may request permission from the bus

manager to transmit information, as needed, for

example, in the event of a significant change in

the value of a measurement, etc,cthe data issued by one station may be used by

one or several other stations, for example, for

distributed processing,

cfinally, the protocol has a number of built-in

systems that make it possible to guarantee a

very high level of transmission dependability.

The FIP bus thus combines the advantages of:

cmaster/slave protocols (deterministic and

guaranteed response time),

crandom-access protocols (transmission of

useful information or following an event).

The FIP bus offers a high level of performance

and meets very severe dependabilityconstraints.


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4 Implementation examples

4.1 Computer centre

Needs

In a computer centre operating 24 hours per day,the primary concern of the electrical manager isto ensure continuous availability of power andfast response when maintenance is required.

In addition to these basic needs, the customermay want to reduce his energy bill by:cimproving the power factor;ctaking advantage of special tariffs with theutility, for example by agreeing to sharply reduceconsumption on peak-demand days uponreception of a special signal.

Surveillance room

VAR

MLVS

G

1 000 kVA20 kV /230 - 400 V

550 kVA

UPSs

MV cubicle

A A A A

A A

D

B

C

C

F

A

VAR

E

fig. 16: solution implemented for a computer centre.

Through these two modifications, the return oninvestment for the installation drops to less thanthree years due to the sharp decrease inelectricity bills.

Implemented solution

cElectrical installationThe electrical installation is supplied by a 20 kVmedium-voltage loop. The MV loop supplies a1 000 kVA transformer which in turn supplies amain LV switchboard (see fig. 16 ).The main LV switchboard is made up of


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withdrawable units. It supplies 23 outgoers,including two reserve outgoers. The high-poweroutgoers are equipped with motor mechanismsfor remote-control purposes. The computers areprotected by two UPSs set up in a redundantconfiguration. A 550 kVA engine-generator set

can replace the power supply for all theelectrical equipment in the computer centre.

cRequired functions

vSource changeover. In the event of a voltageloss downstream of the MV/LV transformer (or ifa load reduction signal is received from theutility), the switchboard is automatically suppliedby the replacement source. The cabinetmanaging the engine-generator set receives theshutdown and start orders from the main LVswitchboard and autonomously manages theengine-generator set.When the load is transferred to the engine-

generator set, the high-power outgoers are shedto reduce the load step change during switching,and are then reconnected one after the otheraccording to an adjustable individual time delay.When utility power returns (or the special utilitysignal is discontinued), the switchboardautomatically transfers the load back to thenormal source and requests shutdown of theengine-generator set.

vContract management. For special tariffcontracts, the power utility sends a loadreduction signal to the customer 30 minutesbefore actually shifting to the special mode. Thesignal, transmitted via the field bus, is decoded

by a specific relay. On reception of the signal,the switchboard transfers the load to theengine-generator set, exactly as if a powerfailure had occurred. When the signal isdiscontinued, the load is automaticallytransferred back.

vReactive power regulation. A 100 kVARcapacitor bank used to compensate for reactive

energy consumption is managed by a reactivepower regulator.

vRemote surveillance. In the event of anincident in the electrical installation, thewatchperson is immediately informed via asupervision console which transmits any alarmsissued by the main LV switchboard.

cThe control and monitoring system

vEach incomer and outgoer in the main LVswitchboard is managed by a module (marked Ain the diagram), which:- acquires the position of the device (open,closed, tripped, withdrawn, etc.);- displays this status locally;- for the remote-controlled incomers andoutgoers, orders opening, closing or resetting.These orders may be given locally or sent via theswitchboard bus;- dialogues with the switchboard central unit via

the digital communications bus.vThe switchboard control unit (marked B in thediagram) located inside the main LV switchboardis in charge of:- managing the control and monitoring functionsfor the incomers and outgoers via the modulesmarked A in the diagram;- directly acquiring two elements of information,namely the presence of utility voltage or engine-generator set voltage (via voltage relays markedC in the diagram), and passage to the specialutility mode (special utility relay marked E in thediagram);- transmitting a start order to the cabinet (markedD in the diagram) managing the engine-generator set;- processing the source changeovers caused bya failure in utility power or reception of thespecial utility signal;- generating and transmitting any alarms to thesupervision console (marked F in the diagram)which then displays them in the appropriatemanner.

4.2 Hospital

Needs

In a hospital, the continuity of electrical powerservice is critical. The example below deals witha mid-sized hospital.

To provide optimum management of theelectrical distribution system and in compliancewith the expressed wishes of the operator:cOutgoers are divided into three categories,backed-up (by a generator set), priority(protected by a UPS) and no-break (protectedby a UPS and a generator set). Each incomerand outgoer is monitored and may be remotelycontrolled from the supervisor;cThe entire installation is remotely supervised.

Implemented solutioncElectrical installation

vThe electrical installation is supplied by a

20 kV medium-voltage loop. The MV loopsupplies three 1 000 kVA transformers which inturn supply an LV distribution switchboard.

vTwo 400 kVA engine-generator sets can stepin to provide back-up power to certain electricalequipment in the hospital.

vTwo UPSs supply the no-break and priorityoutgoers.

vThe outgoers are grouped in three LV switch-boards. The diagram infigure 17makes clear thesupply system for each outgoer in LV switchboard 1.

cOrganisation of power management

vA supervision station (supervisor) may be used

by the operator to monitor the installation, issueorders and set parameters.


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vThe switchboard central unit in the LVdistribution switchboard:- provides control and monitoring of the circuitbreakers on incomers and outgoers;- checks operation of the reactive power relays(reactive-energy compensation) and stops

compensation if utility voltage is absent(operation on the engine-generator sets);- dialogues with the UPS processing units;- supplies the transformers ON information.

vThe switchboard central unit in the engine-generator set LV switchboard:- provides control and monitoring of the circuitbreakers;

- dialogues with the control cabinets of theengine-generator sets for monitoring andtransmission of ON and OFF orders;- dialogues with the LV switchboards (1, 2, 3 andno-break) which issue a starting order for theengine-generator sets and receive a set-point

indicating the maximum power availabledepending on the operating engine-generatorsets and the LV switchboards supplied withpower (all are not necessarily supplied duringmaintenance operations).

vThe central units in the LV switchboards 1, 2and 3:- control and monitor the circuit breakers;

fig. 17: solution implemented for a hospital.

Priority outgoers(mains / UPSs / mains)

No-break outgoers(mains / UPSs / generators)

Backed-up outgoers(mains / generators)

MV cubicle

20 kV line

MLVS 2 MLVS 3

MLVS 2 MLVS 320 kV / 230 - 400 V transformer

3 x 1 000 kVA

2 x 400 kVA

GE GE

MLVS 2 MLVS 3

MLVS 1

MLVS 2 MLVS 3

No-breakMLVS

Gen. MLVS

DistributionMLVS

UPSs withautomatic

bypass


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- provide the automatic source changeoverfunction for the backed-up outgoers on the basis ofthe information supplied by the voltage relays, i.e.:. load shedding of the major outgoers;. transmission of a start request for the engine-generator sets;. closing of the engine-generator set incomingcircuit breaker;- provide load regulation. Depending on thepriority rating of the backed-up outgoers, theyare shed and reconnected according to thepower supplied by one or both engine-generatorsets or by the transformers (1 and/or 2 and/or 3);- dialogue with the insulation monitor for theno-break outgoers.

vThe central unit in the no-break LV switchboard:- controls and monitors the circuit breakers;- controls source changeovers, after requestingstarting of an engine-generator set if the UPS

signals a problem.

In this example, not all the available power-management functions are implemented (theynever are).cTime management is not implementedbecause a hospital operates 24 hours per day.cContract management (smoothing of peaks,special utility modes) was not applicable, onlyreactive-energy compensation was implemented.

cThe power-management system set up is

entirely dedicated to ensuring maximum

availability of electrical power.

cEach switchboard received local and

autonomous processing capacity to carry out its

assigned functions.

cVery little event information circulates on the

bus (automatic source changeover, engine-

generator sets, load regulation) and no

measurement values except for metering values

in the MV switchboard.

Status checks are run periodically.


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5 Conclusion and prospects for the future

Intelligent switchboards, a critical element inelectrical distribution systems, provide solutions

meeting the needs of managers and operators of

electrical installations, notably:

cenergy savings;

cdependability;

cremote control of the installation (with possible

extensions to building management for

commercial applications and process

management in industry);

cinstallation maintainability and upgradeability;

cgradual evolution of the installation over time

toward greater intelligence.

The construction of switchboards with integratedmanagement functions, but with decentralised and

distributed intelligence, is today made much easier

due to the existence of standardised modules,

equipment and software that will remain available

over long periods. In this sense, control and

monitoring can now be implemented using

concepts similar to those of type-tested assemblies

and shows sharp differences with respect to

automatic-control functions for industrial processes.

Integration of intelligence in switchboards hasmade it possible to:

csimplify switchboard and electrical-installation

architecture, during the initial design process and

later during upgrades (distributed electrical

distribution, elimination of half busbar

arrangements, discrimination, knowledge of

switchboard reserves, management of operating

conditions at switchboard maximum limits

(temperature, overloads, etc.)):

cmanage the switchboard over time (black-box

function, up-to-date diagram file, etc.);

ccombine communications functions (low

currents) with power functions (high currents).

In the near future, communication and

processing will continue even further

downstream to the individual devices, sensors

and actuators. This will make the distribution of

intelligence easier and thus further reduce

centralisation. Considerable advances may be

expected in the fields of design, wiring,

installation, operation, dependability andupgradeability.


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Bibliography

Schneider Cahier Technique publications

cIntroduction to dependability designCahier Technique n144P. BONNEFOIcInitiation aux rseaux de communicationnumriques.Cahier Technique n147E. KOENIGcHigh availability electrical power distributionCahier Technique n148A. LONGCHAMPT - G. GATINEcDependability and LV SwitchboardsCahier Technique n156O. BOUJU

186-Intelligent LV Switchboards

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