Ks factors which may be used for circuits supplying commonly-occurring loads, are shown in Figure B13.
Circuit function Factor of simultaneity (ks)
Lighting 1
Heating and air conditioning 1
Socket-outlets 0.1 to 0.2 (1)
10 and more 0.6
Lifts and catering hoist (2) c For the most powerful
motor 1
c For the second most
powerful motor 0.75
c For all motors 0.60
(1) In certain cases, notably in industrial installations, this factor can be higher.
(2) The current to take into consideration is equal to the nominal current of the motor, oncreased by a third of its starting current.
Fig. B13 : Factor of simultaneity according to circuit function
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Fig B14 : An example in estimating the maximum predicted loading of an installation (the factor values used are for demonstration purposes only) 1
Distribution box
Workshop A 5 0.8
0.8
Utilization Apparent Utilization Apparent Simultaneity Apparent Simultaneity Apparent Simultaneity Apparent
power factor power factor power factor power factor power
(Pa) max. demand demand demand demand
kVA max. kVA kVA kVA kVA
Level 1 Level 2 Level 3
Fig. B15: Standard apparent powers for HV/LV transformers and related nominal currents
4.6 Choice of transformer rating
When an installation is to be supplied directly from a HV/LV transformer and the maximum apparent-power loading of the installation has been determined, a suitable rating for the transformer can be decided, taking into account of the following considerations (seeFig. B15):
c The possibility of improving the power factor of the installation (see chapter K) c Anticipated extensions to the installation
Apparent power In (A)
kVA 237 V 410 V
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c Installation constraints (temperature...) standard transformer ratings
The nominal full-load current In on the LV side of a 3-phase transformer is given by:
In a x 103
=P U 3 where
c Pa = kVA rating of the transformer
c U = phase-to-phase voltage at no-load in volts (237 V or 410 V) cIn is in amperes.
For a single-phase transformer:
In a x 103
=P V where
c V = voltage between LV terminals at no-load (in volts) c Simplified equation for 400 V (3-phase load)
c In = kVA x 1.4
The IEC standard for power transformers is IEC 60076.
4.7 Choice of power-supply sources
The study developed in E1 on the importance of maintaining a continuous supply raises the question of the use of standby-power plant. The choice and characteristics of these alternative sources are described in E1.4.
For the main source of supply the choice is generally between a connection to the HV or the LV network of the power-supply utility.
In practice, connection to a HV source may be necessary where the load exceeds (or is planned eventually to exceed) a certain level - generally of the order of 250 kVA, or if the quality of service required is greater than that normally available from a LV network.
Moreover, if the installation is likely to cause disturbance to neighbouring consumers, when connected to a LV network, the supply authorities may propose a HV service.
Supplies at HV can have certain advantages: in fact, a HV consumer:
c Is not disturbed by other consumers, which could be the case at LV c Is free to choose any type of LV earthing system
c Has a wider choice of economic tariffs c Can accept very large increases in load It should be noted, however, that:
c The consumer is the proprietor of the HV/LV substation and, in some countries, he must build and equip it at his own expense. The power utility can, in certain circumstances, participate in the investment, at the level of the HV line for example c A part of the connection costs can, for instance, often be recovered if a second consumer is connected to the HV line within a certain time following the original consumer’s own connection
c The consumer has access only to the LV part of the installation, access to the HV part being reserved to the utility personnel (meter reading, operations, etc.).
However, in certain countries, the HV protective circuit breaker (or fused load-break switch) can be operated by the consumer
c The type and location of the substation are agreed between the consumer and the utility
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Power monitoring and control system may be of high benefice for the operator or the owner of an electrical network.
Companies are moving faster and faster, the use of building facilities either.
An electrical network has then to face successive generation of needs, which will lead to many load evolutions but also certainly to “associated services” evolutions -for example, tracking the costs due to higher level of competition.
Even if the decision is to invest later, the design of the network has to take into account that using a monitoring system will happen eventually, and then it will be a competitive advantage if the Equipment has anticipated its integration.
Nowadays, entering the “Power monitoring and control” approach doesn’t mean setting-up a complex and expensive system.
Some simplest features are really affordable with a very good payback because they can be directly embedded in your Power Equipment.
Such system may simply share the communication medium of the user’s Intranet site.
In addition operation won’t ask specific skills and training. It will only require the use of license-free software such as Intranet browsers.
Upgradability is also now a reality, based on new technologies that come for the Office and Communication world (you can now run multiple protocols on the same medium, the legacy and the new one). Then being in a position of taking advantages of these new possibilities will be more and more a differentiating behaviour.
5.1 Main user’s benefits
Power Monitoring and control is possibly interesting for four main reasons:
c It can contribute to field staff efficiency increase c It can contribute to decrease the cost of Energy
c It may help in optimising and increasing the life duration of the assets associated to the electrical network
c And finally it may be master piece in increasing the productivity of the associated process (industrial process or even office, building management), by preventing, or reducing downtime, or insuring higher quality energy to the loads.
Increase field staff efficiency
One of the big challenges of field staff in charge of the electrical network is to make the right decision and operate in the minimum time.
The first need of such people is then to better know what happens on the network, and possibly form everywhere on the concerned site.
This site-wise transparency is a key feature that enables a field staff to : c Understand the electrical energy flows – check that the network is correctly balanced, what are the main consumers, at what period of the day, or the week…
c Understand the network behaviour – a trip on a feeder is easier to understand when you have access to information from downstream loads
c Be spontaneously informed on events, even outside the concerned site by using today’s mobile communication
c Going straight forward to the right location on the site with the right spare part, and with the understanding of the complete picture if the network status
c Initiate a maintenance action taking into account the real usage of a device, not too early and not too late
Decrease the cost of Energy
Power invoice may be a significant expense for companies, but in the same way, not the one managers are looking to, first.
However, providing to the electrician a way to monitor the electrical network can appear as a powerful mean to optimise and in certain case drastically reduce the cost of power.
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Here are some examples of the main usage of the simplest monitoring systems : c Benchmark between zones to detect abnormal consumption
c Track unexpected consumption
c Ensure that power consumption is not higher that your competitors c Choose the right Power delivery contract with the Power Utility
c Set-up simple load-shedding just focusing on optimising manageable loads such as lights
c Be in a position to ask for damage compensation due to non-quality delivery from the Power Utilities – The process has been stopped because of a sag on the network.
Optimising the assets
One increasing fact is that electrical network evolves more and more and then a recurrent question occurs : Will my network support this new evolution?
This is typically where a Monitoring system can help the network owner in making the right decision.
By its logging activity, it can archive the real use of the assets and then evaluate quite accurately the spare capacity of a network, or a switchboard, a transformer…
Increasing the life duration of assets
A better use of an asset may increase its life duration.
Monitoring systems can provide accurate information of the exact use of an asset and then the maintenance team can decide the appropriate maintenance operation, not too late, or not too early.
In some cases also, the monitoring of harmonics can be a positive factor for the life duration of some assets (such as motors or transformers).
Increasing the productivity by reducing the downtime
Downtime is the nightmare of any people in charge of an electrical network. It may cause dramatic loss for the company, and the pressure for powering up again in the minimum time – and the associated stress for the operator – is very high.
A monitoring and control system can help reducing the downtime very efficiently.
Without speaking of a remote control system which are the most sophisticated system and which may be necessary for the most demanding application, a monitoring system can already provide relevant information that will highly contribute in reducing the downtime:
c Making the operator spontaneously informed, even remote, even out of the concerned site (Using the mobile communication such as GSM/SMS) c Providing a global view of the whole network status
c Helping the identification of the faulty zone
c Having remotely the detailed information attached to each events caught by the field devices (reason for trip for example)
Then remote control of a device is a must but not necessary mandatory. In many cases, a visit of the faulty zone is necessary where local actions are possible.
Increasing the productivity by improving the Energy Quality Some load can be very sensitive to Electricity un-quality, and operators may face unexpected situations if the Energy quality is not under control.
Monitoring the Energy quality is then an appropriate way to prevent such event and / or to fix specific issu.
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Standard network Sensitive electrical networks High demanding sites
System
Fig B16 : Monitoring system positioning
5.2 From Network Monitoring and Control System to Intelligent Power Equipment
Traditionally and for years, monitoring and control systems have been centralised and based on Scada (Supervisory, Control and Data acquisition) automation systems.
Deciding in investing in such system – noted (3) in Figure B16 hereunder – was really reserved for high demanding installation, because either they were big power consumers, or their process was very sensitive to Power non quality.
Based on automation technology, such systems were very often designed, customised by a system integrator, and then delivered on site. However the initial cost, the skills needed to correctly operate such system, and the cost of upgrades to follow the evolutions of the network may have discouraged potential users to invest.
Then based on a dedicated solution for electrician, the other approach noted (2) is much more fitting the electrical network specific needs and really increases the payback of such system. However, due to its centralised architecture, the entree level cost of such solution may still appear high.
On some site Type (2) and (3) can cohabit, providing the most accurate information to the electrician when needed.
Nowadays, a new concept of intelligent Power equipment – noted (1) – has come.
Taking the opportunity of the Web technologies, it has become a truly affordable solution for most of the users. Moreover the site owner can invest gradually into more sophisticated monitoring systems.
Level 1 can then be considered as an entering step for going to level 2 or 3, due the ability of these solutions to co-exist on a site.
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Meter 1
1 2 3
Circuit breakers
Meter 2 Meter 3 Equipment server
Gateway
Modbus
Intelligence Power Equipment Standard remote
Web browser
Standard local Web browser
Intranet (Ethernet/IP) Internet
Intelligent equipment based architecture (see Fig. B17)
This new architecture has appeared recently due to Web technology capabilities, and can really be positioned as an entry point into monitoring systems.
Based on Web technologies it takes the maximum benefits of standard communication services and protocols, and license-free software.
The access to electricity information can be done from everywhere in the site, and electrical staff can gain a lot in efficiency.
Openness to the Internet is also offered for out of the site services.
Fig. B17 : Intelligent equipment architecture
Electrician specialized centralised architecture (see Fig. B18) Dedicated to electrician, this architecture is based on a specific supervision centralised mean that fully match the needs for monitoring an electrical network.
Then it offers naturally a lower level of skill to set up and maintain it – all ED device are already present in a dedicated library. Finally its purchase costs is really minimised, due the low level of system integrator effort.
Fig. B18 : ED specialist monitoring system
Meter 1 Meter 2 Meter 3 Gateway
Modbus
Communicating Power Equipment Dedicated supervisor
for electrician
Modbus (SL or Ethernet/IP)
Circuit breakers
1 2 3
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Conventional general purpose centralised architecture (see Fig. B19) Here is a typical architecture based on standard automation pieces such as SCADA systems, and gateways.
Despite its real efficiency, such architecture suffered from some drawbacks such as : c The level of skills needed to operate it
c The poor upgradability
c And at the end the risky payback of such solutions
They have however no equivalent for high demanding sites, and appears very relevant for central operation rooms.
Meter 1 Meter 2 Meter 3 Gateway
Modbus
Conventional supervisor
Modbus (SL or Ethernet/IP)
Communicating Power Equipment
Circuit breakers
1 2 3
5.3 Typical services possibly brought by intelligent Equipment compared to other solutions
The objective of this comparison is to help the choice of the appropriate system by understanding pro and cons of each one (see Fig. B20).
“Intelligent” service Intelligent Power ED Specialist General purpose
Equipment monitoring site monitoring
Access to electricity real-time information - local ++ +
Access to electricity real-time information - remote ++ +++ ++
Mobile access to information +++ ++
Site-wise monitoring (ED network) + +++ +++
Multi-process monitoring + +++
Data logging + +++ ++
Trending + +++ ++
Alarming + +++ ++
Remote control – automated functions + +++
Advanced functions to optimise + +++
the electrical network management Capabilities
Easiness for use / training for electrician +++ ++
Affordability (based on Initial cost) +++ ++
Upgradability to follow network evolutions ++ ++
Fig. B20 : Typical services compared to other solutions
Fig. B19 : Real-time conventional monitoring and control system
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5.4 Technical inputs on communicating systems
Here is a quick glossary concerning the main terms used associated to communication technologies
Communication layer – OSI model
Communication layer concept is useful to understand the communication glossary, and how these terms can be associated or not.
Referring to the OSI model (see Fig. B21), there are 7 communication layers, but all the communication wording not always refers to the 7 layers. In addition a 8th layer is sometimes added to describe the application specific domain wording and services.
Ethernet
Ethernet is the common word which designates the 802.3 standard family.
Ethernet refers to OSI layers 1 and 2 of a communication mean. Ethernet use is not enough at all to specify a communication mean to interoperate between two devices.
Ethernet 802.3 is usually associated to other words to define others aspects of the network :
Ethernet 802.3 10 Base T ⇒ means Ethernet 10Mb/s using RJ45 connector IP
IP means “Internet Protocol”.
However, even if the Internet has been its effective success factor, IP is not exclusive to the Internet.
IP is also widely used for “internal use” such as on the Intranet, but also in closed
“zone”.
IP is an intermediate communication that enables the communication between two distant devices, even if between them many successive medium types are used.
The switch from one type to another is totally transparent for the “application”.
RS 485
RS 485 is an electrical standard which defines a balanced serial communication mean.
Modbus
Modbus is originally a communication protocol set up by the Modicon company.
Now Modbus definition is under the management and property of Modbus-IDA.org association, an independent and open association whose role is to extend and ensure Modbus interoperability.
Modbus messaging protocol refers to layer 7 of the OSI model.
It can be associated to different medium :
c Serial Line such as RS 485 and RS 232 standard ⇒ the most usual way for defining Modbus
c Ethernet (in fact over TCP/IP, over Ethernet)
But Modbus is also capable of going through modem, whatever their type (PSTN, Radio, GSM, …).
Modbus is now recognized a the de-facto standrad for electricity application in the industry and building field.
Web technologies
By such wording we includes all the technologies usually used through the Web for : c Visualising information (HTML files over HTTP/HTTPS protocol)
c Sending mails (SMTP/POP protocol) c Retrieving/ exchanging files (FTP) c Managing the network (SNMP)
c Synchronising the device attached to the network (NTP/SNTP) c ….
These protocol are managed by the IETF, an international association.
Using Web technologies is very often licence-free for the user as there are the basis of common tool such as Web browsers.
Interoperability
In order to ensure interoperability, at least the 7 OSI layer of communication should be absolutely compatible between themselves. This means for example that having two Ethernet (OSI layer 1 and 2) devices doesn’t mean that these devices will inter-operate.
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5.5 Main constraints to take into account to design a communicating or intelligent power equipment
Equipment bus choice
Here are the main constraints to evaluate when choosing a communication network : c Openness and maturity
c Proven ability to run in harsh Electrical environment
c Availability of bus compliant Power Devices with interoperability guarantee c Level of effort at the Power Equipment interface to make it communicating with the rest of the system (seamless architecture availability)
c Bus communication accessories to ease the wiring inside the cubicle.
Modbus over serial line is today one of the most stable communication mean in the Electrical Distribution environment, and compatible with most of 3d party devices.
It has also been chosen by most of the manufacturers as their preferred network.
Its easy and seamless openness to Ethernet is a guarantee for easy integration into the rest of the system. It can also been seen as an easy way for upgrading in the future, without impact on connected applications.
Equipment bus topology
Equipment bus topology must be flexible enough to be spread on the Equipment structure.
What is also important is the disconnectability of sections within the power equipment for transportation.
Usually there are needs of (impedance) termination at the ends of the bus.
The higher the bus speed is, the more sensitive to wiring, terminations and grounding, the bus is.
Front communication socket
In order to ease the work of operators, introducing a socket on the front door of the equipment may be of great benefit.
This option will be even more effective if from this switchboard, the operator can not only have access to information related to the connected power Equipment, but also to the rest of the site (for exemple downstream or upstream switchboard).
Auxiliary power
In the same way as communication bus, auxiliary power has to be distributed to the main Power devices. Isolated Auxiliary DC Power is usually required.
Its distribution may be merged with the communication means : the same cable includes communication and auxiliary power.
Communication accessories
Communication accessories may be necessary to ease the wiring and the maintenance of the switchboard. It then offers higher ease of reading and
Communication accessories may be necessary to ease the wiring and the maintenance of the switchboard. It then offers higher ease of reading and