communication systems for long haul links on 500kv hvac systems

7/29/2019 Communication Systems for Long Haul Links on 500kV HVAC Systems

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D2-01-A-02

COMMUNICATIONSYSTEMSFORLONGHAULLINKSON 500KV HVAC SYSTEMS

ARIEL CAMPOS CARLOS ALBERTO DI PALMATRANSENER S.A. TRANELSA CONSULTORA S.A.

ARGENTINA ARGENTINA

0 KEYWORDSWavelength-dispersion-DWDM-spectral width-EDF-transponder-attenuation factor

1 INTRODUCTIONThe 500 kV Extra High Voltage Transmission System used in Argentina, has long distance Lines between theinvolved substations. It means communication link lengths from 200-300km to 500km.In order to minimize the probability of malfunctions due to natural disasters and/or vandalism acts, on thecommunication system, it is necessary to eliminate (or minimize) isolated repeater stations, and consequently, toavoid those Non-Availability (NAi) nodes.Additionally, so as to allow the operation and control of those long HVAC Lines, as well as to carry the necessaryinformation for the High Voltage Main Transporter (Transener SA), the communication systems must have bigcapacity for transmitting the whole information such as above mentioned and briefly described later. The both, highbit transmission rate and long distance links are the main waited goal that will be described afterwards.

2 INFORMATION TO BE TRANSMITTED

2.1 Current information to be transmitted along 500kV HVAC Lines:

Data transmission for SCADA system (control function)

Data transmission for Differential Protection (main protection function)

Trip transmission from Teleprotection systems (backup protection function)

Data transmission between PLC devices of the Generating/Demand automaticdisconnecting system (stabilizing resources)

LAN networks links for Generating/Demand automatic disconnection system

Digital trunk links between PABXs telephony exchanges (operation function)

LAN networks links for corporative functions (administrative function)

Protection Systems remote management Communication Systems remote management

2.2 Future information to be transmitted:

SCADA system for transmission over IP or Ethernet

Data transmission for SCADA system between SS and Control Centers according to newIEC 61850 standard

Trip and data transmission for Teleprotection system between SS according to newIEC 61850 standard

VoIP and videoconference functions

Video monitoring of electrical equipment located in remote substations

Video surveillance of both buildings and shelters where communication equipment are

allocated Optical cables` remote management

3 BANDWIDTHa) The main parameters taken into account in optical fiber performance are:

Comm sys for long haul links on 500kV sys-rel v.5 1


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the attenuation factor ()

the bandwidth (B), as well as the factor B.L (MHz.km)

The light source will not emit a unique wavelength, but several wavelengths located into the source spectral width. Due to this condition some light rays will propagate with different speeds and consequently will have differenttime delays

A measure of the variation of the group refraction index (ng) at different wavelengths is represented by the materialdispersion Mo () that is shown in units of ps/nm.km. The value of Mo () is negligible at o: 1302-1322 nm, but it isnot at : 1550 nm.Another important factor that affect the dispersion in single mode fibers, is the waveguide dispersion M1 (), that iscaused by the dependence of wavelength with the light distribution in the fiber core and cladding, as well as due tothe difference between their refraction index

Then, the chromatic dispersion M () is formed by the above mentioned two kinds of dispersion:M () = Mo () + M1 ()

For the wavelength with zero dispersion (o: 1302-1322 nm; with dispersion slope of 0,087 ps/nm.kn), thechromatic dispersion will disappear. But, at that o the attenuation coefficient will be high enough (0,40 dB/km

@1550nm) and consequently will be not acceptable for long distance links.

b) As before mentioned, the light pulse will be launched from the optical emitter to the optical fiber, with a spectralwidth . Consequently, the full root mean square (FRMS) of the spectral width will be:

When it is used : 0,4 nm (like shown in item #5), the spectral width will be (FRMS)= 0,34nm

c) If the input pulse width at the injection point into the optical fiber is called t1 , and the final value of the pulse atthe end of the link (when the light pulse is extracted) is called t2 , consequently the broadening of the pulse will be:

The process of pulse broadening at the receiver end will limit the bit transmission rate; because in order todiscriminate one output pulse from another, it is necessary to separate the input pulses between them (less bitrate). In our projects:

The output pulse broadening due to dispersion will be:

In our projects:

It means that, the output pulse broadening will depend of, both the link length and the spectral width of theemission optical source

d) Taking into account the above mentioned, the SM fiber optic transmission bandwidth must be:

e) Resuming the before comments, as well as the issues mentioned in item #3, it is necessary to take into account

the following parameters: attenuation factor , that will give the loss of optical power along the fiber link

the bandwidth B, in order to be used like value of fiber dispersion



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f) Another topic to consider is the differential group delay (DGD) that takes into account the maximum value that thedigital system can tolerate (*).

DGD (max) = 0,1 t1 = 0,1 x 6,45 nseg = 0,645 nsegIn such case, the consequent spectral bandwidth to be used must be: : 0, 11 nm

(*) note: this rule is applied for NRZ-formatted on-off keyed signals

g) The whole pulse broadening will be affected by the operation time (top) that are formed by:

operation time of the optical emitter, as well as the additional amplification devices to be used in thetransmission end

fiber optic dispersion

operation time of the optical detector, as well as the additional amplification devices to be used in thereception end

Taking into account to check that: top < 0,70 TNRZ (where T is the interval of one bit)That is applied for non-return-to-zero data that is used like transmission code S-NRZ (ITU-T G.957, G.797-Y.1322),as well is shown in the design guide of ENRE558/2003

4 OPTICAL DEVICESThe projected communication systems for 500kV networks include, additionally to the SDH node, several devices

that formed an amplification chain whose features will permit to obtain greater link lengths. In the following item willbe described the main topics of them.

4.1 Optical emittersFor high speed transmission it is desirable to use distributed feedback laser (DFB) in order to generate a unique iwavelength with low bit error rate. With this kind of Laser, the dispersion in the fiber will be lower.That is obtained due to the DFB Laser has a precise control of the longitudinal modes of the emitter oscillation, aswell as the scattering of the wavelength generated.It is used emitters of InGaAsP/InP-DFB Laser:

for operation up to 2,5Gbps

with spectral width between 1 to 0,25 nm

for single mode fibers

emitter high answer time (rise time


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A main design project issue is to consider that the responsivity (R) parameter is applied for each wavelength to beused. That subject is important to take into account in case of transmission of several wavelengths guided to aunique APD device. Consequently, it is necessary to take the worst condition of all transmitted wavelengths. It isnecessary to analyze the curve R= f () that the manufacturer will provide

Additionally, it is convenient to mention some inconvenient of the APD devices, which ones must be taken into

account: big transit time

additional noise generated due to avalanche effectthat will affect the possible maximum frequency of bits for each APD (especially due to transit time)The sensitivity to light signals (S: minimum optical power that can receive the APD device in order to produce auseful output electrical signal), will depend of the project parameters:

wavelength to be used

bit error rate BERTypically, the parameters will be specified for a design objective of BER: 10exp-10 (according ITU-T G.957) formaximum attenuation and dispersion conditions.

Depending of the particular conditions of the information to be transmitted, it could be necessary to use figures ofBER:10exp-12 (according ITU-T G.826). Consequently, it must increase the sensitivity of the optical receiver,

and/or reduce the link attenuation.

5 LIMITATIONS TO BIT TRANSMISSION RATEa) The intermodal dispersion (that produces the pulse broadening) must not appear in a single mode fiber due tothe energy of the light pulse will be transmitted in a unique mode.

Anyhow, the broadening of pulse do not disappear due to the group velocity related with the mode depends of thefrequency due to the chromatic dispersion (like were described at the beginning). It is generated the group velocitydispersion (GVD) or fibre dispersion.The GVD/fiber dispersion has the contribution of two components (as it was mentioned above):

material dispersion

waveguide dispersionThe fiber optic dispersion effect will limit the bit transmission rate of the communication system:

For standard optical fibers, the value of M dispersion is negligible for wavelength =1300 nm, but it is so importantfor other wavelengths like = 1550 nm. It means that the spectral width of the wavelength will strongly affect the bittransmission rateb) Taking into account a conventional link with Laser emitter (not a wavelength division multiplexing link) with a

spectral width of = 2 a 4 nm, the bit transmission rate will be limited to:

For long distance link (i.e. 400km), it means a bit transmission rate of:

(not acceptable for STM-1 hierarchy)

c1) Taking into account a DWDM link with a spectral width of = 0, 80 nm (or less), the bit transmission rate willbe:

(acceptable for STM-1 hierarchy)

c2) Taking into account a DWDM link with a spectral width of = 0, 40 nm (or less), the bit transmission rate willbe:

(acceptable for STM-1 hierarchy)

See Figure AA and BB

6 WAVELENGHT MULTIPLEXING

6.1 Criterion



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The main design concepts in order to decide when to use the WDM technique are:a) when the optical cable capacity is full used, it is more convenient to implement the wavelength divisionmultiplexing instead to replace the existing optical cable by a new one. It means to multiply virtually the capacity ofinstalled fibers of the cableb) when the amount and diversity of services that will be transmitted are very large and it will be necessary to use aparticular wavelength for each function/service. In such case, it is necessary to take into account the partition of the

total optical power in several different wavelengths to be usedc) when the transmission rate of each service is so high that it is not enough the STM-1 hierarchy for transmittingthe whole information (as well as when it is not enough the upgrading steps to STM-4, etc)d) when distances involved in the communication system are long haul links, where the optical fiber dispersion canrestrict the bit transmission rate preliminary use with 1550 nm wavelength with wide source spectral width

For the Transener`s project conditions it was applied the concepts detailed in item d)

6.2 WDM techniqueSince the existence of fiber amplifiers and Laser multiple wavelengths optical emitters, it was possible to increasethe capacity of the transmission systems by using the wavelength division multiplexing WDM technique, withoutmodifying the existent network architecture.

Through WDM is possible to couple the output of several light emitter sources (each one at different i) to a pair ofoptical fibers in the emission end. After being transmitted along the optical fiber link, each i can be

separated by the detectors in the reception end.

The WDM technique allows using all the bandwidth that the fiber has, without to change equipment and/or existinglinks.It is necessary to take into account:

the dispersion characteristics of the optical fibers

the gap between different i

The de-multiplexing process must be done previously that the light arrives to the APD photo detector due to the factthey are wide-band devices where it is not possible to select a particular and independent wavelength (asmentioned above)

7 WDM MULTIPLEXOR The main features that must have the -Mux as well as the -Demux are:

to minimize the interference between i channels

to maximize the gap between i channels (discrimination of each i)

There are two kinds:a) passive units, formed by optical filters that can joint or separate the optical channels. Each subrack has its ownpower supply and network connection, in order to do the management of its modulesFor DWDM systems, those optical filters are array wave guide (AWG), which one has high uniformity betweenchannels, as well as low insertion loss.b) active units, based on passive devices with tuned filters that permit to select a particular i from all thetransmitted wavelengths.

8 WDM FAMILY There are several kinds of DWDM, depending of the link length involved:

DWDM for extra-long-haul links (more than 1000km)

DWDM for long-haul links (order of 800km)

DWDM for medium haul links (order of 300km)It is possible to use for all of them, the range from 1260 to 1625 nm (and up to 1675 nm)

In the first case, the gaps between wavelengths are between 0,1 and 0,8 nm. It is possible to locate up to 160wavelengths, with a total capacity of 40GbpsIn the second case, the gaps between wavelengths are between 0,8 and 1,6 nm. It is possible to locate up to 40wavelengths, with a total capacity of 10Gbps

9 WAVELENGHTS BANDS According to ITU-T G.694.1 y Figure A.1/G.957, there are six bands in the 1260-1675 nm range:

Original band (O-band): 1260 to 1360 nm

Extended band (E-band): 1360 to 1460 nm



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Short band (S-band): 1460 to 1530 nm

Conventional band (C-band): 1530 to 1565 nm

Large band (L-band): 1565 to 1625 nm

Ultra large band (U-band): 1635 to 1675 nm

Additionally, the ITU-T G.694.1 specifies a grid with the wavelength that is possible to use in DWDM technique. The

grid to be used is shown for each band (L-band, C-band, etc), according of the gap between channels. 0,1 nm (12,5 GHz)

0,2 nm (25 GHz)

0,4 nm (50 GHz)

0,8 nm (100 GHz)

1,6 nm (200 GHz)See Figure CC

10 DIGITAL TRANSMISSION

10.1 Links evolutionAt the beginning, the communication projects for 500kV systems have used SDH systems operating in STM-1hierarchy that were installed on HVAC lines:

Up to 200km without optical repeaters

Greater distances with intermediate optical repeaters

In following stages, for long haul links, the migration to DWDM was done in order to enlarge the digital transmissionto long distances, avoiding and/or minimizing the use of optical repeaters located in isolated locations.As it was described above, due to optical fiber attenuation and dispersion, it is limited the maximum distance thatthe optical signal can arrive to the reception end, with enough power for its right detection.It means to use optical devices that allow amplifying all the signals simultaneously, without optical-electrical-opticalconversions

10.2 Devices involvedFor long haul links that operate up to 10Gbps, it is necessary to add an amplification chain between both ends (Tx,

Rx) in order to avoid intermediate regeneration optical repeaters.b1) The optical devices involved in the amplification chain are shown in Figure AA and its main features will bedescribed in item #10.3. It includes:

Emitter side: with EDFA amplifiers

Receiver side: with Raman amplifiers and EDFA preamplifiers

As an alternative to EDFA amplifiers, can be used a semiconductor optical amplifiers (SOA) that function like aLaser emitter. When electrical current flows through the SOA, the electrons of the active layer (third materialintermediate between two semiconductor materials) will be excited and return to the original state in a similarprocedure like EDF.Due to this process, the input light (coming from the optical signal) will excite the SOA`s electrons, consequently itwill generate additional photons that will be aggregated to the those ones that caused the original emission. Finally,the result is that the output optical signal will be increased

In Figure DD has been shown a generic evaluation of the involved levels in the amplification chain. But, in theparticular projects must be considered that the amplification process must be done in the linear region offunctioning of the devices, such as the output amplified signal will be of the same characteristic like the input opticalsignal.It is necessary to maintain linearity through the control of input power levels and avoid that the devices can arrive tosaturation

b2) Optical amplification process includes a spontaneous emission of photons whose phase and polarization isvariable and they are added to the useful signal.The characteristic of noise of an optical amplifier is a measure of degradation in the signal to noise ratio, motivatedby the photon emission process. The noise figure has presence in boosters as well as preamplifiers, but it is morecritical in the second ones.

In the long haul links, the amplifiers form part of a chain of devices that act simultaneously with the optical fiberlosses (from Tx to Rx ends). The induced noise is the more critical factor of the system, due to:

The spontaneous emission (ASE) will be accumulated on several amplifiers and, consequently will degradethe optical signal to noise ratio (OSNR) when it is used amount of devices that were necessary to use inorder to extend the reach of the link



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As much increase the level of ASE, it begins to saturate the optical amplifiers and to reduce the gain of theamplifiers located below in the amplification chain

It means that if the amount of amplifiers is important, the signal to noise ratio will be degraded so much up to thesituation that the APD converter can have a non-acceptable bit error rate BERIt means to take into account the noise figures along the project development, in order to avoid the performance

degradation of the whole system.b3) It is important that all devices involved in the amplification chain will be manageable, through a NMS systemwith Ethernet interface and SNMP protocol. Minimally, it will be necessary to verify: input optical power, outputpower, wavelengths channelsBy this way it will be done the whole control of the communication system, due to the implementation of:

{NMS for the SDH nodes + NMS for the chain amplification + NMS of the optical cables}

10.3 Features of the devices

c1) Erbium doped fiber amplifier (EDFA)This is the first element of the amplification chain that can receive a multiplexed optical signal or a single opticalsignal, in order to amplifier it afterwards based on EDF process.

It will not detailed the functioning of the EDF physic process, where the Erbium ions are excited by a Laser pump,and continuing afterwards with the amplified spontaneous emission process (ASE).It will only consider the result, where the photons in the range of 1550 nm will be amplified as long as they goahead in the doped fiber. It produces that the irradiated photons will have the same wavelength that the inputphotons, but with a output signal totally amplified

This amplification process occurs in:

Wavelength between 1530-1565 nm (C-band)

Wavelength between 1565-1625 nm (L-band)

It is desirable to use EDFA devices of double stage of amplification (first amplifier unit; second amplifier unit), inorder to both amplifiers in a cascade arrange can provide a flat gain in a wide bandwidth, but additionally having alow noise level (no more than 5dB; see item # 10.2b)

In that way it is possible to obtain:

Input power from -10 dBm to +10 dBm

Output power up to +24 dBm (functioning like a booster)

Gains up to +34dB

Operation range of 1529 -1565 nmIt must consider that the available output optical power available in an EDFA can vary depending of if it is used like:

Single channel

DWDM multichannelIt means that the gain per channel varies, and consequently must be revised the calculations of the original Projectin the subsequent adaptations with more j wavelengths (always considering C-band and L-band)

c2) Raman PreamplifiersIt is based in doing the amplification of the optical signal by means of Raman Effect. A Laser pump of shortwavelength that travels along the fiber together with the useful signal will scatter atoms in the optical fiber. It meansthat the original optical signal will have aggregated additional photons, and consequently that optical signal will beamplified in the last meters of the transmission fiber.The main difference with the previously described EDFA amplifiers, is that the Raman amplifiers do not need todope the optical fibre

They are used in the reception end, doing the amplification of the optical signal previously that the signal goes intothe EDFA preamplifier. They operate with two main Lasers and two backup Lasers (reserve). Those ones will beactivated when some of the main Laser fails.

They have gain between 5 dB to 10 dB, with levels in the order of:

Input optical power between -50 dBm and -24 dBm Output optical power between -45 dBm and -19 dBm

Operation range of 1529 - 1565 nm



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c3) PreamplifiersIt is the last device in the amplification chain of the link, and it is located in the reception end for doing theamplification of the optical signal to the suitable level of the reception equipment (APD optical converter)

The optical signal received in the preamplifier can come from:

Directly from the optical fibre of the OPGW cable

After to pass through a Raman amplifierThe preamplifier is based on devices EDFA that operates with one Laser pump. It has a gain of 35 dB, with levels inthe order of:

sensitivity (STM-1; BER: 10exp-10): up to -45 dBm (see note *)

output power of +14 dBm

operation range of 1529 - 1565 nm

(Note *) It is convenient to mention that the acceptable maximum power (i.e. input saturation -10dBm) that isnormally verified in conventional projects of medium/short link distances, it is not necessary to check in case of longhaul links

c4) TranspondersThe wavelength transponder is a bidirectional device that permits to convert the transmitted wavelength (i) from

the SDH node, to a wavelength (j) located in the DWDM grid of ITU-T G.694.1 (the C-band is used in our projects)

The transponder main features are:

input wavelength range: 1260-1600 nm

output wavelength: according ITU-T G.694.1 grid

output optical power: up to + 10dB

The transponder is transparent to STM-1 transmission rate that is used in the projects, as well as to thetransmission protocols that are used by the HV Transporter Agent. Additionally, it will permit future upgradingprocess to STM-4 transmission hierarchy, Gigabit Ethernet, etc

Similarly that it was shown for optical amplifiers, it is necessary that the transponder can allow the remoteconfiguration and supervision, by using SNMP protocol, monitoring al least: input optical power, output opticalpower, i and j wavelengths.

Particularly:

emission side: to allow the conversion of input optical signals (1260-1600 nm) to output optical signals ofthe C-band of the DWDM wavelength grid of ITU-T

reception side: to allow the conversion of DWDM wavelength (1260-1600 nm) to an output optical signal of1310 nm

c) Amplifier with remote pumpIn case of optical long haul links it is possible to use Laser pump remotely located:

the firs Laser pump is an EDFA amplifier totally passive and based on the Erbium doped fiber. It will beinstalled in an aerial box in the OPGW trace, in order to obtain maximal gain for the optical long haul link

the second Laser pump (1480 nm) will be located in the Substation building

The amplifier with a remote Laser pump, will receive:>>through an optical fiber will be received an optical signal to be amplified (useful signal)>>through another optical fiber will be received the 1480 nm Laser pump (feeder)

By this way it is possible to obtain:

gain of 25 dB

noise figures of 5 dB

input optical power of -40dBm

wavelength operation range between 1529-1565 nm

11 OPTICAL CABLES

11.1 Fibers overviewa) As it was described in item #3, one limitation in the operation wavelength range will be determined by theattenuation features of the optical fibres.



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Additionally, another determining factor to the operation wavelength range is the fibre dispersion, as well as thespectral width of the optical emitter.Consequently, the real useful operation wavelength range of the system will be determined by the interaction of thetwo limiting ranges before mentioned.

b) The dispersion features of several types of optical fibres (in the zone of 1550 nm) will be shown generically in

Figure FF,where the shadow area is used by EDFA amplifiers, and it represents the DWDM wavelengths rangebefore described.

The dispersion shifted fibers (DSF) has a good performance for a unique channel

The (+D) NZ-DSF fibers will locate the zero dispersion wavelength out of the 1550 nm zone, and they havepositive slope

The (-D) NZ-DSF fibers are similar to the before mentioned fibers, but they have negative slope

c) It must consider that the modal field diameter of single mode fibres are an important parameter in theirattenuation features, due to:

The bigger the fiber modal field diameter is, the worse the light conduction in fibre bend will be

By the contrast, the bigger the modal field diameter is, the lowest loss in fibre splices and connectors willbe

Resuming:c1) for single mode fibres with simple step index, the modal field diameter (2.a) is 10,4 um @1550nmc2) for single mode fibers optimized for 1550 nm (1550-DS-SM, dispersion shifted, segmented profile with

triangular core), the modal field diameter (2.a) is 7,5 um @1550nm

d) The fiber optic has an important absorption due to peak of water located at 1383 nm. In order to operate in thefull wavelength range (1260-1625 nm), must be necessary to use zero peak water single mode fibers (ZPW-SM)according to ITU-T G.652 C/DThen, the absorption due to the peak of water will be reduced in an important manner, and consequently it ispossible of obtaining an attenuation factor lower than the value for 1310 nm. It permits a lower and stableattenuation figures along the whole 1310-1625 nm range (even after installation process)

e) The standard fibers according to G.652 have bending radius in the order of 30 mm. Then, it is convenient to use

bend-insensitive fibers with bending radius of 7,5 mm. This kind of fibers will allow having low losses due tobending processes when the 1550 nm wavelength operation is used.

Additionally, the fusion losses, due to the splicing process of two bend-insensitive fibers, will allow to obtain splicinglosses as low as 0,01 dB/splice (comparing with the typical 0,2 dB/splice obtained with standard fibers)

11.2 Reducing dispersion effect

a) DCM modulesAs at the beginning mentioned, it is essential to reduce the fiber dispersion effects in order to have a bettercommunication system performance. In order to find it, it must use an additional element in the link with anopposite dispersion from that of the installed optical cable. It is a dispersion compensating module DCM.

It is formed by spools of DCM fibers with opposite dispersion features and guaranteed values. By contrast, it musttake into account the attenuation values that will be introduced in the link.Additionally, it is necessary to take into account that this alternative, when is used in DWDM systems, can be usedfor correcting an unique channel (not the whole band)

b) fiber combinationAnother solution so as to compensate dispersion effects, is to alternate lengths of different kind of fibers(see Figure FF)as follows:

Lengths of fibers whose features are (+D) NZ-DSF, with

Lengths of fibers whose features are (-D) NZ-DSFThe special feature is that this solution must be specifically calculated for the length of the link, and it is notapplicable for several lengths (that situation is not essential for our projects)11.3 Factors to be taken into accountIt is necessary to mention that the OPGW optical cables that are used in the 500kV Lines, as well as the opticalfibers included into them, are fully detailed in the technical specifications included in the project.The main aspects taken into account are:



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a) Intrinsic factors (scattering and absorption)The fiber attenuation implies the loss of optical power and consequently producing adverse effects on thecommunication system, as was detailed at the beginning:

Band with reduction

Bit transmission rate reduction Lower efficiency of the whole system

Consequently, it is necessary to take into account some design criterion as follow:a1) to purchase optical cables manufactured with high quality fiber optics, so as to assure low dispersion features(see Figure GG)a2) to purchase optical cables with fiber optic whose attenuation factor (dB/km) will be as low as 0,20 dB/km or less(in spite of the attenuation range accepted by G.652)a3) to do the optical budget considering 0,30 dB/km (following the criterion of ITU-T G.957 Annex A-Fig A.1), inorder to take into account the features of the installed fiber (including splice losses, repair tasks, temperaturerange, etc)a3) to use zero peak water fibers (ZWP-SM) according to ITU-T G.652C/D so as to increase the range of usefulwavelengths (1280-1625 nm; free of OH ions)It means greater range into the spectrum so as to locate more wavelengths in all zones, and consequently to allow

higher information transmission at the present and future greater benefits.Those criteria imply:

to utilize fiber optics in conventional applications that implies to operate in wavelengths of 1310 & 1550 nm

to utilize fiber optics in new applications by using the E-band (1360-1460 nm)

to increase the allowable bandwidth of each fiber optic up to 60%a4) it is necessary to take into account the polarization mode dispersion (PMD) of the fibers included in the opticalcable. Typically, PMD = 0,07 ps/km is measured during the factory acceptance tests.

The causes of birefringence are:

due to design factors (i.e. core stress, cladding eccentricity, elliptical fiber design)

due to external factors (i.e. fiber twist, fiber stress, fiber bend)Consequently, it is necessary to measure the PMD values during the FAT process, as well as to check it during thecommissioning tests. This last recommendation is typically rejected by Main Contractors arguing that they needspecial instruments, etc.

b) Extrinsic factorsIt means to pay attention about precautions that are necessary to take into account in some external actions thatact over the OPGW cable and consequently can affect their optical fibers.

b1) macro-bendingA bend in the optical cable affect the fiber optic refractive index, as well as the critical angle of the light rays,producing that the light will be refracted in the core (through the cladding). In order to avoid this situation, it isnecessary a very precise control about:

the installation process itself

use of qualified subcontractors (specialized on optical cables tasks)

the parameters involved in the process (pulling stress, bending pulley, etc) utilization of special devices for automatic control of eventual wrong process (disconnection mechanical

fuses, etc)

permanent supervision during the installation process

involved personnel certified by optical cable manufacturer and/or recognized authorities

b2) micro-bendingIt is necessary to take special precautions so as to avoid pressure over the fibers themselves, because it canproduce effects unable to be seen, but that can affect the development of the fiber optics by introducing non-perceptible micro-bending into them.

As well as, it must consider some previsions in the temperature range where the optical cable will operate(especially for low temperature environment). It is necessary to project carefully the appropriated over length of

fibers into the optical cable, so as to avoid localized micro-bending effects produced by straightening and/orcontractions of the optical fibers. Those effects can return to the original conditions or not, due to hysteresis effect(and consequently can affect permanently the cable performance)

b3) splices



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It is necessary to take precautions during the optical fiber splicing process, as follow:

to do the fusion splices by means of automatic instruments of well-known manufacturer

to do the splicing tasks into a vehicle/trailer with enough grade of sealing

to use certified splicing personnel (certification emitted by national authorities and/or the optical cablemanufacturer)

to use a splicing procedure handbook/guide (written by the optical cable manufacturer)

to do a permanent supervision by a representative of the optical cable manufacturer to do measurement of each spliced optical fiber, per each stretch of OPGW that is installed

to protocol each fiber optic per pair of two stretch of OPGW cables

to protocol each fiber optic between optical distribution frames (end-to-end measurement)

b4) fiber optic characterizationAn additional topic to mention for future applications, is the following question:which could be the measures to do to fibers optics so as to know the potential transmission capacity of the OPGWcables?In spite of the current in-use STM-1/SDH systems it is necessary to take into account that new technologies can beused by Transener HV Main Transporter, as well as other Government Entities, in a share utilization of the opticalcables.

12 CONCLUSIONThe objective of eliminating optical repeater stations in long haul links can be better obtained taking into account atleast, the above mentioned concepts and criteria. It means to minimize the probability of malfunctions of thecommunication system due to several kinds of acts that normally can affect the behavior of the 500kV TransmissionSystem. The necessary big capacity for transmitting the information specifically required by the EHV System (notfor eventual other services out of the scope of the EHV Transporter) will be also achieved.The Availability of the whole communication system as well as the Reliability of the EHV System will beconsequently increased.

13 BIBLIOGRAPHY(1) Electronic communications system, fundamentals through advanced, W. Tomasi, Prentice-Hall(2) Optical fiber planning guide for power utilities-Cigre SC 35-WG04(3) Redes comunicaciones SDH en sistemas electricos de potencia, Eriac 2005, Rodriguez-Di Palma-etc(4) Guide for planning of power utility digital telecomm networks- Cigre SC35 WG 02(5) Guias de diseo Enre 558/2003(6) Technology of optical network for electric power utilities ETRA(7) Emergency communication system for operation of HVDC, D2 Colloquium 2009, Galarza-Di Palma(8) New optical access technology-Cigre WGD2.15(9) Fiber optic communication systems, G. Agrawal, John Wiley and Sons(10) ITU-T G.662 Generic characteristics of opt amp devices and subsystems



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FIGURE AA

FIGURE BB



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FIGURE CC



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FIGURE DD



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FIGURE FF



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FIGURE GG

FIGURE HH

Comm sys for long haul links on 500kV sys-rel v 5 16

communication systems for long haul links on 500kv hvac systems

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