Welding of optical fibers.: Cables and cutting, optical instrument, couplings, crosses, connectors and adapters

The fibers are loaded in the welding machine

Hello readers ! Everyone has heard about the optical fibers and cables. No need to tell where and for what uses optics. Many of you will encounter it at work, someone develops the transmission network, someone who works with optical multiplexers. However, I have not met the story about the optical cables, couplings, crosses, about the technology itself, and splicing cables. I - fitter of optical fibers, and in this (his first) post would like to tell and show you how it all happens, and often in his story will be distracted by other things related to this. I will rely mainly on their experience, so I fully admit that someone will say "this is not quite right," "here uncanonical."
Stuff happened a lot, so it was necessary to split the topic into parts.
In this first part you will read about the device and cutting a cable, about an optical instrument, about the preparation of fibers for welding. In other parts, if the topic would be interesting to you, I will discuss the methods and will show on video the process of splicing optical fibers themselves, about the basics and some of the nuances of measurements on optics, touch on welding machines and OTDR and other measuring instruments, show jobs fitter ( roofs, basements, attics, hatches and other field offices), tell a little about the fastener cables, wiring diagrams about, about the placement of equipment in telecommunication racks and boxes. It is certainly useful to those who are going to become fitter.



Network Technology *IT Infrastructure *

The fibers are loaded in the welding machine


Hello readers Habra! Everyone has heard about the optical fibers and cables. No need to tell where and for what uses optics. Many of you will encounter it at work, someone develops the transmission network, someone who works with optical multiplexers. However, I have not met the story about the optical cables, couplings, crosses, about the technology itself, and splicing cables. I - fitter of optical fibers, and in this (his first) post would like to tell and show you how it all happens, and often in his story will be distracted by other things related to this. I will rely mainly on their experience, so I fully admit that someone will say "this is not quite right," "here uncanonical."
Stuff happened a lot, so it was necessary to split the topic into parts.
In this first part you will read about the device and cutting a cable, about an optical instrument, about the preparation of fibers for welding. In other parts, if the topic would be interesting to you, I will discuss the methods and will show on video the process of splicing optical fibers themselves, about the basics and some of the nuances of measurements on optics, touch on welding machines and OTDR and other measuring instruments, show jobs fitter ( roofs, basements, attics, hatches and other field offices), tell a little about the fastener cables, wiring diagrams about, about the placement of equipment in telecommunication racks and boxes. It is certainly useful to those who are going to become fitter. All this I arch a lot of pictures (I apologize in advance for the paint-quality) and photos. Beware, a lot of pictures and text.



Entry

To begin with a few words about me and my work.
I work fitter optics. He started with a telephone operator and installer, and then worked in the emergency team in serving the main optics. Now I work in an organization that takes the general contractor for the construction of communication lines among different companies. A typical construction project - cable line connecting several containers of base stations GSM. Or, for example, several rings FTTB. Or something smaller - such as cabling between the two server on different floors of the building and the splicing at the ends of the cable crossover.
If the tender is won, looking for a suitable sub-contractors performing work (design and survey and construction). In some regions, it is our subsidiaries, some have their own equipment and resources, some hired an independent company. On our own shoulders rests mainly control, elimination of stocks of various subcontractors and force majeure, every agreement with landowners and administrations, sometimes drawing up the executive documentation and other constructed facilities. Often the need to work with optics: cook or digest somewhere optical coupling or cross, eliminate the effects of street racing knocked supports or fallen tree on the cable, hold the input control cable drum, to remove the trace section and so on. These are tasks I perform. Oh, and incidentally, when there is no problems in optics - other tasks from loading and installation via Express-haul to copying paper work. smile.gif



Optical cable, its types and entrails

So what is a fiber optic cable? The cables are different.

 At the point of use - for exterior and interior linings (last rare and typically in data centers high-end, where everything has to be perfectly correct and beautiful). Under the terms of the gasket - Suspension (with Kevlar or cable) to ground (armor of iron wires), for installation in cable ducts (with corrugated metal armor), underwater (complex sverhzaschischayuschaya sandwich construction), for hanging on electric poles (except for the transfer of information vyponyayut role of lightning protection cable). In my experience, the most frequent suspension cables on poles (with Kevlar) and for laying the ground (with armor). Seldom come across a rope and gofrobronёy. More common cable that is essentially a thin coaxial optical patch cord (yellow envelope in singlemode and orange - in multimode, and one bit of Kevlar fiber, the two shells are paired). Other optical cables (without protection, underwater, for installation in the premises) - exotic. Almost all of the cables, with whom I work, have a structure like the one below.


1 - central strength member (in other words - from fiberglass rod, although it may be wire in polyethylene covering). Used for centering tube modules, giving rigidity around the cable. For it is also often fixed cable coupling / cross-country, clamping screw. With strong bending of the cable has a break sneaking property, breaking and passing a part of the fiber module. More advanced cable design contain this bar, wearing a plastic shell: while it is more difficult to break and damage the cable when it is the turn will cause less. Bars and is the same as in the figure, and very thin. The tip of the bar - a great tool for fine abrasive work, for example, to clean relay contacts or a portion of the copper solder parts. If it burn for a couple of centimeters, you get a nice soft brush. smile.gif
2 - the optical fibers themselves (in the figure - in lacquer insulation). The very finest threads, fibers, for which all afoot. In this article we will speak only about the glass fibers, although somewhere in nature, there are plastic, but they are - great exotic, not cooked devices for welding optics (only mechanical connection) and are suitable only for very short distances and I personally did not face them . Optical fibers are single-mode and multimode, I have met with only single-mode, multimode since - outdated technology, it can only be used for short distances and singlemode perfectly replaced. The fiber consists of a glass "shell" made of glass with certain impurities (in chemistry and crystallography will not stop there, because they do not know the subject). Without varnish fiber has a thickness of 125 micrometers (slightly thicker hair), and in its center there is a core diameter of 10 microns high purity glass of different composition and slightly different from the cladding refractive index. It extends the core radiation (due to the effect of total reflection at the "core - shell"). Finally, on top of a 125-micrometer Cylinder "shell" covered by another shell - from a special varnish (clear or colored - for color-coded fibers), which is also a dual-layer EMNIP. It protects the fiber from moderate injuries (without varnish though fiber bends, but bad and easy to break, the fiber elementary crumble from a random position on his mobile phone; and the varnish can be safely wrapped around a pencil and pull strongly enough - it will stand). It happens that span cable slack on some fibers: broke (perezhglo, cut) all shell Kevlar burst central rod, and some 16 or 32 125 micron glass fiber can span weeks to keep the weight of the cable and wind loads! Nevertheless, even in the lacquer fibers can be easily damaged, so the fitter of the most important - the meticulousness and accuracy. One awkward movement can ruin the results of a day of work or, if not particularly lucky and there is no backup for a long time to drop the trunk link (if, digging in "combat" the main clutch, break the fiber DWDM-th under the spine at the outlet of the cable).
Fiber is a lot of varieties: ordinary (SMF or just SM), with dispersion shifted (DSF or just DS), a non-zero dispersion shifted (NZDSF, NZDS or NZ). Outwardly, they can not distinguish the difference - in the chemical / crystalline composition and, probably, in the geometry of the central core and the smoothness of the boundary between it and the shell (unfortunately, for themselves and do not clarify the matter before the end). Dispersion in optical fibers - a harsh and difficult to understand a thing, worthy of a separate article, so easy to explain - for dispersion shifted fiber can transmit a signal without distortion more than in the simple. In practice, the fitter know two types: simple and "with smeschёnkoy." The cable is often isolated the first module under the "smeschёnku" and the rest - a simple fiber. Docked "smeschёnku" and a simple fiber can be, but is not desirable, it is an interesting effect, which I will discuss in another part, about the measurement.
3 - plastic tube modules, which float in the hydrophobe fiber.
The cable to the split modules

 Optical fibers, damaged as a result of careless cutting a cable (was wrongly exposed blade length stripper to remove the inner sheath, causing erupted modules and damage of the fibers)

 In this picture - only a part of the "birth" and "species" optical sockets

 Wall cross-type 16 port FC. By the way, cooked badly: yellow shell P & G-Tail not enter the CRSS and fibers can break, and the fibers are laid in the cassette with small bending radii.



 Work on the 96 cross-type FC ports

Often option and cheaper - when thrown from the cross all that is possible, then it turns out something like this:

  Reduced: 93% of the [731 to 355] - Click to view full image
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Open cross 8-port type SC / APC, 1 unit. Worse what P & G optical-Tail are not protected and they can break those who will delve into the drawer / front, dragging, say, a new cable.



All these crosses are mounted in a rack, but there are options for wall, and other rare.

3.6/6kv-26/35kv Three Core XLPE Insulated,steel wire armoured power cable.

High Voltage Cables

Cable Earth-Gradient Detector Auxiliary Device

Figure 1 is an illustration of an earth-gradient detector. 

This detector has two spikes that are driven into the earth above a buried cable. The current that flows through the earth in the vicinity of a cable when the cable’s insulation breaks down under the stress of the thumper’s high-voltage pulse causes a difference in potential
between these spikes. When connected to the spikes, the microammeter of the detector deflects to the left or to the right according to the direction of the current flowing from one spike to the other.

Earth-Gradient Localization

Figures 2a and 2b illustrate the basic method of using an earth-gradient detector to locate a fault in a buried cable. Current flows in several paths through the earth from the point of the damaged insulation to the driven rod. These paths are represented by broken-line curves in Figure 7. These currents produce a voltage gradient between any two points at the surface of the earth. The technician locates the fault by placing the spikes of the earth-gradient detector at different surface locations along a straight line between the ends of the cable. At successive locations (1, 2, and 3) the technician reads the deflection of the detector until he reads a reversal of deflection (location 4). The technician backtracks until he finds a location (5) where there is a null deflection.

The technician then reads deflections (6, 7, and 8) along a line that crosses the first line at a right angle. The location of the fault is at the second null deflection (location 8). Through the use of this method, the technician does not need to know the route of the buried cable in order to locate the cable fault.

                     

Cable Acoustical Detector Auxiliary Device

Figure 1 is an illustration of an acoustical detector, an auxiliary device that is used with both types of thumpers. An acoustical detector has two sound transducers that are placed on the ground above a buried cable. The sound made by the cable when its insulation breaks down under the stress of the thumper’s high-voltage pulse causes an upscale deflection of the detector’s output level meter. A set of headphones can also be plugged into the detector so that the amplified and filtered sound of the breakdown can be heard.

Acoustical Localization
Figure 2 illustrates the basic method of using an acoustical detector to locate a fault in a buried cable. The pulses transmitted by the cable thumper cause the damaged insulation of the cable to break down repeatedly.

Each breakdown produces a sound. This sound can sometimes be heard above the ground. But for those cases when the sound is not loud enough to be heard, an acoustical detector is used to locate the damaged insulation.

The acoustical detector is able to distinguish the relative intensity and time delay between the arrival of the thump sound at its two pickups. The technician moves the location of the acoustical pickups until the thump sound is equal in intensity in the two earpieces of the headphones. The location of the fault is then directly below and midway between the pickups.

CABLE THUMPING

CABLE THUMPING: EQUIPMENT CONSTRUCTIONS, OPERATIONAL
PRINCIPLES, AND BASIC LOCALIZATION TECHNIQUES

A cable thumper is an electrical test set that generates repetitive high-voltage high-energy pulses. A cable thumper transmits these pulses into a power cable in order to cause a fault in the cable to break down and, consequently, produce an audible sound and a strong current in the earth surrounding the fault. The sound reveals the location of the fault. If the sound is not easily heard at the surface of the earth, an acoustical detector is used to locate the cable fault. Alternatively, an earth-gradient detector can be used to locate the fault by sensing the earth currents that flow near the fault.
 

Thumper Constructions

There are two basic types of cable thumpers: the series-gap type and the pulse type. There are two basic types of detectors: the acoustical detector and the earth-gradient detector. 

Either type of detector can be used with either type of thumper. The constructions of thumpers and detectors are explained in the next four subject headings.

                          Illustration of a Cable Thumper

Series-Gap Type
 

Figure 1 is an illustration of a series-gap type of cable thumper. The illustration shows the following:
· A knob-controlled variable transformer. This transformer controls the magnitude of high-voltage output
pulses.
· A kilovoltmeter. This meter indicates the voltage of the thumper’s built-in impulse capacitor.
· A primary ammeter that indicates the input current.
· A microammeter that indicates the output current.
· A power cord.
· An output test lead.
· Jacks for connecting the battery leads.
· An impulse-control gap handle. This handle adjustments the dimension of the series gap.

Pulse Type

 
Pulse-type cable thumpers have the same general construction as series-gap cable thumpers. The important difference in construction is that a set of additional components allow the rate that output pulses are generated to be adjusted independently from the output voltage adjustment.


Thumper Operational Principles

Generating a High Energy Pulse in a Series-Gap Thumper
Figure 2a is a simplified schematic diagram of a series-gap thumper. The thumper’s high-voltage power supply is similar to the power supply of a DC applied potential test set. This power supply charges an impulse capacitor. A kilovoltmeter indicates the magnitude of the impulse capacitor’s voltage. A variable transformer is used to control the maximum voltage that charges the impulse capacitor.

Before a test, the series gap is adjusted to a maximum dimension. The voltage of the capacitor is adjusted to the level that is appropriate for testing the cable, and the dimension of the series gap is subsequently adjusted until it flashes over. This flashover causes a pulse of high voltage to be transmitted into the cable under test and also discharges the capacitor. A short interval of time (approximately one to 30 seconds) elapses before the capacitor charges to a voltage level high enough to again cause the series gap to flash over. Pulses of high voltage are repeatedly transmitted into the cable. The interval of time between pulses can be shortened by adjusting the gap to a smaller dimension. Making the gap smaller consequently reduces the peak voltage magnitude of the output pulses.

Generating a High Energy Pulse in a Pulse-Type Thumper

Figure 2b is a simplified schematic diagram of a pulse-type thumper. The operational principle of a pulse-type thumper is the same as that of a series-gap thumper except that the time interval between pulses is controlled by a high-voltage contactor and a timing circuit. For a pulse-type thumper, the time interval between pulses can be adjusted without affecting the voltage magnitude of the output pulses.

Electrical Cables Go, No-Go Overpotential Test

The hi-pot test can be conducted as a go, no-go overpotential test. In this test the voltage is gradually applied to the specified value. The rate of rise of the test voltage is maintained to provide a steady leakage current until final test voltage is reached. Usually, 1–1.5 min is considered sufficient for reaching the final test voltage. The final test voltage can then be held for 5 min, and if there is no abrupt increase in current sufficient to trip the test set, the test has been successfully passed. This test does not provide a thorough analysis of cable condition, but provides sufficient information as to whether the cable meets a specific high-voltage breakdown strength requirement. This type of test is usually performed after installation and repair, where only cable that can withstand strength verification without a breakdown is to be certified.

Voltage versus Leakage Current Test (Step-Voltage Test)

In this test, the voltage is raised in equal steps and time is allowed between each step for leakage current to become stable.the current is relatively high as a voltage is applied owing to capacitance
charging current and dielectric absorption currents. As time passes, these transient currents become minimum with the steady-state current remaining, which is the actual leakage current and a very small amount of absorption current. At each step of voltage, the leakage current reading is taken before proceeding to the next step. Usually, it is recommended that at least eight equal steps of voltage be used and at least 1–4 min be allowed between each step. The leakage current versus voltage are then plotted as a curve. As long as this plotted curve is linear for each step, the insulation system is in good condition. At some value of step voltage, if the leakage current begins to increase noticeably, an increase in the slope of the curve will be noticed, as shown in Figure 1.1. If the test is continued beyond this test voltage, the leakage current will increase even more rapidly and immediate breakdown may occur in the cable insulation. Unless breakdown is desired, the test should be stopped as soon as the increase of slope is noticed in the voltage versus leakage current curve.
Maximum leakage current allowable for new cables acceptance can be determined from the ICEA formula for minimum allowable insulation

   
       

        

Figure 1.1 Step-voltage hi-pot test current.

resistance discussed earlier. The formula for leakage current then can be written as follows:

     

where
IL is the conduction or leakage current
E is the test voltage impressed
K is the specific insulation resistance megohms per 1000 ft at 60°F
D is the diameter over insulation
d is the diameter over conductor

The typical specific insulation resistance (K) for various commonly used insulations for cables are given under discussion of insulation resistance measurement test.
In order to explain the use of this formula, an example is given below for determining the maximum leakage current allowable for a 15 kV, 500 kcmil cable for an acceptance test.

Example
A 15 kV cable 500 MCM 220 Mil XLPE insulation conductor OD = 0.813 Class B strand. The circuit is 2500 ft long. Calculate the maximum leakage current at maximum test voltage of 65 kV.

   

Electrical Cables and Accessories Testing 2

DC Overpotential Testing
 
In the past, this test has been extensively used for acceptance and
maintenance of cables. Recent studies of cable failures indicate that the DC overpotential test may be causing more damage to some cable insulation, such as cross-link polyethylene, than the benefit obtained from such testing. It can indicate the relative condition of the insulation at voltages above or near operating levels. This test can be used for identifi cation of weakness in the cable insulation and can also be used to break down an incipient fault. A typical DC test set is shown in Figure 1.1. Generally, it is not recommended that this test be used for breakdown of incipient faults even though some test engineers use it for this purpose. Therefore, the incipient fault breakdown probability should be anticipated before and during the hi-pot test. The impending cable failure will usually be indicated by sudden changes in the leakage current, and before insulation is damaged, the test can be stopped. The test voltage values for DC hi-pot tests are based upon fi nal factory test voltage, which is determined by the type and thickness of insulation, the size of conductors, the construction of cable, and applicable industry standards. The DC test values corresponding to AC factory proof test voltages specified by the industry standards are usually expressed in terms of the ratio of DC to AC voltage for each insulation system. This ratio is designated as K, which when multiplied by the acceptance test factor of 80% and maintenance factor of 60% yields the conversion factors to obtain the DC test voltages for hi-pot tests. These recommended test voltage conversion factors are shown in Table 1.1. Also, the IEEE standard 400.1–2007 lists the voltage values for conducting hi-pot acceptance and maintenance tests in the field for laminated shielded power cables, which are shown in Table 1.2.

Many factors should be considered in selecting the right voltage for existing cables that are in service. As a general rule, for existing cables, the highest values for maintenance should not exceed 60% of final factory test voltage,

 

Figure 1.1 
DC hi-pot test set, 70 kV. (Courtesy of Megger, Inc., Valley Forge, PA.) 

and the minimum test value should be not less than the DC equivalent of the AC operating voltage. If the cable cannot be disconnected from all the connected equipment, the test voltage should be reduced to the voltage level of the lowest rated equipment connected. The hi-pot test can be conducted as a step-voltage test as discussed next.

Table 1.1 Conversion Factors for DC Hi-Pot Tests


   
     
 Table 1.2
Field Test Voltages for Laminated Shielded Cables up to 69 kV System Voltage
  
Note: Voltages higher those listed, up to 80% of system BIL for installation and maintenance testing may be considered in consultation with the suppliers of cable and the accessories.
When equipment, such as transformers, motors, etc., is connected to the cable circuit undergoing a test, voltages lower than recommended values may be used to comply with the limitations imposed by the connected equipment. a Maintained for a duration of 15 min.