TRANSDUCERS (ELECTRICAL) BASICS AND TUTORIALS

Transducers measure power system parameters by sampling instrument transformer secondaries. They provide a scaled, low-energy signal that represents a power system quantity that the SA interface controller can easily accept.

Transducers also isolate and buffer the SA interface controller from the power system and substation environments. Transducer outputs are dc voltages or currents in the range of a few tens of volts or milliamperes. Transducers measuring power system electrical quantities are designed to be compatible with instrument transformer outputs.

Potential inputs are based around 120 or 115 Vac, and current inputs accept 0 to 5 A. Many transducers can operate at levels above their normal ranges with little degradation in accuracy provided their output limits are not exceeded.

Transducer input circuits share the same instrument transformers as the station metering and protection systems; thus, they must conform to the same wiring standards as any switchboard component.

Wiring standards for current and potential circuits vary between utilities, but generally 600-V-class wiring is required, and no. 12 AWG or larger wire is used. Special termination standards also apply in many utilities.

Test switches for “in-service” testing of transducers are often provided to make it possible to test transducers without shutting down the monitored equipment. Transducers may also require an external power source to operate.

When this is the case, the reliability of this source is crucial in maintaining data flow. Transducer outputs are voltage or current sources specified to supply a rated voltage or current into a specific load. For example, full output may correspond to 10 V at up to 1.0 mA or 1.0 mA into 10 kΩ, up to 10 V maximum.

Some over-range capability is provided in transducers so long as the maximum current or voltage capability is not exceeded. The over-range can vary from 20 to 100%, depending on the transducer.

However, accuracy is usually not specified for the over-range area. Transducer outputs are usually wired with shielded, twisted-pair cable to minimize stray signal pickup. In practice, no. 18 AWG conductors or smaller are satisfactory, but individual utility practices differ.

It is common to allow transducer output circuits to remain isolated from ground to reduce the susceptibility to transient damage, although some SA controller suppliers provide a common ground for all analogs, often to accommodate electronic multiplexers.

Some transducers may also have a ground reference associated with their outputs. Double grounds, where transducer and controller both have ground references, can cause major reliability problems.

Practices also differ somewhat on shield grounding, with some shields grounded at both ends, but it is also common practice to ground shields at the SA controller end only. When these signals must cross a switchyard, however, it is a good practice to not only provide the shielded twisted pairs, but it also to provide a heavy-gauge overall cable shield.

This shield should be grounded where it leaves a station control house to enter a switchyard and where it reenters another control house. These grounds are terminated to the station ground mass, and not to the SA analog grounds bus.

SUBSTATION AUTOMATION SYSTEM COMPONENTS BASICS AND TUTORIALS

The electric utility SA system uses a variety of devices integrated into a functional package by a communications technology for the purpose of monitoring and controlling the substation. S

Systems incorporate microprocessor-based intelligent electronic devices (IEDs), which provide inputs and outputs to the system. Common IEDs are protective relays, load survey and operator indicating meters, revenue meters, programmable logic controllers (PLC), and power equipment controllers of various descriptions.

Other devices may also be present, dedicated to specific functions within the SA system. These may include transducers, position monitors, and clusters of interposing relays. Dedicated devices may use a controller (SA controller) or interface equipment such as a conventional remote terminal unit as a means of integration into the SA system.

The SA system typically has one or more communications connections to the outside world. Common communications connections include utility operations centers, maintenance offices, and engineering centers.

Most SA systems connect to a traditional SCADA (supervisory control and data acquisition) system master station serving the real-time needs for operating the utility network from an operations center.

SA systems may also incorporate a variation of the SCADA remote terminal unit (RTU) for this purpose, or the RTU function may appear in an SA controller or host computer.

Communications for other utility users is usually through a bridge, gateway, or network processor.

CIVIL WORKS ON HVDC SUBSTATIONS BASICS AND TUTORIALS

High-voltage power electronic substations are special because of the valve rooms and buildings required for converters and controls, respectively. Insulation clearance requirements can lead to very large valve rooms (halls).

The valves are connected to the yard through wall bushings. Converter transformers are often placed adjacent to the valve building, with the valve-side bushings penetrating through the walls in order to save space.

The valves require controlled air temperature, humidity, and cleanness inside the valve room. Although the major part of the valve losses is handled by the valve cooling system, a fraction of the same is dissipated into the valve room and adds to its air-conditioning or ventilation load.

The periodic fast switching of electronic converter and controller valves causes a wide spectrum of harmonic currents and electromagnetic fields, as well as significant audible noise. Therefore, valve rooms are usually shielded electrically with wire mesh in walls and windows.

Electric interference with radio, TV, and communication systems can usually be controlled with power-line carrier filters and harmonic filters. Sources of audible noise in a converter station include the transformers, capacitors, reactors, and coolers.

To comply with the contractually specified audible noise limits within the building (e.g., in the control room) and outdoors (in the yard, at the substation fence), low-noise equipment, noise-damping walls, barriers, and special arrangement of equipment in the yard may be necessary.

The theory of audible noise propagation is well understood, and analytical tools for audible noise design are available.

Specified noise limits can thus be met, but doing so may have an impact on total station layout and cost. Of course, national and local building codes also apply. In addition to the actual valve room and control building, power electronic substations typically include rooms for coolant pumps and water treatment,

 or auxiliary power distribution systems, air conditioning systems, battery rooms, and communication rooms.

Extreme electric power flow densities in the valves create a certain risk of fire. Valve fires with more or less severe consequences have occurred in the past. Improved designs as well as the exclusive use of flame-retardant materials in the valve, coordinated with special fire detection and protection devices, reduce this risk to a minimum.

The converter transformers have fire walls in between and dedicated sprinkler systems around them as effective fire-fighting equipment.

Many high-voltage power electronic stations have spare transformers to minimize interruption times following a transformer failure. This leads to specific arrangements and bus configurations or extended concrete foundations and rail systems in some HVDC converter stations.

Some HVDC schemes use outdoor valves with individual housings. They avoid the cost of large valve buildings at the expense of a more complicated valve maintenance. TCSC stations also have similar valve housings on insulated platforms together with the capacitor banks and other equipment.

SF6 (SULFUR HEXAFLOURIDE) APPLICATION IN GAS INSULSATED SUBSTATIONS TUTORIALS

A gas insulated substation (GIS) uses a superior dielectric gas, SF6, at moderate pressure for phase to phase and phase-to-ground insulation. The high voltage conductors, circuit breaker interrupters, switches, current transformers, and voltage transformers are in SF6 gas inside grounded metal enclosures.

Sulfur hexaflouride is an inert, non-toxic, colorless, odorless, tasteless, and non-flammable gas consisting of a sulfur atom surrounded by and tightly bonded to six flourine atoms. It is about five times as dense as air. SF6 is used in GIS at pressures from 400 to 600 kPa absolute. The pressure is chosen so that the SF6 will not condense into a liquid at the lowest temperatures the equipment experiences.

SF6 has two to three times the insulating ability of air at the same pressure. SF6 is about one hundred times better than air for interrupting arcs. It is the universally used interrupting medium for high voltage circuit breakers, replacing the older mediums of oil and air.

SF6 decomposes in the high temperature of an electric arc, but the decomposed gas recombines back into SF6 so well that it is not necessary to replenish the SF6 in GIS. There are some reactive decomposition byproducts formed because of the trace presence of moisture, air, and other contaminants.

The quantities formed are very small. Molecular sieve absorbants inside the GIS enclosure eliminate these reactive byproducts. SF6 is supplied in 50-kg gas cylinders in a liquid state at a pressure of about 6000 kPa for convenient storage and transport. .

Gas handling systems with filters, compressors, and vacuum pumps are commercially available. Best practices and the personnel safety aspects of SF6 gas handling are covered in international standards (IEC, 1995).

The SF6 in the equipment must be dry enough to avoid condensation of moisture as a liquid on the surfaces of the solid epoxy support insulators because liquid water on the surface can cause a dielectric breakdown. However, if the moisture condenses as ice, the breakdown voltage is not affected. So dew points in the gas in the equipment need to be below about –10°C. For additional margin, levels of less than 1000 ppmv of moisture are usually specified and easy to obtain with careful gas handling.

Absorbants inside the GIS enclosure help keep the moisture level in the gas low, even though over time, moisture will evolve from the internal surfaces and out of the solid dielectric materials (IEEE Std. 1125-1993). Small conducting particles of mm size significantly reduce the dielectric strength of SF6 gas.

This effect becomes greater as the pressure is raised past about 600 kPa absolute (Cookson and Farish, 1973). The particles are moved by the electric field, possibly to the higher field regions inside the equipment or deposited along the surface of the solid epoxy support insulators, leading to dielectric breakdown at operating voltage levels.

Cleanliness in assembly is therefore very important for GIS. Fortunately, during the factory and field power frequency high voltage tests, contaminating particles can be detected as they move and cause small electric discharges (partial discharge) and acoustic signals, so they can be removed by opening the equipment.

Some GIS equipment is provided with internal “particle traps” that capture the particles before they move to a location where they might cause breakdown. Most GIS assemblies are of a shape that provides some “natural” low electric field regions where particles can rest without causing problems.

SF6 is a strong greenhouse gas that could contribute to global warming. At an international treaty conference in Kyoto in 1997, SF6 was listed as one of the six greenhouse gases whose emissions should be reduced. SF6 is a very minor contributor to the total amount of greenhouse gases due to human activity, but it has a very long life in the atmosphere (half-life is estimated at 3200 years), so the effect of SF6 released to the atmosphere is effectively cumulative and permanent.

The major use of SF6 is in electrical power equipment. Fortunately, in GIS the SF6 is contained and can be recycled. By following the present international guidelines for use of SF6 in electrical equipment (Mauthe et al., 1997), the contribution of SF6 to global warming can be kept to less than 0.1% over a 100-year horizon.

The emission rate from use in electrical equipment has been reduced over the last three years. Most of this effect has been due to simply adopting better handling and recycling practices. Standards now require GIS to leak less than 1% per year. The leakage rate is normally much lower. Field checks of GIS in service for many years indicate that the leak rate objective can be as low as 0.1% per year when GIS standards are revised.

TRANSMISSION LINE BI-METAL CONNECTION AND CORROSION BASICS AND TUTORIALS

Bi-metal connectors

Where an aluminium conductor is terminated on a copper terminal of, say, an isolator a special copper/aluminium joint is necessary to prevent the formation of a corrosion cell. 

A termination of this type usually comprises of an aluminium sleeve compressed onto a copper stalk with an insulating disc separating the two surfaces which are exposed to the atmosphere.

The two dissimilar materials are generally welded together by friction welding as this process ensures a better corrosion resistance at the interface. An additional protection is afforded by the use of an anticorrosion varnish. 

When using such fittings it is always recommended that the aluminium component is above the copper one. Even slight traces of copper on aluminium have a disastrous effect on the aluminium material.

Corrosion

Since overhead lines are erected in different climatic conditions throughout the world knowledge of their performance has been built up over the years.

Aluminium conductors have good corrosion behaviour essentially resulting from the formation of an undisturbed protective surface oxide layer which prevents further corrosion attack.

ACSR is known to suffer from bi-metallic corrosion which is noticeable as an increase in conductor diameter due to corrosion products in the steel core known as ‘bulge corrosion'.

Early problems associated with deterioration of the steel cores used in ACSR conductors have been resolved over the years by the use of high temperature greases. These greases prevent the onset of any galvanic corrosion between the galvanized steel core and the outer aluminium wires.

They have a high drop point which allows continuous operation of the conductor at 75°C and full service life protection. AAAC will obviously offer superior corrosion resistance than ungreased ACSR. 

Conductors that are not fully greased are not recommended for corrosive areas.

The resistant properties of ACSR also depend upon the number of layers of aluminium surrounding the steel core. The conclusions of research carried out in the late 1960s showed that:

• Pure aluminium had the best corrosion resistance under the majority of environmental conditions.

• Smooth body conductors were the most corrosion resistant, especially if the inner layers were greased.

• Small diameter wires were most susceptible to corrosion damage and to failure. Thus for a given conductor area it is preferable to have fewer larger diameter strands.

• The overall corrosion performance of aluminium alloy conductors depends upon the type of alloy used.

For very aggressive environments the following order of preference is suggested:

• Aluminium conductor fully greased.

• Aluminium conductor with alumoweld core fully greased.

• ACSR fully greased.

• Aluminium alloy conductor fully greased.

• Aluminium conductor with alumoweld core ungreased.

• ACSR with greased core.

HALOGEN LAMPS BASIC INFORMATION AND TUTORIALS

It is not so much the melting point of the tungsten (which, at 3653 K, is still a relatively long way from the approx. 2800 K of the operating temperature of incandescents) that hinders the construction of more efficient incandescent lamps, but rather the increasing rate of evaporation of the filament that accompanies the increase in temperature.

This initially leads to lower performance due to the blackening of the surrounding glass bulb until finally the filament burns through. The price to be paid for an increase in luminous efficiency is therefore a shorter lamp life.

One technical way of preventing the blackening of the glass is the adding of halogens to the gas mixture inside the lamp. The evaporated tungsten combines with the halogen to form a metal halide, which takes on the form of a gas at the temperature in the outer section of the lamp and can therefore leave no deposits on the glass bulb.

The metal halide is split into tungsten and halogen once again at the considerably hotter filament and the tungsten is then returned to the coil. The temperature of the outer glass envelope has to be over 250° C to allow the development of the halogen cycle to take place.

In order to achieve this compact bulb of quartz glass is fitted tightly over the filament. This compact form not only means an increase in temperature, but also an increase in gas pressure, which in turn reduces the evaporation rate of the tungsten.

Compared with the conventional incandescent the halogen lamp gives a whiter light – a result of its higher operating temperature of 3000 to 3300 K; its luminous colour is still in the warm white range. The continuous spectrum produces excellent colour rendering properties.

The compact form of the halogen lamp makes it ideal as a point-source lamp; its light can be handled easily and it can create attractive sparkling effects. The luminous efficacy of halogen lamps is well above that of conventional incandescents – especially in the low-voltage range.

Halogen lamps may have a dichroic, heat reflecting coating inside the bulbs, which increases the luminous efficacy of these lamps considerably. The lamp life of halogen lamps is longer than that of conventional incandescents.

Halogen lamps are dimmable. Like conventional incandescent lamps, they require no additional control gear; low voltage halogen lamps do have to be run on a transformer, however.

 In the case of double-ended lamps, projector lamps and special purpose lamps for studios the burning position is frequently restricted.

Some tungsten halogen lamps have to be operated with a protective glass cover.

GUIDE IN SELECTION OF POWER CABLE JOINTS AND TERMINATION

When making a decision as to the best choice of devices to purchase, here are some of the questions and opportunities that should be considered:

Are the components of the device compatible with the cable being spliced or terminated?

Did the device pass all the tests that were specified so that it meets the requirements of the electrical system involved?

Are codes applicable in the decision to use the chosen device? Review all safety requirements involved in the construction, application, and installation of the device.

Will the device meet the mechanical requirements of the installation?

Can the device be assembled with the tooling that is already available or are special tools required?

Consider the positioning of the device.

Splices are not recommended for installation at bends in the cable. Terminations are normally installed in an upright position. Other positions are possible but require special attention.

Environmental conditions are of importance to attain expected life of any device.

Heat may affect the ampacity of the device.

Cold may have an effect on the assembly during installation. Contaminants are critical to the leakage path of a termination.

Moisture is always the enemy of an underground system and must be controlled in construction and installation.

Are there any existing work practices or procedures that will conflict with the application of this device?

Investigate the economics of using different devices such as emergency reserve parts, training new personnel after original installation personnel have gone.

The cost of the device and the cost of installation.

Will the device do the job as well or better than what is presently used?

SPLICING AND JOINTING POWER CABLE BASICS AND TUTORIALS

Jointing Theory

The ideal joint achieves a balanced match with the electrical, chemical, thermal, and mechanical characteristics of its associated cable. In actual practice, it is not always economically feasible to obtain a perfect match. A close match is certainly one of the objectives.

The splicing or joining of two pieces of cable together can best be visualized as two terminations connected together. The most important deviation, from a theoretical view, between joints and terminations is that joints are more nearly extensions of the cable.

The splice simply replaces all of the various components that were made in to a cable at the factory with field components. Both cable ends are prepared in the same manner unless it is a transition joint between say PILC and extruded cables.

Instead of two lugs being attached at the center of the splice, a connector is used. At each end of the splice where the cable shielding component has been stopped, electrical stress relief is required just as it was when terminating.

Connector: Joins the two conductors together and must be mechanically strong and electrically equal to the cable conductor. In this application, the ends of the connector are tapered. This provides two functions:

 1) It provides a sloping surface so that the tape can be properly applied and no voids are created

2) Sharp edges at the end of the connector are not present to cause electrical stress points.

Penciling: On each cable being joined, you will notice that the cable insulation is “penciled back. This provides a smooth incline for the tape to be applied evenly and without voids.

Insulation: In this application, rubber tape is used. Tape is applied to form the stress relief cone at each end of the splice. The overlapped tape continues across the connector to the other side. The thickness at the center of the splice is dictated by the voltage rating.

Conducting Layer: Covering the insulation is a layer of conducting rubber tape that is connected to the insulation shield of the cable at both ends of the splice.

Metallic Shield: A flexible braid is applied over the conducting rubber tape and connects to the factory metallic portion of the cable on each end. This provides a ground path for any leakage current that may develop in the conducting tape.

There must be a metallic neutral conductor across the splice. This may be in the form of lead, copper concentric strands, copper tapes, or similar materials. It provides the fault current function of the cable’s metallic neutral system.

ECONOMICS OF GAS INSULATED SUBSTATION COMPARED TO AIR INSULATED SUBSTATION BASICS AND TUTORIALS

The equipment cost of GIS is naturally higher than that of AIS due to the grounded metal enclosure, the provision of an LCC, and the high degree of factory assembly.

A GIS is less expensive to install than an AIS.

 The site development costs for a GIS will be much lower than for an AIS because of the much smaller area required for the GIS.

The site development advantage of GIS increases as the system voltage increases because high voltage AIS take very large areas because of the long insulating distances in atmospheric air.

Cost comparisons in the early days of GIS projected that, on a total installed cost basis, GIS costs would equal AIS costs at 345 kV.

For higher voltages, GIS was expected to cost less than AIS.

However, the cost of AIS has been reduced significantly by technical and manufacturing advances (especially for circuit breakers) over the last 30 years, but GIS equipment has not shown any cost reduction until very recently.

Therefore, although GIS has been a well-established technology for a long time, with a proven high reliability and almost no need for maintenance, it is presently perceived as costing too much and is only applicable in special cases where space is the most important factor.

Currently, GIS costs are being reduced by integrating functions as described in the arrangement section above. As digital control systems become common in substations, the costly electromagnetic CTs and VTs of a GIS will be replaced by less-expensive sensors such as optical VTs and Rogowski coil CTs.

These less-expensive sensors are also much smaller, reducing the size of the GIS and allowing more bays of GIS to be shipped fully assembled.

Installation and site development costs are correspondingly lower.

The GIS space advantage over AIS increases. GIS can now be considered for any new substation or the expansion of an existing substation without enlarging the area for the substation.

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Those familiar with transmission system problems and policies have developed the following list, sometimes called the “ten commandments” of transmission knowledge:

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2. Effect of generation on transmission and vise versa;

3. Causes of circulating power, parallel path flow, and loop flow;

4. Differences between individual circuit capacities and transmission capacities;

5. Synchronous ac connection advantages and disadvantages;

6. Reactive power and its role;

7. Causes and consequences of blackouts;

8. Need for new technology;

9. Disincentives to building new transmission;

10. Need for special training and education.

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ELECTRICAL ENGINEERING PROFESSIONAL ORGANIZATIONS OF THE WORLD

Many professional organizations are involved in the functioning of the electric

power industry.

IEEE

“The Institute of Electrical and Electronics Engineers, Inc. (IEEE) is a nonprofit, technical professional association of more than 377,000 individual members in 150 countries.

Through its members, the IEEE is a leading authority in technical areas ranging from computer engineering, biomedical technology, and telecommunications, to electric power, aerospace, and consumer electronics, among others. The IEEE is made up of:

• 10 regions;

• 37 societies;

• 4 councils;

• Approximately 1,200 individual and joint society chapters;

• 300 sections; and

• 1,000 student branches are located at colleges and universities worldwide.”

The Power Engineering Society is one of the 37 societies in the IEEE and has 25,000 members.

“Through its technical publishing, conferences, and consensus-based standards activities, the IEEE:

• Produces 30 percent of the world’s published literature in electrical engineering, computers, and control technology;

• Holds annually more than 300 major conferences; and

• Has nearly 900 active standards with 700 under development.”

“Policy matters related to IEEE Standards are the purview of the IEEE Standards Association (IEEE-SA), which establishes and dictates rules for preparation and approval . . .

Overwhelmingly, it is the Computer Society and the Power Engineering Society that dominate in this regard, for instance, about 40% of all IEEE Standards are . . . within the PES.”

CIGRE

Another important organization is the International Council on Large High Voltage Electric Systems (CIGRE). CIGRE is an international organization through which ideas can be exchanged with people from various countries through meetings, committee activities, and its publications.

SYNCHRONOUS GENERATORS DEFINITION BASICS AND TUTORIALS

Essentially all of the world’s electric power is generated by synchronous machines. The synchronous generator has proven to be a reliable and efficientdevice for converting mechanical power to electric power.

 Since the typical power system uses alternating current (60 Hz in the United States), the chief requirement of such a device is that it produces power at a controllable voltage at a constant frequency.

A typical synchronous machine consists of a rotor with a field winding and a stator with a three-phase ac winding. The rotor has a dc power supply and the stator is connected to the power system through a generator step-up transformer. The turbine rotates the field at a constant speed, often as high as 3,600rpm.

If the stator windings are connected to a load, current flows through the windings and the load. As the electrical load increases, the prime mover (turbine) must expend more mechanical energy to keep the rotor turning at a constant speed.

Thus mechanical energy input by the turbine is being transformed into electrical energy. Generators in hydro plants are also synchronous machines, but rotate at lower speeds than steam unit or gas turbines.

The electrical power produced by a synchronous generator is almost equal to the mechanical power input, the efficiency being in the range of 98%. The division of electric load among a number of generators is determined by a number of factors, including economics.

At a given operating point each turbine generator has an incremental cost, which is the cost per kWh to generate an additional small amount of power. Maximum system economy results when all generators are operating at the same incremental production cost.

The control of the real power and regulation of the speed (which must be held constant to provide a constant frequency) is done with the speed governor and automatic generator controls (AGC) and interaction with the system control center.

TYPE OF USE OF POWER GENERATING PLANT BASICS AND TUTORIALS

Generating units may be classified into three categories based on their mode of operation. These are:

1. Base Load;

2. Intermediate;

3. Peaking.

Base load units tend to be large units with low operating costs. They are generally operated at full capacity during most of the hours that they are available.

They are designed to operate for long periods of time at or near their maximum dependable capability. Their low operating costs result from their use of low-cost nuclear and coal fuels and/or lower heat rates (higher efficiencies) than other units on the system.

For a typical region, base load is on the order of 40% to 60% of the annual maximum hourly load and, since this represents the amount of load that will be supplied in the region at essentially all hours, it represents perhaps 60% to 70% of the annual energy requirements of the region.

Base load units are usually shut down for forced outages or maintenance only. Because of their size and complexity, these units may require from 24 hours to several days to be restarted from a “cold” condition.

Once the decision has been made to shut down one of these units, periods of up to 24 hours may be required before another “start-up” may be attempted. When operating a power system decisions on the time of restarting units play an important role in hour-by-hour schedules for generation.

Intermediate units are those generating units which are used to respond to the variations in customer demand which occur during the day. They are designed to withstand repeated heating and cooling cycles caused by changes in output levels.

Intermediate units usually have lower capital costs, and somewhat higher heat rates (lower efficiencies) than base load units. The intermediate load may be on the order of 30–50% of the maximum hourly load for a typical system and represents perhaps 20–30% of the annual energy requirements for the utility.

Peaking units are those generating units that are called upon to supply customer demand for electricity only during the peak load hours of a given period (day, month, year). Combustion turbines, reciprocating engines and small hydroelectric units comprise the majority of peaking units.

These are ordinarily units with a low maximum capability (usually less than 150Mw), which are capable of achieving full load operation from a cold condition within ten minutes. Peaking units usually have the highest heat rate sand lowest capital costs of the three categories of units.

In addition to supplying system needs during peak load hours, they may be called upon to replace the capability of  other base load or cycling units which have been suddenly removed from service due to forced outages. They generally supply about 5% of the total energy requirements of a system.

As generating units age, unit efficiency and performance generally decrease. In addition, newer, more efficient, lower operating cost units are continuously added to a power system. These two occurrences tend to cause most generating units to be operated fewer hours as they age.

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TOOLS IN CONSTRUCTION OF TRANSMISSION LINES

Basic tools needed to construct overhead transmission lines are as follows:

1. Conductor blocks

2. Overhead groundwire blocks

3. Catch-off blocks

4. Sagging blocks

5. Pulling lines

6. Pulling grips

7. Catch-off grips

8. Swivels

9. Running boards

10. Conductor lifting hooks

11. Hold-down blocks

Conductor blocks are made in the following configurations:

1. Single conductor

2. Multiple conductor

3. Multiversal type (can be converted from bundle to single, and vice versa)

4. Helicopter

Conductor blocks should be large enough to properly accommodate the conductor and be lined with a resilient liner such as neoprene or polyurethane and constructed of lightweight, high-strength materials.

Sheaves should be mounted on anti-friction ball bearings to reduce the tension required in stringing and facilitate proper sagging.

Conductor blocks are available for stringing single conductors or multiple conductors. Some are convertible, thus enhancing their versatility.

When stringing multiple conductors, it is desirable to pull all conductors with a single pulling line so that all conductors in the bundle have identical tension history. The running board makes this possible. Pulling lines are divided into two categories:

1. Steel cable

2. Synthetic rope

Because of the extra high tension required in transmission line construction, steel pulling lines and pilot lines are most practical to use. Torque-resistant, stranded, and swagged cable are used so that ball bearing swivels can be utilized to prevent torque buildup from being transferred to the conductor.

Some braided or woven steel cables are also used. If synthetic ropes are utilized, the most important features should include:

1. No torque

2. Very minimum elongation

3. No “kinking”

4. Easily spliced

5. High strength/small diameter

6. Excellent dielectric properties

Stringing overhead groundwires does not normally require the care of current-carrying conductors. Most overhead groundwires are stranded steel construction and the use of steel wire with a fiber optic core for communications has become a common practice.

Special care should be taken to ensure that excessive bending does not occur when erecting overhead groundwires with fiber-optic centers, such as OPT-GW (Optical Power Telecommunications — Ground Wire) and ADSS (All Dielectric Self-Supporting Cable).

Special instructions are available from the manufacturer, which specify minimum sheave and bullwheel diameter for construction. OPT-GW should be strung using an antirotational device to prevent the cable from twisting. 

ELECTRICAL RESISTANCE OF STEEL POLES USED IN TRANSMISSION LINES

An increasing number of utilities are installing metal transmission and distribution poles due to the many advantages of metal poles over wood poles.  The purpose of this white paper is to present evidence that the embedded portion of a representative steel pole offers significant grounding capability.

In fact, the grounding resistance of the embedded portion of a steel pole can be shown to be lower than standard ground rods under specific conditions.

In this white paper, the Numerical Electromagnetics Code (NEC-4) [1] is used to compute the grounding resistance of a variety of grounding electrodes.  NEC-4 is a method of moments [2] code originally designed for the analysis of antennas and scatterers.  

NEC-4 can be used in the computation of ground resistances since it allows for conducting structures over a finitely conducting ground which may penetrate the ground.  Of particular interest is the grounding resistance of a representative steel pole such as a typical 40 foot class 3 steel distribution pole. Read more…

Steel
electrical resistivity = ( electrical resistance * cross-sectional area ) / longitudinal length
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Resistivity of Steel

RESIST.    COND.                SOURCE
ohm-m      SIEMENS/m       % IACS  CODE     MATERIAL
1.611E-07 6.206E+06         10.70   1  Steel, Cast
5.945E-07 1.682E+06          2.90   1  Steel, High Alloy
6.897E-07 1.450E+06          2.50   1  Steel, 304 Stainless
6.897E-07 1.450E+06          2.50   2  Steel, 304 Stainless
7.184E-07 1.392E+06          2.40   1  Steel, 347 Stainless
7.184E-07 1.392E+06          2.40   2  Zircaloy - 2
7.496E-07 1.334E+06          2.30   1  Steel, 316 Stainless
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Galloping Response Prediction Of Ice-accreted Transmission Lines Free PDF White Paper Download Link

Transmission lines are extremely flexible structures, which can suffer from galloping under extreme environmental conditions. A better understanding of the phenomena is therefore necessary to predict occurrence and extent of this phenomenon. In this study, an aero-elastic experiment has been performed on sectional model of four-conductor transmission line considering different structural configurations.

The experiment is reproduced numerically using a nonlinear FEM code, in which aerodynamic force is estimated using quasi-steady and unsteady force model. Dependence of galloping on structural configuration and efficiency of aerodynamic force prediction models is investigated in light of experiment and simulation results.

Transmission lines that vary from supply to local feeders to countrywide supply to remote areas are essential part of every country’s development. These are extremely flexible structures and suffer from various types of structural instabilities. The basic concern of this research is “Galloping”, which refers to large amplitude oscillation in direction perpendicular to the applied load.

During winter, ice accretion takes place on transmission lines, changing their shape, as shown in Figure 1. The modified shape develops aerodynamic lift and rotational moment, which can result in negative aerodynamic damping and lead to galloping. To investigate the galloping phenomena, wind tunnel tests are usually carried out to determine the aerodynamic coefficients as a function of angle of attack. 

The well-known Den-Hartog criterion is employed considering aerodynamic coefficients to evaluate the possibility of galloping occurrence and critical velocity of galloping for a given cable shape. 

In most of the previous works galloping of transmission lines has been regarded as a quasisteady problem. In the last decade, some innovative studies have been carried out to determine influence of conductor motion and conductor wake on the aerodynamic characteristics of transmission lines considering single and 4-conductor bundle ice-accreted cable model (Kimura et al. 1999, Shimizu et al. 2004 and Phuc et. al. 2004).

These references put forth a model for representation of unsteady aerodynamic forces considering angle of attack and rotational velocity of cable to take into account the effect of cable motion. The results show that quasi-steady model provide much different results as compared to unsteady model especially for aerodynamic moment (Phuc et al. 2004) as is evident in Figure 2. The figure shows time history of aerodynamic moment on a cable rotating at amplitude of ±55° with respect to steady wind.

 The unsteady model show very close agreement, whereas the quasi-steady model shows much different results, especially close to 0°.Shimizu and Sato (2001) have used simulation considering quasi-steady model and compared with field observations, some underestimations were observed in the results.

The reason of this difference may be because of the difference between the quasi-steady and unsteady aerodynamic coefficients (from Phuc et al. and Shimizu et al.), which is more distinguished for themoment coefficient.

This paper aims to develop a better understanding of galloping phenomena through an aeroelastic experiment. It investigates performance of the aerodynamic force models (quasi-steady and unsteady model) through a fully nonlinear FEM code considering the model for the aeroelastic experiment. Simulation results are used to explain the galloping phenomena.

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TRANSMISSION LINES CONDUCTOR GALLOPING VIDEO

VIDEO OF TRANSMISSION LINE CONDUCTORS GALLOPING

Joint Relay Selection and Analog Network Coding using Differential Modulation in Two-Way Relay Channels Free PDF Download Link White Paper

In this paper, we consider a general bi-directional relay network with two sources and N relays when neither the source nodes nor the relays know the channel state information (CSI). A joint relay selection and analog network coding using differential modulation (RS-ANC-DM) is proposed. In the proposed scheme, the two sources employ differential modulations and transmit the differential modulated symbols to all relays at the same time.

The signals received at the relay are a superposition of two transmitted symbols, which we call the analog network coded symbols. Then a single relay which has minimum sum SER is selected out of N relays to forward the ANC signals to both sources. To facilitate the selection process, in this paper we also propose a simple sub-optimal Min-Max criterion for relay selection, where a single relay which minimizes the maximum SER of two source nodes is selected.

Simulation results show that the proposed Min-Max selection has almost the same performance as the optimal selection, but is much simpler. The performance of the proposed RS-ANC-DM scheme is analyzed, and a simple asymptotic SER expression is derived. The analytical results are verified through simulations.

In a bi-directional relay network, two source nodes exchange their messages through the aid of one or multiple relays. The transmission in bi-directional relay network can take place over four, three or two time slots. In the four time slots transmission strategy, the relay helps to forward source S1’s message to source S2 in the first two time slots and source S2’s message to source S1 in the next two time slots. Four time slots transmission has been shown to be very inefficient.

When the relay receives two sources’ messages, it combines them before forwarding to the destination, which will save one time slot transmission. This three time slots transmission scheme is usually referred to as the digital network coding [1]– [3]. In this method, two source nodes transmit to the relay, separately. The relay decodes the received signals, performs binary network coding, and then broadcasts it back to both source nodes.

To further improve the spectral efficiency, the message exchange between two source nodes can actually take place in two time slots. In the first time slot, both source nodes transmit at the same time so that the relay receives a superimposed signal. The relay then amplifies the received signal and broadcasts it to both source nodes in the second time slots. This scheme is referred to as the analog network coding (ANC) [4]–[6]. Various transmission schemes and wireless network coding schemes in bi directional relay networks have been analyzed and compared in [7]–[12].

Most of existing works in bi-directional relay communications consider the coherent detection at the destination and assume that perfect channel state information (CSI) are available at the sources and relays [1]–[12]. In some scenarios, e.g. the fast fading environment, the acquisition of accurate CSI may become difficult. In this case, the non-coherent or differential modulation would be a practical solution. In a differential bi-directional relay network, each source receives a superposition of differentially encoded signals from the other source, and it has no knowledge of CSI of both channels.

 All these problems present a great challenge for designing differential modulation schemes in two-way relay channels. To solve this problem, in [13], a non-coherent receiver for two-way relaying was proposed for ANC based bi-directional relay networks. However, the schemes result in more than 3 dB performance loss compared to the coherent detection. To further improve the system performance, a differential ANC scheme was proposed in [14] and a simple linear detector was developed to recover the transmitted signals at two source nodes.

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Microcontroller Interfacing Techniques PDF White Paper Download Link

Micro-controllers are useful to the extent that they communicate with other devices, such as  sensors, motors, switches, keypads, displays, memory and even other micro-controllers.  Many interface methods have been developed over the years to solve the complex problem of  balancing circuit design criteria such as features, cost, size, weight, power consumption, reliability, availability, manufacturability.

Many microcontroller designs typically mix multiple interfacing methods.    In a very simplistic  form, a micro-controller system can be viewed as a system that reads from (monitors) inputs,  performs processing and writes to ( controls ) outputs.

Serial Buses

I2C ( Inter Integrated Circuit bus )

2-wire interface with one master and multiple slaves ( multi-master configurations possible ).

Originated by Philips Semiconductor in the early 80’s to connect a microcontroller to peripheral devices in TV sets.

Signals: DATA (SDA), CLOCK (SCL) and Ground. SDA is always bi-directional; SCL is bidirectional only in multi-master mode.

Maximum allowable capacitance on the lines is 400 pF. Typical device capacitance is 10 pF.  To start the communications, the bus master (typically a microcontroller) places the address of the device with which it intends to communicate (the slave) on the bus. All slave devices monitor the bus to determine if the master device is sending their address.

Only the device with the correct address communicates with the master.

By definition, I2C is 5V.

SPI ( Serial Peripheral Interface )

4-wire interface with one master and multiple slaves. Signals: DATA IN, DATA OUT, CLOCK, CS

( Chip Select )

Originated by Motorola, SPI bus is a relatively simple synchronous serial interface for connecting  low speed external devices using minimal number of wires. A synchronous clock shifts serial data into and out of the microcontrollers in blocks of 8 bits.

SPI bus is a master/slave interface. Whenever two devices communicate, one is referred to as the "master" and the other as the "slave" device. The master drives the serial clock. SPI is full duplex: Data is simultaneously transmitted and received.

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Solenoids, Relays, and Other Analog Outputs Free PDF White Paper Download Link

Solenoids

A solenoid is an electromagnet that activates a mechanical function, such as a plunger. Solenoids are used to latch safety covers closed so they can’t be opened while a machine is in operation, or to unlock the doors in your car when you push the keyless entry button on the remote. Solenoids can open and close valves in industrial processes or push the record head against the tape in a tape player.

Solenoids come in many shapes and sizes, and are capable of exerting a force from less than an ounce to several pounds. There are two basic varieties: continuous duty and pulse duty. Continuous-duty solenoids are designed to be energized all the time. An application such as holding a safety cover closed would use a continuous-duty solenoid.

A pulse-duty solenoid might be used for the doors in your car. Pulse-duty solenoids will overheat if left energized all the time—they are designed for intermittent operation. A pulse-duty solenoid allows a high-force solenoid to be smaller and cheaper because continuous operation is not a concern.

Relays

A relay is a solenoid that operates electrical contacts. When the relay is energized, the contacts are shorted or opened, just like a mechanical switch. Interfacing to Solenoids and Relays For the sake of simplicity, this section will address relays, but the same considerations apply to solenoids. Figure 6.1A shows a relay as it might be connected to a microprocessor. A single bit is used to turn the relay on and off.

The figure shows an NPN transistor connected to a port bit on the processor; you could also use a MOSFET. Some microprocessors have outputs that are capable of sinking sufficient current to activate a relay, as long as the relay is operating from the same voltage as the processor.

Because the relay or solenoid is activated by a coil, there is a flyback voltage that occurs when the drive transistor is turned off and the magnetic field collapses in the coil. This voltage can reach high enough levels to damage the drive transistor. Figure 6.1B shows how a diode can be used to clamp the voltage across the coil to safe levels.

When the transistor turns on, activating the relay, the diode is reverse biased. When the transistor turns off, the top end of the coil is tied to the drive voltage, so a voltage spike appears at the lower end (transistor collector). As soon as this voltage reaches the supply voltage plus one diode drop (about 0.6 V for a silicon diode), the diode conducts.

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POWER CABLE PARTIAL DISCHARGE TESTING BASICS AND TUTORIALS

Partial discharge measurement is an important method of assessing the quality of the insulation of power cable systems, particularly for extruded insulation materials.

This article considers partial discharge from two points of view: the measurement of all partial discharges occurring within the cable system and the location of individual partial discharge sites.

Measurement of Partial Discharge
Perhaps the most significant factory test made on the insulation of full reels of extruded cable is the partial discharge test. This is usually done at power frequency, but can also be carried out at very low frequency and at some voltage significantly higher than normal working voltage to ground. Experience has shown that this test is a very sensitive method of detecting small imperfections in the insulation such as voids or skips in the insulation shield layer.

It would therefore seem logical to repeat the test on installed cables to detect any damage done during the shipping or laying or any problems created by jointing and terminating the cable. Unfortunately this is a difficult measurement to perform in the field due to the presence of partial discharge signals.

However, in spite of the difficulty, this test has been performed in the field where some special circumstances suggest it is worth the time and expense involved. Typically this may be when damage or faulty installation is suspected or the cable route requires it to be of the highest possible reliability.

Once the necessary steps are taken to reduce the noise level below the partial discharge level to be measured, the test can provide a great deal of useful diagnostic data. By observing the magnitude and phase of the partial discharge signals and how they vary with increasing and then decreasing test voltage, results will disclose information on the type and position of the defects and their probable effect on cable life.

Noise reduction methods necessary for field tests of partial discharge usually include the use of an independent test voltage source such as a motor-generator, power line and high voltage filters, shielding and sometimes the use of bridge detection circuits.

Partial discharges can also be detected at system voltage with special sensors connected to the splice or termination, using the fkequency spectrum of the discharges.

In summary, if the cable system can be tested in the field to show that its partial discharge level is comparable with that obtained in the factory tests on the cable and accessories, it is the most convincing evidence that the cable system is in excellent condition.

OLIVER HEAVISIDE - ELECTRICAL ENGINEERING HEROES

Oliver Heaviside is unusual - perhaps even unique - among the scientists and engineers in that he had no formal education beyond leaving school at the age of sixteen. He was somewhat deaf and lived a rather solitary life, and few people could ever claim to have known him at a personal level. His name is attached to at least two phenomena - the Heaviside step function and the Heaviside layer - in common use today.

Oliver Heaviside was born on May 18, 1850, at 55 King Street in Camden Town in north London. He was the youngest of four brothers. His father, Thomas Heaviside, was a wood engraver originally from Stockton-on- Tees in north-east England, and had come to London in 1849. Camden Town in the middle of the 19th century was typical of the developing Victorian metropolitan life, with its crowded, smoke-polluted environment.

He left school at sixteen, and pursued his studies at home. Then, at the age of eighteen he took a job (the only paid employment he ever had) with the Great Northern Telegraph Company, working in Newcastle and in Denmark. There seems little doubt that Wheatstone was instrumental in getting him this job. During this time he had started to study Maxwell’s work, and began to publish articles in the Philosophical Magazine and elsewhere, on various aspects of circuit and telegraph theory.

After six years, in 1874, he left this job and returned to live with his parents. Two years later the family moved to 3 St. Augustine’s Road, a few hundred yards from Heaviside’s birthplace. The house was owned by the Midland Railway Company.

Recognition did ultimately come to Heaviside. He was elected Fellow of the Royal Society in 1891. He was sent a formal notice asking him to come to London to be admitted, but wanted nothing of it.

In 1921 the Institution of Electrical Engineers (IEE) instituted its Faraday Medal, and selected Heaviside as its first recipient. He was asked what form he thought the medal ought to take, and replied ‘about three inches in diameter, one inch thick, and made of solid gold’. Since it was out of the question for him to travel to London, the then President of the IEE, J. S. Highfield went to Torquay to present him with it.

Heaviside’s published output was quite prodigious, and he published in The Electrician and the Philosophical Magazine and elsewhere, as well as collected papers in two books: Electrical Papers (in two volumes) and Electromagnetic Theory (in three volumes).

Heaviside died on 3 February 1925, and his body is buried in Paignton Cemetery. Although there are no blue plaques in Camden commemorating his birth or where he lived, the IEE erected one in Torquay.

EFFECTS OF OXYGEN AND MOISTURE IN INSULATING OIL BASICS AND TUTORIALS

Moisture contamination is the most common cause of deterioration in the insulating quality of oil. This contamination can be readily corrected by purification.

A slow but more serious deterioration, the formation of acids and sludge, is caused by oxidation. Thus, the exclusion of oxygen is of prime importance. In open-breather transformers, the oxygen supply is virtually unlimited and oxidative deterioration is faster than sealed transformers.

Atmospheric oxygen and oxygen contained in water are the sources available for the oxidation of insulating oils. When water is present in insulating oils, oxidation of the oil will take place. Therefore, leaking gaskets and seals constitute a very real hazard since a water leak is, in effect, an oxygen leak.

The rate of oxidation also depends on the temperature of the oil; the higher the temperature is, the faster the oxidative breakdown. An increase in temperature of 10°C (50°F) generally doubles the rate of oxidation.

The fact points to the importance of avoiding overloading of transformers, especially in the summertime. Oxidation results in the formation of acids in the insulating oil and the formation of sludge at a more advance state of oxidation.

Moisture in Oil

Water can be present in oil in a dissolved form, as tiny droplets mixed with the oil (emulsion), or in a free state at the bottom of the container holding the oil. Demulsification occurs when the tiny droplets unite to form larger drops, which sink to the bottom and form a pool of free water.

 Emulsified water typically requires vacuum dehydration, as the emulsification cannot typically be broken by filtration or by excellerated gravity (centrifuge). Water in the free state may be readily removed by filtering or centrifugal treatment.

However, dissolved water is not removed by centrifugal treatment; the filtration process can partially remove dissolved water if the filter papers are thoroughly dried before filtration, but the efficiency of the filtration process depends upon oil temperature and filtration media.

The effect of moisture on the insulating properties of oil depends upon the form in which the moisture exists. A very small amount of emulsified water has a marked influence in reducing dielectric strength of oil.

Free moisture in oil usually shows up above 50 to 60 ppm depending upon temperature. Accepted levels of water in oil. The amount of moisture that can be dissolved in oil increases rapidly as the oil temperature increases.

Therefore, insulating oil purified at too high a temperature may lose a large percentage of its dielectric strength on cooling, because the dissolved moisture is then changed to an emulsion, unless vacuum dehydration is used as the purification process.