power systems loss

BULLETIN 1724D-112: APPLICATION OF CAPACITORS ON RURAL ELECTRIC SYSTEMS How power factor affect the systems loss in distribution system?                                   UNITED STATES DEPARTMENT OF AGRICULTURE                                                                  Rural Utilities Service                                    ...

Which is better for voltage regulation, capacitor ot voltage regulator? One of the greatest advantages gained by the proper sizing and location of distribution capacitors is voltage improvement. By placing leading volt-amperes reactive (VAR) loads (capacitors) near lagging VAR load centers (motors for example), the lagging VARs on a system basis are cancelled with an associated increase in voltage.

What is the difference between substation capacitor and line capacitors? If capacitors are installed primarily to reduce or eliminate bulk power charges for kVAR or for other reasons associated with wholesale purchased power such as contractual requirements, they can be installed in substations to supplement distribution line installations. Installed equipment cost for substation capacitors may be less than that for the same amount of line kVAR because the substation units can package many kVAR in a single installation and can be switched with a single three-phase switching device and control unit. However, the distributor does not get the benefit of reduced distribution line losses by installing capacitors at substations, so such installations should be made only after the maximum practical amount of line capacitors has been installed.

CAPACITOR OPERATION AND MAINTENANCE Basic operation and maintenance of capacitor in distribution system Capacitors on distribution lines must be kept operational if their benefits are to be retained. Lightning surges or other disturbances occasionally cause capacitor fused cut-outs to open, and the distributor should promptly check and refuse such units to keep all capacitors operational. Care should always be taken in refusing capacitor units, since energizing units that have been damaged internally often results in capacitor case failure. Since no consumer complains when a capacitor cut-out opens, some distributors might delay returning the capacitor to service. However, such delays are costly to the distributor because of increased line losses and possible wholesale power factor surcharges. Switched capacitors need to be checked periodically to ensure proper operation of switches and controls. Operation counts should also be recorded. A large or small number of operations may i...

CAPACITOR PLACEMENT AND CAPACITOR & VOLTAGE REGULATORS How does capacitor and regulators affect each other during operation? The installation of capacitors on a feeder can interfere with the proper operation of voltage regulators on that same feeder. This problem is relatively simple to overcome, but should not be ignored. Even fixed capacitors can cause some interference with regulators, but the interference is greater with switched capacitors. Capacitors, either fixed or switched, installed on the upstream side of the load center of a voltage regulator’s line drop compensator setting can thwart the compensator’s reactance setting. This problem is easily solved by setting the reactance compensation to zero and increasing the resistance compensation enough to achieve the same results previously obtained with both types of compensation. A voltage controlled switched capacitor on the load side of a voltage regulator can fail to switch properly because of action being taken by ...

TYPES OF SWITCHED CAPACITOR CONTROLS PART 2 What are the different types of switched capacitor control? In continuation of the types of switched capacitors control, we have include some intrinsic characteristics of the power system as the basis for capacitor switching which includes;  voltage, current, kvar, power factor, and combination of some of mentioned capacitor controls. Voltage Control A voltage control switches a capacitor on when line primary voltage is low, and switches the capacitor off when the voltage is high. The advantages of a voltage control include: (1) Primary line voltage is often closely related with line load and power factor, so the control responds to actual conditions; (2) Line voltage is an important index of the overall quality and efficiency of the feeder, so the control responds to a critical line condition; (3) It is simple to install, set, test and maintain; and (4) Although it requires a voltage signal, it does not require a line c...

TYPES OF SWITCHED CAPACITOR CONTROLS PART 1 What are the different types of switched capacitor control? There are many methods of automatic control of switched capacitors. The On and Off switching controls can be achieved by a time clock, an ambient temperature sensor, a line voltage-sensing device, a line current-sensing device, a power factor sensor, line kVAR flow sensing or other means such as a remote control. Different types of capacitor controls can be used for various installations on the same feeder, and combination control schemes can be used even on a single installation. The following is a summary of the advantages and disadvantages of various capacitor control methods. Time-Clock Control A time-clock control switches a capacitor on for those hours of the day when load is expected to be the highest, and switches the capacitor off for expected light-load hours. Controls are available that automatically change the on-off schedule during weekends or even seas...

TYPES OF CAPACITOR INSTALLATIONS What are the types of Capacitor Installation known? Capacitors are relatively easy to install and are among the most trouble-free electrical devices. Line capacitor installations are protected with conventional cut-out fused switches, and capacitor failure is rare if the appropriate fuse element is used. (Fuse rating should be closely coordinated with capacitor size.) There are several types of capacitors (see figure below). Following Load Reactive Power The most difficult aspect of capacitor application is the maintenance of proper balance between total kVAR of capacitors connected at any particular time and load kVAR present at that time. Like load kW, load kVAR changes over time, so some provision must be made to vary the total connected capacitive kVAR to roughly follow the load kVAR. Installing capacitors based on the peak load kVAR and leaving all these capacitors connected at off-peak times is strictly inadvisable, since excessive capaciti...

CAPACITORS FOR POWER DISTRIBUTIONS SYSTEM How does Capacitors installed in the power distribution system affect the operation? The basic definition of a capacitor would be that it is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric (insulator). Capacitors are used as parts of electrical systems, for example, consist of metal foils separated by a layer of insulating film. When there is a potential difference (voltage) across the conductors, a static electric field develops across the dielectric, causing positive charge to collect on one plate and negative charge on the other plate. Energy is stored in the electrostatic field. An ideal capacitor is characterized by a single constant value, capacitance, measured in farads. This is the ratio of the electric charge on each conductor to the potential difference between them. Th...

RUS BULLETIN 1724E-300 SUBSTATION VOLTAGE REGULATORS Voltage Regulators for Distribution System General Both three-phase and single-phase voltage regulators are used in distribution substations to regulate the loadside voltage. Substation regulators are one of the primary means, along with load-tap-changing power transformers, shunt capacitors, and distribution line regulators, for maintaining a proper level of voltage at a customer’s service entrance. A very important function of substation voltage regulation is to correct for supply voltage variation. With the proper use of the control settings and line drop compensation, regulators can correct for load variations as well. A properly applied and controlled voltage regulator not only keeps the voltage at a customer’s service entrance within approved limits but also minimizes the range of voltage swing between light and heavy load periods. The substation regulators may be located on individual feeders or in the transformer secondary...

LINE VOLTAGE REGULATORS CHARACTERISTICS AND OPERATION Line voltage regulators' discussion and operation. Primary distribution feeders in rural areas often extend so many miles that maintaining proper voltage over the entire length of the feeder will supply poit regulators alone is impossible. Line regulators located approximately at the mid-point of such feeder provide additional regulation to support the voltage on the remote parts of the feeder. Characteristics of Line Regulators The most common types of line regulators operate similarly to substation regulators. However, line regulators are usually smaller, are more likely to be formed from single-phase units, and are physically constructed for platform mounting on a pole or poles. The discussion above of loss characteristics of substation regulators also applies to line regulators. The major operational difference is that line regulators normally are used only for boosting voltage, and there is no way to center t...

How to minimize loss on Voltage Regulators Operation? To minimize losses on substation regulators , either separate units or substaton load tap changers, the high-voltage tap setting on the substation transformer should be set so the regulators will spend the maximum amount of time near the neutral position, since regulator losses increase as the regulator tap position farther away from neutral. Ideally substation regulators should spend approximately the same amount of time bucking voltage as they do boosting voltage. This keeps the regulators near neutral under average system conditions.

VOLTAGE REGULATORS IN DISTRIBUTION SYSTEM Voltage Regulators used in Power Distribution System? Voltage regulators affect the system efficiency in two ways. First, by maintaining proper voltage on the feeders they serve, regulators reduce losses on lines and distribution transformers supplied by the regulated voltage. Second, losses occur on the regulators themselves. Depending on regulator design, loading, and mode of operation, these losses can be quite high. Regulation at Substations Two major decisions are involved in the choice of regulating equipment to be installed in distribution substations. First, the distributor must decide whether to provide separate regulation for each outgoing distribution feeder or whether some of the feeders will share regulating equipment. For modest-sized substations with only one substation transformer bank and three to five feeders, the decision may come down to the choice between regulating equipment for each feeder and a single, large regulatin...

SELECTION OF VOLTAGE REGULATING EQUIPMENT How do we select voltage regulators for installation in lines and substations? Distributors must consider many factors when deciding what regulating equipment to install in substations. These factors include: Equipment Maintenance Intervals, as related to the number of guaranteed tap-changer operations without maintenance. Capability of the equipment tocarry expected through-fault currents. Separate feeder regulators may be inadequate for the fault currents in some locations, whereas transformer LTCs are rated for the same fault duty as the transformer. Overall equipment purchase and installation costs. Space consumption in the substation yard. Whether or not separate regulating action is needed for each feeder, to include separate resistance and reactance settings for line-drop compensators and, Energy loss characteristics. Although energy loss is only one of these factors, a loss evaluation should be part of the engineering and econom...

BUILDING WIRES TYPES AND APPLICATION GUIDE What are the common types of wires used for building wiring installation? TW (Thermoplastic Moisture-Resistant) The TW conductors are solid or stranded annealed (soft) copper, insulated with a moisture resistant and flame retardant polyvinyl compound (PVC). TW wire is used in interior wiring at circuit voltages up to 600 volts. Maximum operating temperature is 60°C in dry or wet application. Type TW building wire is used in residential, commercial and industrial buildings for generalpurpose lighting, appliance, power, control and relay panel applications. It is used for low ampacity rated circuits. This type of wire may be installed in conduits, ducts or raceways. Type TW wire is also suitable for installations in ambient temperatures down to -10°C. THW (Thermoplastic Heat and Moisture Resistant) The THW conductors are solid or stranded annealed (soft) copper, insulated with a tough heat and moisture resistant, and flame retardant po...

ADVANTAGES OF SHIELDED CABLES What are the known advantages of using shielded cables? Electrical insulation surrounding a conductor creates a capacitor when the conductor is electrically energized. Thus, all insulated conductors are capacitors. In the majority of non-shielded cable systems, thecable surface makes intermittent contact with an electrical ground. Where intimate contact with this ground is not made, the intervening air spaces also act primarily as capacitors in ac circuits and as resistors in dc circuits. This forms a series of cable dielectric and air dielectric. Voltage across this circuit varies along the length of the cable depending on the voltage across the air gap. The cable surface becomes a floating voltage point in a voltage divider. This floating point voltage can vary considerably, depending on the cable design and the characteristics of the air gap. If the voltage is high enough, the cable surface can experience detrimental surface tracking of arcing discha...

MEDIUM AND HIGH VOLTAGE WIRES AND CABLES What are the types of conductors/cables used for power distribution? There is no consensus among standard governing bodies like (i.e., IEC, ANSI, IEEE, UL, NEC and others) concerning the classification of voltage level.Thus, for clarity of this manual we will utilize IEEE voltage level classifications wherein 601V to 69,000V is medium voltage and 69,001V to 230,000V is high voltage.Furthermore, conductors are also classified according to their degree of insulation covering (i.e. bare, covered, and insulated). Basically, construction of the wires and cables is the same or similar for medium and high voltage applications. Bare Conductors Bare conductorsare those without covering and primarily used for overhead power transmission and distribution application. Insulating medium is air wherein the conductors are spaced from each other and any grounded object based on the system voltage. Insulators (e.g. porcelain, glass, and polymers) are used to ...

WIRE/CABLE MANUFACTURING PROCESS What are the steps/procedures in manufacturing wires/cables? Copper and aluminum rods undergo several stages of processing beforethey become wires and cables. Below are the processes in manufacturing conductors arranged in order. Drawing Drawing is the process of pulling thecopper or aluminum rods or wires at normal temperature through a die to reduce the cross-sectional area in order to get the desired dimension. The wire is deformed due to the tapering of the die and the force exerted during pulling. Annealing Annealing is the processof "softening" the temper of the wires and improving its cold working properties and machinability through sustained heating at a pre-determined temperature followed by coolingat a defined rate.There are many ways of annealing a wire; the most common practices in annealing copper is the continuous strand or resistance annealing wherein annealing is done by means of a machine placed between the final capstan ...

CABLE/CONDUCTOR MATERIAL CONSIDERATIONS What are the factors considered in making electrical conductors? There are several high conductivity metals that may be used as conductor. A conductor is a metallic material which allows electric current to flow through it with less resistance. The best conductor material is silver but due to its high cost per unit weight and being one of the precious metals, it is not economical to use in the transmission and distribution of electricity. Comparatively, gold with its excellent corrosion resistance and lower resistivitythan aluminum is also a good conductor but, same as silver, is very costly. Resistance and Conductivity Resistance is the opposition of an object to the passage of electric current. For direct current, resistance isdependent on the material length, cross-sectional are and resistivity. The electrical resistance of a conductor is inverselt proportional t the cross-sectional area or diameter of a conductor. Weight Although aluminum...

CABLE DESIGN AND CONSTRUCTION Major Parts of a Power Cable Design An insulated cable appears to be a relatively simple electrical device but, in fact, it can be considered an electrical system with many components. To understand it, let us examine its components and basics of operation. For simplicity, the following discussion shall be confined to a single conductor cable. However, these fundamentals also apply to multiple-conductor cables. The basic components of an insulated cable are the following: Conductor - materials that transmits electrical energy. Shielding - also referred to as screening, are used for medium to high voltage cables. Basically, the use of this stress control layers is to achieve a symmetrical dielectric fields within the cable structure. For somevoltage level, shielding may be applied over the conductor. At higher voltage levels, it is applied over the conductor and the insulation. This results in the confining of all the voltage gradients to within the ...

STRANDING OF WIRES AND CABLES Various Ways of Stranding a Power Cable/Wire The conductor material may be either solid or stranded. A solid conductor is a single, solid strand of conductor for the whole length of the wire, while stranded conductor is composed of several strands of conductor concentrically wounded together over the whole length of the wire/cable. For the same cross-sectional area of a conductor, there are diameter differences between solid and various types of stranded conductors. This is an important consideration in the selection of connectors and in the methods of splicing and terminating. Largesizes ofsoild conductors are too rigid for many applications that the solution would be to aveasmaller wiresandstrand them together to form the conductor. There are several ways of stranding the wires together which is dependent of the type and temper of the metal used. The following subsections will discussthe most commonly used stranding for copper conductors. ...