RD
Frequency meters are instruments that are widely used for the measurement of the frequency in various power system applications. Frequency is a very critical parameter in the electrical system as system stability, equipment performance, grid reliability, power quality, and economic efficiency all depend heavily on system frequency. Hence …
A flexible AC Transmission system includes the use of power electronics for controlling the voltage and the power flow of the AC transmission system. The power electronics include controlled shunt and series reactive power such as static Var compensator, static compensator (STATCOM), Thyristor controlled series compensation system (TCSC) …
The dissolved gas analysis of a transformer also called transformer gas analysis is an essential process or technique through which the condition of the transformer and its life expectancy can be calculated. Periodic dissolved gas analysis or DGA test can forecast the faults present in the oil-insulated electrical …
Air blast circuit breakers are mainly used for high-voltage applications for fast circuit breaking and making. These breakers offer advantages like faster operation, suited for repeated operations, auto reclosing, unit-type multi-break construction, simple assembly and maintenance, etc. The air blast circuit breaker requires a compressor plant to maintain …
VRLA battery or valve-regulated lead acid is a type of lead acid battery that promotes minimum to no water addition maintenance, sealed in a structure with no acid leaks and no mists. It has a one-way valve to allow the escape of gas formed inside above a predetermined …
High voltage vacuum circuit breakers are essentially a switching device which are mostly used for frequent switching of medium voltage level alternating current circuits with vacuum as the dielectric and interrupting medium. The advantage of vacuum in the interrupter is basically because of its high dielectric strength ranging …
The high voltage DC power line transmission is a system in which the bulk power is transmitted over long distances using direct current at a much-elevated voltage level. For long-distance transmission, the conventional AC system incurs various power losses making it an expensive mode of transmission. However, high …
Electrical continuity essentially means that there exists a conductive part, through which electricity can flow sufficiently. Electrical continuity can present itself in the insulated electrical part making it unsafe for further operation or is a much-needed aspect for the conductors for efficient propagation of electricity into any circuit. …
A smart meter is an electronic device that keeps a record of energy consumption, and electrical parameters like voltage levels, current, power factor, etc. These meters have a built-in communication channel through which it can communicate both ways between the meter and a central system. This communication can …
An uninterruptible power supply or UPS is a much-needed system for catering reliable, uninterrupted, high-quality power to vital loads such as data centers, critical health care support equipment, domestic equipment, and many more. Uninterruptable power supply is mostly a backup to the main power source from the utility …
Air Circuit Breaker (ACB) Air circuit breaker is the simplest form of circuit breaker. In this circuit breaker, the interruption of the arc is mainly based on the natural deionization of gases by a cooling action and lengthening of the arc. Working Principle The working principle of the …
Design Parameters for EARTHMAT DESIGN 132 KV Reference Standard IEEE – 80 – 2000 Resistivity Data for EARTHMAT DESIGN 132 KV SS Soil Resistivity, ρ = 90 Ω m Surface layer resistivity, ρs = 3000 Ω m Surface layer thickness, hs =0.10 m Reflection factor between different resistivities …
Thermographic inspection Thermographic inspection is a nondestructive testing method, part of the maintenance schedule that is applied in different sectors. The power sector is one of them, and its use is quite widespread. It is applied to all types of facilities and voltage levels. Although, thermographic inspection points …
Grounding conductors selection and connecting leads selection should be done considering the design life of the substation and should meet the following requirements Good conductivity. There should be no major local potential difference on the grounding conductor caused by its self resistance. In the worst scenario of the …
Tower Grounding Device A transmission line tower footing is usually made from reinforced concrete, and the tower footing itself is effective as a tower grounding device. Since, the size of the high-voltage steel tower essentially requires a very large tower footing base, the grounding resistance that is required …
Ground Rods In a high soil resistivity area, it is very difficult to meet the requirement of grounding resistance. Especially in gas-insulated substations or small-sized substations, these can be used to decrease the grounding resistance. A vertical ground rod, of large size is also useful in domestic earthing. …
Requirement for a Tower Grounding Device The grounding devices for the transmission tower and distribution tower are used to direct any lightning current and power-frequency short-circuit currents into the earth. They are designed to maintain suitable lightning protection levels for transmission and distribution lines and ensure the safety …
Methods for decreasing grounding resistance Decreasing grounding resistance of a grounding system decreases the maximum ground potential rise, it also can decrease the maximum transfer potential. During a earth fault, a serious hazard may take place from transfer of high potential from the substation’s grounding grid to outside …
Methods for improving the safety of grounding system If calculations based on the initial design of the grounding system indicate that dangerous potential differences can exist within a substation, the following remedies should be studied and applied where appropriate for improving the safety of grounding system. Decrease the …
Fault Current Division Factor During an earth fault in the substation, be it local or remote, the earth is used as a path for the fault current to reach the neutral of the power system. Part of this earthing grid current flows to the earth, the ratio between …
Decrement Factor for grounding design Decrement factor Df is basically the ratio between the rms value of the asymmetrical fault current and the symmetrical grounding fault current. IG is the maximum asymmetrical alternating current flowing from the grounding grid to the surrounding earth, which includes the rms symmetric …
Principle to Determine Maximum Grounding Grid Current The maximum grounding grid current to earth refers to the maximum fault current which flows into the earth through the grounding grid under the fault conditions within the substation, or which flows into the grounding grid from the earth when the …
Data Required for the Design of Earth Mat of a Substation (i) Soil resistivity model for the site of the substation or soil resistivity test data where earth grid or earth mat has to be constructed. (ii) Electrical circuit single line diagram for the station where earth grid …
Soil treatment for reducing earth resistance It is quite hard to achieve the required reduction in ground resistance by adding more grid conductors or ground rods to the earth grid. A probable alternative is to effectively increase the diameter of the electrode by modifying the properties of the …
ELECTRIC SHOCK An electric shock or accident is normally determined by the frequency, magnitude, and duration of the current flowing through the vital parts of a human body, generally referred to as the heart. When the current passes through the heart it results in ventricular fibrillation, and when …
GROUNDING RESISTANCE Grounding resistance is the ratio between the difference of potential of the grounding device to the earth and the current flowing to the earth through the grounding device. It is related to the soil characteristics and the size and shape of the used grounding device. COMPONENTS …
Reducing Insulation Level of Electrical Equipment by Effective Grounding Under normal situations, the voltage on the insulation of a power apparatus such as a power transformer is the phase voltage. Considering the neutral point is insulated when the single-phase grounding fault occurs, the voltage on the insulation of …
Electrical Earthing practices adopted at various stages of the power system are of great importance. The codes of practice, Technical Reference books, and Handbooks contain a chapter on this subject but they are often skipped considering them as elementary or even as unimportant. Reference books on this subject …
Safety Clearances There are many different values used for the insulation and safety clearances used by different utilities throughout the world. These clearances have been derived in many different ways, sometimes not following any particular logic related to the operational voltages. The method adopted commonly uses a common …
Substations presents a significant risk to personnel, working on electrical powered equipment, particularly from electric shock. Consequently, the design of electrical substations has always had to take into account the relevant safety techniques for live bare equipment to protect people who may be building, or commissioning an equipment, …
Site Selection of a Grid Substation The site selection of a Grid Substation is the first and most important activity. This needs meticulous planning, foresight, skillful observation, and handling so that the selected site is technically, environmentally, economically, and socially optimal and is the best suited to the …
The optimum arrangement for capacitor bank depends on the best usage of the available voltage ratings of capacitor units, fuses, and protective relaying. Nearly all substation units are linked wye/star. Distribution capacitor units, nevertheless, may be linked wye or delta. Some units utilize an H arrangement for capacitor …
Shunt capacitor Banks Shunt capacitor Banks or SCBs are typically used to deliver capacitive reactive power compensation or power factor correction. The use of shunt capacitor units has been quite advantageous because it being quite affordable, simple to install and commission, and can be placed anywhere in the …
Energy Stored in a Capacitor Charging of a capacitor means transferring electrons between the plates of the capacitor through the dielectric medium. This process of electron transfer is possible only at the expense of energy because the electrons have to be moved against the opposing forces in the …
Leakage Resistance of a Capacitor The resistance of the dielectric of the capacitor is called the leakage resistance of a capacitor. The dielectric medium in the ideal capacitor is considered a perfect insulator (i.e., it has infinite resistance), with zero current flowing through it when a potential difference …
Potential Gradient in a Cylindrical Capacitor The dielectric stress at any point in a cable is in fact the potential gradient (or electric intensity) at that point. Under operating conditions, the insulation of a power cable is subjected to electrostatic forces. This is known as dielectric stress. Mathematical …
Cylindrical Capacitor Two co-axial cylinders separated by an insulating medium is a basic cylindrical capacitor. A single-core cable is a practical example of a capacitor of this kind. The conductor (or core) of the cable is the inner cylinder while the outer cylinder is represented by the lead …
Capacitance of Parallel-Plate Capacitor The capacitance of a capacitor can be calculated from its electrical properties using the relation C = Q/V. However, at times it is desirable to calculate the capacitance of a capacitor in terms of the dimensions and relative permittivity of the dielectric or insulating …
Capacitance of an Isolated Conducting Sphere The capacitance of sphere, an isolated spherical conductor can be calculated by assuming that the “missing” plate is Earth (zero potential). Let us consider an isolated sphere of metal with a radius r is placed in a medium of relative permittivity ɛr. …
When an electric current is passed through a conductor, heat is produced in the conductor because of the resistance to the flow of current. This effect is called the heating effect of electric current which is discussed below. Cause of Heating When a potential difference is applied across …
Capacitors generally are made of two conducting surfaces (say metal plates) that are separated by an insulating material (e.g., air, mica, paper, etc.). The dielectric media has the property to store electrical energy in the form of electrostatic charge. Different media hold different charges on the application with …
Series Circuit The circuits where many resistances are connected end to end so that the current flows through only one path is popularly called a series circuit. Consider the resistances R1, R2, and R3 ohms that are connected in series across a battery source of V volts as …
Parallel Circuit A parallel circuit is among the basic electrical circuits in which each end of the resistances are joined to form two common points so that there are as many paths for the electric current to flow through as the number of resistances connected. Consider resistances R1, …
Nonlinear resistors A nonlinear resistor is a circuit element that shows nonlinearity in opposition to the current or, whose V/I characteristic is not a straight line and exhibits a resistance that is nonlinear in nature. Various examples of nonlinear resistors are thermistors, varistors, diodes, and filaments of incandescent …
In general, the electrical resistance of a material changes with the change in temperature. The effect of temperature on resistance varies according to the type of material as discussed below EFFECT OF TEMPERATURE ON RESISTANCE OF PURE METALS The effect of temperature on resistance is such that the …
As we have already discussed the electrical resistance in detail in the previous article, we shall proceed with the discussion on different type of resistors. Carbon Composition It is a type of resistor, which is a combination of particles of carbon and a binding resin with varying proportions …
Electrical Resistance may be defined as the property of a substance due to which it opposes or restricts the flow of electricity or its transmission i.e., electrons passing through it. Metallic classes, acids, and solutions of salt can conduct electricity efficiently. However, among the pure metals, silver, copper, …
The CT core sizing depends on the relay consideration for the feeder protection. FOR METERING CT CORE SIZING: The CT can be a multi-radio CT and the turns ratio or CTR can be calculated based on the estimated load/demand/requirement in the feeder. Also to take into consideration the …
The relay selection for transmission line protection utilizes one of the two major relaying philosophies. One is distance protection and the other is differential protection. Both of these protection philosophies are discussed in detail in previous posts. The other relays such as an overcurrent and earth fault relay …
PROTECTION CORE OF CT It is known that current transformers are used for protection and metering purposes. A current transformer or CT can have more than one core in the case of a multi-core CT that is normally used in power stations. One is used for metering purposes, …
INSTRUMENT SECURITY FACTOR OF CT Instrument security factor, ISF is the times of rated current above which the CT metering core will saturate. The ratio of the saturating primary current to the CT-rated current is known as the Instrument security factor. The multi-functioning meters or energy meters connected …
The burden of current transformer is basically the apparent power that is consumed at the secondary side at a specific power factor, rated secondary voltage, and current. It is because of the impedance/ admittance at the secondary circuit expressed in Siemens or ohm and power factor. Unlike a …
The accuracy class of Current Transformers used in the industry is designated by the highest permissible percentage ratio error at rated primary current and rated output. The RATIO ERROR in the accuracy class of current transformer The ratio error plays a major role in determining the accuracy class …
SIGNIFICANCE OF CT POLARITY Current transformer polarity is the direction of current in the secondary winding in relation to the primary current. It is often marked by square markings or P1 and P2. The polarity of the CT connection is of utmost importance in substation protection as the …
Step potential and touch potential are very essential factors in the designing of the earthing system of any substation. Step potential and touch potential also decide the overall safety of personnel working in the substation. As for humans, 25mA current can prove fatal hence calculation of step potential …
CONDUCTOR SIZING WITH IEEE-605 We have already discussed the busbar and the conductors in the previous articles. Now the essential part is to know how the conductor sizing is done for the main busbar of any substation. To explain this, we shall take the example of a 132KV …
MINIMUM PERMISSIBLE BENDING RADII OF CABLE LAYING. The electrical power cables should not be bent in a very sharp radius in the process of cable laying. The minimum bending radius for cable laying as per IS-1255 is listed below. It is to be noted that D is the …
CABLE SELECTION CRITERIA The design is based on a minimum of three factors: Short circuit current rating: It is the most important part of the cable selection criteria. It basically is the maximum current that the cable has to handle in case of a fault until the fault …
PVC CABLES: INSULATED (HEAVY DUTY) ELECTRIC CABLES These PVC cables are generally used up to & including 11 kV installations. The insulation material used is polyvinyl chloride (PVC) and conductors are made from electrical-grade aluminum or copper. To give flexibility, the conductors of PVC cables are stranded. The …
CLASSIFICATION OF ELECTRICAL CABLES The constructional feature of electric cables has been discussed in the previous article POWER CABLE CONSTRUCTION EASY EXPLANATION101, here, we shall proceed to discuss the electrical cable classifications. Classification based on application Wiring cables These electrical cables are used for internal wiring of the …
POWER CABLES Power cables are basically insulated conductors which carry electricity. Insulation is provided to the conductor for it to not be grounded or electrically shorted with some other conductors. Mostly, power cables are classified on the basis of insulation. The insulating material is the single most important …
The high-temperature low sag conductors find their application in the transmission sector, distribution sector. A detailed description of the application guide is cited below along with the possible areas where the application of these conductors can be avoided. APPLICATION IN TRANSMISSION SECTOR (a) Those utilities have a large …
KNEE POINT TEMPERATURE When the temperature of a composite conductor is increased, the aluminium (or aluminium alloy) envelope wires usually expand at a higher rate than the core. This expansion is accompanied by a corresponding reduction in its share of the total tensile load on the conductor. With …
DIFFERENT TYPES OF HTLS CONDUCTORS As discussed in the last article about the manufacturing of HTLS conductors. A brief overview of HTLS conductors produced on different combinations of core and envelope is emphasized here. As per our last discussion, it is seen that the high-performance conductors are made …
HIGH-TEMPERATURE LOW SAG HTLS CONDUCTORS The full form of HTLS conductors is HIGH-TEMPERATURE LOW SAG conductors. Manufacturing of HTLS conductors becomes essential as the conventional conductors used in the power industry are now being saturated to their capacity. Any further increase in the ampacity of the line will …
POWER CONDUCTORS Power Conductors are the most essential part of the transmission and distribution of electricity. It is the medium via which the current flows. Normally it is made of copper or aluminium alloy as these metals have proven good service and have less resistivity and cost. TYPES …
POWER CLAMPS Electrical energy flows through many equipment and various lines to reach the end consumer or load. In this process, it requires many terminations of conductors to all the equipment it passes through. This termination is made possible through the use of various clamps and connectors that …
KNEE POINT VOLTAGE OF A CURRENT TRANSFORMER As we know from our previous discussions the function of a current transformer is to translate the current of its primary winding into a proportional value of current in the secondary winding. This stepping down of current from higher primary values …
CT SATURATION: In the ideal scenario of the operation of a current transformer, the secondary current of the CT, (Is) is directly proportional to its primary current (Ip). However, in the case of saturation of the CT, the proportionality does not remain the same. Let us discuss why. …
RESTRICTED EARTH FAULT PROTECTION The most vital and important protection for a transformer is the biased differential relay protection of the transformer, which is discussed in detail in previous articles. It provides excellent protection against phase-to-phase faults and phase-to-earth faults within the differential zone of protection. It covers …
OVER FLUXING PROTECTION OF TRANSFORMER In transformer design practice the rated value of flux density is 1.7 to 1.8 Tesla. However, the saturation flux density of the CRGO steel sheet is of the order of 1.9 to 2.1 Tesla. This means the transformer core can handle a flux …
Supply of continuous electricity is the main moto of power generation, transmission and distribution. However, from our previous discussions, it is known to us that a continuous supply of power is an ideal case. Auto recloser is therefore a relay that functions to reclose the contacts of a …
STUB PROTECTION: It is basically an in-built function of a distance relay. It falls under the auxiliary part of the distance relay. It is mostly used in one-and-half-bus bar schemes. As we already know from our previous article on the bus bar scheme in one-and-a-half bus bar schemes, …
MULTIPLICATION FACTOR OF ENERGY METERS We generally use a Special energy meter for keeping the count of energy flowing through the system. The meter we use has an input connection from the current transformer’s metering core’s secondary side. With current input, we also provide the voltage input to …
ENERGY METER The meter used for the measurement of electrical energy consumed by loads is called an energy meter. Generation, Transmission, or distribution stations from where energy is transmitted in bulk need to keep a measurement of the energy transmitted, and hence special energy meters are often found …
OLTC On-load tap changers have been in the power industry for quite a long time now. On-load tap changer is a device that is used for voltage regulation and phase shifting of a transformer without power interruption. The tap changing is used mainly to change the turns ratio …
CARRIER AIDED PROTECTION The main aim of electrical power transmission is to maintain an uninterrupted power supply of electricity to all consumers. Electrical faults however cause interruption of supply. When the fault is detected by the protective relays, the fault current is interrupted by the circuit breaker. In …
The trip circuit supervision relay is one of the most important parts of the protection scheme. It is mounted in the Control and Relay panel in a substation. To isolate a fault in the power system, the protective relay senses the fault and gives command to the trip …
MASTER TRIP RELAY A master trip relay is an auxiliary relay used in the control and relay panel of a substation or any plant. It is a very essential part of the control and protection scheme of any substation. It offers high reliability and high contact ratings with …
BAY CONTROL UNIT The term BCU refers to the Bay Control Unit. It is a unit of the control and relay panel that is used for several purposes in power system operations which are described below. The Bay control unit is required as it performs various bay operations …
Temperature indicator As we know from the previous posts the transformer is the most important instrument in the power system. Therefore, any abnormalities in its operation impact the overall efficiency of any plant majorly. Temperature indicators are therefore used to monitor the internal condition of the transformer. There …
PRESSURE RELIEF VALVE OF A TRANSFORMERS or PRV A pressure relief valve of a transformer or PRV is a mechanical safety device used for the protection of transformers, on-load tap changers OLTC and other similar equipment which can release the excess pressure inside them because of various reasons. …
A protective relay works like a brain in the power system. It collects the electrical parameters from the field and computes them, senses faults, takes decisions, and gives output to the associated circuit breaker to isolate the faulted section. Protective relays can be broadly classified into three types. …
Buchholz relay is a mechanical device that is utilised in the protection of any transformer above 750 KVA rating. It is a gas-actuated device used in oil-immersed transformers for protection and alarm against any incipient faults. Incipient faults are those faults which are slowly developing. Buchholz relays have …
A fault that involves the ground is called an earth fault. Examples are—single line-to-ground (L-G) faults and double line-to-ground (2L-G) faults. Faults that do not involve ground are called phase faults. The protective scheme used for the protection of an element of a power system against such faults …
Directional Relay A directional relay is one which is actuated by two electrical parameters namely current and voltage. The directional elements in the relay help the relay recognize the forward electrical faults and not the faults behind the relaying point. This feature can be best explained with the …
OVERCURRENT PROTECTION RELAY Earlier in the history of power system protection in the name of overcurrent protection fuses were commonly used. However, they are still in use for overcurrent protection in LT lines of distribution networks. Nowadays all relays have turned numerical and digital, electromechanical ones are obsolete. …
Differential protection Differential protection is a relaying scheme used to protect an element of a power system from electrical faults. The differential protection scheme utilizes the vector difference of two or more similar electrical parameters and compares it to a preset value. If the preset value is exceeded …
Distance protection It is basically a non-unit form of protection in the power system. It is economical and offers technical benefits. Unlike the phase, neutral overcurrent protection the key advantage of distance relay protection is that the fault coverage of the protected circuit is virtually independent of source …
Local breaker backup LBB Local breaker backup or LBB protection is a circuit breaker failure scheme that operates to protect or limit the fault current from penetrating more into the system and causing equipment damage. A circuit breaker is required to clear the faults in the system or …
Disconnector or Isolator: In the substation, the disconnector / Isolator does the same work as the circuit breaker do i.e., isolation of the circuit from the power supply. But the difference is that initially automatic circuit isolation/ tripping is achieved by a circuit breaker or CB due to …
Lightning Arrester Though the earthing screen and ground wires provide protection to the electrical system against direct lightning strokes, they cannot provide protection against the indirect travelling waves resulting from lightning strokes or switching surges which can potentially reach the terminal of the electrical apparatus causing damage. The …
Potential Transformer: Any electrical equipment is sized based on its operating voltage. The higher the voltage, the more insulation will be used for a safe operation. The usage of more insulation thus adds to the cost of the equipment and size of the equipment. That means the bulkiness …
Current Transformer: A Current transformer is a type of instrument transformer that is used to step down the current of the primary side to a minimal value on the secondary side for ease of metering using standard ammeters and for protection purposes. As nowadays most relays are numeric …
An ideal transformer is one with NO energy loss. But in practice, Transformers do undergo power losses due to various reasons. As the electrical transformer is a static device, kinetic loss in the transformer normally does not come into the picture. We generally consider only electrical losses and …
Mineral oil is commonly referred to as ‘Insulating oil’ or ‘Transformer Oil’. Though it is widely used not only in transformers but also in a variety of electrical equipment it is still referred to as transformer oil. Because of this reason referring to electrical quality mineral oil as …
Distribution of electricity starts from the sub-transmission level in some countries. It starts from a voltage level lower than 66KV. Distribution of electricity is often undertaken by discoms. The distribution of electricity plays a very critical role in shaping any economy. Distribution transformer plays an important role in …
Electrical Insulators are components of electrical power systems through which electric current cannot flow. This is possible due to a physical property of such material known as resistivity, which restricts the flow of electrons through it. Insulators have higher resistivity than conductors and semiconductors. However, there is no …
What is MCB (Miniature Circuit Breaker) Miniature Circuit Breakers (MCBs) are very important components in electrical systems nowadays, it offers enhanced safety and operational convenience compared to electrical fuses. Unlike fuses, which require manual replacement after they melt due to overcurrent, Miniature circuit breakers work as automatic switches …
Automatic Switch/Circuit Breaker The Basic Principles of Circuit Breaker: – The simplest circuit-interrupting device is the switch. By closing the switch against the action of a spring, we have an automatic device in which the energy for opening the contacts is stored by the closing operations. Here only …
