Differences Between Indoor And Outdoor Sub Station 2144d

Differences Between Indoor and Outdoor Sub Station  Capital Cost : The Capital required to install indoor substation is very high because a lot of buildings are to be manufactured in case of Indoor substation while the capital required for outdoor sub station is small as compare to Indoor sub station.  Civil Work : In case of Indoor substation, first we have to prepare building to host larger electrical equipments like Transformers and have to make cut outs for power cables that are bringing power to the sub station. these requires a lot of civil work and hence increasing time required to install the sub station in opposition to this only a small construction work is required in outdoor sub stations.  Fault Location : Indoor substations are very compact in arrangement and hence if there is any fault then the location of fault become very difficult while in outdoor sub stations the equipments are placed at different locations so the fault can be sensed easily.  Future Expansion : In Indoor sub stations the buildings are constructed according to the size of present transformer so if in future we want to increase the rating of sub station then we have to demolish or make some civil works in the building to host new transformer while in outdoor substations transformers are placed outside so they may be replaced by just increasing the area of fencing.  Safety : Indoor substations are more safe as they restrict the entry of animals or any unauthorized person near the transformer while outdoor substations are not much safe.  Appearance : Indoor sub stations looks good because there is not and electrical equipment that is visible from outside while in outdoor sub stations appearance is not very good.

 Maintenance : Maintenance of Indoor substation is not easy. It require both time and specialized labor so it is costly while maintenance of outdoor substation is cheap. Distribution Feeder Systems Let’s take a look at the four most common distribution feeder systems applied nowdays. There are few other variations, but we will stick to the basic ones. It’s very important to understand why and where each of distribution feeder systems (topologies) are used, because whatever you do (design of secondary substations, performing testing of secondary switchgears or transformers or planning etc.) this would be the very first thing to know. So, these are the distribution feeder systems we’ll speak about // 1. Radial 2. Parallel feeders 3. Ring main 4. Meshed systems 1. Radial Many distribution systems operate using a radial feeder system. A typical radial feeder system is shown schematically in Figure 2. Radial feeders are the simplest and least expensive, both to construct and for their protection system. This advantage however is offset by the difficulty of maintaining supply in the event of a fault occurring in the feeder. A fault would result in the loss of supply to a number of customers until the fault is located and cleared. The next level of reliability is given by a ‘parallel feeder’ system.

3. Ring main A similar level of system reliability to that of the parallel arrangement can be achieved by using ring main feeders. This usually results from the growth of load supplied by a parallel feeder where the cabling has been installed along different routes. These are most common in urban and industrial environments. Whilst the start and finish ends of the ring are at the same location, power is delivered by both pathways of the ring into substations located around the ring. Should a fault occur on a feeder cable at any point around the ring the faulty section may be isolated by the operation of the protecting circuit breakers, at the same time maintaining supply to all substations on the ring. In typical urban / suburban ring main arrangements, the open ring is operated manually and loss of supply restored by manual switching.

Figure 4 – A ring main feeder system Current practice is to use distribution automation, where operation and supply restoration in the feeder rings is done automatically by centrally controlled supervisory systems. This gives the advantages of ring main systems as line voltage drops are reduced at the various load substations there is a ‘firm’ supply (i.e. an alternative path is available if the primary one fails) to each load substation. Equipment for substations :The power system is a constituent of power generation, transmission and

distribution systems. For all the power system operations, substations are required for their course of action. Substations are congregation of electrical equipment through which consumers get supply of electrical power from generating stations. By varying the voltage levels or frequency or any other aspects, the required electrical quantity can be altered in substations to provide quality power to consumers Based on the application of substations, they are classified into different types: Generation substation, Indoor substation, Outdoor substation, Pole mounted substation, Switching substation, Transmission substation, Converter substation and Distribution substation. In rare cases like wind farm power generation system, multiple hydroelectric and thermal power plants one can observe the collector substation which is used for transferring power from multiple turbines into one transmission unit. The substation is an assembly of the following major electrical equipments:  Electrical Power transformers  Instrument transformers  Conductors& Insulators  Isolators  Bus bars  Lightning arresters  Circuit breakers  Relays  Capacitor banks and miscellaneous equipment Electrical Power Transformer

Electrical Power transformer

A static electrical machine used for transforming power from one circuit to another circuit without changing frequency is termed as Power transformer. The transformers are generally used to step down or step up the voltage levels of a system for transmission and generation purpose. These transformers are classified into different types based on their design, utilization purpose, installation methods, and so on. Instrument Transformers:

Instrument transformers The current and voltage transformers are together called as the Instrument transformers. Current Transformer Current transformer is used for the measurement of the alternating current by taking samples of the higher currents of the system. These reduced samples are in accurate proportions with the actual high currents of the system. These are used for installation and maintenance of the current relays in substations for protection purpose which are normally have low-current ratings for their operation. Potential Transformer Potential transformer is quite similar to the current transformer, but it is used for taking samples of high voltages of a system for providing low-voltage to the relays of protection system and also to the low-rating meters for voltage measurement. From this low-voltage measurement, the actual system’s high voltage can be calculated without measuring high voltages directly to avoid the cost of the measurement system. Conductors The material or object that obeys the electrical property conductance (mostly made of metals such as aluminum and

copper) and that allows the flow of electric charge is called conductor. Conductors permit free movement of the flow of electrons through them. These are used for the transmission of power or electrical energy from one place (generating station) to another place (consumer point where power is consumed by the loads) through substations. Conductors are of different types and mostly aluminum conductors are preferred in practical power systems. Insulators The metal which does not allow free movement of electrons or electric charge is called as an insulator. Hence, insulators resist electricity with their high resisting property. There are different types of insulators such as suspension type, strain type, stray type, shackle, pin type and so on. A few types of insulators are shown in the above figure. Insulators are used for insulation purpose while erecting electric poles with conductors to avoid short circuit and for other insulation requirements. Isolators Isolator is a manually operated mechanical switch that isolates the faulty section or the section of a conductor or a part of a circuit of substation meant for repair from a healthy section in order to avoid occurrence of more severe faults. Hence, it is also called as a disconnector or disconnecting switch. There are different types of isolators used for different applications such as single-break isolator, double-break isolator, bus isolator, line isolator, etc. Bus bars The conductor carrying current and having multiple numbers of incoming and outgoing line connections can be called as

bus bar, which is commonly used in substations. These are classified into different types like single bus, double bus and ring bus. Lightening Arresters The substation equipments such as conductors, transformers, etc., are always erected outdoor. Whenever light surges occur then, a high-voltage through these electrical components causing damage to them (either temporary or permanent damage based on the amount of voltage surge). Therefore, to avoid this difficulty, lightening arresters are placed to the entire lightening surges to earth. There are other arresters which are used to ground the switching surges called as surge arresters. Circuit Breakers For the protection of substation and its components from the over currents or over load due to short circuit or any other fault the faulty section is disconnected from the healthy section either manually or automatically. If once the fault is rectified, then again the original circuit can be rebuilt by manually or automatically. Different types of circuit breakers are designed based on different criteria and usage. But in general mostly used circuit breakers are Oil circuit breaker, Air circuit breaker, SF6 circuit breaker, Vacuum Circuit Breaker, and so on. Relays Relays are used for disconnecting the circuits by manual or automatic operation. Relay consists of the coil which is excited or energized and such that making the s of relay closed activates the relay to break or make the circuit connection. There are different types of relays such as over current relays, definite time over current relays, voltage relays, auxiliary relays, reclosing relays, solid state relays, directional relays,inverse time over current relays, microcontroller relays, etc. The above figure shows some basic relays and their operation.

Capacitor banks A Capacitor bank is a set of many identical capacitors connected in series or parallel within a enclosure and is used for the power factor correction and basic protection of substation.These capacitor banks are acts as a source of reactive power, and thus, the phase difference between voltage and current can be reduced by the capacitor banks. They will increase the ripple current capacity of the supply. It avoids undesirable characteristics in the power system. It is the most economical method for maintaining power factor and of correction of the power lag problems. The electric power can be transmitted either by means of d.c. or a.c. Each system has its own merits and demerits. 1. D.C. transmission. For some years past, the transmission of electric power by d.c. has been receiving the active consideration of engineers due to its numerous advantages. Advantages. The high voltage d.c. transmission has the following advantages over high voltage a.c. transmission : 1. It requires only two conductors as compared to three for a.c. transmission. 2. There is no inductance, capacitance, phase displacement and surge problems in d.c. transmission. 3. Due to the absence of inductance, the voltage drop in a d.c. transmission line is less than the a.c. line for the same load and sending end voltage. For this reason, a d.c. transmission line has better voltage regulation. 4. There is no skin effect in a d.c. system. Therefore, entire crosssection of the line conductor is utilized. 5. For the same working voltage, the potential stress on the insulation is

less in case of d.c. system than that in a.c. system. Therefore, a d.c. line requires less insulation. 6. A d.c. line has less corona loss and reduced interference with communication circuits. 7. The high voltage d.c. transmission is free from the dielectric losses, particularly in the case of cables. 8. In d.c. transmission, there are no stability problems and synchronizing difficulties. Disadvantages 1. Electric power cannot be generated at high d.c. voltage due to commutation problems. 2. The d.c. voltage cannot be stepped up for transmission of power at high voltages. 3. The d.c. switches and circuit breakers have their own limitations. 2. A.C. transmission. Now-a-days, electrical energy is almost exclusively generated, transmitted and distributed in the form of a.c. Advantages 1. The power can be generated at high voltages. 2. The maintenance of a.c. substations is easy and cheaper. 3. The a.c. voltage can be stepped up or stepped down by transformers with ease and efficiency. This permits to transmit power at high voltages and distribute it at safe potentials. Disadvantages 1. An a.c. line requires more copper than a d.c. line. 2. The construction of a.c. transmission line is more complicated than a d.c. transmission line. 3. Due to skin effect in the a.c. system, the effective resistance of the line is increased.

4. An a.c. line has capacitance. Therefore, there is a continuous loss of power due to charging current even when the line is open.