Source Of Mechanical Energy Engineering Essay
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Published: Mon, 5 Dec 2016
Electricity is a basic part of nature and it is one of our most widely used forms of energy. It is a secondary energy source that we get it from the conversion of other sources of energy, like coal, natural gas, oil, nuclear power and other natural sources, which are called primary sources. Many cities and towns were built alongside waterfalls (a primary source of mechanical energy) that turned water wheels to perform work.
Electricity consists of the presence of electric charges, as well as the flow of those charges. There are three forms of electricity. One form is static electricity, which is the presence of either positive (+) or negative (âˆ’) electric charges in or on an object, usually a non-conducting material. The second form of electricity is the flow or movement of free electrons through a conducting material, such as a metal wire, toward an area of positive electric charges
Electricity appears in two forms: alternating current (AC) and direct current (DC). Direct current does not change directions– the electron flow is always from the negative pole to the positive pole– although as we mentioned before, the electrons themselves don’t really “move,” it’s the holes that are created that “move.” Direct current is almost always what is used inside of electronic devices to power the various internal components, but it is a harmful thing in audio signals, which are alternating current.
Alternating current (AC) electricity is the type of electricity commonly used in homes and businesses throughout the world. While direct current (DC) electricity flows in one direction through a wire, AC electricity alternates its direction in a back-and-forth motion. The direction alternates between 50 and 60 times per second, depending on the electrical system of the country.
AC electricity is created by an AC electric generator, which determines the frequency. What is special about AC electricity is that the voltage can be readily changed, thus making it more suitable for long-distance transmission than DC electricity. But also, AC can employ capacitors and inductors in electronic circuitry, allowing for a wide range of applications.
Direct current or DC electricity is the continuous movement of electrons from an area of negative (âˆ’) charges to an area of positive (+) charges through a conducting material such as a metal wire. Whereas static electricity sparks consist of the sudden movement of electrons from a negative to positive surface, DC electricity is the continuous movement of the electrons through a wire.
A DC circuit is necessary to allow the current or steam of electrons to flow. Such a circuit consists of a source of electrical energy (such as a battery) and a conducting wire running from the positive end of the source to the negative terminal. Electrical devices may be included in the circuit. DC electricity in a circuit consists of voltage, current and resistance. The flow of DC electricity is similar to the flow of water through a hose.
Electrical wiring system is a network of electrical conductors for carrying electrical current to the electrical equipment involved. This method is related to the wiring system for buildings in Malaysia. In Malaysia, the electric wiring system is subject to the rules established by the Energy Commission as provided under the Electricity Supply Act 1990, Electricity Regulations 1994, the MS IEC 60364:2003 Standard ‘Electrical Installations of Building’, MS 1936:2006 ‘ Electrical Installations of Building – Guide To MS IEC 60364 ‘and the MS 1979:2007 “Electrical Installation of Building – Code of Practice’. Wiring systems used in Malaysia is very similar to the electrical wiring standards used by the United Kingdom but by the standards of the wire conductor already changed.
NEW TOWN DEVELOPMENT SDN BHD PROJECT
The high-rise building electrical system
For The New Town Development Sdn Bhd project, this building was a high-rise commercial building. The building comprises of 4 storey basement parking and 7 storey shopping complex and the rest are offices lot. So, for the electrical installation should at every floor there were a number of electrical panels to serve all the lighting and power requirements on that floor including the lighting, switched socket outlets, toilet exhaust fans and anything else.
Some areas of the office used an open floor office systems so under floor trunking was also used here. Besides, a few of the panel were located inside the riser room of each floor. However, since each was a large area some panels needed to be located at the office area. Wiring directly from the electrical riser would be unnecessarily too long.
Therefore, the electrical consultant locates these electrical panels along the corridors throughout the building. The design architect was requested to provide small rooms to house the panel. Alternatively, small electrical cabinets with lockable doors and sufficient work access and ventilation would be acceptable.
If the planned building is very high example like 40 storey office building or in cases where heavy loads are located at higher levels of the building, it may be necessary to provide substations at the higher levels of the building.
For the 40-storey office building, an 11/415 kV substation may be necessary at one of the upper floor. It may be located at twentieth floor, for example. All the electrical substation room spaces as explained earlier will then need to be provided except the authority’s electrical rooms. The floors of this substation would then need to be specifically designed by the appointed structural consultants to handle the loads of all the substation equipment.
Based on the structures and other factors was related. We propose the installation of electricity for this building using the radial system and ring main system. Because it’s easier to maintain and simple system for the design and construction. In addition, using the rising main distribution system is important because the building is more than 5 levels. So, to distribute electric power at every level is appropriate to use the ‘rising main’ for the building.
A basement is one or more floors of a building that are either completely or partially below the ground floor. Basements are typically used as a utility space for a building where such items as the furnace, water heater, breaker panel or fuse box, car park, and air-conditioning system are located; so also are amenities such as the electrical distribution system, and cable television distribution point.
In British English the word “basement” is used for underground floors of, for example, department stores but is used for a space below the ground floor of a house only when it is habitable, with windows and (usually) its own access. The word cellar is used to apply to any such large underground room. Subcellar is a cellar that lies further underneath.
Based on the planned building project, the level of 1st to 4th is the basement. In part this is a car park. Therefore, we recommend the installation of electricity in the area using ring system. Ring system is ideal because in this part do not use electrical appliances and many others.
Basement car parks.jpg
Ring Main System in Basement
A ring main wiring circuit is the alternative to a radial wiring circuit. In a radial wiring circuit, the wiring starts at the circuit breaker and connects to each device on the circuit (fans, outlets, lamps, etc) in turn. When it reaches the last device, the wiring simply ends.
Ring main wiring goes one step further instead of ending the wiring at the last device; it pulls more wiring back from the last device to the circuit breaker, completing a loop. Ring main wiring is required in some places, and illegal in others.
The main advantage to a ring main system is smaller wiring. Since each device on the ring has two hot wires connecting it to the circuit breaker (one on each side of the loop), smaller wiring can be used to safely carry the electric current. Smaller wire is both cheaper and easier to work with. It bends more easily, can be pulled around corners with less effort, and is easier to fit into the screws and connectors you need to attach it to.
One other advantage is wiring distance. Wire has some small amount of resistance, and the longer the wire goes to reach the device it is powering, the more resistance it has. This results in a voltage drop over the length of the wire run (by Ohm’s Law), which could affect the operation of your electrical devices if it drops too low. The maximum distance from the circuit breaker around the ring is the midpoint of the ring, while the maximum distance in a radial circuit is the end of the chain. In this manner, the ring setup effectively cuts the distance to the farthest device in half.
The radial system does have one advantage over ring main. If a break were to occur somewhere in the wiring loop of a ring main system, you wouldn’t know it. Everything would still function normally because it is still powered from one end. However, this means that if you took advantage of the ability to run smaller wiring (and everyone does), your wire is now undersized for the current it is expected to handle because the system is no longer powered from two wires, only one. This can result in overheating of the wires, which in turn breaks down the insulation and can start a fire.
In electricity supply, a ring final circuit or ring circuit (informally also ring main or just ring) is an electrical wiring technique developed and primarily used in the United Kingdom that provides two independent conductors for live, neutral and protective earth (ground) within a building for each connected load or socket.
Ring Main Distribution
Size of cable used to ring system is 2.5 mm2.
Installation Rules of Ring System at basement
Rules for ring circuits say that the cable rating must be no less than two thirds of the rating of the protective device. This means that the risk of sustained overloading of the cable can be considered minimal. In practice, however, it is extremely uncommon to encounter a ring with a protective device other than a 30 A fuse, 30 A breaker, or 32 A breaker, and a cable size other than those mentioned above.
The IEE Wiring Regulations (BS 7671) permit an unlimited number of socket outlets to be installed on a ring circuit, provided that the floor area served does not exceed 100 m2. In practice, most small and medium houses have one ring circuit per storey, but for this building should having more.
An installation designer may determine by experience and calculation whether additional circuits are required for areas of high demand; for example, it is common practice to put kitchens on their own ring circuit or sometimes a ring circuit shared with a utility room to avoid putting a heavy load at one point on the main downstairs ring circuit. A heavy concentration of load close together on a ring circuit can cause minor overloading of one of the cables if near the end of the ring, so kitchens should not be wired at one end of a ring circuit.
Unfused spurs from a ring wired in the same cable as the ring are allowed to run one single or double socket (the use of two singles was previously allowed but was banned because of people replacing them with doubles) or one fused connection unit (FCU). Spurs may either start from a socket or be joined to the ring cable with a junction box or other approved method of joining cables. Triple and larger sockets are generally fused and therefore can also be placed on a spur.
It is not permitted to have more spurs than sockets on the ring, and it is considered bad practice by most electricians to have spurs in a new installation (some think they are bad practice in all cases).Where loads other than BS 1363 sockets are connected to a ring circuit or it is desired to place more than one socket for low power equipment on a spur, a BS 1363 fused connection unit (FCU) is used.
In the case of fixed appliances this will be a switched fused connection unit (SFCU) to provide a point of isolation for the appliance, but in other cases such as feeding multiple lighting points (putting lighting on a ring through is generally considered bad practice in new installation but is often done when adding lights to an existing property) or multiple sockets, an unswitched one is often preferable.
Based on commercial building a project was planned by the New Town Development Sdn Bhd. A 40 storey high building will put the shopping complex of seven stories are starting at level 5th to 11th. Thus, the electrical installation for this we propose to use a radial system.
We feel the radial system is suitable for shopping complex. Because there are a lot of use of electrical appliances such as lights, air conditioners and so on. In addition, the radial system is easy to designed, built and maintained.
Shopping Complex at level 5th
Shopping Complex at level 5th – 8th
In this building project, a total of 29 levels will be provided for offices start from level 12th to 40th. Based on this, we agreed to use the same method of electrical installations such as shopping complexes, namely the radial system. This method is ideal because it is easy to maintain. In addition, if there is damage to the wire. It is easily known and easily repaired than the ring system.
Radial System in Shopping Complex and Offices
The radial system is widely used, economical systems often found in low-load density areas. To reduce the duration of interruption, overhead feeders can be protected by automatic reclosing devices located at the substation or at various locations on the feeder. This device reenergizes the feeder if the fault is temporary. To further reduce the duration and extent of customer interruptions, sectionalizing fuses are installed on branches of radial feeders allowing unaffected portions of a feeder to remain in service.
Radial distribution systems are the simplest systems to plan, construct, and maintain, but are also the least reliable because of the radial nature of the design being served from a single source at a time. If any part of the system experiences a failure, some or all of the customers served by the radial feeder will be without power until a repair is completed. Straightforward design, lower cost, and decent reliability are the distinguishing characteristics of the RDS.
An auto-loop distribution system is a special type of radial distribution system and is differentiated by having two feeders that tie to a customer load. The auto-loop system automatically senses the loss of one source of voltage and quickly and automatically switches the load to the second feeder. This type of system adds reliability benefits by keeping outages to a few seconds (or less) but the added cost of having two sets of utility equipment at one location, could be as high as hundreds of thousands of dollars for each installation.
Radial system distribution
Size of cable commonly used for circuit radius is 4 mm2
Rising Main Distribution for commercial building
For multi-storey buildings such as this are ideal to use the rising system. This is because, to ensure that each level of the building is fully supplied with electricity from renewable sources of electricity.
A “riser” is a feeding cable or pipe giving supply to upper floors of a multi-storey building (high rise building). The above picture shows a typical installation of bus duct rising mains in the riser room at individual floor of a high rise building (The Bus duct was taken in the riser room at one of the upper floors of a high rise building). Most of the major components of a bus duct riser system.
In electrical works, a riser is a set of cables the supply the upper floors. The feeding cables “rise” up straight to the top floor. Then at each floor a tap-off unit is connected so electricity can be supplied to that floor (for this project, we propose the radial distribution system). An alternative is to run one individual set of cables to each floor. Then there would be many cables that need to be installed the number of which is directly proportional to the number of upper floors.
There are actually three risers, first one is the “normal” main electricity supply. This supply is just the normal authority supply like the one you have in your house. The 100A tap off unit is for this riser. The second tap off, which is one of the 60A units, is what is called “essential supply”, or “emergency supply”. It is a normal authority supply like the one you have from the 100A tap off unit above.
However, it is also backed by a standby diesel generator. This means that if the electricity supply from the authority distribution network fails due to problem with their underground distribution cables or whatever, the standby electric generator would kick in and switch in the locally generated electricity to this electrical riser. Large capacity electric generators are expensive.
Therefore, it is not economical to supply all electricity needs in the building from this generator. That is why separate electrical risers are used, and the “normal” riser is not backed by the generator supply. The third tap off unit (the second 60A unit) is for the air conditioning system. It is quite common (and is considered a better design) to have a separate feeder cable for the air conditioning and mechanical ventilation (ACMV) system in a large building. That is the reason for the third electrical riser here.
rising main detail
Rising Main Distribution
Rising main distribution is use to distribute 415v 3-phase electricity from main distribution board to all floors. The copper vertical bus bars which run up in electricity cable riser. The vertical duct or trunking to the height of the building. To prevent the spread of fire and smoke, fire barriers are incorporated with the bus bar chamber at each compartment floor level.
One more point to note here is that some office buildings use the generator-backed supply example like essential supply to feed the electrical riser for the air-conditioning system. With this arrangement, ACMV equipment that need to continue operating even during the mains failure do not need to be connected to “ESSENTIAL” supply riser, which is why it is given a separate riser in the first place.
Observe the large flexible conduits coming out from the bottom of the tap off units and connect to the orange-colored electrical trunking. Some installations use rigid metal trunking for this purpose. Cables are run from a tap off unit into the flexible conduit to go to the orange metal trunking. They run inside the trunking to connect to the respective sub-switchboard.
The switchboard for the air conditioning system is normally located inside the AHU room of that particular floor. From the sub-switchboards, separate outgoing cables are run inside the trunking to connect to separate distribution boards (DB) on that particular floor. Even though electrical installations at hospitals are relatively much more complex than the office building above, the installation at their hostel and staff quarters buildings are usually very simple.
Typical bus duct rising main at individual building floors
The electrical riser room
Basically, there only two new components at each riser, which is the Termination Box (Feed In Box) and the incoming cables that terminate into the termination box. The generator-backed “Essential” supply cables need to have red colored insulation. It is because this supply is part of the fire emergency system of the building.
A fire-rated cable must be able to continue operating for a certain number of hours during fire before it fails. This is the requirement. It used to be MICC (mineral insulated copper cables) cables that play this role, but now people use mostly the “fire-rated cables” for this purpose except in very special installation condition. The fire-rated cables are cheaper, easy to install and maintain.
The black-colored cables are from the “Normal” supply. That means the other ends of the cables are connected to the “Normal Supply” main switchboard. While the red cables are connected to the “Essential Supply” main switchboard. Which means the “Essential Supply” main switchboard is the one that is backed by the standby electric generator.
The bus duct risers at riser room
The front view of one of the 60A TPN tap off units
A closer view of the vertical bus duct showing the arrangement of the conductors inside
Cables and busways
A busbar trunking system comprises a set of conductors protected by an enclosure. Used for the transmission and distribution of electrical power, busbar trunking systems have all the necessary features for fitting: connectors, straights, angles, fixings, etc. The tap-off points placed at regular intervals make power available at every point in the installation. A busbar trunking is placed at the offices.
Busbar trunking system design for distribution of currents from 25 to 4000A.
The various types of busbar trunking
Busbar trunking systems are present at every level in electrical distribution: from the link between the transformer and the low voltage switch switchboard (MLVS) to the distribution of power sockets and lighting to offices, or power distribution to workshops.
Radial distribution using busways at the offices
There are essentially three categories of busways that we proposed for the commercial building, that is;
1) Transformer to MLVS busbar trunking
Installation of the busway may be considered as permanent and will most likely never be modified. There are no tap-off points. Frequently used for short runs, it is almost always used for ratings above 1,600 /2,000 A, i.e. when the use of parallel cables makes installation impossible. Busways are also used between the MLVS and downstream distribution switchboards.
The characteristics of main-distribution busways authorize operational currents from1,000 to 5,000 A and short-circuit withstands up to 150 kA.
2) Sub-distribution busbar trunking with low or high tap-off densities
Downstream of main-distribution busbar trunking, two types of applications must be
Mid-sized premises (industrial workshops with injection presses and metalwork machines or large supermarkets with heavy loads). The short-circuit and current levels can be fairly high (respectively 20 to 70 kA and 100 to 1,000 A).
Small sites (workshops with machine-tools, textile factories with small machines,supermarkets with small loads). The short-circuit and current levels are lower (respectively 10 to 40 kA and 40 to 400 A). Sub-distribution using busbar trunking meets user needs in terms of:
Modifications and upgrades given the high number of tap-off points
Dependability and continuity of service because tap-off units can be connected under energized conditions in complete safety
The sub-distribution concept is also valid for vertical distribution in the form of 100 to
5,000 A risers in tall buildings.
3) Lighting distribution busbar trunking
Lighting circuits can be distributed using two types of busbar trunking according to whether the lighting fixtures are suspended from the busbar trunking or not.
Busbar trunking designed for the suspension of lighting fixtures
These busways supply and support light fixtures (industrial reflectors, discharge lamps, etc.). They are used in supermarkets, department stores and warehouses. The busbar trunkings are very rigid and are designed for one or two 25 A or 40 A circuits. They have tap-off outlets every 0.5 to 1 m.
Busbar trunking not designed for the suspension of lighting fixtures
Similar to prefabricated cable systems, these busways are used to supply all types of lighting fixtures secured to the building structure. They are used in commercial buildings (offices, shops, restaurants and etc.), especially in false ceilings. The busbar trunking is flexible and designed for one 20 A circuit. It has tap-off outlets every 1.2 m to 3 m. Busbar trunking systems are suited to the requirements of a large number of buildings.
Industrial buildings: garages, workshops, farm buildings, logistic centers, etc.
Commercial areas: stores, shopping malls, supermarkets, hotels, etc.
Tertiary buildings: offices, schools, hospitals, sports rooms, cruise liners, etc.
Examples of Canalis busbar trunking systems
Flexible busbar trunking not capable of supporting light fittings : Canalis KDP (20 A)
Rigid busbar trunking able to support light fittings : Canalis KBA or KBB (25 and 40 A)
Lighting duct : Canalis KBX (25 A)
A busway for medium power distribution: Canalis KN (40 up to 160 A)
A busway for medium power distribution: Canalis KS (100 up to 1000A)
A busway for high power distribution: Canalis KT (800 up to 1000 A)
Trunking and Conduit System in Commercial Building
Conduit and trunking
This picture shows how the electrical conduit and trunking installation should be coordinated with water pipes on the building. Trade subcontractors (water piping sub-contractors, electrical sub-contractors, telephone cabling contractor, computer network contractor and others) must not be allowed to proceed with the installation of their individual services and equipment on the “first come, first served basis”.
Prior to the commencement of the installation works by trade sub-contractors, a set of proper coordinated drawings, endorsed by all relevant parties, should be made available to all the sub-contractors involved in a particular area.
Electric trunking running below soffit of a concrete floor slab
There is no electrical installation work of a significant size can be done properly without the use of an electric trunking. A trunking is a larger size of a conduit. When you need to run a number of electric conduits along each other for a significant distance, then consider using a trunking in place of the conduits. There are so many sizes you can choose from.
The above picture is an example of a trunking installation above ceiling level, under the soffit of the concrete floor slab. we also labeled some of the other services there for the benefit of those non-electrical readers who need pictures like this for reference, to know what is what among the myriads of pipes, conduits and trunking running above the ceiling level.
Electrical trunking in and out of the electric panels
There are electrical trunking connecting the panels at above and below the panels. But the box-up walls have hid them. This picture is metal trunking. In future, the maintenance electrician would need to access and open the cover of the trunking in the repair and upgrading works. Therefore, a means of access is required, which was not provided at all at the mock-up unit.
Under floor trunking installation
The under floor trunking system has been around for a long time. An under floor trunking system is an alternative way of providing the dedicated routes to run electrical cables, telephone cables or any other wiring cables. An 11KV cable is not a wiring cable. A 25 sq.mm electrical feeder cable to supply an 11 KW fire pump panel is not a wiring cable. The 1.5 sq.mm cables that are used for wiring the office lights are categorized wiring cables.
The conduits are used to protect the wiring cables that carry the electrical current. Electricity is dangerous. Even though the electric conductors that carry the current is insulated by some PVC covering materials or whatever, the covering material is not strong enough to protect the cable from damage.
When the covering is damaged, the electrical conductor inside may be exposed to touch or it can also unintentionally come into contact with things that can carry electric current. This scenario would present a high risk of electric shocks.
Therefore, we protect the electric cables so that they do not present the dangers of electric shocks to people (or animals). A second reason to protect the cables is to make sure the electrical system stays reliable. When the cable PVC covering is damaged, the conducting metal can come into contact with other metals that are in contact with earth.
A motorized overhead projector
The electrical contractor produced a mock-up unit of the installation bracket for motorized overhead projector. The overhead projector was for meeting rooms (offices level). There were about thirty units to be installed through the building.
Compound lighting feeder pillar
A building construction of significant size is usually not complete without at least one small outdoor weatherproof feeder pillar.
High rise building electric closets
The electric closet in the following pictures has been done for a multi storey bui
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