They may have another rubber insulation or PVC insulation. Control cables have several cores, each having independent insulation. To avoid interference due to stray magnetic fields, the control cables should be properly laid and their sheath should be properly earthed. In this type the front and rear walls are erected independent with a common cover. The sides are open except the end panels, which are provided with doors and door switch for internal illumination.
In between front and rear there is adequate space to move for inspection and wiring. In this type, the protective relays are mounted on rear board and the control and indication equipments on the front panels. The standard size of individual panel is Depth — mm, width- limited to mm, height — mm. Panels are dust, moisture and vermin proof. These are free standing, floor mounting type but grounded with foundation bolts. Cable entries to panel are from bottom.
The bottom plates of the panel are fitted with removable gland plates and fixed with cable glands. The cable glands are screwed type made of brass and suitable for PVC armored cable. Mimic Diagram Colored mimic diagram and symbols showing exact representation of the system are provided in the front panel. Mimic diagram are made of anodized aluminum or plastic, screwed to panel. The mimic buses are generally 2mm thick; width of mimic bus is 10mm for bus bar and 7mm for other connections.
Indicating lamp, one for each phase for each bus is provided on mimic of bus coupler panel to indicate bus charged condition. One HRC fuse-unit both at positive and negative side shall be provided for the DC incomer at the bus coupler panel. DC supply to each individual panel thus teed off and distributed within the panel as below [1] C.
The above bus is teed off to each panel through separate switch-fuse unit. One supervision relay for incoming AC fail with test push button and reverse flag indication shall be provided for monitoring of AC supply healthiness through DC operated fascia annunciation of bus coupler panel. Selected PT secondary supply to protective relays of each panel shall be fed through individual fuses and links.
Necessary arrangement for supervision of PT secondary supply is provided. Selected PT secondary supply to metering and indicating instrument of each panel shall be fed through fuses and links. Annunciation Scheme Other trip and non trip alarm scheme. Fascia annunciation system has to be provided in each control panel by means of visual and audible alarm to draw attention of operator. The annunciation can be divided into the following categories Trip annunciation Warning annunciation Incoming DC fail and annunciation bus DC fail alarm scheme.
The scheme comprises of DC supervision relay with push buttons for incoming DC supply and annunciation bus DC system, one AC operated alarm accept relays, one indication lamp, one AC operated hooter and one push button for cancellation of audible alarm. Alarm inscriptions are engraved in facial window and the same should be prominently visible when fascia light is ON.
Accept reset and lamp test push buttons for acknowledgement of alarm, reset of visual indicator and checking correctness of lamps are provided below each fascia. The annunciation scheme should be such that momentary closing of any fault contacts shall cause operation of annunciation.
Trip Annunciation Trip annunciation shall draw attention of operation when a C. The audible common alarm should buzz and the visual annunciation is provided by flickering of window fascia. Warning Annunciation Warning annunciation is used to draw attention of operator to abnormal operating conditions of equipment for immediate action to avoid tripping of C.
Protection Philosophy The philosophy of protection is to design the protection scheme for lines, transformers, bus couplers, bus transfer bay depending upon the substation layout arrangement.
The scheme shall be generally based on the requirement listed below. Line Protections Numerical distance relay with built-in auto enclosure or in standalone mode. Disturbance Recorder may be built in with Distance Relay. Back up directional over-current relay Back up directional earth fault relay. Local break up back up protection at HV side only.
Over flux protection and overload alarm at HV side. Flag relays for internal protection of transformer like buchholz relay, winding temperature, oil temperature and pressure relief Valve KV Bus Coupler Protections Bus differential protection scheme. Local breaker back up protection. AC supervision relay. DC fail relay 3phase trip relay. During the period of transfer the line side CT operated protection of transferred circuit will trip the transfer bus breaker in place of respective bay circuit breaker through trip transfer switch.
Current transformers CT : The lines in substations carry currents in the order of thousands of amperes. The measuring instruments are designed for low value of currents. Current transformers are connected in lines to supply measuring instruments and protective relays. Potential transformers PT : The lines in substations operate at high voltages. The measuring instruments are designed for low value of voltages.
Potential transformers are connected in lines to supply measuring instruments and protective relays. These transformers make the low voltage instruments suitable for measurement of high voltages. Circuit breaker CB : Circuit breakers are used for opening or closing a circuit under normal as well as abnormal faulty conditions. Different types of CBs which are generally used are oil circuit breaker, air-blast circuit breaker, vacuum circuit breaker and SF6 circuit breaker.
Isolators or Isolating switches: Isolators are employed in substations to isolate a part of the system for general maintenance. Isolator switches are operated only under no load condition. They are provided on each side of every circuit breaker. Lightning arresters LA : Lightning arresters are the protective devices used for protection of equipment from lightning strokes.
They are located at the starting of the substation and also provided near the transformer terminals. Earth switch: It is a switch normally kept open and connected between earth and conductor. If the switch is closed it discharges the electric charge to ground, available on the uncharged line. Wave trap: This equipment is installed in the substation for trapping the high frequency communication signals sent on the line from remote substation and diverting them to the telecom panel in the substation control room.
Coupling capacitor: A coupling capacitor is used in substations where communication is done by AC power line. Isolator switches are operated only under no load condition.
They are provided on each side of every circuit breaker. Lightning arresters LA : Lightning arresters are the protective devices used for protection of equipment from lightning strokes. They are located at the starting of the substation and also provided near the transformer terminals.
Earth switch: It is a switch normally kept open and connected between earth and conductor. If the switch is closed it discharges the electric charge to ground, available on the uncharged line.
Wave trap: This equipment is installed in the substation for trapping the high frequency communication signals sent on the line from remote substation and diverting them to the telecom panel in the substation control room.
Coupling capacitor: A coupling capacitor is used in substations where communication is done by AC power line. It offers very low impedance to high frequency carrier signal and allows them to enter the line matching unit and blocks the low frequency signal. Bus-bar: When number of lines operating at the same voltage levels needs to be connected electrically, bus-bars are used.
Bus-bars are conductors made of copper or aluminum, with very low impedance and high current carrying capacity. Single bus-bar arrangement: It consists of single bus-bar.
Both incoming and outgoing lines are connected to the single bus-bar. The advantages of this arrangement are low maintenance, low initial cost and simple operation.
The drawback of this arrangement is if any repair work is to be done on bus-bar, complete system get interrupted. Figure below shows that three incoming and three outgoing line are connected to the single bus arrangement. Single bus-bar with sectionalisation: Single bus-bar is divided into sections.
Any two sections are connected by circuit breaker and isolators. During fault or maintenance particular section can be de-energised. Grid station will 1st step down to low voltage so different components in grid station are used for different purpose like metering, measuring and protection of equipments etc.
Grid station consists of transformer have 4 parts Line bay, Main bus bar, Transformer bay and Power transformer. Line bay contains line insulator, breaker, line CT, isolator. After main bus bar transformer bay located and contain isolator, CT, breakers and lighting arrester. Single line diagram of each grid station identify the input incoming and output outgoing of the grid, mean which is primary source and where we feed its output or consumers.
Zero point has 2 direct lines while 2 indirect lines. Zero point have 3 circuit output line are I- 10, I-8 and Satellite town. Above all transmission line are handle by national transmission and dispatch center NTDC. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions. Between the generating station and consumer, electric power may flow through several substations at different voltage levels.
Substations may be owned and operated 5. Grid station report of internship at IESCO Grid station components and their functioning by an electrical utility, or may be owned by a large industrial or commercial customer. A substation may include transformers to change voltage levels between high transmission voltages and lower distribution voltages, or at the interconnection of two different transmission voltages.
Substations are classified by two broad categories:- 1. These are generally located in the power houses and are of outdoor type.
The primarygridsubstationisgenerallyof outdoortype. The 11KV linesrunsalongthe importantroadof the city. The secondarysubstationsare alsoof outdoortype. It means GSS take supply from anyone and provide other one. One source Sangjani kva step down kva in zero point and Sangjani feed from Burhan GS which feed from Tarbela power house.
Single line Key Diagram Single line key diagram of CANTT grid station, In which we see it have 2 source of main bus bar One is Islamabad and other one is chaklala cantt And in ring system it can take supply from one Source to and provide supply other source in case Of emergency.
At start we have line bay which Feed into main bus bar and after it connect with Transformer bay and a power transformer and Current transformer and isolator before incoming panel in control room. It also indicate a capacitor bank for power factor increase. While at the end we have incoming and outgoing feeder for distribution of power supply to the consumers for domestic and commercial use. Similarly other grid stations have same type of diagram but every grid station have different power source and outgoing panel.
According to the capacity of grid station the protection and other grid equipment install with respect to them. All circuits may be restored after isolating the faulty circuit breaker. Grid station report of internship at IESCO Grid station components and their functioning Introduction of bypass isolators between bus bar and circuit isolator allows circuit breaker maintenance facilities without loss of that circuit.
Earthing and Bonding The function of an earthing and bonding system is to provide an earthing system connection to which transformer neutrals or earthing impedances may be connected in order to pass the maximum fault current. The earthing system also ensures that no thermal or mechanical damage occurs on the equipment within the substation, thereby resulting in safety to operation and maintenance personnel.
The earthing system also guarantees equipotent bonding such that there are no dangerous potential gradients developed in the substation. In designing the substation, three voltages have to be considered these are: 2.
TouchVoltage Thisis the difference inpotential betweenthe surface potential andthe potential atearthedequipment whilstaman isstandingand touchingthe earthedstructure. StepVoltage Thisis the potential difference developedwhenamanbridgesa distance of 1m withhisfeetwhile not touchinganyotherearthedequipment. MeshVoltage Thisis the maximumtouchvoltage thatisdevelopedinthe meshof the earthinggrid.
Substation Earthing Calculation Methodology Calculations for earth impedance touch and step potentials are based on site measurements of ground resistivity and system fault levels. A grid layout with particular conductors is then analyzed to determine the effective substation earthing resistance, from which the earthing voltage is calculated. In practice, it is normal to take the highest fault level for substation earth grid calculation purposes. Additionally, it is necessary to ensure a sufficient margin such that expansion of the system is catered for.
To determine the earth resistivity, probe tests are carried out on the site. These tests are best performed in dry weather such that conservative resistivity readings are obtained. EarthingMaterials 2. Conductors Bare copper conductor is usually used for the substation earthing grid. The copper bars themselves usually have a cross-sectional area of 95 square millimeters, and they are laid at a 9. In addition to the buried potential earth grid, a separate above ground earthing ring is usually provided, to which all metallic substation plant is bonded.
Connections Connections to the grid and other earthing joints should not be soldered because the heat generate during fault conditions could cause a soldered joint to fail. Joints are usually bolted. EarthingRods The earthinggridmust be supplementedbyearthingrodstoassistinthe dissipationof earthfaults currentand furtherreduce the overall substationearthingresistance. These rodsare usuallymade of solidcopper,orcopperclad steel. SwitchyardFenceEarthing The switchyard fence earthing practices are possible and are used by different utilities.
The fence is then bonded to the grid at regular intervals. This earthing rod systemis not coupled to the main substation earthing grid. These forces comprise self- weight, and weight of other conductors and equipment, short circuit forces and atmospheric forces such as wind and ice loading. The most suitable material for the conductor system is copper or aluminums. Steel may be used but has limitations of poor conductivity and high susceptibility to corrosion.
In an effort to make the conductor ideal, three different types have been utilized, and these include: Flat surfaced Conductors, Stranded Conductors, and Tubular Conductors. The choice is influenced by the height of towers and the proximity to the substation. The following clearances should be observed: 2. It works on the principle of static induction principle. When the energy is transformed into a higher voltage, the transformer is called step up transformer but in case of other is known as step down transformer.
It also having a big in size as compare to distribution transformer, it used in generating station and Transmission substation at high insulation level. Instrument Transformers These transformersare usedforthe measurementpurposesatthatpointswhere standardvoltmeters and ammeterscannotbe used. They are of twotypes:- 2.
When current in a circuit is too high to apply directly to measuring instruments, a current transformer produces a reduced current accurately proportional to the current in the circuit, which can be conveniently connected to measuring and recording instruments. A current transformer isolates the measuring instruments from what may be very high voltage in the monitored circuit.
They are designed to present negligible load to the supply being measured and to have an accurate voltage ratio to enable accurate metering. A potential transformer may have several secondary windings on the same core as a primary winding, for use in different metering or protection circuits.
Auto Transformers An autotransformer is an electrical transformer with only one winding. The "auto" prefix refers to the single coil acting on itself and not to any kind of automatic mechanism. In an autotransformer, portions of the same winding act as both the primary and secondary sides of the transformer. The winding has at least three taps where electrical connections are made.
Autotransformers have the advantages of often being smaller, lighter, and cheaper than typical dual-winding transformers, but the disadvantage of not providing electrical isolation.
On the basis ofworking On the above basis,transformersare of twotypes:StepupTransformerand StepdownTransformer. Distribution Transformers A distributiontransformerisa transformer that provides the final voltage transmission in the electrical power distribution system, stepping down voltage to the level used by customers.
Power-line communication PLC carries data on a conductor that is also used simultaneously for AC electric power transmission or electric power distribution to consumers. By using the existing AC power lines as a medium to transfer the information, it becomes easy to connect the houses with a high speed network access point without installing new wirings.
This technology has been in wide use since and was mainly used by the grid stations to transmit information at high speed. All type of information is modulated on carried wave at frequency 50Hz to KHz. The modulated HF carrier fed into the power line conductor at the sending end and filtered out again at the respective stations. Long earlier system double side band amplitude modulation was more common but the present amplitude modulated system.
Since high voltage power lines are designed to carry large quantities of energy on the high voltage and the communication system at low voltage, they cannot be directly connected to high voltage lines. Suitably designed coupling equipments have therefore to be employed which will permit the injection of high frequency carrier signal without undue loss and with absolute protection of communication equipments or operating personal from high voltage hazard.
Therefore, the coupling equipment essentially comprises the following: 2.
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