REPORT PRESENTATION

IN PLANT TRAINING REPORT PRESENTATION

INTRODUCTION

MSETCL (Maharashtra State Electricity Transmission Co. LTD.) is a Gov. owned substation. It was found on 6th June 2005. It has its headquarters at Bandra, Mumbai MSETCL operates a transmission network of 39871 circuit KM of transmission lines and 559 EHV substation with 89178 MVA transformation capacity.

MSETCL(Kalwa)• It is fully computerized and has ultra modern facilities. It also has a Load dispatch centre.

The SLDC is being renovated and modernized 140 nos. of SCADA-RTU.• • 400KV, MSETCL Kalwa, has 4 incoming lines.• It converts 400 kV to 220 kV• The 4 incoming lines are• 1)Padgha 1• 2)Padgha 2• 3)Lonikand• 4)Kharghar• • The substation consist of 3 ICT (Interconnected Transformers ) Which has 10

Autotransformers (3 at each ICT and 1 spare Autotransformer)• 3 ICT’S have ratings of • ICT 1-500 MVA• ICT2-600 MVA• ICT 3-500 MVA

SINGLE LINE DIAGRAM OF 400/220 KV SUBSATTION

COMPONET DESCIRPTION

LIGHTNING ARRESTER

LIGHTNING ARRESTER • Lightning arrester or surge diverter is a protective

device which conducts the high voltage surges on the power system to the ground

• The earthing screen and ground wires can well protect the electrical system against direct lightning strokes but they fail to provide protection against travelling waves which may reach the terminal apparatus. The lightning arrester provides protection against such surges.

BASIC LIGHTNING ARRESTER ACTUAL ARRSTERS

• PLCC, Power Line Carrier Communication, is an approach to utilize the existing power lines for the transmission of information

• Each end of transmission line is provided with identical PLCC equipment consisting of equipment:

Transmitters and Receivers Hybrids and Filters Line Tuners Line Traps Power amplifier Coupling capacitors• Distance protection relay in relay panel at one end of

the transmission line gets the input from CT and CVT in line. The output of relay goes to modem of PLCC.

COUPLING CAPACITOR

Coupling capacitor connects the carrier equipment to the transmission line. The coupling capacitor’s capacitance is of such a value that it offers low impedance to carrier frequency (1/ωC) but high impedance to power frequency (50 Hz).For example 2000pF capacitor offers 1.5MΩ to 50Hz but 150Ω to 500kHz.Thus coupling capacitor allows carrier frequency signal to enter the carrier equipment.To decrease the impedance further and make the circuit purely resistive so that there is no reactive power in the circuit, low impedance is connected in series with coupling capacitor to form resonance at carrier frequency.

CAPACITOR UNITSCAPACITIVE VOLTAGE TRANSFORMER(CVT)

WAVE TRAP

line trap unit/Wave trap is inserted between busbar and connection of coupling capacitor to the line. It is a parallel tuned circuit comprising of inductance (L) and capacitance (C). It has low impedance(less than 0.1) for power frequency (50 Hz) and high impedance to carrier frequency.This unit prevents the high frequency carrier signal from entering the neighbouring line.

Transmitters and Receivers

The carrier transmitters and receivers are usually mounted in a rack or cabinet in the control house, and the line tuner is out in the switchyard . This then means there is a large distance between the equipment and the tuner, and the connection between the two is made using a coaxial cable.

Hybrids and Filters• The purpose of the hybrid circuits is to enable the

connection of two or more transmitters together on one coaxial cable without causing intermodulation distortion due to the signal from one transmitter affecting the output stages of the other transmitter. Hybrids may also be required between transmitters and receivers, depending on the application.

• The hybrid circuits can, of course, cause large losses in the carrier path and must be used appropriately. High/low-pass and band-pass networks may also be used, in some applications, to isolate carrier equipment from each other.

Oscillator and Amplifiers

• High frequency carrier signal is generated in oscillator.• Oscillator can be crystal oscillator with which operation for

a particular bandwidth can be achieved. The output voltage of a oscillator is held constant by voltage stabilizer.

• The output of oscillator is fed to amplifier so that loses in transmission can be compensated. Losses occurring in carrier current is termed as attenuation of carrier signal.

• They are mainly: Losses in coupling equipment which are constant losses for a given carrier frequency bandwidth.

Isolators

• Isolator is a mechanism which is used to separate the certain part of the power system for maintenance purpose.

• Isolator breaks the circuit or opens the circuit manually.

• In practice there are various types of isolator Central break isolator Pentagraph type isolator

CURRENT TRANSFORMER

• Produces step down replica of primary current .Transform currents from usually a high value to a value easy to handle for relays and measuring instrument .Insulate relays and instruments from primary high voltage .Standardises the relay current for the relays and the instrument . The rated secondary current is generally 1A/5A.

• Single CT can be used for multiple purposes.• Core Utilization of CT• 1stcore : Main protection • 2ndcore : Back up protection• 3rd core : Metering purpose• 4th core : Bus bar protection (main zone)• 5thcore : Bus bar protection (check zone)

ACCURACY CLASS OF CT• Ideally the Secondary current should be exact replica of primary

current. The extent to which the Secondary current magnitude differs from calculated value by virtue of CTR is defined by “accuracy class of CT”. The Accuracy class includes both Ratio and phase angle errors.

• Accuracy class of CT is expressed as 0.2/0.5/1.0 for Metering core and 5P/10P/PS for Protection core.

• CT cores are usually either Measuring or Protective types.• The principle requirement of Measuring type CT is, it should give fairly

accurate secondary up to 120-125% of primary current as per the Class of Accuracy.

• A desirable characteristics of Measuring CT is, it should saturate when primary current exceeds the percentage of rated current specified as upper limit in Class of Accuracy.

• The principle purpose of Protective type CT is to provide Secondary current proportional to fault current which is many times the rated Primary current. At this higher current it should not go to saturation.

• For general purpose protection like O/C and E/F protection Class P CTs are used. P denotes for Protection and it is defined so that, at rated connected burden errors shall not exceed the rated values.

OPEN CIRCUTING OF CT SECONDARY

• Normal voltage appearing across CT secondary of 15 VA, 5A CT is 3V.

• However, if CT secondary is open circuited, very high voltage will appear across secondary if primary is loaded. Secondary emf increases due to higher working flux.

• It is risky for the personal working on secondary side of a CT and even may lead to break down of insulation between Primary and Secondary winding or between core and winding.

• Hence, Secondary should never be opened when primary of a CT is loaded.

•

CIRCUIT BREAKERS

• A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and interrupt current flow. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high-voltage circuits feeding an entire city.

• All circuit breakers have common features in their operation, although details vary substantially depending on the voltage class, current rating and type of the circuit breaker.

• The circuit breaker must detect a fault condition; in low-voltage circuit breakers this is usually done within the breaker enclosure. Circuit breakers for large currents or high voltages are usually arranged with pilot devices to sense a fault current and to operate the trip opening mechanism. The trip solenoid that releases the latch is usually energized by a separate battery, although some high-voltage circuit breakers are self-contained with current transformers, protection relays, and an internal control power source.

• Once a fault is detected, contacts within the circuit breaker must open to interrupt the circuit; some mechanically-stored energy (using something such as springs or compressed air) contained within the breaker is used to separate the contacts, although some of the energy required may be obtained from the fault current itself.

• The circuit breaker contacts must carry the load current without excessive heating, and must also withstand the heat of the arc produced when interrupting (opening) the circuit. Contacts are made of copper or copper alloys, silver alloys, and other highly conductive materials. Service life of the contacts is limited by the erosion of contact material due to arcing while interrupting the current.

• When a current is interrupted, an arc is generated. This arc must be contained, cooled, and extinguished in a controlled way, so that the gap between the contacts can again withstand the voltage in the circuit. Different circuit breakers use vacuum, air, insulating gas, and oil as the arc quenching medium.

SF6 CIRCUIT BREAKER

• SF6 gas has high dielectric strength which is the most important quality of a material for use in electrical equipments and in particular for breaker it is one of the most desired properties. Moreover it has high Rate of Rise of dielectric strength after arc extinction. This characteristics is very much sought for a circuit breaker to avoid restriking.

• SF6 is colour less, odour less and non toxic gas. SF6 is an inert gas. So in normal operating condition the metallic parts in contact with the gas are not corroded.

• SF6 has high thermal conductivity which means the heat dissipation capacity is more. This implies greater current carrying capacity when surrounded by SF6 . The gas is quite stable. However it disintegrates to other fluorides of Sulphur in the presence of arc. But after the extinction of the arc the SF6 gas is reformed from thedecomposition.SF6 being non-flammable so there is no risk of fire hazard and explosion

Construction and workingThe piston is fixed but the cylinder is movable. The cylinder is tied to the moving contact so that for opening the breaker the cylinder along with the moving contact moves away from the fixed contact. But due to the presence of fixed piston the SF6 gas inside the cylinder is compressed. The compressed SF6 gas flows through the nozzle and over the electric arc in axial direction. Due to heat convection and radiation the arc radius reduces gradually and the arc is finally extinguished at current zero. The dielectric strength of the medium between the separated contacts increases rapidly and restored quickly as fresh SF6 gas fills the space. While arc quenching, small quantity of SF6 gas is broken down to some other fluorides of sulphur which mostly recombine to form SF6 again. A filter is also suitably placed in the interrupter to absorb the remaining decomposed byproduct

• The gas pressure inside the cylinder is maintained at around 5 kgf per sq. cm. At higher pressure the dielectric strength of the gas increases. But at higher pressure the SF6 gas liquify at higher temperature which is undesired. So heater is required to be arranged for automatic control of the temperature for circuit breakers where higher pressure is utilised. If the SF6 gas will liquify then it loses the ability to quench the arc

BUCHHOLZ RELAY

• If an arc forms, gas accumulation is rapid, and oil flows rapidly into the conservator. This flow of oil operates a switch attached to a vane located in the path of the moving oil. This switch normally will operate a circuit breaker to isolate the apparatus before the fault causes additional damage. Buchholz relays have a test port to allow the accumulated gas to be withdrawn for testing. Flammable gas found in the relay indicates some internal fault such as overheating or arcing, whereas air found in the relay may only indicate low oil level or a leak.

PRESSURE RELIEF VALVE

• The relief valve (RV) is a type of valve used to control or limit the pressure in a system or vessel which can build up by a process upset, instrument or equipment failure, or fire.

• The pressure is relieved by allowing the pressurized fluid to flow from an auxiliary passage out of the system. The relief valve is designed or set to open at a predetermined set pressure to protect pressure vessels and other equipment from being subjected to pressures that exceed their design limits. When the set pressure is exceeded, the relief valve becomes the "path of least resistanceas the valve is forced open and a portion of the fluid is diverted through the auxiliary route. The diverted fluid (liquid, gas or liquid–gas mixture) is usually routed through a pipingsystem known as a flare header or relief header to a central, elevated gas flare where it is usually burned and the resulting combustiongases are released to the atmosphere.As the fluid is diverted, the pressure inside the vessel will drop. Once it reaches the valve's reseating pressure, the valve will close. The blowdown is usually stated as a percentage of set pressure and refers to how much the pressure needs to drop before the valve reseats. The blowdown can vary from roughly 2–20%, and some valves have adjustable blowdowns.

• In high-pressure gas systems, it is recommended that the outlet of the relief valve is in the open air. In systems where the outlet is connected to piping, the opening of a relief valve will give a pressure build up in the piping system downstream of the relief valve. This often means that the relief valve will not re-seat once the set pressure is reached. For these systems often so called "differential" relief valves are used. This means that the pressure is only working on an area that is much smaller than the openings area of the valve. If the valve is opened the pressure has to decrease enormously before the valve closes and also the outlet pressure of the valve can easily keep the valve open. Another consideration is that if other relief valves are connected to the outlet pipe system, they may open as the pressure in exhaust pipe system increases. This may cause undesired operation.

• In some cases, a so-called bypass valve acts as a relief valve by being used to return all or part of the fluid discharged by a pump or gas compressor back to either a storage reservoir or the inlet of the pump or gas compressor. This is done to protect the pump or gas compressor and any associated equipment from excessive pressure. The bypass valve and bypass path can be internal (an integral part of the pump or compressor) or external (installed as a component in the fluid path). Many fire engines have such relief valves to prevent the over pressurization of fire hoses.

• In other cases, equipment must be protected against being subjected to an internal vacuum(i.e., low pressure) that is lower than the equipment can withstand. In such cases, vacuum relief valves are used to open at a predetermined low pressure limit and to admit air or an inert gas into the equipment so as control the amount of vacuum.

•

CAPACITIVE VOLTAGE TRANSFORMER

• In high and EHV network CAPACITOR VOLTAGE TRANSFORMER are used to provide the potential output to the metering instruments and protective relays. In addition when equipped with carrier accessories, CVTs can be used for Power Line Carrier Coupling (PLCC).

• The capacitor voltage Transformers are used as voltage transformers for voltages > 100 kV. The size of conventional PT for higher voltages is proportional to rated voltage. Thus cost of PT increases at disproportionate rate. Hence, for higher voltages CVTs become more economical.

• The application of CVT is similar to conventional PT. in addition it can be used as coupling capacitor for PLCC equipments for telecommunication, remote control etc..

• Thus the dual purpose of CVT as voltage transformer as well as coupling capacitor make CVT most economical for voltages> 100 kV.

OPERATING PRINCIPLE• This device is basically a potential divider. It has two capacitors and an electromagnetic

transformer connected at tapping points. As with a resistance divider, the output voltage is seriously affected by load at tapping point.

• In case of a CVT, the equivalent source impedance is capacitive and compensated by a reactor connected in series with tapping point.

• With an ideal reactor coil, there would have no regulation and supply at any value of output. A reactor has some resistance at which limits the output voltage.

• For a secondary voltage of 110 V, the capacitors would have to be very large to provide useful output with keeping errors within limit.

• The solution for this is to use the higher secondary voltage and further transform it to a lower value by using a relatively inexpensive electromagnetic transformer.

• The coupling capacitors of the CVT function as a voltage divider to step down the line voltage to an intermediate line voltage typically from 15 to 22.5 kV.

• The electromagnetic transformer used in CVT has voltage ratio in the order of 15 to22.5 kV/110 V.

• The basic difference between the equivalent diagram of CVT and PT is the presence of C & L.

• The compensating reactor cancels the coupling capacitors reactance at the system frequency.

• The reactance cancellation prevents the phase shift between the primary and secondary voltages at the system frequency. At normal frequency when C & L are in resonance therefore cancelling out and offer zero impedance and circuit behaves in similar manner of PT.

• With no voltage drop across the LC circuit, the output of CVT will become independent of the current drawn by the burden.

• The other frequencies, however, IC and IL do not get cancelled out and a reactive component exists which modifies the error.

• The compensating reactor and the electromagnetic transformer have iron core. It will both produce iron losses.

• Further, the compensating reactor and the electromagnetic transformer also produces Ferro-resonance due to non linearity of iron cores.

• To compensate this phenomenon, a Ferro-resonance suppression circuit is added on secondary of the electromagnetic transformer.

DC BATTERY

• Substation requires 220 V DC power for relay operation and 48 V DC power for power line carrier communication (PLCC). Battery room has 110 batteries of 2V set connected in series for relay operation and 24 batteries of 2V set connected in series for power line carrier communication (PLCC).

• Electrolytic solution is used in these batteries. If the level of this solution drop down below a predefined limit then to increase the level of this solution distilled water is used. For the charging of these batteries two types of chargers are used, one is normal float charger and another is float cum boost charger.

• Float charger is for charging battery normally used for providing regulated output dc to battery and float cum boost charger is used to charge battery instantaneously.

• • Float Boost Battery Charger

The charger works into different modes of operation which are automatically selected between themselves depending on charge condition of battery.

Auto-Float Mode : Under this mode of working charger delivers regulated DC output voltage suitable to maintain the battery in Float Charger condition, with variation of main supply voltage as well as output load variation from no load to full load. Adjustment of this regulated voltage is possible by voltage control pre set.

Auto Boost Mode : Under this mode of working charger deliver a constant regulated current to the battery while its terminal voltage is in the range of 1.8V to 2.4V/Cell Manual adjustment of this regulated current to the battery is possible by current control trinpot. The terminal voltage of battery charger builds up as the battery gets charged.

In Float cum Boost battery charger automatic mode is provided. Under this mode of working charger works either in auto float or in auto boost mode according to the State of Charger(SOC) of the batteries. Both battery and equipment are connected to the charger. Initially its starts in auto float charging. In this mode if current drawn by battery exceeds a preset value charges a automatically charges from auto float to auto boost mode. As battery picks of charge charging current starts decreasing and charger automatically comes back from auto boost to auto float mode