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Pair Tube Amplifier

Defense mechanism Ss

Defense mechanism of the SS

BREAKER:

I. Introduction

The main functions of a circuit breaker is to interrupt the rated short-circuit the normal current, switching ON and OFF normal loads, and providing the necessary insulation between live parts and earthed parts. Maintenance problems with contributed to the bulk oil circuit breakers were huge. Low oil technology has replaced the bulk petroleum technology during the 1950s. Similarly, the air-jet technology has been developed to obtain higher performance characteristics. However, the air-blast circuit breakers are quite expensive and cumbersome operation and maintenance. And therefore it became necessary during the 1960s for reduced maintenance.

SF6 has been previously obtained from fluorine and sulfur in 1900 by M / s. Mossane H. and PLEBEAU. Behavior of SF6 in the electric field has been studied by m / s. HG Cooper and PS PQLLOCK 4936 known for more than two decades, the perfection of the commercial exploitation has been achieved during the 1960s. This evolution allowed for the SF6 gas at low pressure to be used in circuit breakers for isolation and BIN are "for tempering some properties Remarkable SF 6 gas that make it ideal in EHV circuit. breakers are:

1. Inertia

2. Non-toxicity

3. Electro negativity

4. High dielectric

5. Unique are the property of hardening

6. The chemical and thermal stability

7. Good thermal conductivity

8. No corrosivity

9. Non-flammability

The combined electrical, physical, chemical, and thermal properties of SF6 has the following features outstanding when used in the current breaker.

1. Security

2. downsizing

3. Weight reduction

4. simplified calculation

5. high reliability

6. Capacitive switching currents without rebooting

7. Very quiet towing

8. Easy for processing

9. Easy to install

10. Maintenance free service

2. Properties of sulfur hexafluoride (SF6)

a) Physical properties:

SF6 is a colorless, odorless and non-flammable. The fluorine atoms are placed at the corners of hedran regular octa-sulfur atom with the core placed at a distance of 1.58 Angstrom units. The bonds are predominantly covalent and the equation dissociation is

SF6 - to SF5 + F __________

The decomposition potential is 15.7 eV. SF6 gas is very heavy and its density is about 5.5 times that of air. It is very stable. It is more compressible than air and follows the ideal gas law.

b) Electrical properties

The di-electric strength of SF6 gas is 3 times that of air at atmospheric pressure and is sentence reduced by the presence of air as an impurity. The increase of dielectric strength with increasing pressure. At a pressure three bars, the dielectric strength is equal to that of transformer oil. The size and nature electro molecule explain this negative force. The molecule has a large diameter electron collision. The result is a snapshot of electrons not reaching an energy sufficient to create others. Current-carrying particles. SF6moiecuie also has the ability to store energy in the vibrational levels and electronic 'Of the molecule is forming stable ions of low mobility.

The dielectric strength of SF6 remains unchanged over a wide range of frequencies. since SF6 has no dipole moment, dielectric constant does not vary with frequency. AT 27.30c and the atmospheric pressure is the dielectric constant and 1.00191 angle of loss is 2 x 10-7.

The dielectric properties of SF6 remain unchanged, even at low temperatures. Unlike materials solid insulation power outage in SF 6 does not lead to permanent deterioration of its properties. Pause in all units filled can result in enormous increase in pressure due to gas formation, but these risks do not exist in the case of SF6-filled equipment.

c) Arc quenching properties:

The ability to quench arc is unique in SF 6. It follows high dielectric gas and fast recovery of dielectric strength after arcing occurs. SF6 is about 100 times more effective in this regard that the air under similar conditions. The low constant arc-time and its ability to absorb free electrons because of the nature of electro negative, it is a great way to break the arc. The movement of SF6 molecular complex allows it to absorb energy Electrical and form stable negative ions. Its tendency to form negative ions around zero current results of the rapid disappearance of electrons released during an arc. Unlike oil, SF6 arc not produce carbon deposits or carbon tracking.

Property electro-negative SF6 may be due to several factors, including the diameter of major collision. If electrons stray electric field can be absorbed before reaching a sufficient energy to create new particles carry current if collision, the breakdown can be slowed or even stopped. Diameter of major collision of the molecule SF6 helps capture these electrons. energy can be stored in the vibrational levels of the atom SF6 forming stable negative ions of low mobility. Thus, the gas is electronegative in nature and shows. Consumer Electronics binding capacity. Thus displays SF6 splendid performance of arc-extinguishing.

The arc time constant is directly proportional to the radius of the arc, it is possible to have many failures at full capacity of the breaker. The curve of the arch is such that b power extinction low. In a typical case where the power of extinction is about 20 kW for a SF6 circuit breaker, the corresponding value of a circuit breaker air jet has been in hundreds KW.

Some processes of formation of ions of SF6 are:

Resonance capture: SF6 + eA (SF6) - SF5-+ F

the formation of positive ions: SF6 + eA (SF6 +) + 2e-+ SF5-F + 2e-

Excitation and dissociation: SF6 + eA (SF6-) + e-SF5-+ F + e

the formation of positive and negative ions: SF + eA (SF6-) eF + SF5 + - + e

d) the heat transfer characteristics:

SF6 has excellent heat transfer characteristic, an important criterion for dielectric gas in power applications. The molecular weight higher with a low viscosity of SF6 gas allows heat transfer by convention, more efficient than gas common. The transmission coefficient Thermal SF6 is about 2.5 Tip1 the air under the same conditions. Therefore, when the breaker is turned on, the increase temperature small.

e) Wide temperature range:

SF6 gaseous follows the ideal gas law closely enough. Therefore, the change in pressure is moderate to a considerable change of temperature. Weaknesses sublimation of SF6 provides greater dielectric strength even at low temperature liquefaction temperature is-270C at a pressure of 12 kg / cm ². Therefore, no heater is needed.

f) danger of:

SF6 is a non-toxic gas and produces no toxic effect on the human body. But the decomposition products produced by the discharge (SF4, SF2, S2, F2, etc.) are harmful. These products are minimized by controlling the humidity in the switch and by absorbing the products of decomposition by synthetic zeolite.

g) chemical and thermal stability:

SF6 gas is inert and it is one of the least reactive substances known under normal operating conditions. It can be heated in the quartz 5000C, without going into decay. SF6 does not react with water, acids and alkalis. Tests showed virtually no corrosion of dissimilar metals exposed to SF6

h) constants:

Some of the outstanding properties of SF6 which makes it ideal for high voltage applications are:

Molecular Weight .. 146.05

Sublimation point at 1 atm .. 63.9 ° C

Density of gas at 1 atm C 21.19 .. 6.139

viscosity liquid to 13.52 ° C .. 0.305

Gas 31.16 C .. 0.0157

Critical temperature etc. .. 318.80

Critical pressure bars .. 37.772

cu.metre critical volume / g .. 1.356

N2 = dielectric rei al 50 Hs -1.2 MHS .. 2.3 -2.5

Dielectric constant at 25 ° C 1atm .. 1.002049 "

The thermal conductivity at 30 ° C, Cal / sec. In C .. 3.36 x 10-5

3. Breakdown phenomena in SF6:

Distribution of gas emission occurs when free electrons gain enough kinetic energy, under the influence of an electric field and collide with gas molecules neutral electron-releasing their outer shells. A chain reaction, as it follows an avalanche of electrons. In the case of electro-negative gases such as SF6 this mechanism is slightly modified. The free electrons attached to molecules forming negative ions. SF6 SF6 + Z e-e. The negative ions are too massive to produce collisional ionization. This commitment represents an effective way to eliminate the electrons which would otherwise have contributed an avalanche of electrons. This particular behavior results in very high dielectric strength electronegative gas.

The breakdown voltage of an electro-negative gas in a uniform field is a simple function of the product of pressure and spacing. breakdown characteristics in non-uniform will be different because the primary ionization can be designed locally due to the presence of regions of high stress. It is the corona. This may be due to surface roughness, from large, floating conductive or semi-conductive particles. In facilities SF6 special care is taken to ensure that these points do not exist in the circuit breaker so that the fairly uniform distribution on the ground can be achieved.

4. Principles break SF6

Technical staff from the interruption of SF6 can be classified into two:

a) dual pressure.

b) single pressure system.

It may still be classified as dual stream nozzle fixed breakers and single piston flow series.

a) the double pressure:

The function of insulation and interruption are performed in separate rooms. SF6 at a pressure of 14 kg / m². cm. is stored in a pressure chamber. It is used to extinguish the SF6 are low pressure (2.5 to 3.5 kg / m². cm.) ensures insulation. When the contacts separate under the fault, high pressure gas is forced into the arc region and it follows for the low pressure region. The gas exhausted in the region of low pressure is compressed and returned to the reservoir high pressure. The arcing occurs between the tip of the bow and bow ring relieving the contact zone of the stress of the arc. A graduated filter Reality is kept at the entrance of the compressor so that all products of decomposition of gas can be absorbed before recirculation in of the system. A heating system controlled by a thermostat is provided in the high pressure tank to prevent condensation of gas at low temperature.

b) single pressure system:

In this case, SF6 at low pressure (3 to 6.5 kg / sq.cm.) provides insulation and energy of the interruption. The cutting chamber includes fixed and movable contacts, and the arrangement of the piston in the pump type fixed contact. As the moving contact separates under the fault, the piston moves forward with speed. This compresses the SF 6 within the fixed contact and sanctify the gas forces the arc resulting in quenching. The force with which the gas furnace may be dependent on the design of the piston and energy control mechanism.

Another improvement is the magnetic circuit breakers type pump where the control force on mobile contact rod is increased by magnetic repulsion force. The short circuit current is passed through a set of coils fixed on the support of the Fed moving contact. A ring is positioned near the secondary circuit and magnetically coupled to primary winding. This ring serves as the piston. This interaction between them. two fields produces a repulsive force and the growth of the contact rod forward. The addition of this simple magnetic drive mechanism improves capacity of the circuit breaker interruption.

The single pressure system has an inherent advantage of simplicity in construction. It does not require additional compression, as required in the double pressure. The cost of manufacturing equipment such as pump is lower.

5. Construction:

The arc suppression system uses a synchronized flow of type double definition touch pump. This leads to a simple construction.

SF 6 circuit breaker includes mainly the following:

1. Poles Breaker it.

2. Base tube and box mechanism

3. Control Unit

4. Compressor operating mechanism electro-hydraulic

1.Movable cylinder (cylinder Puffer) 2.Moving Contact

3.Fixed Contct 4.Insulating nozzle

5.Fixed piston 6.Gas Trapped in before compression

7.Compressed gas between 1 and 5

8.The arc extinct by pump action

Pole 5.1.Breaker:

The main functions of a circuit breaker poles are made of circuit breaker. The cluster consists of unit cutting and isolating switch support.

The unit consists of a tube switch fixed contact, guide tube, the displacement of the tube contact, pump or furnace cylinder and piston. The tube fixed contact is connected to the upper boundary through. Contact support.

The guide tube is attached to the lower limit. The other ends of the tube fixed contact and guide tube are subjected to an electric arc during the interruption arc are provided with arc quenching nozzles. The nozzles are made of graphite materials maintains contact with wear to a minimum. The contact tube Mobile consists of fingers loaded spring contacts arranged in the form of a ring. The front end of the tube is provided with movable contact resistance arc grommet and arcing high arc-resistant materials ring

The cylinder explosion, which is composed of materials, high arc resistance and insulation tube movable contact are integral to each other and connected to the control rod in the insulator in support. The piston explosion, which is composed of aluminum is attached to the lower terminal block. The contact tube fixed guide tube, the displacement the contact tube, cylinder piston stoves and furnaces are "all housed inside a porcelain insulator. When the breaker is closed current upper bound to the lower bound, through contact support, the contact tube fixed, mobile or contact tube and guide tube.

The insulation support outside the support of the switch unit provide insulation between live parts and earthed parts. It houses the control rod (insulated), with one end connected to the unit of the switch and the other end is connected mechanism.

5.2. Tube box basic mechanism:

The base tube which supports the pole breaker and the mechanism housing acts as a reservoir of local air. The box joint mechanism of electromagnetic valves, the closing of the coil, trip coil and the cylinder operation. Tiny mechanism contains the entire lever system to transmit the operation force of the box mechanism for circuit breaker pole.

5.3.Control Unit:

This accommodates the pressure switches gas detector, gas density, gas pressure gauge, pressure gauge, air heater, air valve, auxiliary relays, terminal blocks, etc. for the electrical control and pneumatic control circuit breaker. The devices control the air and SF6 gas are common to the three-pole circuit breaker.

5.4. Compress

Since the energy needs of the operation is more MOCBS or air compressor or a mechanism of electro-hydraulic operation is used.

6. The principle of arc extinction:

When the breaker is in closed position, the movable bridges Assembly contact with the tube fixed contact and the guide tube. When an open operation is initiated, cylinder explosion moves the piston furnaces shut down for the SF6 gas in the cylinder is compressed to a breath pressure required to extinguish the arc. The compressed gas during the process above is released when the contacts are separated by the displacement of the Assembly contact acting as a drawer. At the instant of contact separation, the arc strikes between the front end of the nozzle of extinction of the arc tube and the stationary contact ring arc tube movable contact. The compressed gas cylinder in the blast is released into the radical break that contacts are separated. While all mobile contacts, the arc between the front end of the nozzle and the ring fixed contact arc the movable contact is transferred from the ring arc moving contacts of the nozzle guide tube, gas jet and its own forces electrodynamics. arc is further improved by the axial gas flow through nozzles and safety off. Although the arc is interrupted, the cylinder blast that is arc insulating material resistant to the Assembly closed quenching arc there protecting the porcelain insulator of an arc effect. After arc extinction, the Assembly moving contact and the breath is free to all parts of the room which can have a transition effect or influence electric field distribution.

7. Principle of operation:

7.1. Operation hours:

When the trip coil is energized, the space of the pilot valve is filled with compressed air and the valve moves to load line. The space in the operating cylinder is filled with compressed air from the air has been operating and the piston is rapidly leads to the left. the control rod connected to the piston operation is pulled in the direction of the opening drive of the cylinder pump with High Speed to the control rod isolated in the insulation support. SF6 gas in the metering roll is compressed and SF6 gas explosion off the arc generated between moving and stationary contacts.

Coinciding with the opening operation, the cam rotates and causes the solenoid valve to return to its original position. Accordingly, the compressed air in the space of the pilot valve is vented to the atmosphere and the valve filling is reset to the original piston. As the open state is retained by the link mechanism attached to the end piston operation.

7.2. closure process:

When the closing coil is energized, nature arc is rotated causing the hook to disengage. Thus, the sector line rotates to release the roller and the piston operating is driven by the closing direction by the spring force closure after closure, the link mechanism is maintained in a state of being ready for the opening operation later.

8. Attention:

When you use the CB observes the following:

I) is holding pressure SF6 gas and the pressure of operation as specified.

2) Operate the shutoff valves correctly.

3) Do not allow penetration of moisture and dust in the SF6 providing point.

4) Do not pump the gas piping and air piping with any object.

5) Do not damage the seal and the seal face on the seal leak gas and air system.

6) At the opening of the breaker handwheel. "

a) confirms that the circuit is not energized.

b) Make sure you turn off the power control.

c) Confirm that the compressed air in receivers is released.

d) Verify that the operating rod manual and the handle are removed before changing the receiver to the compressed air.

7) Do not operate any party other than the mode employment before completing the handful of SF6 gas pressure rated. Do not fill with air before filling with SF6 gas.

When control switch interior parts of the blowing air in the system long enough time and confirm that the supply sufficient air is available before starting any work.

9.Gas Leak Detection:

If leaks gas through any point, which may reduce pressure and loss of insulation properties of gas leak detection is done with the help detector type halogen torch. The sensor operates on the principle that SF6 absorbs a number of electrons as it passes through an atmosphere where the free movement of electrons. The free electrons are generated in the sector by a small radio active source in the presence a carrier gas. These electrons are collected at the anode of the detector and provide a baseline low current is amplified. When the sensor probe is placed near the joints of the SF6 filled equipment and in case of SF6 leaks, it will change the valve amplified current due to absorption electrons by SF6. The variation can be directly calibrated to the magnitude of the leak.

9.2. Detention of the presence conductive particles:

This is done by taking a test when the dielectric test voltage is applied there will an inner ring if metal particles or sharp comers are present. The presence of internal shocks is found with the help of an ultrasonic detector which is very sensitive in the detection of noise from the inner corona. The sector is reflected by the ultrasonic vibrations into audible frequencies and directly indicates sound intensity in decibels. The probe is pressed firmly against the tube envelope grounded while the driver is switched to different AC I DC voltage. If the noise disappears at low voltage is a certain tension, intermediaries and the intensity continues to increase, it is certain the noise is due to the inner corona. It has also been observed that in some cases the little pot in high branched areas of stress high dielectric burns or particles leads to low stress areas. The effect of conductive particles on the breaking strength of SF6 is more serious for the power test voltage frequency of the voltage pulses.

10. Performance of SF6 Breaker:

SF6 circuit breaker gas combines the advantageous features and minimum oil circuit breakers breath of air and has a number of additional benefits over time.

1) It is possible to have many cuts close to the complete failure the ability of any excessive wear.

2) Due to the rapid recovery of the electrical resistance across the contact gap during the interruption.

a) These circuit breakers are free to restrict while passing capacitive currents.

b) These circuit breakers are encouraged to lack of time and are able break every great values and RRRV

c) These circuit breakers are suitable for the closure of new multi-court with any reduction in breaking capacity

3) It is not necessary to modify parts of the chute, even after a period of ten years of service in the system current. This means that there is virtually no problem of maintenance of SF6 circuit breakers.

4) Operation is silent because the gas is used in a closed circuit. There will be no discharge of substances into the arc atmosphere.

5) Puffer type circuit breakers are autonomous and independent because no auxiliary equipment is required.

6) fire hazards are eliminated.

RELAY

A relay is an electrical switch that opens and closes under the control of another electrical circuit. In the original form, the switch is actuated by an electromagnet to open or close one or more sets of contacts.

Operation

When a current flows through the coil, the resulting magnetic field attracts an armature that is mechanically linked to a movable contact. The movement makes or breaks a connection with a fixed contact. When the coil current is turned off, the armature is returned by a force of nearly half as strong as the magnetic force of his position. Usually, this is a spring, but gravity is also commonly used in the startup industrial motors. Most relays are manufactured to operate quickly. In an application to low voltage, is to reduce the noise. In a high voltage or high current application, is to reduce arcing.

If the coil is supplied with DC, a diode is frequently installed across the coil, to dissipate the energy of the magnetic field to the collapse of deactivation, which would have generated a peak of tension and could cause damage circuit components. Some automotive relays already include that diode inside the relay case. Similarly, a network contact protection, consisting of a capacitor and resistor in series, can absorb the increase. If the coil is designed to be powered by AC, a small copper ring can be crimped at the end of the valve. This ring "Shading" creates a small out-of-phase current, which increases minimum tensile reinforcement during the AC cycle.

By analogy with the original unit of electromagnetic a semiconductor relay is made with a thyristor or other Solid State switching device. To achieve electrical isolation an optocoupler can be used which is a light - emitting diode (LED) coupled to a photo transistor.

Relay Types

• Lock Relay
• Reed Relay
• mercury wetted relays
• Polarized relay
• Relay Machine Tool

• Contactor
• Solid state relay contactor State
• Buchholz relay
• Contacts force guided relay
• SSR
• Relay protection against overloads
• Pole & Throw

The types of relays are commonly encountered:

SPST - Single pole once. These two terminals can be connected or disconnected. Two for the coil, like a relay has four terminals in total. It is doubtful that the pole is normally open or normally closed. The terminology "SPNO" and "CNPC" is sometimes used to resolve the ambiguity.

SPDT - Single Pole Double Throw. A common terminal connects to one of the other two. Two for the coil, as a relay of five terminals in total.

DPST - Double Pole once. They have two pairs of terminals. The equivalent of two SPST switches or relays actuated by a single coil. Two for the coil, such relay has six terminals in total. It is doubtful that the poles are normally open, normally closed, or one of each.

DPDT - Double Pole Double Throw. These two rows of change on the terminals. Equivalent to two SPDT switches or relays actuated by a single reel. Such a relay has eight terminals, including the coil.

QPDT - Quadruple Pole Double Throw. Often referred to as Quad Pole Double Throw, or 4PDT. These have four rows of change on the terminals. Equivalent to four SPDT switches or relays actuated by a single coil, DPDT relay or two. In total, fourteen terminals, including the coil.

• protection relay
• Real Overcurrent
• Distance relay

Stop AND SURGE Insulation Coordination

I. Introduction:

Electrical systems in nature have two forms of protection than most current and voltage over current protection against equipment Electric are well known to all, it is not developed here. Protection against overvoltages on the other hand, remains a relatively new to many engineers. The two types of protection just as necessary for the functioning of the system safely.

The importance of protection against Surge of a power system can not be overemphasized. major equipment failures, costly repairs, safety Staff time and facilities are some of the consequences of inadequate protection against surges.

The arresters are designed to limit dangerous tensions in the system. Whether it's lighting system produced reliable values when they occur on power systems. A firewall is a device surge. The functions are to discharge the energy associated with a more state of tension, and withdrawal limits colleagues to present the following transient current through the barrier and return to an insulating state prepared for the next event more tension.

In exercising its power limiting function, some characteristics of lightning protection must be coordinated with the levels of insulation effect on the protected system. Isolation is a fundamental factor that must be taken into account in the application of surge arresters on a system. Coordination isolation is only a small part of most any subject of the application surge. Several other factors must also be reviewed by the engineer when selecting protection against surges. The location of the arresters, the inter-connection of the son to the ground, the insulation level of equipment protection and the rating of the arresters play an important role in protecting equipment more harmful tension.

II.Surge arrester operations:

The basic operation of an arrester is unique. In his state noffi1al, an arrester should act as an insulator. When a high voltage surge occurs. The arrester must cease to be an insulator and must turn in a short-floor then a second million. Operation the type most widely used value of lightning, the type of arrester is processed. Other types of surge protectors, such as expulsion arresters and line oxide arresters (surge protectors uninterrupted) are either declining or too new for a general discussion at this time. The active elements of a arrester type of valve is the spark and valve block. they are housed in a porcelain shell to protect the atmosphere and isolation Outdoor.

The assembly consists of a differential number of air gaps in series with the dielectric sufficient to withstand the highest frequency of power system. During severe stress conditions, the gap should always, a breakdown this voltage level below the insulation withstand voltage level of the device it protects other damage or plant wise and downtime occurs. The gap is therefore the switch that turns the cup. the voltage level at which the arrester is the passive (insulation) Transactions (direction) state, is called the spark more tension.

The block valve control what happens after the arrester has been activated. If only one gap is used, once the surge was diverted to ground, a short circuit between line and dead land and energy 50-Hz current system tries to land causing a fuse or re-close the circuit breaker being interrupted the fault of the current system.

The valve element is exactly as its name indicates. He led the current peaks when it is fluid and constantly conduct online 50 Hz current begins to flow. block valves are able to do because it is composed of a material's nonlinear resistance of silicon carbide. The control block provides a very high resistance at 50 Hz current while maintaining a low resistance to the current rise. In addition, he also consumes energy wave passes through.

Spark and discharge voltage are the two characteristics of a lightning protection are used in calculating margins of protection in the study coordination of isolation. These protection features are published by manufacturers arrester.

III. Arrester Classification:

There are three classifications of arresters used for protection voltage on a system.

1.Distribution Type:

The arresters are generally used in the system distribution for equipment protection. lightning distribution standards are used to protect the oil. distribution transformer isolated These arresters are also used to suppress input line, 11kV and 22kV lines. They are the lowest cost.

2.Intermediate Type:

These units cost about two or three times more than the equivalent units of distribution. To do this, the spark arrester offers lower maximum more and the discharge voltage characteristics that provide a greater margin of protection and the ability to meet levels increased significantly. These arresters also have a decompression system safely evacuate the internal pressure, if the unit is above the porcelain shell has a chance of rupture. These arresters are used for protection of power transformers in ie110/33/22/11KV LV substation 66/22/11KV and sub-transmission substation.

3.Station Type

            These arresters offer the best protection features and the highest heat capacity, but they cost about twice more than the equivalent units intermediaries. As intermediate arresters, surge arresters station have a decompression system safely evacuate the internal pressure if the device fails before a porcelain shell has a chance of failure. These arresters are generally used in 230kV, 66kV and 110KV systems.

4.Basic isolation level:

Basic Impulse Insulation Level (BIL) is the voltage that the insulation of equipment can withstand without damage. The breakdown voltage of insulation is a function of time. Inorder to establish levels of insulation volt-time pulse transformers crash test standard resistant the standard voltage tests are performed on selected units in the essay type. The transformers are subjected to pulse voltage tests (BIL to nominal) and a chopped wave test (15% above BIL). A steep front - wave test (65% above BIL) is also performed on some units. A curve traced by these three points defines the minimum insulation resistance curve insulation coordination (Fig. 3) The real level of support the transformer lies above the curve traced.

5. Surge application:

With an understanding of how a lightning discharges its functions and knowledge of the insulation of equipment, we can now move to the area of application and consider the various factors that make up the application in respect of lightning protection voltage transformers, the selection of surge arresters are worth careful consideration. Various factors must be taken into account to arrive at a reliable and at the same time the economic means of protection. The important points are:

i) selection of the rated voltage.

ii) selection based on standards, codes, recommendations for coordination of insulation.

i) The opinion of arresters:

The nominal voltage of a lightning arrester is defined as the highest 50 Hz at which the arrester is designed to operate efficiently and close after a surge has passed. Because of the grounding and connection, that, voltage is generally higher than the voltage phase to ground / on the healthy phases will increase temporarily and it depends on the ground or factor system. The selection of a voltage surge protection for the station depends on system connection to the land and the nominal system voltage.

As the tension in a lightning impressed during a deep cycle is directly proportional to the voltage surge is a surge 10,000 amps produces a higher voltage discharge if it is poured through a cut-10KV it flowed through a barrier 9KV generally, it is desirable from the standpoint of protecting the equipment to select the lowest voltage rating for the application.

ii) location of lightning:

Surge arresters must always be located as close as possible to the terminal equipment protected. In the case of transformer protection, installation of surge arresters directly on the processor is the best insurance. Appreciable distance between the arrester and the protected equipment reduces the protection provided by lightning and also increases the voltage impressed on the transformer When the discharge voltage. Also because of additional travel distance between the device and its surge, wave could rise above the point of damage, before the surge was to his rescue.

n addition, the barrier-son connection should be as short as possible because of their contribution to the voltage discharge voltage. During the current to the ground by a lightning, the son of interconnection provide a contribution voltage because the current passing through an impedance. Depending on the magnitude of voltage, rate of climb like a conductor, a typical value of input voltage to the discharge voltage by interconnecting conduit is 1.6 kV / ft.

In practice, the protection range is given by the following simple formula.

L = U - Ua Where V x

2 xs

L = Protection line cutting meters

(Measured along the line)

U = voltage withstand shock protected equipment KV. (BIL equipment)

Ua = Spark over voltage arrester in KV (Peak) system. In terms of earth fault, the voltage

V = speed of progression of the wave

line V = 300 m / sec microphone.

Cable V = 150 m / sec microphone.

S = slope of receipt of wavefront kV / sec.

(The range of a lightning protection increases with the difference between the impulse voltage IV and the spark voltage on Go, a surge protector with a level of protection widens the range of protection)

iii) interconnection of grounds:

It is essential that the arrester ground terminal being interconnected with the transformer tank and the secondary neutral to ensure a reliable protection against surges for transformers.

Iv) Insulation Coordination:.

Now consider the choice of an arrester according to standards, codes or recommendations for insulation coordination. Calculation of safety margin is much of one. insulation coordination study. Insulation Coordination is the process of comparing the momentum of the insulation with the tension that may occur through the lens of the severity of the discharge voltage which protection is desired. For a transformer, this means a comparison of the resistance of insulation volt-time curve with the pulse and switching spark up more, and the curve of the arrester discharge voltage.

After determining the rated voltage of a surge, the level protection must be carefully selected. For complete protection of the equipment, the level of "protection" to know. the level at which tensions over were omitted by the barrier must be below the level of resistance by a factor of at least 1.2 for lighting surges and 15 for switching overvoltages. The value thus selected should be checked against that given in the ISS or the technical details provided by the lens manufacturer.

To reach the discharge voltage of a surge in the calculations of discharge voltage of 10,000 amps. Surge is normally used. The following formula defines these two margins of protection calculations:

CWW-FOW IX + N BIL-DV)

MP1 CWW = x 100% = 100% x BIL MP2

Where

CWW = Chopped-wave withstand voltage transformer winding BIL = 1.15

NA = FOW Front wave spark more lightning in KV (CREST)

BIL = Basic Impulse insulation level of the transformer.

DV = discharge voltage of the cut to 10 surge KA.

IX = voltage cables contribution rate of 1.6 KV / ft

MP = Margin of Protection

Insulation coordination in an important aspect to consider when lightning must be given to processors BILS reduced to

Protection against direct hits vi:

i) Protection against direct hits can be handled by protecting the equipment of the station by providing two

a) pole or rod or

b) a net work of ground wires so that the equipment and switches all in the protected area.

ii) The protected area for mast rod is generally accepted as a cone with a base radius equal to the height of the rod or pole above the ground.

iii) For small sub-stations, it may be sufficient to execute a son or IM opposite the railway station adjacent pylons. additional son can be run from tower structure and the top of the station.

iv) The grounds Shield station must be securely attached to the station ground bus to avoid voltage potential difference between the shield and other parts of the g-round resort.

SAFETY IN THE SUB-STATION

Preventing damage to the equipment of the men working on and then because of an accident is an essential aspect of all creation. Preventing accidents is the unexpected is more essential aspect of any institution or organization.

Accidents happen mainly due to the execution dangerous actions and circumstances, these accidents can be prevented through safety measures, implementation of safety procedures and following safety rules.

General methods Security:

I. Although the execution of work, this part of the equipment or the line must be isolated from supply.

2. Using stem discharge load current if any must be paid.

3. Using rods of Earth, all the phases / path leading to the property are grounded in ensuring good earthing.

4. Even opening an AB switch or removing the fuse, it is also advisable and preferable to wear rubber gloves.

5. Use rope belt is another method to take when working in high places.

Security methods to adopt in the sub-stations:

In all work must be present throughout the line, first and foremost element Working to obtain proper authorization from the competent authority to control the execution of work identifying date, time, duration, place of work, etc. affected parties.

For departures and gate stations, the authorized agent issuing Accreditation is SE (LD Centre), Madras, for 110 KV, 66 KV feeders radial Superintending Engineer / Distribution is the competent authority. Of even Divisional Engineer InCharge 33 KV distribution is the competent authority.

Above details of the list of authorized agents is attached (Annex I)

Without obtaining the appropriate approval of the competent authority, no LC should be issued, nor exercised by anyone. If the above procedure is not respected, it is nothing but a suicide. Plus it also amounts to murder other.

Thus, after proper approval, the clear line must be issued to the requested party. But the question and the receiver must be aware of / have a perfect knowledge of the details of the equipment of the SS, the board room etc.

The clear line person emission must clearly record the following:

a) What have been tripped breaker

b) What AB switches have been opened

c) When ground was made

d) What is Safer Place / Line of performing work

Security arrangements in the control room:

A) Key Board should be in an open state so that the keys could be taken quickly in any emergency.

Clear line keyboard should be locked to the state to prevent others from using the keys inside, before the cancellation the clear line permits.

The keys must be placed in the key board in an orderly manner according to their number. Otherwise, lock requested could not be opened in time and the possibility of opening a lock error can happen.

2) Carpets Rubber should be provided on the ground in front of the dashboard.

3) The following information must be clearly displayed in the control room.

Approved instructions for operating all equipment.

Break instructions down.

Mode employment, including for emergency operations to perform when operating the Buchholz relay. differential relay, trip control group, Total power failure, network failure. The operator must be thoroughly familiar with the instructions above and must be able to act quickly and effectively.

4) The Council containing provision of DC cables. A wiring diagram and panel available Grounding must be displayed in the control room. This is necessary to attend the faults immediately after their accident.

5) DC earth leakage test system must be available.

6) It should not be any defective sockets, switches and sockets in the control room wiring.

7) A respirator should be available in the Ready state.

formed Stools of insulation material must be used to operate the equipment high voltage communication (telephones).

9) An adequate number of rubber gloves, rope belt, rod, discharge, and ground rods in Good Condition should be available in the control room.

Battery room:

1. Hall of the battery must be enclosed in the condition.

Naked flame is prohibited inside the hall of the battery "and" no smoking "warnings should be kept in writing on the door of the hall of the battery.

2. An exhaust fan should operate.

3. Specifies DC volt meter test cell, electricity meters and thermometers should be available in the battery room.

4. cell voltage driver, the gravity specific and temperature must be taken each week.

5. The specific gravity should not be kept below 1195 to 15.6 C and less than 1183-32. 20 ° C. The battery should not be allowed to discharge below 1160.

6. Cell voltage should be maintained between 1.95 V to 2.05 V. The battery should not be allowed to discharge below 1.85 V.

7. Batteries should be allowed or more responsible not tax enough. It should not be slowed.

8. electrolyte level should be checked each shift. Ensure that the level is 10mm above the top of the plates.

9. small cells must be corrected on the spot.

10. While taking readings of density, we must be careful not to allow the acid to come into contact with eyes.

Security adopted for processors:

1. Transformers are held periodically on schedule. High-voltage switches side and LV side must be isolated after the reduction of the load by tripping circuit breakers.

2. Kiosks and OCB: All parties Live booth would tape HT. To be protected by wire mesh. There should be evidence of vermin. The keys are kept with the lock. When more than open the door of the kiosk, booth must be triggered link should be opened by the key lock. The opening of ties should be physically verified. After all the above precautions, the tank must be lowered down. adequate care must be taken and we must keep in mind that the offer is available to the roof.

Oil leak must be stopped. Back Power is avoided.

Cotton waste should not be used for cleaning.

3. AB Switches:

Handle AB switch must be grounded properly. Blades must be kept in the open position. It should not be automatically closed, proper maintenance must be done for that. AB needles should be opened fully. AB switches must be locked on the two conditions. AB switches should be opened only after the triggering of circuit breakers.

. Arcing 4:

Arcing used to circumvent the lightning surges and thus protect the equipment. Only after the execution is correct for arresters, he should be tempted to attend maintenance.Fencing must be provided around arresters. Door arrangements with the lock must be provided. separate groundings are expected to surge.

5. Current transformers:

Transformer current secondary side is short-circuited during maintenance and testing. Before testing, the current transformers must be discharged.

6. Voltage transformers:

primary side voltage transformers must be grounded during maintenance and testing. The secondary side must be grounded in one place. Whenever the context given, or the removal of meters on the secondary side of die potential transformer fuses must be removed and replaced.

7. Capacitors and HT Coupling Capacitors:

The capacitors must be provided within the enclosure. Before attempting to do a job, a good discharge is do. They should not be attempted for maintenance work. Proper grounding must be ensured during the execution of the work. After completion, ground must be removed.

Earth pits. 8:

earthing substation must be properly maintained so that the earth resistance is minimum. Water should be poured into the earth pits daily. earth connections must be capable of protecting workers in electrical equipment and protect the equipment during gross negligence in course. resistance to ground must not exceed the following limits.

stations of the grid: I Ohm other sub-stations .. 2 Ohm.

Distribution transformers .. 5 Ohm.

They must have a distance of 5 feet between the fence and substation / equipment electrical points life. The fence shall be grounded every 200 feet, separately. In general, the grounding of fence must not be linked The ground at the substation. But if the game is less than 5 feet of fence to land the feet must be tied to the grounding substations. Doors iron fence of the substation must also be grounded separately.

9. Fight against the burning of equipment:

These facilities are to be kept in good condition and working. appropriate schedule of maintenance must be done to keep them in good conditions. These facilities should be maintained in an easily accessible way to use them immediately in an emergency. pile of dry sand must be available where needed. empty buckets should be provided.

10. Yard SS

1. SS court should be provided with fencing.

2. unauthorized persons do not enter the court

3. Cable ducks must be provided with the plates.

4. Better lighting is required for the court.

5. A council warning with a screen "Dogs umbrella" should not be brought within the court "must be provided at the entrance to the court.

6. A separate room shall be provided to maintain the empty barrels. At the entrance of the room "no smoking" the Council must be provided.

General

1. The territory of the workplace that has been declared safety work must be clearly identified by attaching a rope. Within this limit must be set by hanging a green flag. Beyond this limit where it is dangerous work must be identified by a red flag.

NOTE 2. whenever necessary advice such as "Men on the work "Do not" safe for work ", etc., must be provided.

3. If an unauthorized, unqualified staff to find near the equipment that can be done with the help and under the watch of experienced personnel and licensed.

4. The conversation is strictly forbids execution of any work Wile. It should be totally avoided, especially when the work is done on all busbars.

5. Place the materials, tools and plants and people must be at a safe distance from the Live. parts.

6. T & PS as keys, etc. must be lifted and lowered by means of ropes and not by throwing and catching.

7. Study and a ladder safely with steps at appropriate intervals should be used. To avoid slippage of the ladder precaution must be taken at the bottom of the ladder by providing empty gunny bags.

8. Lifting a ladder or rods (Earth) to only horizontally. Vertical

lifting can cause damages, interrupting with security clearances.

9 The bus and the art of online links; be held open while work on OCB

About the Author

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