Defense mechanism of the SS Circuit Breaker
I. Introduction
The main functions of a circuit breaker interrupts the short circuit current, current-carrying normal up and shutdown normal loads, and providing necessary insulation between live parts and earthed parts. Maintenance problems involved with switches of bulk oil circuit were immense. Minimum oil technology had replaced the oil in bulk technology during the 1950s. Also, technology air jet was developed to obtain higher performance features. However, air separators ovens are very expensive, and operation and maintenance heavy. Therefore, and felt the need during the 1960s for reduced maintenance.
SF6 was obtained from fluorine and sulfur in 1900 by M / s. H. PLEBEAU Mossad. Performance of SF6 in the electric field was studied by M / s. COOPER PS PQLLOCK HG in 4936 and known for more than two decades, the perfection of commercial exploitation was reached during the 1960s. These developments made it possible for low-pressure SF6 gas to be used in isolation switches and BIN are "for cooling purposes, some of the excellent properties of SF6 gas which make it ideal for use in the MAT circuit. switches are:
1. Inertia
2. The toxicity not
3. Electro negativity
4. High dielectric strength
5. Unique are owned by cooling
6. The chemical and thermal stability
7. Good thermal conductivity
8. Non corrosive
9. No Flash
The electrical, chemical, physical, and combined thermal properties of SF6 has the following characteristics outstanding when used in circuit breakers.
1. Security
2. Size Reduction
3. The weight loss
4. Simplified design
5. High degree of reliability
6. Switching of capacitive currents without reignition
7. Very noise coupling
8. Easy to manage
9. Easy Installation
10. Free maintenance service
2. Properties of Sulfur hexafluoride (SF6)
a) Characteristics Physical:
SF6 gas is a flammable colorless, odorless and non-governmental organizations. The fluorine atoms are placed at the corners of a regular octa hedra with the sulfur atom centrally placed at a distance of 1.58 angstrom units. The bonds are predominantly covalent and the equation of dissociation is
SF6 - à SF5 + F __________
The decomposition potential is 15.7 ev. SF6 gas is a very heavy gas and its density is approximately 5.5 times that of air. It is very stable. It is more compressible than air and is the perfect gas law.
Electrical properties b):
The di-electric strength of SF6 gas is 3 times higher than that of air at atmospheric pressure and is only slightly reduced by the presence of air as an impurity. The increase in dielectric strength with increasing pressure. At a pressure of three bars, the dielectric strength becomes equal to the transformer oil. The size molecule of nature and the negative electro explain this strength. The molecule has a diameter of collision of electrons. This results in the capture of electrons that prevents them from achieving additional energy to create. Particle transport current. SF6moiecuie also has the ability to store energy in vibration and electronic levels of the molecule there for the formation of stable ions of low mobility.
The dielectric of SF6 remains unaltered over a wide frequency range. since SF6 has no dipole moment, dielectric constant does not vary with frequency. AT 27.30cy atmospheric pressure, the dielectric constant is 1.00191 and the angle of the loss is 2 x 10-7.
The dielectric properties of SF6 remain the same, even at low temperatures. Unlike the solid insulation materials an electrical fault in SF 6 gas does not result in permanent deterioration of their properties. They break down all equipment filling may lead to a huge increase in pressure due to gas formation, but those risks do not exist in the case of SF6 filling equipment.
c) Arco cooling properties:
The cooling capacity of arc is unique to SF 6. This results in high dielectric strength gas and very rapid recovery of dielectric strength occurs after an arc. SF6 is about 100 times more effective in this regard that the air conditions similar. The low arc time constant and its ability to absorb free electrons due to the negative electro nature makes it an excellent medium for the interruption of arc. The movement of SF6 molecular complex allows it to absorb electrical energy and a stable negative ions. Its tendency to form negative ions around zero current results in the rapid disappearance of electrons released during arcing. Unlike oil, SF6 arcing produces no carbon deposits or monitoring carbon.
The electro-negative property of SF6 may be due to several factors including the diameter of large shock. If the field of electrons lost Power can be absorbed before reaching the energy to create more current carrying particles while a collision, the distribution may be slow or even stop. The diameter of the major collision of SF6 molecule aid in the capture of these electrons. energy can be stored in the levels of SF6 vibration of the atom, forming stable negative ions of low mobility. Thus, the gas is electronegative in nature and shows. Great binding capacity Electron. Therefore the sample gas SF6 arc extinguishing splendid performance.
The arc time constant is directly proportional to the radius of the arc can have a lot of breaks in full capacity of the wave. The characteristic curve of the arch is such that the extinction of low energy b. In a typical case where the power of extinction was the order of 20 KW of SF6 switch, the value of a blast of air is broken into hundreds of kilowatts.
Some ion formation process with 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
Training of positive and negative ions: SF + eA (SF6) + e-+ SF5 F - + e
d) Heat transfer characteristics:
SF6 has excellent heat transfer characteristics, an important criterion for dielectric gas energy applications. The higher molecular weight, with low viscosity SF6 gas allows the convention heat transfer more effectively than common gases. The heat transfer coefficient of SF6 is approximately 2.5 Tip1 that of air under the same conditions. Therefore, when the switch is activated, the small temperature rise.
Wide range e) the temperature:
SF6 in gaseous form and follow the ideal gas laws very closely. Consequently, the pressure change is only modest for a considerable change in the temperature. The low sublimation point of SF6 dielectric ensures greater resistance, even at low temperature, the temperature is-270C liquefaction at a pressure 12 kg / cm ². Therefore, no heater is needed.
toxity f):
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 breakdown products of synthetic zeolite.
g) the chemical and thermal stability:
SF6 gas is inert and is one of the less reactive substances known under normal conditions operation. Can be heated in the quartz at 5000C, not least in the decomposition. SF6 will not react with water, acids and alkalis. Tests have shown virtually no corrosion of dissimilar metals exposed to SF6
h) several constants:
Some properties SF6 exceptional making it ideal for high voltage applications are:
Molecular weight .. 146.05
Sublimation point at 1 atm .. 63.9 ° C
Gas density to 21.19 C at 1 atm 6.139 ..
Liquid Viscosity at 13.52 ° C 0.305 ..
Gas to 31.16 C .. 0.0157
Critical temperature, etc. .. 318.80
Critical pressure bars .. 37.772
Cu.metre volume critical / g 1.356 ..
Dielectric strength rei N2 at 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 phenomenon SF6:
Breakdown of gases are produced when free electrons gain sufficient kinetic energy under the influence of an electric field and collide with neutral gas molecules liberate electrons from their outer shells. A chain reaction, as this leads to an avalanche of electrons. In the case of electro-negative SF6 gas as this mechanism has been slightly modified. The free electrons attach themselves to molecules forming negative ions. SF6 and SF6 + Z-e. The negative ions are too large to cause ionization by collision. This attachment is an effective way to remove the electrons that would otherwise have contributed to an avalanche Electron. This particular behavior leads to very high dielectric strength for electronegative gases.
The breakdown voltage of an electro-negative gas in a uniform field is a simple function of the product of pressure and spacing. degradation characteristics in nonuniform fields will be different because ionization may be the main goal local, due to the presence of regions of high stress. This is the corona. This may be due to surface roughness, corners sharp, conducting or semi-conductor floating particles. SF6 equipment in special care to ensure that these points do not exist in the switch so that a distribution fairly uniform field can be achieved.
4. Principles of SF6 interruption:
Techniques used for SF6 interruption can be classified into two:
a) Double pressure.
b) single pressure system.
The latter can be classified as dual flow nozzle fixed and the only set of piston flow switches.
a) Double pressure:
The roles of isolation and the interruption is performed in separate chambers. SF6 at a pressure of 14 kg / m². cm. stored in a high-pressure chamber. This is used for cooling in SF6 pressure is low (2.5 to 3.5 kg / m². Cm.) Provides insulation. When the contacts separate under fault, high pressure gas is forced into the region of the arch and then continues to the low pressure region. The gas is depleted as the region of low pressure is compressed again and returned to the reserve of high pressure. The arc is between the tip of the bow and ring arcs thus relieving the contact area of branch voltages. A filter with real student remains in the compressor inlet so that all gas decomposition products can be absorbed before returning to move to the system. A system heating with thermostat is provided in the high-pressure tank to prevent condensation of gas at low temperature.
b) Individual pressure system:
In this case, in SF6 at low pressure (3 to 6.5 kg / sq.cm.) provides insulation and energy for the interruption. The switch of the camera consists of fixed and movable contacts, and piston arrangement in the balloon fixed contact. As contact between the mobile guilt, the piston moves forward with great speed. This compresses the SF 6 within the fixed contact sanctify and gas forces the arc resulting in cooling. The force with which the gas could be the explosion depends on the design of the piston arrangement and energy of the control mechanism.
Another improvement magnetic switches is the type world where performance increases strength in moving contact bar by the force of magnetic repulsion. The short circuit current is passed through a set of fixed coils, with the support of the Fed moving contact. A second short-circuiting ring and placed magnetically coupled with primary winding. This ring also acts as a piston. This interaction between. two fields and produces a repulsive force pushes the moving contact bar. The addition of this simple mechanism Magnetic drive improves the wave break.
The only pressure system has an inherent advantage of simplicity in construction. You do not need additional compressor that is relevant in the double pressure. The manufacturing cost balloon-type equipment is lower.
5. Construction:
The arc suppression system uses a single twin synchronized flow pressure balloon type design. This leads to a simple construction.
SF6 circuit breaker, consisting mainly of the following:
Poles of the switch 1. It.
Tube base 2. And the mechanism box
Control Unit 3.
4. Electric air compressor, hydraulic drive mechanism
1.Movable Cylinder (cylinder Puffer) 2.Moving Contact
4.Insulating Contct 3.Fixed Mouthpiece
5.Fixed piston Trapped in 6.Gas before compression
7.Compressed gas between 1 and 5
8.The arc is extinguished action by the balloon
5.1.Breaker Polo:
The main functions of a circuit breaker are carried out of switch pole. The pole consists of the unit switch isolator switch and support.
The unit includes switch fixed contact tube, tube guide, moving the contact tube, balloon or the ignition cylinder and piston. The fixed contact tube is connected to the upper end through. Support.
The guide tube is fixed to the bottom of the terminal. The other end of fixed contact tube and guide tube in which they are subjected to an arc during the arc interruption arc nozzles are provided with cooling. the nozzles are made of graphite material that maintains contact with the wear to a minimum. The moving contact tube consists a spring finger contacts arranged in a ring. The front of the moving contact tube is fitted with a ring arc resistance insulating ring arcs arc of high strength materials
The cylinder blast, which consists of high strength arc of insulating material and movable contact tube are rigidly coupled together and connected to the bus operating in the support insulator. The piston ignition, which is composed of aluminum is attached to the lower platform terminal. The fixed contact tube, guide tube, moving the contact tube, the explosion of the cylinder and the piston explosion are "all housed within one of porcelain insulator. When the switch is in the current position of the streams near the terminal up and down through the terminal support, contact with the fixed tube, moving the contact tube and guide tube.
The insulator support, apart from supporting the switch unit to provide insulation between the parties live and earthed parts. It houses the bar operation (isolation), one end that connects to the switch unit and the other end is connected to the mechanism.
5.2. Box Stem underground facility:
The tube base which supports the pole switch and the box acts as a mechanism of local air tanks. The case of the electromagnetic valve mechanism closed, the closure of the coil, trip coil and the operating cylinder. Lowercase mechanism encloses the entire lever system to transmit force from the operation of the box mechanism for the switch pole.
Unit 5.3.Control :
This accommodates the gas pressure switches, gas detector density, gas pressure gauge, pressure gauge, air valve Heater, auxiliary relays, terminal blocks, etc. for the electrical and pneumatic control and control of the switch. On the air control devices and systems SF6 gas are common in 3-pole switch.
5.4. Compress
Since the energy required for operation the greater the MOCBS good air compressor or the mechanism of electro-hydraulic actuator is used.
6. The principle of arc extinction:
When the switch is in the closed position of the mobile assembly bridges contact the fixed contact tube and guide tube. When you start an open operation, the explosion of the cylinder moves the piston explosion fixed for the SF6 gas in the ignition cylinder is compressed to a pressure necessary to extinguish the arc. The compressed gas during the previous process is released only when the contacts are separated by movement of the Assembly of contact acting as a slide valve. In the instant of contact separation the arc strikes between the front of the nozzle arc extinguishing tube fixed contact and the ring arc moving contact tube. The compressed gas cylinder explosion released into the radical break as separate contacts. As the moving assembly more contact, the arc between the front of the nozzle fixed contact and ring contact arc motion is transferred from the arc ring mobile contacts the mouthpiece of the guide tube, gas jet and his own forces of electrodynamics. the arc is elongated by the axial gas flow in nozzles and safety of extinction. While the arc is interrupted, the cylinder is made explosion, arc resistant insulating material and closed off the Assembly of arc, not protection of the porcelain insulators arc effects. After arc extinction, the Assembly moving contact and the shock wave is free from any part of the camera that can have a transition effect or influence the electric field distribution.
7. Principles of operation:
7.1. Opening operation:
When you activate the trip coil, the area of the pilot valve is full compressed air refueling valve moves to the right. The space in the operating cylinder is filled with compressed air from the air is received and the operating piston is rapidly driven to the left. operating rod to operating piston is pulled in the direction of opening to push the cylinder into the high-speed balloon through the insulated operating rod bushings support. SF6 gas in the cylinder and the balloon is compressed SF6 gas blast extinguishes the arc generated between the movement and the stationary contacts.
Simultaneously with the opening operation, the camera rotates and causes the valve coil to return to his position original. As a result, the compressed air in the space of the pilot valve is exhausted into the atmosphere and the load valve is restored to the original piston. As the State kept open by the connection mechanism attached to the end of the piston operation.
7.2. Operation time:
When activated the coil end, the nature of the arc is rotated causing the hook to be disconnected. Thus, the line rotates sector to release the roller and the piston operation is driven in the closing direction by the force of the spring end, the end of closing, the connection mechanism was held in a state of readiness for the subsequent opening operation.
8. Caution:
By operating the switch observes the following:
I) To maintain the correct pressure of SF6 gas and air pressure specified operation.
2) Operate the valves correctly.
3) Do not allow the entry of moisture and dust at the point of SF6 gas.
4) Do not pump the gas and air lines with any object.
5) Do not damage the seal and face seal leakage in the sealing of the union in the gas and air system.
6) When you open the switch circuit by the operation manual. '
a) confirm that the main circuit is not activated.
b) Make sure to turn off the source control supply.
Confirm c) released the compressed air in the receivers.
Confirm d) that the bar of service and retire before driving to change the compressed air receiver.
7) Do not operate any other party that the handling instructions before filling the SF6 gas nominal pressure. Do not fill compressed air before filling SF6 gas.
When control of the interior parts of the switch, the air blows into the system sufficiently long time to confirm that sufficient air supply is available before commencing any work.
9.Gas Detection Leak:
If gas leakage through any point, this can result in reduced pressure and the consequent loss of properties insulation gas leak detection is done with the help of a halogen-type detector of the torch. The detector works on the principle SF6, which removes a certain number of electrons passing through an atmosphere where the flow of free 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 and the detector to give a small baseline current that is amplified. When the detector probe is held near the SF6 filled joints SF6 leaks computer and will change in valve current amplification due to absorption of electrons by SF6. The variation can be directly calibrated to indicate the magnitude of the leak.
9.2. Detecting the presence of conducting particles:
This is done by performing a dielectric test when the test voltage is applied there will be an inner ring where the metal particles or sharp corners are present. The presence of internal discharges found with the help of an ultrasonic detector that is sensitive in the detection of noise due to corona inside. The sector translates the ultrasonic vibrations at audible frequencies and directly shows the sound intensity in decibels. The probe is pressed firmly against the tube envelope of land, while the driver is activated in different voltage AC I. If the noise disappears at low voltage, appears at some intermediate voltage and the intensity continues increasing, the fact is that the noise is due to the inner corona. Has also been observed that in some cases the bathroom small sharp branched into areas of tension dielectric particles are burned or taken to the areas under stress. The effect of conducting particles in SF6 breaking strength is more serious for the power tests voltage frequency of voltage impulses.
10. Performance of SF6 Breaker:
SF6 gas circuit breaker combines the advantageous features minimum oil circuit breakers and air and has a number of advantages over both.
1) It is possible a large number of breaking operations near complete break with the capacity to carry out any undue.
2) Due to the rapid recovery of the dielectric strength between contacts during interruption farewell.
a) These switches are free while restricting the change of currents capacitive.
b) These switches are an incentive to faults quickly and are able to last an hour in each RRRV high values and
c) These switches are suitable for the closure of several short re any reduction in their ability to break
3) No need to change any parties in the chamber last minute, even after a period of ten years of service in the real system. This means there is practically no problem maintenance for SF6 circuit breakers.
4) The operation is silent because the gas is used in a closed circuit. There will undertake any landfill arc products in the atmosphere.
5) balloon-type switches are autonomous and independent, because no auxiliary equipment is necessary.
6) The fire hazards are eliminated.
IC
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 contact in motion. The move makes or breaks a connection with a fixed contact. When the current to the coil is off, the armature is returned by a force of about half as strong magnetic force to its relaxed position. Usually it is a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low-voltage application, this is to reduce noise. In a high voltage or high current application, this is to reduce arcing.
If the coil is activated by the DC, a diode is to often installed through the coil, to dissipate the energy of the magnetic field collapsing at deactivation, which otherwise would generate an increase in blood and can cause damage to circuit components. Some automotive relays already include that diode inside the relay box. Either a contact protection network, consisting of a capacitor and resistor in series, can absorb the increase. If the coil is designed to be activated with air conditioning, a small copper ring can be waved to the end of the solenoid. This "shadow ring" creates a little out of the current phase, which increases the minimum pull the truss during AC cycle.
By analogy with the functions of the original electromagnetic device, a solid state relay is made with a thyristor or solid state another switching device. To achieve electrical isolation optocoupler can be used one which is a light - emitting diode (LED), along with a photo transistor.
Types of relay
- Interlock relay
- Reed Relay
- Mercury-wetted relay
- Polarized relay
- Relay machine tool
- Contactor relay
- Contactor Solid State Relay
- Buchholz relay
- Forced-guided contacts relay
- Solid State Relay
- Overload protection relay
- Pole & Throw
The following types of links are often:
SPST - Single Throw a single pole. These have two terminals that can be connected or disconnected. Among them, two for the coil, for example, a relay has four terminals in total. It is ambiguous whether the pole is normally open or normally closed. The terminology "SPNO" and "SPNC" is sometimes used to resolve ambiguity.
SPDT - Single pole double throw. A common terminal connects to any of the other two. Among them, two for the coil, for example, a relay has five terminals in total.
DPST - Double pole single throw. These have two pairs of terminals. Equivalent to two switches or relays SPST powered by a single coil. Among them, two for the coil, for example, a relay has six terminals in total. It is unclear whether the poles are normally open, normally closed, or one of each.
OHM - Double pole double throw. These have two rows of change through terminals. Equivalent to two SPDT switches or relays actuated by a single coil. This relay has eight terminals, including the coil.
QPDT - Quadruple Pulling double pole. Often called pole double throw quad, or 4PDT. These have four rows of change through terminals. Equivalent to four SPDT switches or relays actuated by a single coil or two DPDT relays. In total, fourteen terminals including the coil.
- Protection Relays
- Real Overcurrent
- Distance relay
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