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168 kV Contract Circuit Breakers Make

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Constructional Features

The Contract circuit breakers are low oil content type circuit breakers. The main components of this circuit breaker are.

  • Interrupting part (contract chamber)
  • Intermediate mechanism part.
  • Operating porcelain insulator.
  • Base mechanism.
  • Supporting porcelain insulator.
  • The operator part.
  • Foundation frame.
  • Auxiliary air receiver.
Contract Chamber :
(a)

The contract chamber is installed facing downward, and the moving contacts moving contacts move downwards. Therefore, the moving contacts move in the opposite direction to the direction in which the gas rises after interruption, and a perfectly oil,-immersed isolator is thus formed.
(b)

The primary arc and the secondary arc are generated almost at the same time, and the equipment is constructed such that a pure oil flow will be given to the secondary arc by the oil pressure of the primary arc. thus, there is a short arcing time, and a highly superior interrupting performance is displayed.
(c)

The movement of the primary moving contact is performed by means of the auxiliary rod, of the auxiliary rod, which moves parallel to the secondary moving contact. As shown in the diagram, the primary moving contact is closed by the auxiliary rod, which pushes up the bottom of the insulating rod, At interruption, it is lowered a definite distance by the compression spring following the movement of the auxiliary rod, and it is stopped automatically by the dashpot operation.
(d)

There is a pressure oil piston on top of the primary stationary contact. It is pressed upwards by the moving at closing. This compensates for the insufficient arc quenching power when a small current is being interrupted. It also eliminates residual gases at reclosing, thus improving the interrupting performance. The oil flow caused by the pressure oil piston enters the primary arc chamber from the back of the stationary contact and descends towards the secondary arc chamber through the primary oil spouting port. At this time, the primary arc is expanded by blasting it towards the oil spouting port. This blasting also has a direct arc, extinguishing effect on the primary arc. Besides, the gas produced by the arc which has been expanded several times, also performs blasting operation with respect to the secondary arc. When the interrupting current is very high, the movement of the pressure oil piston will be stopped by the reaction of the pressure of the gas generated during interruption, and the generation of excessive gas pressure will be prevented automatically.
(e)

Like the primary arc chamber, the secondary arc chamber is also composed of arc resistant synthetic insulating materials. It is designed to display the most effective arc extinguisher effect. The oil pressure generated by the primary arc is utilized, and the oil flow, mainly axial flow, is added to the primary arc.

In addition, the residual suspended gas of the primary arc escapes through the little holes of the exhaust valve on top of the contract chamber. besides, when the gas pressure becomes extraordinarily high, the excess gas is discharged through the safety valves so that the pressure inside the contract chamber will not rise above a definite pressure.
Intermediate Mechanism Part :
 

The intermediate mechanism consists of the straight line motion mechanism, comprising the roller guide, the straight line lever, etc., and the opening spring which accelerates them.

The straight line lever, which performs the straight line movement, is coupled with the parts outside the oil by means of the axial rotation of the operating lever. The oil seal in the axial rotation part is maintained strictly by means of the V-shaped oil seal packing made of special oil-resistant synthetic rubber.

The mechanism for converting the vertical rotating movement of the quick-break spring of the intermediate mechanism, the operating rod, and the operating porcelain insulator into horizontal movement are all located outside of the oil; therefore, they can be inspected easily.

The operating lever for the axial rotation is equipped with a strike indicator, so that the movements of the moving contacts inside the oil  can be understood by observing the indicator.
Operating Porcelain Insulator :
 

Since the operating porcelain insulator is sailed by means of synthetic rubber packing, there is no possibility of moisture penetrating inside and causing deterioration of the insulation.
Base Mechanism :
 

The base mechanism consists of devices for converting the horizontal movements of the opening spring for interrupting and the horizontal operating rod into rotary movements of the operating insulator.
Operator :
 

The operator is of the upright type and is located at an elevation tower than the surface where the circuit breaker is installed. Therefore, it can be inspected easily and safely even when electrically charged.

The operator consists of the operating mechanism box, the operating valve box, the operating cylinder, and the operating valve box, the operating cylinder, and the auxiliary air reservoir.

Operating Mechanism :

The operating mechanism consists of a high simple link device. It is of the mechanical trip-free system. In other words, it can be made to trip freely even when the operating piston is in operation.

A special roller type tripping mechanism is used; it is manufactured with a particularly high precision. Thus, the tripping operations are performed quickly, smoothly and accurately, and the tripping time is quite stable.

The mechanism is also provided with an indicator telling the number of times of operation. This is convenient in maintenance services, since the number of operations is automatically recorded.

Operating Valve Box :

The magnetic valve, the main valve, the rust-proof tank and the electric heater are contained in the operating valve box. The solenoid valve can also be operated manually by pressing the manual push button. The solenoid valve is also be provided with a low-pressure inter locking device; the solenoid valve will not operate even if energized after the atmospheric pressure has dropped below a specified level. This prevents incomplete closing caused by dropping of the atmospheric pressure.

The interlocking pressure is set at about 80-85% of the rated operating pressure.

The rust proof tank is a device for supplying oil to the walls inside the operating cylinder during closing operations. It guarantees smooth closing operations. Always use a low-viscosity machine oil in this rust-proof tank.

Trip-Free Contactor :

The trip free contactor is used together with a limit switch which closes at the position at which closing operations have been completed. This makes it possible to conduct electrical trip free operations.

It has the following distinctive features :

Closing operations are performed accurately and safely. Overheating of the closing coils is prevented. The amount of compressed air required in closing operations can be economized.

Repeated closing is absolutely impossible.

Explanation Of Closing Operations :

As soon as the solenoid valve has been energized, the compressed air which has passed through the solenoid valve will function to drive the piston of the main valve and to open the main valve. Compressed air from the auxiliary air reservoir will be introduced inside the cylinder, where it will drive the operating piston and perform closing operations. Simultaneously with the completion of closing of the circuit breaker, the limit switch will be closed, and the current of the solenoid valve will be interrupted by the trip-free contactor.

As the solenoid valve closes, the air is discharged from inside the main valve cylinder. As the main valve closes, the air is discharged from inside the operating cylinder. With this, the closing operations are completed.

Explanation Of Interrupting Operations :

As soon as the trip coil has been energized, the armature is attracted, and No. 1 and 2 hooks are released, in that sequence & the circuit & the circuit breaker is rapidly interrupted.

The current of the trip coil is cut off by the auxiliary switch. The operating piston is reset by the piston resetting switch, and the mechanism is rest.

Reclosing Switch :

High-speed reclosing can be performed by the reclosing switch by combining the mechanical part with the non-trip-free mechanism (No. 2 tripping mechanism).

As soon as the protective relay for the main circuit has operated, the No. 1 trip coil will energized, and the circuit breaker will be opened by the No. 1 tripping mechanism.

As soon as the closing solenoid valve has been energized during the interrupting stroke, compressed air will for inside the cylinder and a change can be made immediately to the reclosing stroke. In the event of another interruption immediately after reclosing, as soon as the No. 2 trip coil has been energized, the circuit breaker will be opened by the No. 2 tripping mechanism.

The equipment is constructed such that immediately after interruption has been performed by the No. 2 tripping mechanism, the No. 1 tripping mechanism will be tripped in preparation for the next closing. Time limit contacts are also provided so that the reclosing time can be selected easily.

Operational Features :

  • Manual Operation :
    During installation and adjustment, do not perform closing by means of compressed air or tripping either by solenoid operation or by means of the manual tripping handle.
    Toe perform closing manually, remove the plug of the operator cylinder cover, and screw the operating spindle into the screw hole in it. Turn this around with manual handle, and close the circuit by pressing the piston.
    Before making manual adjustments, be sure to insert the safety wedge into the armature part. (Also be sure to remove it after the manual adjustments have been completed).
    The circuit breaker is closed when the roller at the tip of the piston rod has been energized on the supporting latch at the bottom of the operating part. There is also a margin of about 3 mm more (one-third revolution for the manual handle) on the piston stroke. Be sure to check that enough margin is present, as closing will be impossible if this margin is not there.
    Also be careful not to force the piston beyond this point.
    To make the circuit breaker open screw the handle further-in, then it will be easy to remove the supporting latch. Remove the supporting latch. Remove the supporting latch and turn the handle back gradually to its original position. The open position is that where the piston rod has stopped moving. The same thing apply to reclosing type operators, the only difference is that the latch substitutes for the No. 1 tripping hook.
    Before, operation, lubricate the threaded part and the tip of the manual operating spindle.
    The manual closing handle is to be used only during adjustment, it is absolutely forbidden to use it during electric charging.
  • Inspection Of Three-Phase Simultaneous Contacts And Measuring The Touch Length :
    • Checking And Adjusting The Three-Phase Simultaneous Contacts
      Electric lamps are connected in series to the interrupting part for each phase, and manual switching is performed. In this way, a check is made to see whether contacting occurs simultaneously by observing whether the lamps glow on simultaneously or not. If there are discrepancies in the contacting, adjust by screwing in or out the horizontal adjusting rods between the phases, taking phases A as reference.
    • Measuring The Touch Length :
      Measure the touch length of each phase by means of the contact measuring rod above the spring of the oil piston. The contacting dimensions can be obtained by measuring the dimensions of movement after the lamps go on above in (a) until the completion of closing.
      The following are standard values of the contact dimension.
Class 168 kv Class

Closing Methods

Manual Closing

 34 mm.

Pneumatic closing

40 mm.
  • Pneumatic Operation :
    Before beginning pneumatic operation, all parts must be subjected to a careful examination for air leakage. Air leakage must be eliminated ass more than 10-hours is required for the air pressure to drop 1 am. from the rated operating pressure after the stop-valve at the entrance for the auxiliary reservoir has been closed.
    Operation should be conducted in the beginning with a low air pressure, then raise the operating pressure, after check have been made for abnormalities. At this time, examine the interlocking pressure of the low-pressure interlocking device of the solenoid valve. It is usually adjusted at 80% of the rated operating pressure.
    When these pneumatic operations could be performed, then all the adjustments of the circuit breaker are completed. After the completion of the adjustments, measurements should be taken of the following items. They are to be compared with the initial test results and also to be used as maintenance datas for the periodic inspections, to be made in the future.
    The operator is provided with an electric heater to keep away moisture. This heater should be switched on during the winter (at temperature of 50C or less) and during the rainy season (at humidity of 80% or more.)
    • Minimum Closing Pressure :
       The magnetic valve is equipped with a low-pressure interlocking device. It prevents incomplete closing by preventing the magnetic valve from operating at a low pressure even if the operating switch is operated. Putting this interlocking device out of operation, gradually reduce the operating air pressure, and measure the minimum closing air pressure. There is a point for installing a manometer on the side of the auxiliary air reservoir. Measurement can be taken conveniently by attaching a manometer here.
      If this minimum closing pressure is extremely high, this is a sign that there is something obstructing the movement of the moving parts or the friction has increased abnormally somewhere. On the contrary, if the minimum closing pressure is extremely low, this means that the opening spring has either broken or dropped out of place.
    • Minimum Tripping Current :
      The minimum tripping current is measured by gradually raising the current of the trip coil. At this time, be careful against temperature rise in the trip coil. (The trip coil has a 30-second rating.)
      The minimum tripping current is an indication by which one can judge the condition of the tripping hook. If it is too high, there is either excessive friction on the hook, or the hook is not engaged properly.
      On the contrary, if it is too low, the hook is not securely engaged and is in an unstable condition.

Monthly Maintenance

20 G-01 M Check the porcelain portions of the breaker.
20 G-02 M Check all interlocks provided by the firm.
20 G-03 M Drain-out the compressed Air tank through drain valve, for a short duration to discharge moisture.

Quarterly Maintenance :

20 G-04 Q Check the oil gauge float of the breaker poles. Float should be at the mark of the level.
20 G-05 Q Check the tripping and closing coils and for its deterioration of insulation.
20 G-06 Q Check the operation mechanism.
20 G-07 Q Check the proper working of the heater.
20 G-08 Q Check for any leakage from gaskets etc.
20 G-09 Q Check the rotary insulation for smooth rotation and operation after doing slow closing of the Breaker.

Half Yearly Maintenance :

20 G-10 H Clean the insulators and examine for cracks and chipped sports.
20 G-11 H Take a sample of oil from exhaust valve before and after monsoon and test it for dielectric strength and presence of excessive carbon. If the results are not satisfactory, change the oil after thoroughly flushing and clean all internal parts. Also top-up the oil, if necessary.
20 G-12 H Check oil in the dash pots. Top up, if necessary.
20 G-13 H Fill machine oil in the rust proof tank inside the operating valve box about 70% to ensure automatic oil feeding to the operating cylinder.
20 G-14 H Check the following operations for smoothness :
  • Local electrical tripping.
  • Remote tripping and closing by the switch.
20 G-15 H Lubricate the operating mechanism and Close the doors.

Yearly Maintenance :

20 G-16 Y
  • Dismantle and inspect contraction chamber of each pole.
  • Inspect the contacts and baffler.
  • Check inside of covers of inter phase connecting rods and lubricate the pins and bearings (to be done earlier, if number of tripping on fault exceeds 5)
20 G-17 Y Check gas vent for blocking by insects.
20 G-18 Y Inspect operation of oil piston of the contraction chamber.
20 G-19 Y
  • By using tamp test method and by using slow closing operation.
  • Check that all the 3 poles are closing simultaneously. Adjust by screwing in or out the horizontal adjusting rods between the phases.
  • Measure the touch length of each phase by means of contact measuring rod above the spring of oil piston. It should be 34 mm in each pole, from the point the contacts are just made to the point when CB is fully closed.
20 G-20 Y Measure insulation resistance of each pole between the contact and between, earth connection contact when the CB is open.
20 G-21 Y Carry out mili volt drop test.
20 G-22 Y Measure opening and closing time. It should be 0.06 sec. and 0.3 sec. respectively.
20 G-23 Y Check the local pneumatic closing operations for smoothness.
20 G-24 Y Check tightness of lock nuts of horizontal operating rods.
20 G-25 Y Check wiring for tightness and deterioration of insulation.
20 G-26 Y Check the operation of ON/OFF indication on the Intermediate mechanism.
27 G-27 Y Clean no. 2 hook and armature of reclosing mechanism.
27 G-28 Y Inspect air leakage from main valve and piping.
27 G-29 Y Check that the low pressure interlocking device of magnetic valve operates at the set value of 80 to 85% of rated pressure and stop closing of the CB.
27 G-30 Y Measure the minimum closing pressure after making the low pressure interlocking device of the magnetic valve operative. Compare with commissioning results.
27 G-31 Y Check the operations of antipumping device (Trip free contact) to prevent repetition of close/open motion.
27 G-32 Y Check auto reclosing operation of the CB.
20 G-33 Y Check all interlocks.
20 G-34 Y Get all the protection tested.
20 G-35 Y Check the minimum DC operating voltage.
20 G-36 Y Check foundation bolts for tightness.
20 G-37 Y Check tightness of all HV connections.
20 G-38 Y Check the earth connections.
20 G-39 Y Check heater in the operating mechanism. Keep the heaters 'ON' during rains.
20 G-40 Y Check painting.

Maintenance After 2 Years

20 G-41 TW Dismantle and inspect interior of cylinder and main valve.
20 G-42 TW Inspect contacts of auxiliary switches.

Maintenance After 3 Years

20 G-43 TH Inspect secondary moving contacts of all the poles.
20 G-44 TH Inspect sliding contacts in the contraction chamber.
20 G-45 Th Dismantle and inspect interior of cylinder and main valve.
20 G-46 TH Inspect the contacts of Auxiliary switches.
20 G-47 TH Replace the oil of the dash pot after cleaning from inside.
20 G-48 TH Inspect tower valve of solenoid.
20 G-49 TH Inspect and clean tripping springs, and levers.

Maintenance After 4 Years

20 G-50 FR Inspect lower valve of solenoid.
20 G-51 FR Inspect spring and levers.
20 G-52 FR Inspect slide elements.