Air Blast Circuit Breaker (Type DCVF) HBB Make

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The breaker is designed on the unit construction principle comprising the following main blocks :-

Arc Extinction Units.
Control Units
Supporting insulators.
Air receivers.
Apparatus cubicle.

A complete 220 kV 132 kV breakers consist of three identical poles with control cabinet containing the controls.

Constructional Features:

Basically each pole of a breaker comprises a compressed air receiver, which are mounted on the vertical supporting hollow insulators which carry the arc extinction chambers. The receiver also carries the control unit and the main valves which are placed just below the hollow in insulators columns. These insulators columns also act as pressure pipes for transmitting the compressed air from the reservoir to the arc extinction chambers through main valves. Each pressure pipe is provided with ventilating cartridge which keeps the hollow insulator continuously ventilated with dry expanded air preventing condensation inside the insulator when the breaker is closed.

The control block mounted on the receiver is the nerve centre of the breaker and contains all the elements for the centre of the breaker such as control solenoids, control pistons and valves for closing and opening of the breaker. Each control block is also provided with a heater and an auxiliary switch.

The arc interrupter units, which are housed in the arc chamber insulators are connected electrically in series, the number of interrupters depending upon the voltage rating and the breaking capacity.

Each breaker is provided with a control apparatus cubicle which houses the following :-

A double control valve operated locally by push buttons for opening and closing of the breaker, with a device to block, in the event of low pressure.
A pressure gauge.
A set of pressure switches to block closing, opening and re-closing respectively in the event of low pressure.
A pneumatic supervision device with ‘ON’ & “OFF’ indicator and auxiliary switch.
Heater elements to keep the air in the cabinet dry and warm.
Series terminals for wiring connectors to breaker poles and control room.

Operation:

The control of the main breaker is extremely simple. If there is no compressed air in the chamber, the contacts are kept closed by strong springs. When the compressed air flows into the chamber, the contact open. after extinction of the arc the exhaust of the chamber is closed so that the open contacts remain under compressed air. Thus the entire control operation consists in supplying compressed air through the insulator columns to the arc extinction chambers and venting these columns. No mechanical coupling whatsoever is provided between the base of the breaker unit and the arc extinction chambers.

when an order to open or to close the breaker is given, this passes from the control cabinet to electro pneumatic valves incorporated in the control block mounted on their receiver. These control valves in turn actuate all the main valves of the breaker. These main valves are fitted directly on their tank at the foot of the corresponding columns.

Pneumatic Supervision :

In case of a command to close, if anyone pole does not close, and other tow poles close then immediately closed poles will open again and similarly in case of a command to open, if one of the poles does not open, it receives a direct command to open after a set time lag. In both the above cases, an alarm contact is energized which is used to sound a bell or a hooter.

Yearly Maintenance :

20 A-01 Y	Cleaning :
	Open operating switch cubicle and clean the cubicle for webs, dusts etc. Check whether the insulators are dust free, if not, then clean the outside surface with non fluffy cloth. (Preferably mulmul cloth). Open control block cover and clean the cubicle for webs, dust etc. Dismantle filters (4003 & 4004) (Reference to HBB Manual MKR-1101/74) and clean them carefully with petrol. Drain out air of air - receivers and open the side covers, clean the inside of the tank by mulmul cloth tied on a bamboo. Check for any moisture condensation. Clean and flush compressed air pipes.
20 A-02 Y	Air Leakage :
	Check and compare running hours of compressors which can indicate excessive increase in air leakage. Check for air leakage from various valves, pressure gauge (4800), back control apparatus (4200) and air pipe lines, main valves, piston, chamber and insulation column. replace packing rings if leakage is detected. Check whether air from compressors coming to ABCB is perfectly free from oil and water. Check whether service pressure of the breaker is always between 15-16 Kg./Cm.^2. Check whether non return valve (4002) is working alright and prevents the air receivers from being drained off in case of fall in pressure in the incoming lines due to leakage or any other reason. Check the alarm which functions for any reasons the pressure in the breaker drops to the minimum level for operation of the breaker.
20 A-03Y	Earthing :
	Check that earth connection of main structures and control cubicles are intact and tight.
20 A-04Y	Lubrication :
	Proper lubrication (as detailed in manual) be done at following points. Control block pins and moving parts. Auxiliary switch pins in apparatus cubicle. Bearing of main valves. Note : Graphite oil and DC 55 M Silicon Grease are only to be used.
20 A-05 Y	Foundation :
	Check that foundations are not having any cracks and foundation bolts and nuts are tight.
20 A-06 Y	Heaters :
	Check that heaters provided in control cubicle, switch cubicles are working and thermostat is alright.
20 A-07 Y	Wiring Connections :
	Check that wiring connections are tightly secured, no loose connections should be left which shall lead to malfunctioning of the breaker.
20 A-08 Y	Jumpers and Clamps :
	Check that jumpers and terminal clamps are properly tightened.
20 A-09Y	Tripping of Breker :
	Check the tripping and closing of the breaker locally and from remote, if not in order then rectify the defect.
20 A-10 Y	Tripping of Breaker At 50% D.C. Voltage :
	Check whether tripping coil operates on 50% of its rated D.C. voltage. If not then check the coil and remove the defect.
20 A-11 Y	Contact Resistance :
	Measure and compare contact resistance with initial values.
20 A-12 Y
	Record, the other defect.

Tripping Based Maintenance :

20 A-13 T	Record short circuit trappings if any and identity the phase which has cleared the short circuit fault current. Arcing contact (After 5000 operators) Inspect arcing contacts (3002) Replace arcing tip (3001) when it is burnt in the form of a crater or when its front is burnt about 2 mm. Before inserting the new nozzle contact (3002) in to tube apply a very fine film of Silicon DC 55M Grease. Replace packing rings (3021) and lubricate with DC 55M grease check the resistance of arcing contact (3202).
20 A-14 T	Valve cartridge of control block (After 5000 operations) Dismantle valve- cartridge and replace it in control valve (1212) and (1213), resetting Device (1214), and reloading device (1211). Before inserting the new cartridge, apply a very thin film of graphite oil. Ensure that the matching of various levers is as per the instructions, check the engagements and settings using filler gauge. Roll pins for locking be sealed with apoxy putty.

Maintenance After Every 5 Years :

To be carried out regardless of number of operations executed by the breaker.

20 A-15 F	Hollow Insulator Columns :
	Examine inside of all hollow insulators including those of resistor contacts. Clean inside with acetone and mulmul cloth and ensure that no remains of cloth is left out before reassembly. Please follow instruction manual.
20 A-16 F	Ventilation Cartridge :
	Remove ventilation cartridge (1005) and carry out test according to instruction in appendix 'C' of maintenance manual. Do not interchange the V-cartridge valve.
20 A-17 F	Back Signaling Device :
	Dismantle back signaling device, clean it carefully with petrol, before assembly apply thin film of graphite oil to piston (4203) and (4214) and to the internal wall of the cylinder.
20 A-18 F	Main Valve :
	Dismantle back signaling device, clean it carefully with petrol, before assembly apply thin film of graphite oil to piston (4203) and (4214) and to the internal wall of the cylinder.
20 A-19 F	Air Receivers :
	Inspect (Clean and dry) the inner side of air receiver (proceed as per 20 A-15 F)
20 A-20 F	Control Block :
	Remove control block and dismantle into its principal points. Clean it carefully. Reassemble it carefully and in particular also avoid any deformations of locking pin and valve tappet. Ensure control block bearings are not jammed. Replace packing rings. Apply a very thin film or two/three drops of graphite oil on all joints. Proceed as per sub Para 20 A-14 T.
20 A-21 F	Apparatus Cubicle :
	Examine installation of apparatus cubicle externally, check tightness and correct position. Apply 2/3 drops of oil on all joints marked with dots.
20 A-22 F	Filters :
	Dismantle filters (4003 and 4004) and clean them carefully with petrol. Before re-assembling clean all pipes as per instruction manual.
20 A-23 F	General :
	Check painting of apparatus cubicle and air receivers from inside with emalite paint. Check earthing of each point. Check and tight the connection between different poles and jumpers. Check vermin proofing of apparatus cubicle. Check and tight all electrical connections in the cubicle.
20 A-24 F	Important :
	Do ensure that all the gaskets and O-rings which are removed from various sub assemblies shall be replaced by new ones. for sticking gaskets, just a bare minimum quantity of Hylomer or Dunlop Maxi fix, at a few points only, should be used. Do not use lubricants other than Graphite oil and Silicon Grease DC 55m. Seek Firm's assistance if required.
20 A-25 F	Refilling and Checking of ABCB :
	Fill the ABCB with air gradually. Measure loss of pressure during operation. Check pole discrepancy operation. Check operating times. Following timings are required to be recorded. Closing time. Operating Time. Close-Open Time. Check all indications alarm and inter locks. Heater Circuit. Compare these results with commissioning results. Take Advice of firm, if necessary.