VCB vs OCB

Oil circuit breaker was commonly used in the voltage ranges upto 33kv before VCB became more common.There are 2 types of OCB --- minimum oil or low oil circuit breakers( LOCB ) and bulk oil CB (MOCB).Min oil CB,LOCB uses several litres of insulating oil per phase with individual "bottle" for each phase thus phase segregation is achieved.MOCB require much more oil and all the 3 phases' breaking contacts are immersed in oil in a common tank.While it is good that the oil medium is able to quench the electric arc while breaking the circuit,itself is sujected to carbonisation and degeneration over several years (more than 10 years) of switching operations.It is common to see 30 to 40 years oil OCB still in operation.

VCB are simpler and lighter in construction and does not need any change of oil.It is a trouble free CB though has a shorter history,it has been in used longer than its intended life span of say 30 years.For system voltages upto 22KV,select VCB without any doubt.The advantages are cheaper cost,still compact,very reliable (10,000 switchings at normal currents,20 times breaking fault currents at 20/25 KA,3 seconds ) and maintenance free.Forget about OCB which is already obsolute in many parts of the world.

Regards,

Khor

Do you have practical experience of VCB. verses OCB.

If vacuum is finished there isno indication so when ever there is VCB in off its contact will remain in ON position and if it is not rack out there is chance of accident .VCB are costlier then OCB almost Twice in price.In VCB male and female contact are horizontal and if there is uneven floor there is danger of chattering due to misalignment may result damaging of contacts.

Dear Guest,

All the articles that I have writen in CR4 forum are knowledge or my first hand experience that I had acquired in the past 29 years as an electrical engineer.Much of it were repeated many times over.I write without referring to anything as I did not bring with me those records when migrating to another country.

Yes ,I have good enough experience and knowledge of VCB vs. OCB vs SF6 CB.

If vacuum is "finished" due to leakage of air into the vacuum interrupter of any one phase,and switching "on" or "off" is performed on this faulty VCB,this particular VCB or its up stream VCBs will safely trip on either earth fault or over current depending on the CT ratios and relay settings.Leakage of air into VCB seldom/very rarely happens when the 3 poles are assembled or replaced/repaired by the manufacturer or person who knows.

For many years I was also involved in projects that replaces OCB panels with VCB or SF6 CB panels while OCB were being phased out.I remember that in year 2000, there was an up grading project that replaced about 30 complete working panels of LOCB panels within a 30-hour shutdown period.The whole lot were sold at scrap value of steel of US$0.15 per kilogramme.The original OCB manufacturers also try to extend their product life by replacing the interrupters in oil to vacuum interrupters within the same space originally occupied by oil immersed components.(both bulk oil and min oil CB manufacturers are involved).They sell retrofit truck with VCB in bulk tank without oil.

Today,I can get you fully KEEMA/ASTA/CESI type tested,11kv,3-phase,metal-clad,fully compartmentalised,segregation for VCB truck,busbars,circuit and CTs / PTs chambers,LV metering and protection panel,20KA 3 sec,IP3X VCB panels with 800A main bus bars (single bus bar design) complete with a 630A,20KA 3 sec,3-phase vacuum circuit breaker with motorised and manual spring charging mechanism,6 NO and 6 NC aux contacts,20KA 3 sec integral earth switch mechanically interlocked with VCB which is interlocked with the fix panel thus is an idiot-proof ( better than foolproof ) design; complete with CTs and IDMT relays for O/C and E/F,meters,phase indicators etc. for less than US$ 9,000. for EACH VCB panel.For a few panels,the price can cover packing and shipping cost via shipping container to any container port in the world.

I doubt Oil Circuit Breaker ( not to be confused with 11 KV Oil Load Break Switch or RMU ) can even match this price if it is available.

The most common and simple with-drawable VCB mouted-on-truck design is arranging the 3 poles from left to right on the X-axis.As it is advantageous to have top busbars,the actuating rod that operate the make and break actions ( vertically along the Y-axis ) of the vacuum interrupters are at the bottom of the interrupters.Only one direction of travel ( along the Z-axis ) is needed for this design,that is inserting the VCB truck with horizontal Sprouts ( pointing into the panel ) into the fixed panel before the switching operations.You need to get only 1 alignment right.

In the case of bulk oil tank OCB,the vertical (pointing to the sky)sprouts ("male contacts") of the main contacts for circuit and busbar sides are mounted on the top of the CB oil tank,you have to insert the CB truck into the panel ( along the Z-axis ) and then raise/rack-up the tank ( along Y-axis ) to plug in the main contacts.You need to get 2 alignments right plus the lower tolerence for error in the depth of racking in the CB truck.This is more difficult to manufacture and operate after installation.

If you are interested,kindly read the other link that I wrote to answer on VCB vs SF6 CB some time ago.Are you in the consulting,manufacturing/trading or consumer area of CB?

The many VCB panels that I had manufactured/supplied and installed are still operating well after so many years.I can only hope that my son may have the chance to replace/repair it some day and make some money!

Best regards,

Khor.

The vacuum circuit breaker is fast in operation so ideal for fault clearing. It is suitable for repeated operation and almost maintenance free. When oil circuit breaker, during arcing, oil decomposes and becomes polluted by carbon particles, which reduces its dielectric strength. Hence, it requires periodic maintenance and replacement.