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ACB and VCB PM experience

This article will also discuss the differences between ACB and VCB.

I’m going to share with you what I have experienced and learned about Air Circuit Breakers and Vacuum Circuit Breakers. Photos in this post were captured during maintenance activities for ACB and VCB in our low and medium voltage Switchgear. I’m grateful to experience and dismantle some parts to see what’s more inside and how the parts are working to make it function.

Photo showing the housing and internal parts of vacuum circuit breaker

When you work in a substation and electrical rooms, switchgear is one of the common panel enclosure you could see. One of the main equipments in switchgear is circuit breaker either Air Circuit Breaker or Vacuum Circuit Breaker depending on the voltage level.

These two types circuit breakers have the same purpose of opening and closing the circuit weather manually or automatically. This article, I will tackle the differences between them in terms of tripping mechanism, construction, rating and specific purposes.

Air Circuit Breaker for Low Voltage Application

ACB or Air Circuit Breaker

  • For short circuit and overcurrent protection
  • Commonly used for low voltage applications
  • Rating is up to 15kV with 800A to 10kA.
  • Operating mechanism with the use of air-blast to quench the arc when a trip occurs. Arc will go direct to the arc chutes as pushed by the air-blast
Arc Chutes or Chambers of ACB
Terminals and Arcing contacts of ACB
  • There are two type of contacts such as main contacts and arcing contacts which are connected to spring charged mechanism that will open and close the circuit with enough time. When trip occurs, the main contacts are the first contacts to open followed by arcing contact. Opening of arcing contacts is when pressurized air push the arc to arc chutes.
  • Maintenance should be done by cleaning the contacts and bus bars, simulation of tripping mechanism by local and auto, testing of trip settings, insulation and contact resistance test, application of grease, etc.
Application of Contact Cleaner to Arcing Contacts

VCB – Vacuum Circuit Breaker

  • For short circuit and overcurrent protection
  • Commonly used for medium voltage applications
Internal parts of ACB showing the Open, Close and Trip Coils and other essential for mechanism
  • Operating mechanism where opening and closing of contacts happen inside a vacuum bottle or interrupter. Arc will be quenched because of lack of ionization development due to negative pressure which is 10– 6 bar and should be maintained.
Internal parts of Vacuum Circuit Breaker
  • Contacts that are inside the vacuum bottle are connected to opening and closing mechanism that is spring charged. This will give enough time in case a trip occurs.
  • Maintenance is done regularly to check the mechanism and insulation and contact resistance. Vacuum test should be done to know the vacuum bottle integrity. Trip settings and timings should be done to ensure the functionality of the VCB
Vacuum Chambers for Contacts

As I study the wiring diagram and panel layout. Air Circuit Breakers and Vacuum Circuit Breakers are always partnered with multi-function relays. Settings can be programmed by means of softwares available when you’ll buy the Multifunction Relay.

During the activity, the settings such as over-current, overload, tripping curve, timing, etc. were programmed to multi-function relay in coordination with the circuit breaker.

Coordination of two equipments can be tested with several procedures while injecting voltage and current to terminals for functionality test. Contact timing can be traced if will match the actual time depending on the magnitude of the current.

This will make sure that all your current sensing, accessories and circuit breaker mechanism will work in the event of failure.

Both circuit breaker can be tested locally by means of charging the spring using the handle at the front of the breaker. By manually pressing the button for closing, opening and tripping coils you can make sure that mechanism will work in Local Mode.

Both terminals must be cleaned and greased for better operation and contact to switchgear enclosure.

External Power Supply for control simulation

Circuit Breaker control circuit can be supplied by an external battery as shown in the photo above. It its used to simulate circuit breaker locally using its own digital operator.

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