High voltage circuit breaker (also known as high voltage knife switch or isolation knife switch) is one of the most widely used and basic high voltage switching equipment in power plants and substations. Its core function can be summed up in one sentence: it does not interrupt current, and its sole function is to completely isolate the equipment from the power supply during maintenance, providing a safe working environment for maintenance workers.
Because it does not have an arc extinguisher, it must never operate under load and must be used in conjunction with a high voltage circuit breaker.
I. What does it look like?
The structure of high voltage circuit breaker is very simple. It consists of the following parts:
Conductive knife switch: A metal blade that rotates or moves up and down. It inserts fixed contacts when closed and separates when open.
Fixed contact point: Fixed contact point, usually connected to a power supply.
Insulation bracket (porcelain insulator): Supports the conductive parts and provides insulation for the floor. Outdoor-type porcelain insulators also have ceramic skirts for rain protection.
Actuation mechanism: Manual or electric operation, drive knife switch.
Common outdoor types include unipolar, bipolar and tripolar. Single-column circuit breakers occupy a small area and are most commonly used in ultra-high voltage (110kV and above) substations. Two-column type circuit breakers are simple in structure and low in cost. They are commonly found in 110kV systems.
ii. Its Three Core Functions
Function 1: Power Isolation-This is the most important and irreplaceable function of power supply.
During the maintenance of electrical equipment, the equipment and power supply must be completely disconnected. While high voltage circuit breakers can interrupt current, their contacts are sealed in an arc extinguishing chamber, so you can't see where the circuit breaker is and you're not sure if it's actually broken.
However, when the a disconnecting switch is turned on, there is a noticeable disconnection gap between the knife switch and the fixed contact point (opening distance is no less than 160mm, or angle is no less than 65 degrees), which is a visual confirmation that "the power has been cut." The visible breakthrough is the "lifeline" for maintenance workers.
So, in a substation, a set of break switches is installed on either side of the circuit breaker-one providing double protection before the circuit breaker isolates the power supply and the other providing double protection after the circuit breaker prevents reverse power supply.
Function 2: Switch operation --change the way of operation of power system.
In a a double busbar system, it is necessary to switch the line from busbar A to bus B. This is done with a disconnected switch and circuit breakers, operating in sequence to "move" the line to another bus. This operation, called switching, is the second most important use of disconnecting switches.
Other applications, such as connecting standby busbars, bypassing the bus and changing the system wiring configuration, depend on disconnecting the switch.
Function 3: Switch Small Current Circuits-not completely unable to handle current
While disconnecting switches cannot cut the load current or short-circuit current, they can safely switch on some very small currents:
Switches and connection voltage transformer and surge arrester circuits
Switching and Connecting of Charged Current of unloaded busbars
Switches and connections for unloaded transformers with excitation current not exceeding 2A (outdoor type can only switch on 560kVA and below, indoor type can only switch on 320kVA and below)
Capacitor current switch and connection to an unloaded lines up to 5A (10kV and up to 5km in length)
These operations do not produce powerful arcs, and the disconnected switch is perfectly capable of handling them.
III. Its biggest feature: No arc extinguisher.
The fundamental difference between a circuit breaker and a circuit breaker is:
Comparison items: High-voltage disconnecting switch, highvoltage circuit breaker
Arc extinguishers: None, Yes (vacuum/SF6/oil)
Can it interrupt load current? No, it is
Can it interrupt short-circuit current? No, it is
Are there clear disconnection point? Yes, visible to the naked eye, no (contact in arc extinguishing chamber)
Operation sequence: The circuit breaker must be operated after opening and can be operated directly under load.
Since there is no arc extinguisher, if the disconnecting switch is switched on under load, a strong arc will occur when the contact is separated. Such arc cannot be extinguished in the air and can result in flying arcs (where they are thrown to other phases or the ground), causing short circuits in both phases, equipment burnout and even endangering the lives of operators.
Therefore, there is an iron law in power system: it is forbidden to open or close the off switch under load.
IV. INTRODUCTION Operating Sequence-The start and finish steps cannot be reversed
Since circuit breakers donot operate under load, there is a strict sequence of operations between circuit breakers and circuit breakers, with interlocking mechanisms in place to prevent mishandling:
When plugged in (connect the disconnecting switch, then switch off the circuit breaker):
Turn off the busbarside disconnect switch first.
Then close the wireside disconnect switch.
Finally, turn off circuit breaker.
When the power goes out (break the circuit breaker, then break the switch):
Disconnect circuit breaker.
Then disconnect the line-side disconnecting switch.
Finally, disconnect the disconnect switch on theside of the bus. Reversing means breaking the switch under load, which can lead to a major accident.
V. Distinctions between indoor and outdoor types.
Interior Type (GN Series):
Vertical mounting with fixed contact at the top. Small phase to phase distance, can only switch 320 kVA and below the unloaded transformers. Used for indoor switchgear.
Outdoor Type (GW Series):
Horizontal installation, ceramic insulator and ceramic skirt provide rain protection. Only empty transformers of 560kVA and below can be turned on / off. Used in open substations.
VI. INTRODUCTION Summing up in one sentence
High voltage break switch = Highvoltage knife switch without arc extinguishing ability but with significant break. It doesn't cut the current, it just "isolates the power"; it doesn't provide protection, it only makes sure you can see "the power is cut." It's the perfect partner for a circuit breakers and a lifesaving switch for maintenance workers.
