What are the operating structures of high-voltage circuit breakers? What is the difference between isolation switch and isolation switch?

Circuit Breakers are commonly referred to as "switches" in use, while isolating switches are commonly referred to as "knife switches" in use, and the two are often used in combination. The difference between high-voltage circuit breaker and isolation switch is as follows:

1) High voltage load switches can be disconnected with load and have self extinguishing arc function, but their breaking capacity is very small and limited.

2) High Voltage Isolating Switches are generally not capable of breaking loads. They do not have arc extinguishing enclosures in their structure, and there are also high-voltage isolating switches that can break loads. However, their structure is relatively simpler compared to load switches.

3) High voltage load switches and high-voltage isolation switches can both form obvious disconnection points. Most high-voltage circuit breakers do not have isolation functions, and there are also a few high-voltage circuit breakers with isolation functions.

4) High voltage isolation switches do not have protective functions, and the protection of high-voltage load switches is generally achieved by adding fuses, with only quick break and overcurrent protection.

5) The breaking capacity of high-voltage circuit breakers can be made very high during the manufacturing process. Mainly relying on the use of current transformers in conjunction with secondary equipment for protection. It can have functions such as short circuit protection, overload protection, and leakage protection.

Classification of switch operating mechanisms

1. Classification of switch operating mechanisms

The switches we encounter nowadays are generally divided into three types: high oil (older models, almost non-existent now), low oil (some user stations still have them) SF6、 Vacuum, GIS (combination electrical) and other types. These are all about the arc extinguishing medium of switches, and for us, the operating mechanism of switches is closely related.

The types of mechanisms can be divided into electromagnetic operating mechanisms (relatively old, usually equipped with high or low oil circuit breakers); Spring operated mechanism (currently the most common, SF6, vacuum, GIS are generally equipped with this mechanism); Recently, ABB has launched a new permanent magnet operating mechanism (such as VM1 vacuum circuit breaker).

2. Electromagnetic operating mechanism

The electromagnetic operating mechanism relies entirely on the electromagnetic attraction generated by the closing current flowing through the closing coil to close and compress the trip spring. When tripping, it mainly relies on the trip spring to provide energy.

So the tripping current of this type of operating mechanism is relatively small, but the closing current is very large, reaching over 100 amperes in an instant.

This is also why the DC system of the substation needs to control the opening and closing of the busbar. The closing mother provides the closing power supply, and the control mother supplies power to the control circuit.

The closing busbar is directly hung on the battery pack, and the closing busbar voltage is the battery pack voltage (usually around 240V). When closing, it uses the battery discharge effect to instantly provide a large current, and at the same time, the voltage drops sharply when closing. The control bus is connected together through silicon chain voltage reduction and busbar closing (usually controlled at 220V), and closing will not affect the stability of the control bus voltage. Because the closing current of the electromagnetic operating mechanism is very high, the protective closing circuit is not directly connected to the closing coil, but to the closing contactor. The trip circuit is directly connected to the trip coil.

The coil of the closing contactor is generally voltage type, with a relatively high resistance value (usually a few K). When cooperating with this type of circuit for protection, attention should be paid to closing the circuit to ensure that it generally cannot be started. But this is not a big problem. The TBJ can generally be started when tripped, so the anti trip function still exists. This type of mechanism has a longer closing time (120ms~200ms) and a shorter opening time (60~80ms).

3. Spring operating mechanism

This type of mechanism is currently the most commonly used, and its closing and opening rely on springs to provide energy. The tripping and closing coil only provides energy to pull out the positioning pin of the spring, so the tripping and closing current is generally not large. Spring energy storage is achieved by compressing the spring energy storage through an energy storage motor.

For the spring control mechanism, the closing busbar mainly supplies power to the energy storage motor, and the current is not large, so the difference between the closing busbar and the control busbar is not significant. Protection is usually not particularly important to pay attention to when cooperating with it.

4. Permanent magnet operating mechanism

The permanent magnet operating mechanism is a mechanism applied by ABB to the domestic market, first applied to its VM1 type 10kV vacuum circuit breaker.

Its principle is somewhat similar to that of electromagnetic type, with the active shaft made of permanent magnet material and electromagnetic coils around the permanent magnet.

Under normal circumstances, the electromagnetic coil is not charged. When the switch is to be opened or closed, the polarity of the coil is changed to use the principle of magnetic attraction or repulsion to drive the opening or closing.

Although the current is not small, the switch stores energy through a large capacitor and provides a large current by discharging the capacitor during operation.

The advantage of this mechanism is its small size and fewer transmission mechanical components, so its reliability is better than that of a spring operated mechanism.

In conjunction with our protective device, we drive a high resistance solid-state relay for the tripping and closing circuit, which actually only requires us to provide it with an action pulse.

So for this switch, the circuit will definitely not start, and the anti bounce protection will not start either (the mechanism itself has anti bounce).

However, it should be noted that due to the high operating voltage of solid-state relays, the conventional design of connecting the TW negative and closing circuits together will not cause the solid-state relay to operate. However, it is possible that the position relay may not start due to too much voltage division.

This situation has been encountered on site, and the specific analysis and handling process can be found in the debugging case section of this article, which provides a detailed description.

There are also products with permanent magnet operating mechanisms in China, but the quality used to be unsatisfactory. In recent years, with the improvement of quality, they have gradually been introduced to the market. Due to cost considerations, domestic permanent magnet mechanisms generally do not require capacitors and are directly supplied with current by the closing busbar.

Our operating mechanism drives the opening and closing contactors (usually current type), which can be activated for holding and anti tripping.

5. FS type "switch" and others

What we mentioned above are all circuit breakers (commonly known as switches), but we may encounter situations where users refer to them as FS switches during power plant construction. FS switch is actually the abbreviation for load switch+fast fuse.

Because the switch is relatively expensive, this FS circuit is used to save costs. The normal current is cut off by the load switch, and in case of a fault, the current is cut off by the fast fuse.

This type of circuit is commonly found in the 6kV auxiliary power system of power plants. In conjunction with this type of circuit protection, it is often required to prohibit tripping or delay the fast fuse to cut off the current when the fault current exceeds the allowable breaking current of the load switch. Some power plant users may not want to protect the holding circuit.

Due to poor switch quality, auxiliary contacts may not be in place, and once the circuit is started, it must rely on the auxiliary contacts of the circuit breaker to open before returning. Otherwise, the tripping current will continue to be applied to the tripping coil until it burns out.

The circuit breaker coil is designed for short-term power on, and if the current is applied for a long time, it is easy to burn out. And we definitely hope to have a holding circuit, otherwise it's easy to burn the protective contacts.

Of course, if the on-site user insists, the holding circuit can also be removed. A generally simple method is to cut off the connection between the normally open contact of the relay and the positive control bus on the circuit board.

At the debugging site, it is important to note that if the switch is opened or closed, all position indicator lights will turn off. The control power must be immediately turned off to prevent burning of the switch coil, excluding cases where the panel displays an alarm indicating that the spring is not storing energy due to the spring not storing energy. This is a basic principle that should be remembered on site.