Auto reclosing, a pivotal mechanism in modern electrical engineering, refers to the automatic closure of a circuit breaker after it has been opened due to a fault. This process is key in maintaining the continuity of electrical supply and minimizing service interruptions. The device responsible for this task is known as an auto recloser or automatic circuit recloser. This article explores the evolution, principles, and types of auto reclosers, highlighting their roles and functionalities in electrical systems.

History before the invention of automatic reclosers

In the past, the lines were often touched, causing the circuit breaker tripping mechanism to occur, thus causing the line to lose power.

For example, if a bird touches the wire, the circuit breaker will trip and the power will be cut off. However, in general, the event of a bird touching the wire is temporary and will not last for a long time. However, the circuit breaker tripping requires manual re-operation, which requires a lot of labor and time, resulting in a lot of downtime and inefficiency.

Moreover, data shows that 90%-95% of the events that cause circuit power outages are temporary events, that is, instantaneous faults, which can often be restored by resetting the circuit breaker without other maintenance operations. Long-term power outages and numerous manual needs have made people start to think about whether there can be an automatically reset circuit breaker.

So the automatic reclosing circuit breaker was born.

Compared with traditional circuit breakers in the past, the automatic reclosing circuit breaker can quickly reset and restore power supply in a short time after power outage, but it should be noted that: this does not mean that the automatic reclosing circuit breaker only resets under certain circumstances. 

Principles of Operation

Auto reclosers are designed to detect when an interruption occurs in the electrical network, typically caused by transient faults such as lightning strikes or temporary contact with foreign objects. Here’s how they work:

1. Fault Detection: Once a fault is detected, the auto recloser temporarily opens its contacts, interrupting the current flow.
2. Wait Period: The device then enters a wait period, allowing time for the fault to clear (such as when the offending object falls away or the surge dissipates).
3. Reclosure: If the fault clears, the recloser automatically closes the contacts, restoring the circuit’s continuity. If the fault persists, this open-wait-close cycle repeats a predetermined number of times before locking out to prevent damage.

Types of Auto Reclosers

Auto reclosers are classified based on their operational phases and the number of poles they control:

1. Single-Phase Reclosers: Operate on a single-phase line, common in rural distribution where each recloser controls a single phase independently.If only one phase has a fault, then only one phase is disconnected, the balancing two phases continue to operate, and the recloser will continue to attempt to reopen.
2. Three-Phase Reclosers: Manage all three phases simultaneously, typically used in urban and industrial settings for a balanced load management across all phases.

But it should be noted that single-phase reclosing can only be performed using the EGO (Electrically controlled, Gas Operated), which means that each phase of the circuit breaker has an independent dedicated mechanism. In this case, the circuit breaker can trip or close each of the three phases separately. If the circuit breaker is a MGO (Magnetic Gas Operated), it cannot perform single-phase automatic reclosing tasks, it can only perform three-phase reclosing tasks, tripping or reclosing three-phase circuits at the same time.

Tongou Auto Recloser