Reclosers and circuit breakers have similar applications in medium voltage distribution systems, but they serve different functions. A recloser can be considered a lightweight circuit breaker (even though it is not a breaker). Conversely, high voltage circuit breakers equipped with the appropriate protective relays can also serve as reclosers, applicable in distribution systems rated for 12kV, 15kV, 27kV, and 38kV.

1. Definitions

Reclosers: Formally known as automatic circuit reclosers, they are defined by IEEE (and IEC) as “self-controlled devices used to connect, carry, and automatically interrupt and reclose AC circuits, with predetermined opening and reclosing sequences, followed by reset, holding closed, or locking operations. It includes a set of control elements needed to detect overcurrent and control recloser operation.” (IEEE/IEC C37.60 (62271-111)).

Circuit Breakers: Defined by IEEE as “a mechanical switching device capable of closing, carrying, and interrupting current under normal circuit conditions and making, carrying for a specified time, and interrupting current under abnormal circuit conditions, such as short circuits.” (IEEE C37.100).

The characteristic of a recloser is its mandatory automatic control and protective devices, though this is not critical since most high voltage circuit breakers used in utility distribution systems also feature protective relays with similar (or even identical) functions.

2. Standards

Reclosers are governed by dual-identification IEEE/IEC standards, specified as IEEE/IEC C37.60 (62271-111). High voltage circuit breakers follow numerous IEEE standards and guidelines, including:

· C37.04: Rating structure for AC high voltage circuit breakers

· C37.06: AC high voltage circuit breakers – preferred ratings

· C37.09: Testing procedures for AC high voltage circuit breakers

· C37.010: Application guide for AC high voltage circuit breakers

There are also additional guidelines covering capacitor-current switching, transient recovery voltage, and reactor switching. IEEE C37.06 will be withdrawn soon as ongoing revisions will move preferred ratings to the fundamental C37.04 standard.

3. Continuous Current

Reclosers typically have rated currents of 630 A or 800 A, with some suppliers offering additional ratings like 400 A and 1,200 A. Circuit breakers generally have rated currents of 1,200 A, 2,000 A, 2,500 A, or 3,000 A. Circuit breakers are more commonly used in distribution substations, while reclosers are mainly utilized on overhead distribution lines outside substations.

4. Short-Circuit Current

Reclosers usually have symmetrical short-circuit ratings of 12.5 kA or 16 kA, with some products available at lower or higher values. Circuit breakers typically have symmetrical short-circuit ratings of 20 kA, 25 kA, 31.5 kA, or 40 kA. The higher short-circuit ratings are suited for conditions where short-circuit currents exceed those found outside distribution substations.

5. Size

Reclosers are compact and lightweight (approximately 200-300 pounds, requiring no supporting structure) because they are most often installed on utility poles in overhead distribution systems. They may be infrequently installed in smaller distribution substations mounted on substation frames.

Circuit breakers are primarily used in distribution substations, mounted on concrete pads or piles. Their weights range from about 1,800 pounds to over 3,000 pounds, depending on voltage class, continuous current, and accessories.

6. Seismic Resistance

Reclosers generally do not have seismic ratings, as their seismic capabilities largely depend on the supporting pole, which is beyond the manufacturer's control. Circuit breakers installed on ground foundations can offer the highest levels of seismic certification in North America.

7. Mechanical Durability

The mechanical durability of reclosers and circuit breakers is essentially comparable. Reclosers are typically required to withstand 2,000 mechanical (no-load) operations, although most (but not all) recloser suppliers state a durability capability of 10,000 operations. Similarly, outdoor (S2-rated) high voltage circuit breakers also comply with IEEE C37.06 standards requiring 2,000 mechanical (no-load) operations, with many suppliers publishing durability capabilities of 10,000 operations.

Over the long term, 2,000 operations would translate to about 50 operations per year over a 40-year lifespan. Although many of these products can last 40 years, few operate 50 times annually.

8. Electrical Life

The electrical life of reclosers and circuit breakers differs. For reclosers, there is no requirement in the standard for electrical life at rated continuous current. Instead, reclosers specified to have a breaking capacity of at least 8 kA are tested with loads that include 116 operations, with 16 at full fault rating, 56 at half fault rating, and 44 at 15-20% fault rating. After completing these standard operations, it is estimated that the contacts will reach their half-life. In most cases, suppliers do not specify the tolerable capacity for reclosers under rated continuous current, but they likely can operate 10,000 times under rated continuous current. Based on the standard operating tasks from IEEE 62271-111, the estimated number of full fault interruptions may be about 100, with some manufacturers claiming reclosers can handle up to 250 full fault interruptions.

For circuit breakers, IEEE C37.06 specifies 100 operations under rated continuous current. However, most suppliers publish capabilities for 10,000 operations under rated continuous current.

One issue related to electrical durability is the contact wear in vacuum circuit breakers. For most (if not all) reclosers, it is impossible to directly determine the amount of contact wear because the vacuum interrupters are encapsulated within an epoxy resin shell, making contact wear measurement impossible. Depending on the recloser control equipment used, contact wear can be estimated based on the cumulative current (or the square of the cumulative current) interrupted. Because vacuum circuit breakers are integrated into molded shells, they are usually not replaceable.

For circuit breakers, if the vacuum circuit breaker is not housed within a molded shell, contact wear can be directly measured, and the vacuum interrupters can be replaced if necessary. While it is unlikely that the vacuum interrupter will be replaced during the circuit breaker's lifespan, it is reassuring that it can be replaced when needed.

Circuit breakers are designed for maintainability, whether for the operating mechanism itself or for replacing vacuum circuit breakers. Reclosers typically do not allow user maintenance; any required internal maintenance must be performed by the manufacturer.

Circuit breakers are installed near the ground, making maintenance relatively easy. In contrast, reclosers are typically mounted high on utility poles, meaning that any potential maintenance requires bucket trucks and specialized procedures due to proximity to high voltage.

9. Applications

Reclosers can be configured as three-phase, single-phase, or even as a three-phase unit (three single-phase units in one component). They are commonly used on single-phase overhead distribution lines, often as single-phase units. High voltage circuit breakers are generally installed in distribution substations as three-phase designs. Reclosers integrate current sensors within their molded shells, making it impossible to directly add extra current transformers within the recloser assembly. If needed, additional current transformers must be added separately, increasing the overall installation cost.

Furthermore, the control cabinet of the recloser is fixed in size, often leaving no room for bringing additional current transformer secondary leads into the recloser control cabinet. Thus, reclosers are not easily adaptable for added metering or additional relays (such as for transformer differential protection or other protective measures).

On the other hand, circuit breakers typically have space for up to four current transformers within their shells, allowing easy accommodation of complex differential schemes, dedicated precision metering devices, and similar options. Additionally, circuit breaker enclosures provide ample space for secondary devices, instruments, relays, transmitters, and similar items, allowing configuration according to user needs.

Reclosers are designed for automatic reclosure functions, generally allowing for a maximum of three reclosure operations in the sequence before the controller locks the recloser in a tripped state. This is typically expressed as O-t-CO-t-CO-t-CO, where O = open operation, CO = close-open operation, and t = time delay, which is adjustable. The time intervals for reclosers can be as short as a few seconds, but usually require longer durations to allow ionized gases at the fault location to dissipate before re-energizing the circuit.

Circuit breakers can be similarly configured, depending on the capabilities of the specified protective relay. The first closing operation should occur no sooner than 0.3 seconds after the first trip, and subsequent reclosure intervals should be at least 10-12 seconds to ensure that the breaker operating mechanism (whether spring-operated or magnetic actuator) has time to recharge.

10. Economic Considerations

In the past, the acquisition cost of circuit breakers was higher than that of reclosers, particularly older hydraulic reclosers. However, in today's utility environment, communication technology has become essential, and older reclosers do not integrate well with communication devices. Consequently, the costs of reclosers have risen significantly, while the acquisition costs for circuit breakers have remained relatively stable or even decreased. Depending on the required options, modern circuit breakers may have little to no premium compared to reclosers.