How Do Reclosers Work? Settings and Operation

Reclosers, otherwise known as autoreclosers (derived from “automatic reclosing” capability) or ACRs (Automatic Circuit Reclosers) have been widely used in transmission and distribution systems. The purpose of reclosers is mainly to increase system reliability by isolating only the faulted part of the power system. Unlike fuses, reclosers can automatically re-energize the line following a trip operation from a transient or temporary fault thus the term ‘reclose’ meaning to close again.

In medium voltage distribution systems, overhead power lines are very common. Most faults on these lines are either transient, resulting from lightning-induced transient high voltage, or temporary, as a result of contact from foreign objects such as animal contact or vegetation e.g. falling tree branches or momentary tree contact caused by the wind. These faults include the following, with very approximate percentages of occurrence^[1]:

• Single phase-to-ground: 70% – 80%
• Double phase-to-ground: 10% – 17%
• Phase-to-phase: 8% – 10%
• Three-phase: 2% – 3%

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How Do Reclosers Work?

Unlike fuses, reclosers can automatically re-energize the line following a trip operation. The automatic reclose operation can be single or multiple shots. Figure 1 shows a typical sequence of a recloser operation.

Recloser States^[1][2]

• Reset State – The circuit breaker is closed for a pre-configured reset time and the autoreclose function is waiting to receive an initiate signal to start timing to reclose after the breaker opens.

• Cycle State – The recloser is going through the autoreclose cycle after the circuit breaker opens and following a successful initiation, reclosing as many times as programmed.

• Lockout State – All reclose attempts are unsuccessful or the reclose initiation fails or other conditions that drive the recloser into lockout. The circuit breaker remains open until a manual close operation is made.

Referring to figure 1, the circuit breaker is initially in a close position (normal loading condition). At this point, the recloser is in the reset state (assuming that the circuit breaker has been closed for a duration greater than the pre-configured reset time). The recloser in reset state waits for an initiate signal before it can start timing after the breaker opens. The initiate signal is usually a protection trip signal such as an overcurrent trip.

Following a successful initiate, the recloser goes into the cycle state, closing the breaker at a pre-configured time interval after the breaker opens. If the breaker remains closed for a duration greater than the pre-configured reset time, the recloser goes back into the reset state. However, if the breaker trips after reclosing, the recloser will try to close the breaker again depending on the programmed number of reclose attempts. The cycle repeats until the recloser exhausts its remaining reclose attempts. In figure 1, the total reclose attempts is two.

After exhausting all reclose attempts, the recloser goes into the lockout state. The circuit breaker remains open until a manual close operation is made. When the circuit breaker is manually closed, the recloser goes back into the reset state after a pre-configured reset time. However, if the breaker trips before the reset time expires, the recloser goes directly into the lockout state.

It is important to note that the recloser may not attempt to reclose and go directly to the lockout state depending on the programmed conditions such as but not limited to the following:

• Reclosing is disabled by user
• Manual open
• High Current Trip or Instantaneous lockout overcurrent trip
• Trips from the operation of protection elements other than the overcurrent protection such as voltage (27/59), frequency (81), etc.
• Trip by Hot Line Tag

Recloser Settings^[3][4][5]

Setting reclosers might be a little confusing especially with the different terms used by vendors or manufacturers. As such, familiarity with how reclosers work and the basic settings associated with their operation is important to make the configuration a fairly straightforward process. The following settings are integral in the operation of reclosers.

Number of Reclosing Attempts

This setting refers to the number of close attempts before the recloser goes to lockout. Different vendors have different implementations of this setting. Some require a simple as specifying the number of reclosing operations while others, the number of trips to lockout. Some others relate the number of reclosing attempts to the dead time or open interval setting. For example, if there are three available dead time or open interval settings in the recloser, setting all dead time or open interval setting to a non-zero value effectively sets the number of reclosing attempts to three. If for example, the third dead time or open interval setting is set to zero, the effective number of reclosing attempts is two.

Other vendors have a very specific way to set the number of reclosing attempts such that the setting depends on which protection element has operated. In figure 5, the protection element OC1+ is set to R-R-L-L, this means that the number of reclosing attempts if OC1+ operated is two.

Dead Time

Dead Time refers to the time delay before a reclosing attempt can be made after the tripping of the circuit breaker. Some vendors refer to this as ‘Open/Reclosing Interval Time’ while others call this ‘Reclose Time’. There can be one or more dead time setting available depending on the number of reclosing attempts which are set independently from each other.

According to the IEEE Guide for Automatic Reclosing of Circuit Breakers for AC Distribution and Transmission Lines,

“… an autoreclose attempt without sufficient time delay to allow the dielectric to re-establish its strength results in an unsuccessful reclose attempt.”

IEEE Std C37.104-2012

In order to prevent this, the dead time should be set not lesser than the recommended minimum time delay based on the following equation.

t = 10.5 + V_L-L/34.5

where

t is the minimum time delay in cycles

V_L-L is the rated line-to-line voltage in kV

Table 1 shows the recommended dead time intervals for distribution systems.

Dead Time Interval	Typical Setting Range (seconds)
Initial Trip to 1st Reclose	0 – 5
2nd Trip to 2nd Reclose	10 – 20
3rd Trip to 3rd Reclose	10 – 30

Reset Time

Reset time refers to the time delay before the recloser goes into the reset state from either the cycle or lockout state. Some vendors implement a single reset timer while others use two separate reset timers, one for the reset time from reclose cycle state and the other for the reset time from lockout state.

Setting the reset time usually depends on the preference between excessive tripping and autoreclosing or undesirable lockout operations. It should be noted however to set the reset time longer than the dead time.

References

[1] Blackburn, J., “Protective Relaying Principles and Application, 4th ed.,” Boca Raton, FL: CRC Press, 2014

[2] “IEEE Guide for Automatic Reclosing of Circuit Breakers for AC Distribution and Transmission Lines,” in IEEE Std C37.104-2012 (Revision of IEEE Std C37.104-2002) , vol., no., pp.1-72, 6 July 2012, doi: 10.1109/IEEESTD.2012.6232415.

[3] “SEL-351-5, -6, -7 Relay Instruction Manual,” Schweitzer Engineering Laboratories, Inc., 20160715

[4] “OSM User Manual OSM Automatic Circuit Recloser 15kV, 27kV & 38kV Models”, NOJA Power

[5] “Recloser Control EVRC2A-NT User’s Manual”, ENTEC Electric & Electronic Co., 2018