Circuit Breaker Rated Operating Sequence

Short answer

The rated characteristics of a circuit breaker, such as the breaking and making current, are referred to its rated operating sequence (IEC 62271-100, edition 2.1, clause 4.104). That sequence states how many consecutive operations the breaker can make and with what waiting times between them, without running out of stored energy or losing performance. To dig deeper into what the rated power of a transformer means, read transformer rated power.

For whoever programs or reviews an auto-reclosing scheme, it is the piece of data that ties the breaker to the relay: the dead time of the protection scheme must not be shorter than the time the breaker is rated for.

The two sequences of the standard

Clause 4.104 gives two alternatives.

Sequence a: O – t – CO – t’ – CO

Unless otherwise specified:

• t = 3 min, for breakers not intended for rapid auto-reclosing.
• t = 0.3 s, for breakers intended for rapid auto-reclosing (this is the dead time).
• t’ = 3 min.

Note from the standard: instead of t’ = 3 min, for rapid auto-reclosing breakers t’ = 15 s and t’ = 1 min are also used.

Sequence b: CO – t” – CO

• t” = 15 s, for breakers not intended for rapid auto-reclosing.

The symbols mean:

If the dead time is adjustable, the adjustment limits must be specified.

The sequences in service (clause 8.103.5)

The application guidance of the standard itself repeats the sequences, with their default values:

The note adds that, instead of 3 min, 15 s is also used for rated voltages of 52 kV or less, and 1 min in rapid auto-reclosing breakers. The interval chosen depends, in principle, on what the system asks for, for example continuity of service.

What the breaker must meet

The breaker must have enough stored energy to perform the operations of the sequence properly at the declared minimum pressures. According to clause 5.103, the manufacturer may declare the pressure limits with which the breaker can, each one separately:

• Break its rated breaking current: one O operation.
• Make onto its rated making current and break immediately: one CO cycle.
• For rapid auto-reclosing breakers: break, wait the time t, make onto the making current and break again, that is, O – t – CO.

In the tests, operating devices that have a minimum operating condition (pressure, energy) are used at that minimum at the start of the rated sequence (clause 6.102.3).

Relation to auto-reclosing

The dead time of the relay is the t of the sequence. With 0.3 s, the breaker must already have recovered its making and breaking capability when the relay commands closing. That is why:

• Breaker without a rapid auto-reclosing rating: its rated t is 3 min. A faster reclosing than that exceeds what the standard guarantees. If you need it, ask the manufacturer.
• Breaking current at reclosing: if the current the breaker can break on reclosing is lower than its rated value, the manufacturer must specify it.
• More severe duty: if your duty requires more operations or less time than the sequences of the standard, state it in the enquiry so that the manufacturer adjusts the capability. The standard cites arc furnaces, electrode boilers and, in certain cases, rectifiers as examples.
• Single-pole operation: the standard mentions single-pole operation of a multipole breaker as another special case.

For setting the reclosing from the protection, see auto-reclosing 79, and if it fails, the auto-reclose does not reclose. The sequence also defines the duty cycle that current transformers must withstand: the guide on C-O and C-O-C-O duty cycles of a CT explains it.

The breaking current to which the sequence applies is in rated breaking and making current, and the voltage that follows interruption in transient recovery voltage (TRV). The opening and break times are explained in opening time and break time.

To see how this fits with the rest of the IEC 62271 series, see the standards for primary equipment testing.

How it is verified at commissioning

Clause 10.2.102 of the standard, which deals with the checks and the commissioning test programme, recommends verifying that the breaker can meet its rated operating sequence (10.2.102.2.4). The tests are made with the recharging device in service, with the supply voltage of the site and, if applicable, starting from the pump start pressure. The supply voltage of the site is the voltage available at the breaker, and it must be compatible with the rated supply voltage of the auxiliary and control circuits.

Evidence must also be given that the operating levels of the interlocks coordinate with the minimum operating pressures measured during the sequence. In other words, the lockout for low pressure or low energy must act before the mechanism runs out of capacity to complete the sequence. The standard also recommends measuring the pressure consumption in a three-phase O operation, in a three-phase C operation and, if applicable, in the three-phase O – 0.3 s – CO sequence (10.2.102.2.3).

For the opening and closing times, see the operating time test.

How to read the sequence on a data sheet

Among the rated characteristics listed by the standard (clause 4), the sequence goes together with the breaking current, the making current and the time quantities. To read it on the data sheet:

1. Look for the complete sequence: if it says only “CO” or “O-CO”, ask for the complete data.
2. If it carries 0.3 s, the breaker is intended for rapid auto-reclosing. If it carries 3 min, it is not.
3. If t’ is 15 s or 1 min, it is a variant the standard recognizes for rapid auto-reclosing.
4. Compare the t of the data sheet with the dead time you will set in the relay.

What data to ask the manufacturer for

1. The rated sequence, complete, with t, t’ and t”.
2. Whether the breaker is intended for rapid auto-reclosing, with the minimum dead time.
3. The limits of the adjustable dead time, if there is one.
4. The breaking current available at reclosing, if it is lower than the rated one.
5. The pressure or energy limits with which each operation is guaranteed.

What not to do

• Do not set a dead time shorter than the t of the rated sequence without the manufacturer’s backing.
• Do not assume that a frequent-operation breaker withstands sequences more severe than those of the standard.
• Do not forget the pressure or energy limits: the mechanism must be charged when the sequence starts.

When to call us

At Tiza Group we set and test auto-reclosing schemes and check with you that the relay times match the rated sequence of the breaker. Relay settings are a remote service, available worldwide; field testing is done in Colombia, or elsewhere on request. See our control, protection and communications configuration service and write to us for a quote.

Related guides

• Circuit breaker rated breaking and making current
• Circuit breaker TRV: transient recovery voltage
• Circuit breaker opening time and break time
• Auto-reclosing 79 (RREC): what it is and how it works
• Auto-reclose fails to reclose: causes of 79 lockout
• Transformer Rated Power: What It Means (IEC 60076-1)

References

• IEC 62271-100, High-voltage switchgear and controlgear - Part 100: Alternating-current circuit-breakers, edition 2.1 (2008 with amendment 1 of 2012), clauses 4.104, 5.103, 6.102.3, 8.103.5 and 10.2.102.

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