Circuit Breaker Electrical Endurance Classes E1 and E2

Short answer

The electrical class of a circuit breaker states how much the circuit that interrupts the current can withstand, that is, the interrupter and its contacts. IEC 62271-100 (2008 edition with Amendment 1:2012) defines it in clauses 3.4.112 and 3.4.113:

The standard gives lubrication, gas replenishment and cleaning of external surfaces as examples of minimal maintenance, where applicable. Annex G explains why class E2 was introduced.

Up to what voltage it is defined

The E2 definition is restricted to distribution breakers with a rated voltage above 1 kV and up to and including 52 kV. In that range, clause 4.111 states when a breaker is classified as E2:

• If the breaker requires electrical endurance and is intended for service with auto-reclosing, as is usual in overhead-line networks, it is E2 and is tested according to clause 6.112.2 and Table 33.
• If it requires electrical endurance but is intended for service without auto-reclosing, for example in cable networks, it is E2 and is tested according to clause 6.112.1.
• If it does not require this capability, it is E1.

How it is tested with and without auto-reclosing

Without auto-reclosing (clause 6.112.1). Electrical endurance is proven with the basic short-circuit tests of clause 6.106, performed with no intermediate maintenance. No additional tests are required.

With auto-reclosing (clause 6.112.2). In addition to the basic tests of clause 6.106, which are also performed with no intermediate maintenance, the program of Table 33 is run. The rules are:

• A clean, new breaker is tested, identical to the one subjected to the basic short-circuit tests.
• The current levels of Table 33 are 10 %, 30 %, 60 % and 100 % (symmetrical) of the rated short-circuit breaking current, with open and close-open with auto-reclosing sequences.
• For a gas breaker, the test is performed at the rated insulation or operating pressure and at the rated supply voltage of the closing, opening and auxiliary circuits.
• Arcing times are random in the 10 % and 30 % tests. In the 60 % and 100 % tests they are adjusted according to clause 6.102.10.
• The manufacturer declares the minimum interval between operating sequences.
• At the end, the breaker must meet the conditions of clauses 6.102.9.2 and 6.102.9.3.

The letter M for the mechanical class is covered in M1 and M2 mechanical endurance classes and the capacitive letter C in C1 and C2 classes for capacitive currents. The basic short-circuit duties used by class E2 are in short-circuit test duties T10 to T100a. The reclosing cycle that is simulated is explained in automatic reclosing 79.

Breaker condition after the test

Clause 6.102.9.2 requires that, after each short-circuit test, the breaker be able to close and open its normal current at rated voltage, even if its short-circuit capability may have been reduced. The main contacts must be in a condition to carry the normal current without their temperature rise exceeding the values of Table 3 of IEC 62271-1 by more than 10 K.

These criteria are the same ones already applied to an E1 breaker. What changes in E2 is that they are required with no intermediate maintenance and, with auto-reclosing, after a longer program.

Breakers above 52 kV

For 72.5 kV and above, the bibliography of IEC 62271-100 refers to technical report IEC TR 62271-310 (2008 edition). Its scope is class E2 for breakers above 52 kV for overhead lines. Its test programs are based on the electrical stresses accumulated over 25 years, a period taken as representative of a maintenance-free interval.

The same report states that most applications are covered by E1. Considering E2 makes sense, among other reasons, because of the trend toward maintenance-free breakers and the advantage of having a single standardized program instead of a different one for each user. For networks with very high arcing stress, or if the user expects more than 25 years between major maintenance of the wear parts, the report states that a tailored test program is needed.

What not to do

• Do not read E2 as «never touched»: the standard allows minimal maintenance of the rest of the breaker, plus lubrication, gas replenishment and cleaning.
• Do not assume that a 72.5 kV or higher breaker is E2 because of its manufacturer: ask for the test report and the program that was used.
• Do not mix this class with the mechanical one: class M measures the mechanism with no current and E measures what happens to the interrupter when it interrupts.
• Do not expect the standard to state how many interruptions a specific model performs. That figure comes from the manufacturer.

What to request from the manufacturer

• The electrical class with the complete breaker designation.
• The type test report with the program used, with or without auto-reclosing.
• The minimal maintenance expected during the lifetime.
• For voltages above 52 kV, the reference to the program of technical report IEC TR 62271-310 that was followed.

When to call us

At Tiza Group we test power circuit breakers on site and at commissioning: operating times, contact travel and contact resistance, and we compare the results with factory values. Field work is done in Colombia, or elsewhere on request. See our circuit breaker testing service or write to us with your breaker data and we will send a quotation.

Related guides

• M1 and M2 mechanical endurance classes of the circuit breaker
• C1 and C2 classes: circuit breakers for capacitive currents
• Short-circuit test duties T10 to T100a
• Power circuit breaker: parts, SF6 and vacuum, and tests
• Medium-voltage vacuum circuit breaker: function and tests

References

• IEC 62271-100, High-voltage switchgear and controlgear - Part 100: Alternating-current circuit-breakers, 2008 edition with Amendment 1:2012, clauses 3.4.112, 3.4.113, 4.111, 6.102.9.2, 6.112.1, 6.112.2 (Table 33) and Annex G.
• IEC TR 62271-310, Electrical endurance testing for circuit-breakers above a rated voltage of 52 kV, 2008 edition, introduction and clause 1.

Frequently asked questions