Disconnector Mechanical Classes M0, M1 and M2

Short answer

IEC 62271-102 classifies the mechanical endurance of the disconnector as M0 (1,000 operating cycles, normal disconnector), M1 (2,000) and M2 (10,000). The last two are intended for disconnectors that operate together with a circuit breaker of the same class. M1 and M2 are proven with the extended endurance test, which allows lubrication and adjustment between series but not replacement of contacts.

Short answer

The mechanical class of a disconnector states how many operating cycles (one closing and one opening) its mechanism withstands, with the maintenance program declared by the manufacturer. IEC 62271-102 (2001 edition with Amendment 1:2011 and Amendment 2:2013) defines three classes in clauses 3.4.101.1 to 3.4.101.3 and the figures in clause 4.106 (Table 3a):

Class	What it is	Operating cycles
M0	Normal disconnector, for distribution and transmission according to the general requirements of the standard	1,000
M1	Extended mechanical endurance, for applications where it operates together with a circuit breaker of the same class	2,000
M2	Extended mechanical endurance, for applications where it operates together with a circuit breaker of the same class	10,000

The class is checked with a type test and measured with no voltage and no current in the main circuit. It says nothing about how much current the disconnector can open or close.

The mechanical endurance test, M0

Clause 6.102.3 defines the test for class M0. Its conditions are:

1,000 operating cycles, with no voltage and no current in the main circuit.
Where applicable, 50 % of the rated static terminal load is applied in the longitudinal direction. In a disconnector with two or three insulators and horizontal isolating distance, it is applied on both sides in opposite directions.
In each cycle the closed and open positions must be reached.
The specified operation of the control and auxiliary contacts and of the position indicators is verified.
Lubrication according to the manufacturer’s instructions is allowed. No mechanical adjustment or other maintenance is allowed.
If the mechanism is motor-operated, 900 cycles are made at the rated supply voltage or pressure, 50 at the minimum and 50 at the maximum.

Before the test, the manufacturer states the parameters that will be compared before and after, such as operating time, maximum energy consumption or, for manual mechanisms, the maximum operating force. Before and after, five close-open cycles are made at minimum voltage or pressure and, depending on the control, at maximum pressure or manually. The variation of the mean values must be validated by the manufacturer and included in the report.

After the test, all parts, including the contacts, must be in good condition with no undue wear. The main circuit resistance is measured before and after, and it must not vary by more than 20 % from the initial value. For gas-insulated disconnectors a tightness test is made before and after.

Clause 6.102.4 adds a test with the rated static terminal load: 20 cycles with the rated supply, or 10 if the disconnector is manually operated only.

The extended endurance test, M1 and M2

Clause 6.102.5 applies to M1 and M2 disconnectors. The standard justifies it as follows: disconnectors that are operated frequently, for example together with circuit breakers, require extended mechanical endurance tests.

The program is close-open cycles made according to clauses 6.102.1 and 6.102.3.1. There are 2,000 for M1 and 10,000 for M2.
After each series of 1,000 cycles, or at the maintenance intervals, the operating characteristics are recorded or evaluated.
Between series, maintenance such as lubrication and mechanical adjustment is allowed, according to the manufacturer’s instructions.
Replacing major subcomponents, such as the contacts, is not allowed.
The manufacturer defines the maintenance program before the test and it is recorded in the report.
For GIS disconnectors, the enclosure is not opened during the test.

Before and after the program, the operating characteristics are verified as in M0. The contact zone test and the test with static terminal load are also repeated, if applicable. At the end, operation is checked with the minimum duration of the operating signal given by the manufacturer, along with the condition of the end-of-travel stops and of the force limiters, if any. All parts must be in good condition.

How to choose the class

The standard states for which applications M1 and M2 were conceived: disconnectors operated together with a circuit breaker of the same class. The disconnector class then follows that of the breaker in its bay.

Which mechanical class to request for the disconnector

Does the disconnector operate together with an M1 or M2 circuit breaker?
- No: Class M0: 1,000 cycles, normal endurance
- Yes: Is the circuit breaker class M2?
  - Yes: Disconnector class M2: 10,000 cycles
  - No: Disconnector class M1: 2,000 cycles

The circuit breaker mechanical class follows the same letter: M1 and M2 mechanical endurance classes. The disconnector is presented in substation disconnector and its operation in motor-operated mechanism. Position, locking and indication are explained in disconnector position: locking and indication.

What not to do

Do not pair different classes without a reason: the definitions of M1 and M2 assume the disconnector with a circuit breaker of the same class.
Do not confuse the mechanical class with the capability to switch current. An M2 disconnector still opens only negligible currents, unless it has another rated capability.
Do not replace the maintenance declared by the manufacturer with your own and still count on the class.
Do not accept a report without the maintenance program with which the extended test was made.

What to request from the manufacturer

The mechanical class of the disconnector, M0, M1 or M2, in the complete designation.
The mechanical endurance type test report, with the maintenance program used.
The rated, minimum and maximum supply voltages and pressures of the mechanism, which are the test conditions.

When to call us

At Tiza Group we test disconnectors in AIS and GIS substations: contact resistance, mechanism operation, auxiliary contacts and position indication. Field work is done in Colombia, or elsewhere on request. See our testing and commissioning services or write to us with your disconnector data and we will send a quotation.

References

IEC 62271-102, High-voltage switchgear and controlgear - Part 102: Alternating current disconnectors and earthing switches, 2001 edition with Amendment 1:2011 and Amendment 2:2013, clauses 3.4.101.1 to 3.4.101.3, 4.106 (Table 3a), 6.102.3, 6.102.4 and 6.102.5.

Frequently asked questions

How many cycles must an M0, M1 and M2 disconnector withstand?

The standard sets 1,000 operating cycles for M0, 2,000 for M1 and 10,000 for M2 (Table 3a, clause 4.106), taking into account the maintenance program specified by the manufacturer. A cycle is one closing operation and one opening operation.

Why does the standard relate M1 and M2 to a circuit breaker?

Because the definitions of M1 and M2 state that they are intended mainly for applications in which the disconnector operates together with a circuit breaker of the same class. A disconnector that is operated as often as the breaker needs comparable mechanical endurance.

What is verified after the mechanical endurance test?

That the disconnector operates properly and that its parts, including the contacts, are in good condition with no undue wear. The main circuit resistance is measured before and after, and it must not vary by more than 20 %. For gas-insulated disconnectors a tightness test is also made before and after.