3AT maintenance


The Siemens 3AT high-voltage circuit breaker began production in the late 1980s and has a reliable track record in the field. As with any breaker, periodic maintenance is required to ensure long-term reliability. Below, we have reprinted the maintenance manual from 1988.


(Reprinted from Manual SW 8760, published 1988)


Siemens circuit breakers require very little maintenance. Involved are those parts that are subject to normal wear and aging. The paint finish and the degree of contamination of the insulators should also be checked. The criteria governing the breaker condition are as follows:

  • The number of short-circuit interruptions,

  • The switching frequency and

  • The actual service time.

Maintenance and inspection should be carried out in accordance with the attached schedule. The servicing intervals indicated below are only approximate and should be adjusted to suit the particular operating conditions.


The inspection and servicing jobs have been divided into three groups (see section 710 of full manual):

  1. Visual checks to be made every five years; include only checks to be done at earth potential. Transferring the SF6 is not necessary.

  2. Expanded visual checks after 1500 operations or 10 years of service; in the case of breakers operated more than 1000 times a year, after a maximum of 3000 operations. Transferring the SF6 is not necessary.

  3. Inspection after 3000 operations or 20 years of service; in the case of breakers operated more than 1000 times a year, after a maximum of 6000 operations.

If the number of short-circuit interruptions should be attained before an inspection becomes due; check the contact system in accordance with Point 3.1 in the inspection schedule, and also after 3000 interruptions of load currents up to the level of the rated normal current. The spare parts required for inspections are contained in corresponding maintenance kits.


Precautions to be taken before starting work on the breaker, carry out the following routine:

  1. Isolate the breaker.

  2. Discharge the capacitors by reclosing the breaker.

  3. Earth and short-circuit the breaker in accordance with VDE 1 05, Part 1.

  4. Disconnect the auxiliary supply by tripping the lineside MCB.

  5. Reduce the oil pressure of the electrohydraulic operating system to zero by opening pressure release valve 14.37. When the pressure in the hydraulic circuit is released, the priming pressure in the storage cylinder remains. Any work on these cylinders must be carried out by specially trained personnel.

  6. Transfer the SF6 to a service unit and? vent the pole columns.

  7. Comply with all the local safety regulations.

Points to be noted


The locking elements of any screwed joints opened for inspection must be replaced.


The same applies to all seals and gaskets exposed in the process. AII open breaker parts should be covered to prevent the ingress of dirt while assembly is in progress.


During normal operation, no dust should result from switching. If dust is found after repeated interruption of high, short-circuit currents, proceed as follows. Any seitching dust should be removed immediately the breaker is opened and any subassemblies have been removed. When this dust is exposed to the air for some time it will absorb moisture and can then only be removed with difficulty.


Gloves should be worn.


Remove the dust with a piece of cloth or use a vacuum cleaner. Do not stir it up unnecessarily. Cloths and switching dust should be disposed of in keeping with environmental regulations.


Care is advised when working near the auxiliary switches and the piston rods of the operating mechanism, since any damage may cause leakage.


Note: With the piston rod, operating rod, and connecting rod fitted, the interrupter unit may not be raised by more than