ABB AMVAC Technical Manual page 6

AMVAC. Low maintenance
permanent magnet technology.
6
Following the advance of vacuum
interruption in the field of medium voltage
circuit breakers in the last 20 years, a natural
teaming of technology has been achieved
with the addition of magnetic actuator
technology. The requirements of one
technology are optimally matched by the
opportunities of the other. Magnetic actuator
technology naturally provides the suitable
travel-time and force-travel characteristics for
the vacuum switching devices. All operating
mechanism functions are integrated in the
magnetic actuator of the AMVAC circuit
breaker. The actuator is a bi-stable magnet
system, in which armature change-of-state is
accomplished by the magnetic field of two
electrically excited coils. The armature is held
magnetically in the limit positions by the
fields of two rare-earth permanent magnets.
Switching operations are achieved by
excitation of one of the two coils until the
retaining force of the permanent magnets is
exceeded. Even on complete failure of
auxiliary power, electrical operation is still
possible for a period of 60 to 90 seconds.
When capacitor stored energy is no longer
sufficient to achieve tripping, the circuit
breaker can then be opened with the assis-
tance of a manual opening handle.
The armature of the magnetic actuator is
linked to an operating shaft connected via
insulated push rods to each of the vacuum
interrupters. The only points of lubrication
for this mechanism are at the union of the
armature to the operating shaft, the pivot
points of the operating shaft, and the pivot
points of the operating shaft to the push
rods. Long life synthetic lubricants are applied
during assembly to further reduce the need
for lubrication during the life of the
circuit breaker. During circuit breaker racking,
mechanical interlocks from the racking mech-
anism block the movement of the
magnetic actuator armature so that the circuit
cannot be closed electrically in any racking
position other than "Test" or "Connect".
Instantaneous
representation of
magnetic flux density
distribution
Magnetic latching in a
limit position.
Magnetic latching plus
current build up in one
coil.
Armature reaching the
opposite limit position.