|
|
|
مواقع
مفضله
Figure 3. Interruption
in a Vacuum When
the circuit breaker is closed, the contacts within the interrupter touch,
allowing current to flow. When
a fault occurs and interruption is required, the contacts are quickly separated
and an arc forms. An arc is formed because
the voltage tries to keep the current moving. Figure 4. Enclosing
Contacts in a Vacuum The
arc burns in the metal vapor evaporated from hot spots on the contact surfaces.
This metal vapor continuously leaves the contact region and recondenses on the
contact surfaces and surrounding metal shield, which protects the ceramic
envelope. At
Current
Zero, the arc extinguishes, contact vapor production stops,
and the original vacuum condition is restored. Current zero is a point in the AC
current sine wave where the value is zero. The
vacuum in the envelope is considered a Dielectric.
The Dielectric
Strength is the maximum voltage the dielectric can withstand
without breaking down. The Transient
Recovery Voltage (TRV) is the most severe waveform the interrupter
will have to withstand. This is why the speed of the dielectric recovery and the
strength of the dielectric inside the interrupter are critical issues for
successful circuit interruption. If the dielectric does
not reach sufficient strength fast enough, the arc will re-ignite. Vacuum
interrupters for circuit breaker duty must be capable of interrupting currents
of 12 to 50 kA (and up), at voltages up to 38 kV (Figure 11). Figure 5. Rear View of
Circuit Breaker with
Another
arc extinguishing technology is SF6
(sulfur hexafluoride) technology. It is popular outside the United States. It is
specifically associated with European manufacturers of medium and higher voltage
circuit breakers. SF6
technology was briefly discussed in Fundamentals of Circuit Breakers. The main
contacts are enclosed in a chamber of SF6
gas, which happens to be a very good dielectric (Figure 6). Figure 6. Enclosing
Contacts in SF6 Gas In
short, this arc interruption technology results the in arc energy being used and
absorbed, while the arc is simultaneously cooled. BACK HOME SWITCHING DEVICES MENU |
|
تصميم المهندس : محمد صبري محمود فهيم إستعداد تام لتصميم المواقع إستعداد تام للعمل داخل أو خارج مصر E-Mail: Mohamedmsm@Masrawy.com |
SF6
Gas Technology