What arc supression techniques are used in AC Locos?

Namely, is it "magnetic blowout," "pneumatic blowout," or others.
On Electric locos such as AEM-7, ALP-44, ALP-46, etc.
And on EMU trains like Arrow (NJ Transit, SEPTA) M2,M4,M^ (MetroNorth)

Due to high voltage and currnet in catenary, an electric arc remains on contacts even after opening the circuit. So, the circuit remain ON, and can be burned by arc.

So there are two ways of blowing out the spark:
magnetic blowout
By Magnetic Currents (all the electrons in spark will fly together, directed to the arc chute, when electromagnet is on)

Pneumatic Blowout
THe arc is blown off, by a streat of compressed air, which lasts for a second, as sounds like a "sneeze"

no contactors on AC locomotives mostly semi conductors, but on older cars like M2/M4/M6 and Septa silverliners magnetic blow out coils are used on contactors and cam controllers.

I am speaking namely about German locomotives, like these:
http://www.railfaneurope.net/pix/de/ele ... 9/pix.html
When I was there, it sounded as a slight "sneeze." Some did not sound anyhow (probably magnetic blowout) I heared the same about Locos in Switzerland. in both of these countries, railroad voltage is 15kV 17Hz, AC I did not hear the sound of 25kV European Locos.

In Russia (former USSR) railroads were electrified either at 3000 v DC, or at 25kV AC. DC units defenetly use magnetic blowout. AC units (both EMUs and Locos) use only pneumatic blowout. The pressure of a blow is 5 Atmospheres. It sounds louder, that that one of German units.
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I used to be student of Electrical Engineering Technology, but now I switched back to Master's in Computer Science. Please explain me, how semiconductors are used in arc suppression.

They're not.

They replaced contactors in most applications.

AC inverters don't really have many contactors in them anyway. They're not needed due to the design of an AC inverter.

The voltage at the contact line means nothing on an AC system, since it's dropped down to a lower voltage by the main transformer.

Historically, locomotives and EMUs in the US have used magnetric blowouts on their contactors.

The Pioneer III cars also briefly shut off their rectifiers whenever the line breaker opened. This greatly reduced arc curents.

Reversers generally don't have blowouts at all, because they're intended to operate with the train at standstil

There are still a few applications where the old style contactors with magnetic blowout coils are still used on both GE and EMD AC locomotives. the largest contactors are the ones connecting the DC link to the grids. These contactors should not drop out when carrying large amounts of current. Really, they should be completely de energised by the time they drop out but loose wires or other problems could cause them to drop out under load and could cause alot of damage if arc suppression was not used. Other appications include generator field contactors and those used in the starting circuits. Note that all these contactors are in conventuional DC circuits even though they are on locomotives with AC propultion systems.