Type B Vital Relays - Alstom

Theory of Operation
EDDY CURRENT INDUCED BY
PERMANENT MAGNET IN
NON-MAGNETIC DISC
N
DISC
S
Figure 2–45. Eddy Current Induction by Permanent Magnet
In the vane relay, two electromagnets are constantly energized while the relay is picked
up, but the magnetism produced by one of the electro-magnets lags in time with respect
to the other. The reaction on the vane relay of the two independent magnetisms, which
are out of phase, produces rotation, the same as that produced by the moving
permanent magnet in Figure 2–45.
Figure 2–46 shows a complete cycle of local track currents plotted with the track current
lagging the local current. The alternating current produces a lateral movement of flux in
the air gap, as shown. Reference lines A, B, C, D, etc., divide the complete alternating
current cycle into eighths, and the small figures represent instantaneous pictures or
"snapshots" of what occurs in the relay magnetic circuit.
P1457, Rev. Nov/07 2–47 Alstom Signaling Inc.