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PRINCIPLE OF OPERATION
‐1.1 SOME BASIC RULES
Right‐hand screw rule (cross product operation in vector algebra)
A1 X A2= A3
A1, A2, and A3 are vectors. Rotate RH fingers from the direction of the first vector , A1, to the
direction of the second vector, A2, through the small angle (<180o
) between them; the direction
of A3 is then given by the extended RH thumb. In our applications, the magnetic field B is always
the second vector.
Given a straight conductor lying in a magnetic field, and oriented perpendicular to the direction
of the field. Let
B= magnetic flux density (also called magnetic induction), [T=tesla=weber/m2
];
L=active length of conductor,[m]. u
Induced voltage (emf): E=B.L.u.sinα volts
u= speed of conductor perpendicular to its length[m/s];
α= small angle from u to B.
Direction of E : RH screw rule from u to B .
Developed force : Fd= B.I.L newtons [N]
I= current through conductor, [A].
Direction of Fd : RH screw rule from I to B.
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Electrical Machines Notes Dr. AF BATI Page 3
‐1.2 Single conductor
Consider a straight conductor moving at a uniform speed u in a uniform magnetic field B, and
carrying a current I. Let
L= active length(i.e. length of conductor segment immersed in the field);
Fm= applied mechanical force, [N].
u & B give E=B.L.u and I & B give Fd=B.I.L
E.I= (B.L.u).I=(B.I.L). u= Fd. u ‐‐‐‐‐‐‐‐‐‐‐‐‐Æ E.I= Fd.u= Pc = conversion power
Note: Because the speed u is constant, Fd and Fm must be equal and opposite( otherwise there
would be acceleration or deceleration).
E.I is electrical power , and Fd .u (Fm. u) is mechanical power.