- convert electromagnetic energy into kenetic energy
- v(t)=N(dΦ/dt)=di/dt L
- can be modelled as an RL circuit
- p=LI^2/2
- as current increases more energy is stored in magnetic field in inductor
- if L changes then conservation of energy states that the change in electrical energy stored equals work done moving the actuator rod in/out the coil
- this is basis of electric solenoid
- if the rod is high reluctance, it effects inductance greatly by its presence
- if rod is attached to spring, the work done on it keeps it in circuit, else with circuit off it is pushed out
- F=1/2 i^2 dL/dx
- F is force, x is distance moved by actuator rod
- B(g)= µ0 Ni/2g
- air gap is g
- Fx=Fspring at equilibrium
- torque T=1/2 i^2 dL/dθ where θ is angle
- DC generators work by moving a coil through magnetic flux lines
- there are 2 main components, the stator and the rotor
- stator is stationary and holds magnetic field in place
- rotor spins, holding coils which pass through field lines
- e=Blv
- generated emf using flux density, length of coil and velocity
- emf is only induced as coils pass through flux lines
- thus as coils pass parallel to flux lines nothing is induced
- time taken to turn from position 1 to 2 of rotation = θ2-θ1/ω =θ2-θ1/2πf
- where f is revolutions per second
- peak generated = epk= NΦmax*n/15 *α
- where a is pole arc/pole pitch ~0.7
- e=CnΦ in general, where C is machine constant
- electromagnetic torque T=BILR
- where R is radius of armature
- T = K(m)ΦI(a) where K(a) is machine constant
- the reversibility of electric machines is the principle that a generator can be a motor and vice versa
- In a motor, n motor speed = V-IR/CΦ
- e= K(e)n for back emf
- If is approximately constant determined by supply voltage
- R(a) is always very small
- because resistance is s small current surge is possible, so starts with low controlled current
- increasing R(a) reduces speed
- greater resistance in field windings increases
