3B4 Machine design, Induction, Thermal, Universal AC

What are the main functions of the cooling system of the machine?

• Reducing loss (increasing efficiency)

• Ensure acceptable temperature of machine (through proper design)

Thermal block model for simple representation of machine?

How to get general equation of machine temperature from thermal block model?

Pδt = C δθ + k θ δt

What do the variables in the general equation of machine temperature represent?

Equivalent electrical circuit of thermal network?

loss = current

temperature = voltage

Dissipation coefficient, k, of a better cooling system?

k = higher

(for same loss, high k = smaller temp increase)

What is thermal capacitance, C, normally determined by?

Size of machine

(large machine = high C)

Temperature change with high C?

Slow

(for same loss, high C = longer time to heat up AND cool down)

Have you uploaded the 7 different cases for when B changes?

No

Full specific magnetic loading equation?

What is specific magnetic loading?

Average flux density perpendicular to one pole pitch of the cylindrical surface at the circumference of the airgap

Pros of distributed winding?

• Low torque ripple

• Low harmonics

Cons of distributed winding?

• Long end turns

• Higher cost

• Complex winding structure

Pros of concentrated winding?

• Low cost

• Short end turns

• Simple winding structure

Cons of concentrated winding?

• High torque ripples

• High harmonics

• Lower winding factor

MMF equation?

N (θ) = sinusoidal distributed winding (in cos (θ) form)

θ is electrical angle

Current expressions for all three phases?

MMF at all three phases?

Does distributed or concentrated have higher utilisation of slots?

distributed

When does V_ph = E_rms ?

When neglecting leakage inductance and resistance (small)

Find electrical angle from mechanical angle?

θ_e = p θ_m

What is the phase band, m?

Number of slots occupied per phase per pole

Equation for m?

Equation for phase EMF induced by flux density?

Equation for k?

Equation for k_d?

Equation for k_p?

Simplified specific magnetic loading equation?

What does short-pitching improve?

And another advantage relevant to 2-pole motors?

Harmonics

Length of end-connections of phase coils shortened (shorter length of wire needed) by < πd/2 i.e ½ (2πr)

What can you generally neglect from the per-phase equivalent circuit?

And why?

L₂

In steady-state → linear region → small slip → ωL₂ small

What does

represent?

number of turns per coil (MUST be integer!)

Slip at no load?

s≈0

Rough visual representation of CW vs DW?

Slip in linear region of torque-speed characteristic?

And what does this mean for motor operation?

very small slip

= motor operates stably

Have you made a “what is a phase band” FC?

No

Have you made a design process steps FC?

No

What is field weakening?

Increasing speed well above the nominal speed BUT reduced torque & efficiency

Why is high k_w desirable?

Improve harmonics and higher EMF (??double check this)

What is the specific magnetic loading?

Average flux density perpendicular to one pole pitch of the cylindrical surface at the circumference of the airgap

Specific magnetic loading equation?

Induction machine per phase equivalent circuit?

Equation for magnetic flux density in airgap?

What is the specific electric loading?

axial average current per metre at circumference of the airgap

Simplified T expression?

And when is it valid?

Torque expression when neglecting R1 & L1?