In DC series motor Torque (Ta) increase as the Square of armature current (Ia) Ta ∝ Ia2. So DC motor provides high starting torque.
In two wattmeter method the phase angle is tanφ = √3(W1 − W2)/(W1 + W2) tanφ = √3(500 − 500)/(500 + 500) tanφ = 0° φ = tan−10° = 0° Power factor = cosφ PF = cos0° = 1
The average value of the sine wave over one complete cycle is actually zero. Hence, for a sine wave, the average value is defined over half the period. The average value expressed in terms of peak value is given by
Average value = 0.637 × peak value
Mutual inductance between two coupled coils is given by the relation
M = K√L1L2
L1L2 = Inductance of the coil
K = Coefficient of coupling
When K = 1 coils are said to be tightly coupled and if K is a fraction the coils are said to be loosely coupled.
∴ m ≤ (L1 L2 )0.5