PYQs Based test 8: Electrical Machines

A 25 kVA, 400 V, Δ-connected, 3-phase, cylindrical rotor synchronous generator requires a field current of 5 A to maintain the rated armature current under short-circuit condition. For the same field current, the open-circuit voltage is 360 V. Neglecting the armature resistance and magnetic saturation, its voltage regulation (in % with respect to terminal voltage), when the generator delivers the rated load at 0.8 pf leading, at rated terminal voltage is __________.

A single-phase $400V,50Hz$ transformer has an iron loss of $5000W$ at the rated condition. When operated at $200V,25Hz$, the iron loss is $2000W$. When operated at $416V,52Hz$, the value of the hysteresis loss divided by the eddy current loss is ______.

Consider a system consisting of a synchronous generator working at a lagging power factor, a synchronous motor working at an overexcited condition and a directly grid-connected induction generator. Consider capacitive VAr to be a source and inductive VAr to be a sink of reactive power. Which one of the following statements is TRUE?

An alternator with internal voltage of 1∠δ₁ p.u. and synchronous reactance of 0.4 p.u. is connected by a transmission line of reactance 0.1 p.u. to a synchronous motor having synchronous reactance 0.35 p.u. and internal voltage of 0.85 ∠δ₂ p.u. If the real power supplied by the alternator is 0.866 p.u., then (δ₁ - δ₂) is _____ degrees. (Round off to 2 decimal places.)

(Machines are of non-salient type. Neglect resistances)

A belt-driven DC shunt generator running at 300 RPM delivers 100 kW to a 200 V DC grid. It continues to run as a motor when the belt breaks, taking 10 kW from the DC grid. The armature resistance is 0.025 Ω, field resistance is 50 Ω, and brush drop is 2 V. Ignoring armature reaction, the speed of the motor is ____________ RPM. (Round off to 2 decimal places.)