Name THREE losses that occur in a transformer.

• Copper losses (or $I^2R$ losses)
• Iron losses (or Core losses, which include Hysteresis losses and Eddy current losses)
• Stray losses

Protective devices are crucial for transformers to prevent damage from overcurrents, short circuits, and overvoltages. They isolate faulty sections, ensuring the transformer's longevity and reliable operation by minimizing downtime and repair costs, thus contributing to efficient energy transfer.

• More efficient for the same power rating.
• Smaller in size and lighter for the same power rating.
• Generates a uniform magnetic field, leading to smoother operation.

• Stator
• Rotor (squirrel cage type)
• End shields/bearings

The direction of rotation of a three-phase motor can be reversed by interchanging any two of the three supply phase connections to the motor. This changes the phase sequence, which reverses the direction of the rotating magnetic field.

• Insulation resistance test (Megger test)
• Continuity test (or Resistance test of windings)
• Earth continuity test

Given:
$V = 400 \text{ V}$ (line voltage for delta connection, so $V_{ph} = V_L = 400 \text{ V}$)
$pf = 0.85$
$I_{ph} = 20 \text{ A}$
The formula for active power in a three-phase system using phase values is:

Substitute the given values:

The active power is $\boxed{\text{20.4 kW}}$.

Given:
$f = 50 \text{ Hz}$
poles $= 36$
The formula for synchronous speed in revolutions per minute (rpm) is:

Substitute the given values:

The synchronous speed is $\boxed{\text{166.67 rpm}}$.

Given:
Slip $s = 5\% = 0.05$
Synchronous speed $N_s = 166.67 \text{ rpm}$ (from Step 8)
The formula for rotor speed is:

Substitute the values:

The rotor speed is $\boxed{\text{158.34 rpm}}$.

Given:
$I_L = 8.59 \text{ A}$ (line current)
The motor is delta-connected. For a delta connection, the relationship between line current ($I_L$) and phase current ($I_{ph}$) is:

Rearrange to solve for $I_{ph}$:

Substitute the given line current:

The phase current of the motor is $\boxed{\text{4.96 A}}$.