Question

A Long Shunt Compound Motor Has The Following Nameplate Parameters:

rated line voltage = 380V rated speed = 1200rpm
amature resistance = 0.3Ω Shunt field resistance = 47.5Ω

The Efficiency At Rated Load Is 80%, And The Machine Is Driving A Constant Torque Load. Determine At Rated Conditions:

Armature Current

Answer 1

To determine the armature current for a long shunt compound motor, you need to calculate the input power and the armature voltage, then use Ohm's Law. However, with the information provided in the question, there is insufficient data to find the exact value of the armature current as additional data on the series field or back emf is needed to complete the calculation.

Step-by-step explanation:

To determine the armature current of a long shunt compound motor at rated conditions, we first need to know the input power, which is the product of the line voltage and efficiency. Since the motor's efficiency at rated load is 80%, we can calculate the input power. The formula for calculating the power consumed by the armature and field coils is P = IV, where I is the armature current and V is the armature voltage.

Given that the rated line voltage is 380V and the rated efficiency is 80%, the input power at rated load can be found by multiplying these values. However, to find the armature current, we must first find the armature voltage, which is the difference between the line voltage and the voltage drop across the shunt field and series field coils. The armature voltage (Va) can be calculated using Ohm's Law, Va = V - Ish Rsh, where Ish is the shunt field current and Rsh is the shunt field resistance.

However, there is insufficient data in the question to provide the exact value of the armature current, as the current through the series field and the voltage drop across it are not provided. Therefore, we are unable to definitively provide the armature current without making additional assumptions. In practice, one would typically solve this by also considering the power wasted as heat in the armature resistor. With the back emf, the armature power would be Pa = (V - back emf) * Ia, and we would have to work backward using the efficiency or power output to solve for the back emf, and then the current.

Answer 2

In this case, the armature current (I) at rated conditions is approximately 7.95 Amperes.

Step-by-step explanation:

To determine the armature current of a long shunt compound motor at rated conditions, we can use the formula for armature current:

Armature current (I) = Rated line voltage (V) / Total resistance (R)

In this case, the total resistance is the sum of the armature resistance and the shunt field resistance:

Total resistance (R) = Armature resistance + Shunt field resistance

Step 1: Calculate the total resistance:

Total resistance (R) = 0.3Ω + 47.5Ω = 47.8Ω

Step 2: Calculate the armature current:

• Armature current (I) = Rated line voltage (V) / Total resistance (R)
• Armature current (I) = 380V / 47.8Ω

Now, we can calculate the armature current by dividing the rated line voltage by the total resistance:

Armature current (I) = 380V / 47.8Ω

Simplifying the calculation, we find:

Armature current (I) ≈ 7.95 Amperes

Therefore, the armature current (I) at rated conditions is approximately 7.95 Amperes.

Your question is incomplete, but most probably the full question was:

A long shunt compound motor has the following nameplate parameters: rated line voltage=380V rated speed=1200 rpm output power=24hp, armature resistance=.3 ohm shunt field resistance=47.5 ohm series field resistance=.1 ohm The efficiency at rated load is 80% and the machine is driving a constant torque load determine armature current

converted power and developed torque

output torque and constant losses

the value of the starting resistor needed to limit the initial armature current to no more than 250 percent of its rated armature current