Concept Flashcards

Power Generation and Transmission

What are motors?

Devices that convert electrical energy into rotational mechanical energy (output is a rotating shaft that can do work).

What are generators?

Devices that convert rotational mechanical energy into electrical energy (essentially the opposite of a motor).

What is a commutator?

A commutator is a metal contact mounted on the rotor’s shaft that connects the rotating coil to the external circuit.

What is a brush?

Brushes are conductive pieces (often carbon/metal) that press against the commutator to transfer current to a moving rotor.

How can you change the polarity of a magnet?

For an electromagnet, reverse the current’s direction to flip its north/south poles; for a permanent magnet, you’d physically flip the magnet’s orientation.

What is efficiency?

The ratio of a device’s usable output power to the power supplied (input), usually expressed as a percentage.

Write the efficiency equation.

\[ \text{Efficiency} = \frac{P_{\text{out}}}{P_{\text{in}}} \times 100\% \]

How is heat modeled in electric machines?

As copper losses – the resistive heating in the windings (I²R losses) that turn electrical energy into heat.

Write the copper loss equation.

\[ P_{\text{loss}} = I^2 R \]

What are examples of core losses in a motor?

One example is magnetic flux leakage – some of the magnetic field lines do not stay in the intended path (the motor’s iron core), causing energy loss. (Other core losses include eddy currents and hysteresis in the iron, though those aren’t detailed here.).

What are examples of mechanical losses in a motor?

Mechanical losses include friction (e.g., in bearings) and windage (air drag as the rotor spins).

What is base power in power generation?

The base load power is the minimum continuous power demand that must be supplied at all times.

What is intermediate power in power generation?

Intermediate power (load) is the predictable rise in demand above the base load during an average day. It covers the typical daily increase as people wake up, businesses open, etc., sitting between base and peak demand.

What is peak power in power generation?

Peak power refers to periods of highest demand, which occur occasionally and often unpredictably (short bursts of maximum load). The system must be able to supply this peak load to avoid brownouts.

What is Ampère’s Law?

A law stating that the magnetic field in space around an electric current is proportional to the electric current that produces it.

What is Faraday’s Law?

Faraday’s Law: a changing magnetic field through a closed loop induces an electromotive force (voltage) in that loop. In simpler terms, moving magnets or fluctuating fields will generate a current/voltage in a nearby conductor.

Why do we increase voltage for power transmission?

Because transmitting at a higher voltage (and thus lower current for the same power) dramatically reduces I²R line losses, improving efficiency. In short: raising the voltage lets us send the same power with much less current, so resistive losses are minimized.

Write the transmission line power loss equation.

\[ P_{\text{loss}} = I^2 R \]

where \(P_{\text{loss}}\) is the power lost as heat in the line, equal to the current squared times the line resistance.

What is the primary side of a transformer?

he primary side (primary winding) of a transformer is the side connected to the input source – the coil to which the incoming AC voltage is applied.

What is the secondary side of a transformer?

The side of the transformer where the output voltage is taken.

What material is used between transformer windings?

An iron (ferrous) core is placed between the windings to channel the magnetic flux between the primary and secondary coils.

What is the name of the force induced in a transformer?

It uses electromotive force (EMF) – i.e. the induced voltage generated by changing magnetic flux (Faraday’s Law drives the transformer’s action).

What is a step-up transformer?

A transformer that increases the voltage from primary to secondary. In a step-up, the secondary voltage is higher than the primary voltage (while the secondary current is proportionally lower).

What is a step-down transformer?

A transformer that decreases the voltage from primary to secondary. The secondary voltage is lower than the primary, and the secondary current is higher (it “steps down” voltage to a usable level).

What is turns ratio?

The ratio of the number of turns in the primary coil to the number of turns in the secondary coil is often denoted by

\[ a = \frac{N_1}{N_2} \]

This ratio governs how the transformer scales voltage and current: the voltage ratio equals the turns ratio, and the current ratio is the inverse.

Write the transformer voltage ratio equation.

\[ \frac{V_p}{V_s} = \frac{N_p}{N_s} \]

Write the transformer current ratio equation.

\[ \frac{I_p}{I_s} = \frac{N_s}{N_p} \]

Write the ideal transformer power relationship.

\[ P_p = P_s \quad \text{(ideal transformer, neglecting losses)} \]