Electrical Engineering Concepts Quiz

The waveform shape for a form factor of 1 is a pure DC waveform.

A DC motor starter controls the starting current to protect the motor from excessive current draw during startup.

The superposition theorem satisfies the principle of linearity in circuits. This means the total effect in a circuit is the sum of the effects of each individual source acting alone.

In a Buck converter, the output voltage is lower than the input voltage, while in a Boost converter, the output voltage is higher than the input voltage.

The current represented by L1 lags the current represented by L2 by 60 degrees.

The maximum efficiency of a transformer occurs when copper losses are equal to iron losses.

The frequency of the induced EMF in the rotor of a 3-phase, 50 Hz induction motor at standstill is equal to the supply frequency (50 Hz).

The field of a synchronous generator is excited by DC current.

The power dissipation is maximum in the resistor with the lowest resistance. Power is inversely proportional to resistance in a circuit with constant voltage.

In a 3-phase system, the phase voltages are 120 degrees apart. Imagine a circle divided into 3 equal parts, each representing a phase voltage.

The self-inductance of a coil is directly proportional to the square of the number of turns. More turns mean a stronger magnetic field and therefore higher inductance.

Electric potential (or voltage) is the amount of energy an electric charge would gain by moving from one point to another. Electric potential difference is the difference in potential between two points in an electric field. Imagine a hill, potential difference is the height difference

In an a.c. circuit with R, L, and C in series, increasing the frequency will reduce the current if the circuit is operating on a lagging power factor. This is because the inductive reactance increases with frequency, which leads to a higher impedance.

Kirchhoff's Current Law (KCL) is a consequence of the conservation of charge. It states that the sum of currents entering a node is equal to the sum of currents leaving the node.

The resistance between the primary and secondary windings of a transformer should be infinite. Ideally, there should be no direct electrical connection between the two windings.

The armature of a D.C. machine is laminated to reduce eddy current losses. Lamination breaks the conductive path for eddy currents, effectively reducing their magnitude.

In a balanced 3-phase 4-wire system, the neutral wire carries the vector sum of the phase currents. Since the phase currents are balanced and 120 degrees apart, their vector sum is zero. Therefore, the current through the neutral wire is zero.

Inductive reactance (XL) is the opposition to the flow of alternating current (AC) due to the presence of an inductor. It is calculated using the formula XL = 2πfL, where f is the frequency and L is the inductance.

The three-phase EMFs (electromotive forces) in a balanced system are 120 degrees apart from each other. This ensures that the total power delivered remains constant over time.

The commutator in a DC machine acts as a full-wave rectifier. It switches the current direction in the armature winding to convert the alternating current induced in the armature to direct current.

Hysteresis loss in a transformer is caused by the magnetic domain realignment within the core material. Using silicon steel core reduces this loss due to its lower hysteresis coefficient.

A three-phase slip-ring induction motor has a wound rotor. The rotor winding is connected to slip-rings, allowing external resistance to be added for speed control.

The direction of rotation of a DC shunt motor can be reversed by interchanging the connections of the armature and field windings.

The superposition theorem states that in a linear network, the total response (current or voltage) due to multiple sources is equal to the sum of responses due to each individual source acting alone.

The number of poles in a three-phase induction motor determines its synchronous speed. The synchronous speed is calculated using the formula N = 120f/P, where N is the synchronous speed in RPM, f is the frequency in Hz, and P is the number of poles. By substituting the given values, we can determine the number of poles.

A three-phase induction motor operates by applying a three-phase AC supply to the stator winding. The rotating magnetic field produced in the stator induces a current in the rotor winding, causing it to rotate.

Slip is the difference between the synchronous speed and the actual speed of the rotor, expressed as a percentage. It's calculated as (Ns - Nr) / Ns * 100%, where Ns is the synchronous speed and Nr is the rotor speed.

In an AC circuit, the current constantly changes direction, flowing in one direction and then the other. This constant fluctuation is due to the alternating nature of the voltage.

In a star-connected three-phase system, the line voltage is the voltage between any two lines, while the phase voltage is the voltage across one phase winding. The relationship is: Line voltage = √3 * Phase voltage .

When a pure inductance is connected to an AC source, the voltage always leads the current by 90 degrees. This means that the voltage reaches its peak before the current, due to the opposition offered by the inductor to changes in current.

A pure capacitance connected to an AC source does not consume any real power. This is because the capacitor stores and releases energy during each cycle, but the average power consumed is zero.

The phase difference between the applied AC voltage and current in a series RL circuit increases when the inductive reactance (XL) is increased. This happens because the inductive reactance opposes the flow of current, leading to a larger phase difference.

The power factor in a circuit with only an inductor is 0, meaning the circuit does not consume real power – energy is merely stored and released by the inductor.

Superposition theorem is not applicable for power responses because power is not a linear function of voltage and current, so just summing individual power contributions from each source would be inaccurate.

The total instantaneous power supplied by a 3-phase AC power supply to a balanced R-L load is constant and equal to the sum of the instantaneous power supplied by each phase.

In an RL series circuit, the voltage across the inductor (VL) lags the voltage across the resistor (VR) by 90 degrees.

The RMS (Root Mean Square) value of a sinusoidal AC current is equivalent to its value at 90 degrees.

An ideal current source has infinite internal resistance. This means that it can supply a constant current regardless of the load connected to it.

The excitation current of a transformer is small, typically around 2-5% of the full load current. It's the current that flows in the primary winding when the secondary is open-circuited.

In a series RLC circuit, the power factor at resonance is unity (1), meaning the circuit acts like a purely resistive load.

The principle of Minimum Circuit Breaker (MCB) operation is based on the concept of overcurrent protection. It works by sensing an abnormally high current flow in a circuit, which could indicate a fault like a short circuit or overload. When the current exceeds a predetermined threshold, the MCB trips, interrupting the circuit and preventing damage to the wiring and appliances.

RCCB stands for Residual Current Circuit Breaker (also known as an Earth Leakage Circuit Breaker). It is an electrical safety device that provides protection against electric shock by detecting and interrupting the flow of current when there is an imbalance between the current going out and the current returning to the source.

Voltage Grades refer to the standard electrical potential differences used in power systems. Common voltage grades include:

• Low Voltage (LV): typically up to 1000V
• Medium Voltage (MV): typically between 1000V and 33000V
• High Voltage (HV): typically above 33000V
• Extra High Voltage (EHV): typically above 110000V These voltage grades are associated with specific applications and safety considerations.

Earthing is the practice of establishing an intentional connection between an electrical circuit and the Earth. It aims to provide a low-resistance path for fault current, reducing the risk of electric shock. Neutral, however, is a conductor that carries current back to the source in a standard AC circuit. Though sometimes connected to the Earth at the transformer, they have different roles.

Earth resistance is a measure of how much opposition a path to the Earth has. It is measured in ohms. High earth resistance means the flow of fault current to Earth is hindered, increasing the risk of electric shock. We can measure it using specialized instruments like a Megger or Earth Tester, which inject a known current and measure the resulting voltage drop.

A primary cell is a non-rechargeable battery, meaning it can be used only once. While secondary cells are rechargeable batteries, they can be repeatedly recharged and discharged.

EMF (Electromotive Force) is the maximum potential difference a cell can provide under ideal conditions. It represents the total energy the cell can supply per unit charge. PD (Potential Difference) is the actual voltage across the cell terminals when a current is flowing. It is less than EMF due to internal resistance within the cell.

UPS stands for Uninterruptible Power Supply. It is a device that provides backup power during power outages by using a battery to keep connected equipment running. It ensures uninterrupted power flow, protecting computers, servers, medical equipment, and other critical systems from data loss or disruptions.