Electrical Engg (EEE) - MCQ Practice Questions

In a parallel plate capacitor used for dielectric strength testing, the breakdown voltage of air at standard atmospheric pressure (1 atm, 25°C) for a gap of 1 cm is approximately:

According to Paschen's law, the breakdown voltage of a gas is a function of:

A Marx generator is used to generate impulse voltages. If each stage capacitor is charged to a voltage $V_0$ and the generator has $n$ stages, the theoretical maximum output voltage is:

The standard lightning impulse voltage waveform used in high voltage testing is designated as:

In the Schering bridge used for measurement of capacitance and dielectric loss, the loss tangent $\tan \delta$ at balance is given by (where $R_4$ is a variable resistor and $C_4$ is a standard capacitor in the bridge arm, and $\omega$ is the angular frequency):

The phenomenon of corona discharge on a high-voltage transmission line first occurs when the electric field at the conductor surface exceeds the critical value. For a single cylindrical conductor of radius $r$ in air, at which condition does corona onset first occur?

An electrostatic voltmeter is preferred over other instruments for high-voltage measurements primarily because:

In a resistive voltage divider used for impulse voltage measurement, the ratio $n$ of the divider is defined as $n=(R_1+R_2)/R_2$. If $R_1=9\text{k}\Omega$ and $R_2=1\text{k}\text{Omega}$, and the measured output voltage across $R_2$ is $10\text{kV}$, the actual high voltage is:

Townsend's second ionization coefficient $\gamma$ (gamma) in gas discharge theory represents:

A sphere gap is commonly used for measurement and calibration of high voltages because:

The dielectric strength of transformer oil is tested using a standard test cell. If the electrode gap is $2.5\text{ mm}$ and the breakdown voltage is $50\text{ kV}$ (rms), what is the dielectric strength of the oil?

In a cable with inner conductor radius $r_1=1\text{ cm}$ and outer sheath radius $r_2=4\text{ cm}$, the maximum electric field $E_{\max }$ for an applied voltage $V$ is given by:

The optimum radius ratio $r_2/r_1$ for a single-core coaxial cable that minimizes the maximum electric stress for a given outer radius $r_2$ is:

In a standard lightning impulse test, the peak voltage of a $1.2/50\mu \text{s}$ waveform is $1000\text{ kV}$. The voltage at $50\mu \text{s}$ (tail time to half-peak) is approximately:

Which of the following correctly expresses the Streamer criterion for spark breakdown in a gas? ($\alpha$ is Townsend's first ionization coefficient and $d$ is the gap length)

A capacitor bank of $0.1\mu \text{F}$ is charged to $100\text{ kV}$ for an impulse generator. The energy stored in the capacitor is:

In high voltage testing laboratories, the term 'grading rings' (or guard rings) on test bushings and post insulators are used primarily to:

The power factor (dissipation factor, $\tan \delta$) of a healthy high-voltage cable insulation is typically in the range:

In partial discharge (PD) measurement, the quantity 'apparent charge' $q$ is expressed in units of picocoulombs (pC). If a PD pulse results in a voltage change $\Delta V$ across a coupling capacitor $C_k=1000\text{ pF}$, and $\Delta V=5\text{ mV}$, then the apparent charge is:

The back-flashover phenomenon on a transmission line tower occurs when: