1.
What type of circuit breaker can carry the most current on a HV trans line 555 kv and higher?
Correct Answer
A. SF6
Explanation
SF6 circuit breakers are the most suitable for carrying the highest current on a HV transmission line of 555 kV and higher. SF6, or sulfur hexafluoride, is a highly efficient and reliable insulating gas that allows for compact designs and high interrupting capabilities. It has excellent electrical insulation properties, high thermal conductivity, and arc-quenching ability. SF6 circuit breakers can handle large currents without overheating or damaging the equipment, making them the preferred choice for high voltage transmission lines.
2.
What is the medium used for circuit interruption used on a 555 kV circuit breaker?
Correct Answer
B. SF6
Explanation
SF6 (Sulfur Hexafluoride) is the medium used for circuit interruption in a 555 kV circuit breaker. SF6 is a highly effective and reliable insulating gas that has excellent electrical insulation properties. It is used in high-voltage circuit breakers because it allows for efficient and rapid interruption of electrical currents. SF6 gas is also non-toxic, non-flammable, and chemically stable, making it a safe choice for circuit interruption.
3.
In the High-end side of an Automatic Transfer Switch (ATS), what is not true in an Industrial Station?
Correct Answer
D. ATS will not transfer to an alternate circuit when there's a fault
Explanation
The given answer states that in an Industrial Station, an Automatic Transfer Switch (ATS) will not transfer to an alternate circuit when there's a fault. This means that the ATS will not automatically switch to a backup circuit in case of a fault or failure in the primary circuit. This statement is not true because one of the main functions of an ATS is to provide seamless power transfer to an alternate circuit in the event of a fault or power outage in the primary circuit.
4.
A medium that is NOT used in power circuit breakers
Correct Answer
D. CO2 gas
Explanation
CO2 gas is not used in power circuit breakers because it does not have the necessary dielectric properties to effectively interrupt the flow of current. Power circuit breakers require a medium that can withstand high voltage and current levels without ionizing or breaking down. Air break, SF6, and oil are commonly used as dielectric mediums in power circuit breakers due to their high dielectric strength and ability to extinguish arcs. However, CO2 gas does not possess these properties and is therefore not suitable for use in power circuit breakers.
5.
Which is a characteristic of a circuit breaker?
Correct Answer
A. Interrupting time = arcing time + opening time
Explanation
The correct answer is "Interrupting time = arcing time + opening time." This equation accurately represents the characteristic of a circuit breaker. The interrupting time, which is the time it takes for the circuit breaker to stop the flow of current, is equal to the sum of the arcing time and the opening time. The arcing time is the duration of the electrical arc that forms when the circuit is interrupted, and the opening time is the time it takes for the circuit breaker to physically open and break the circuit.
6.
At a temperature of 500 degrees Celsius in an oil filled equipment, the gas form is ----- in the absence of an arc
Correct Answer
B. Hydrogen
Explanation
At a temperature of 500 degrees Celsius, in the absence of an arc, hydrogen gas is the most likely form to be present in an oil-filled equipment. This is because hydrogen has a low boiling point and is highly volatile, making it more likely to exist as a gas at high temperatures. Methane, ethylene, and acetylene have higher boiling points and are less likely to exist as gases at this temperature.
7.
See the following system schematic
For a Fault at F and a circuit breaker / relay no operation at 4, what would be the operation of the circuit breaker for a backup relay?
Correct Answer
B. 1,2,3,10,6
8.
Symmetrical components have the most usage in
Correct Answer
C. 3 phase unbalanced systems
Explanation
Symmetrical components are primarily used in 3 phase unbalanced systems. This is because symmetrical components allow for the analysis and understanding of the behavior of unbalanced systems by breaking them down into a set of balanced components. By doing so, it becomes easier to analyze and solve problems in unbalanced systems, such as identifying the causes of voltage or current imbalances and designing appropriate corrective measures. In contrast, single phase systems only have one phase and do not require symmetrical components for analysis, while 3 phase balanced systems have symmetrical voltages and currents, making the use of symmetrical components less necessary.
9.
In adjacent overlapping zones in the DWP 500-kv system, what component or device is normally overlapped?
Correct Answer
C. Circuit breaker
Explanation
In adjacent overlapping zones in the DWP 500-kv system, the component or device that is normally overlapped is the circuit breaker. Circuit breakers are used to protect electrical circuits from damage caused by overload or short circuits. In the case of overlapping zones, circuit breakers are installed in each zone to ensure that any faults or abnormalities in the electrical system can be isolated and controlled effectively. This overlapping arrangement helps to enhance the reliability and stability of the power transmission system.
10.
Adjacent protective zone for voltage below 500KV, the overlap usually occurs at
Correct Answer
A. Circuit Breaker
Explanation
In a power system, the adjacent protective zone is designed to provide backup protection in case of a fault or abnormal condition. When the voltage is below 500KV, the overlap between protective zones typically occurs at the circuit breaker. The circuit breaker is responsible for interrupting the flow of current in the event of a fault, thereby protecting the system. By having the overlap at the circuit breaker, it ensures that any fault within the adjacent zone is quickly detected and cleared by tripping the circuit breaker, preventing further damage to the system.
11.
For transient stability, the most important factor is fast relaying
Correct Answer
A. True
Explanation
Transient stability refers to the ability of a power system to maintain synchronism after a large disturbance, such as a fault or the sudden loss of a generator. Fast relaying plays a crucial role in detecting and isolating faults quickly. By rapidly disconnecting the faulty element, fast relaying helps to prevent cascading failures and stabilize the system. Therefore, in the context of transient stability, fast relaying is indeed the most important factor.
12.
Whats is the power factor of the circuit?
What is the reactive power?
What sized capacitor can be used to correct for this reactive power?
Correct Answer
0.65, 1.754, 80.761uF
Explanation
Apparent Power = (9.615 A) (240 V) = 2.308kVA Power Factor= P/S Power Factor =1.5/2.308=.065
Reactive power= square root [Apparent power)^2 -(True power)^2]= Q=1.754
Q=E^2/Q X=E^2/Q X=(240^2)/(1.754kVAR) =X=32.845 X=1/(2pifC) C=1/(2pifX) =80.761uf
13.
Which is the symbol for a ACB with a thermal tripping protection?
Correct Answer
C.
Explanation
The symbol for an ACB (Air Circuit Breaker) with thermal tripping protection is a rectangle with a diagonal line inside, representing the breaker, and a curved line above it, indicating the thermal tripping feature. This symbol is commonly used in electrical diagrams and schematics to represent this specific type of circuit breaker.
14.
Which symbol represents an ACB with a magnetic overload protection?
Correct Answer
D.
Explanation
The symbol that represents an ACB with a magnetic overload protection is a circuit breaker symbol with a small coil or zigzag line inside it. This coil represents the magnetic trip unit that detects overloads and trips the circuit breaker to protect the circuit from damage. The magnetic overload protection feature is commonly used in ACBs to provide additional protection against excessive current flow.
15.
Which is the symbol for a CB with a thermal/magnetic tripping protection?
Correct Answer
A.
Explanation
The symbol for a CB with a thermal/magnetic tripping protection is a combination of the symbols for a circuit breaker and a thermal/magnetic trip unit. It typically includes a rectangle with a diagonal line inside, representing the circuit breaker, and additional symbols such as a thermometer and a magnet, indicating the thermal and magnetic trip units respectively. This symbol is used to represent a circuit breaker that can trip based on both thermal and magnetic conditions.
16.
Which is the most severe fault on the department machine theory with respect to systematical components to solve the problem?
Correct Answer
C. Three lines to ground
Explanation
The most severe fault on the department machine theory with respect to systematical components to solve the problem is the "Three lines to ground" fault. This fault involves three lines being connected to the ground, which can cause significant damage to the system and result in a more severe problem compared to the other options listed.
17.
The momentary duty and the interrupting duty of a circuit breaker refers to:
Correct Answer
D. The magnitude 0.5 to 1 cycle after a short circuit occurs and the magnitude of the current after 5 to 6 cycles
Explanation
The momentary duty and the interrupting duty of a circuit breaker refers to the magnitude of the current at different time intervals after a short circuit occurs. Momentary duty refers to the magnitude of the current 0.5 to 1 cycle after a short circuit occurs, while interrupting duty refers to the magnitude of the current after 5 to 6 cycles. This distinction is important in determining the capability of the circuit breaker to interrupt the short circuit current and protect the electrical system.
18.
The advantage of a breaker-and-a-half system versus a double breaker system is:
Correct Answer
A. Lower Cost
Explanation
The advantage of a breaker-and-a-half system versus a double breaker system is lower cost. This means that implementing a breaker-and-a-half system is more cost-effective compared to a double breaker system.
19.
Is the highest load current that the circuit breaker is designed to carry for extended time periods:
Correct Answer
A. Maximum Continuous Current
Explanation
The highest load current that the circuit breaker is designed to carry for extended time periods is known as the Maximum Continuous Current. This refers to the maximum amount of current that the circuit breaker can handle without tripping or causing damage to the circuit. It is important to ensure that the load current does not exceed this value to maintain the safe and efficient operation of the circuit breaker.
20.
Circuit breakers are rated according to this:
Correct Answer
B. Maximum Interrupting Current
Explanation
Circuit breakers are rated according to the maximum interrupting current they can handle. This refers to the maximum amount of current that the circuit breaker can safely interrupt or stop in the event of a fault or overload. The higher the maximum interrupting current rating, the more capable the circuit breaker is at handling larger electrical currents and protecting the circuit from damage.
21.
Is the period from the instant current begins to flow through the trip coil until the circuit breaker interrupts the fault:
Correct Answer
C. Interrupting Time
Explanation
The interrupting time refers to the period from the instant current starts flowing through the trip coil until the circuit breaker interrupts the fault. It is the time taken for the circuit breaker to open and stop the flow of current in the event of a fault. This time is crucial as it determines how quickly the circuit breaker can protect the system from potential damage caused by excessive current. A shorter interrupting time is generally preferred as it ensures faster response and minimizes the risk of damage.
22.
Is the time it takes to close a breaker from the instant the close coil is energized until current begins to flow through the breaker
Correct Answer
D. Closing Time
Explanation
Closing time refers to the time it takes for a breaker to close and for current to start flowing through it after the close coil is energized. This is an important parameter to consider in electrical systems as it affects the overall response time and efficiency of the breaker. By knowing the closing time, operators can ensure that the breaker is functioning properly and that the current is flowing as intended.
23.
Which one do you like?
Correct Answer
A. Option 1
24.
The stability of an arc in a vacuum depends upon:
Correct Answer
D. A combination of both b & c
Explanation
The stability of an arc in a vacuum depends on a combination of both the contact material and its vapor pressure, as well as the circuit parameters. The contact material affects the arc stability by determining the quality of the contact surface and its ability to withstand the heat generated by the arc. The vapor pressure of the contact material plays a role in determining the arc's stability by affecting the ionization and recombination processes within the arc. Additionally, the circuit parameters, such as the current and voltage levels, also influence the stability of the arc.
25.
Where voltages are high and current to be interrupted is low the preferred breaker is:
Correct Answer
C. Vacuum CB
Explanation
In situations where voltages are high and the current to be interrupted is low, the preferred breaker is a Vacuum CB. This is because vacuum circuit breakers are specifically designed to handle high voltages and low currents. They use a vacuum as the arc quenching medium, which allows for efficient interruption of the electrical current without the need for any additional substances like oil or air. Vacuum CBs are also more reliable and require less maintenance compared to other types of circuit breakers. Therefore, in this scenario, a vacuum CB would be the most suitable choice.
26.
SF6 gas has excellent heat transfer properties because of its:
Correct Answer
D. A combination of both a & b
Explanation
The correct answer is a combination of both a & b. SF6 gas has excellent heat transfer properties due to its higher molecular weight and low gaseous viscosity. The higher molecular weight allows for more efficient heat transfer, while the low gaseous viscosity ensures smoother flow and less resistance, further enhancing heat transfer.
27.
The most suitable CB for a short line fault without switching resistor is:
Correct Answer
C. SF6
Explanation
SF6 (Sulfur Hexafluoride) is the most suitable circuit breaker for a short line fault without a switching resistor. SF6 circuit breakers are known for their high interrupting capacity and excellent arc quenching properties. They can effectively extinguish the arc generated during a short circuit fault, ensuring the safety of the electrical system. SF6 circuit breakers also have a compact design and require less maintenance compared to other types of circuit breakers. Therefore, SF6 is the most suitable choice for a short line fault without a switching resistor.
28.
For a lumped inductive load, with increase in supply frequency:
Correct Answer
C. P decreases Q increases
Explanation
For a lumped inductive load, as the supply frequency increases, the inductive reactance also increases. This leads to a decrease in the active power (P) consumed by the load because the increase in inductive reactance causes a phase shift between the current and voltage, reducing the power factor. On the other hand, the reactive power (Q) consumed by the load increases because the inductive reactance is directly proportional to the reactive power. Therefore, P decreases and Q increases with an increase in supply frequency for a lumped inductive load.
29.
In case of a 3-phase short circuit in a system, the power fed into the system is:
Correct Answer
A. Mostly reactive
Explanation
In a 3-phase short circuit, the power fed into the system is mostly reactive. This is because a short circuit occurs when there is a fault in the electrical system, causing a direct connection between the phases. As a result, the current flow increases significantly, leading to a high reactive power demand. Reactive power is required to establish and maintain the magnetic fields in the system, which is necessary for the operation of inductive loads such as motors and transformers. Therefore, during a short circuit, the power being fed into the system is primarily reactive in nature.
30.
Resistance switching is normally utilized in:
Correct Answer
C. Air blast CBs
Explanation
Resistance switching is normally utilized in air blast CBs. Air blast circuit breakers (CBs) are a type of circuit breaker that use a high-pressure air blast to extinguish the arc formed during circuit interruption. Resistance switching refers to the use of a resistor in the circuit to control the rate at which the circuit breaker contacts separate, allowing for a controlled and efficient interruption of the electrical current. This technique is commonly used in air blast CBs to ensure safe and effective circuit interruption.
31.
An RLC circuit remains predominantly inductive
Correct Answer
C. Above resonance freq
Explanation
Above resonance frequency, the capacitive reactance of the circuit becomes dominant, causing the circuit to behave predominantly as a capacitive circuit. This means that the circuit's impedance decreases as the frequency increases, resulting in a higher current flow and a lower voltage across the circuit. Consequently, the circuit becomes less inductive and more capacitive at frequencies above resonance.
32.
The coefficient of reflection of a short circuited line is
Correct Answer
B. -1
Explanation
The coefficient of reflection of a short-circuited line is -1. This means that when a signal is sent down the line and reaches the short circuit, it is completely reflected back with a phase inversion. In other words, the amplitude of the reflected signal is equal to the amplitude of the incident signal, but with the opposite polarity. This is because a short circuit creates a low impedance path, causing the signal to be reflected without any loss or attenuation.
33.
If Pm is the maximum power transferred, the loss on the system is:
Correct Answer
B. Pm / 2
Explanation
The correct answer is Pm / 2. This is because in a system, the maximum power is transferred when the load impedance matches the complex conjugate of the source impedance. At this point, the power loss on the system is equal to half of the maximum power transferred. Therefore, the loss on the system is Pm / 2.