- What effect does the overvoltage surge have on the electrical system?
Over-voltage in the power system causes insulation failure in the equipment. It causes the line insulation to flash over and may potentially harm the surrounding transformer, generator, and other line-connected equipment.
- What does crawl in an induction motor mean?
Induction motors, particularly squirrel cage induction motors, can occasionally run stably at speeds as low as one-seventh of their synchronous speed Ns. This phenomenon is known as crawling of an induction motor and the speed is called as crawling speed.
- What are the various slip measurement methods?
Stroboscopic approach based on actual rotor speed measurement based on rotor frequency measurement
- Why is the transformer core laminated?
Eddy current loss should be reduced. They are isolated from one other and composed of thin laminated sheet. Finally, the air gap is removed by pressing the solid structure.
- Name the types of power in electrical power?
There are three types of power in electrical power. They are
- Apparent power
- Active power
- Reactive power
- Explain the cooling effect of a transformer.
We employ cooling mechanisms such as cooling fins to manage the temperature of the transformer. It is connected to a tank to prevent the negative effects of high temperatures.
- Define is CMRP?
It is defined as the ratio of differential voltage gain to common voltage gain. If a differential amplifier is perfect, CMRP is infinite since common mode voltage gain is zero.
- Why is the field rheostat set to the minimum setting while the armature rheostat is set to the maximum?
When starting a motor, the armature resistance is introduced to lower the high starting current and the field resistance is kept to a minimum to provide a high starting torque.
- What is a two-phase motor?
A two-phase motor is one that features a phase split between the starting and running windings. For example, consider an alternating current servo motor with a 90-degree phase difference between the auxiliary and control windings.
- What is a differential amplifier?
Differential amplifiers are used to amplify the voltage difference between two input lines, neither of which is grounded. This decreases the amount of noise injected into the amplifier because any noise coming simultaneously on both input terminals is rejected as a common mode signal by the amplifying circuitry.
- Define inrush current?
The current drawn by an electrically driven device when electricity is first provided is known as inrush current. It can happen with either AC or DC powered equipment, and it can even happen with a low supply voltage.
- Define Stepper Motor?
A stepper motor is a motor that works or acts on the applied input pulse. This stepper motor is classified as a synchronous motor, which does not always rely on the entire cycle. It prefers to work in any direction when it comes to stages. It is primarily utilised in automation parts for this purpose.
- Define is electrical traction?
Traction refers to the use of electric power in a traction system. Electric traction, for example, involves the use of electricity for railways, trams, trolleys, and so on. Magnetic traction is now also used in bullet trains. DC motors are mostly used in electric traction systems.
- Why are transformer ratings in KVA?
Because transformer power factor is load dependent, we just define VA rating and exclude power factor. In the case of motors, power factor is determined by construction, hence motor ratings are in KW and include power factor.
- What is the primary application of a rotary phase converter?
Because a rotary phase converter converts single phase power into genuine balanced three phase power, it is also known as a single phase to three phase converters. The benefits of three-phase motors and other three-phase equipment frequently make it beneficial to convert single-phase to three-phase so that small and big users do not have to pay the extra expense of a three-phase service but can still utilise three-phase equipment.
- What is excitation?
In DC motors, excitation is the application of an external voltage to the DC shunt coil.
- What is the meaning of the electrical diversity factor in electrical installations?
The electrical diversity factor is the ratio of the sum of the individual maximum demands of distinct subdivisions of a system or part of a system to the total maximum demand of the system or part of the system under consideration. Electrical diversity is frequently more than one.
- What is the distinction between a resistance grounding and a resistance earthing system?
Resistance grounding refers to connecting the neutral point of the load to the ground in order to carry residual current in the event of unbalanced conditions through the neutral to the ground, whereas resistance earthing is done in an electric equipment in order to protect the equipment in the event of a fault in the system.
- What role does vector grouping play in power transformers?
The manufacturer of each power transformer specifies a vector group. It essentially tells you how the windings are linked (delta or wye) and the phase difference between the current and voltage.
- What are the benefits of a VSCF wind energy system?
- There is no need for a complicated pitch-changing system.
- Aero turbines are constantly at their most efficient.
- Extra energy can be derived from the speed – duration curve in the high wind speed zone.
- Aerodynamic stresses associated with constant-speed operation are significantly reduced.
- Why is Cu loss influenced by power factor?
Cu loss is proportional to the current in the primary and secondary windings. It is commonly known that when the power factor is low, the current required increases.
- Why do capacitors only function on alternating current?
Capacitors, in general, provide unlimited resistance to dc components (i.e., block the DC components). It enables ac components to pass through.
- What is a Buchholz relay and what role does it play in the transformer?
Buchholz relay is a gas-based relay that is used to safeguard transformers from internal defects. When an internal defect develops in a transformer, the Buchholz relay immediately sounds a horn for a short period of time; if the transformer is isolated from the circuit, the sound stops; otherwise, the circuit is tripped by its own tripping mechanism.
- Define ferrantic effect?
The output voltage exceeds the input voltage, or the receiving end voltage exceeds the transmitting end voltage.
- Why are Delta Star Transformers used to power lighting loads?
Lighting loads require a neutral conductor, therefore the secondary must be star wound, and this lighting load is always imbalanced in all three phases. To reduce current unbalance in the primary, delta winding is used in the primary. For lighting loads, a delta / star transformer is utilised.
- Define QMS?
QMS is an abbreviation for Quality Management System; it provides all required information regarding a firm’s design and operational controls, such as issue reporting, monitoring, continuous improvement, and training, to ensure that the organisation delivers a consistent product.
- What is the difference between a four-point starter and a three-point starter?
In four-point stater, the shunt connection is given independently from the line, however in three-point stater, it is connected with the line, which is the disadvantage of three point stater.
- What happens when the impedance of an electrical load is equal to the internal impedance of the power source?
The source can deliver maximum power to the load
- Define BOM?
The term “Bill of Materials” refers to a list of items or parts that comprise a product assembly. A lawn mower, for example, requires a handle assembly, a metal deck assembly, a control system, a motor, and a blade assembly.
- What is the most difficult aspect of product manufacturing?
The fundamental issue in manufacturing is to develop better production processes, assure the proper material and component supplies at the lowest possible cost, reduce production time, eliminate waste, and maintain product quality.
- What is a system?
When a group of elements or components are connected in a precise order to perform a given function, the group of elements is referred to as a System.
- What is the definition of “factory overhead”?
During the production process, whatever costs are incurred are referred to as “factory overhead,” which excludes the cost of materials and direct labour.
- Define control system?
When the output and inputs of a system are interconnected in such a way that the output quantity or variable is controlled by the input quantity, the system is referred to as a control system. The controlled variable or response is the output quantity, while the command signal or excitation is the input quantity.
- What is feedback in a control system?
The feedback in a control system is one in which the output is sampled and a proportionate signal is supplied back to the input for automatic error correction (any change in the desired output) for additional processing to obtain the desired output.
- Why is Negative Feedback preferred in Control Systems?
Feedback’s job in a control system is to return the sampled output to the input and compare the output signal to the input signal for errors (deviation from the desired result).
Negative Feedback improves system stability by rejecting any disturbance signals and making the system less susceptible to parameter alterations. As a result, negative feedback is considered in control systems.
- In the electricity system, how are relays connected?
The relays are linked to the power supply via the current transformer (CT) or potential transformer (PT) (PT).
- What are the various operating principles of electromechanical relays?
Eletromechanical relays work on two different principles. Electromagnetic attraction and induction are two different phenomena. In electromagnetic attraction, the relay plunger is drawn to the solenoid or an armature is drawn to the electromagnet poles. The functioning concept of electro-magnetic induction is similar to that of an induction motor. The electromagnetic induction principle is used to generate torque.
- What is reverse polarity, and how can it be corrected?
It is a condition in which one or more receptacles are connected incorrectly. To repair reverse polarity, verify the receptacle’s wire connection at the outlet. In a reverse polarity receptacle, the wire will be screwed to the black wire and the hot side will be connected to the neutral side. You can, however, rectify the problem by swapping the cables.
- Define trunk cable?
Trunk Cable refers to the main H1 or HSE link single pair cable that connects the control system to the Foundation Fieldbus junction box in the field.
- Define Spur cable?
Spur Cable refers to the H1 or HSE link cable used to connect field instruments such as transmitters, switches, valves, solenoid valves, and so on to the Foundation Fieldbus junction box.
- Define Safety Earth?
A safety earth is a connection between an installation’s exposed electrical components and the primary earthing connection. The function of the safety earth is to provide a safe low resistance path for any leakage current in the body of an installation, equipment, or device to pass to the earth, allowing workers to operate safely in the installation, equipment, or device.
- What is reactance?
Capacitance or inductance creates resistance to the flow of alternating current.
- What should the resistance of safety earth be?
5 Ohms or less
- What should the resistivity of the instrument/signal earth be?
1 Ohm or less
- Define Megger?
The Megger is the instrument used to measure the insulation’s resistance.
- What is a bus bar?
A bus bar is a conductor that transports current and has numerous incoming and outgoing line connections. Bus bars are commonly found in substations and are classified as single bus, ring bus, or double bus.
- What are the advantages of DC transmission?
- Only two conductors are required.
- Inductance, capacitance, and phase displacement issues that we observe in AC transmission won’t exist.
- For the same load and sending end voltage, voltage drop is reduced.
- No system instability, such as AC transmission, will exist.
- There would be less corona loss and less interference with communication circuits for a DC transmission.
- Name some most commonly used conductors
- Copper
- Aluminium
- Galvanized steel
- Cadmium copper
- A description of medium and short line transmission
Medium transmission lines have a range of 50 to 150 kilometres and a line voltage of 20 to 100 kilometres. The 150Km-long long-distance transmission line would be capable of carrying voltages greater than 100KV.
- Describe the brief transmission line.
A transmission line is considered short if its length is less than 50 km and its line voltage is less than 20 KV.
- Which motor is a single-phase, unexcited synchronous motor?
Reluctance motor
- How do relays identify errors?
Voltage, current, and frequency would act strangely under a fault scenario. Relays have the ability to measure current and voltage as well as detect changes in those parameters. Relays have a variety of other detection techniques in addition to being able to identify overcurrent or undervoltage situations.
- Why does proximity matter?
when there are two nonparallel AC carrying conductors. The proximity effect is the result of internal current in both conductors being redistributed so that the AC current density is lower on the side closest to the other conductor than it is at the other end.
- Describe switchyard
A junction where power is transmitted can be thought of as a switchyard. A switchyard can assist secure a power plant and aid in power transmission.
The heart of a power plant is the switchyard, which connects the generation plant and the transmission system and is referred to as a switching station. Switchyard manages reactive power equipment.
- What does a switchyard’s machinery look like?
- Transformer for voltage and current
- Lightning arrestor
- Transformers and isolators for power
- Circuit breaker and bus bar
- Switch for the earth and a wave trap
- The maximum power developed in the synchronous motor is depended upon?
The maximal coupling angle and rotor excitation voltage are dependent on the supply voltage.
- Why is electrical clearance required?
Electrical is required to provide the required physical separation for phase to phase, phase to structure, and phase to ground. Air gaps are used to create a safe working environment and to prevent flashovers.
- What exactly is short circuit force?
Structure loads induced by short circuit forces are known as short circuit forces.
- What happens to the synchronous motor’s power factor if the excitation current is increased?
The power factor will rise if the excitation current is increased.
- What is the electrical grid’s islanding operation?
If the electrical grid’s frequency falls below the rated pre-determined frequency, the grid will be divided into a number of small islands, each with some generation units and load centres. The purpose of dividing the electrical grid into separate sections is to protect the system’s health.
- What are the drawbacks of constant voltage transmission?
The short circuit current in the system will rise.
- Why is the induction motor’s efficiency lower than that of the transformer?
Mutual induction is the operating concept of both a transformer and an induction motor. The flux in a transformer flows from primary to secondary windings through the core of the transformer, whereas the flux in an induction motor travels from stator to rotor through the air gap. As a result, the power factor of the induction motor will be lower than that of the transformer.
- Which insulators are utilised in 220KV transmission lines?
Suspension type
- In a transmission line where grounding is performed?
On the supply side
- Why is a thermal protection switch utilised in a power line system?
It serves as a safeguard against overburden.
- Typical location of the earthing switch?
It is often mounted on a circuit breaker frame.
- In a transmission line, which wire is higher than the others?
The earth wire
- Explain the forward, static, and dynamic resistances of a PN junction diode.
Forward Resistance: Forward resistance is the resistance produced by a diode circuit when it is forward biased.
DC resistance, also known as static resistance, is defined as the ratio of the dc-voltage across the diode to the direct current flowing through it.
AC, or Dynamic Resistance, is defined as the reciprocal of the slope of the diode’s forward characteristic. It is the resistance that a diode provides to the changing forward current.
- Name different losses in a transformer?
- Constant losses or Iron losses,
- Variable losses or copper losses
Iron losses are again divided into two. They are
- Eddy current loss
- Hysteresis loss.
- State Maximum power transfer theorem.
The Maximum power transfer theorem explains about the load that a resistance will extract from the network. This includes the maximum power from the network and in this case the load resistance is being is equal to the resistance of the network and it also allows the resistance to be equal to the resistance of the network. This resistance can be viewed by the output terminals and the energy sources can be removed by leaving the internal resistance behind.
- What is the effect of doping intrinsic semiconductors?
To move the Fermi level away from the center of the forbidden band
- Why are bundled conductors used in high-voltage transmission lines?
Because the corona effect is more likely at higher voltages, bundled conductors are used in extra high voltage transmission lines to lessen the corona effect. Sub conductors have been inserted at regular intervals across the transmission line to prevent corona discharge loss and interference with adjoining communication lines.
- What do you mean by “self-regulation”?
Self-regulation is the process by which the output changes from one stable state to another in order to achieve a sustained change in input. The output variable fluctuates in response to changes in the input variable until the output value reaches a steady state. The method of using a specific value of the controlled variable for the rated load without performing any control operations.
- What is impedance?
The opposition to the flow of current in an AC circuit
- What is the Thomson effect?
The evolution or absorption of heat when current passed through a conductor in which there is a difference in temperature along its length.
- What is Hysteresis?
The inability of molecules in a ferromagnetic material to rapidly change their magnetization in response to a change in an applied magnetic field is referred to as hysteresis.
- What is reset-wind up?
When a reset operation is applied to controllers when the measurement has been far from the setpoint for an extended period of time, the rest can raise the output to its maximum, terminating the break. When the process is restarted, the output will remain at its peak until the measurement crosses the point, resulting in significant overshoots. This problem can be prevented by including an anti-reset winding circuit, which eliminates output saturation.
- Define Corona Discharge?
Corona Discharge (or the Corona Effect) is an electrical discharge caused by the ionisation of a fluid around an electrically charged conductor, such as air. The corona effect will occur in high-voltage systems unless care is taken to limit the strength of the surrounding electric field.
