- Define Substation?
A substation is a switching, transforming, or converting station located between the generating station and the low tension distribution network, typically near the consumer’s load center.
- Name the types of substation?
- Indoor substation
- Outdoor substation
- Pole mounted substation
- Underground substation.
- Define Indoor Substation?
The indoor Substation is one in which the equipment is located indoors for voltages up to 11kV due to cost considerations. In the event of a contaminated atmosphere, these substations can be built at voltages up to 66kV.
- Define Outdoor Substation?
The term “outdoor substation” refers to a substation with a voltage of 33kV or more where the equipment is installed outside because the clearance between wires and the space required for diverse equipment becomes so enormous at such voltages that it is not economical to put within.
- Define Pole Mounted Substation?
Pole mounted substation is the most cost-effective outdoor type of substation for voltages not exceeding 33kV, in which the equipment is located overhead on an H-pole or 4-pole structure and electric power is virtually entirely supplied through such substation.
- Define Underground Substation?
In densely populated locations where available space for substation equipment and buildings is limited and land costs are high, substation equipment is installed underground and is referred to as an underground substation, which requires more careful consideration than other types of substation.
- What is cable grading?
Grading of cables refers to the process of achieving uniform electrostatic stress in the dielectric of wires.
- What is the composition of transmission cable?
Rubber, vulcanised India rubber, impregnated paper, varnished cambric, and polyvinyl chloride are the most common insulating materials used in cables.
- What is the function of Substation?
The Substation receives power from the generating station by a signal or many feeders at high voltage, converts it to different distribution voltages, and distributes it to various consumers via the distribution network.
- What are the things need to be considered while selecting space for outdoor substation?
The following factors must be considered when deciding where to locate an outdoor type substation:
- The site should be near the center of its supply area.
- A sufficient amount of land must be accessible at a fair cost.
- The location should be away from intensively inhabited areas.
- The place should be easily accessible by transportation.
- Define Converting Substation?
A converting substation is one that converts alternating current energy to direct current energy.
- Define Frequency Substation?
A frequency substation is a substation in which the frequency is changed from one value to another using a frequency converter.
- Define Switching Substation?
A switching substation is one that performs simple switching operations on power lines without regard for voltage level.
- Define Power Factor Correction Substation?
Power factor-correction substations are positioned at the receiving end of transmission lines and perform power factor correction utilising generally synchronous condensers.
- Define transformer substation?
A transformer substation is one in which the voltage is either stepped up or stepped down by means of a transformer.
- Define Industrial Substation?
An industrial substation is a substation from which power is provided to particular industrial concerns.
- Name the advantages of Outdoor type substations?
- Because all equipment is visible and accessible, malfunctions and defects can be easily identified and corrected.
- The substation equipment can be suitably separated.
- The problem in one segment has no influence on the healthy section.
- The cost of construction is lower because no massive buildings are required to house the substation equipment.
- The time necessary for construction is reduced.
- Future expansions and modifications are simple to implement.
- Name the disadvantages of Outdoor type substations?
- Because the equipment is exposed to the elements, the impact of fast changes in ambient temperature, dust, and filth deposited on the equipment necessitates the installation of specially designed, more expensive equipment.
- The outdoor substation requires extra room because the buses and other live parts are bare and require additional clearance.
- In rough and stormy weather, different switching operations, fault repair, and maintenance become challenging.
- Define Mining Substation?
The mining substation is a specially constructed substation created for the purpose of mining installation that provides additional safety precautions in the operation of electric supply.
- Define Mobile Substation?
The mobile substation is a substation that is built for temporary needs, primarily for construction purposes.
- Define Distribution Substation?
The distribution substation is the location where the sub transmission voltage or primary distribution voltage is stepped to supply voltage to customers via a network of distribution lines.
- What is the difference between Bulk Supply and an Industrial Substation?
A bulk supply and industrial substation is a distribution substation built for an individual bulk supply consumer or an industrial consumer of large or medium supply ground.
- Define Mining Substation?
The mining substation is a specially constructed substation created for the purpose of mining installation that provides additional safety precautions in the operation of electric supply.
- Define mobile substation?
The mobile substation is a substation that is built for temporary needs, primarily for construction purposes.
- What is Arc formation?
When a short circuit occurs, a large current passes through the circuit breaker contacts, which are opened by the safety system. When the contacts begin to separate, the contact area rapidly diminishes, and a significant fault current generates increased current density and thus a rise in temperature. The heat generated in the medium between the contacts is enough to ionise it. An arc is formed between the contacts when ionised air or vapour acts as a conductor.
- What is three-phase power supply?
It is a sort of polyphase system and the most popular technique of power transfer utilised by grids globally. Three circuit wires in a three-phase system carry three alternating currents (of the same frequency) that reach their instantaneous peak values at different times.
- Explain the function of a fuse.
When a short circuit or overload occurs, the current through the fuse exceeds its rated value, raising the temperature and causing the fuse element to melt (or blow out), disconnecting the circuit it protects.
- What is feedback in a control system?
The Feedback in Control System is one in which the output is sampled and the proportional signal is given back to the input for automatic error correction (any change in desired output) and further processing to obtain the desired output.
- Why is Negative Feedback favoured in Control Systems?
Feedback’s job in the 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.
- What is ACSR cable and how is it used?
ACSR is an abbreviation for Aluminium conductor steel reinforced. This wire is utilised in transmission and distribution.
- Define current chopping?
Current chopping in CB is the occurrence of arc current interruption prior to normal current zero. If this current is sufficient to deliver a voltage greater than the restriking voltage, the arc will resume. However, as the current decreases, so does the voltage, until the restriking voltage is reached and the arc is extinguished. It causes voltage oscillation in the line, affecting electrical equipment.
- What is a Wave trap?
Wave trap is another name for line trap. It aids in the capture of high-frequency communication signals transmitted via the line from the remote substation and their redirection to the telecom/tele-protection panel in the substation control room (through coupling capacitor and LMU). The Line trap has a high resistance to high frequency communication signals, obstructing their flow into the substation Bus bars.
- Define diversity factor?
Diversity Factor is the Sum of Individual Maximum Demand/ Maximum Demand on Power Station
- What are the benefits of using a freewheeling diode in a Full Wave rectifier?
It minimises harmonics as well as sparking and arching over the mechanical switch, resulting in a lower voltage spike in an inductive load.
- What is the definition of Specific Electric Loading?
Specific Electric Loading is defined as the number of Armature (or Stator) Ampere Conductors per Meter of Armature (or Stator) Periphery at the Air Gap.
- What is the definition of Specific Magnetic Loading?
Specific Magnetic Loading is the average flux density over a machine’s air gap.
- What is a runaway speed?
It is defined as the speed of the prime mover if it is unexpectedly emptied while operating at its rated load.
- What is a Field Form Factor?
It is the ratio of the average flux density to the highest flux density over the pole pitch. It is sometimes referred to as the flow distribution factor.
- What is creepage distance?
Creepage distance is the smallest distance between two conducting points on the insulating material’s surface.
- What is the Basic Impulse Level (BIL)?
The term “basic impulse level” (BIL) refers to the peak value of the equipment’s lightning induced voltage withstand capabilities.
- Why EHV busbars are hallowed and circular?
To avoid corona effect.
- Why does surge impedance loading (SIL) rise as voltage level increases?
Because SIL varies with the square of the operating voltage, it increases as the voltage level rises.
- What is a Window Space Factor?
It is defined as the copper area in the window divided by the overall window area.
- Which is preferred, underground or overhead cables?
Despite the fact that many low voltage, local electric distribution lines are buried underground, practically all high-voltage electric transmission lines are attempted to be installed as overhead cables due to cost differences.
- What is the difference between a relay and a fuse?
A relay is a switch that is not typically intended to open under fault conditions (high current).
A fuse is a device that protects against faults. Large currents will flow if a short circuit forms, and the fuse link will melt, forcing the circuit to open.
- What is a PLCC?
Power line communication (PLC), also known as power line digital subscriber line (PDSL), mains communication, power line telecom (PLT), power line networking (PLN), or broadband over power lines (BPL), are data transmission and electric power transmission technologies. For many applications ranging from home automation to Internet connectivity, a diverse set of power line communication technologies is required.
- What are the various substation components?
Circuit breakers, disconnect switches, grounding switches, current transformers, potential transformers or capacitor voltage transformers, line traps, lightning arrestors, power transformers, shunt reactors, current limiting reactors, station buses and insulators, grounding system, series and shunt capacitors.
- Why are Delta Star Transformers used to power lighting loads?
The neutral conductor is required for lighting loads, hence the secondary must be star wound. In all three phases, the illumination burden is always uneven.
To reduce current unbalance in the primary, delta winding is used in the primary. For lighting loads, a delta/star transformer is utilised.
- What caused the computer humming sound in the HT transmission line?
This computer buzzing sound is caused by ionisation (the breakdown of air into charged particles) in the vicinity of the transmission cable. This is known as the Corona effect, and it is classified as power loss.
- What is Latching current?
To activate the thyristor in safe mode, a gate signal is applied to it.
When the thyristor begins to conduct forward current over a certain threshold, known as the latching current, the gate signal used to trigger the device is no longer required to keep the SCR in the ON position.
- What exactly is Holding current?
When conducting current in the forward conduction state, the SCR will return to the forward blocking state when the anode current or forward current falls below a low level known as the Holding current.
- Is latching current and holding same?
It should be noted that latching current and holding current are not the same thing. Latching current is related to the SCR’s turn-on process, whereas holding current is related to the SCR’s turn-off process. In general, the holding current is less than the latching current.
- What is the power factor of an alternator when no load is applied?
The angle difference is caused by the alternator’s synchronous impedance when there is no load. As a result, it should have zero latency, just like an inductor.
- What does anti-pumping in a circuit breaker do?
When the breaker is closed by the close push button all at once, the anti-pumping contactor prevents the breaker from being closed again by the close push button if it has previously been closed.
- In distribution lines, where should the lighting arrestor be installed?
Lightning arresters are installed near distribution transformers, 11kv outgoing feeders, 33kv incoming feeders, and power transformers in substations.
- Which form of switching scheme is used in a distribution network?
Ring Main busbar technique is used for distribution network. It provides that if power is interrupted to one bus segment due to maintenance or a problem, power can be provided to the bus from the other side of the power system.
- Which bus configuration is more expensive and reliable?
The most dependable and expensive method is the one and a half breaker scheme. Three circuit breakers are provided for two bus-bars in the one and half breaker scheme. As a result, the name “one and half breaker scheme” was established.
- Will a DC Shunt Motor work with an alternating current supply?
The Shunt winding has a large number of turns, resulting in a significant inductance. When alternating current is delivered to a shunt motor, the huge inductive reactance of the shunt winding reduces the field current excessively. As a result, shunt motors are rarely powered by alternating current.
- Name the various electrical clearances in the Substation?
Ground Clearance: It is the shortest distance between a live conductor and the earth or ground.
Phase Clearance: The clearance between various phases in a circuit or the same phases in separate circuits is referred to as phase clearance.
Sectional Clearance: It is the minimum clearance between the live conductor and the boundaries of work, whereas spatial clearance is related to the operating personnel’s safety. The ground or the platform on which the person is working may be the bounds of the work section.
- Define Scott-connected transformer?
A Scott-T transformer (also known as a Scott connection) is a type of circuit that converts two-phase electric power (2-, 90-degree phase rotation) from a three-phase (3-, 120-degree phase rotation) source. The Scott connection distributes a balanced load evenly between the source’s phases.
- Name the types of substation based on their location in power system networks?
- Step up substation
- Primary grid substation
- Secondary substation
- Distribution substation
- Bulk supply and industrial substation
- Mining substation
- Mobile substation.
