Unit - 1
Electrical System Components
Q1) Define Switches.
A1) Used to switch the power supply to the appliance "on" or "off". There are several switches such as Surface switch, flash switch, ceiling switch, pull switch, push button switch, bed switch.
(I) Surface switch: It can be attached to a wooden board fixed to the surface of the wall. There are 3 types
1. One-way switch
2. Bidirectional switch
3. Intermediate switch
i. Flush Switch: It used for decorative purpose
ii. Bed Switch: As the name implies, it is used to turn the light "on" from a location other than the switchboard or near the bed. This switch is connected with a flexible wire
Q2) What is PVC Casing Capping Wiring?
A2) PVC capping is done to cover the wires. Casing is also included. This casing capping wiring is also called open wiring because it is done outside the wall. The materials required for PVC casing capping wiring Wire 2. Plastic Casing Enclosure 3. Plastic Capping 4. T. Joint VIR (Vulcanized Indo Rubber) or PVC (Polyvinyl Chloride) Included.) Insulated wires 5. Junction box 6. Elbow 7. Casing and capping joint Wooden Casing-Capping wiring is archaic. Currently, PVC or VIR insulated wire is enclosed within a PVC casing enclosure and PVC capping is used to cover the casing.
Q3) Give some example of fault limiting devices?
A3) Some examples of fault limiting devices are as follows:
Q4) What are the effects of Electrical Faults?
A4) The effects of electrical faults are as follows:
Q5) How many types of faults are there in 3 phase power system?
A5) The faults that occur in the three-phase power system are as follows:
Q6) “Electric cables are the nerve of any electrical network.” Justify the statement.
A6) Electric cables are the nerve of any electrical network. Cables make up the majority of capital investment in electrification projects. And they are also the most vulnerable to failure. Most cable failures can be due to improper selection.
Selection Parameters
I. Rated Voltage: This is the rated voltage of the system in which the cable is installed and used. It is also important to know how to ground the system. The rated voltage of the cable is usually specified as a dual rating (eg 6.6kV (UE) / 11kV (E)).
"UE" means that the cable can be used at the specified voltage in an ungrounded or effectively ungrounded system. An "E" means that the cable can be used at the specified voltage in a well-grounded system. Therefore, cables with rated voltages of 6.6kV (UE) / 11kV (E) can be used with either 6.6kV non-earthing systems, 6.6kV non-effective earthing systems, or 11kV solid earthing systems. I will.
II. Conductor Type: The most commonly used conductors in cables are either copper or aluminium. As is known, for the same voltage rating, type, insulation, cross-sectional area, and installation method, the continuous current rating, short-time current rating, and cost per unit length of copper cable are significantly higher than aluminium. Become. cable.
III. Insulation Type: Most cables today are insulated with either PVC or XLPE. Obviously, for the same conductor material, voltage rating, type, insulation, cross-linked area, and installation method, the continuous current rating, short-time current rating, and cost per unit length of the XLPE insulated cable are significantly higher. Become. PVC insulated cable.
IV. Cable Types: Armored or unarmored cables are used in indoor equipment and ground equipment such as cable trays and pre-built concrete cable trenches. An armored cable is required to install the underground cable.
The armor can be galvanized iron or aluminium wire or strips. Often, this armor is connected to the plant's grounding system, preferably only one end, generally the transmitting end.
V. Continuous Current Ratings: Continuous current ratings for cables with aluminium / copper conductors are available in the catalog of various cable manufacturers. However, keep in mind that these catalog list continuous current ratings for certain standard installation conditions. In reality, it is not possible to obtain or maintain these standard conditions. Therefore, certain rating factors are applied to reach the actual continuous current rating.
VI. Evaluation Factors: The general evaluation factors to consider are:
a) Rating factor for fluctuations in ground temperature or duct temperature
b) Evaluation coefficient for fluctuations in ambient temperature
c) Evaluation coefficient for fluctuations in soil thermal resistance
d) Group evaluation factor – vertical spacing
e) Group evaluation factor – horizontal spacing
All these rating factors for different conditions are also available in the cable manufacturer's catalog.
VII. Voltage Drop: The cable consists of a resistor and reactance. Therefore, the current flowing through such impedance causes a voltage drop. This reduction should not affect the cabled load.
The actual voltage drop of the cable is indicated by V / km / A in the cable manufacturer's catalog for different types of cables. It is also stipulated in the Indian standard IS 1255 (implementation standard for installation and maintenance of power cables up to 33 kV rating).
It is necessary to calculate not only the steady-state voltage drop, but also the accelerated state voltage drop at the start of a large load.
It is also necessary to confirm that the steady-state voltage drop at the load terminal is 10% or less and the accelerated voltage drop at the load terminal is 15% or less.
Q7) What are the causes of electrical faults?
A7) The causes of electrical faults are as follows:
Q8) What are the Physical Parameters of Electric cables?
A8) When choosing a wire / cable, the most important physical parameters are temperature, fluid exposure, installation, and performance when exposed to wear at operating temperatures. In terms of temperature, insulation and conductor limits need to be considered. For shielded cables, shielded plating should also be considered as a limiting factor. When a conductor overheats, the plating deteriorates rapidly, the conductivity decreases, the signal deteriorates more, and it becomes more susceptible to corrosion.
For liquid exposure, many aircraft wire / cable insulation types are inert to common chemicals, which should be evaluated according to the application. If unusual chemicals are used in either manufacturing or maintenance of the platform, the suitability of the material should be evaluated. There are some recent examples of fleets that have implemented new cleaning or deicing solutions just to cause significant deterioration of electrical components. Tests such as AS4373 Method 601 provide the basis for assessing wire / cable degradation due to fluid exposure.
Abrasion resistance should be evaluated at operating temperature. How wire insulation works at ambient temperature is not the same as how it works at high temperatures. A rise of only 10 ° C can reduce the performance of some insulation types by up to 50%. These performance changes do not have to be above 140 ° C, but in some cases can range from 50oC to 60 ° C. If the environment in your installation zone is vibrating or subject to regular maintenance traffic, we recommend that you choose components that are highly wear resistant.
Q9) Define per unit value.
A9) It is defined as the ratio of actual value to its base value. 96. Mention the inductance value of the Peterson’s coil.
L=1/3ωc2
Q10) Define single line diagram.
A10) Representation of various power system components in a single line is defined as single line diagram.
Q11) What are the three main curve types that allow surges in different electrical environments?
A11) Three main curve types that allow surges in different electrical environments.
Q12) What are the three types of High voltage fuse (HV)?
A12) All types of high voltage fuses are used at rated voltages up to 1.5 Kv to 138 Kv. High voltage fuses are used to protect instrument transformers and small transformers. Made of silver, copper and tin. When heat is generated, an arc is generated and boric acid produces a large amount of gas. Therefore, they are used outdoors.
There are three types of these: -
a) Cartridge Type HRC Fuse: -Similar to the low voltage type, except for some design features.
b) Liquid Type HRC Fuses: -These are used for circuits with up to 100A rated current and systems up to 132Kv. The glass tubes of these fuses are filled with carbon tetrachloride. One end of the tube is packed and the other end is secured with phosphor bronze wire. When the fuse is activated, the liquid in the fuse extinguishes the arc. This will increase the short circuit capacity.
c)Ejection Type HRC Fuse: -This is an escapable fuse that has the effect of exhausting the gas produced by the internal arc. In this case, the fuse link chamber is filled with boric acid to expel the gas.
d)Resettable Fuse: -This is a type of fuse commonly known as a self-reset fuse that uses a thermoplastic conductive type thermistor known as the Polymer Positive Temperature Coefficient (PPTC). When a failure occurs. The current increases and the temperature rise. The increase in resistance is due to an increase in temperature. The applications in which it is used are non-exchangeable military and aerospace.
Q13) What is an arc?
A13) Arc is a phenomenon occurring when the two contacts of a circuit breaker separate under heavy load or fault or short circuit condition.
Q14) Briefly explain the two types of fuses.
A14) There are two types of fuses: -
Q15) How do you select the pickup value of the relay?
A15) The pickup value of the relay should be more than the maximum load and it should allow the normal load as well as the certain degree of overload to be supplied. The relay should be sensitive enough to respond to the smallest fault, therefore, the pickup value should be less than the smallest fault current.
Q16) What is the difference between a fuse and a breaker?
A16) The difference between Fuse and a circuit breaker is that fuse works on the principle of the thermal and electrical properties of the conducting materials, whereas the circuit breaker works on the principle of electromagnetism and switching principle. We can use the fuses only once but circuit breakers can be used many more times, and the breaking capacity of the fuse is low as compared with the circuit breaker.
Q17) What is the characteristic features of Fuse?
A17) Fuse Features:
Current (Cin) = 75% current (rated)
2. Voltage Rating: With this characteristic, the voltage connected in series with the fuse does not increase the voltage rating. In other words
V (fuse)> V (open ckt)
3. I2t Rating: This is the amount of energy carried by the fuse element in the event of an electrical failure or any short circuit. It is generated when the fuse blows by measuring the thermal energy (energy due to electric current) of the fuse.
4. Breaking or Breaking Capacity: This is the maximum rating of current without breaking by the fuse and is known as the breaking or breaking capacity of the fuse.
Breaking capacity> Maximum rated voltage
Breaking capacity <short ckt current
5. Voltage Drops: Excessive current will melt the fuse element and open the circuit. This resistance change reduces the voltage drop.
6. Temperature: This will increase the operating temperature, lower the rated current and melt the fuse
Q18) How to operate fuse?
A18) The fuse operates on the principle of the heating effect of electric current. It consists of thin strips of non-flammable material or strands of metal wire. It is connected to both ends of the terminal. The fuse is always connected in series with the electrical circuit.
When a large current flow through the circuit and excessive current or heat is generated, the fuse melts and the circuit open because the melting point of the element is low. Excessive flow can lead to wire breakage and stop current flow. The fuse can be replaced or replaced with a new fuse of the appropriate rating. Fuse can be composed of elements such as zinc, copper, silver and aluminium. It also acts as a circuit breaker used to break the circuit in the event of a sudden circuit failure. This is not only a protective device, but also used as a safety measure to prevent danger to the human body. So this is how the fuse works. It is the figure which showed the operation of the fuse, the fuse barrel (container), and the fuse link.
Q19) What all properties should tariff have?
A19) The tariff must have the following desirable properties of the tariff:
Similarly, consumers whose load conditions do not deviate significantly from their ideals, that is, non-variable consumers, need to charge at a lower rate than consumers whose load conditions have changed significantly from their ideals.
3. Simplicity: The price should be simple for the general consumer to understand. Complex charges can cause opposition from the general public, who generally distrust the supplier.
4. Reasonable Profit: The profit factor of the fee must be reasonable. Power companies are utilities and generally benefit from monopolies. Therefore, the investment is relatively safe as there is no competition in the market. This requires that profits be limited to around 8% per year.
5. Attractive: Prices must be attractive so that many consumers are encouraged to use electrical energy. Efforts should be made to fix prices in a way that consumers can easily pay.
Q20) Write short note on Weighing System Selection.
A20) The metering system consists of things of metering equipment. Voltage transformers, current transformers, meters and outstations, wiring and connections between items, and therefore the connections needed to transfer metered data to the surface world (modems, communication lines, etc.).
There are many factors to think about when choosing the proper electric meter. Whether for tenant submetering, commercial building submetering, power monitoring for energy management, or other applications, the wattmeter must meet certain specifications. Although each application has its own requirements, there are some common factors to gauge. When considering electric meter options, it's important to understand the following: