Assignment Questions- U14EET402- MAR-16

Assignment Questions

Course Code: U14EET402

Course Name: Transmission and Distribution

Course Faculty: V. Sharmila Deve ASP/EEE,  D. Sharmitha AP 1/EEE

Issue Date: 04.03.2016                                              Dead line: 04-04-16

Assignment Questions

1.      In KCT, power house 1 is supplying a power of 520 KVA to A block. Find the total connected load of the building also calculate the surge impedance and surge impedance loading of the line. Suggest suitable compensation to be provided for the reliable operation of the line. ( A-1)

2.      In KCT, power house 1 is supplying a power of 370 KVA to B block. Find the total connected load of the building also calculate the surge impedance and surge impedance loading of the line. Suggest suitable compensation to be provided for the reliable operation of the line. (B-1)

3.      In KCT, power house 1 is supplying a power of 360 KVA to C block. Find the total connected load of the building also calculate the surge impedance and surge impedance loading of the line. Suggest suitable compensation to be provided for the reliable operation of the line.(A-2)

4.      In KCT, power house 1 is supplying a power of 240 KVA to D block. Find the total connected load of the building also calculate the surge impedance and surge impedance loading of the line. Suggest suitable compensation to be provided for the reliable operation of the line. (B-2)

5.      In KCT, power house 1 is supplying a power of 100 KVA to E block. Find the total connected load of the building also calculate the surge impedance and surge impedance loading of the line. Suggest suitable compensation to be provided for the reliable operation of the line. (A-3)

6.      In KCT, power house 2 is supplying a power of 320 KVA to Ladies hostel. Find the total connected load of the building also calculate the surge impedance and surge impedance loading of the line. Suggest suitable compensation to be provided for the reliable operation of the line. (B-3)

7.      In KCT, power house 2 is supplying a power of 320 KVA to Gents hostel 1. Find the total connected load of the building also calculate the surge impedance and surge impedance loading of the line. Suggest suitable compensation to be provided for the reliable operation of the line. (A-4)

8.      In KCT, power house 2 is supplying a power of 320 KVA to Gents hostel 2. Find the total connected load of the building also calculate the surge impedance and surge impedance loading of the line. Suggest suitable compensation to be provided for the reliable operation of the line. (B-4)

9.      In KCT, power house 2 is supplying a power of 350 KVA to Vallalar kitchen. Find the total connected load of the building also calculate the surge impedance and surge impedance loading of the line. Suggest suitable compensation to be provided for the reliable operation of the line. (A-5)

10.  In KCT, power house 2 is supplying a power of 100 KVA to Students center. Find the total connected load of the building also calculate the surge impedance and surge impedance loading of the line. Suggest suitable compensation to be provided for the reliable operation of the line. (B-5)

11.  In KCT, power house 2 is supplying a power of 80 KVA to TIFAC KORE. Find the total connected load of the building also calculate the surge impedance and surge impedance loading of the line. Suggest suitable compensation to be provided for the reliable operation of the line. (A-6)

12.  In KCT, power house 2 is supplying a power of 320 KVA to Administrative block. Find the total connected load of the building also calculate the surge impedance and surge impedance loading of the line. Suggest suitable compensation to be provided for the reliable operation of the line. (B-6)

13.  In KCT, power house 2 is supplying a power of 320 KVA to seminar halls. Find the total connected load of the building also calculate the surge impedance and surge impedance loading of the line. Suggest suitable compensation to be provided for the reliable operation of the line. (A-7)

14.  In Coimbatore, the TANGEDCO has planned to erect a 400 kV line, Design a tower with suitable height, suitable spacing between conductors, conductors and earth, and spacing between each tower. Also suggest the type of tower to be selected if the line is erected outside/inside the city. (B-7)

15.  In the following blocks of KCT Conduct energy auditing and suggest essential measures to be followed or restricted for the efficient use of Energy in the buildings. (A-8)

Students Center

Tifac Kore

Kitchen

Ladies Hostel

Gents Hostel 1

Gents Hostel 2

Administrative building

Seminar halls

You can use online support for enhanced energy auditing. Use data collected by other batches for the respective blocks.

16.  In the following blocks of KCT Conduct energy auditing and suggest essential measures to be followed or restricted for the efficient use of Energy in the buildings. (B-8)

A-Block

B-Block

C-Block

D-Block

E-Block

You can use online support for enhanced energy auditing. Use data’s collected by your friends for the respective blocks.

1.      Reference: http://www.spc.tn.gov.in//12plan_english/9-Energy.pdf

In tandem with the Tamil Nadu Generation and Distribution Corporation (TANGEDCO), the Tamil Nadu Transmission Corporation (TANTRANSCO) has also taken up establishment of transmission network adequate to evacuate the power generated from the proposed new power plants and also to efficiently distribute further down the channel. It is proposed to establish 400KV substations with 2500 ckt km of 400 KV lines, 230 KV substations and 200 numbers of 110 KV substations during Twelfth Five Year Plan. In addition to this for efficient flow of power across the State, TANTRANSCO will lay a backbone network of 400 KV double circuit line with Quad conductors connecting the following substations during the plan period

i.e., Kayathar(New Sub Station (SS))- Karaikudi (existing PGCIL SS) - Pugalur (existing PGCIL SS) – Singarapet (New SS) – Ottiyambakkam (New SS).

Further, to harness the full potential of eco–friendly wind power, an exclusive

corridor for evacuation of wind power is also programmed during the plan period as set

out below:

• Thappagundu (New SS) - Anaikadavu (New SS) -Rasipalayam (New SS) - Salem(765 KV new SS by PGCIL).

• Abhisekapatty(PGCIL SS) –Kanarpatty (Prop. New SS) – Kayathar (New SS) –

Thennampatti (New SS) – Kovilpatty (New 765 KV PGCIL SS).

• Vagarai (New SS) – Singarapet (New SS)

17.  From Reference 1, Find efficiency ,regulation and cost required for  Kayathar(New Sub Station (SS))- Karaikudi (existing PGCIL SS) - Pugalur (existing PGCIL SS) – Singarapet (New SS) – Ottiyambakkam (New SS). (A-9)

18.  From Reference 1, Find efficiency ,regulation and cost required for  Thappagundu (New SS) - Anaikadavu (New SS) -Rasipalayam (New SS) - Salem(765 KV new SS by PGCIL). (B-9)

19.  From Reference 1, Find efficiency ,regulation and cost required for  Abhisekapatty(PGCIL SS) –Kanarpatty (Prop. New SS) – Kayathar (New SS) – Thennampatti (New SS) – Kovilpatty (New 765 KV PGCIL SS). (A-10)

20.  From Reference 1, Find efficiency ,regulation and cost required for  Vagarai (New SS) – Singarapet (New SS) (B-10)

21.   ISSUE 1:  TN was heavily affected by lack of transmission lines to evacuate power from plants in one part of the state to regions that require power. Despite the availability of power, especially from windmills with a capacity of more than 7,000MW, TN lost over 2.1 billion kwh of power last year alone due to lack of transmission infrastructure, it is estimated.

"The commissioning of the transmission lines will help improve the power situation in Chennai as power generated from windmills in the southern part can be transmitted to the rest of the state and to Chennai, which are power starved," said K Venkatachalam, chief adviser of Tamil Nadu Spinning Mills Association, which owns most windmills in the state.

How to resolve the above issue. Do detail analysis ( Efficiency, Regulation and cost)

Explain green energy corridor project in India. (A-11)

22.  Explain Growth in transmission sector in India. Write technical solution (lke strengthening transmission corridor between region)  to reduce power deficits in southern region of India. (B-11)

23.  Explain difference between 3 phase and 6 phase transmission line. Under smart city plan TRANSCO planned to convert all 3 phase HV to 6 Phase HV,  Find efficiency , Regulation. (A-12)

24.  Explain difference between Cable transmission line and Overhead Transmission line. Under smart city plan TRANSCO planned to convert all 3 phase HV to Cables Find efficiency  and cost. (B-12)

25.  Explain Sakthi sugars Power system Structure. Write your suggestion ( transmission point of view)  to improve its performance.

26.  Explain Suzlon Power system Structure. Write your suggestion ( transmission point of view)  to improve its performance.

25.SUB STATION BUS SCHEME

SUB STATION BUS SCHEME

CIRCUIT BREAKER:
 A circuit breaker is a device whose main purpose is to break the circuit carrying load current or fault current. As the breaker is opened then current is interrupted in the circuit. But it is not safe to work with opened breaker as one or both sides of the breaker terminals may be still energised. The breaker is then isolated from the rest of the circuit by opening the isolators on both sides of breaker. The isolators are used to isolate the breaker or circuit.  It should be remembered that the isolators are never opened or closed to interrupt or make the circuit. That means when the circuit is to be made on, first the isolators on both sides of a breaker are closed then breaker is closed to allow current flow. When the circuit is to be made off or interrupted, first the breaker is opened(tripped), hence load current is interrupted. Then to isolate the breaker, isolators are opened. Isolators are designed to interrupt small current. Breakers are designed to interrupt large load current and heavy fault current. Both breaker and isolator carry load current in normal state.

There are mainly six bus schemes. these are:

Single Bus

Main Bus and Transfer Bus

Double Bus Double Breaker

Double Bus Single Breaker

Ring Bus

Breaker and Half

 Single Bus

As the name indicate the substation with this configuration has a single bus (Fig-B). All the circuits are connected to this bus.  A fault on the bus or between the bus and a breaker results in the outage of the entire bus or substation. Failure of any breaker also results in outage of the entire bus. Maintenance of any circuit breaker requires shutdown of the corresponding circuit/line and maintenance of bus requires complete shutdown of the bus. A bypass switch across the breaker should be used for maintenance of the corresponding breaker. This case the protection system is disabled.

Single Bus configuration is the simplest and least cost of all configurations. The system can be easily expanded. This configuration requires less area. The reliability of this system being low, it is not to be implemented in the substation where high reliability is expected. Large substations usually do not utilize this scheme.  By sectionalising of the bus the reliability and availability of the single bus system can be improved.

DISADVANTAGE:

–      Serious outage in the event of bus failure

–      Difficult to do any maintenance

–      Cannot be extended without de energizing the substation

Main Bus and Transfer Bus  

In this scheme one more bus is added. See Figure-C  how the equipments are arranged and circuits are connected between main and transfer bus. In this arrangement one more breaker may be used, known as tie circuit breaker. No circuit is associated with this tie breaker.

When the tie CB is not present, for maintenance of a circuit breaker, the transfer bus is energized by closing the isolator switches to transfer bus. Then the breaker to undergo maintenance is opened and isolated (opening isolators on both sides of CB) for maintenance. In this arrangement there is no protection for the circuits. The circuits can be protected from outside the substation.

When the tie breaker is present, for maintenance of a breaker the transfer bus is energised by closing the tie breaker. Then the isolator near the transfer bus of the breaker of circuit to be maintained is closed. Now the breaker to be maintained is opened. Then corresponding isolators on both sides of breaker are opened. The breaker is removed for maintenance.  The circuit is transferred to transfer bus. Remember that the isolator to the transfer bus corresponding to the breaker not to be maintained remain open. Here the tie breaker protects the circuit in place of removed breaker. In this scheme the relay setting is quite complex due to the requirement of the tie breaker to handle each situation for maintenance of any of the other breakers. This scheme is somewhat more costly than the single bus scheme but is more reliable. The scheme can be easily expanded. The switching procedure is complicated for maintenance of any circuit breaker. Failure of a breaker or fault on the bus results in outage of complete substation.

          ADVANTAGES:

–      Low initial cost

–      Any breaker can be taken out of service for maintenance and potential device may be used on the main bus for relaying

DISADVANTAGES:

-switching is some what complicated when maintaining a breaker, failure of a bus or any circuit breaker result in shut down of entire substation and requires an extra circuit breaker.

Switching Operation for Transferring a Feeder to Transfer Bus from Main Bus without Interruption of Power
(i) First close the isolators at both side of the bus coupler breaker.
breaker as well as bus coupler breaker via transfer bus.
So it can be concluded that in Main & Transfer Bus System the maintenance of circuit breaker is possible without any interruption of power. Because of this advantage the scheme is very popular for 33KV and 13KV system.

(ii) Then close the bypass isolator of the feeder which is to be transferred to transfer bus.

(iii) Now energized the transfer bus by closing the bus coupler circuit breaker from remote.

(iv) After bus coupler breaker is closed, now the power from main bus flows to the feeder line through its main

(v) Now if main breaker of the feeder is switched off, total power flow will instantaneously shift to the bus coupler breaker and hence this breaker will serve the purpose of protection for the feeder.

(vi) At last the operating personnel open the isolators at both sides of the main circuit breaker to make it isolated from rest of the live system.

Double Bus Double Breaker

In this scheme there are two buses and two circuit breakers per circuit are used (See Fig-D). In normal state both the buses are energised. Any circuit breaker can be removed for maintenance without interruption of the corresponding circuit. Also the failure of one of the two buses does not interrupt any circuit as all the circuits can be fed from the remaining bus and isolating the failed bus. By shifting circuit from one bus to other the loading on the buses can be balanced.
The substation with this configuration requires twice as much equipments as single bus scheme. This scheme has high reliability. But due to more equipments this scheme is costly and requires more space. This scheme is usually used at EHV transmission substation or generating station where high reliability is required.

•          ADVANTAGE

–      Each circuit has two dedicated breakers

–      Flexibility to connect any one bus

–      Any breaker can be taken out for maintenance

–      More reliable

•          DRAWBACK

–      Most expensive

 Double Bus Single Breaker

This scheme is shown in Fig-E. This scheme has two buses. Each circuit has one breaker and connected to both buses by isolators as shown. There is one tie breaker between two buses. The tie breaker is normally closed. For the tie breaker in closed position the circuit can be connected to either of the buses by closing the corresponding switch. It is clear that fault on one bus requires isolation of the bus and the circuits are fed from the other bus.

From the figure you can guess that the configuration has some improvement over the single bus system. This arrangement has more flexibility in operation than the single bus scheme. This scheme is costlier and requires more space than the single bus scheme. Many EHV transmission substations use this scheme with an additional transfer bus.

•          Advantage:

–      Flexibility with two operating buses

–      Either bus 1 or bus 2 may be isolated for maintenance

–      Circuit can be transferred by use of bus tie breaker and the isolators

DRAWBACKS:

–      One extra breaker is required

–      4 isolators are required per circuit

–      High exposure to bus fault

–      Bus tie circuit breaker fault takes entire substation out of service

–      It does not permit breaker maintenance without causing stoppage of supply.

–      Bus protection may cause loss of substation when it operates if all circuits are connected to that bus

Ring Bus 

The Ring Bus configuration is shown in Fig-F. The breakers are so connected and forms a ring. There are isolators on both sides of each breaker. Circuits terminate between the breakers. The number of breakers is same as the numbers of circuits. Each of the circuits in ring bus system is fed from both sides. Any of the breaker can be opened and isolated for maintenance without interrupting any of the circuits. A fault on any of the circuit is isolated by tripping of two breakers on both sides of the circuit. By tripping the two breakers only the faulted circuit is isolated and all other circuits continue to operate in open ring state. This scheme has good operational flexibility and high reliability. The main disadvantage is that when a fault happens and the ring is split and may result into two isolated sections. Each of these two sections may not have the proper combination of source and load circuits. To avoid this as far as possible the source and load circuits should be connected side by side (see figure). The ring bus scheme can be expanded to accommodate more circuits. The ring bus scheme is not suitable for more than 6 circuits (although possible). When expansion of the substation is required to accommodate more circuits, the ring bus scheme can be easily expanded to One and Half Breaker(See below and compare) scheme. The scheme is required to be planned properly to avoid difficulties in future expansion.

•          ADVANTAGES:

–      Low initial cost

–      Flexible operation for breaker maintenance

–      Any breaker can be taken out for maintenance without interrupting load

–      No main bus

–      Each circuit fed by two circuit breakers

–      All switching is done through breakers

•          DISADVANTAGE:

if fault occurs during a breaker maintenance period, the ring will be divided into two sections.

Automatic reclosing and protective relaying circuitry is complex

Breaker failure during a fault on one of the circuit caused loss of one additional circuit owing to operation of breaker failure relay.

Breaker and Half

The Breaker and Half scheme has two main buses (Fig G). Both the buses are normally energised. Three breakers are connected between the buses. The circuits are terminated between the breakers as shown. In this bus configuration for two circuits three numbers of breakers are required. Hence it is called one and half scheme.  It is something like, for controlling one circuit we require one full and a half breakers. The middle breaker is shared by both the circuits. Like the ring bus scheme here also each circuit is fed from both the buses.

Any of the breakers can be opened and removed for maintenance purposes without interrupting supply to any of the circuits. Also one of the two buses can be removed for maintenance without interruption of the service to any of the circuits. If fault happens on a bus it is isolated without interruption of supply to any of the circuits. If the middle circuit breaker fails then the breakers adjacent to the buses are tripped so interrupting both the circuits. But if a breaker adjacent to the bus fails then the tripping of middle breaker does not interrupt power supply to circuit associated with healthy breaker. Only the circuit associated with failed breaker is interrupted.

This configuration is very flexible and highly reliable. The relaying of the scheme is complicated as the middle breaker is associated with both the circuits. This scheme is economical in comparison to Double Bus Double Breaker scheme. This scheme also require more space in comparison to other schemes to accommodate more equipments.

In one substation you can find two or more schemes implemented as per the requirement. In most of the modern substations it is usual to add one transfer bus in most of the schemes above. Which enhances the availability and maintainability of the system and operational flexibility

BEYOND THE SYLLABUS: SUBSTATION DESIGN

SUBSTATION DESIGN:
The main considerations taking into account during the design process are:
1. Reliability
2. Cost (sufficient reliability without excessive cost)
3. Expansion of the station, if required.
 Selection of the location of a substation must consider many factors:
 1. Sufficient land area
 2. Necessary clearances for electrical safety
3. Access to maintain large apparatus such as transformers.
4. The site must have room for expansion due to load growth or planned transmission additions.
 5. Environmental effects( drainage, noise and road traffic effects.
6. Grounding must be taking into account to protect passers-by during a shortcircuit in the transmission system
 7. The substation site must be reasonably central to the distribution area to be served.

LAYOUT DESIGN
The first step in planning a substation layout is the preparation of a one-line diagram which shows in simplified form the switching and protection arrangement required, as well as the incoming supply lines and outgoing feeders or transmission lines.
One-line diagram should include principal elements: Lines ,Switches ,Circuit breakers and Transformers
Incoming lines should have a disconnect switch and a circuit breaker.
A disconnect switch is used to provide isolation, since it cannot interrupt load current.
A circuit breaker is used as a protection device to interrupt fault currents automatically
Both switches and circuit breakers may be operated locally or remotely from a supervisory control center.

Following the switching components, the lines are connected to one or more buses.
An electrical bus, derived from bus bar, is a common electrical connection between multiple electrical devices.
The arrangement of switches, circuit breakers and buses used affects the cost and reliability of the substation. For important substations a ring bus or double bus.
Substations feeding only a single industrial load may have minimal switching provisions.
Once having established buses for the various voltage levels, transformers may be connected between the voltage levels. These will again have a circuit breaker in case a transformer has a fault.
A substation always has control circuitry to operate the various breakers to open in case of the failure of some component.
SWITCHING FUNCTIONS
Switching is the operation of connecting and disconnecting of transmission lines or other components to and from the system.
Switching events may be "planned" or "unplanned".
A transmission line or other component may need to be deenergized for maintenance or for new construction.
 To maintain reliability of supply, it is not cost efficient to shut down the entire power system for maintenance.
All work to be performed, from routine testing to adding entirely new substations, must be done while keeping the whole system running.
Also, a fault may develop in a transmission line or any other component. The function of the substation is to isolate the faulted portion of the system in the shortest possible time.
LOAD
The size of the load to be served determines the capacity of the substation.
The load must be distributed such that it can be served with reasonable feeder loss or more.
Critical loads (industrial districts) are served by more complex substations, designed for maximum reliability and speed of power restoration compare to the ones used in residential areas where a short time power loss is usually not a disaster.
Other substations in the area influence the design of a new substation.
The presence of the other substations will increase the overall power capacity and as a result can satisfy the demand for heavy loads.
Substations for critical loads usually use more than one transformer so that the load is served even if one transformer is out.
Otherwise a single large three-phase transformer is used because it costs less per kVA of capacity, and requires less room, bussing, and simpler protective relaying. 

23. Types of Substation

SUBSTATION
The assembly of apparatus used to change some characteristics ( i.e voltage, a.c to d.c, frequency, power factor, etc., ) of electric supply is called a sub station .

Factors Considered:

•          Located at proper site

•          Provide safe and reliable arrangement

•          Easily operated and maintained

•          Minimum capital cost

TYPICAL SUBSTATION:

Types of Substation

 •          Step-up Transmission Substation

•          Step-down Transmission Substation

•          Distribution Substation

•          Underground Distribution Substation

   Step-up Transmission Substation

•          A step-up transmission substation receives electric power from a nearby generating facility and uses a large power transformer to increase the voltage for transmission to distant locations.

•           A transmission bus is used to distribute electric power to one or more transmission lines. There can also be a tap on the incoming power feed from the generation plant to provide electric power to operate equipment in the generation plant.

•          A substation can have circuit breakers that are used to switch generation and transmission circuits in and out of service as needed or for emergencies requiring shut-down of power to a circuit or redirection of power.
The specific voltages leaving a step-up transmission substation are determined by the customer needs of the utility supplying power and to the requirements of any connections to regional grids.

•          Typical voltages are:
 High voltage (HV) ac:69 kV, 115 kV, 138 kV, 161 kV, 230 kVExtra-high voltage (EHV) ac:345 kV, 500 kV, 765 kVUltra-high voltage (UHV) ac:1100 kV, 1500 kV ,Direct-current high voltage (dc HV): ±250 kV, ±400 kV, ±500 kV

STEP DOWN TRANSMISSION SUBSTATION:

•          Step-down Transmission Substation are located at switching points in an electrical grid.

•          They connect different parts of a grid and are a source for subtransmission lines or distribution lines.

•          The step-down substation can change the transmission voltage to a subtransmission voltage, usually 69 kV.

•          The subtransmission voltage lines can then serve as a source to distribution substations.

•          Sometimes, power is tapped from the subtransmission line for use in an industrial facility along the way. Otherwise, the power goes to a distribution substation

DISTRIBUTION SUBSTATION

A distribution substation transfers power from the transmission system to the distribution system of an area.

The input for a distribution substation is typically at least two transmission or subtransmission lines.

Distribution voltages are typically medium voltage, between 2.4 and 33 kV depending on the size of the area served and the practices of the local utility.

 Besides changing the voltage, the job of the distribution substation is to isolate faults in either the transmission or distribution systems.

Distribution substations may also be the points of voltage regulation, although on long distribution circuits (several km/miles), voltage regulation equipment may also be installed along the line. Complicated distribution substations can be found in the downtown areas of large cities, with high-voltage switching, and switching and backup systems on the low-voltage side.

COLLECTOR SUBSTATION

In distributed generation projects such as a wind farm, a collector substation may be required, which is similar to a distribution substation although power flows in the opposite direction, from many wind turbines up into the transmission grid.

For economy of construction the collector system operates around 35 kV, and the collector substation steps up voltage to a transmission voltage for the grid.

The collector substation can also provide power factor correction if it is needed, metering and control of the wind farm.

Collector substations also exist where multiple thermal or hydroelectric power plants of comparable output power are in proximity

SWITCHING SUBSTATION

 A switching substation is a substation which does not contain transformers and operates only at a single voltage level. Switching substations are sometimes used as collector and distribution stations. Sometimes they are used for switching the current to back-up lines or for paralellizing circuits in case of failure.

UNDERGROUND DISTRIBUTION SUBSTATION

•          Underground Distribution Substation are also located near to the end-users. Distribution substation transformers change the sub transmission voltage to lower levels for use by end-users. Typical distribution voltages vary from 34,500Y/19,920 volts to 4,160Y/2400 volts.

 An underground system may consist of these parts: 

•          Conduits

•          Duct Runs

•          Manholes

•          High-Voltage Underground Cables

•          Transformer Vault

•          Riser

•          Transformers

From here the power is distributed to industrial, commercial, and residential customers.

SUBSTATION FUNCTIONS

•          Change voltage from one level to another

•          Regulate voltage to compensate for system voltage changes

•          Switch transmission and distribution circuits into and out of the grid system

•          Measure electric power qualities flowing in the circuits

•          Connect communication signals to the circuits

•          Eliminate lightning and other electrical surges from the system

•          Connect electric generation plants to the system 

•          Make interconnections between the electric systems of more than one utility

•          Control reactive kilovolt-amperes supplied to and the flow of reactive kilovolt-amperes in the circuits