Download Electrical Notes and Articles PDF

TitleElectrical Notes and Articles
TagsElectric Power Distribution Transformer Electric Power Transmission Capacitor Electrical Resistance And Conductance
File Size16.1 MB
Total Pages458
Table of Contents
                            1.pdf
2.pdf
3.pdf
4.pdf
5.pdf
6.pdf
7.pdf
8.pdf
                        
Document Text Contents
Page 1

Total Losses in Power Distribution and Transmission Lines-Part 2

JULY 2, 2013 2 COMMENTS

3 Votes

Non-technical losses are at and related to meter reading, defective meter and error in meter reading, billing of

customer energy consumption, lack of administration, financial constraints, and estimating unmetered supply of energy

as well as energy thefts.

Theft of power is energy delivered to customers that is not measured by the energy meter for the customer. Customer

tempers the meter by mechanical jerks, placement of powerful magnets or disturbing the disc rotation with foreign

matters, stopping the meters by remote control.

Losses due to metering inaccuracies are defined as the difference between the amount of energy actually delivered

through the meters and the amount registered by the meters.

All energy meters have some level of error which requires that standards be established. Measurement Canada,

formerly Industry Canada, is responsible for regulating energy meter accuracy.

Statutory requirements5 are for meters to be within an accuracy range of +2.5% and – 3.5%. Old technology meters

normally started life with negligible errors, but as their mechanisms aged they slowed down resulting

in under-recording. Modern electronic meters do not under-record with age in this way.

Consequently, with the introduction of electronic meters, there should have been a progressive reduction in meter errors.

Increasing the rate of replacement of mechanical meters should accelerate this process

Unmetered losses are situations where the energy usage is estimated instead of measured with an energy meter. This

happens when the loads are very small and energy meter installation is economically impractical. Examples of this are

street lights and cable television amplifiers.

Unmetered supply to agricultural pumps is one of the major reasons for commercial losses. In most states, the

agricultural tariff is based on the unit horsepower (H.P.) of the motors. Such power loads get sanctioned at the low load

declarations.

Once the connections are released, the consumers increasing their connected loads, without obtaining necessary

sanction, for increased loading, from the utility.

Further estimation of the energy consumed in unmetered supply has a great bearing on the estimation of T&D losses on

account of inherent errors in estimation.

Most of the utilities deliberately overestimate the unmetered agricultural consumption to get higher subsidy from the

State Govt. and also project. reduction in losses. In other words higher the estimates of the unmetered consumption,

lesser the T&D loss figure and vice versa.

Moreover the correct estimation of unmetered consumption by the agricultural sector greatly depends upon the cropping

http://electricalnotes.wordpress.com/2013/07/02/total-losses-in-power-distribution-transmission-lines-part-2/
http://electricalnotes.wordpress.com/2013/07/02/total-losses-in-power-distribution-transmission-lines-part-2/#comments

Page 2

pattern, ground water level, seasonal variation, hours of operation etc.

Proper Calibrated Meter should be used to measure Electrical Energy. Defective Energy Meter should be replaced

immediately.

The reason for defective meter are Burning of meters, Burn out Terminal Box of Meter due to heavy load, improper

C.T.ratio and reducing the recording, Improper testing and calibration of meters.

Faulty and untimely serving Bill should be main part of non-Technical Losses.

Normal Complain regarding Billing are Not Receipt of Bill, Late Receipt of Bill, Receiving wrong Bill , Wrong Meter

Reading, Wrong Tariff, wrong Calculations.



Many Distribution pockets of Low Voltage (430V) in Town are surrounded by higher voltage feeders. At this lower voltage,

more conductor current flows for the same power delivered, resulting in higher I2R losses.

Converting old LV (430V) feeders to higher voltage the Investment Cost is high and often not economically justifiable but

If parts of the LV (430V) Primary feeders are in relatively good condition, installing multiple step-down power

transformers at the periphery of the 430 volt area will reduce copper losses by injecting load current at more points (i.e.,

reducing overall conductor current and the distance traveled by the current to serve the load).

Design the distribution network system in such a way that if it is Possible than large consumer gets direct Power Line

from feeder.

In High Voltage direct service (HVDS) ,11KV line direct given to cluster of 2 to 3 Agricultural Customer for Agricultural

Pump set and employed small distribution Transformer (15KVA) for given these 2 to 3 customer through smallest (

almost negligible) LT distribution Lines.

In HVDS there is less distribution losses due to minimum length of Distribution Line, High quality of Power Supply with

no Voltage drop, Less Burn out of motor due to less voltage fluctuation and Good quality of Power, to avoid overloading of

Transformer.

Where LT Line are not totally avoidable use Arial Bundle Conductor to minimize faults in Lines, to avoid direct theft from

Line (Tampering of Line).

Reduce the number of transformation steps.

Transformers are responsible for almost half of network losses.

High efficiency distribution transformers can make a large impact on reduction of Distribution Losses

Page 229

Like this:

FILED UNDER UNCATEGORIZED

Type of Electrical Power Distribution systems

SEPTEMBER 5, 2011 2 COMMENTS

5 Votes

:

Electrical power is distribution either three wires or Four wires (3 wire for phases and 1 wire for Neutral). Voltage between Phase to Phase Called Line Voltage and

Voltage between Phase and Neutral is Called Phase Voltage.

This Forth wire may or may not be distributed in Distribution System and Same way this neutral may or may not be earthed

Depending of this neutral condition (Earthed-not Earthed-access-not access) there are various type of earthing System.

The neutral may be directly connected to earth or connected through a resistor or a reactor. This system is called directly earthed or Earthed System.

When a connection has not been made between the neutral point and earth, we say that the neutral is unearthed.

In a network, the earthing system plays a very important role. When an insulation fault occurs or a phase is accidentally earthed, the values taken by the fault currents, the

touch voltages and over voltages are closely linked to the type of neutral earthing connection.

A directly earthed neutral strongly limits over voltages but it causes very high fault currents, here as an unearthed neutral limits fault currents to very low values but

encourages the occurrence of high over voltages.

In any installation, service continuity in the event of an insulation fault is also directly related to the earthing system. An unearthed neutral permits service continuity during

an insulation fault. Contrary to this, a directly earthed neutral, or low impedance-earthed neutral, causes tripping as soon as the first insulation fault occurs.

The choice of earthing system in both low voltage and medium voltage networks depends on the type of installation as well as the type of network. It is also influenced by

the type of loads and service continuity required.

The Main objectives of an earthing system are Provide an alternative path for the fault current to flow so that it will not endanger the user, Ensure that all exposed

conductive parts do not reach a dangerous potential, Maintain the voltage at any part of an electrical system at a known value and prevent over current or excessive voltage

on the appliances or equipment.

Different earthing systems are capable of carrying different amounts of over current. Since the amount of over current produced in different types of installation differs from

each other, required type of earthing will also differ according to the type of installation. so in order to ensure that the installation goes with the existing earthing system or

else to do any modification accordingly, we need to have a proper idea of the present earthing system. It would enhance the safety as well as the reliability

As per IEC 60364-3 There are three types of systems:

IT System.

TT

TN (TN-S, TN-C, TN-C-S).

The first letter defines the neutral point in relation to earth:

1. T = directly earthed neutral (from the French word Terre)

2. I =unearthed or high impedance-earthed neutral (e.g. 2,000 Ω)

The second letter defines the exposed conductive parts of the electrical installation in relation to earth:

1. T =directly earthed exposed conductive parts

2. N =exposed conductive parts directly connected to the neutral conductor



First Letter I= the neutral is unearthed at Transformer or Generator side.

Second Letter T= Frame parts of the loads are interconnected and earthed at Load Side



http://electricalnotes.wordpress.com/category/uncategorized/
http://electricalnotes.wordpress.com/2011/09/05/type-of-earthing-systems-in-electrical-distribution/
http://electricalnotes.wordpress.com/2011/09/05/type-of-earthing-systems-in-electrical-distribution/#comments

Page 230

It is compulsory to install an over voltage limiter between the MV/LV transformer neutral point and earth.

If the neutral is not accessible, the overvoltage limiter is installed between a phase and earth.

It runs off external over voltages, transmitted by the transformer, to the earth and protects the low voltage network from a voltage increase due to flashover between the

transformer’s medium voltage and low voltage windings.

1. System providing the best service continuity during use.

2. When an insulation fault occurs, the short-circuit current is very low.

3. Higher operational safety only a capacitive current flows, which is caused by the system leakage capacitance if an earth fault occurs.

4. Better accident prevention the fault current is limited by the body impedance, earthing resistance and the high impedance of the earth fault loop.

1. Requires presence of maintenance personnel to monitor and locate the first fault during use.

2. Requires a good level of network insulation (High leakage current must be supplied by insulating transformers).

3. Overvoltage limiters must be installed.

4. Requires all the installation’s exposed conductive parts to be Same Voltage level. If this is not possible RCDs must be installed.

5. Locating faults is difficult in widespread networks.

6. When an insulation fault with reference to the earth occurs, the voltage of the two healthy phases in relation to the earth take on the value of the phase-to-phase voltage So

when Select Size of equipments it is need to higher insulation level of the Equipments.

7. The risk of high internal over voltages making it advisable to reinforce the equipment insulation.

8. The compulsory insulation monitoring, with visual and audible indication of the first fault if tripping is not triggered until the second fault occurs.

9. Protection against direct and indirect contact is not guaranteed.

10. 10. Short-circuit and earth fault currents may cause fires and destroy parts of the plant.

First letter T=the neutral is directly earthed.

Second letter T= the exposed conductive parts of the loads are interconnected and earthed.

The transformer neutral is earthed;

The frames of the electrical loads are also connected to an earth connection

1. High earth fault loop impedance

2. Low earth fault current

3. Utility company need not to provide earth for consumer

Page 457

When the bending stresses in a conductor or OHSW due to Aeolian vibration exceed the endurance limit, fatigue

failures will occur.

In a circular cross-section, such as a conductor or OHSW, the bending stress is zero at the center and

increases to the maximum at the top and bottom surfaces (assuming the bending is about the horizontal axis).

This means that the strands in the outer layer will be subjected to the highest level of bending stress and will

logically be the first to fail in fatigue.

When the damper is placed on a vibrating conductor, movement of the weights will produce bending of the steel

strand. The bending of the strand causes the individual wires of the strand to rub together, thus dissipating

energy. The size and shape of the weights and the overall geometry of the damper influence the amount of

energy that will be dissipated for specific vibration frequencies.

Since, as presented earlier, a span of tensioned conductor will vibrate at a number of different resonant

frequencies under the influence of a range of wind velocities, an effective damper design must have the proper

response over the range of frequencies expected for a specific conductor and span parameters.

Some dampers, such as the VORTX Damper utilize two different weights and an asymmetric placement on the

strand to provide the broadest effective frequency range possible.

The “Stockbridge” type vibration damper is commonly used to control vibration of overhead conductors and

OPGW. The vibration damper has a length of steel messenger cable. Two metallic weights are attached to the

ends of the messenger cable. The centre clamp, which is attached to the messenger cable, is used to install

the vibration damper onto the overhead conductor.

Placement programs, such as those developed by PLP for the VORTX Damper, take into account span and

terrain conditions, suspension types, conductor self-damping, and other factors to provide a specific location in

the span where the damper or dampers will be most effective.

The asymmetrical vibration damper is multi resonance system with inherent damping. The vibration energy is

dissipated through inter-strand friction of the messenger cable around the resonance frequencies of the

vibration damper. By increasing the number of resonances of the damper using asymmetrical design and

increasing the damping capacity of the messenger cable the vibration damper is effective in reducing vibration

over a wide frequency or wind velocity range.

For smaller diameter conductors (< 0.75”), overhead shield wires, and optical ground wires (OPGW), a different

type of damper is available that is generally more effective than a Stockbridge type damper.

Page 458

Share this:

Like this:

Share this:

Like this:

Facebook 5 Email Twitter LinkedIn

Facebook 2 Email Twitter LinkedIn

http://electricalnotes.wordpress.com/2011/03/20/vibration-damper-in-transmission-line/?share=facebook&nb=1
http://electricalnotes.wordpress.com/2011/03/20/vibration-damper-in-transmission-line/?share=email&nb=1
http://electricalnotes.wordpress.com/2011/03/20/vibration-damper-in-transmission-line/?share=twitter&nb=1
http://electricalnotes.wordpress.com/2011/03/20/vibration-damper-in-transmission-line/?share=linkedin&nb=1
http://electricalnotes.wordpress.com/2011/03/10/hello-world/?share=facebook&nb=1
http://electricalnotes.wordpress.com/2011/03/10/hello-world/?share=email&nb=1
http://electricalnotes.wordpress.com/2011/03/10/hello-world/?share=twitter&nb=1
http://electricalnotes.wordpress.com/2011/03/10/hello-world/?share=linkedin&nb=1
http://electricalnotes.wordpress.com/category/uncategorized/
http://electricalnotes.wordpress.com/2011/03/10/hello-world/
http://electricalnotes.wordpress.com/2011/03/10/hello-world/#comments
https://wordpress.com/
http://electricalnotes.wordpress.com/category/uncategorized/

Similer Documents