Transposition

Transposition of conductors in Power Transmission Lines

Parameters of Transmission Line:

A transmission line has four parameters, namely resistance, inductance, capacitance and conductance. The resistance ‘R’ of a line is because of conductor resistance, series inductance ‘L’ is due to the magnetic field surrounding the conductors, shunt capacitance ‘C’ is due to the electric field between conductors, and shunt conductance, ‘G’ is because of the leakage current between phases and ground.

What is Transposition of Conductors?

The interchange of conductor positions of a transmission line at regular intervals along the route is known as Transposition of Conductors.

Why transposition is needed?

In the power transmission line when the line conductors are asymmetrically spaced i.e. not equally spaced, the inductance of each phase is different causing voltage drops of different magnitudes in the three phases even if the system is operating under balanced condition (load currents are balanced in the three phases). Also the magnetic field external to the conductors is not zero thereby inducing voltages in adjacent communication lines and causing what is known as “telecommunication interference”. This can be overcome by the interchange of conductor positions at regular intervals along the route and this practice is known as “transposition of conductors”.

How transposition is done?

In a transposed transmission line each of the three conductors occupies all the three positions relative to other conductors (position 1, position 2, and position 3) for one-third of the total length of the transmission line. Transposition also balances out the line capacitance so that electro-statically induced voltages are also balanced. Figure shows the transposition of conductors over a complete cycle.

A complete cycle of transposition of line conductors.

Complications of Conductor Transposition:

Frequent transposition usually leads to complication of support structures (as can be seen by the picture below), increase the cost because of increased number of insulator strings and total weight of supports. 

Transposition on 400 kV, double circuit transmission line, near Bhopal, M.P.  

Digital Meter vs Electromechanical Meter

Some one asked me,
Do the new digital electric meters runs faster than the old electromechanical or revolving type meter?
So let make this very clear and simple 😊,
If by faster you are implying more accurately at low currents than the answer is yes.

For example, most utilities purchase electricity meters for residential applications with a nameplate rating of 240 Volts, 2 to 200 amps, 1 phase , 3 wire, Form 2S.

These nameplate ratings would apply to both the legacy electro-mechanical “induction disc” devices or the newer solid state or digital meters.

As a former supervising technologist at a large utility meter facility, I can share with you that modern digital meters perform much more accurately at low currents than the older electro-mechanical models they have replaced.

Since there is no friction or starting torque to overcome, digital meters will respond very accurately at very low loads.

So some customers may see an increase in their kWh consumption since the old electro-mechanical meters would not respond well to electrical usage where the only devices in operation in the home ( typically in the middle of the night) drew small amounts of current. These load devices may include clock radios, cable TV boxes, cell phone chargers, etc. Digital meters will measure and record these loads accurately.

Also I can personally attest to digital meters being much more accurate in the normal operating range pf test currents applied between 5 amps to 50 amps.

From our extensive laboratory testing of meters owned by our utility and in-service meter evaluations, electro-mechanical meters have typical accuracy tolerances of +/- 0.5 % but digital meters are much more precise, typically at +/- o.2 %.

As electro-mechanical meters age some devices tend to under-respond or “slow down”. Digital meters will be accurate throughout their entire life span.

What “Neutral” Means

What “Neutral” Means

The neutral conductor is the conductor that leads back to the center tap of the utility transformer. It is connected to earth at two locations: the utility transformer and the main panel. That is why it is sometimes referred to as the grounded neutral conductor. Its designation is white or a white tape on a black cable. Neutral current is commonly referred to as return current, because once the current passes through the load, the white insulated neutral conductor makes the complete circuit back to the utility transformer. All electrical current must make a complete loop. The current starts at the utility transformer and must therefore return to the transformer; the neutral is simply the return part of that loop.
The neutral cable or wire can kill you just as readily as a “hot” cable. The same current that flows in a hot conductor flows out the neutral. If you place yourself in series within that loop, even on the neutral side, you will be electrocuted.

How Electricity Flows

How Electricity Flows

Wire works much like a garden hose, but instead of conveying water, it conveys electricity from one location to another. When you turn on a hose faucet, water entering from the spigot pushes on water already in the hose, which pushes water out the other end. Electricity flows in much the same way. An electron flows in one end of the wire, which knocks an electron, which in turn knocks another electron, until an electron eventually comes out the other end. The water analogy can be used to describe the other elements of electricity. To get water to flow, we need water pressure. To get electricity to flow, we need electrical pressure. 

Electrical pressure, or voltage, can be provided
from either an electrical utility or a battery. And just as greater water pressure means more water flow, higher voltages provide greater electrical flow. This flow is called “current.” With both water and electricity, the diameter of the hose or wire limits what you get out of it in a given amount of time. This flow restriction is referred to as “resistance.”

Which bulb glows brighter?

Very important question:

Two bulbs of 40W and 60W are connected in series with an AC power supply of 100V. Which bulb will glow brighter and why?
Ans:
1. When connected in series: In a series connection, current flowing across each element is same. So when 40W bulb and 60W bulb are connected in series, same current will flow through them. To find which bulb will glow brighter we need to find the power dissipation across each of them. From the relation
P=(I*I) R
since current is same we can say that power dissipation will be higher for the bulb with higher resistance i.e. 40W bulb.
Hence 40W bulb will glow brighter in series connection.
2. When connected in parallel: In a parallel connection, voltage across each element is same. So when 40W bulb and 60W bulb are connected in parallel, voltage across them will be same (100 V in the given case). To find which bulb will glow brighter we need to find the power dissipation across each of them. From the relation
P=(V*V)/R
since voltage is same we can say that power dissipation will be higher for the bulb with lower resistance i.e. 60W bulb.
Hence 60W bulb will glow brighter in parallel connection.
NOW HOW TO REMEMBER THIS-
***At our homes, loads (such as bulbs) are connected in parallel and you always see that higher rated bulb glows more brightly i.e 100W bulb glows more brightly than 60W bulb or 40W bulb.
***So always remember if bulbs are connected in parallel, the bulb with higher rated power will glow brighter and if they are connected in series, the bulb with lower rated power will glow brighter.

Limit Switches

Limit switches
Trustworthy detection devices
Limit switches are electro-mechanical devices. The contacts are mechanically linked to an actuator. By combining different types of actuators, casings and contacts, our limit switches are perfectly suited to a large variety of applications whatever the environment.

Main benefits

Reliable operations
Visible operations
Each application gets the right limit switch.
Main features

Plastic or metal casing, IP65 or IP67
Able to switch strong current up to 10 A
Mechanical durability up to 10 millions of operations.

Reclosers

MV outdoor vacuum reclosers
Single and three phase reclosers up to 38 kV, 16 kA and 1250 A for outdoor pole mount or substation installation.
Reclosers are predominantly located on the distribution feeder, though as the continuous and interrupting current ratings increase, they are seen in substations, where traditionally a circuit breaker would be located. Reclosers have two basic functions on the distribution system: reliability and overcurrent protection.



Why RECLOSERS?

Increased reliability - the highest creep distance among the recloser poles on the market ensures long-term performance in any environment
Unparalleled performance - the HCEP (Hydrophobic Cycloaliphatic Epoxy) material of the poles provides the best insulation for outdoor use, shedding water and debris, thus reducing the probability of flashovers even in heavily polluted areas
Simple, fast and safe maintenance as all the electronics are in the low voltage unit, eliminating the need for a bucket truck to isolate potentials to service electronics
Easy integration with multiple controller options, including the PCD, RER615, RER620 and SEL-651R, to accommodate any grid modernization application.