FlamingIdea: April 2016

Electrical Power Transmission System and Network

Electrical Power Transmission System

Electrical power is generated at different generating stations. These generating stations are not necessarily situated at the load center. During construction of generating station number of factors are considered from economical point of view. These all factors may not be easily available at load center, hence generating stations are not normally situated very nearer to load center. Load center is the place where maximum power is consumed. Hence there must be some means by which the generated power must be transmitted to the load center. Electrical transmission system is the means of transmitting power from generating station to different load centers.

Factor to be considered for constructing a Generating Station.

During planning of construction of generating station the following factors to be considered for economical generation of electrical power.
1) Easy availability of water for thermal power generating station.
2) Easy availability of land for construction of power station including its staff township.
3) For hydro power station there must be a dam on river. So proper place on the river must be chosen in such a way that the construction of the dam can be done in most optimum way.
4) For thermal power station easy availability of fuel is one of the most important factors to be considered.
5) Better communication for goods as well as employees of the power station also to be kept into consideration.

power plant

6) For transporting very big spare parts of turbines, alternators etc., there must be wide road ways, rain communication, and deep and wide-river must pass away nearby the power station.
7) For nuclear power plant, it must be situated in such a distance from common location so that there may be any effect from nuclear reaction the heath of common people.
Many other factors also to be considered, but there are beyond the scope of our discussion. All the factors listed above are very difficult to be available at load center. The power station or generating station must be situated where all the facilities are easily available. This place may not be necessarily at the load center. The power generated at generating station then transmitted to the load center by means of electrical power transmission system as we said earlier. The power generated at generating station is in low voltage level as low voltage power generation has some economical values. Low voltage power generation is more economical than high voltage power generation. At low voltage level, bot weight and wide of insulation is less in the alternator, this directly reduces the cost and size of alternator. But this low voltage level power cannot be transmitted directly to the consumer end as because this low voltage power transmission is not at all economical. Hence although low voltage power generation is economical but low voltage electrical power transmission is not economical. Electrical power is directly proportional to the product of electrical current and voltage of system. So for transmitting certain electrical power from one place to another, if the voltage of the power is increased then associated current of this power is reduced. Reduced current means less I²R loss in the system, less cross sectional area of the conductor means less capital involvement and decreased current causes improvement in voltage regulation of power transmission system and improved voltage regulation indicates quality power. Because of these three reasons electrical power mainly transmitted at high voltage level. Again at distribution end for efficient distribution of the transmitted power, it is stepped down to its desired low voltage level. So it can be concluded that first the electrical power is generated at low voltage level then it stepped up to high voltage for efficient transmission of electrical energy. Lastly for distribution of electrical energy or power to different consumers it is stepped down to desired low voltage level. This brief discussion of electrical transmission system and network, but now we will discussed little bit more details about transmission of electrical energy.

Transmission of Electrical Energy

Fundamentally there are two systems by which electrical energy can be transmitted.

(1) High voltage DC electrical transmission system.

(2) High voltage AC electrical transmission system. There are some advantages in using DC transmission system-

i) Only two conductor are required for DC transmission system. It is further possible to use only one conductor of DC transmission system if earth is utilized as return path of the system.

ii) The potential stress on the insulator of DC transmission system is about 70% of same voltage AC transmission system. Hence less insulation cost is involved in DC transmission system.

iii) Inductance, capacitance, phase displacement and surge problems can be eliminated in DC system.

Even having these advantages in DC system, generally electrical energy is transmitted by three (3) phase AC transmission system.

i) The alternating voltages can easily be stepped up & down, which is not possible in DC transmission system.

ii) Maintenance of AC substation is quite easy and economical compared to DC system.

iii) The transforming in AC electrical substation is much easier than motor-generator sets in DC system.

But AC transmission system also have some disadvantages like,

i) The volume of conductor used in AC system is much higher than that of DC.

ii) The reactance of the line, affects the voltage regulation of electrical power transmission system.

iii) Problems of skin effects and proximity effects only found in AC system.

iv) AC transmission system is more likely to be affected by corona effect than DC system.

v) Construction of AC electrical power transmission network is more completed than DC system.

vi) Proper synchronizing is required before inter connecting two or more transmission lines together, synchronizing can totally be omitted in DC transmission system.

Short Transmission Line

The transmission lines which have length less than 80 km are generally referred as short transmission lines. For short length, the shunt capacitance of this type of line is neglected and other parameters like electrical resistance and inductor of these short lines are lumped, hence the equivalent circuit is represented as given below,

Let’s draw the vector diagram for this equivalent circuit, taking receiving end current I_r as reference. The sending end and receiving end voltages make angle with that reference receiving end current, of φ_s and φ_r, respectively.

short transmission lines

As the shunt capacitance of the line is neglected, hence sending end current and receiving end current is same, i.e. I_s = I_r. Now if we observe the vector diagram carefully, we will get, V_s is approximately equal to, V_r + I_r.R.cosφ_r + I_r.X.sinφ_r That means, V_s ≅ V_r + I_r.R.cosφ_r + I_r.X.sinφ_r as the it is assumed that φ_s ≅ φ_r As there is no capacitance, during no load condition the current through the line is considered as zero, hence at no load condition, receiving end voltage is the same as sending end voltage. As per dentition of voltage regulation of power transmission line,

As there is no capacitance, during no load condition the current through the line is considered as zero, hence at no load condition, receiving end voltage is the same as sending end voltage. As per dentition of voltage regulation of power transmission line, As there is no capacitance, during no load condition the current through the line is considered as zero, hence at no load condition, receiving end voltage is the same as sending end voltage. As per dentition of voltage regulation of power transmission line,As there is no capacitance, during no load condition the current through the line is considered as zero, hence at no load condition, receiving end voltage is the same as sending end voltage. As per dentition of voltage regulation of power transmission line,

Here, v_r and v_x are the per unit resistance and reactance of the short transmission line.

Any electrical network generally has two input terminals and two output terminals. If we consider any complex electrical network in a black box, it will have two input terminals and output terminals. This network is called two - port network. Two port model of a network simplifies the network solving technique. Mathematically a two port network can be solved by 2 by 2 matrix. A transmission as it is also an electrical network, line can be represented as two port network. Hence two port network of transmission line can be represented as 2 by 2 matrixes. Here the concept of ABCD parameters comes. Voltage and currents of the network can represented as,

Where A, B, C and D are different constant of the network. If we put I_r = 0 at equation (1), we get,

Hence, A is the voltage impressed at the sending end per volt at the receiving end when receiving end is open. It is dimension less. If we put V_r = 0 at equation (1), we get

That indicates it is impedance of the transmission line when the receiving terminals are short circuited. This parameter is referred as transfer impedance.

C is the current in amperes into the sending end per volt on open circuited receiving end. It has the dimension of admittance.

D is the current in amperes into the sending end per amp on short circuited receiving end. It is dimensionless. Now from equivalent circuit, it is found that, V_s = V_r + I_rZ and I_s = I_r
Comparing these equations with equation 1 and 2 we get, A = 1, B = Z, C = 0 and D = 1. As we know that the constant A, B, C and D are related for passive network as,

AD − BC = 1.

Here, A = 1, B = Z, C = 0 and D = 1

⇒ 1.1 − Z.0 = 1

So the values calculated are correct for short transmission line. From above equation (1),

When I_r = 0 that means receiving end terminals is open circuited and then from the equation 1, we get receiving end voltage at no load.

and as per definition of voltage regulation of power transmission line,

Efficiency of Short Transmission Line

The efficiency of short line as simple as efficiency equation of any other electrical equipment, that means

R is per phase electrical resistance of the transmission line.

Medium Transmission Line

The transmission line having its effective length more than 80 km but less than 250 km, is generally referred to as a medium transmission line. Due to the line length being considerably high, admittance Y of the network does play a role in calculating the effective circuit parameters, unlike in the case of short transmission lines. For this reason the modelling of a medium length transmission line is done using lumped shunt admittance along with the lumped impedance in series to the circuit.

These lumped parameters of a medium length transmission line can be represented using two different models, namely- 1).Nominal Π representation. 2).Nominal T representation. Let’s now go into the detailed discussion of these above mentioned models.

Nominal Π Representation of a Medium Transmission Line

In case of a nominal Π representation, the lumped series impedance is placed at the middle of the circuit where as the shunt admittances are at the ends. As we can see from the diagram of the Π network below, the total lumped shunt admittance is divided into 2 equal halves, and each half with value Y ⁄ 2 is placed at both the sending and the receiving end while the entire circuit impedance is between the two. The shape of the circuit so formed resembles that of a symbol Π, and for this reason it is known as the nominal Π representation of a medium transmission line. It is mainly used for determining the general circuit parameters and performing load flow analysis.

As we can see here, V_S and V_R is the supply and receiving end voltages respectively, and I_s is the current flowing through the supply end. I_R is the current flowing through the receiving end of the circuit. I₁ and I₃ are the values of currents flowing through the admittances. And I₂ is the current through the impedance Z. Now applying KCL, at node P, we get.

Similarly applying KCL, to node Q.

Now substituting equation (2) to equation (1)

Now by applying KVL to the circuit,

Comparing equation (4) and (5) with the standard ABCD parameter equations

We derive the parameters of a medium transmission line as:

Nominal T Representation of a Medium Transmission Line

In the nominal T model of a medium transmission line the lumped shunt admittance is placed in the middle, while the net series impedance is divided into two equal halves and and placed on either side of the shunt admittance. The circuit so formed resembles the symbol of a capital T, and hence is known as the nominal T network of a medium length transmission line and is shown in the diagram below.

Here also V_s and V_r is the supply and receiving end voltages respectively, and I_s is the current flowing through the supply end. I_r is the current flowing through the receiving end of the circuit.

Let M be a node at the midpoint of the circuit, and the drop at M, be given by V_m. Applying KVL to the above network we get,

Now the sending end current is,

Substituting the value of V_M to equation (9) we get,

Again comparing equation (8) and (10) with the standard ABCD parameter equations,

The parameters of the T network of a medium transmission line are

Long Transmission Line

A power transmission line with its effective length of around 250 Kms or above is referred to as a long transmission line. Calculations related to circuit parameters (ABCD parameters) of such a power transmission is not that simple, as was the case for a short transmission line or medium transmission line.

The reason being that, the effective circuit length in this case is much higher than what it was for the former models (long and medium line) and, thus ruling out the approximations considered there like.

a) Ignoring the shunt admittance of the network, like in a small transmission line model.

b) Considering the circuit impedance and admittance to be lumped and concentrated at a point as was the case for the medium line model. Rather, for all practical reasons we should consider the circuit impedance and admittance to be distributed over the entire circuit length as shown in the figure below. The calculations of circuit parameters for this reason is going to be slightly more rigorous as we will see here. For accurate modelling to determine circuit parameters let us consider the circuit of the long transmission line as shown in the diagram below.

Here a line of length l > 250km is supplied with a sending end voltage and current of V_S and I_S respectively, where as the V_R and I_R are the values of voltage and current obtained from the receiving end. Let’s us now consider an element of infinitely small length Δx at a distance x from the receiving end as shown in the figure where,

V = value of voltage just before entering the element Δx. I = value of current just before entering the element Δx. V+ΔV = voltage leaving the element Δx. I+ΔI = current leaving the element Δx. ΔV = voltage drop across element Δx. zΔx = series impedence of element Δx yΔx = shunt admittance of element Δx Where Z = z l and Y = y l are the values of total impedance and admittance of the long transmission line. Therefore, the voltage drop across the infinitely small element Δx is given by,

Now to determine the current ΔI, we apply KCL to node A. ΔI = (V+ΔV)yΔx = V yΔx + ΔV yΔx Since the term ΔV yΔx is the product of 2 infinitely small values, we can ignore it for the sake of easier calculation. Therefore, we can write dI ⁄ dx = V y ----------------- (2)

Now by derivation both sides of eq (1) w.r.t x, d² V ⁄ d x² = z dI ⁄ dx

Now substituting dI ⁄ dx = V y from equation (2) d² V ⁄ d x² = zyV or d² V ⁄ d x² − zyV = 0 ------------ (3)

The solution of the above second order differential equation is given by. V = A₁ e^x√yz + A₂ e^−x√yz -------------- (4)

Derivation equation (4) w.r.to x. dV/dx = √(yz) A₁ e^x√yz − √(yz)A₂ e^−x√yz ------------(5)

Now comparing equation (1) with equation (5)

Now to go further let us define the characteristic impedance Z_c and propagation constant δ of a long transmission line as

Z_c = √(z/y) Ω

δ = √(yz)

Then the voltage and current equation can be expressed in terms of characteristic impedance and propagation constant as

V = A₁ e^δx + A₂ e^−δx ----------- (7)

I = A₁/ Z_c e^δx + A₂ / Z_c e^−δx --------------- (8)

Now at x=0, V= V_R and I= I_r. Substituting these conditions to equation (7) and (8) respectively.

V_R = A₁ + A₂ --------------- (9)

I_R = A₁/ Z_c + A₂ / Z_c --------------- (10)

Solving equation (9) and (10), we get values of A₁ and A₂ as,

A₁ = (V_R + Z_CI_R) ⁄ 2

And A₁ = (V_R − Z_CI_R) ⁄ 2

Now applying another extreme condition at x=l, we have V = V_S and I = I_S.

Now to determine V_S and I_S we substitute x by l and put the values of A₁ and A₂ in equation (7) and (8) we get

V_S = (V_R + Z_C I_R)e^δl ⁄ 2 + (V_R − Z_C I_R)e^−δl/2 --------------(11)

I_S = (^V_R ⁄ _ZC + I_R)e^δl/2 − (^V_R /_ZC − I_R)e^−δl/2--------------- (12)

By trigonometric and exponential operators we know

sinh δl = (e^δl − e^−δl) ⁄ 2

And cosh δl = (e^δl + e^−δl) ⁄ 2

Therefore, equation(11) and (12) can be re-written as

V_S = V_Rcosh δl + Z_C I_R sinh δl

I_S = (V_R sinh δl)/Z_C + I_Rcosh δl

Thus comparing with the general circuit parameters equation, we get the ABCD parameters of a long transmission line as,

A = cosh δl

B = Z_C sinh δl

C = sinh δl ⁄ Z_C

D = cosh δl

ABCD Parameters of Transmission Line

A major section of power system engineering deals in the transmission of electrical power from one particular place (e.g. generating station) to another like substations or distribution units with maximum efficiency. So it’s of substantial importance for power system engineers to be thorough with its mathematical modelling. Thus the entire transmission system can be simplified to a two port network for the sake of easier calculations.

The circuit of a 2 port network is shown in the diagram below. As the name suggests, a 2 port network consists of an input port PQ and an output port RS. Each port has 2 terminals to connect itself to the external circuit. Thus it is essentially a 2 port or a 4 terminal circuit, having,

Given to the input port P Q.

Given to the output port R S. As shown in the diagram below. Now the ABCD parameters or the transmission line parameters provide the link between the supply and receiving end voltages and currents, considering the circuit elements to be linear in nature. Thus the relation between the sending and receiving end specifications are given using ABCD parameters by the equations below.

Now in order to determine the ABCD parameters of transmission line let us impose the required circuit conditions in different cases.

ABCD Parameters, When Receiving End is Open Circuited

The receiving end is open circuited meaning receiving end current I_R = 0. Applying this condition to equation (1) we get,

Thus it implies that on applying open circuit condition to ABCD parameters, we get parameter A as the ratio of sending end voltage to the open circuit receiving end voltage. Since dimension wise A is a ratio of voltage to voltage, A is a dimension less parameter. Applying the same open circuit condition i.e I_R = 0 to equation (2)

Thus its implies that on applying open circuit condition to ABCD parameters of transmission line, we get parameter C as the ratio of sending end current to the open circuit receiving end voltage. Since dimension wise C is a ratio of current to voltage, its unit is mho. Thus C is the open circuit conductance and is given by C = I_S ⁄ V_R mho.

ABCD Parameters, When Receiving End is Short Circuited

Receiving end is short circuited meaning receiving end voltage V_R = 0 Applying this condition to equation (1) we get,

Thus its implies that on applying short circuit condition to ABCD parameters, we get parameter B as the ratio of sending end voltage to the short circuit receiving end current. Since dimension wise B is a ratio of voltage to current, its unit is Ω. Thus B is the short circuit resistance and is given by B = V_S ⁄ I_R Ω. Applying the same short circuit condition i.e V_R = 0 to equation (2) we get

Thus its implies that on applying short circuit condition to ABCD parameters, we get parameter D as the ratio of sending end current to the short circuit receiving end current. Since dimension wise D is a ratio of current to current, it’s a dimension less parameter.

∴ The ABCD parameters of transmission line can be tabulated as:-

Parameter	Specification	Unit
A = V_S / V_R	Voltage ratio	Unit less
B = V_S / I_R	Short circuit resistance	Ω
C = I_S / V_R	Open circuit conductance	mho
D = I_S / I_R	Current ratio	Unit less

Performance of Transmission Line

The transmission lines are categorized as three types-

1) Short transmission line– the line length is up to 80 km.

2) Medium transmission line– the line length is between 80km to 160 km.

3) Long transmission line – the line length is more than 160 km.

Whatever may be the category of transmission line, the main aim is to transmit power from one end to another. Like other electrical system, the transmission network also will have some power loss and voltage drop during transmitting power from sending end to receiving end. Hence, performance of transmission line can be determined by its efficiency and voltage regulation.

Voltage regulation of transmission line is measure of change of receiving end voltage from no-load to full load condition.

Every transmission line will have three basic electrical parameters. The conductors of the line will have electrical resistance, inductance, and capacitance. As the transmission line is a set of conductors being run from one place to another supported by transmission towers, the parameters are distributed uniformly along the line. The electrical power is transmitted over a transmission line with a speed of light that is 3X10⁸ m ⁄ sec. Frequency of the power is 50 Hz. The wave length of the voltage and current of the power can be determined by the equation given below, f.λ = v where f is power frequency, λ is wave length and υ is the speed of light.

Hence the wave length of the transmitting power is quite long compared to the generally used line length of transmission line.

For this reason, the transmission line, with length less than 160 km, the parameters are assumed to be lumped and not distributed. Such lines are known as electrically short transmission line. This electrically short transmission lines are again categorized as short transmission line (length up to 80 km) and medium transmission line (length between 80 and 160 km). The capacitive parameter of short transmission line is ignored whereas in case of medium length line the capacitance is assumed to be lumped at the middle of the line or half of the capacitance may be considered to be lumped at each ends of the transmission line. Lines with length more than 160 km, the parameters are considered to be distributed over the line. This is called long transmission line.

Voltage in Power Electric Lines

In generating station electrical power is generated at medium voltage level that ranges from 11 kV to 25 kV. This generated power is sent to the generating step up transformer to make the voltage level higher. From this point to the user end voltage level varies in different levels. We can realize this voltage level variation step by step.

At 11 kV or more than that up to 25 kV voltage level is maintained at alternator stator terminals to generate electrical power in the generating station.
This generated power is fed to the generating step up transformer to make this medium voltage level to higher level, i.e. up to 33 kV.
Power at 33 kV is sent to the generating substation. There the transformer increases the voltage level to 66 kV or 132 kV.
From this generating substation power is sent to the nearer substation to increase the voltage level higher than previous. This level of voltage is increased at different suitable levels, it may be at 400 kV or 765 kV or 1000 kV. This high voltage or extra high voltage level is maintained to transmit the power to a long distant substation. It is call primary transmission of power.
At the end point of primary transmission of power, in the substation, the step down transformers are used to step down the voltage level to 132 kV. Secondary transmission of power starts from this substation.
Power transformer at the end of the secondary transmission, just makes 132 kV voltage level step down to 33 kv or 11 kV as per requirement. From this point, primary distribution of power starts to distribute power to different distribution stations.
At the end of primary distribution, the distribution stations receive this power and step down this voltage level of 11 kV or 33 kV to 415 V (Line Voltage). From these distribution stations to consumer ends, 415 V is kept to sustain for utilization purpose.

Type of Power Lines

From the very beginning of power generation to the user end transmission lines are broadly classified based on different voltage levels.

Why High Voltage is used for Long Transmission Line?

Generally long distant transmission lines are designed to operate at high voltage, extra high or ultra high voltage level. It is because of line power loss reduction purpose. Practically long distant transmission line resistance is comparatively more than medium and short transmission line. Due to this higher valued transmission line resistance considerable amount of power is lost. So we need to decrease the amount of current through each conductor by making the operating voltage very high for same amount of power transmission. We know that the power in AC system to transmit is,

Total power loss P_Loss = 3I_L²R considering three phases altogether. R is the resistance in ohm per phase of the transmission line. Now, rearranging Equation (1) we get,

So,

Again in DC system, there is no phase difference between voltage and current, i.e. cosƟ = 1, and only two conductors (positive and negative) are used. So, in DC system transmitted power P = VI, and power loss,

From equation (2) and (3), it is clear that power loss in transmission line is inversely proportional to the square of line voltage. The higher value of line voltage the lesser amount of power loss occurs. Hence transmission line conductor is used with less diameter, hence savings of conductor material.

Why HVAC is used for Long Transmission Line?

Now a day’s electrical energy is generated, transmitted and distributed in AC form. Especially for long distant transmission line High Voltage AC is transmitted for several reasons, they are:

AC voltage can be stepped up or down as per requirement easily by transformer.
Maintenance of AC substation is easy and cheaper.
Throughout electrical power system AC voltage is handled. So no extra hazard of rectification or inversion like DC voltage transmission.

Why HVDC is used for Long Transmission Line?

High Voltage DC is used at extra or ultra-high voltage level. HVDC transmission is used at fixed level of voltage in primary transmission only as it cannot be stepped up or down by transformer. Only in long distant transmission line it is used only, because

Only two conductors (positive and negative) are required.
Absence of inductance, capacitance and phase displacement power loss is very less. Hence better voltage regulation.
Surge problem never occurs.
No skin effect.
Less insulation requires due to less potential stress.
Less corona effect, thus less power loss.
Highly stabilized and synchronized.

Why Low and Medium Voltage is Used in Distribution Line?

In primary distribution, power is handled at 11 kV or 33 kV. As voltage level gets stepped down from 132 kV to 11 kV or 33 kV, current level gets higher valued. But this high valued current distributed among various local distribution stations (distribution transformers) nearby. These distribution transformers again steps down the voltage to 415 V. It is because; Power at 415 V is used at the user end. Distance between these distribution transformers and the primary distribution stations is very short, hence conductor resistance is not large. Very small amount of power is lost in this section.

Disadvantages of AC or HVAC Transmission

The main disadvantages of AC transmission are

AC lines require more conductor material than DC.
AC transmission line construction is more complicated than DC.
Effective resistance is increased due to skin effect, hence power loss.
Continuous power loss due to charging current because of line capacitance.

Disadvantages of DC or HVDC Transmission

The main disadvantages of DC transmission are

Electric power is not generated in HVDC form due to commutation problem. Only HVDC is achieved for transmission from HVAC by rectification. So special arrangement is required for this conversion.
DC voltage cannot be stepped up or down for transmission.
DC switches and circuit breakers are expensive and with certain limitations.

High Voltage Transmission Lines

Distribution in simple words means to make available a number of product or services to end customers. Same is the case when we are talking about electrical distribution system. Means making available that 415v or 240v to a number of end consumers through a distribution system. The generation normally takes place around 11 Kv to 25 Kv which is generally termed as medium voltage. Since we all aware of the fact that this is not the proper voltage for transmission. So this voltage is the stepped up to a level of 220 kv or 400 kv or 132 kv depending on the power transmitted or we can say that depends upon the distance. This power is carried away through a transmission network of high voltage lines. These transmission lines are of hundreds of kilometres. These lines are then terminated to some substations which step down the desired voltage to either 11kv or 33 kv or 66 kv. This can be termed as sub transmission network.

Now if we are particularly taking about distribution network then everything below 33kv i.e 11 kv feeders emanates from 33 kv is branched into several 11 kv feeders. The main motto of these 11 kv feeders is to carry power close to the nearby localities which include industrial area, villages etc. here the transformer further reduce the 11 kv to 415v or 240v and it provides the voltage through 415v feeders which in turn gives 415v or 240 v. now 415v is a three phase supply so this is given to the places where we have to give three phase supply. Similarly you all are aware of 220 v supply, it’s a single phase and is used in homes. Example of Simple distribution system Let it there are 4 generating unit generating a total of 20kv this is step up to 400kv and transmitted to the distribution network as explained above The distributing substation receive it as either 66/33/11Kv there may be chance that there are separate 66kv feeders but at the end. Those 11 kv or 33 kv are directly given to DISCOMS. So in short if i am saying distribution system then it starts from 33or 11 kv downwards this is step down to 430/250 v for the customers by considering the fact that there is voltage drop in transmission lines
A simple example demonstrates this Input HT lines 11kv from X grid 11 kv from Y grid transformer rated primary voltage 11kv secondary voltage 416/240 v For domestic users a phase and a neutral connection is supplied and for heavy load 3 wire connection is supplied For the distribution to the consumer end, we can use either overhead line or underground line. Underground one are good in appearance and safe but they are costly one. A typical length of 11 kv feeder on city os around 3 km. where as in rural areas this length is up to 15-18 kms. A 415 feeder normally is of 0.5m to 1 km max Ring Main Unit - RMU It is mainly used by distributors when more than one feeder is supplying input and in case of failure from any feeder, powers can be fed uninterruptedly from other feeders at same point. Now a days it is of SF₆ type. It is used for two inputs or one outgoing to the load or one input or two outgoing to the load.

Electricity supply to consumers

The secondary winding of the transformer is mostly of wye connection type. This supply system with a neutral wire is termed as 4 wire 3 phase supply.4 wire supplies are normally used to distribute domestic supplies since they can provide an earthed neutral. The three phase wires together give a 3-phase 3-wire supply (240x1.73=415Volts) suitable or heavy machinery such as 3-phase motors.

Issues in distribution Power system

Lack of priority is given to 33kv substations related to load and maintenance also the health status of 11KV/415V. Absence of monitoring, overloading, result in the improper voltage distribution which also leads to the breakdown of equipment at consumer end. We are currently using circuit breakers for load management moreover we don't have switches in distribution network, in order to isolate certain loads for load shedding purpose. We know have CB(circuit breakers) for 11kv feeders. So when desired it will leads to the isolation of that particular network.

Thursday, 14 April 2016

EQUIVALENT CIRCUIT, ROTOR SLIP and INDUCED TORQUE OF AN INDUCTION MOTOR

THE EQUIVALENT CIRCUIT OF AN INDUCTION MOTOR

The Transformer Model of an Induction Motor

The Rotor Circuit Model.

The Final Equivalent Circuit.

THE CONCEPT OF ROTOR SLIP IN AN INDUCTION MOTOR

THE DEVELOPMENT OF INDUCED TORQUE IN AN INDUCTION MOTOR.

Sunday, 10 April 2016