Electrical Load Flow Analysis in Power Network System

Load flow (or power flow) in a power network system is an analysis that calculates how electrical power is distributed and flows through an electrical power system from the generation sources to the loads (or consumers). The main objectives are to determine the voltage levels at each bus (node), and the power flowing through each transmission line, and to ensure the system is operating within its limits and constraints.

What Happen If Cables Placed In Magnetic Metal Conduit

What Happens If Cables Placed In Magnetic Metal Conduits 

Do we know what happens if cables are in a magnetic metal conduit? Yes, at least we know that in any circumstances, the individual phase of an AC (alternating current) circuit is in a separate magnetic metal conduit. 

Bangladesh Power Transmission and Distribution Line Privatization Plan

Bangladesh Power Transmission and Distribution System Planned to Operate through Private Ownership.

National electricity transmission and distribution line going to the private sector As a result, the private sector is also involved with the transmission system after the production of electricity. In the meantime, plans have been made to construct two transmission lines through the private sector.

Besides, the government has set a target of investing more than 4.5 billion taka by 2040 in private power sector. In this case, new investors will be given preference.

Bus-Bar Arrengement Design upto 400kV Capacity Substation

Typical Bus-Bar Arrangement System for High Voltage and Extra High voltage up to 400kV Capacity Substations.

Bus-Bar actually works as a matchmaker between higher voltage level transformers and lower voltage level transformers connecting others equipment to functional a co-relation between them.

The commonly used bus bar schemes for high voltage and extra high voltage at 132kV, 230kV, or 400kV Sub Stations are as below:

1. Single bus bar;
2. Main and Transfer bus bar;
3. Double bus bar;
4. Double main and transfer bus bar; 
5. One and a half-breaker scheme.

You may be interested to read:

01. Copper and Aluminum Bus-bar Size Selection Chart.

02. METAL-CLAD BUS BARS AND CONNECTIONS.

The schematic line diagram for the bus-Bar arrangement for each type of scheme is described below:

Single Bus-Bar Arrangement:

The single bus-bar arrangement is the simplest and easiest switching scheme in which each circuit is provided with one circuit breaker. 

This arrangement can ensure limited security against bus bar faults and no switching flexibility, as a result, go into quite extensive outages of bus-bar and frequent maintenance of bus bar isolators. 

In the single bus-bar scheme, in any bus-bar, isolator, or other equipment that needs maintenance or goes outage due to fault, the entire substation is lost or go in shutdown.

Another disadvantage of this switching scheme is that in case of maintenance of the circuit breaker, the associated feeder has also to be shut down.

Main and Auxiliary Bus-Bar Arrangement:

To overcome the disadvantages of a single bus-bar arrangement, additionally, a bus-coupler circuit is arranged as an Auxiliary bus that can be used during the main bus maintenance period without de-energizing the circuit controlled by that breaker as that circuit then gets energized through bus coupler breaker.

Main and Auxiliary Bus-Bar is technically a single bus bar arrangement with an additional bus bar called Auxiliary Bus energized from the main bus bars through a bus coupler circuit. 

This bus-bar scheme also suffers like a single bus-bar system in the event of a fault on the main bus bar or the associated isolator, the entire substation is lost. 

This type of arrangement is widely used for 132kV substations.

Double Bus-Bar Arrangement:

A Double Bus-Bar arrangement scheme is used to overcome the disadvantages of the single or main and auxiliary bus-bar schemes. The schematic diagram is shown below where each circuit can be connected to either one of these bus bars through the respective bus bar isolator. 

The advantage of the double bus-bar arrangement is such away that the circuits can be switched on from one bus to the other on load. 

This scheme suffers from the disadvantage that when any circuit breaker is taken out for maintenance, the associated feeder has to be shut down.

This bus-bar arrangement is widely used in 220kV or 230 kV substations.

Double Main and Auxiliary Bus-Bar Arrangement:

Using the double main and auxiliary bus-bar scheme, it is possible to overcome the limitation of the double bus-bar scheme.

In Double Main and Auxiliary Bus-Bar Arrangement, the feeder is transferred to the Auxiliary bus during maintenance of its controlling circuit breaker without affecting the other circuits.

This Bus bar arrangement is generally used nowadays in 220 or 230kV substations.

One-and-a-Half Breaker Arrangement:

In one and a half-breaker arrangement scheme three circuit breakers are used for controlling two circuits that are connected between two bus bars.

 Normally both bus bars are in operation if a fault occurs then the associated circuit breaker opens and the fault remove.

Easily any circuit breaker can be taken out in need of any maintenance without causing an interruption.

The main advantage is to load transfer is achieved through the breakers and, therefore, the operation is simple.

The one-and-a-half breaker arrangement is best for those substations which handle large quantities of power and where the orientation of outgoing feeders is in opposite directions.


This scheme has been used in the 400 kV substations.

Hope, you got the idea to select the arrangement for your bus-bar system.

 

What Is the Voltage Classification?

Nominal Voltage Classification in Transmission and Distribution System

To identify the voltage level effortlessly in a transmission and distribution system a significant voltage classification is essential. The voltage class is used not only to identify the level of system voltage, but the main importance is to classify the Apparatus voltage ranges for the operation and maintenance of an electrical energy transmission and distribution system.

CT (CURRENT TRANSFORMERS) IN ELECTRICAL DISTRIBUTION SYSTEM

What is CT or Current Transformer in an Electrical Distribution System

The CT an abbreviation of Current Transformer is a type of instrument transformer that is used to measure the current in AC or Alternating Current systems, taking the reduced amount from its secondary winding which is proportional to the primary winding that is being measured.

What are the Ring Circuit and Radial Circuit?

What Is Radial and Ring Circuits?

Think of a simple Circle that has a radius and periphery. The electrical circuit in your wiring system that looks like a radius is called a Radial circuit and which one looks like a periphery or ring is called a Ring circuit. Oh! this definition seems to layman, not professional; let's know the details-  

A radial circuit is an electrical circuit where the feeders to each socket are taken directly from the consumer unit or distribution board (DB) or circuit Breaker (CB) like a 20A MCB. 

A ring circuit is an electrical circuit that has two feeders both coming from the same 32A MCB or RBCO in the consumer unit and heading off to different ends of a loop circuit. Ring circuit also known as Ring Main circuit.

Distrubution Lines and Substation Equipment Maintenance and Testing Procedure

Fig-Distribution Lines and Substations Equipment

Maintenance and Testing of Electrical Distribution Lines and Substations Equipment

This article contents as per Bangladesh Electric distribution codes that follow in electrical energy distribution lines and substation equipment maintenance and preventive maintenance works.

The level of performance of all line and substation equipment shall meet the standards of performance for the Distribution Licensee specified by the Commission.

Automatic Transfer Switch Diagram And Operation Procedure

What Is Transfer Automatic Transfer Switch and How Does Work?

A transfer switch is nothing but an electrical device that allows transferring of electrical flow safely from multiple sources to load. On the other way, the load can trans-receive electrical energy from multiple sources safely.

To prevent a power outage from the main utility power supply a transfer switch can take power from an alternate utility source or standby generator source or even an emergency power backup source.

Transfer Switch can operate automatically as soon as a failure of the main source or after a certain period of time to reinstate the main source. This type of transfer switch is known as Auto Transfer Switch or in short ATS.

Another Transfer Switch is known as a manual transfer switch which operates manually. When the utility power goes out, it simply needs to plug the alternate source into the transfer switch to start it up and flip the transfer switch from the main source position to the alternate source position.

In very basic, transfer switches are two types-

1. Auto Transfer Switch, &
2. Manual Transfer Switch.

In common transfer switch is known as ATS or Change Over Switch.

What is the main feature of ATS (Automatic Transfer Switch)?

The principal purpose of an ATS (Automatic Transfer Switch) is to ensure the continuous delivery of electrical power from one of two power sources to a connected load circuit. 

The main elements of an ATS are-

01. Normal grid supply;

02. Emergency supply.

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Why Transfer Switch Is Needed

You can use your generator power in your home to feed your TV, Refrigerator, or Internet while utility power or main power is outage, just change over the switch from utility to generator. Life becomes easier and faster;

In industry, each minute is seeking production. To continue a production chain break-less, the uninterrupted power supply is very essential, and ATS takes a vital role in this case;

In data processing or data storage centers, a continuous power supply is essential to back up important data. ATS plays the main rules in keeping the power supply alive;

Signal controlling stations like airports, metro, fire-department, defiance, etc. need a troubleless power supply to transfer important information; ATS needs to ensure uninterrupted power supply;

In the hospital, so many life-supporting types of equipment are operating and can not be off for a moment. ATS works to continue the life-supporting power supply.

Wiring Diagram for Change Over Switch or Transfer Switch

In the schematic line, the diagram shows how to wire the Transfer Switch with the main service disconnect switch for the utility power source and generator power source along with your load disconnecting circuit breakers.

Here, in Line-1 & Line-2, the neutral and grounding connection is shown perfectly which will help to work with your own job.

This is not followed by any specific regulation, this is demonstrated just to improve your basic knowledge. Before performing your practical job must follow the local safety rules and regulations. 

If it is helpful, share your friends, and to improve this article delivery your valuable comments below.

Transfer Switch Operation Modes

A Transfer switch has the ability to operate in different modes of operation. In a given mode of operation, the transfer system will respond in a given way to changing system conditions. The transfer system will respond differently to the selection of different modes of operation.

The basic mode of operation of a transfer switch is as below:

01. Manual Mode;

02. Automatic Mode.

Manual mode: Selected via a selector switch position or other pre-determined user input via the user interface into manual mode position, the automatic mode will be inactive and the switch will able to operate manually.

 Automatic Mode: When the sector switch is selected in automatic position or other pre-determined user input via the user interface. The switch will be able to act in automatic mode.

What is the nominal capacity of an ATS?

The nominal capacity of an ATS (Automatic Transfer Switch) is designed to meet the continuous current carrying capacity from 30-4000 amperes. Typically, the most commonly used ampere ratings include 30, 40, 70, 80, 100, 150, 225, 260, 400, 600, 800, 1000, 1200, 1600, 2000, 3000, and 4000 amperes.

MCB: MINIATURE CIRCUIT BREAKER OPERATION BASIC

What is MCB?

MCB is a device designed to protect an electrical circuit's wiring from the serious damage which would be caused if it has to carry a current that is too high for the diameter of its wires.

The MCB or Miniature Circuit Breaker is actually working for both electrical circuits' make or break switch and protection device fuse.

Likely normal fan/light switches, MCB also can operate manually as circuit ON or OFF; its specialty is, it can break the circuit automatically to protect from overcurrent.

Fuse is the very first protection device for an electrical circuit. A fuse is actually nothing but a thin wire that is enclosed in a protective casing and plugged into the circuit.

Why Happen Over-voltage In Power System?

The Major Causes to Why Over-voltage Develop in  Power Distribution System.

The causes of happening over-voltage in the power transmission system may many more reasons. In short, we can define internal causes and external causes to develop over-voltage in electrical power transmission or distribution networks. We can sum up the whole causes of overvoltage in the power system in the major five cause as below:

1.     Power System Surges:

If absence or poor quality devices like Relay, AVR, Auto-transformer Auto-transformer regulator etc. are used in the transmission network, the system will function as poor regulation of the power source that may cause voltage fluctuations either over or under. This type of power supply system may cause serious damage to users’ equipment, especially to electronic or computer-controlled equipment;

2.     Insulation Failure:

This is the most common reason failure the insulation of conductor and cause grounding or near to grounding of the conductor. Failure takes place when there is no insulation between the line and the earth that allows the current to flow downward or earth;

3.     Arcing Ground:

This happens normally in the three-phase system when there is the presence of a sporadic arc in line-to-ground fault. In this case, short-live oscillations are produced, if this happen continuously or again and again that would be a serious problem for system cause of insulation breakdown of the connected equipment;

4.      Resonance: 

Happening resonance is a bad effect on the power system. In this case when resonance occurs means when the value of the inductive resistance becomes equal the value of capacitive resistance, system voltage increases absurdly;

5.      External Causes:

Above mentioned causes are mainly happening internally in the system. Many causes may happen externally to the system and may inject over-voltage into the system. Lightning is one good example that is responsible for the high magnitude of surges, leading to very serious high voltage injection to the system.

What Is Internal Causes for Over-voltages?

Demonstration of Over-voltage developing in the steady system:

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There are many internal causes for over-voltage in the power distribution network, we will focus only on some main causes for over-voltage that will help to over-voltage detection and selection of over-voltage protection devices like an over-voltage relay, over-voltage AVS, over-voltage detection circuit specification, etc. and finally help to protect the system from over-voltage damages or over-current damages.

The definition of over-voltage may define as “the excess potential required for the discharge of an ion at an electrode over and above the equilibrium potential of the electrode”; in short- voltage over the normal operating voltage of a device or the system is known as over-voltage.

The major internal causes for developing over-voltage is as-

a.      Switching Operations on Unloaded Line;

b.      Sudden Opening of Loaded Line;

c.      Insulation Failure;

d.      Arcing Grounds;

e.      Resonance, etc.

Internal over-voltages actually two major groups first- for switching over voltages or Transient over operation voltages of high frequency and second temporary over-voltages.

Switching over-voltages are caused when switching operation is carried over the network system, Ferranti Effect the receiving end voltage is increased when an unloaded long line is charged or stitch ON, similarly, overvoltage of transient nature occurs when the primary side of the transformers or reactors is switched ON.

Temporary over-voltages may occur due to disconnect a major load from the long line under normal or steady-state condition.

What Are External Causes for Over-voltages?

The external causes of over-voltage may occur due to various reasons from atmospheric disturbances, it originates mainly due to lightning that takes the form of a surge and has no direct relationship with the operating voltage of the system network. The major cause of external over-voltage developing in the system is as-

a.      Direct lightning stroke;

b.      Indirect lightning strokes;

c.      Electromagnetically induced over voltages due to lightning discharge taking place near the line, called 'side stroke';

d.      Voltages induced due to atmospheric changes along the length of the line;

e.      Electrostatically induced voltages due to the presence of charged clouds nearby; &

f.       Electrostatically induced over voltages due to the frictional effects of small particles like dust or dry snow in the atmosphere or due to change in the altitude of the line.

What Happen Due to Over-voltage in Power Distribution Network?

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All line equipment and appliances desire a stable power supply to function properly in its long span of life. Overvoltage is disposed to stress the insulation of the electrical equipment’s and possible to cause damage to them when it frequently over-voltage hits them. Especially for electronic circuits, over-voltage is very harmful to them.

Inline equipment, over-voltage may cause in spark over and flashover between phase and ground at the weakest point in the distribution network and the result is damages property if not the over-voltage protection devises function.

If you have more information about over-voltage, over-voltage protection and over-voltage devices share in comments.

SURGE ARRESTERS SPECIFICATION FOR 132 KV & 33 KV LINE

Surge Arrester Specification

Surge Arrester Requirements for 132kV and 33kV Underground Cable Line Projects

 

Surge arresters shall be of the type employing non-linear metal oxide resistors without spark gaps. The Contractor shall demonstrate by calculations that the surge arresters will adequately protect the switchgear arrangement proposed.

Arresters shall be designed and tested in accordance with the requirements of IEC 99 4. Any departure shall be the subject of agreement between the Engineer and the Contractor. Routine tests shall be carried out in accordance with the requirements of Section 15 of this Specification.

Surge arresters shall be housed in porcelain insulators designed to withstand extremes of the environment described. The insulation shall have a minimum creepage distance of 25 mm/kV rated system phase-to-phase voltage. Porcelain shall comply with IEC 233. The method of sealing against the ingress of moisture shall be of a type well proven in service and the manufacturing procedures shall include a practical leak test which can be demonstrated to the inspecting engineer if required.

The internal components of arresters shall be arranged to minimize radial voltage stresses, and internal corona and to ensure minimal capacitive coupling with any conducting layer of pollutant on the outside of the porcelain housing except where approved, organic materials are not permitted.

Good electrical contact shall be maintained between resistor blocks, considering any thermal expansion and contraction of the block or mechanical shock during transport and erection, by installing a well-proven clamping system.

Metal oxide arresters installed outdoors shall be able to dissipate when new, twice the energy generated in the resistor blocks when energized at their maximum continuous operating voltage immediately having been subjected to the discharge duties specified in IEC 99 4 and assuming that the porcelain housing and the surrounding air is at least 5˚C higher than the maximum ambient air temperature specified.

Good quality control of the manufacturing process of the resistors shall be ensured by rigorous testing procedures. The procedures shall ensure that the characteristics of the blocks are, and will remain, within the specified limits when new and throughout the anticipated life of the arresters. Samples may be selected at random by the Engineer for special tests to be agreed upon with the manufacturer.

All surge arresters shall be fitted with a pressure relief diaphragm which shall prevent explosive shattering of the porcelain housing in the event of an arrester failure and the arrester shall have been tested according to the high and low current tests specified in IEC 99 1.

Arresters shall be supplied completely for installation in an outdoor switchyard, including supporting structures, insulating bases, and surge counters, one per phase, and, if applicable, grading rings. The material used for terminals shall be compatible with that of the conductors to which they are to be connected.

Each arrester shall be identified by a rating plate in accordance with the requirements of IEC 99 4. In addition, an identification mark shall be permanently inscribed on each separately housed unit of a multi-unit arrester so that units can be replaced in the correct position in the event of them being dismantled.

Surge counters shall have an internal assembly that is matched to the line discharge capability of the arrester and shall include a leakage current meter with a bilinear scale for ease of reading. Auxiliary contacts are to be provided to signal remote indications of the counter operation.

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Technical Data Schedule for 132 kV and 33 Surge Arrester

Sl. No.	Item no.	Unit	Nominal System Voltage
			132 kV	33 kV
1.	Manufacturer
2.	Model Number
3.	Type:
4.	Continuous operating voltage	kV RMS
5.	Rated voltage	kV RMS
6.	Standard nominal discharge current	kV
7.	Reference current at ambient temperature	mA
8.	Reference voltage for above	kV RMS
9.	Steep current impulse residual voltage	kV pk
10.	Lightning impulse residual voltage at
	5 kA	kV pk
	10 kA	kV pk
	20 kA	kV pk
11.	Duty Class
12.	Discharge Class
13.	Pressure relief class
14.	Nominal Diameter of resistor blocks	mm
15.	Number of resistor blocks connected electrically in parallel
16.	Number of separately housed units pre-phase
17.	Overall height of arrester (without supporting structure)	m
18.	Overall height of arrester including grading ring if applicable	mm
19.	Clearances:
	Phase to earth (from center line)	mm
	Phase to phase (center line to center line)	mm
20.	Overall height of arrester (without supporting structure)	kg
21.	Maximum cantilever strength	Nm
22.	Maximum force due to the wind (at maximum specified gust speed)	Nm
23.	Minimum creepage distance over the insulator	mm