Voltage Classification - LV, MV and EHV

AC voltages have been classified in various manners. In earlier times, there were just two categories LV and HV. As the level of voltages increases, there was a need for more levels. However, there was ambiguity as to where each band ended and the other began. For instance, 11kV can be MV in some systems and HV in another.

The International Electrotechnical Commission has classified the voltages into the following levels(IEC 60038). This classification system is fast gaining acceptance.

• Low Voltage - upto 1000V
• Medium Voltage - 1000V to 35kV
• High Voltage - 35kV to 230 kV
• Extra High Voltage - above 230 kV

In some situations, the term Ultra High Voltage is used to denote voltages above 800 kV.

In addition, the IEC defines a voltage band known as the Extra Low Voltage with a AC voltage less than 70 V.

Extra Low Voltage

Extra low voltage refers to reduced voltages which are used in houses, parks, gardens, swimming pools to eliminate the risk of electric shock.

AC voltages below 50 volts and DC voltages below 120 volts are considered to be Extra low Voltage.

In many countries, Extra Low Voltage supplies are used to power traffic signals. This has been facilitated with the advent of LED lighting technology.

Extra Low voltage systems can also be easily integrated with solar panels as the generating voltage is lower.

A comparison of Overhead and Underground Transmission

Electric Power needs to be carried over long distances from the point of generation to the point of consumption. This Transmission is done either through overhead lines or underground cables. Each of these two methods of transmission has its own advantages and disadvantages.

Overhead Transmission lines are cheaper as the insulation cost is lesser and the conductor material cost is lesser too. They also have better heat dissipation.

However, they have significant disadvantages. Overhead lines are vulnerable to lightning strikes which can cause interruption. Overhead lines use bare conductors and can cause damage if they break. They are considered to be unsightly as they mar the scenery of the landscape. The maintenance cost of overhead lines is more and the voltage drop in overhead lines is more.

Underground transmission due to cables is costlier than overhead transmission as the ground needs to be excavated. This can be difficult when passing though geographic obstructions such as hills, marshes and rivers. Special trenches need to be constructed when passing through loose soil. Besides, heat dissipation in underground cables is an issue. Hence, the conductors have to be thicker. The insulation required for the cables is expensive. Hence, it is difficult to use underground cables for voltages at HV levels (> 33 kV).

Underground cables may have to be rerouted to accommodate other underground structures such as pipelines, sewage lines, etc. It is necessary that the routes of underground lines are clearly marked with sign boards to prevent accidents when excavations are carried out for other reasons at a later date.

Advantages of Three Phase Power over single Phase power

Three phase power transmission has become the standard for power distribution. Three phase power generation and distribution is advantageous over single phase power distribution.

Three phase power distribution requires lesser amount of copper or aluminium for transferring the same amount of power as compared to single phase power

The size of a three phase motor is smaller than that of a single phase motor of the same rating.

Three phase motors are self starting as they can produce a rotating magnetic field. The single phase motor requires a special starting winding as it produces only a pulsating magnetic field.

In single phase motors, the power transferred in motors is a function of the instantaneous current which is constantly varying. Hence, single phase motors are more prone to vibrations. In three phase motors, however, the power transferred is uniform through out the cycle and hence vibrations are greatly reduced.

The ripple factor of rectified DC produced from three phase power is less than the DC produced from single phase supply.

Three phase motors have better power factor regulation. Motors above 10HP are usually three phase.

Three phase generators are smaller in size than single phase generators as winding phase can be more efficiently used.

Single Circuit and Double Circuit Transmission Lines

Transmission lines which carry three phase power are usually configured as either single circuit or double circuit. A single circuit configuration has three conductors for the three phases. While a double circuit configuration has six conductors (three phases for each circuit).

Double Circuits are used where greater reliability is needed. This method of transmission enables the transfer of more power over a particular distance. The transmission is thus cheaper and requires less land and is considered ideal from an ecological and aesthetic point of view. However, running two circuits in close proximity to each other will involve inductive coupling between the conductors. This needs to be taken into account when calculating the fault level and while designing the protection schemes.

Double circuit transmission lines usually contain bundled conductors with the conductors placed as far as possible to minimize inductance.

The Benefits of SCADA Systems Automate Electrical Distribution to increase uptime and improve utilization

Rapid power transmission and distribution systems from power plants to customers in residential or office safe is a challenge today's power generation industry. Electric utilities parties must be able to meet the electricity needs of the community well, minimizing disruptions and power cuts as much as possible. Electricity utility must collect and distribute electricity from the various sources of electricity generation, many of them intermittent, and distribute to customer by utilizing automated monitoring and control of SCADA.

Substation power plants have a complex system and have varying amounts of control and operator interface points. Substation power plants will be controlled and monitored in real time by a Programmable Logic Controller (PLC) and by special devices such as circuit breakers and power monitor. Data from the PLC and the device is then transmitted to a PC-based SCADA node in the substation.

SCADA implementation in the electrical distribution system is greatly assisting the authorities of electricity in various ways such as:

1. Improve the performance of the electrical distribution system automatically

SCADA systems are able to make the process safer, faster and completely automated start of collecting data to provide automatic control that greatly benefits utilities. One application is when there are problems in the field Alarm they detect problems in the system, and analysis of this issue allows adjustments and corrections, often prevent the outage automatically. When there are problems e.g. outage caused by an unexpected event such as a hurricane, SCADA a sophisticated system of data collection capability helps field workers to quickly identify the exact location of outages without having to wait for customer calls.

2. Data collection for the electricity distribution process automatically

As automatic control systems, SCADA able to change the system work a lot of utilities that still rely on manual labor to perform tasks automatically power distribution. This process is able to cut labor costs, making the process safer and more comfortable and minimize distractions. Modern SCADA system also features built-in redundancy and backup systems to provide sufficient reliability, and can respond more quickly and consistently than manual process.

3. Alarm Monitoring System is able to detect problems that occur quickly and accurately

Excellence SCADA system is able to significantly increase the speed of recovery in the event of power outage. These problems occur when the SCADA-enabled switches and closers line so it can help isolate the location in case of a blackout by means of open automatic switch adjacent to the power switch quickly to other parts without the need for line workers to visit the site to perform a visual inspection long.

4. Worker protection and detection of hazardous location automatically

Modern SCADA systems that provide multiple benefits in the security system and keeping the level of workers due to the substation and at DER connection point, the data should be collected and made available to the SCADA system so that it can detect problems that occur more quickly. DER automates monitoring in real-time with the SCADA system allows the operator to make more information more rapid adjustments, and to uncover trends and issues before a problem occurs.

5. Facilitate the early detection of problems and routine equipment repairs

SCADA system improvements make it easier to do on a regular basis. For example, if a power monitoring device has a protocol and some types of hardware then with the SCADA system in more easily configured and installed. In addition some offer a DNP3 SCADA software package is required and IEC-60870-5-104 protocol so as to facilitate early detection if a problem occurs automatically.

6. Improved efficiency of system performance based on the data trend analysis

SCADA is able to analyze and identify quickly and automatically condition of excess capacity and so the power can be transferred from the area approaching overload. The control system can also analyze trends and historical data also helps maintain the desired power factor, voltage level and other parameters of the distribution system at the desired level.

Conclusion

SCADA systems are designed to simplify power distribution applications with the help of PC-based software. Data collected from the electrical distribution system, with most of the data that comes in the substation to be processed in the SCADA control system so that the process control can be run automatically, quickly and accurately.

The difference between Net Calorific Value and Gross Calorific Value in Boilers

Calorific value is the total energy contained in fuel. It is indicated in kilojoules per litre or cubic meter.

All fuels, such as coal, oil or wood contain a small amount of water in the form of moisture. When fuel is consumed in the furnace, some of the energy is used to evaporate the water contained in the fuel. This water escapes as steam in the flue gases.

Gross Calorific Value

This includes the total energy in the fuel which includes the energy used in heating the water. The Gross calorific value is also known as the higher heating value.

Net Calorific Value

Net Calorific Energy is calculated after subtracting the energy used to evaporate the moisture in the fuel. Net Calorific Energy is used for boiler efficiency calculation. The Net calorific value is also known as the lower heating value. The Net Calorific Value is generally 10 % less than the Gross calorific value.

VB Cycle 2x100 MW

Working of Steam Power Plant

Steam power plant basically operates on the Rankine cycle. Coal is burnt in a boiler, which converts water into steam. The steam is expanded in a turbine, which produces mechanical power driving the alternator coupled to the turbine. The steam after expansion in prime mover (turbine) is usually condensed in a condenser to be fed into the boiler again. In practice, however, a large number of modifications and improvements have been made so as to effect economy and improve the thermal efficiency of the plant.

The entire arrangement for sake of simplicity may be divided into four main circuits namely:

1. Fuel and ash circuit
2. Air and fuel gas circuit
3. Feed water and steam circuit and
4. Cooling water circuit.

1. Fuel and Ash Circuit

Coal is delivered from the supply points to the storage site by road, rail or water. The coal after necessary landing and treatment (handling) is passed on to the furnaces through the fuel feeding devices. Ash resulting from combustion of coal collects at the back of the boiler and is removed to the ash storage by means of scrap conveyors. Combustion is controlled by controlling the great speed, quantity of coal entering the grate and the damper openings.

2. Air and Fuel Gas Circuit

Air is drawn from the atmosphere by a forced draught fan or induced draught fan through the air pre-heater, in which it is heated by the heat of flue-gases passing to chimney, and then admitted to the furnaces. The flue-gases after passing around boiler tubes and super heater tubes are drawn by the induced draught fan through dust collector (or precipitator) economizer and air pre-heater and finally exhausted to the atmosphere through chimney.

3. Feed Water and Steam Circuit

The condensed water is extracted from the condenser by the condensate pump and then forced to the I p feed water heater; where its temperature is raised by the heat from bled steam. The feed water is now pumped to high pressure water heater, where it gets heated by the heat from bled steam extracted at suitable point of steam turbine. It is then pumped into boiler through economizer, in which it is further heated by the heat of flue gases. In boiler water is converted into high pressure steam which is wet. Wet steam is passed through super-heater, where it is dried and further super heated, and then supplied to the steam turbine through the main valve. After giving out its heat energy to the turbine it is exhausted to the condenser where its latent heat is extracted and steam is converted into feed water. At one or more stages a quantity of steam is bled or withdrawn and steam is converted into feed water. Making up water for boiler is taken through the evaporator, where it is heated by low pressure steam extracted at suitable points of turbine.

4. Cooling Water Circuit

Cooling water is supplied from a natural source of supply such as river, canal, sea or lake or cooling towers through screens to remove the matter that might choke the condenser tubes. It is circulated through the condenser for condensing the steam and finally discharged to the suitable position near the source of supply. During the passage, its temperature rises and in the case of cooling towers the heat must be extracted before the water is again pumped to the condenser. The circulation of cooling water to the condenser helps in maintaining a low pressure in the condenser.

Why We're Here? (in this universe)

Why we're here? what a big question, well if we belief in God we'll asked to the systems, and many-many answerd and interpertation. If There's God out there, why we're here? what purpose? why The Divine Creature create us? For his own purpose? to acknowledge him? or He need his creatures to praise him? Is God a concept? And we're the creature should experience the universe? Until we get knowledge? Try and error about the universe until he find the suitable universe for us? that's it? that's why we're here?

Basic Boilers

The boilers is comprised of two basic systems. One system is the steam water system also called the waterside of the boiler. In waterside, water is introduced and heated by transference through the water tubes, converted to steam, and leaves the system as steam.

Boilers must maintain a chemical balance. The manner in which this is done can interact with the feedwater control system. The amount of blowdown must be considered in the feedwater control scheme, especially if the blowdown is continous. Often the blowdown flow is divided by concentration ratio times the feedwater flow. Continous blowdown is the common method for controlling the chemical concentration. On large boilers this may be done automatically by measuring the water conductifity to control the blowdown rate. The blowdown rate may also be achieved combining the conductifity with ratio control of blowdown, ratioing blowdown to feedwater flow. In utility plants, conductifity is usually measured and blowdown is achieved manually. This required on a periodic basis or when the conductifity gets too high.

Conductifity is measured in micro mhos which is equal to the reciprocal of 1 mechanical ohm (resistance). The other boiler system is fuel air-flue gas system, also referred to as the fireside of the boiler. This system provides the heat that transferred to the water. The inputs to this system are the fuel and air required to burn the fuel. The fuel and air chamber is also referred to as the windbox. The outputs are the flue gas and ash.

Difference between a steam boiler and a steam generator

A boiler, as the name suggests, boils the water before turning it into steam at subcritical pressure - the pressure at which bubbles can form. Steam generators, on the other hand, convert water into steam into steam without boiling at a super-critical pressure.

There are also constructional differences between a boiler and a steam generator. A boiler contains many tubes which carry the water. A steam generator has, generally, only one tube in which the heating occurs.

Boiler Control Fundamentals

When working with balance draft boilers, regardless of the basic process control system or fuel being burned, there are six basic functions that must be controlled: furnace draft, drum level, feed water, fuel, air, and steam temperature.

The basic understanding of boiler operation and control:

• Boiler Components 
• Enclosure symbols
• Draft (control)
• Drum Level Control
• 2 and 3 element Feed Water Control
• Steam Temperature Control
• Boiler Swell and Shrink

and I&C Engineer should be able to:

• Describe the boiler components and their function
• Discuss furnace draft, drum level, feed water, fuel, air, and steam temperature
• Describe how the systems interact and how to set up the controls
• Describe "swell" and "shrink"