Modern Electrical Supply System

What is an Electric Supply System?

The modern electrical supply system is an important part of the electrical power system. Electrical power generates in the generating station, transmit through the transmission line, and distribute to the consumer, this system is called an electrical supply system. The electrical supply system consists of three main stages or components such as

  • Generating station
  • Transmission
  • Distribution system

Electrical Generating Station

Power generating stations generate electricity by converting energy from some other forms of energy (like mechanical energy) into electrical energy at relatively low voltage levels. Generating electricity at low voltage levels is economical in many ways. This generation voltage (11KV) is a step up to the high voltage by using a step up transformer (132KV, 220KV, 400KV).

And step down the voltage level in the secondary transmission line (132KV/33KV, or 220KV/33KV). Again step down the voltage level in the primary distribution (33KV/11KV), and again step down the voltage in (11KV/0.4KV, or 400V) by using step down transformer, or distribution transformer.

Electrical Power Transmission System

The transmission line is used to transmit the electrical energy from generating station to another substation. There are two main types of transmission to transmit electrical energy such as

  • Primary transmission
  • Secondary transmission  

Primary Transmission System

The power supply from the generating station (132KV, 220KV, 400KV or more) is transmitted to the load center through a three-phase three-wire (3 phase – 3 wires also known as delta connection) overhead transmission system. Since the voltage level is generated from the generating station is about (11KV, 13.8KV, 15KV, 20KV), the load center should be placed at a different voltage and very far from the generating station.

Modern-Electrical-Supply-System

For example, the generating station can generate a voltage of 11 kV but if the load center is 1000km away there is a need to transmit a moderate amount of power to reduce the transmission loss. The transmission line can be subdivided into three main categories depending on the transmission voltage and distance.

  • Long transmission
  • Medium transmission
  • Short transmission

Long Transmission Line

If the length of the overhead transmission line becomes more than 150 miles from the generating station or supply center, and the voltage range becomes more than 100 kV such kind of line is called a long transmission line.    

Medium Transmission Line

If the overhead transmission length becomes 50 miles to 150 miles from the generating station or supply center, and line voltage becomes more than moderately high like 20KV to 100KV this kind of transmission line is called a medium transmission line.

Short Transmission Line

If the length of the transmission line becomes 50 miles and the voltage range is comparatively low like 20KV such kind of transmission line is called a short transmission line.

Secondary Transmission System

When electrical energy reaches a receiving station, the voltage is usually converted to a voltage between 33 kV and 66 kV. It is then transmitted from this acceptable station to the electrical substations near the load centers such as cities, villages, and urban areas through the raised transmission lines. This process is known as a secondary transmission line. When the electrical power reaches a substation or receiving station. The voltage is stepped down like 132KV/33KV in the secondary transmission (receiving station).

Distribution System

The distribution system is an important part of the power system. From which center electrical power is distributed on the various side for the consumer use which is called a distribution system. It is a pretty much high voltage (11KV) to use for this reason this distribution voltage is reduced to (0.4KV or 400 V) by using a step-down transformer for the consumer. There are two major types of the distribution system 

  • Primary distribution
  • Secondary distribution

Primary Distribution System

Primary distribution is the part of an AC distribution system that operates at slightly higher voltages than normal residential voltage. The primary distribution voltages that are commonly used in most countries are 11kV, and 6.6kV. Primary distribution manages large customers such as factories, industries, and others. Electric power is supplied from the primary distribution to the secondary distribution center for local use. The primary distribution system has a lot of value able components

  • Transformers
  • Feeder
  • Switches
  • Protective component
  • Primary Circuits
  • Secondary circuit

Secondary Distribution System

The secondary distribution substation is the law voltage substation. The secondary substation receives power through the 3-phase 3 wire system from the primary substation and steps down the voltage such as 11KV/400V. The secondary distribution is located near the consumer localities. The power is supplied by a 3-phase 4-wire system from the secondary distribution substation. The voltage between two phases is 400 V and the voltage between a phase and neutral is 230 V.   

What is Line Voltage and Phase Voltage?

The high voltage passes through the 3-phase 3-wire system, and the secondary distribution voltage passes through the 3-phase 4-wire system. The voltage between two phases is called line voltage (like 400V), and the voltage between phase and neutral is called phase voltage (like 230 V). On the other hand, an electrical power system consists of three main steps: generation, transmission, and distribution.

These three parts are more essential, and we get electricity through these three steps. We know that electrical energy can be distributed in the two ways, such as three phase three wire and three phase four wire systems. But there is a difference between line voltage and phase voltage. The voltage between any two lines is called line voltage or line to line voltage. If the voltage is measured between phase and neutral it is called phase voltage.

Difference between single phase and three phase voltage

Single phase power and three phase power both are the most important consideration for the distribution system. Basically, three phase three wire system is used to transmit the high voltage electric power but we will discuss here the difference between 1 phase and 3 phase power distribution system. Basically, three phase three wire system is used to distribute the electric power but those are the three phase load (three phase induction motor) they directly receive three phase voltage 400 volts or 440 volts. It is noted that 3 phase power load doesn’t require a neutral wire to connect.

Whereas single-phase power carries 220 volts or 230 volts for small domestic loads, municipal loads, and others where 220 volts or 230 volts is required. It is noted that a single-phase power load requires a neutral wire to connect. If we calculate the single phase voltage then it will be clear. Let’s see we know that line to line voltage or phase to phase voltage is 240 volts but if we measure phase to neutral then we will get 120 volts. The 120/240-volts notation identifies the neutral voltage from the phase and the phase to phase voltage.

Electrical Power Transmission and Distribution System

We know that Modern Electrical Supply System consists of generation, transmission, and distribution systems. The generation voltage of the power plant is about 11kV (phase to phase). If it is sent directly to a distance of about 100 km, then all the energy will be lost due to the resistance in the line. And the voltage at the receiving end will be very low. So it is enhanced with a step-up transformer during operation. In Bangladesh it is up to 132KV, 230KV, 400KV. However, the 65KV system is going to come in front.

three-phase-Modern-Electrical-supply-system

It is first lowered to 33KV, then to 11KV, and finally to 0.4KV before being given at the customer level. I have already said that these are the phase-to-phase voltages of all three-phase systems. The three phase system has three live phases. In this house residential connection is provided with neutral with any one phase of 0.4KV or 400 volts three phase line. The phase-to-neutral voltage is 63% lower than the phase-to-phase voltage, which is why you get 220 volts at home.

Why 220 volts, 400 volts, 33 kV, 132 kV in these ranges? Why can’t it be kept at any other voltage?

If you keep the voltage as you wish, you will not be able to use the charger of your expensive smartphone brought from China to your home. And not all countries make all the equipment in the power system. So if there is a different standard, foreign machines or transformers will not work in your country.

Is 0.4 Volt Given at Consumer Level?

No. It depends on the amount and type of load of the customer. Industrial connections are also provided in very high voltages. Small industries are loaded at 11KV, medium, and big industries at 33KV. But they can use 230V or 400V. It is mainly based on their operating system.

What Type of Conductors is Suitable for an Overhead Transmission Line?

Those conductor is flexible, able to carry extra-high-voltage, and cost-effective such conductor is suitable for the transmission line. There are different types of conductors and these are used depending on the transmission voltage and transmission cost but Aluminum Conductor Steel Reinforced (ACSR) is more popular.

Nowadays Aluminum Conductor Steel Reinforced (ACSR) is widely used for high voltage overhead transmission lines.

Does the Consumer need to Pay Electricity Charge until the Consumer doesn’t use Electricity and why?

We know that if we use electrical energy we have to pay the charge. For this reason, if the power line is connected to your meter but you have never used electricity yet. In this case, you have to pay the minimum charge. Because the power line is connected to your energy meter due to your service money. For this reason, consumers need to pay electricity charges.  

How does a Supply Company divide Power Demand between Consumers?

 Basically, the electricity supply company distributes load based on the consumer load demand. The power is divided into four categories based on the consumer requirements, such as 

  • Small power: The power demand is less than 100 KW
  • Medium power: The power demand is more than 100 KW but less than 5000 KW
  • Large power: Those who have power demand more than 5000 KW
  • Domestic load: Basically, the power corresponds to the needs of houses.

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