Power substations play an important role from power generation to power users. The power substation is responsible for converting low voltage to high voltage and high voltage to low voltage. In this way, the work of controlling the passing electricity, as well as measuring the incoming and outgoing electricity is also done here. It doesn’t matter if the substation is called the heart of the power distribution system.
There are two types of substations depending on whether the voltage is high or low.
- Step up Substation
- Step down Substation
What is a step up Substation?
What is a step up Substation?
Substations in which low voltage is converted to high voltage and further power is supplied are called step up substations. Generally, there are step up substations at the place of Genrating Stations. Where the power supply is further transmitted by converting 11kv to high voltage.
What is a Step Down Substation?
The substation in which the power supply is carried forward by converting the high voltage to low voltage. Asha substations are called step down substations.
Such substations are constructed in the center of a normal load center. By suppressing high voltage, power is supplied to different parts or substations through different feeders (circuits).
Such substations are constructed in the center of a normal load center. By suppressing high voltage, power is supplied to different parts or substations through different feeders (circuits).
What is a switching station?
The power is supplied to the substation at the same voltage. Where only the power supply is controlled and measured, the voltage is not increased or decreased. Asha substations are called switching stations.
Equipment in the substation
The in-door breaker system is called switchgear. 11K. V. Indoor 11K in control panels. V. Circuit Breakers, Bus Bar, C.T. Are fitted. All the panels are mounted in the level. If the level is missed, it affects the operation of the circuit breaker.
There are no cracks anywhere in the panel, just as the holes from where the power cables and control cables enter the panel are completely closed, otherwise there is a risk of rats going inside and shifting. Good earthing to power cable box and panel
Is done. Earth resistance does not exceed 2 Ohm.
Isolators and earth switches and interlocking
The substation has isolators to isolate the power supply. Isolators are also called gang operating switches (G.O.D.). But isolators should never be operated on load. This is the most important rule to follow while operating isolators. If you want to turn off the isolators, first turn off the circuit breaker and cut the load and then turn off the isolator. Insulators used for insulators have higher resistance than insulators on line. The main reason for this is that, occurring on the line
Any faults affect the tools and equipment in the substation. Therefore, the isolators in the substation are likely to deteriorate quickly. Similarly, the flow of electricity falling from the sky on the line reaches the sub station. So
Why not for a moment but it comes to the isolators in the electric current and electric pressure sub station. Therefore, isolators are designed and manufactured in such a way that they do not deteriorate. 33 KV isolators are installed in the substation at an altitude of 3500 mm above the ground. (Distance from ground to conductor jumper)
What are the types of isolators?
There are two types of isolators.
- Single brake Isolators
- Doublebreak Isolators
Double brake isolators are always better than single brake isolators. This is because it has a system to disconnect the power supply on both sides. This reduces sparking in male and female contact. It also has high load carrying capacity. So the type of isolator to be installed is decided by looking at the load in the substation. It is very important to follow the definite sequence to turn on or off the isolators. Experience has shown that, in switching operations
The errors are due to the operator not following the definite sequence. This is illustrated by the following example.
Opening on isolator load.
Turning the line without removing the earthing done earlier when the work is completed.
- Opening isolators by turning off the wrong circuit breaker.
Basic rules for turning on and off isolators
Switching operations should be done only by the right and qualified (authorized, competent) person.
11 K. V. All switching operations in the above sub station should be done by two men.
While one person is performing switching operations, it is important to see if the other person is performing the operations correctly. It is better for the supervisor to be of a higher standard than the one who conducts the operations.
Circuit breaker in metal clad switchgear, substation with single transformer and where 11 kV. Switching operations in a place where the voltage is not higher than the voltage can be done even if done by a single but suitable person. The isolators in the substation should be operated only by the breaker, after breaking the load current. This is because isolators, like breakers, do not have an arc control device.
Isolators should never be used for the following purposes:
To change the load from one bus to another.
To close or open the bus when the circuit breaker is closed, rubber gloves must be used while the isolators are on or off and checked from time to time.
How to do isolator maintenance?
The power supply should be switched off in proper order while maintaining the isolator. After that, maintenance should be done only by making sense,
Dust on the isolator etc. All should be cleaned.
Male – Female contacts should be wiped and cleaned with polish paper, check if their springs etc. are correct and see if they fit tightly. The connections of the jumpers should be tight.
Check if the insulator is cracked or cracked, if necessary, replace it.
See if the operations are done on and off correctly, if there is no alignment.
Apply petroleum jelly to all contacts. Grease / oil the rotating parts and make sure the operation is smooth.
The function of the earth switch in the substation
Most substations have earth switches fitted with line isolators. This type of switch allows you to do the same thing on the side where the line is isolated. These means are connected to the terminals with the blades off. The line that he is off is nothing. But such switches should never be fitted to ringfeeding or backfeeding feeders.
What is an isolator interlocking system?
- H. V. Isolators of major substations are provided for interlocking. This means that no isolator can be accidentally turned off on load or the isolator can be turned off without turning off the breaker. In the inter-locking system, a plunger is mounted in the lever of the isolators. So d. C. Works on supply. Some places have an isolator key. C.V. This key cannot be taken out until it is turned off, which means the isolator cannot be turned off. In some substations the handle of the isolator and the earth switch are different and the key does not come out and the earth switch cannot be turned on unless the isolator is turned off. The alignment of the isolator should be in order, the three leaves should fit inside as well as the outside, and the height of the handle should be appropriate.
Care to be taken while using power cable in substation
33/11 KV 11 KV in the transformer. Make sure the cables coming to the side panel are the right size. Otherwise cable fault, cable melt, overheating, insulation leak etc. Things will happen. It should be loaded according to the size of the cable.
When laying cables, they should be laid carefully through the trench, making sure that the cable does not get hit.
Note that if several cables pass through the same trench, the current carrying capacity of that cable decreases.
Cable lugs must be properly connected and tightened, otherwise heat will build up and break contacts, leading to faults.
Appropriate action should be taken if cable insulation is melting.
Substation control cables
Control cables are relays, ammeters, volt meters, frequency meters etc. Used as a supply medium for.
These cables are multicore and are used by other devices such as circuit breakers to carry signals from the control room. The control cables also come from the trench.
What is Corona Loss in Substation?
When two bare conductors are carrying power through the air, it is necessary to keep a certain distance between the two conductors. If the distance is reduced, you will always see the corona process and there are adverse effects on the line from that corona.
Suppose two conductors are passing close by. The distance between two conductors is less than the diameter of the conductor. So the surface air of that conductor is the conductor. There is a buzzing sound, and if the same thing happens in the dark, that is, at night, then a bluish purple flame (like rain gas) appears around the conductor, and at the same time there is a special smell of ozone gas. This process is called “corona” *. And this process takes place due to ionization of air. The specific minimum voltage at which this process occurs is called the dispersive critical voltage. It is safe to assume that the surface of the conductor is not rough or clean in places where the blue flame is brighter.
How to identify the corona process?
The corona process can be clearly identified from the following.
A bluish purple flame appears around the surface of the conductor.
It sounds like hissing.
The smell of ozone gas.
The bluish purple flame is more intense in areas where the conductor is rough and not clean.
If a watt meter is installed in an electric circuit, the watt meter reading shows that power loss is caused by the corona process.
The charging current increases as the corona produces harmonic current.
What exactly is happening in the Corona process?
Corona is caused by the following process. There are some free electrons in the air. As the voltage gradient between the two conductors increases, these free electrons gain momentum. At a certain speed, the electrons collide with a low-speed molecule, causing some of the electrons in the molecule to come out (free).
Some electrons are released by pushing some molecules. It starts out like this. When the air near the conductor surface is saturated with free electrons, the insulating properties of the air are lost and the air is conducting. This is called the corona process. If there is a lot of water vapor in the air, the air becomes saturated quickly and this causes an early corona effect. Humidity is high in the air during monsoons so corona can appear. 400K. V. Since the voltage of the line is very high, the corona appears high on that line.
Adverse effects of corona process in electric field
Corona should be avoided as it causes power loss. For this the distance between the conductors should be increased. Also the conductor must be kept as smooth as possible. And keeping clean as well as increasing the diameter of the conductor or using a bundled conductor is the solution above Corona.
Requirement and connection of power capacitors
It is the rule of the power distribution company that every electric consumer using electric motors (using electric pumps for industrial or agricultural purposes) should keep the power factor to a minimum of “0.90”. The power factor of electric motors ranges from 0.5 to 0.6. Installing a capacitor improves the power factor.
The full load current of an electric motor is usually half the capacity of that motor (horsepower). This means that the full load current of a ten horse power motor is 15 amperes but if you add a capacitor of suitable capacity in the circuit of this motor then it will be found that the same motor will take 15 amperes of current instead of 15 amperes while running at full load. . This means that the motor consumes about 3 amperes less current when the capacitor is connected. This means that a cable with low current carrying capacity can be used. Similarly transformer e.g. Can be given. Suppose there is a 100 KVA capacity distribution transformer. Suppose its fullload rated current is 150 amperes. This means that the transformer can be loaded at 100 (HP) horsepower. But if you add a power capacitor of suitable capacity to the electric circuit of this motor, the same motor will take 120 ampere current (current) instead of 150 ampere. This means that the current load on the transformer will be less than 30 amperes. So without increasing the capacity of the transformer, we can safely give it an additional load of 20 horsepower, thus adding a capacitor can benefit the power company, according to Ohm’s theory as the load on the line increases. As the electric current of the line increases, the voltage of the line decreases. (That is, as the voltage drop increases, the voltage decreases.) In this case, by adding capacitors in the electrical company (in the circuit), the load on the line remains the same, but the current decreases. So electric
As the pressure improves, the voltage across the line increases. This helps the power consumers to get the right amount of electricity.
What are the types of power capacitors?
There are two types of capacitors.
- L. T. Capacitors
- H.T. Capacitors
- L.T. Capacitors
L.T. Capacitors have a pressure of 440 volts. They are connected in parallel to the circuit of the electric motor. H.T. Capacitors are generally 11 k. V. The pressure is 33 KV / 11 KV. In the sub station c. B. Are connected to the panel bus with the help of. If the power supply of the capacitors is switched off, it will be shocked if it is touched immediately. Because static charge is generated in the capacitor, it should always be kept in mind that whenever you want to work on the capacitors, you must first turn off the current and discharge the capacitors first with the help of a discharge rod.
Why residual voltage transformer is used in power capacitor bank? | R. V. T. What is it?
11K exiting the sub station. V. Capacitor banks are fitted to improve the power factor of the line. A bank typically has a total of twelve capacitors, four in each phase, with a separate fuse for each capacitor. In order to avoid any risk in case of a fault in a capacitor unit, Rs. V. T. is used.
Procedure of Residual Voltage Transformer (RTC)
RVT as shown in the figure. The cable is connected to the neutral volts displacement relay in the control room by connecting cables from terminals A and B in general. When the capacitors in all the three phases are the same, the voltage between A and B is zero. If the fuse of a capacitor blows, voltage comes to this terminal and the relay operates and a breaker trip occurs. At this time it is necessary to check the entire capacitor back.
Restricted Earth Fault C.T.
This current transformer operates on the principle of a common current transformer. Hee C.T. The power is connected to the neutral of the transformer and the restricted earth fault relay is connected to the control panel of the transformer. When any electrical fault occurs inside the transformer c. T. Flows through. And hence r. E. F. The relay operates and the transformer trips.
In some transformers this C.T. is mounted on the neutral lead inside the transformer.
Special care to be taken while handling capacitor bank
Capacitors are used to improve the power factor of substation. Since the capacitor has the property of accumulating charge, great care must be taken while handling the capacitor bank. Due to the neutral voltage displacement relay when the power supply to the capacitor
The doer breaker trips. At that time it should be assumed that there is some defect in the capacitor bank and in such a case it is necessary to check the entire capacitor bank. After obtaining the permit, first open the insulator of the capacitor back and discharge the capacitor bank to the capacitor bank by earthing rod / discharge rod, discharge the cable of the capacitor back, discharge each capacitor unit by another discharge rod and attach the working rod / shooting rod to the capacitor bank.
If a meger is used to check insulation resistance, it should not be touched without discharging the cable and capacitor after measuring. If you want to do some work of capacitor bank breaker, first close the capacitor breaker, open the isolator of capacitor bank and shoot only after shooting near the cable box near the capacitor breaker.
Protection of electrical substations from lightning in the sky
How is Lightening generated in the sky?
The sun’s rays in the atmosphere cause the separation of different gases in the air, creating (+ Ve) and (-Ve) positive and negative charges in the air.
During the rainy season, some clouds in the sky get charged (+ Ve) and some clouds get charged (-Ve). When these clouds come in contact with tall towers or tall buildings on the ground, the object generates the opposite kind of charge (induced).
The air is moist during monsoons. Therefore, when a charged cloud comes close to this high point, a spark starts, which is called lightning or lightning.
Sparks are formed when the clouds charged by money and krana come close to each other. This is what we call lightning in the sky.
How does Lightning from the sky come directly to the power substation?
Due to the increasing power generation and distribution of electricity day by day, where there is a network of wires, high towers and power lines are at high risk due to lightning falling from the sky.
When electricity falls on a conductor line, a high voltage is generated in the line (the voltage of lightning falling from the sky can range from 10,000 volts to 400,000 volts) and it flows on both sides of the line and eventually reaches the ultra high voltage sub station.
Which of the following devices in a power substation can be damaged by lightning in the sky?
Extremely high voltage waves can damage the following electrical equipment and devices in a power substation.
- Transmission line insulator strings
- CTPT in the Sub Station Equipment
- Bushing of circuit breaker
- Power transformer bushings
- HTV LT of Power Transformer Widing coils
- Isolators and busbars
How is the equipment in the power substation protected from the ultra high voltage waves of electricity in the sky?
The equipment at the substation can be solar-protected from lightning in the sky using the following devices.
- Arcing horns
- Power resistor
- Lightning Arrester
The Arcing horns, Tower Line Insulators Strings, C.T. PTs, circuit breakers and transformer bushings etc. are fitted. The gap between the two Arcing horns is kept in such a way that no current flows through the gap when there is a normal rated voltage.
But when a higher voltage than normal rated voltage is generated on the line, this high voltage current (through the horn gap) goes to the ground (to some extent).
If the voltage increases 5 to 10 times of the normal voltage, a spark will appear in the horn gap. Since the other end of the horn gap is connected to the ground, the excess pressure goes to the ground and does not affect the insulators of the bushings.
The same type of electric rectifier is installed in the sub station as the punch metal electrical rectifier is installed on a tall building. There are two benefits to this remedy. One is that the power falling on the building or sub station goes to the ground through the resistor. So the substation is not in danger. The second is that the opposite type of charge is generated in the atmosphere or a static charge is discharged.
In the sub station, the upper ends of all the gutters and towers are connected to each other by earth wire and a kind of earth wire is attached to the substation. It is used as a shield. Hence it is called Earth Shield. The earth shield has to be strong and the earth resistance must not exceed 2 ohms.
Lighting arresters can also be installed to protect the equipment from lightning strikes. There are three types of lightning arresters.
- Station type
- Line type
- Distribution type.
These types are categorized according to the lightning arrester’s current carrying capacity.
The + ve and -ve charges generated in the atmosphere generate electricity and affect the substations and conductors. There are two types of electricity.
- Direct stroke
- Indirect strokes
They use overhead earthing shields as well as overhead spikes or lightning rods to protect the substation from direct strokes.
But lightning arresters are also installed on the line and in the substation to protect the sun from the “traveling waves” created on your line by indirect strokes and lightning, also known as surge dividers.
There are three types of lightning arresters according to the method used. They are as follows.
|Types of Lightning Arresters||Capacity In Ampere|
|Substation type||5000 to 10,000|
|Line type||2500 to 5000|
|Distribution type||500 to 2500|
Lightning affects the sub station the most intensely. So lightning arresters are installed in the substation with the capacity to carry more current. It is followed by the number of transmission lines and the lowest result is L. T. Distribution occurs on lines.
Therefore, lightning arresters of distribution type have the lowest carrying capacity. Once the sub station type lightning arrester is used on the line it is fine but it should always be kept in mind that the line type lightning arrester should not be installed in the sub stations.
How is a lightning arrester designed? | How does a lightning arrester work?
It has a porcelain vertical insulator. It has a metal cap on the top and bottom and is tightly fitted to prevent water from entering. A nutbolt is attached to connect the upper phase wire and another nutbolt is attached to the lower side to connect the earth wire.
The phase wire and earth wire are to be tightened by filling the logs. Care is taken to ensure that there is no loose connection in both the places. Insulators have electrodes inside and air gaps as shown in the figure. The lower electrode and nut bolt are fitted with Metrosil or Thyrite metal powder pads.
This metal is a kind of high resistance. The characteristic of this metal is that as the electric pressure increases, its resistance decreases sharply, so when it is in normal condition, it acts as a resistor and when the electric pressure increases (above a certain level), it acts as a conductor.
This lightning arrester is also called an autovalve because this action happens automatically. The metrosil / thyrite metal in it acts like a valve. High voltage causes the air in the air gap to ionize and the current flows to the thyroid metal. It reduces the resistance of the metal and makes it a good conductor.
And most of the current generated by lightning goes to the ground. But when the voltage returns to normal, the same non-linear metal becomes a good resistor and blocks the flow of electricity. In this way the lightning arrester is used to protect the electrical substation equipment from the lightning in the sky.