Protection System and its Attributes

INTRODUCTION : Protection System and its Attributes

The Electrical power system was always considered to be a natural monopoly.The industry is being deregulated.In this scenario,big electric utility companies are no longer monopolizing the generation of electric power.The field is open for smaller players.The consumers have a choice to buy electricity from cheapper bidder.

A Protection System

cb

The electrical substation is a network of electrical equipment that is connected in a structured way to  incoming and outgoing circuits, each of which has circuit breakers, isolators, transformers and bus system, etc. for the correct functioning of the system. The power supply system has numerous ingredients, such as distribution, transmission and generation systems, and the substations act as the necessary ingredient for the power system’s operations. Substations are entities from which consumers obtain their electricity supply to manage their loads, while the required energy quality can be provided to customers by changing the frequency and voltage levels, etc.

The designs of the electrical substations depend exclusively on the need, for example, of a single bus or a complex bus system, etc. In addition, the design also depends on the application, e.g. internal substations, generation substations, transmission substations, polar substations, external substation, converter substation and switching substation, etc. A collector substation is also required for large power generation systems, e.g. e.g. several thermal and hydroelectric plants connected together to transfer energy to a single transmission unit from numerous turbines placed together

Objective of Power System Protection

The objective of power system protection is to isolate a faulty section of electrical power system from rest of the live system so that the rest portion can function satisfactorily without any severe damage due to fault current.

Isolators:

Substation insulators are mechanical switches that are implemented for circuit isolation in the event of a power failure. These are also known as the operation of disconnected switches in the absence of load and are not fortified with arc extinguishing devices. These switches do not have a specific power failure value nor do they have a socket value. These are mechanically operated switches.

Bus bar:

The busbar is among the most important elements of the substation and is a conductor that carries the current to a point that has numerous connections to it. The busbar is a type of electrical junction with both outgoing and incoming current paths. Whenever a busbar failure occurs, it is necessary to trip the entire components connected to that specific section to provide complete insulation in a short time, for example 60 ms to prevent the danger from increasing due to the heat of the conductor. These are of different types, such as the ring bus, the double bus and the single bus, etc. The following figure shows a simple busbar considered one of the most important components of the electrical substation.

The lightning rod:

Lightning rods can avoid as early components of a substation. These have the function of protecting the substation equipment from high voltages and are also limiting the amplitude and duration of the current flow. These are connected between earth and line, i.e. connected in line with the equipment in the substation. These are intended to deflect the ground current in the event of overvoltage, thus protecting the insulation and the conductor from damage. These are of various types and are distinguished by their obligations.

Circuit breakers:

Circuit breakers are those types of circuit breakers used to close or open circuits when a fault occurs within the system. The switch has 2 moving contacts which are in the OFF condition in normal situations. When a system failure occurs, a relay sends the triggered command to the switch that separates the contacts, thus avoiding any damage to the circuits

SF6 Circuit Breaker

In the SF6 breaker, the current carrying contacts operate on gaseous sulfur hexafluoride, known as the SF6 breaker. It is an excellent insulating property and high electro-negativity. It can be understood that, high affinity for absorption of free electrons. The negative ion is formed when a free electron collides with the SF6 gas molecule; it is absorbed by that gas molecule. The two different ways of bonding electrons with SF6 gas molecules are

SF6 + e = SF6

SF6 + e = SF5- + F

SF6 switch

The negative ions that are formed will be much heavier than a free electron. Therefore, compared to other common gases, the overall mobility of the charged particle in the SF6 gas is much lower. The mobility of charged particles is mainly responsible for driving the current through a gas. Therefore, for heavier and less mobile charged particles in the SF6 gas, it acquires a high dielectric rigidity. This good gas heat transfer property is due to the low viscosity of the gas. SF6 is 100 times more effective in arc extinguishing media than the automatic air switch. It is used for medium and high voltage power systems from 33KV to 800KV.

Types of SF6 switches

• Automatic switch SF6 switch applied up to 220

• SF6 switch with two switches applied up to 400

• SF6 switch with four switches applied up to 715 V.

A vacuum switch is a circuit used to extinguish the arc. It has a dielectric recovery character, excellent interruption and can interrupt the high frequency current resulting from the instability of the arc, superimposed on the line frequenc In the VCB operating principle you will have two contacts called electrodes which will remain closed under normal operating conditions. Suppose that when a fault occurs in any part of the system, the tripping coil of the switch is energized and finally the contact separates.

When the contacts of the circuit-breaker open in a vacuum, i.e. from 10-7 to 10-5 Torr, an arc occurs between the contacts ionizing the metallic vapors from the contacts. Here the arc quickly dies out, this is because the electrons, metal vapors and ions produced during the arc quickly condense on the surface of the CB contacts, resulting in rapid recovery of the dielectric strength.

benefit

• VCBs are reliable, compact and long lasting.

• They can interrupt any power failure.

• There will be no fire risk.

• No noise

• Has a higher dielectric strength.

• Requires less energy for checking operation.

Oil switch

Oil is used in this type of switch, but mineral oil is preferred. It works best by isolating the properties of the air. The moving contact and the fixed contact are immersed in the insulating oil. When the current separation occurs, the load-bearing contacts in the oil, the arc in the switch is initialized at the time of contact separation and, due to this arc in the oil, it vaporizes and decomposes into gaseous hydrogen and finally creates a hydrogen. bubble around the arch. current.

Bulk Oil Circuit Breaker (BOCB)

In the BOCB, the oil is used to arc the cooling fluid and also to isolate the fluid between the earth parts of the switch and the current transport contacts. The same insulating oil is used for transformers.

The operating principle of BOCB states that when the current transport contacts in the oil separate, an arc is generated between the separate contacts. The established arc will produce a rapidly growing gas bubble around the arc. The moving contacts will move away from the fixed arc contact and consequently the arc resistance will increase. Here increasing the resistance the temperature is lowered. Therefore, the reduced gas formations surround the arc.

When the current passes through zero, arc cooling occurs in the BOCB. In the fully airtight container, the gas bubble is enclosed within the oil. The oil will surround with high pressure in the bubble, this results in a highly compressed gas around the arc. As the pressure increases, the deionization of the gas also increases, resulting in arc cooling. Hydrogen gas will help cool the cooling arc in the oil circuit breaker.

advantage

• Good cooling property due to decomposition.

• The oil has a high dielectric resistance.

• It acts as an insulator between earth and living parts.

• The oil used here will absorb the arc energy as it breaks down.

Disadvantages

• It will not allow a high interruption speed.

• It takes a long arc time.

Minimum oil circuit breaker

It is a circuit breaker that uses oil as a means of interruption. The minimum oil circuit breaker will place the breaker unit in an isolating chamber at live potential. But the insulating material is available in the interrupting chamber. It requires less amount of oil, so it is called as minimum oil circuit breaker.

benefit

• Requires less maintenance.

• It is suitable for both automatic and manual operation.

• Requires a smaller space

• The cost of the breaking capacity in MVA is also lower.

disadvantages

• The oil deteriorates due to carbonization.

• There is a possibility of explosion and fire.

• Since it has a smaller quantity of oil, carbonization increases.

• It is very difficult to remove gases from the space between the contacts.

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