Blackout: Reasons, Causes, and Sequence



Blackout known as cascade tripping. It is nothing but a power outage means the loss of the electrical power supply. This loss of power can apply to a part of the system or to the entire power system.

In an interconnected power system, all the power station connected. A blackout is a failure of interconnected parts in which this can trigger the failure of successive parts.

When one of the parts of the system is failing and shifts its load to a nearby part of the system. That nearby part operated beyond their capacity. so, this part becomes overloaded and shifts their load to another part to set off more overload and in this way, the entire system is taking down in a very short time.

Reasons for Blackout

There are several reason to cause a black in power system network.

  1. The power plant shuts down due to any reason.
  2. Due to an increase in the current of the transmission line, it will produce high thermal energy and it will heat up. In the worst condition, the conductor fails.
  3. Natural calamities
  4. When a part of the system is overstressed

Causes of Blackout

The blackout in power system is causes due to

  1. Thermal overload
  2. Voltage instability
  3. Imbalance in power generation and power demand
  4. Dynamic instability

Sequence of Blackout

The blackout causes in following sequence.

  • Initiating events
  • System separation
  • Formation of island
  • Load/generation imbalance on the island
  • Blackout to island
  • Restoration process

Types of Blackout

  1. Localized blackout
  2. Partial system blackout
  3. Full system blackout

Black Start

Black start is a process of restoring power plants to operate without relying on external energy sources.

In case of a blackout, all generating stations are shut down and power cannot flow to the grid. In this situation, a black start needs to be performed.

For a black start, some of the power plants need diesel generators which can be used to start larger generators. These diesel generators have capacity up to the startup power. The power required for the startup the auxiliaries while the generating unit is restored is called startup power.

In a thermal power plant. the startup power needed to operate auxiliaries like FD fan, cooling water pump, ID fan, etc. In the hydropower plant, the startup power not requires, it needs only a flow of water to start the plant.

A hydroelectric plant needs a very small initial power to start and can produce power very quickly. These plants are used to start the thermal power plants.

Black Start Sequence

The sequence to start system after blackout is as follows;

  1. A small generator installed at a hydroelectric plant starts with the help of a battery bank.
  2. The power of the diesel generator used to operate the hydroelectric plant.
  3. Power of the hydroelectric plant transmitted to other power station by the transmission line.
  4. The power of the baseload plant used to restart all of the other power plants in the system.
  5. Power supplied to the distribution system and sent to the consumer.

Limitation of Black Start

  • All power plants are not suitable for black start capability. i.e. a wind power plant.

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