WAZIPOINT Engineering Science & Technology: Electrical Substation Equipment: Disconnector and Its Functions

Friday, July 21, 2023

Electrical Substation Equipment: Disconnector and Its Functions

In an electrical substation, a disconnector, also known as an isolator or disconnect switch, is a vital piece of equipment used to disconnect or isolate sections of an electrical circuit or equipment from the power source. Unlike circuit breakers, disconnectors do not provide protection against overcurrent or short circuits. Instead, they serve specific functions related to the safe operation, maintenance, and isolation of electrical components within the substation.

Why Disconnectors are Used in Electrical Substations?

Here are the main functions of a disconnector in an electrical substation:

Isolation of Equipment: One of the primary functions of a disconnector is to physically isolate a particular section of an electrical circuit or a specific piece of equipment, such as transformers, circuit breakers, or busbars. This isolation is essential for the maintenance, repair, or replacement of the isolated component without affecting the rest of the electrical system.

Safety During Maintenance: Before any maintenance work can be performed on electrical equipment, it must be de-energized to protect personnel from electric shocks. Disconnectors allow operators to open the circuit and isolate the equipment, ensuring a safe work environment.

Visual Verification of Isolation: Disconnectors often have visible blades or contacts, allowing operators to visually verify that the circuit or equipment is indeed isolated before any work is carried out. This visual indication helps prevent accidental contact with live parts.

Emergency Shutdown: In case of emergencies or abnormal operating conditions, disconnectors provide a means of quickly and effectively shutting down sections of the electrical system, preventing further damage or hazards.

Testing and Commissioning: During the testing and commissioning phase of a substation, disconnectors are used to isolate specific components to assess their functionality and verify proper integration into the overall system.

Busbar Transfer and Sectionalizing: In some substation configurations, disconnectors are used for busbar transfer or sectionalizing, allowing for flexibility in the substation's operation and maintenance.

Load Shedding and Reconfiguration: Disconnectors can be employed as part of a load-shedding strategy to shed non-essential loads during peak demand or emergency situations. They can also facilitate reconfiguration of the electrical network to restore power to critical areas.

It's important to note that disconnectors should only be operated by trained and authorized personnel, and proper safety procedures must be followed during their use. Additionally, disconnectors are often interlocked with other protective devices in the substation, such as circuit breakers, to ensure safe and coordinated operation during isolation and re-energization processes.

Types of Disconnectors Used in Electrical Substations

Disconnectors, also known as isolators or disconnect switches, are essential components in electrical substations. They are used to physically isolate or disconnect sections of the electrical network for maintenance, repair, or safety purposes. Disconnectors are not designed to break the load current, but they provide visible isolation points to ensure personnel safety during maintenance activities. There are several types of disconnectors used in electrical substations, each with specific applications and characteristics. Here are the main types:

  1. Vertical Break Disconnector: This type of disconnector consists of two vertical insulating columns supporting a moving blade in the center. When the blade is lowered, it makes contact with fixed contacts at the base. When raised, it isolates the circuit by creating a gap between the moving blade and the fixed contacts. Vertical break disconnectors are commonly used in medium voltage applications.
  2. Horizontal Break Disconnector: In a horizontal break disconnector, the moving blade moves horizontally to create or break the circuit. It is supported by insulators mounted on a horizontal axis. Horizontal break disconnectors are frequently used in high-voltage applications and are suitable for outdoor installations.
  3. Pantograph Disconnector: Pantograph disconnectors consist of a horizontally mounted moving arm with a sliding contact. The arm can be extended or retracted to create or break the circuit. This design allows for a more compact solution compared to traditional horizontal break disconnectors. Pantograph disconnectors are often used in substations with space constraints.
  4. Center Break Disconnector: Center break disconnectors have a rotating blade that moves around a central pivot. When the blade is in the closed position, it bridges the contact gap. By rotating the blade, the circuit can be disconnected. Center break disconnectors are suitable for both indoor and outdoor substations.
  5. Double Break Disconnector: Double break disconnectors consist of two sets of contacts that open and close simultaneously, providing redundancy and increased safety during operation. They are commonly used in extra high voltage (EHV) substations and critical installations where reliability is paramount.
  6. Pantograph Side Break Disconnector: This type combines the features of a pantograph and a side break disconnector, providing a compact design and flexibility in installation. The moving blade moves both horizontally and vertically, allowing for effective disconnection of the circuit.
  7. Knife Switch Disconnector: Although not as common in modern electrical substations, knife switches were historically used as disconnectors. They consist of a pivoting knife-like blade that makes or breaks the circuit by rotating around a hinge.

It's important to select the appropriate type of disconnector based on the specific requirements of the electrical substation, including voltage levels, operating conditions, and available space. Regular maintenance and inspection of disconnectors are essential to ensure their reliable operation and to guarantee the safety of maintenance personnel.

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