Writer: Amirhosein Taheri
An insulator is a device used for separating or enclosing conductors and must possess acceptable electrical and mechanical resistance properties. Essentially, an insulator can be described as a path with very high resistance that does not allow the flow of current.
In general, an insulator should exhibit the following characteristics:
• Maximum mechanical strength
• Ability to withstand maximum rated voltage and prevent electrical breakdown (internal breakdown and creepage)
• Stability against temperature variations
• Capacity to bear the weight of conductors
• Resistance to moisture and water infiltration
• Absence of cracks or bubbles within the insulator’s structure (no bubbles should be present if the insulator is cut).
Types of insulators include:
1. Aerial Insulators: Used as insulating barriers between conductors and poles or transmission lines.
2. Panel Insulators: Employed to hold busbars and act as insulators between the busbars and the panel body.
Types of aerial insulators include:
• Pin-type Insulators: Used in distribution lines with voltage levels of 11, 20, and 33 kilovolts.
• Suspension Insulators: Due to the impracticality of using pin-type insulators in lines with voltages exceeding 50 kV, suspension insulators are used in high voltage distribution lines.
• Disc Insulators: These insulators have greater mechanical durability compared to suspension insulators and are used at the beginning and end of distribution lines where the path becomes horizontal.
• Stay Insulators: These are utilized at the start and end of a line and are made of steel wire. One end is connected to a plate and a steel rod buried two meters deep in the ground, while the other end is attached to the base or tower. A stay insulator is also used in the middle of the stay wire to neutralize the tensile force. The structure is designed so that even if the insulator is broken, the stay wire will not be released.
• Cylindrical Insulators: These are one-piece cylindrical insulators made from materials with high electrical resistance, and water does not spread on their surface. Generally, these types of insulators are lighter than disc insulators and are more cost-effective. However, if damaged, the entire insulator is affected. In contrast, in disc insulators, only the broken part is affected, and no disruption occurs.
• Rotating Insulators: Used in low-pressure lines, they serve as tension insulators and are fastened to the supports of aerial distribution lines.
Panel Insulators:
Panel insulators are employed as insulating barriers between busbars and the panel body. Different standards are defined for the production of panel insulators, and these standards must be met based on the specific characteristics of the insulators’ structure. Test reports are provided by laboratories to manufacturers as part of quality control.
Types of panel insulators include:
• LV (Low Voltage) Insulators: Used in low-voltage (LV) fixed and withdrawable panel boards.
• MV (Medium Voltage) Insulators: Used in medium-voltage (MV) panel boards, switchgear, circuit breakers, and more.
The materials used for making insulators are often composed of resins like BMC, epoxy resin, and SMC, which have suitable mechanical and electrical properties.
• BMC Composites: Essentially, BMC is a formulation of composite fibers, glass fibers, and other materials that are combined with resin, then hardened under pressure and heat to create a polymeric structure. It is used in various low and medium voltage insulators, busbar supports, streetlight internal frames, and automotive components, among other applications.
• SMC Composites: SMC is similar to BMC but has different compositions and mixing times for materials, along with some distinct elements. Its applications are almost identical to BMC.
• Epoxy Resin Composites: Epoxy resin composites are made up of two primary components: resin bases and hardeners (either non-solvent polyamine or solvent polyamide hardeners). These materials are injected into molds, and they are used in low-pressure and medium-pressure insulators, resin tabletops, resin jewelry, and more.
Types of LV Insulators:
• Bolted Insulators
• Cylindrical Insulators
• U-shaped or Grooved Insulators
• Step Insulators
• Busbar Supports
LV insulators are used in fixed and withdrawable low-voltage (LV) panel boards, and in some specific cases, in racks and data centers.
Types of MV Insulators:
• Capacitor Insulators
• Standard or Cylindrical Insulators
MV insulators find applications in medium-voltage (MV) panel boards, switchgear, circuit breakers, disconnector switches, and more.
