A 20 kV disconnecting switch—also called an isolator—is a key safety device in medium-voltage power systems. Its main job is to make a physical break in the circuit during maintenance. This break is a visible air gap over 150mm wide, helping workers check the circuit has no power.

The switch also stops the circuit from getting power by accident. It uses mechanical or electrical links to circuit breakers, and these links follow the “five prevention” rules. One rule, for example, stops it from switching loads.

Remember: this switch can’t stop electric arcs. So never use it to switch loads. When you use it, follow this order: the circuit breaker opens first, then you use the isolator—only after the current hits zero.

For structural design, the contact system has main contacts with silver-plated surfaces. The silver layer is at least 20 μm thick, and surface hardness is at least 120 HV. This coating keeps resistance low and stops oxidation. Finger contacts use spring pressure for stable point contact.

Insulation: air is the usual type, but some switches use SF₆ gas for polluted areas. The switch’s dielectric strength must handle 42 kV for 1 minute, following GB/T 1985.

Hollow insulators are basic parts in many places. In Gas Insulated Switchgear (GIS), they make the grounded cases. They also keep different phases and sections insulated from each other. In dead tank circuit breakers, they hold the interrupter units and contain the insulating gas. For surge arresters, they hold the active parts inside. In instrument transformers (current and voltage types), they separate the primary conductor and act as the insulating cover. For bushings, they guide high-voltage conductors through grounded walls or tanks—like those on transformers, circuit breakers, and capacitors. In disconnectors and earthing switches, they support moving contacts and provide insulation. They are also used in Capacitor Voltage Transformers (CVTs).

Lightning arresters, or surge arresters, protect electrical equipment from harmful voltage surges. These surges come from lightning or switching operations. Knowing their key parts helps in choosing, using, and maintaining them right. Modern high-voltage arresters use Zinc Oxide (ZnO) technology. They have several basic components.

The Metal Oxide Varistor (MOV) Blocks are the core. These are ceramic blocks made mainly of zinc oxide grains. They also have small amounts of other metal oxides like Bi2O3, Sb2O3, CoO, MnO. Their voltage and current relationship is highly nonlinear. At normal system voltage, they have high resistance. Only a tiny current, in microamps, leaks through. When a surge above their reference voltage hits, their resistance drops fast—within nanoseconds. This lets the big surge current go safely to the ground. Once the surge ends, they quickly go back to high resistance. This stops power from flowing through. To get the right voltage rating and energy handling, these blocks are stacked in series or parallel inside the housing.

The Housing, or Enclosure, has many roles. It supports the arrester mechanically. It protects the inside from moisture, pollution, and UV rays. It also insulates the internal MOV column. Different materials are used. Porcelain is traditional. It is strong. Its hydrophobic glazing helps with pollution. But it is heavier and more likely to break than polymer. Polymer, like Silicone Rubber or EPDM, is getting more popular. It repels water well. It is lighter. It can take more impact without shattering. It works better in dirty places. The housing has sheds, which are ribs. These increase the creepage distance, improving pollution handling.

A 150 kV disconnecting switch—also called an isolation switch—is a basic safety device in high-voltage electrical networks. Its main job is to make a clear, physical gap in circuits that have no power. This gap keeps things safe when people do maintenance or repairs. It can’t stop electric arcs, though. You have to use it only after the upstream circuit breakers have turned off the load current in the circuit.

Visible isolation is a big part of how it works. It gives a clear visual sign that the circuit is disconnected. This is more important for safety than just using electrical indicators. The switch has a contact setup with two breaks per phase. These two gaps in a row make the dielectric strength much better than switches with just one break. That’s good for reliability at 150 kV.

It uses strong motorized drives—usually brushless DC motors—to move. These drives have closed-loop control for position and speed. This precise control stops the switch from being only partly engaged, which would be unsafe. It also makes sure the switch works the same way no matter the environment. For insulation, it uses high-strength polymer composite or porcelain insulators. These are made specifically to handle 150 kV, including the system voltage and sudden high-voltage spikes.

Electrical integrity is key for safety and performance. The switch is built to handle standard power frequency voltages—like 275 kV AC—and lightning impulse voltages, such as 650 kV BIL, following IEC 62271-102. It keeps its insulation working even when there’s a transient recovery voltage (TRV).

Composite insulators, also called polymer or non-ceramic insulators (NCIs), are a big step forward in high-voltage electrical insulation. They have two main parts. One is a strong fiberglass-reinforced polymer (FRP) core rod that holds weight. The other is an outer cover with polymeric weather sheds. These sheds are usually made from silicone rubber (SIR), ethylene propylene diene monomer (EPDM), or cycloaliphatic epoxy (CEP).

The FRP core is key here. It has great tensile strength. That means it can handle mechanical loads—like the weight of conductors, wind, and ice. It also has high dielectric strength. Unlike brittle materials, it doesn’t break easily. And it’s much lighter—about 80-90% lighter than similar porcelain or glass insulators. This light weight makes it more durable and easier to install.

The outer cover, mostly made of silicone rubber, has important features too. Silicone rubber naturally keeps water away. That stops a uniform conductive water film from forming on the surface. Even after pollution, this water-repelling property often comes back. It can even transfer to pollutants. This is a big deal. It cuts down on leakage currents a lot. It also stops pollution flashover—a common problem for ceramic insulators in dirty or coastal areas.

Being lightweight helps in other ways. It makes handling, transporting, and installing the insulators simpler. That lowers costs for labor and structural support. Composites are tough against impacts and vandalism too. Unlike brittle ceramics, they don’t shatter if shot or hit. This makes the power grid more resilient.

They work well in polluted places. The water-repelling feature, along with good leakage distance designs, lets them operate reliably in heavy industrial areas, deserts, or coastal regions. Good manufacturing is important here. It ensures a tight seal between the core and the cover. That keeps moisture out and prevents core corrosion—something that could make them fail.

Composite pin insulators play a key role in modern overhead power lines. They take the place of old porcelain units with advanced polymer designs. They work better in harsh environments. They also cut down on maintenance costs.

These insulators have three connected layers. The fiberglass epoxy rod is the core that bears the load. It has a tensile strength over 100 kN. It resists breaking suddenly. The silicone rubber housing acts as a weather-resistant cover. It repels water, which helps it shed dirt and grime. The metal end fittings are forged steel caps. They are crimped to the rod with more than 120 tons of pressure. They are sealed to keep moisture from getting in.

They have several big performance advantages. They are light—only 2–4 kg. Porcelain ones weigh 8–12 kg. This light weight cuts installation time by 40%. It also means the poles do not need to be as strong. They handle pollution well. In coastal or salt-fog areas, they keep a Basic Impulse Level over 150 kV. That is twice what porcelain can do. They stand up to vandalism. The elastic housing can take gunshot impacts. It passes IEC 62217 ballistic tests. They help stop flashovers. Their ability to repel water keeps leakage current below 5 mA at 15 kV, even when very dirty.

They have standard voltage ratings. For distribution, these are 15–36 kV. They follow ANSI 55-5 and 55-6. They can handle strong mechanical loads—at least 12,000 lb. They meet ANSI Class 55-5 minimum failing load. The creepage distance is 432–890 mm. It depends on the pollution level, following IEC 60815. They work in a wide range of temperatures—from -50°C to +80°C. They do not get brittle.

A fuse cutout—also called a fused cutout or drop-out fuse—is a key protective device on overhead power lines. When it’s in the “open” state, it intentionally disconnects the part of the circuit with a fault. This stops equipment from getting damaged and keeps the grid stable.

Disconnecting switches (isolators) serve as critical safety components in 115 kV substations and transmission networks. These devices provide visible circuit isolation for maintenance, system reconfiguration, and grounding operations. Unlike circuit breakers, disconnecting switches do not interrupt load current or fault current.

Composite tension insulators—often called composite strain insulators—are key in overhead transmission lines. Engineers fit them to strain towers, such as dead-end or angle structures, because they must handle high pulling forces.  

They replace older porcelain or glass insulators. Made by combining a fiber-reinforced polymer (FRP) core, a silicone rubber cover, and metal end pieces, this design gives them strong mechanical strength and good electrical performance. It works especially well in tough environments.