**1. Introduction to Zinc Oxide Arrester**
Zinc oxide arresters are advanced protective devices developed in the 1970s, designed to safeguard electrical equipment from overvoltage events such as lightning strikes and switching surges. These arresters primarily consist of zinc oxide varistors, which exhibit non-linear voltage-current characteristics. Under normal operating conditions, when the voltage is below the varistor's threshold, the device behaves like an insulator with high resistance. However, during overvoltage situations—such as lightning strikes—the varistor rapidly conducts, allowing large currents to flow to ground and limiting the voltage to a safe level. Once the overvoltage subsides, the varistor returns to its high-resistance state, ensuring the system continues to operate normally. This makes zinc oxide arresters highly effective in protecting power systems and connected equipment from damage caused by transient voltages.
**2. Seven Key Characteristics of Zinc Oxide Arresters**
1. **Current Handling Capacity**: These arresters can absorb various types of overvoltages, including lightning, power frequency transients, and operational surges.
2. **Protection Performance**: Due to their excellent non-linear V-I characteristics, they allow only a small leakage current under normal conditions, making them ideal for gapless designs. When overvoltage occurs, they quickly conduct, limit the voltage, and then return to a high-resistance state.
3. **Sealing Performance**: High-quality composite jackets ensure long-term reliability and protection against environmental factors. Sealing measures like compression rings and sealants enhance performance.
4. **Mechanical Strength**: Designed to withstand seismic forces, wind pressure, and tensile loads, ensuring stability in different environments.
5. **Pollution Resistance**: They are resistant to contamination and have a high creepage distance, meeting national standards for different pollution levels.
6. **Operational Reliability**: Long-term reliability depends on product quality, proper design, and sealing. High-quality valve discs and robust structures contribute to stable operation.
7. **Power Frequency Withstand Capability**: They can handle temporary overvoltages caused by system faults or load changes without failure.
**3. Working Principle of Zinc Oxide Arrester**
At rated voltage, the current through the zinc oxide valve is minimal, behaving like an insulator. When the applied voltage exceeds the threshold, the valve conducts, allowing large currents to be discharged to ground. The residual voltage remains below the equipment’s withstand level, ensuring protection. Once the overvoltage disappears, the valve returns to a high-resistance state, restoring normal operation. This rapid response and recovery make zinc oxide arresters highly efficient in voltage regulation and protection.
**4. Technical Parameters of Zinc Oxide Surge Arresters**
- **Rated Voltage**: The maximum power frequency voltage the arrester can withstand during normal operation.
- **Maximum Continuous Operating Voltage (MCOV)**: The highest voltage that can be continuously applied without degradation.
- **Reference Voltage**: The voltage at which a specific current flows through the arrester, used to evaluate performance.
- **Residual Voltage**: The voltage across the arrester during discharge, indicating its ability to limit overvoltage.
- **Pressure Ratio**: The ratio of residual voltage at high current to that at low current. A lower ratio indicates better protection performance.
The primary function of a zinc oxide arrester is to provide a path for lightning currents to reach the ground, thereby preventing direct lightning strikes on protected equipment. It creates an electric field that attracts the lightning discharge toward itself, safely diverting the current through grounding systems.
**5. Role of Zinc Oxide Arrester**
Zinc oxide arresters act as intelligent protectors in power systems. At normal voltages, they remain inactive, acting like insulators. During overvoltage events, they activate to divert dangerous currents to ground, protecting equipment and infrastructure. Their non-linear behavior ensures quick response and minimal impact on the system, making them essential components in modern electrical networks.
**6. Meaning of Zinc Oxide Arrester Models**
- **H** – Composite jacket
- **Y** – Zinc oxide arrester
- **5** – Nominal discharge current (in kA)
- **W** – No gap
- **Z/X/S/D/R/L** – Type (power station, line, distribution, motor, capacitor, explosion-proof)
- **90** – Rated voltage (in kV)
- **220** – Residual voltage (in kV) at nominal discharge current
For example, **HY5WR-17/46** means a zinc oxide arrester with a rated voltage of 17 kV, a residual voltage of 46 kV, and a nominal discharge current of 5 kA.
**7. Installation of Zinc Oxide Lightning Rods**
- **On Chimneys**: Install 1–3 rods depending on chimney height. Add disconnect clips at 1–8 m above ground and use angle steel for protection.
- **On Buildings**: Follow standard installation guidelines for roof and wall-mounted rods. Ensure all components are properly secured.
- **On Metal Containers**: Mount rods on the top and walls according to safety standards.
- **Independent Lightning Rods**: Two types are available—standard and reinforced concrete ring rods. Heights vary, and proper foundation preparation is essential to prevent soil disturbance and water ingress.
These installation practices ensure effective protection against lightning strikes, enhancing the safety and longevity of electrical and structural systems.
Cold Shrink Tube
Cold shrinkable cable accessories are made of elastomer materials (commonly used silicone rubber and ethylene-propylene rubber) injected and vulcanised in the factory, and then expanded and lined with plastic spiral supports to form various components of cable accessories. Field installation, these pre-expanded parts in the treated cable ends or joints, pull out the internal support of the plastic spiral strip (support), pressed on the cable insulation and the composition of the cable accessories. Because it is at room temperature by elastic retraction force, rather than like heat shrinkable cable accessories to be heated by fire shrinkage, so commonly known as cold shrinkable cable accessories. Early cold shrink cable termination head just additional insulation using silicone rubber cold shrink parts, electric field processing is still using stress cone type or stress band wrapping type.
Universal use of cold shrinkage stress control tube, voltage level from 10kv to 35kv. cold shrink cable joints, 1kv level using cold shrink insulation tube as reinforced insulation, 10kv level with internal and external semi-conductive shielding layer of the joints cold shrink insulation parts. Three-core cable terminal bifurcation using cold shrink branch sleeve.
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