Ingredients of zinc oxide arrester
The core of the zinc oxide arrester is composed of zinc oxide valve plates.
The valve plate is made of zinc oxide (ZnO) and a small amount of other oxides that are fully mixed, ground and stirred, sprayed, granulated, pressed and then fired at high temperature.
Microstructure: ZnO grains (diameter about 10μm) are low-resistivity media, and their surface layer, the grain boundary area (0.1um thick), is high-resistivity. The two are closely connected.
Working principle: low electric field area, medium electric field area and high electric field area (tunnel effect) to achieve nonlinear characteristics.
Volt-ampere characteristics of zinc oxide arrester
The typical volt-ampere characteristics of zinc oxide arrester valves are as follows, which are generally divided into small current area, voltage-limiting working area and overload area.
The normal operation is in the small current area, the voltage limiting area is used as a buffer area, and the protection range is in the overload area. For example, the actual working voltage of a 10KV zinc oxide arrester is 10kV, while the continuous working voltage of the nameplate is 12~17kV, and the protection voltage is above 25kV.
The role of lightning arrester
Lightning arresters are used to absorb operating overvoltages and atmospheric overvoltages in the power grid
●At normal voltage: the arrester is in a high resistance state and there is basically no current.
When overvoltage arrives: the arrester is turned on, and the passing current reaches the kiloamp level, releasing high-voltage energy, limiting excessive voltage, and maintaining a certain voltage to ground.
●After the overvoltage disappears: the arrester can automatically return to the high resistance state.
Basic parameters
Rated voltage: The maximum effective value of T-frequency voltage allowed to be applied to both ends of the arrester. It indicates the arrester's ability to withstand temporary overvoltage.
Continuous operating voltage: The effective value of the power frequency voltage allowed to be continuously applied to both ends of the arrester for a long time.
Nominal discharge current: lightning current unit KA passed under 8/20 standard waveform
Reference voltage: The effective value of the voltage across the arrester under the specified reference current.
Power frequency reference voltage: should not be lower than the rated voltage of the arrester. Arresters of 35kV and above need to be measured.
DC reference voltage: does not reflect the characteristics of the AC arrester, but is only for convenience of on-site detection. Typically DC voltage at 1mA.
0.75U1mA: Leakage current at 0.75 times the DC reference voltage. Used to measure whether the arrester automatically cuts off after the voltage drops.
Residual voltage: the voltage across the arrester when it passes the nominal discharge current.
Operating conditions
●1. Ambient temperature: within the range of -40°C~+40°C.
●2. The altitude does not exceed 1000m
●3. The alternating current frequency is not less than 48Hz and not more than 62Hz
●4. The power frequency voltage applied between the arrester terminals for a long time should not exceed the continuous operating voltage of the arrester.
●5. Wind speed is less than 35m/s
●6. Areas with earthquake intensity level seven and below.
●7. Vertical installation.
