6
VIII. Packing List of Instrument:
1. Host
1
2. Voltage signal sampling line
1
3. Current signal sampling line
1
4. Power line
1
5. Fuse
2
6. Special protector
1
7. Operating manual
1
8. Product certificate
1
Appendix:
I. Main Problems of Metal Oxide Arrester in Operation
1. As the series gap of the the metal oxide arrester is eliminated, the metal oxide arrester
withstands the system voltage for a long time, and the current flows through it. The active
component valve disc in the current heats to cause the change to volt-ampere characteristics.
After long-term action, the valve disc will be aged, even thermally broken down.
2. If the metal oxide arrester is used under the surge voltage, the valve disc will be aged under
the action of surge voltage energy.
3. If the inside of the metal oxide arrester is affected with damp or its insulation performance
is poor, the power current and the power consumption will be increased, and the internal
discharge will be caused in severe case.
4. If the metal oxide arrester is polluted by rain, snow, condensation or dust, the radial
discharge will be caused by the large potential difference between the internal valve disc and the
external insulator due to the distribution difference of internal and external voltages.
II. Tasks Completed by the Instrument
To judge whether the valve disc of the metal oxide arrester is aged or affected with damp,
usually observe the change of resistive leakage current flowing through the zinc oxide valve disc in
the normal operation, i.e., observe whether the resistive current is increased as the judgment
basis.
III. Main Failures of the Instrument
1. The metal oxide arrester has thermal breakdown
The final reason for the thermal breakdown of the metal oxide arrester is that its heating
power is larger than the heat dissipation power. The heating power of the zinc oxide valve disc
depends on its current and voltage (the current is the active component of the current flowing
through the valve disc).
2. The metal oxide arrester is internally affected with damp
Untight sealing will cause the arrester to be internally affected with damp, or internal water
immersion in the installation will also cause the total current of the arrester to be increased under
the voltage. If the arrester is affected with damp to a certain degree, the discharge will occur along
the surface of the zinc oxide valve disc or the inner wall surface of the insulator to cause the
explosion of arrester.
The increase of total current caused by the damp of metal oxide arrester results from the
increase of resistive leakage current. Whether the arrester is affected with damp can be judged by
detecting the amplitude of angle variation.
To sum up, the above failures can be reflected by the change of resistive leakage current. If
