Engineers who have just started testing lightning arresters often don't understand why it takes so much effort to separate the "resistive current" from the "full current" - isn't the full current already the current flowing through the lightning arrester? Can't we just look at the full current? This question is well posed, and the underlying principles are worth clarifying.

Composition of full current

The leakage current (full current Ix) flowing through a zinc oxide lightning arrester is not a simple quantity, but is composed of two components with completely different properties superimposed:

Capacitive current: Zinc oxide lightning arrester is equivalent to a capacitor, which will inevitably generate capacitive current when an AC voltage is applied. This component leads the voltage by 90 ° in phase and is almost unrelated to the insulation aging state of the lightning arrester. It mainly depends on the geometric structure (capacitance) of the lightning arrester and is the "normal background current".

Resistive current: In phase with (or close to in phase with) the voltage, it is the component generated by the actual consumption of electrical energy by the valve plate. When the valve plate ages or becomes damp, the resistive component increases; When the valve plate is in good condition, the resistive component is extremely small (usually only about 10% to 20% of the total current).

Why can't we just look at the full current

The full current of a normal lightning arrester is mainly composed of capacitive current, with resistive current accounting for only a small portion. Even though the lightning arrester valve plate has significantly deteriorated and the resistive current has increased by 50%, due to its already small proportion in the total current, the change in the total current may only be a few percentage points, making it difficult to judge from the absolute value change of the total current.

Resistive current is the sensitive indicator

After separating the resistive current from the full current and comparing it with historical reference values, the sensitivity is significantly improved. A 50% increase in resistive current is a very obvious signal that needs to be taken seriously; And the same degree of degradation is only reflected as a few percentage points of change in the total current, which is easily overlooked.

The HZ-20A adopts advanced Fourier harmonic analysis technology to accurately measure the phase relationship between voltage and current, separate the two components accurately, and output VNet (peak resistance current), Ir1p (peak resistance current fundamental wave), and 3rd, 5th, and 7th harmonic components, providing complete lightning arrester state evaluation data.