Electric conductivity is a measure of a fluid’s electrostatic chargeability. It normally is express in picosiemens every meter (pS/m). In enhancement to the kind of fluid, conductivity additionally depends ~ above the concentration of movable charge carriers. Because that example, pure distilled water is only slightly conductive. However, if the water includes impurities such as salts, mountain or bases, then its conductivity increases.

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Lubricants are typically only slightly conductive and therefore can work together insulators in transformers or switches. However, oil can additionally conduct electrical current. Their conductivity is dependency on several various factors, consisting of the basic oil, additives and polarity.

Oil Conductivity

The an ext polar a lubricant is, the much less refined and much more conductive the is. Based upon the manufacturing technique and level that refining, the American Petroleum academy (API) has classified base oils into five groups (see Table 1).


The lightly refined, mineral-oil-based base oil of group I stand for the easiest option and previously accounted for the biggest proportion that lubricant production. Over the last few years, that proportion has remained in steady decline, together the an ext refined base oils of teams II, III and IV are increasingly being used for contemporary lubricants.

This trend of using an ext refined base oils and also synthetic options is based on the reality that they generally have far better characteristics together as higher aging stability. However, when the higher-quality base oils have plenty of advantages, over there are involves over some of their adjusted properties, which can lead to problems, particularly when unfavorable combinations occur.

One such an effect is varnish, which can be because of the basic oil’s transformed dissolving performance through regard to aging and also reaction products. One more consideration is component and also lubricant damage, which have the right to be brought about by electrostatic discharges. The lubricant’s conductivity is an essential factor in the fee buildup, and also conductivity is dependence on the kind of basic oil used (see Table 2).

Table 2. Conductivity of oils and also synthetic fluids in ~ 23 degrees C (73 levels F)

Along through the basic oil, additives have actually a far-ranging effect on an oil’s conductivity. The greater the relationship of metal-organic additives, the greater the lubricant’s conductivity. A prime example would it is in metal-organic additive such as those commonly used in zinc dithiophosphate (ZnDTP). Together a proven multi-purpose additive in engine and also hydraulic oils, ZnDTP enhances wear and corrosion defense while all at once functioning as an antioxidant.

However, zinc is thought about to have dangerous wellness implications, so ZnDTP have to be mainly avoided. This way that the oil’s conductivity decreases and also the risk of revolution charging increases.

A lubricant’s conductivity not just is affected by the base oil and the additive package but additionally depends on temperature. The greater the temperature, the higher the oil’s conductivity. Unfortunately, over there is no linear correlation in between the 2 parameters, as each oil type has its very own conductivity/temperature relationship.

Furthermore, at a consistent temperature, conductivity still changes during operation because of additive reactions, wear metals, reactions with metal surfaces, water and the development of aging and oxidation products.

Electrostatic Charges

Although security conductivity so far has to be unable to accomplish much success in the area that sensor technology, that is obtaining significance v regard come electrostatic charges and discharges in lubricant and hydraulic systems.

Figure 1. The relationship in between lubricant conductivity and temperature

In oil-circulating systems, electrostatic charges generally can take place if over there is friction in the flow between the oil and the surfaces bordering it. The stamin of the static charge depends on numerous different and also partly interconnected factors.

The energy density, which builds up in the system and also leads to subsequent discharges, is random on the oil’s conductivity and volume flow. The much more oil the flows through a circulation pipe and also the reduced the oil’s conductivity, the greater the potential because that an electrostatic charge.

Oil can be especially electrostatically charged if:

It is formulated with a base oil from group II or III.It consists of no polarizing (zinc-containing) additives.The conductivity of the new or old oil is less than 400 pS/m.It is fed into pipes that are too small.It is relocated with as well high a circulation velocity.It produce friction in poorly draft filter elements.Pipes and also hoses room not grounded.The oil level has actually dropped too low.It has high proportions that undissolved air (bubbles).

Electrostatic Discharges and feasible Consequences

If the level of electric charge in the system becomes as well great, an electrostatic discharge (ESD) will occur. In together cases, microsparks or sparking results. Typically, a crackling or click sound will certainly be heard close to the filter or in the tank.

If the fee is high enough, the discharge might be repetitive several times in quick succession. Discharges generally take location in areas with vastly different material combinations. Contemporary filters with a high relationship of plastic are often affected.

The microsparks brought about by a revolution charge can lead to temperatures approaching 1,000 degrees C. This can be very dangerous if the fluids are also slightly flammable. In addition, if hydrocarbon vapors have formed in the tank ventilation area, the system can spontaneously combust.

However, as soon as discharge sparks occur within a generator or hydraulic oil-circulation system, they are typically smothered really quickly by the oil. Nevertheless, this mini-explosions can burn feet in filters or also seriously damage the oil because of increased sludge buildup.

Effects top top Turbine and also Hydraulic Oils

In recent years, electrostatic charges and also discharges have been occurring more frequently in turbine and also hydraulic oil systems. Several advances are responsible for this, including:

New systems function a much more compact design with a significantly smaller tank capacity and a proportionally larger displaced volume.Oil purity requirements have increased. This in turn has led to higher filtration rates.The filtration intensity and also electrostatic charge properties that the oil (resulting from filtration) have increased.The oils’ short conductivity, which often is far below 1,000 pS/m in particular conditions, has resulted in one increased tendency for electrostatic charging.


Measuring Conductivity to prevent Damage

In order come prevent damage from electrostatic discharges, more than just the conductivity of brand-new oil must be identified. The parameter is also important because that older lubricants, especially when handling larger quantities, if naught is known about the provided oil or a burning odor or soot particles space noticeable.

Therefore, some oil analysis laboratories now offer conductivity dimensions at different temperatures. The process has been tested for number of years and also is performed in accordance with ASTM D2624. It originally was emerged for inspecting airplane kerosene to avoid crashes caused through jet fuel charging.

As pointed out previously, oil’s conductivity worth is measure up in pS/m. If the conductivity is an ext than 400 pS/m at 68 levels F (20 levels C), over there is tiny risk of damages to the oil or the system from electrostatic charges. However, if the value is lower, there is a really real opportunity that the phenomenon could occur.

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If an oil through an enhanced ESD danger is being used, ground connection the entire system is not a viable option. The voltage inside the device cannot it is in discharged v a ground connection wire. Fortunately, there room several various other approaches for prevention.

4 ways to avoid Electrostatic Problems

Install distinct stat-free filters rather of traditional filter cartridges. These filters can discharge or also prevent the fee from occurring.Use one oil through a various makeup and higher conductivity value.Choose or modify the system’s material combinations for this reason microspark development is prevented regardless of an electrostatic charge.Optimize circulation diameter, tank host times or tank volumes to minimization the charge potential.