Electric conductivity is a measure up of a fluid’s electrostatic chargeability. It generally is expressed in picosiemens per meter (pS/m). In addition to the form of fluid, conductivity likewise depends on the concentration the movable charge carriers. Because that example, pure distilled water is only slightly conductive. However, if the water consists of impurities such as salts, mountain or bases, then its conductivity increases.

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Lubricants are typically only slightly conductive and therefore have the right to work as insulators in transformers or switches. However, oil can also conduct electrical current. Their conductivity is dependence on several various factors, including the basic oil, additives and polarity.

Oil Conductivity

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


The easy refined, mineral-oil-based base oil of team I stand for the most basic option and also previously accounted for the largest proportion of lubricant production. Over the last few years, that proportion has been in steady decline, together the more refined base oil of teams II, III and also IV are progressively being used for modern lubricants.

This tendency of using more refined basic oils and synthetic alternatives is based upon the fact that they usually have much better characteristics such as greater aging stability. However, if the higher-quality base oil have countless advantages, there are concerns over several of their changed properties, which deserve to lead come problems, especially when unfavorable combinations occur.

One such repercussion is varnish, which have the right to be due to the basic oil’s transformed dissolving performance with regard come aging and reaction products. An additional consideration is component and also lubricant damage, which can be caused by electrostatic discharges. The lubricant’s conductivity is an important factor in the fee buildup, and also conductivity is dependence on the type of base oil offered (see Table 2).

Table 2. Conductivity that oils and also synthetic fluids at 23 degrees C (73 degrees F)

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

However, zinc is thought about to have dangerous health implications, therefore ZnDTP should be largely avoided. This means that the oil’s conductivity decreases and also the danger of revolution charging increases.

A lubricant’s conductivity not only is influenced by the basic oil and also the additive package but likewise depends ~ above temperature. The higher the temperature, the greater the oil’s conductivity. Unfortunately, there is no straight correlation in between the two parameters, together each oil form 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 monitoring conductivity so far has been unable to achieve much success in the area of sensor technology, it is acquiring significance v regard come electrostatic charges and also discharges in lubricant and hydraulic systems.

Figure 1. The relationship in between lubricant conductivity and also temperature

In oil-circulating systems, electrostatic charges generally can happen if there is friction in the flow in between the oil and the surfaces neighboring it. The strength of the revolution charge depends on plenty of different and also partly interconnected factors.

The energy density, which builds up in the system and leads to succeeding discharges, is random on the oil’s conductivity and volume flow. The an ext oil that flows v a circulation pipe and also the reduced the oil’s conductivity, the better the potential for an electrostatic charge.

Oil have the right to be particularly electrostatically fee if:

It is formulated through a basic oil from group II or III.It contains no polarizing (zinc-containing) additives.The conductivity of the new or old oil is much less than 400 pS/m.It is fed into pipes that room too small.It is moved with also high a circulation velocity.It produce friction in poorly design filter elements.Pipes and also hoses room not grounded.The oil level has dropped also low.It includes high proportions of undissolved waiting (bubbles).

Electrostatic Discharges and feasible Consequences

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

If the charge is high enough, the discharge could be repeated several times in quick succession. Discharges mainly take ar in locations with vastly different material combinations. Contemporary filters v a high ratio of plastic are regularly affected.

The microsparks caused by a static charge can lead to temperatures approaching 1,000 levels C. This can be extremely dangerous if the fluids are even slightly flammable. In addition, if hydrocarbon vapors have created 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, these mini-explosions deserve to burn feet in filters or also seriously damages the oil as result of increased sludge buildup.

Effects on Turbine and Hydraulic Oils

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

New systems feature a more compact architecture with a considerably smaller tank capacity and a proportionally bigger displaced volume.Oil purity requirements have actually increased. This in turn has led to higher filtration rates.The filtration intensity and electrostatic fee properties that the oil (resulting native filtration) have increased.The oils’ short conductivity, which frequently is far below 1,000 pS/m in specific conditions, has actually resulted in an increased tendency for electrostatic charging.


Measuring Conductivity to avoid Damage

In order to prevent damages from electrostatic discharges, much more than simply the conductivity of new oil need to be identified. The parameter is likewise important for older lubricants, particularly when handling larger quantities, if naught is known around the offered oil or a burning odor or soot particles are noticeable.

Therefore, part oil analysis laboratories now offer conductivity measurements at different temperatures. The procedure has been tested for numerous years and is conducted in accordance v ASTM D2624. It initially was emerged for inspecting plane kerosene to avoid mishaps caused by jet fuel charging.

As stated previously, oil’s conductivity worth is measure up in pS/m. If the conductivity is an ext than 400 pS/m in ~ 68 degrees F (20 levels C), over there is tiny risk of damages to the oil or the device from electrostatic charges. However, if the worth is lower, there is a an extremely real possibility that the phenomenon can occur.

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If an oil through an enhanced ESD threat is gift used, ground connection the entire system is not a viable option. The voltage within the device cannot be discharged with a ground connection wire. Fortunately, there are several other approaches because that prevention.

4 methods to stop Electrostatic Problems

Install distinct stat-free filters rather of conventional filter cartridges. This filters have the right to discharge or also prevent the fee from occurring.Use one oil through a different makeup and higher conductivity value.Choose or modify the system’s product combinations therefore microspark development is prevented in spite of an electrostatic charge.Optimize circulation diameter, tank organize times or tank quantities to minimize the charge potential.