Power transformers are at the base of the modern electric power industry. Their reliability influences a power supply to large industrial facilities and ordinary consumers. In this article, we will learn about transformer oil, which is an important part of transformer insulation system, and oil maintenance.
Let’s start with oil functions. Oil in transformer isolates active parts and removes heat, which is in excess in transformer during operation at elevated temperatures. Oil takes away some of the negative effects that may result in faults. Therefore, an oil condition should be regularly monitored and maintained.
Oil maintenance: oil testing and analysis
Transformer visual inspection includes tests of top layer temperature of the oil. It is provided by thermosignal rods and thermometers. The standard value of this parameter is 95 ° C. If oil temperature exceeds this value, it is recommended to reduce the existing load.
The simplest and the least labor-intensive test of transformer oil is a dielectric strength test. It tests dielectric breakdown voltage, as well as a presence of mechanical impurities and moisture, but only visually.
The following and more complex is Oil Screen test. It includes the previous tests in addition with testing flash point and acid number. The last parameter shows the degree of oil aging, since this process is always associated with an increase of acidic compounds. Oil Screen is recommended after repairs to insure proper maintenance.
The full package of tests analyzes all parameters and characteristics of oil. It is valuable for assessing new and regenerated oil.
Transformer oil maintenance
Tests results demonstrate the current state of oil. These results are compared to the standard values that are test limits recommended by international organizations. When test results do not exceed the standard limits, the oil performs well, protecting the transformer from overheating and breakdown. If oil parameters exceed the standard values, it is regenerated or replaced with new oil.
In the absence of serious structural changes, transformer oil can be restored through cleaning and drying in UVM units. The aging products can be removed by regeneration in CMM-R units. GlobeCore regeneration equipment processes oil directly in a transformer, without switching a transformer off-line. In practice, the restoration of oil is possible, when its acid number does not accede 0.4 mg KOH. A well scheduled regeneration prolongs oil service life and also the life of transformer.
The regular oil maintenance includes preventative measures to reduce moisture content and oxidation. For prevention and protection against these negative factors a transformer is equipped with additional devices, such as thermosiphon rods and air filters, as well as special nitrogen protection and film coatings.
The important part of oil maintenance is additive refill. Though new oil contains resins, which act as antioxidants, their quantity decreases with time, and special additives are introduced to increase the antioxidant stability.
Oil maintenance for hydraulic systems and equipment
A hydraulic drive is a drive that converts energy of hydraulic fluid to power mining and road construction machinery. It is also applied in machine-tool construction, aviation and automotive industry. Reliability and durability of hydraulic drive is provided by good quality of hydraulic oil and oil maintenance.
Why does hydraulic oil deteriorate?
During operation of hydraulic machinery, moisture may enter hydraulic oil from poor joint connections, hard particles may get into oil as a result of wear of metal parts, dust may enter from the environment. Foreign substances in oil clog the entire system and cause failure. It can result in an unscheduled downtime and expensive repairs.
Oil maintenance: which approach to choose?
For hydraulic machines and equipment the condition of oil and oil maintenance is extremely importance. A correctly chosen strategy allows to reduce financial expenses on the following:
- Purchase of fresh oil;
- Utilization of used oil;
- Unplanned repairs.
Unfortunately, the common approach is to simply replace the used hydraulic oil that reaches a certain (often critical) degree of pollution with a new one. The owners of equipment rely on stationary filters in the oil system, but they are not always capable to solve the tasks. One of the reasons is installation of contaminated new oil that got dirty during long-term storage. The second factor that limits the effectiveness of stationary filters is their filtration fineness. By detaining the largest particles, the filters let through the smaller ones that can still cause a significant damage to the hydraulic system.
Therefore, the hydraulic oil maintenance must include at least three mandatory items:
- Oil filtration before installation in a system.
- Determining the degree of oil contamination.
- Regular oil regeneration
Methods of hydraulic oil cleaning
Hydraulic oils are cleaned with the help of the following forces:
The principle of gravitational cleaning is based on gravity which brings the contaminants to the bottom of the oil tank. Magnetic cleaning removes metal impurities the size of 0.5-5 microns. Electrostatic cleaning draw away impurities that are charged as a result of friction against oil. The fluid is passed between two electrodes that attract the opposite charged particles. Centrifugal cleaning separates heterogeneous systems under the influence of centrifugal forces.
When choosing filters for the hydraulic system, it is necessary to take into account many factors, that are:
- Size of equipment;
- Sensitivity of equipment to contamination;
- Degree of reliability;
- Type of hydraulic fluid;
- Operating conditions.
Comprehensive solution from GlobeCore
GlobeCore offers a compact and energy efficient equipment for hydraulic oil maintenance, which treats the hydraulic fluid through filtration, temperature and vacuum, adsorption, etc. Regular oil maintenance with CMM unit helps to:
- Extend the service life of equipment;
- Improve its operational reliability;
- Reduce costs on purchase of fresh oil and used oil disposal.