With the term “filling” the transformer we mean both filling newly installed equipment for the first time on the final site, and filling as a result of maintenance or internal inspections that have requested the equipment to be emptied.
In both cases, filling a transformer (especially those with a maximum voltage greater than 72.5 KV is an extremely delicate operation that requires the work of qualified experts, suitable operating procedures, suitably trained personnel and state of the art equipment.
Note that approximately 10-15% in terms of weight of the oil used for factory tests (before transporting the transformer to the operating site) remains inside the transformer (adsorbed by the solid insulation and deposited on the inner surfaces) even after it being emptied before transporting it to the final site. Given that often the oil used in factory tests is NOT the one purchased or accepted by the owner of the transformer, if this oil is contaminated there may be cases of cross contamination.This means that the new and compliant oil, used on the final site, might be contaminated by the oil previously used, having remained in the inner parts of the transformer.
Described below are the phases that make up the filling process of electric power equipment with a maximum voltage greater than 72.5 KV.
- Control analysis of the filling oil
- Preliminary treating the filling oil
The filling oil is transferred into tanks and subjected to physical treatment (filtration, degassing and dehydration in a vaccuum). The purpose is to obtain an oil with parameters that conform to IEC 60296.
- Preparation of the transformer with a vacuum
The accessories and components which can not resist the vacuum are isolated by closing the shut-off valves or applying blind flanges. Then a sensor is applied to measure the vacuum and a vertical pipe to monitor the oil level inside the tank during filling.
- Application of vacuum
The vacuum is applied until a residual pressure of less than 2 mbar (200 Pa) is obtained and maintained for the duration of between 12 and 36 hours according to the maximum voltage of the machine to be filled. During this draining step the tightness of the seals is checked
- Partial filling with a vacuum
The oil is inserted into the caisson through the bottom gate until completely covering the reels, while maintaining the suction of the vacuum in the upper part. Upon reaching a level of about 20 cm with respect to the lid, the vacuum pipe is shut off and the filling is continued, filling up to the Buchholz relay.In cases where the connection is to the tank, it is completely filled (see next step).
- Final filling and checking of levels and vents
- Filling accessories
The separated accessories (variators, radiators, AT passers tanks) that are resistant to the vacuum are filled simultaneously with the main caisson, the ones that are not resistant to the vacuum are filled after the transformer.
- Final oil treatment
The oil is subjected to a final filtration treatment, degassing and dehydration with a vacuum by continuously circulating it in a closed circuit. The oil treatment should ensure that all regulatory requirements are met (see table 3 IEC 60422 ed. 4 2013), as well as technical and contractual ones and therefore counter any cross contamination.
- Final analysis of the oil for quality control
Saturation time before applying energy
Once the transformer has been completely filled it is advised to wait for the cellulosic insulation to become saturated before applying energy to the transformer. Typically, manufacturers specify a saturation time between 12 and 96 hours on the basis of the equipment’s maximum voltage.
Oil treatment: limit of the parameters according to the standards
– Full electrical supply blocks in case of serious alarms (temperature,leakages or power surges)
– Automatic reports to the responsible technician via a GSM call, or if there is no GSM network, the call is made by means of the client’s centralized network.
– Residual pressure in the degassing chamber,
– Hourly flow rate of oil circulation,
– Oil temperature at the main treatment stages (system entrance, heater, degassing chamber, system output),
– The maximum pressure and clogged filters
– At the same time, water extraction and condensation and the oil discharge voltage (IEC 60156) are monitored daily
The treatment units' small dimensions
Highly qualified personnel
Numerous international case histories
that highlight the strict compliance with standard requirements and contractual specificationsi
Diagnosis of functional or critical environmental issues
Accredited certification of the individual analytical results
Sea Marconi is committed to obtaining the following results, measured by the sample taken at the end of the final treatment.
|Water content (mg/kg)
|Breakdown Voltage (kV)
|Total Dissolved Gases (%v)
|< 2 %