Transformer is a static device, thus it requires less attention but with proper Periodic inspection & diagnostics of transformer it would be possible to avoid the unwanted break down & frequent interval of schedule maintenance.
As transformer is the heart of power network, the maximum availability of it and also to meet the full life time of transformer is a matter to think of.
The four main parameters that are defining the transformer health and thus highly important for transformer inspection & diagnostics are
· Paper used for conductor insulation.
· pressboard used for the major insulation
· winding support
· Transformer oil
Among these, transformer oil is the highly important. Modern transformer design are such that by just inspecting the status of transformer oil, the health of the transformer can be easily defined.
The regular data reading of different parameters is very important for maintenance of transformer. The deviation in regular readings is effective to point out a likelihood of a fault or a fault that is slowly forming.
· Temperature (oil temperature of conservator tank, OLTC tank, radiator etc.)
· Hot point.
· Oil leak.
· Oil level (LTC, Transformer tank, bushings, radiator etc.)
· Supporting system-Silica gel, cooling fan, control heater, door gaskets conditions.
· Load tap changer – noise & misalignment in operation, amount of LTC in different position.
· Any loose or displaced parts- such as loose earth connection, loose base etc.
· Crack in structure.
· Sign of burning.
As per ANSI (American National Standards Institute), the maximum temperature permitted for oil is of 90°C and the maximum temperature of the hottest point is 110°C.
Oil level in a transformer conservator tank and that of the OLTC or radiator has no specific rules. The requirement is to maintain the oil presence in the oil tanks. Standard oil level is maintained in consideration of oil low level in low temperature and high level in high temperature or in loading condition. The requirement is to maintain oil in the oil tank by avoiding empty tank in low temperature and over flow of oil in loading or high temperature.
The function of silica gel is to absorb moisture from the air to maintain the transformer safe from the demerits of moisture. Color of the silica gel is changed when it becomes saturated that is it cannot absorb moisture any more. There is confusion about color changing. Some silica gel changes to black or red or become white when they become saturated. So saturated silica gel color can be confirmed from the manufacture recommendation.
Oil leak is basically due to deterioration of some gaskets or they are in wrong position.
Noise is an important parameter. Some fault can be readily identified with comparison of regular noise and abnormal noise of transformer.