Oil Leakages in Transformers

Oil Leakages are a frequent issue in Transformers which if not properly addressed can result in serious accidents such as fire or explosions.  Oil can also cause accidents due to slipping. 

Besides, Transformer oil is an environmental pollutant.  Spillage of Transformer oil can result in severe penalty for environmental violations. 

Oil Leakages can be detected visually most of the times.  However, some minor leakages are not always detectable by the naked eye.  Special techniques such as the application of special fluids which indicate oil leakage by changing colour.

Once an oil leakage is detected, it needs to be arrested and the point of leakage should be plugged.  Welding the leakage would require switching off the transformer and draining the oil.

Transformer oil leaks can be rectified by the application of special polymeric compounds and putties which cure and seal off the leakage. 

Leakages can be prevented by ensuring that the elastomeric components of the transformer such as the gaskets, O rings, etc are replaced at the scheduled replacement intervals.  The Transformer should be properly painted and any damage to the painting should be properly rectified. 

In addition to oil leakages, in transformers filled with Nitrogen the leakage above the oil surface can result in the leakage of nitrogen.  The leakage of the inert gas can be confirmed by applying a soapy solution and observing the bubbles. 

What are Air Capacitors?

Air Capacitors are capacitors which use air as the dielectric medium.  Air capacitors are used in tuning circuits.  

An Air capacitor is made of two banks of semicircular plates which are mounted on a single shaft.  The rotation of the shaft controls the amount of overlap between the two plates.  This determines the capacitance value of the capacitor. 

Since air has a low dielectric constant, it cannot be used for high voltages.  The capacitance of air capacitors ranges between 100pF to 1 nF. 

Air capacitors are not polar which means that they can be connected in any polarity.

There can be a shift in the capacitance value due to deposition of dust on the plate surfaces and the change in air parameters such as temperature and humidity.  Small insects can also get caught between the plates and create a short circuit. 

Detection of SF6 gas using Thermography

SF6 gas detection is important in Circuit Breakers, Gas Insulated Switchgear and other equipment.  SF6 gas leakages can be expensive, can cause equipment tripping.  In addition, they can also result in damage to the environment as SF6 is a green house gas. 

SF6 gas is usually detected by hand held detectors which work on the ultrasonic principle.  These detectors are vulnerable to interference from noise and wind.  Another technique which has gained popularity in recent years is the use of thermographic cameras for SF6 detection.  These cameras detect the leakage of a gas by sensing the difference in temperature between the gas and the surrounding atmosphere.  This technique can be used to detect SF6 leakages from large distances. 

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Non inductive Resistors

Resistors are passive components in electric and electronic circuits which are used to introduce a resistance value.  While resistors have their resistive value, they sometimes also have a small inductive value. 

This is due to the fact that the resistance elements are wound.  This winding of the elements introduces an inductance.  This small value may not be significant at low frequencies.  However at higher frequencies and during surges which have steep fronts, the inductance value may become significant and introduce oscillations and other disturbances. 

In order to eliminate the inductance, non-inductive resistors are used.  Non inductive resistors are designed in a manner that there is no inductance in the assembly.  For instance, ceramic resistors which do not have a wound structure are considered non-inductive. 

Wound resistors can also be designed to be non-inductive by having half the winding in one direction and the other half in the other direction.  This ensures that the net inductance is nil.  Film type resistors are also designed to be non-inductive. 

What is a Rectifier Transformer

Rectifiers Transformers are Transformers which have an in-built Rectifier in the secondary side.  The Diodes are mounted inside the Transformer Assembly itself.    The Rectifier Transformer is used in applications which require high DC power such as in DC Traction Systems and in processes such as electrolysis and smelting. 

Voltage regulation is achieved using Tap Changers in the HV side. 

Rectifier Transformers are sometimes also known as Rectiformers. 

Rectifier Transformers are usually connected to a bank.  Each Rectifier-Transformer is designed with an inherent phase shift such that the transformers attain the peak voltage one after another.  This ensures a steady supply at peak voltage.  Thus a system with five banks of rectifier transformers with twelve pulses at a phase shift of +12°, – 6°, 0°, + 6° and +12° will result in a system  with 60 pulses .