Transformer oil testing

Transformer oil testing
In this article we will discuss about the transformer oil testing and maintenance  of transformer. here we will discuss in detail about transformer oil testing.

Transformer oil testing
conservators are so designed that the lower part acts as a sump in which impurities and sludge may collect. A valve is fitted at the lowest portion of the conservator for draining and sampling . the inside of the conservator  should be cleaned periodically.

Oil indicator glass should be kept clean so that oil level is clearly visible . Broken indicate glass should be replaced immediately. when conservator is taken for maintenance magnetic oil level indicator mechanism  should also be cleaned  and inspected for operation. float should be checked to see that there is no oil in the float.

Transformer oil testing and maintance of transformer

Silica gel breather
Breather should be inspected frequently especially in a situation where temperature and humidity changes are considerable and when transformer is subjected to fluctuating loads so as long as silica gell is in active stage. its clour is dark blue as it becomes saturated with moisture , its color changes to pale blue/pink when it should be reactivated.

Buchholz Relay
Routine operation and mechanical inspection tests should be caries out as recommended. during service. if gas is found to be collecting and giving alarm,the gas should  be tested and analysed to find out the portable nature of the fault.  Sometimes , it may be noticed that the gas collected is only air. the reason for  this may be that the  oil is releasing  absorbed air due to change in temperature. the absorbed air released on in initial period of six month can be identified to a great extent by a chemical analysis of gas.
Buchholz rely will also give alarm or trip the breaker due to oil level falling below the buchoholz rely . Isolating valve between the conservator and buchholz rely facilities removal buchholz rely for repairs / checking without lowering the oil level in conservator it should be ensured that isolate ring  valves of buchholz ely are kept fully open for  unhindered oil flow

Temperature indicators of transformers
at each yearly maintenance inspection the level of oil in the pockets holding thermometer bulbs should be checked and the oil replenishment is required. the capillary tubing should be fastened down again if it has become loose. dial gases should be kept clean and if broken,replaced as soon as possible to prevent damage to the instrument. temperature indicators found reading incorrectly should be calibrated with standard thermometer immersed in hot water and  it found ,clean the pocket and refill with fresh oil and seal the ping properly. if armoring of capillary is exposed . then retyping must be done by PVC tape of good quality to prevent  further damage to the  armoring or capillary.
Bushings
porcelain insulators and connectors should be cleaned at convenient intervals and minutely examined for any cracks or other defects or narrow are difficult to detect, however they are likely to devoplop rapidly. all such bushing should be replaced. similarly all inside the oil communicating type bushing should be checked by unscrewing air release screws provided on bushing top. the cause  of any serious loss of oil should be investigated. in case  of any sign of oil leakage in the bushing he matter should be refereed to us.
External connections including earthing
all connections should be tight. if they appear blackened or corroded, unbolt the connection and clean down to the bright metal with emery paper. remark the connections and give it a heavy coating of grease. it is particularly that heavy current carrying connections should properly maintained.
Transformer oil testing
In this article we will discuss about the transformer oil testing and maintenance  of transformer.here we will discuss in detail about transformer oil testing.
Transformer oil testing
conservators are so designed that the lower part acts as a sump in which impurities and sludge may collect. A valve is fitted at the lowest portion of the conservator for draining and sampling . the inside of the conservator  should be cleaned periodically.

Oil indicator glass should be kept clean so that oil level is clearly visible . Broken indicate glass should be replaced immediately. when conservator is taken for maintenance magnetic oil level indicator mechanism  should also be cleaned  and inspected for operation. float should be checked to see that there is no oil in the float.
Transformer oil testing and maintance of transformer

Silica gel breather
Breather should be inspected frequently especially in a situation where temperature and humidity changes are considerable and when transformer is subjected to fluctuating loads so as long as silica gell is in active stage. its clour is dark blue as it becomes saturated with moisture , its color changes to pale blue/pink when it should be reactivated.
Buchholz Relay
Routine operation and mechanical inspection tests should be caries out as recommended. during service. if gas is found to be collecting and giving alarm,the gas should  be tested and analysed to find out the portable nature of the fault.  Sometimes , it may be noticed that the gas collected is only air. the reason for  this may be that the  oil is releasing  absorbed air due to change in temperature. the absorbed air released on in initial period of six month can be identified to a great extent by a chemical analysis of gas.
Buchholz rely will also give alarm or trip the breaker due to oil level falling below the buchoholz rely . Isolating valve between the conservator and buchholz rely facilities removal buchholz rely for repairs / checking without lowering the oil level in conservator it should be ensured that isolate ring  valves of buchholz ely are kept fully open for  unhindered oil flow

Temperature indicators of transformers
at each yearly maintenance inspection the level of oil in the pockets holding thermometer bulbs should be checked and the oil replenishment is required. the capillary tubing should be fastened down again if it has become loose. dial gases should be kept clean and if broken,replaced as soon as possible to prevent damage to the instrument. temperature indicators found reading incorrectly should be calibrated with standard thermometer immersed in hot water and  it found ,clean the pocket and refill with fresh oil and seal the ping properly. if armoring of capillary is exposed . then retyping must be done by PVC tape of good quality to prevent  further damage to the  armoring or capillary.

Bushings
porcelain insulators and connectors should be cleaned at convenient intervals and minutely examined for any cracks or other defects or narrow are difficult to detect, however they are likely to devoplop rapidly. all such bushing should be replaced. similarly all inside the oil communicating type bushing should be checked by unscrewing air release screws provided on bushing top. the cause  of any serious loss of oil should be investigated. in case  of any sign of oil leakage in the bushing he matter should be refereed to us.
External connections including earthing
all connections should be tight. if they appear blackened or corroded, unbolt the connection and clean down to the bright metal with emery paper. remark the connections and give it a heavy coating of grease. it is particularly that heavy current carrying connections should properly maintained.

Gaskets
check  the transformer for leakages periodically. the bolts should be tightened evenly around the joints to avoid uneven pressure. broken or leaking gaskets should be replaced as soon as possible.
Rollers
after the transformer has been in service for long period , rollers should examined carefully . they should be greased and rotated to see that they turn freely.

Faults and failures in transformer
Although failure in transformers is rare, faults do occur and the reason may be broadly classified as ;
1. failure in magnetic circuit
2. failure in electrical circuit.
3. failure in dielectric circuit
4. failure in structural and mechanical fittings.

Comments

Post a Comment

More useful post

Electrical symbol

Image
Resistance code ******************************* Symbol of DC machine ************************** Rotating machinery symbol ************************** More useful post 1.  Buchholz Relay- Transformer Protection   2.  Basic Principle of Auto Transformer
Read more

Basic Principle of Auto Transformer

Image
A Transformer, in which a part of the winding is  common  to both the Primary and Secondary circuit is called an Auto Transformer. It shall be noted that in Two Winding Transformer, Primary and Secondary windings are electrically isolated but in Auto Transformer, the two windings are not electrically isolated. A simplified diagram of a Step-down Auto Transformer is shown in figure below. As shown in the figure above, N 1  and N 2  are the number of turns between winding AB and AC respectively.  If a voltage V 1 is applied across AB, an exciting current will start flowing through the full winding. Therefore, voltage per turn in winding AB is V 1 /N 1 and hence voltage across CB is (V 1 /N 1 )N 2 . As the load current is I 2 and the current taken from the source is I1, neglecting losses Input Power = Output Power V 1 I 1 CosØ 1 = V 2 I 2 CosØ 2  ………………….(1) Assuming internal impedance drop and losses to be negligible, pow...
Read more

Buchholz Relay- Transformer Protection

Image
Buchholz relay is a gas actuated protection relay which is generally used in large oil immersed transformers of rating more than 500 kVA. It is used for the protection of a Transformer from the faults occurring inside the transformer. A typical Buchhloz Relay is shown below. The gas actuated protective relay is designed to detect faults as well as to minimize the propagation of any damage, which might occur within oil-filled Transformers. The Buchholz relay is therefore particularly effective in case of: Short-circuited core laminations Broken-down of core bolt insulation Overheating of some part of the windings Bad contacts Short circuits between phases, turns Earth faults-puncture of bushing insulators inside tank Buchholz relay `can prevent the development of conditions leading to a fault in the transformer, such as the falling of the oil level due to leaks, or the penetration of air as a result of defects in the oil circulating system. ...
Read more