Why do we use Delta-Wye in transformers?
The delta–wye connection is the most commonly used three-phase transformer connection. The wye-connected secondary allows single-phase load to be distributed among the three phases to neutral instead of being placed all on one winding as with a four-wire delta secondary.
How can you tell if a transformer is Delta or Wye?
In a Wye system, 120V can be measured from any hot wire to neutral. Additionally, 208V is measured from hot wire to hot wire. This is also the same for Delta configurations. By comparison, a Delta circuit inside a transformer appears as a triangle with equal sides, resulting in a closed path.
How does transformer differential protection work?
Differential protection works on the principle of Kirchhoff’s Current Law (KCL). This law states that the total sum of current flowing in to a node is zero. If the per unit primary side current is equal to per unit secondary side current, then KCL is verified and no fault is present in the transformer.
What is protection transformer?
Transformer protection can be broadly categorized as electrical protection implemented by sensing mainly the current through it, but also voltage and frequency and, as mechanical protection implemented by sensing operational parameters like oil pressure/ level, gas evolved, oil & winding temperature.
Can a Delta transformer have a neutral?
The only way to get a neutral point in a three-phase system is to use a star topology. The only (real) way to convert a delta into a star topology is to use a delta-to-star transformer (AKA Delta-Wye transformer). You often find them at the top of wooden poles.
What are the types of transformer protection?
Common Types of Transformer Protection
- Overheating protection.
- Overcurrent protection.
- Differential Protection of Transformer.
- Earth Fault Protection (Restricted)
- Buchholz (Gas Detection) Relay.
- Over-fluxing protection.
What is OSR in transformer?
– The protective Oil Surge Relay (OSR) is used to protect the malfunction developed inside the On Load Tap Changer (OLTC). It is installed in the pipe between OLTC head and oil conservator. – Any malfunction builds pressure which leads to increased oil flow.
Which is used for transformer protection?
The protection of a transformer against the overloads is performed by a dedicated protection usually called thermal overload relay. This type of protection simulates the temperature of the transformer’s windings.
Where is Buchholz relay used?
distribution transformers
Buchholz relays have been applied on oil-filled power and distribution transformers at least since the 1940s. The relay is connected to the oil piping between the overhead conservator tank and the main oil tank of a transformer.
What is 25 kV Catenary protection?
The 25 kV supply for traction system is drawn through a single phase step down transformer. This is modeled as a 25 MVA, 220 kV/25kV, two winding single phase transformer with impedance of 12% at 25 MVA base. The average length of the catenary to be protected during normal feed conditions is 40 km.
What is OTI and WTI in transformer?
Product Description. The WTI means winding temperature Indicator and OTI means Oil Temperature Indicator which indicates the winding temperature & oil temperature of the transformer and operates the alarm, trip, and cooler control contacts.
What is difference between OSR and Buchholz relay?
OSR relay is actuated when the flow rate of oil exceeds the preset value. Buchholz relay detects the fall in oil level due to the formation of gases after an internal fault inside the transformer. OSR detects excessive oil surges after any fault occurs inside OLTC Chamber.
What is a Buchholz protection?
The Buchholz protection is a mechanical fault detector for electrical faults in oil-immersed transformers. The Buchholz (gas) relay is placed in the piping between the transformer main tank and the oil conservator. The conservator pipe must be inclined slightly for reliable operation.
Which oil is used in transformer?
mineral oil
Transformer oil is most often based on mineral oil, but alternative formulations with different engineering or environmental properties are growing in popularity.
Why mercury is used in Buchholz relay?
Gas produced by abnormal conditions in the transformer, collects in the Buchholz relay which lowers the oil level so that the top float gradually comes down and ultimately operates the mercury switch when it reaches a certain level. This switch is usually connected to external alarm circuit.
What is electrical SSP?
Sub-Sectioning and Paralleling Post (SSP): One or more SSPs are provided between each FP and adjacent SP depending upon the distance between them. In a double track section, normally three interrupters are provided at each SSP i.e. two connecting the adjacent sub-sectors of up and down tracks.
What is meant by SP and SSP in traction system?
There will be 25 to 30km interval between TSS and the sectioning and paralleling post (SP). And, there will be sub-sectioning and paralleling post (SSP) in the midway of the SP and TSS. (2) Connection Method of Traction Transformers.