Mechanism of Polarization
What is transformer? Definition and Working Principle of Transformer
EMF Equation of Transformer | Turns Voltage Transformation Ratio of Transformer
Theory of Transformer on Load and No Load Operation
Resistance and Leakage Reactance or Impedance of Transformer
Equivalent Circuit of Transformer referred to Primary and Secondary
Hysteresis Eddy Current Iron or Core Losses and Copper Loss in Transformer
Voltage Regulation of Transformer
Single Three Phase Transformer vs bank of three Single Phase Transformers
Parallel operation of Transformers
Magnetizing Inrush Current in Power Transformer
Current Transformer CT class Ratio Error Phase Angle Error in Current Transformer
Voltage Transformer or Potential Transformer Theory
Knee Point Voltage of Current Transformer PS Class
Accuracy Limit Factor and Instrument Security Factor of Current Transformer
Transformer Insulating Oil and Types of Transformer Oil
DGA or Dissolved Gas Analysis of Transformer Oil | Furfural or Furfuraldehyde Analysis
Transformer Accessories | Breather and Conservator Tank | Radiator
Silica Gel Breather of Transformer
Conservator Tank of Transformer
Radiator of Transformer | Function of Radiator
Magnetic Oil Gauge or MOG | Magnetic Oil Level Indicator of Transformer
Oil Winding and Remote Temperature Indicator of Transformer
Transformer Cooling System and Methods
On Load and No Load Tap Changer of Transformer | OLTC and NLTC
Tertiary Winding of Transformer | Three Winding Transformer
Core of Transformer and Design of Transformer Core
Restricted Earth Fault Protection of Transformer | REF Protection
Buchholz Relay in transformer | Buchholz Relay operation and principle
What is Earthing Transformer or Grounding Transformer
Differential Protection of Transformer | Differential Relays
Over Fluxing in Transformer
Transformer Testing | Type Test and Routine Test of Transformer
Transformer Winding Resistance Measurement
Voltage and Turn Ratio Test of Transformer
Vector Group Test of Power Transformer
Open and Short Circuit Test on Transformer
Insulation Dielectric Test of Transformer
Transformer Oil and Winding Temperature Rise Test
Impulse Test of Transformer
Maintenance of Transformer
Sweep Frequency Response Analysis Test | SFRA Test
Installation of Power Transformer
Commissioning of Power Transformer
Electrical Power Transformer | Definition and Types of Transformer
What is Auto Transformer ?
High Voltage Transformer
Distribution Transformer | All Day Efficiency of Distribution Transformer
Dry Type Transformer
Air Core Transformer
Design of Inductor in Switched Mode Power Supply Systems
Design of High Frequency Pulse Transformer
Single Three Phase Transformer vs bank of three Single Phase Transformers
Comparison between Single Three Phase and Bank of Three Single Phase Transformers for Three Phase SystemIt is found that generation, transmission and distribution of electrical power are more economical in three phase system than single phase system. For three phase system three single phase transformers are required. Three phase transformation can be done in two ways, by using single three phase transformer or by using a bank of three single phase transformers. Both are having some advantages over other. Single 3 phase transformer costs around 15 % less than bank of three single phase transformers. Again former occupies less space than later. For very big transformer, it is impossible to transport large three phase transformer to the site and it is easier to transport three single phase transformers which is erected separately to form a three phase unit. Another advantage of using bank of three single phase transformers is that, if one unit of the bank becomes out of order, then the bank can be run as open delta.
Connection of Three Phase TransformerA verity of connection of three phase transformer are possible on each side of both a single 3 phase transformer or a bank of three single phase transformers.
Marking or Labeling the Different Terminals of TransformerTerminals of each phase of HV side should be labeled as capital letters, A, B, C and those of LV side should be labeled as small letters a, b, c. Terminal polarities are indicated by suffixes 1 and 2. Suffix 1’s indicate similar polarity ends and so do 2’s.
Star-Star TransformerStar-star transformer is formed in a 3 phase transformer by connecting one terminal of each phase of individual side, together. The common terminal is indicated by suffix 1 in the figure below. If terminal with suffix 1 in both primary and secondary are used as common terminal, voltages of primary and secondary are in same phase. That is why this connection is called zero degree connection or 0° - connection. If the terminals with suffix 1 is connected together in HV side as common point and the terminals with suffix 2 in LV side are connected together as common point, the voltages in primary and secondary will be in opposite phase. Hence, star-star transformer connection is called 180°-connection, of three phase transformer.
Delta-Delta TransformerIn delta-delta transformer, 1 suffixed terminals of each phase primary winding will be connected with 2 suffixed terminal of next phase primary winding. If primary is HV side, then A1 will be connected to B2, B1 will be connected to C2 and C1 will be connected to A2. Similarly in LV side 1 suffixed terminals of each phase winding will be connected with 2 suffixed terminals of next phase winding. That means, a1 will be connected to b2, b1 will be connected to c2 and c1 will be connected to a2. If transformer leads are taken out from primary and secondary 2 suffixed terminals of the winding, then there will be no phase difference between similar line voltages in primary and secondary. This delta delta transformer connection is zero degree connection or 0°-connection.
But in LV side of transformer, if, a2 is connected to b1, b2 is connected to c1 and c2 is connected to a1. The secondary leads of transformer are taken out from 2 suffixed terminals of LV windings, and then similar line voltages in primary and secondary will be in phase opposition. This connection is called 180°-connection, of three phase transformer.
Star-Delta TransformerHere in star-delta transformer, star connection in HV side is formed by connecting all the 1 suffixed terminals together as common point and transformer primary leads are taken out from 2 suffixed terminals of primary windings. The delta connection in LV side is formed by connecting 1 suffixed terminals of each phase LV winding with 2 suffixed terminal of next phase LV winding. More clearly, a1 is connected to b2, b1 is connected to c2 and c1 is connected to a2. The secondary (here it considered as LV) leads are taken out from 2 suffixed ends of the secondary windings of transformer. The transformer connection diagram is shown in the figure beside. It is seen from the figure that the sum of the voltages in delta side is zero. This is a must as otherwise closed delta would mean a short circuit. It is also observed from the phasor diagram that, phase to neutral voltage (equivalent star basis) on the delta side lags by − 30° to the phase to neutral voltage on the star side; this is also the phase relationship between the respective line to line voltages. This star delta transformer connection is therefore known as − 30°-connection. Star-delta + 30°-connection is also possible by connecting secondary terminals in following sequence. a2 is connected to b1, b2 is connected to c1 and c2 is connected to a1. The secondary leads of transformer are taken out from 2 suffixed terminals of LV windings,
Delta-Star TransformerDelta-star transformer connection of three phase transformer is similar to star – delta connection. If any one interchanges HV side and LV side of star-delta transformer in diagram, it simply becomes delta – star connected 3 phase transformer. That means all small letters of star-delta connection should be replaced by capital letters and all small letters by capital in delta-star transformer connection.
Delta-Zigzag TransformerThe winding of each phase on the star connected side is divided into two equal halves in delta zig zag transformer. Each leg of the core of transformer is wound by half winding from two different secondary phases in addition to its primary winding.
Star-Zigzag TransformerThe winding of each phase on the secondary star in a star-zigzag transformer is divided into two equal halves. Each leg of the core of transformer is wound by half winding from two different secondary phases in addition to its primary winding.
Choice Between Star Connection and Delta Connection of Three Phase TransformerIn star connection with earthed neutral, phase voltage i.e. phase to neutral voltage, is 1/√3 times of line voltage i.e. line to line voltage. But in the case of delta connection phase voltage is equal to line voltage. Star connected high voltage side electrical power transformer is about 10% cheaper than that of delta connected high voltage side transformer.
Let’s explain, Let, the voltage ratio of transformer between HV and LV is K, voltage across HV winding is VH and voltage across LV winding is VL and voltage across transformer leads in HV side say Vp and in LV say Vs.