What advantage has the star connection over the delta connection ?

What advantage has the star connection over the delta connection ?
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1 Answer

Answer :

A. Each star connection transformer is wound for only 57.7% of line voltage . In hv transmission, this admits of much smaller transformer being built for high voltage than possible with delta connection, because of less insulation.
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Related questions

What is the advantage is obtained in the delta connection ?

Description : What is the advantage is obtained in the delta connection ?

Last Answer : A. When three transformer are obtained in delta, one may be removed and two remaining unit will carry 57.7% of the original three phase load and thus maintain the continuity of supply.

Why Delta Star Transformers are used for Lighting Loads?

Description : Why Delta Star Transformers are used for Lighting Loads?

Last Answer : A. For lighting loads, neutral conductor is must and hence the secondary must be star winding.This lighting load is always unbalanced in all three phases. To minimize the current unbalance in the primary we use delta winding in the primary. So delta / star transformer is used for lighting loads.

What is the difference between delta-delta, delta-star transformer?

Description : What is the difference between delta-delta, delta-star transformer?

Last Answer : A. Delta-delta transformer is used at generating station or a receiving station for Change of Voltage (i,e) generally it is used where the Voltage is high & Current is low whereas Delta-star ... star neutral is taken as a return path and this configuration is used for Step down voltage phenomena.

If an unsymmetrical line to ground fault occurs at the secondary terminals of a delta/star, ungrounded

Description : If an unsymmetrical line to ground fault occurs at the secondary terminals of a delta/star, ungrounded transformer, then  (A) zero sequence currents are present on both sides of the transformer  (B) ... side  (D) zero sequence currents are present on the primary side but not on the secondary side

Last Answer : If an unsymmetrical line to ground fault occurs at the secondary terminals of a delta/star, ungrounded transformer, then zero sequence currents are absent on both sides of the transformer 

A 4000 kVA, 11 kV/132 kV delta-star connected 3-phase transformer has reactance, x1 = 0.12 p.u.

Description : A 4000 kVA, 11 kV/132 kV delta-star connected 3-phase transformer has reactance, x1 = 0.12 p.u. The actual value of x1 referred to the low voltage side is (A) 0.85 Ω (B) 3.63 Ω (C) 36.3 Ω (D) 252 Ω

Last Answer : A 4000 kVA, 11 kV/132 kV delta-star connected 3-phase transformer has reactance, x1 = 0.12 p.u. The actual value of x1 referred to the low voltage side is 3.63 Ω

Delta/star transformer works satisfactorily when?

Last Answer : Delta/star transformer works satisfactorily when on balanced as well as unbalanced loads.

Which type of connection is used in distribution transformer?

Description : Which type of connection is used in distribution transformer?

Last Answer : Distribution transformers are connected in delta-star. This arrangement requires 3 conductors in the high voltage side and 4 in the low voltage side, as well as it provides the star point conductor as a neutral point. This can serve single phase as well as three phase loads.

What will happen if transformer in parallel connection have different phase sequence ?

Description : What will happen if transformer in parallel connection have different phase sequence ?

Last Answer : If the phase sequence is in an incorrect manner, in every cycle each pair of phases will get short-circuited.

What will happen if transformer in parallel connection have different percentage impedance or X/R ratio ?

Description : What will happen if transformer in parallel connection have different percentage impedance or X/R ratio ?

Last Answer : A difference in the ratio of the reactance value to resistance value of the per unit impedance results in a different phase angle of the currents carried by the two paralleled transformers; one ... of the combined output. Hence, the real power will not be proportionally shared by the transformers.

What will happen if transformer in parallel connection have different voltage ratio?

Description : What will happen if transformer in parallel connection have different voltage ratio?

Last Answer : Two transformers in Parallel should have the same primary and secondary voltage ratings. Any error in the voltage ratio would cause heavy circulating currents to flow between the transformers. ... in overloading of one transformer. This circulating current will result in increased copper losses.

What will happen if transformer in parallel connection have opposite polarity?

Description : What will happen if transformer in parallel connection have opposite polarity?

Last Answer : Connecting transformers with wrong polarity can result in circulating currents or short circuits

State the voltage and current relation in star and delta connection.

Description : State the voltage and current relation in star and delta connection. 

Last Answer : In star connection line current is equal to the phase current and line voltage is √3 times that of phase voltage. In delta connection line voltage is equal to the phase voltage and line current is √3 times that of phase current. 

What are the value of voltage and current in star connection and in delta connection?

Description : What are the value of voltage and current in star connection and in delta connection?

Last Answer : Star connection a. IL = IPh. b. VL = √3 VPh. ∴ VPh = VL/√3. Note: in star connection we are getting neutral point and we can able to measure the phase as well as line voltage. Delta connection a. VL = VPh. b. IL = √3 IPh. ∴ IPh = IL/√3.

32 With S2 closed and S1 open, the current waveform in the delta winding will be [GATE 2009] A. a sinusoidal at fundamental frequency B. flat-topped with third harmonic C. only third-harmonic D. none of these

Description : 32 With S2 closed and S1 open, the current waveform in the delta winding will be [GATE 2009] A. a sinusoidal at fundamental frequency B. flat-topped with third harmonic C. only third-harmonic D. none of these

Last Answer : C. Only third harmonic

7 The main advantage of auto transformer over a two winding transformer is A. Hysteresis losses are reduced B. Saving in winding material C. Copper losses are negligible D. Eddy losses are totally eliminated

Description : 7 The main advantage of auto transformer over a two winding transformer is A. Hysteresis losses are reduced B. Saving in winding material C. Copper losses are negligible D. Eddy losses are totally eliminated

Last Answer : A) hysteresis losses is reduced

Which of the following 3-phase connection of a transformer causes interference with the

Description : Which of the following 3-phase connection of a transformer causes interference with the neighbouring communication lines:  (A) Delta-Star (B) Star-Delta (C) Delta-Delta (D) Star-Star

Last Answer : Which of the following 3-phase connection of a transformer causes interference with the neighbouring communication lines: Star-Star

To protect the power transformer (Y-Y with neutral grounded) against fault, what type of connection do the CTs have ?

Description : To protect the power transformer (Y-Y with neutral grounded) against fault, what type of connection do the CTs have ?

Last Answer : To protect the power transformer (Y-Y with neutral grounded) against fault, what type of connection do the CTs have ? Δ-Δ connection

What are the advantages of three phase transformer over three single phase transformer?

Description : What are the advantages of three phase transformer over three single phase transformer?

Last Answer : 1.Saving in iron material 2. Small size 3. Less transformer oil 4. Economical 5. Higher efficiency

What are the advantages of three single phase transformer over three phase transformer?

Description : What are the advantages of three single phase transformer over three phase transformer?

Last Answer : 1. Continuity of supply 2. Less Installation of cost 3. Easy transportation 4.Stand by function 5.Unbalanced load supply

What are the advantages of shell type transformer over core type transformers?

Description : What are the advantages of shell type transformer over core type transformers?

Last Answer : In shell type transformers the coils are well supported on the all sides and so they can withstand higher mechanical stresses developed during short circuit conditions. Also the leakage reactance will be less in shell type transformers.

Star/star transformers work satisfactorily when?

Last Answer : Star/star transformers work satisfactorily when load is balanced .

Draw the star and delta connection. State any one conversion formula.

Description : Draw the star and delta connection. State any one conversion formula.

Last Answer : star and delta connection

for Delta-Star connection of 3-phase transformer: i) Draw the connection diagram ii) List any two advantages of this connection iii) State its area of application.

Description : for Delta-Star connection of 3-phase transformer: i) Draw the connection diagram ii) List any two advantages of this connection iii) State its area of application. 

Last Answer : Disadvantages: i) In this type of connection, the secondary voltage is not in phase with the primary. Hence it is not possible to operate this connection in parallel with star-star or delta-delta ... iv) As line current is equal to phase current the conductor size of winding should be large. 

Compare star and Delta Connection.

Description : Compare star and Delta Connection.

Last Answer : Compare Star and Delta connected system:  Star connected system Delta connected system   In STAR connection, the starting or finishing ends (Similar ends) of three coils are connected together to form the ... VPH Line Current is √3 times of Phase Current. i.e. IL = √3 IPH

What is difference between Star and Delta Connection?

Description : What is difference between Star and Delta Connection?

Last Answer : Star is        1. Open ckt       2. At center point present  neutral   Delta is     1.   Closed ckt 2.      Neutral not present in this case 

What are the transformer losses?

Description : What are the transformer losses?

Last Answer : Answer: TRANSFORMER LOSSES - There are mainly two kinds of losses in a transformer namely 1. Copper loss (ohmic loss) and 2.magnetic loss (core loss). Copper losses are caused by the ... ohmic loss the following two losses are also present in the transformer stray load loss and dielectric loss.

Why Silica gel is used in transformers?

Description : Why Silica gel is used in transformers?

Last Answer : Silica Gel is used to remove the moisture in the air entering in to the transformer. During the breathing of the transformer air enters in to the transformer. This air makes contact with the hot ... Silica gel crystals will be in blue color initially and after absorbing moisture it turns to pink.

What are the conditions for parallel operation of two transformers ?

Description : What are the conditions for parallel operation of two transformers ?

Last Answer : Transformers which are to be operated parallel should have to satisfy the following conditions: Polarities of both the transformers should be same else lead to short circuit Voltage rating of ... Phase displacement of transformers should be same Phase sequence of two transformers should be same

At what power maximum efficiency of power transformer and distribution transformer is designed

Description : At what power maximum efficiency of power transformer and distribution transformer is designed

Last Answer : Maximum efficiency of the transformer is attained at certain load factor (α) when core losses of transformer is equal to the copper losses. PCore loss = α ^2 X PCopper loss From the ... the day. Hence distribution transformers are designed to have maximum efficiency at 50% of the rated full load

What happen when Transformer is given DC supply ?

Description : What happen when Transformer is given DC supply ?

Last Answer : When DC supply is given to the transformer primary winding no back emf is induced in the transformer. Importance of Back emf is that it limits the current drawn by the machine. In the absence ... in burning down of primary winding. So when dc supply is given to transformer primary windings will burn

During No load why the power factor of the transformer is very low ?

Description : During No load why the power factor of the transformer is very low ?

Last Answer : Current flowing through the transformer consists of two components. Magnetizing current (Im) which is in quadrature (90 0 ) to the applied voltage and in phase current which is in phase to the applied voltage ... power factor of transformer during no load condition will by in the order of 0.1 to 0.2

What is the significance of vector grouping in Power Transformers?

Description : What is the significance of vector grouping in Power Transformers?

Last Answer : Answer:Every power transformer has a vector group listed by its manufacturer. Fundamentally it tells you the information about how the windings are connected (delta or wye) and the phace difference betweent ... Delta primary, Wye Secondry and the current is at 11 o clock reffered to the voltage.

What is the supply rated o/p if two single phase transformer connect to give three phase o/p from a three phase I/p?

Description : What is the supply rated o/p if two single phase transformer connect to give three phase o/p from a three phase I/p?

Last Answer : A. Each transformer is only capable of supplying 86.6%of its o/p rating

How to connect two single phase transformer to give three phase o/p from a three phase I/p ?

Description : How to connect two single phase transformer to give three phase o/p from a three phase I/p ?

Last Answer : A. They would have to connect in an open-delta.

What is the 3 ph transformer ?

Description : What is the 3 ph transformer ?

Last Answer : A. A 3ph transformer is that transformer which is equivalent to three single phase transformer but wound on one core and enclosed within one common case.

What parameters or technical particulars are important to be considered while designing protection scheme of the transformer?

Description : What parameters or technical particulars are important to be considered while designing protection scheme of the transformer?

Last Answer : 1.Network Diagram showing the position of the transformer in the system 2.kVA or MVA rating of the transformer 3.Fault Level at the transformer 4.Voltage Ratio 5.Winding Connections 6.Per Unit ... Oil Filled 11.Length and area of cross section of the connecting leads between CTs and Relay Panel

What can be the reasons for the failure of the transformer?

Description : What can be the reasons for the failure of the transformer?

Last Answer : Answer: Transformer is one of the most expensive equipments in the Power System. Failure of the transformer can cause outage of power supply for even days. However, multiple things can go wrong with ... relays. 3.Short Circuits 4.Open Circuits 5.Earth Faults 6.Over Voltage 7.Reduced system frequency

How Transformer Protection provided for internal faults?

Description : How Transformer Protection provided for internal faults?

Last Answer : 1.Bucholz Relay (1st Stage Alarm and 2nd Stage Trip) 2.Sudden Pressure Relay (1st Stage Alarm and 2nd Stage Trip) 3.Pressure Relief Valve (1st Stage Alarm and 2nd Stage Trip) 4.Pressure Switch ... 8.Gas Temperature Indicator (Alarm) 9.Silicon Breather (Passive - no alarm) 10.Smoke Detector (Alarm)

What are the tests done to minimize internal faults?

Description : What are the tests done to minimize internal faults?

Last Answer : 1.Dissolved Gas Analysis (DGA): Faults due to arcing, high current breakdown of oil, localized sparking, partial discharge of oil, localized overheating or hot spots, etc. causes ... Over current relays with under voltage blocking 6.Zero sequence protection. 7.Negative phase sequence protection

What are the reasons for Oil degradation?

Description : What are the reasons for Oil degradation?

Last Answer : 1.Degradation 2.Oxidation 3.Contamination a) Dielectric breakdown voltage indicates the presence of electrically conductive contaminants in oil. b) Interfacial tension and acid number (sometimes called ... c) Water content is temperature dependent. d) Power factor is also temperature dependent.

How does change in frequency affect the operation of a given transformer?

Description : How does change in frequency affect the operation of a given transformer?

Last Answer : a) Iron loss .........increases with a decrease in frequency. A 60-Hz transformer will have nearly 11% higher losses when worked on 50Hz instead of 60 Hz. However, when a 25-Hz ... ....since total loss is greater at a lower frequency, the temperature is increased with decrease in frequency.

What effects are produced by change in voltage?

Description : What effects are produced by change in voltage?

Last Answer : a) Iron loss.........varies approximately as V2. b) Cu loss.........it also varies as V2 but decreases with an increase in voltage if constant kVA output is assumed. c ... ..for constant kVA output, iron temperatures increase whereas Cu temperatures decrease with increase in voltages and vice-versa.

Does the transformer draw any current when its secondary is open?

Description : Does the transformer draw any current when its secondary is open?

Last Answer : Yes, no-load primary current.

In practice, what determines the thickness of the laminate or stampings?

Description : In practice, what determines the thickness of the laminate or stampings?

Last Answer : Frequency.

How can eddy current loss be minimized?

Description : How can eddy current loss be minimized?

Last Answer : By laminating the core.

Mention the factors on which hysteresis loss depends?

Description : Mention the factors on which hysteresis loss depends?

Last Answer : (i) Quality and amount of iron in the core (ii) Flux density and (iii) Frequency.

How is magnetic leakage reduced to a minimum in commercial transformers?

Description : How is magnetic leakage reduced to a minimum in commercial transformers?

Last Answer : By interleaving the primary and secondary windings.

What are the conditions for parallel operation of two transformers ?

Description : What are the conditions for parallel operation of two transformers ?

Last Answer : Transformers which are to be operated parallel should have to satisfy the following conditions: Polarities of both the transformers should be same else lead to short circuit Voltage rating of ... Phase displacement of transformers should be same Phase sequence of two transformers should be same

WHAT is ZIG ZAG Grounding Transformer

Description : WHAT is ZIG ZAG Grounding Transformer

Last Answer : ANSWER: Three Single Phase Transformers can be connected to have a three phase Zig Zag Transformer. This system can be used for either grounding or developing a fourth WIRE from a three phase neutral. An example ... - three phase - three wire system to a 480Y/277 V - three phase - four wire system

Can Transformers be Reconnected as Autotransformers to Increase Their KVA Rating?

Description : Can Transformers be Reconnected as Autotransformers to Increase Their KVA Rating?

Last Answer : ANSWER: Several of standard single phase transformers can be connected as autotransformers. The KVA capacity will be greatly increased when used as an Autotransformer, in comparison to the ... This voltage is normally used for operating fluorescent lamps or similar devices requiring 277 volts