Delta circuit
- Thread starter mjc1060
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If I had to guess would say no because in a series circuit the current is the same throughout, in the Delta the current across each winding is almost always different.
kwired
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Interesting question. Non energized you have continuity between all three corners of the delta.
Energized but with no external load connected is there any current between coils? I'm guessing in perfectly wound coils with equal inputs the answer is no, some imperfections maybe will lead to some current flowing though. Some math that is sort of above my skills probably helps with understanding how this works.
Energized but with no external load connected is there any current between coils? I'm guessing in perfectly wound coils with equal inputs the answer is no, some imperfections maybe will lead to some current flowing though. Some math that is sort of above my skills probably helps with understanding how this works.
LarryFine
Master Electrician Electric Contractor Richmond VA
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Physically speaking, yes, they're in series, but not in the usual sense of the usage of the term.
In theory, one could open any corner of a delta secondary and there will be no voltage across the opening. In theory.
In theory, one could open any corner of a delta secondary and there will be no voltage across the opening. In theory.
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:thumbsup:
Physically speaking, when you take the existence of a load into consideration the three windings of a delta form a series parallel circuit feeding each phase of the load. If you put only a single line to line load on a delta secondary it will be fed by a single winding in parallel with the series combination of the other two windings.
mbrooke
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Old timer once told me delta was better at filtering out spikes from relays and switching in industrial because the "surge" would just circulate (filter) out in the closed delta circuit.
gar
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mjc1060:
Quite obviously it is a series circuit.
If I connect a 6 V battery to a resistor to the secondary of a 6 V 60 Hz secondary to an inductor to a resistor to a light bulb and then back to the other side of the battery I have a series circuit as another example of a series circuit.
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mjc1060:
Quite obviously it is a series circuit.
If I connect a 6 V battery to a resistor to the secondary of a 6 V 60 Hz secondary to an inductor to a resistor to a light bulb and then back to the other side of the battery I have a series circuit as another example of a series circuit.
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gar
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To expand on my answer.
The question as presented had no loads on the delta. Thus, a series circuit. If loaded in any fashion, then it becomes a series parallel circuit.
The circuit as presented in an ideal condition with 3 equal sine wave voltages and phased 120 deg apart has no circulating current. As soon as there is a lack of equality, then a current flows. This does not change the fact that the circuit is a series circuit.
Also consider what happens when the ideal circuit has one primary open. Now there are two voltage sources each with the same internal impedance. Primarily internal resistance and leakage inductance of the respective energized transformers.
But the opened primary transformer now becomes an inductor of much higher inductance than its original leakage inductance, and a resistance about 1/2 of its original resistance as viewed from its secondary side. The voltage applied to this inductor is about what it would have been if the primary was not opened.
Substantial series current will exist. This will be about the excitation current of the transformer with the open primary when viewed as that transformer being back driven.
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To expand on my answer.
The question as presented had no loads on the delta. Thus, a series circuit. If loaded in any fashion, then it becomes a series parallel circuit.
The circuit as presented in an ideal condition with 3 equal sine wave voltages and phased 120 deg apart has no circulating current. As soon as there is a lack of equality, then a current flows. This does not change the fact that the circuit is a series circuit.
Also consider what happens when the ideal circuit has one primary open. Now there are two voltage sources each with the same internal impedance. Primarily internal resistance and leakage inductance of the respective energized transformers.
But the opened primary transformer now becomes an inductor of much higher inductance than its original leakage inductance, and a resistance about 1/2 of its original resistance as viewed from its secondary side. The voltage applied to this inductor is about what it would have been if the primary was not opened.
Substantial series current will exist. This will be about the excitation current of the transformer with the open primary when viewed as that transformer being back driven.
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gar
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Something else to consider:
Suppose I put a load on one secondary, could be a resistance. Now I have a series parallel circuit.
But for analysis purposes I can determine a series equivalent circuit for that one secondary and its load that consists of a voltage source of some voltage and phase angle, and a series equivalent internal impedance. If this equivalent circuit replaces the original secondary, then for analysis purposes I am back to the delta being a series circuit.
One definition of a series circuit says that a single current flows thru all elements of the circuit.
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Something else to consider:
Suppose I put a load on one secondary, could be a resistance. Now I have a series parallel circuit.
But for analysis purposes I can determine a series equivalent circuit for that one secondary and its load that consists of a voltage source of some voltage and phase angle, and a series equivalent internal impedance. If this equivalent circuit replaces the original secondary, then for analysis purposes I am back to the delta being a series circuit.
One definition of a series circuit says that a single current flows thru all elements of the circuit.
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kwired
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But going back to what OP said delta secondary is basically a closed loop. This is something I never thought of before - what prevents a circulating current from developing in that loop. Something tells me there can be some circulating current in that loop as a result of minor differences between each segment of the loop.
gar
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kwired:
Circulating currents do exist. The amount is determined by the sum of the voltages divided by the sum of the impedances. Harmonics become a very important consideration.
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kwired:
Circulating currents do exist. The amount is determined by the sum of the voltages divided by the sum of the impedances. Harmonics become a very important consideration.
.
kwired
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Any circulating current would have to result from an imbalance on the primary side. If the primary source is a delta bank it will be close to balanced, barring voltage drop from heavily unbalanced loads.
If, on the other hand the source is a wye, the imbalance in the delta secondary could be quite large. This same effect is why it is not recommended to connect the primary wye point of a wye to delta transformer, leaving it floating instead.
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