Voltage Unbalance - Alternator

How can you say phase voltages are balanced and line voltages are varied? In delta connection of stator/armature.

It would appear that you have slightly more resistance in one of the windings than in the other windings. Since you are star connected, I am assuming what you are referring to as "Line Voltages" are measured line to ground. A further clue is the slight difference in the phase angles. I would suspect the connections first- most likely at the common ground point. If as is common, you have each phase built from multiple windings in series, the connections between the windings can also cause such symptoms.

You need to check the resistance of each winding- use a four wire measurement technique for good measurements at low resistance. You also should measure the inductance of each winding.

It is also possible that you have some faulty insulation on one of the windings. You can look at the windings with a TDR, which will tell you if you have any impedance changes in the winding, and where such impedance changes occur.

How line voltage is measured between line to ground ?it should be line to line know?

There is some ambiguity in terminology, and not being an electrical engineer, I may have it backwards.

In your star connection, you have three (assuming three phase power) sets of series-connected windings all connected on one end to a common point, which is your ground reference, and is generally connected to earth ground, and the load is connected to the free ends of each set, either in combination or between the end point and ground. It is the voltage between the end point of each series of windings and the common connection point of the three sets that I refer to as "line" voltage, and that is the measurement that seems imbalanced from the information you have provided. Here is a picture of a simple star configuration using only three windings:

Note that normal "neutral" connection for the return of each single phase is through the common point on ground. If you draw a vector diagram with your measurements, using your line voltage measurement and phase angle measurements, then inscribe a circle through the end points of the vectors, you will find that the center point no longer coincides with the center point of the vectors. The center point of the circle will have shifted toward or away from one of the end points of the vectors. This means that you do not have equal impedance (resistance plus inductance) in the three phases. Drawing the vector diagram will help you understand what the real issue is with the imbalance, and where to look.

Dear All,

Thank you very much for the Great Response.

I would like to clarify -

This is STAR connected Alternator - Neutral Open ( Floating - Not Connected to Earth) - The Line Voltages are the Voltages measured LIne to Line & the Phase Voltages are the Voltage between Phase & the Neutral.

We have Measured the Resistances of each phase winding it is 40.02 milli Ohms Balanced for all Phases. We have also carried out the Impedance Matching Test with the Test Voltage of 2.5 kV ( Alternator Rated Voltage is 415 Volts), the Impedances are same.

Would also like to specify -

The Stator Laminations are not segmented - (48 Slots in the Main Stator Lamination).

It is 4 Parallel Path, Double Layer Lap Winding wound for 4 Pole (2 Pole Pairs) Design, No of Conductors in the Slot are ODD - 35-30-35-30 in sequence.

I suppose these would be as per your requirements.

Meanwhile we are also doing some experiments, I will post the observations as measured..

Based on the information furnished, the possibility of error caused due to difference in slot pitches of various slots in core lamination seems to be higher. Are you staggering the laminations while core building? if not then staggering may eliminate the problem. You may also like to measure the voltages of various parallel paths and find the difference if any particular path is generating higher / lower voltage.

Good answer from Panama.

Kindly furnish further details of the generator Specially the following:

Type of stator core segments (full circle or part segments)

Overlap of the sore segments if it is part segment core.

Number of parallel path, number of pole, type of winding, turns per slot, Voltage of generator.

I may be able to help you after getting this information.

Is this loaded or unloaded, do you have 3 phase voltage sensing