I shall be grateful if someone has ideas to share on my question.

Why it is important to know the armature time constant (Ta) of a turbogenerator? Suppose a machine was designed to have a Ta of 0.2 seconds but was tested for Ta = 0.4 seconds, how does it show that the machine has failed the test or is it better than the designed value? Which standard stipulates the value for Ta of turbogenerator? Lastly on what values of the turbogenerator design does the Ta depend (e.g. air gap, SCR etc.)?

Thanks.

 

Responding to Abby's Nov 15, 12:35 am inquiry:

1) Function
A generator's current contribution to an electrical fault at (or beyond) its terminals, decays exponentially at a rate determined by the time constant, Ta.

2) Magnitude Basis.
Ta is simply the armature (stator) winding's inductance-to-resistance ratio. The inductance is found from its negative-sequence reactance, X2, while its resistance is Ra. Often, the subtransient-reactance value is used.

3) Standard.
I am not aware of a standard, but there are typical values shown in reference documentation. Typically, in the USA, a 2-pole machine has an average value of 0.13, but ranges between 0.04 to 0.24. The 4-pole machine values are 0.20, and 0.15 to 0.35, respectively! I also believe that European machines have comparable values.

4) Contribution-to-Performance.
The higher value indicates, at least to me, that there is more copper than "usual!"

5) References.
I used Westinghouse's T&D Electrical Reference Book (ca 1950). I'm sure you should be able to obtain data from the manufacture. However, if not, let me know and I will send you a copy of the "Typical Constants" Table!

Regards, Phil Corso, PE {Boca Raton, FL, USA} [[email protected]] ([email protected])

 

Further to my Nov 18 response:

Ta is used for faults at the generator's terminals. Ta' is used for faults beyond the generator's terminals. Ta' is the value Ta, but adjusted to include the circuit impedance between the generator and the fault location!

Contact me if the adjustment factor is needed!
Regards, Phil Corso, PE

 

Dear sir

please tell me Armature time constant And Demagnetisation time constant both are same or not

 

Prasad… these terms are used interchangeably depending upon the electrical apparatus you are speaking of:

o DC Machines.

o AC Alternators with DC excited field.

o AC Alternators with PM excitation.

Can you provide additional detail?

Regards, Phil