Because it gives us the information about overshoot and transient time.

Thank you. So you mentioned overshoot info to imply its importance for online estimation. No?

Ref.:Hensngameh Kojooyan Jafari's Question

We use synchronous reactance and the Voltage behind it for steady state analysis as we are interested in conditions after all the transients have died down completely.

We use transient reactance and the Voltage behind it for Stability Studies as we are interested in conditions after the fault occurs to find the critical clearing time or angle because if the fault is not cleared the system may go into unstable condition .

We use sub-transient reactance and the Voltage behind it for Fault analysis as we are interested in finding out the maximum possible current flow immediately after the fault occurs so as to design the Circuit Breaker Rating. Maximum peak value of the fault current for three phase fault at the terminals of the Generator multiplied by a factor 1.8 (or 1.6) is used in deciding the C.B. rating to provide for Doubling Effect of the current if the fault occurs at the instant when voltage is zero.

This is a pertinent question.

Dr.P.S.

Yes. Overshoot is information about dynamics.If we use only static behavior we can make a mistake in estimation. For example, we estimated from steady state an object with description: y=K*x(where y is an output,x is an input,K is a gain), but true description is y=K*x/(T*p+1)(where T is constant time, p is differentiation operator).

Refer Mr.Boris Pyakillya's answer:

He is correct in saying that under Steady state we have Y=k*x (where y is an output,x is an input,K is a gain), but true description is y=K*x/(T*p+1)(where T is constant time, p is differentiation operator).

The reasoning is as follows:

The machine can be represented by its Resistance R and Inductance L in an Electric circuit.

An RL series circuit can be represented by its Laplace Transform Impedance

Z(s)=(R+s*L ) and I(s)= V(s) / Z(s). The s operator corresponds to the Differential Operator D or p. The Time Constant T=R/L decides the Rise time,Settling time etc.

under transient conditions. This Form is useful in getting the value of current in time domain easily. Under Steady state s -> j w and we have Z=(R+j w L).

To study the behavior of the M/C under Transient or Sub Transient conditions as described by my answer given above you have to estimate the Transient or Sub transient Reactances only. For steady state state only Synchronous reactance is used,not transient reactances.

The values of the reactances are different for Salient and Non Salient Pole Machines.

In addition we also have Positive,negative and Zero Sequence Reactances used for analysis of Unsymmetrical Faults.

Dr.P.S.

In addition I may state that we have two other types of reactances -Direct axis reactance and Quadrature axis reactance for Salient Pole Machines. For non salient Pole Machines since the air gap between the stator and rotor is uniform we have only one reactance -direct axis rectance.

Dr.P.S.

Thank you. I want to know more answers. It is very important to know if you use electrical transient region program for machine parameter estimation because my program just uses mechanical transient region which in it, machine electrical parameters are constant. My machine equations are linear for least square method but I have not worked in saturation with nonlinear machine equations if you have worked I am very interested to know about it also please.

The simple answer is that steady state estimation ignores the electrical/ mechanical dynamics which are present under transient conditions. Remember that all power transfered from electrical machine stator to shaft is done via the internal magnetic field of the iron in the stator / rotor. As such it is subject to the non-linear effects of hysteresis under transient or dynamic conditions. Also the mechanical shaft will not be subject to torsional twist etc. This is why, as was pointed out above, one has synhcronous (steady state), transient and sub transient voltages for syncronous machines for example as they represent different dynamic conditions in a simple way. It would also help if you more clearly defined what machine it is that you are referring to and under what conditions you wish to conduct estimation. Your test will also depend on the nature and quality of your motor power supply.

The Mechanical Transients are very slow compared to Electrical Transients.

That is why in mechanical transient region the machine electrical parameters are constant.

Also I endorse the answer given by G.Diana.

Dr.P.S.

Years ago I have studied adaptive control and energetic optimization of aerobic fermenters, having both air flow and agitation speed as manipulated variables. The power dissipated by agitation was accessed by a torque meter inserted at the impeller shaft. The parameters from the (O2 mass-transfer) KLa correlation were successfully estimated using sinusoidal excitation of air flow and agitation speed, through the recursive least squares algorithm with forgetting factor. The (adaptive) control algorithm compared favourably with PID. This investigation was reported at the following MSc Thesis:

Thesis Controlo do Oxigénio Dissolvido em Fermentadores para Minimi...