I am interested in three tests used on the insulation systems; both stator and rotor windings. These test are the Poalrization Index, Dielectric Discharge and Step Voltage. I have used PI testing on my generators forever and am considering adding both Dielectric Discharge and Step Voltage to...
What is the typical setpoint and basis for unbalance protection on an induction motor. Specifically, magnitude differences between the 3 phase currents, negative sequence current and negative sequence voltage.
Background - Induction generator when fully loaded trips off due to current...
Fit your data with TableCcurve 2D
www.systat.com/products/TableCurve2D
It will give you the best fit, the statics for the fit, residuals, prediction interals and fit intervals with a select confidence level.
Then put the formula into a spread sheet
Did you check the Diodes and fuses to insure the the bridge is working correctly? I believe on a rotating exciter you use an indirect measurtement for field current. A blown diode or open fuse may be limiting the field current.
If the bridge is working correctly. perfrom an open circuit...
Work in the power industry (Mechanical and Electrical) will be up in future. It is estimated that the retirement rate will be 50% in the next 5 to 10 years. Several utilities expect to lose 70% in that time frame. At my company I am already seeing the rate of retirements grow. I also am...
motorspert
You sent me back to my books (and associates) to review the calculation of machine impedances and time constants (at Design).
Here is what I condensed from that review.
Reactance and time constants will be the same for a machine with the same parallel to coil turn ratio. A change...
Generator reactances and time constants are a function of the stator geometry. Rewinding the generator with a different winding configuration will not change the reactance of the machine. Increased copper sizes will decrease the resistance.
At least with my company (Electric Utility)we are hiring new EE graduates (or graduates with 1 to 2 years of experience. Then putting them with seasoned engineers to develop there power expertise. We do no not look overseas for new grads. Due to the nature of utilities being part of local...
I am in the power industry (utility). One thing interesting about this industry is the retirement issue. 40% to 50% of this industries employees are eligible for retirement within the next 5 years. Management is figuring this out and is getting concerned. In addition, a ton of new power...
You should inspect your damper bars. During an out of syncronization large currents can flow in the damper bars.
I have inspected several units that have been closed in out of synch and on both I found burning on the damper bars.
In addition, you should check the slip rings. During a out of...
Two flanges bolt together with an electrical insulating gasket between them. A bolt from the outside of the 'vessel' hold the inner piece to the outer piece. The bolt hole is electrical insulated by a washer and nonconducting tube.
The bolt head is at air atmophere pressure. The insulated...
When evaluating your machine for a generator you have to assume that a load rejection happens and the wicket gates do not close, hence the unit goes to the runaway speed. Your generator must survive this speed the specific amount time necessary to shut the unit by additional means. Example...
You can use a synchronous motor as a generator. However, for hydro application over speed becomes a critical concern. Upon a load rejection the turbine generator can easily reach speeds of 2 times normal running speed.
In the event of load rejection and failure of the wicket gates to close the...
We had a similar problem at one of our combustion turbine generators.
The problem was a result of non-uniform coil expansion under the retaining ring. As the coils grew out the imbalance became worse and coil growth was a function of field current.
Based on your description I would 'guess'...
I realize this is too late to be of use, but I have been in the field since May working on our generators. If the situation happens again maybe this will be useful.
The same situation has occurred several times in the last few years on the generators I manage. On all of the occasions I...
A 3-phase induction generator has balanced terminal voltages but an unbalance in the currents. One phase current is about 25% lower than the other two. Voltages are balanced to the low-side of the step-up transformer.
What can cause this and what tests (simple) can be performed to find out...
We have several induction generators. We performed a test that measured inrush current on the generator verses unit speed at breaker closing. We found that the lowest inrush occurred at around 105% rated speed.
We performed the test by placing a resistor in the CT circuit and recording the...
I have seen red dust on wedges before. In my experience the dust is iron oxide from the wedge abraiding the iron laminations. The only force in the slot that can result in wedge movement is coil force.
Two test I use.
First I perform a tap test. I use a tac hammer. This hammer has a split...
My experience is that comparisons between different generators is of little value. This may be due to different insulation systems and winding configurations. Comparison of test results for a single generator when normalized for temperature provide better trending. I find that a detailed...
