Hello friends, I hope all of you are fine. In today’s tutorial, we are gonna have a look at Synchronous Generator Ratings. There are numerous restriction on the power and the speed of synchronous generator that generator follows during its operation. Such restrictions are known as the ratings of the generator. The main benefit of these limits or ratings is to operate the generator within the safe conditions. For safe operation, every machine either generator or motor has many ratings that are mentioned on its nameplate.
Normally ratings that are mentioned on the nameplate of the synchronous generator are its apparent power in kilovolt-ampere, speed, operating voltage, frequency, P.F, IF and temperature-pressure conditions. In today’s post, we will discuss all these ratings of the synchronous generator with the detail. So, let’s get started with the Synchronous Generator Ratings.
Synchronous Generator Ratings
Voltage, Speed, and Frequency Ratings of Generator
- The rated frequency of the synchronous generator depends on the power system with which generator is attached.
- In Asian and European countries, the frequency of the power system is fifty hertz while in the united states of America is sixty hertz.
- If we know the frequency of the system than we can easily find the speed for the specified poles of the machine.
- The famous relation among the frequency and the speed of the machine is given as.
fe =(nmx P)/120
- Possibly the very important rating is the voltage according to voltage, structure of the generator is designed.
- There are some factors at which voltage of the generator are depended like speed, design of the generator and the flux.
- For a specific structure size and speed of the generator, as desired voltage increases the flux of the generator also increases.
- Nevertheless, flux cannot be increased continually, because there are some limits for the field current IF.
- Additional deliberation in setting the extremely acceptable voltage is the break-down value of the winding insulation, standard operating voltages must not reach break-down so easily.
Is it possible to operate a 6O-Hz generator at 50 Hz?
- The answer to this question is ‘yes’ but there are some conditions that generator should follow.
- Principally, the issue is that there is an extreme flux attainable in any machine, as we know that the EA =Køw the maximum internal voltage varies with the change in the speed.
- If we operate sixty-hertz generators at fifty-hertz frequencies, then the rated voltage of the generator will de-rated up to the (50/60) or 83.3% of its real value.
- Similarly, if we operate the fifty-hertz generator on the sixty-hertz frequency then the opposite effect will happen.
Apparent Power and Power-Factor Rating of Synchronous Generator
- There are 2 main facts that describes the power limitations of the electrical machines like a synchronous generator.
- The first one is the torque on the shaft of the generator and the second one is heating of the windings of the generator.
- The shaft of the generator has capability to bear the larger mechanical power than the rated power of the generator, so the practically steady-state parameters are controlled by the heating of the windings.
- There are 2 main windings of the generator, first is armature windings that wound on the stator and second is field winding that wound on the rotor, both of these windings should be laminated from over-heating.
- The value of the apparent power S of the generator defined by the armature current of the generator, and it is given as.
- If the rated voltage value of the generator is already given, then the extreme adequate armature current can be used to find the rated value of the apparent power in kilovolt amperes.
Srated =3Vø,rated IA,max
Srated =√3VL,rated IL,max
- It is significant to understand that, for heating the armature windings, the P.F of the IA is inappropriate. The heating effect of the stator I2 R losses is given here.
- These losses are not depending on the angle of the current with respect to Vø.
- Since the current angle is unrelated to the heating of armature’s windings because the generator is rated in KVA, not in KW.
- The field windings copper losses are given here.
- Thus, the extreme acceptable heating sets an extreme field current for the generator.
- As EA =Kwø this equation finds the value of the internal generated voltage as these voltage depends on the speed and the flux.
- The effect of having an extreme field current and a extreme internal generated voltage interprets directly into a limit on the lowermost adequate P.F of the generator when it is working at the rated KVA.
- In below figure you can see the phasor diagram of the generator’s rated voltage and the armature current.
- The current can undertake numerous different angles, you can see in the above figure.
- The EA is obtained with the addition of the Vø and jXsIA.
- Note that for some probable current angles the essential internal generated voltage EA surpasses the EA, max.
- If the generator were functioned at the rated IA and these P. F’s, the windings of the rotor will burn out.
- The angle of the armature current that needs the extreme internal generated voltage, whereas Vø retains the rated value and provides the rated P.F of the generator.
- It is likely to function the generator at a lesser or lagging P.F than the rated value, but only by decreasing the KVA provided by the generator.
You can also read some related topics to synchronous generator that are listed here.
This is the detailed article on ratings of synchronous generator if you have any query ask in comments. See you in the next tutorial Synchronous Generator Capability Curves.