Synchronous machine stator current

• bizuputyi
In summary, when the load on a synchronous machine is constant, the stator current can be varied by changing the excitation of the machine. This can be achieved by connecting the alternator to the grid or infinite bus. By increasing the excitation, the induced voltage and current supplied to other machines increases, resulting in an increase in total current and a decrease in power factor. This keeps the active power supplied constant while increasing the reactive power supplied. Phasor diagrams can be used to illustrate this effect.
bizuputyi

Homework Statement

Explain how the synchronous machine stator current can be varied if the load is constant. Justify your answer with phasor diagrams.

2. The attempt at a solution

If load is constant then load angle, the angle between induced e.m.f. and terminal voltage remains the same. Phase angle is the angle between stator current and terminal voltage, so if I change power factor that will alter stator current? But how can power factor be changed if the load is constant? Does this make any sense?

Are these the phasor diagrams that are expected to see?

Attachments

• phasor diagrams.png
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This can be achieved by changing the excitation of the machine. But the alternator must be connected to the grid or infinite bus to make this happen. In this situation, frequency(rpm of the generator) and terminal voltage are constant as the machine is tied synchronously with the grid. Now if the excitation of the machine is increased, induced voltage(or generated emf) increases and supplies a current to other machines. This way, this extra current flows between the machine and other machines and not through the load. This current is superposed on the load current of the machine. One interesting thing is that the total current I of the machine increases and its power factor decreases such that IcosΦ remains constant. This way, the active power(kW) supplied by the machine is constant but the reactive power supplied(RkVA) increases.

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Thank you, it starts making sense now, so changing excitation will alter stator current. I think my phasor diagrams show all that, don't they?

bizuputyi said:
Thank you, it starts making sense now, so changing excitation will alter stator current. I think my phasor diagrams show all that, don't they?
In your phasor diagrams, terminal voltage V is not constant. I believe they are showing the effect of armature reaction on the terminal voltage of an isolated generator at different power factors. You can google "alternator on constant load and variable excitation" or refer any good machinery book to learn this in terms of phasor diagram.

Last edited:
Right, that seems a good phrase to google with. Thank you.

1. What is synchronous machine stator current?

Synchronous machine stator current refers to the electrical current that flows through the stator windings of a synchronous machine, which is a type of electric motor or generator. It is responsible for creating the rotating magnetic field that interacts with the rotor to produce mechanical energy or convert mechanical energy into electrical energy.

2. How is synchronous machine stator current controlled?

Synchronous machine stator current can be controlled through various methods such as varying the excitation voltage, adjusting the field current, or changing the load on the machine. By controlling the stator current, the speed and torque of the machine can be regulated to meet the desired requirements.

3. What factors affect synchronous machine stator current?

There are several factors that can affect synchronous machine stator current, including the load on the machine, the excitation voltage, the field current, the mechanical load, and the power factor. Any changes in these factors can cause variations in the stator current, which can impact the performance of the machine.

4. How is synchronous machine stator current measured?

Synchronous machine stator current can be measured using various techniques such as ammeters, clamp-on meters, or digital multimeters. These instruments are connected in series with the stator windings to measure the current flow. Advanced methods such as power analyzers can also be used to measure and analyze the stator current in real-time.

5. What are the applications of synchronous machine stator current?

Synchronous machine stator current has various applications in industries such as power generation, renewable energy, electric vehicles, and industrial processes. It is used to control the speed and torque of the machine, maintain power factor, and regulate the overall performance of the machine. It is also important for the protection and monitoring of the machine.

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