Influence of mechanical speed on generation voltage and frequency for a wind turbine and Grid synchronization of wind turbine.

Experiment No.: – 08

Aim of the Experiment: –

Influence of mechanical speed on generation voltage and frequency for a wind turbine and Grid synchronization of wind turbine.

Apparatus Required: –

Sl. No.	Name	Specification	Quantity
1	Wind turbine system with module of DFIG		1 no.
2	Computer System		1 no.

Diagram: –

Theory: –

The generator’s stator is connected via a power contactor to the grid. The generator’s rotor is fed via an inverter. Despite changing wind conditions, i.e. fluctuating speeds, the generator must produce voltage of a constant frequency and amplitude in order to feed energy into the grid. This is achieved through proficient regulation of the current supply for the rotor. The operating principle is demonstrated in the animation below.

Grid synchronization of wind turbine-

The following conditions must be met to connect the generator to the grid:

a. Grid frequency = generator frequency

b. Grid voltage = generator voltage

c. Grid phase angle = generator phase angle

If a large-scale plant fails to meet any of these conditions, connecting the generator to the grid results in high compensation currents which can damage individual plant components.

Procedures: –

1A: – Influence of mechanical speed on generation voltage and frequency for a wind turbine–

1. Switch on the machine test stand and control unit for the doubly-fed induction generator.
2. Switch on the three-phase grid voltage for the control unit, making sure that the transformer’s circuit breaker is not tripped.
3. Open the DFIG control instrument (the USB interface must be connected to the PC).

4. On the machine test stand, select the SPEED CONTROL mode and set the speed to 1200 rpm.

5. Actuate the ENABLE button on the virtual instrument.

6. Set the amplitude to 40% at a frequency of 0 Hz.

7. Determine the mechanical frequency (in Hz) and generator voltage’s frequency.

8. Repeat the measurements at 1300 rpm and 1400 rpm.

1B: – Grid synchronization of wind turbine.

1. Switch on the machine test stand and control unit for the doubly-fed induction generator.
2. Switch on the three-phase grid voltage for the control unit, making sure that the transformer’s circuit breaker is not tripped.
3. Open the SYNCHRONIZER instrument (the USB interface must be connected to the PC).

4. On the machine test stand, select the SPEED CONTROL mode and set the speed to 1200 rpm.

5. Actuate the ENABLE button on the virtual instrument.

6. Slowly increase the amplitude on the instrument until the generator’s stator voltage has attained roughly 80% of the grid voltage.

7. Increase the frequency until the power grid and generator frequencies are equal.

8. Vary the voltage generator’s amplitude and frequency so that all criteria for connection to the grid are met.

9. Use the synchroscope for adjustment.

10. Actuate the LINE button to connect the generator to the grid. The generator is now online.

11. Actuate the LINE button again to disconnect the generator from the grid.

12. Actuate the ENABLE button to de-energize the generator.

Observation Table: –

1A: – Influence of mechanical speed on generation voltage and frequency for a wind turbine–

1. At a mechanical speed of 1200 rpm: The mechanical frequency is ____Hz; the voltage frequency is ____ Hz.
2. At a mechanical speed of 1300 rpm: The mechanical frequency is ____Hz; the voltage frequency is ____ Hz.
3. At a mechanical speed of 1400 rpm: The mechanical frequency is____Hz; the voltage frequency is ____ Hz.
4. The generator behaves like a:

a. Shunt dynamo.

b. Synchronous generator.

c. Series dynamo.

1B: – Grid synchronization of wind turbine. (tick the correct answer)

1. How can the phase shift between the power grid and generator be adjusted ?

a. If the generator and grid frequencies are approximately equal, the phase shift can be adjusted by changing the rotor current’s amplitude.

b. The phase angle between the power grid and generator corrects itself automatically if the grid and generator frequencies are identical.

c. If the generator and grid frequencies are similar, a phase shift occurs between the generator and grid. In this case, the phase angle can be adjusted through minor changes in the generator frequency.

2. How does the rotor current influence synchronization with the grid ?

a. The rotor current influences both the output voltage’s magnitude and generator frequency.

b. The rotor current influences the generator voltage’s magnitude.

c. The rotor current only influences the generator frequency.

3. Repeat synchronization of the generator at 1300 rpm and 1400 rpm.

Copy the timing diagram of the grid and generator voltages during unsynchronized and synchronized operation to the placeholders provided for this purpose.

4. Compare the generator voltages in the offline and online modes.

a. When the generator is online, its voltage is equal to the grid voltage.

b. When the generator is offline, the voltages differ in terms of amplitude, frequency and phase angle.

c. The ripple in the generator’s voltage is caused by the rotor current control mechanism.

d. Even when the generator is online, its voltage differs from the grid voltage.

5. (i) Repeat synchronization of the generator at 1300 rpm. Use the automatic mode for synchronization. In this process, the appropriate rotor values are set but the generator’s stator is not connected automatically to the grid.

(ii) Do not connect the generator to the grid.

( iii) Vary the generator speed between 1200 rpm and 1400 rpm. What is the result ?

Observe the generator voltage.

a. As the speed changes, only the generator frequency is regulated automatically.

b. Only the generator amplitude is regulated automatically.

c. As the speed changes, the generator voltage, frequency and phase angle are regulated to achieve synchronization with the grid.

Conclusion: –

To be written by student.