# Prepare to synchronize a generator with the grid

Terms & Conditions

To synchronize a generator on the grid, four conditions must be fulfilled:

1. Phase sequence
2. Voltage magnitude
3. Frequency
4. Phase angle

1. Phase sequence

The phase sequence ( or phase rotation ) of the three phases of the generator must be identical to the phase sequence of the three phases of the generator. electrical system ( synchronize a generator)

The phase sequence can be wrong only during initial installation or after maintenance. There are two possible sources of problems.

The generator or transformer power cables could in fact be interchanged during maintenance or the potential transformer cables could be interchanged during maintenance.

2. Voltage amplitude

The amplitude of the sinusoidal voltage produced by the generator must be equal to the amplitude of the sinusoidal voltage of the network.

If all other conditions are met but the two voltages are not the same, i.e. there is a voltage differential, closing the AC generator output circuit breaker will cause a potentially large MVAR Flow.

Remember that before synchronizing a generator with the network, there is no current, no armature reaction and therefore the internal voltage of the generator is the same as the voltage at the terminals of the generator.

If the generator voltage is higher than the grid voltage, it means that the internal generator voltage is higher than the grid voltage. When connected to the grid, the generator will be overexcited and output an MVAR value.

If the generator voltage is lower than the grid voltage, it means that the internal generator voltage is lower than the grid voltage. When connected to the grid, the generator will be under-excited and absorb the MVAR.

3.frequency

The frequency of the sinusoidal voltage produced by the generator must be equal to the frequency of the sinusoidal voltage produced by the network.

The synchroscope would turn rapidly counterclockwise. If the generator circuit breaker were to be accidentally closed, the generator would no longer be in phase with the external electrical system. It would behave like a motor and the network would try to upgrade it.

In doing so, the rotor and stator would slip off the poles and damage ( possibly destroy ) the generator as previously described. The same problem would arise if the generator was faster than the grid.

The grid would try to slow it down, causing the poles to slip again.

The high points and zero crossings of sinusoidal voltages occur at the same rate.

However, if you notice a 2 with the grid and a phase angle exists between them. It would look like a non-rotating synchroscope ( generator and network at the same frequency ), where the pointer would seem stuck around 9 o’clock ( heat-insulating generator ).

If the generator breaker were to be closed at this time, the grid would drive the generator running.

However, this would again cause a large current flow to the generator and high stress on the rotor/stator with subsequent damage to the generator. If the generator set were to lead the grid, it would immediately try to supply the grid with the same destructive forces as mentioned. To get free training of more this kind of website click here.

Therefore, the generator should be brought to a point where the grid voltage waveform exactly matches what it is producing.

4. Phase angle

As mentioned earlier, the phase angle between the voltage produced by the generator and the voltage produced by the network must be zero.

The phase angle (0 to 360 °) can easily synchronize a generator observed by comparing the simultaneous occurrence of peaks or zero crossings of sine waveforms.

If the generator breaker is closed when they match exactly, the connection will appear smooth and transparent.

At this instance, the pointer on the synchroscope would indicate 12 o’clock.

The worst-case happens if the generator is exactly out of phase, with a phase angle of 180 ° and the synchroscope pointing at 6 o’clock.