When the active load is
full, the power factor is too high, that is, the reactive power is too low,
reducing the reactive power margin of the system, which will affect the
stability of the generator. Although the economy is improved, in the long run,
this is in exchange for increasing the probability of accidents. In the event
of an emergency, the generator may not be able to withstand small disturbances
or oscillations, may be out of step.
In addition, the low
reactive power will cause the generator terminal voltage to drop, which will
affect the auxiliary power. The current drawn by the motor rises, causing the
voltage to be lower, creating a vicious circle that may cause the entire system
to lose its stable operation and collapse.
1. Too high power factor
will also increase the chance of the generator phase operation, and make the
generator end heat easily.
2. If it is too low, the
reactive power is too high, the excitation current rises, the rotor winding
temperature rises, and the service life is shortened.
3. Too low causes the
genset voltage to rise, the magnetic flux density in the core increases, the
loss increases, and the core temperature rises.
When the generator is
running under the rated load, the power factor is too low, the excitation
current and stator current of the generator increase, which will cause the
equipment to heat up, increasing the chance of equipment aging, switch tripping
and so on.
In the normal operation
monitoring, it should be adjusted according to the voltage. More reactive power
should be generated when the voltage is low, and less reactive power should be
generated when the voltage is high. By adjusting the ratio of active power and
reactive power, control voltage and running current, ensure that the generator
runs under safe and economic conditions.
Generator power factor
adjustment
1. The power factor of
most generators is 0.8, and the individual power factor can reach 0.85 or 0.9.
Under normal
circumstances, when the power factor changes from the rated value to 1.0, the
output of the generator can remain unchanged, but in order to maintain the
static stability of the system, the required power factor cannot exceed 0.95,
that is, the reactive load should not be less than 1/3 of the active load. When
the power factor of the generator is lower than the rated value, the rotor
temperature will increase due to the increase of the rotor current. At this time,
the load should be adjusted to reduce the output of the generator. Otherwise,
the rotor temperature may exceed the limit.
Therefore, the duty
personnel must pay attention to adjusting the load so that the rotor current
does not exceed the allowable value at the inlet temperature of the cooling
air. In general, the power factor is around 0.8-0.9! This is based on the power
factor parameters specified by the unit and the requirements of the power grid.
If the genset is a peaking genset, it may be different during the day and
night.
2. If more reactive
power the generator set generates, the smaller the power factor will be. When
the generator output power remains unchanged, the voltage at the generator end
will rise. The more reactive power, the excitation current will increase, the
stator and the rotor temperature of the unit will rise, if too high, the
insulation of the two may also be affected. Conversely, if the power factor is
too high, the reactive power generated by the unit is very little, and the
terminal voltage will also decrease, which will reduce the stability of the
operation and affect the operation of the generating set.
Therefore, when the unit
is in operation, pay attention to the terminal voltage at the specified value
and ensure that the unit does not run in phase.
3. In order to ensure
the stable operation of the diesel generator, the power factor of the generator
should generally not exceed 0.95 of the late phase, or the reactive load should
be less than 1/3 of the active load. If the generator automatically adjusts the
excitation device to be put into operation, the generator can run for a short
time with a power factor of 1.0 when necessary. Long time operation will cause
the generator oscillation and out of step. At present, large units are
basically not allowed to enter phase operation, and some large units are
undergoing phase-in phase tests, the operating personnel should timely adjust
according to the situation of the genset.
The tests shows that
when the power factor is equal to 0.7, the output of the generator will be
reduced by 8%. Therefore, in the operation of generator, if the power factor is
lower than the rated value, the on-duty personnel must adjust it in time so as
to bring the output to the allowable value as much as possible, and the rotor
current shall not exceed the rated value.
The generator voltage
variation within ±5% of the rated value is allowed for long-term operation, and
the voltage is reduced by 5%, and the current can be increased by 5%. This is
to consider the voltage reduction will reduce the iron consumption. If the
voltage is too low or too high, it will have an effect on the current
operation. First, if it is too high, the temperature rise of the rotor windings
may exceed the allowable value. The voltage is generated by the magnetic field
reaction. The strength of the magnetic field is related to the magnitude of the
excitation current. If the active output is kept constant and the voltage is
increased, the excitation current is increased, so the temperature rises.
Comments
Post a Comment