Relationship Between Active Power and Reactive Power of Generator
Active
power is the electrical power required to keep a consumer operating normally,
that is, the electrical power that converts electrical energy into other forms
of energy (mechanical, optical, thermal). Various lighting devices convert
electrical energy into light energy for people to live and work with. The sign
of active power is denoted by P and is expressed in watts (W), kilowatts (kW),
megawatts (MW).
Reactive
power is relatively abstract, it is used to exchange electric and magnetic
fields in the circuit, and is used to establish and maintain the electrical
power of the magnetic field in electrical equipment. It does not work
externally, but instead transforms it into other forms of energy. For
electrical equipment with electromagnetic coils, reactive power must be
consumed to establish a magnetic field. Because it does not work outside, it is
called "reactive." The sign of reactive power is represented by Q,
and the unit is either Var or kVar.
Reactive
power is by no means useless power, and it is very useful. The motor needs to
establish and maintain a rotating magnetic field to rotate the rotor, thereby
driving the mechanical motion. The rotor magnetic field of the motor is
established by taking reactive power from the power source. The transformer
also needs reactive power to generate a magnetic field in the primary coil of
the transformer and induce a voltage in the secondary coil. Therefore, without
reactive power, the motor will not rotate, the transformer will not be
transformed, and the AC contactor will not pull.
Under
normal circumstances, the powered device not only needs to obtain active power
from the power supply, but also needs to obtain reactive power from the power
supply. If the reactive power in the power grid is in short supply, the power
equipment does not have enough reactive power to establish a normal
electromagnetic field. Then, the power equipment cannot be operated under the
rated condition, and the terminal voltage of the power equipment is lowered.
Thereby affecting the normal operation of the electrical equipment. Reactive
power has certain adverse effects on supply and use of electricity, mainly in:
1.
Reduce the output of the generator's active power.
2.
Reduce the power supply capacity of transmission and transformation equipment.
3.
This causes an increase in line voltage loss and an increase in power loss.
4.
This results in low power factor operation and voltage drop, resulting in
insufficient electrical equipment capacity.
The
reactive power supplied from the generator and the high-voltage transmission
line can not meet the needs of the load, so some reactive power compensation
devices should be set in the power grid to supplement the reactive power to
ensure the user's need for reactive power. Electrical equipment can operate at
rated voltage. This is the reason why the grid needs to install reactive power
compensation devices.
Relationship between
active power and reactive power of diesel generator
Principle of power
generation
Generators
are divided into two major categories: DC generators and alternators. The
latter can be divided into synchronous generators and asynchronous generators.
The most commonly used in modern power stations is synchronous generators. This
type of generator is characterized by DC current excitation, which can provide
both active power and reactive power to meet the needs of various loads.
Synchronous generators are classified into three types: turbine generators,
hydroelectric generators and diesel generators according to the different prime
movers used. By installing the brushless synchronous alternator coaxially with
the diesel engine crankshaft, the rotor of the generator can be driven by the
rotation of the diesel engine. By using the principle of 'electromagnetic
induction', the generator will output an induced electromotive force, and a
current can be generated through the closed load circuit. .
Synchronous generator
power calculation
According
to the active power calculation formula, we can see that: 1) the load angle δ
controls the magnitude of the active power P; 2) the voltage amplitude E
controls the magnitude of the reactive power Q.
When
the terminal voltage of the generator is kept at the rated value and the active
power of the output is P, the relationship between the maximum reactive power Q
of the allowable output and the active power P is Q=f(P), which is called the
output capacity of the generator curve.
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