There are many forms of
generator, but the working principle is based on the law of electromagnetic
induction and the law of electromagnetic force. Therefore, the general
principle of its construction is to use appropriate magnetic conductive and
conductive materials to form magnetic circuits and circuits for mutual
electromagnetic induction to generate electromagnetic power and achieve the
purpose of energy conversion.
Working
principle of alternating-current generator
The mechanical energy of
the prime mover is converted into electrical energy output by using the
principle of electromagnetic induction in which the cutting of magnetic lines
of force by a wire induces electric potential. A synchronous generator consists
of a stator and a rotor.
The stator is the
armature that emits power, and the rotor is the magnetic pole. The stator is
composed of armature iron core, three-phase winding with uniform discharge,
base and end cover. The rotor is usually a hidden pole type, which is composed
of excitation winding, iron core and shaft, guard ring, center ring and so on.
A direct current flows into the rotor's excitation winding to generate a nearly
sinusoidal distributed magnetic field (called the rotor field), and its
effective excitation flux intersects the stationary armature winding. When the
rotor rotates, the rotor's magnetic field rotates with it. With each
revolution, and the magnetic field lines sequentially cut each phase winding of
the stator, and the three-phase AC potential is induced in the three-phase
stator winding. When the generator is running with a symmetrical load, the
three-phase armature current is combined to produce a rotating magnetic field
with synchronous speed. The stator magnetic field interacts with the rotor
magnetic field to generate braking torque.
Alternating-current
generator/alternator is divided into single-phase generator and three-phase
generator. Alternator is often used in diesel generator sets.
The
AC generator installation inspection steps are as follows:
1) When installing the
generator, ensure that the cooling air inlet is unobstructed, and avoid
exhausted hot air from entering the generator. If there are blinds on the
ventilation cover, the window should face down to meet the requirements of the
protection level. For mechanical coupling of single-bearing generator, special
attention should be paid to the uniform air gap between the stator and rotor.
2) The coupling of AC
generator and diesel generator requires the parallelism and concentricity of
the coupling to be less than 0.05 mm. The requirements in actual use can be
slightly lower, within about 0.1 mm, too much will affect the normal operation
of the bearing, resulting in damage, the coupling should be fixed with a
positioning pin. Retest the coupling before installation.
3) The U, V, W, N marks
are printed on the terminal head in the generator outlet box, which does not
indicate the actual phase sequence and depends on the direction of rotation.
The UVW printed on the certificate indicates the actual phase sequence of
clockwise rotation, and VUW indicates the actual phase sequence of
counterclockwise rotation.
4) When the generator
with sliding bearing is coupled, the height of the center of the generator
should be adjusted slightly lower than the center of the diesel engine, so that
the weight of the flywheel on the diesel engine will not be transferred to the
generator bearing, otherwise the generator bearing will bear the additional
weight of the flywheel, which is not conducive to the formation of the oil film
of the sliding bearing, resulting in heating and even burning of the bearing.
5) If the neutral points
of each generator in the power supply system are connected to each other, or
when the generator neutral point is connected to the transformer and its load
neutral point, the genset will have a neutral current of 3 times the frequency
on the neutral line in operation. Therefore, the neutral-line current of the
generator must be measured under various load conditions that may occur during
operation. In order to prevent the generator from overheating, the line current
shall not exceed 50% of the rated current of the generator. The neutral-line
power is too large, and a neutral line reactor should be installed on the
neutral line to limit it.
6) According to the
schematic diagram or wiring diagram, select the appropriate power cable and use
copper connectors for wiring, copper joint and busbar. After the busbar and the
busbar are firmly fixed, the local gap at the joint is not greater than 0.05 mm,
and the distance between the wires is not greater than 10mm, also need to
install the necessary grounding wire.
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