P安全生产金句age1 Generators and Motors
From reference 1
1. Direct-current generators impress on the line a direct or continuous emf, one that is always in the same direction. Commercial dc generators have commutators, which distinguish them from ac generators. The function of a commutator and the elementary ideas of generation of emf and commutation are discusd in Div. 1. Additional information about commutation as applied to dc motors, which in general is true for dc generators, is given below.
麻纺2. Excitation of generator fields. 论文致谢词范文To generate an emf, conductors must cut a magnetic field which in commercial machines must be relatively strong. A permanent magnet can be ud for producing such a field in a generator of small output, such as a telephone magneto or the magneto of an insulation tester, but in generators for light and power the field is produced by electromagnets, which may be excited by the machine itlf or be parately excited from another source.Self-excited machines may be of the ries, shunt, or compou
nd type, depending upon the manner of connecting the field winding to the armature. In the ries type of machine,the field winding (the winding which produces the magnetic field) is connected in ries with the armature winding. In the shunt type, the field winding is connected in parallel,shunt, with the armature winding. Compound machines have two field windings on each pole. One of the windings is connected in ries with the armature winding, and the other is connected in parallel or shunt with the armature winding.
3. Armature winding 微乎其微的近义词of dc machines may be of the lap or the wave type. The difference in the two types is in the manner of connecting the armature coils to the commutator.A coil is the portion of the armature winding between successive connections to the commutator.In the lap type of winding (e Fig. 7.1) the two ends of a coil are connected to adjacent commutator gments. In the wave type of winding (e Fig. 7.2) the two ends of a coil are connected to commutator gments that are displaced from each other by approximately 360 electrical degrees.The type of armature winding employed affects the voltage and current capacity of the machine but has no effect upon the power capacit
y. This is due to the fact that the number韵母表图片 of parallel paths between armature terminals is affected by the type of winding. For a wavewound machine there are always two paths in parallel in the armature winding between armature terminals. For a lap-wound machine there are as many parallel paths in the armature winding as there are pairs of poles on the machine. For the same number and size of armature conductors, a machine when wave-connected would generate a voltage that would equal the voltage generated when lap-connected times the number of pairs of poles.But the current capacity would be decread in the same proportion that the voltage was incread. The current capacity of a machine when wave-connected is therefore equal to the capacity when lap-connected divided by the number of pairs of poles.
三角魔方公式4. The value of the voltage generated by a dc machine depends upon the armature winding, the speed, and the field current. For a given machine, therefore, the voltage generated can be controlled by adjusting either the speed or the field current. Since generators are usually operated at a constant speed, the voltage must be controlled by adjusting the field current.
5. Separately excited dc generators are ud for electroplating and for other electrolytic work for which the polarity of a machine must not be reverd. Self-excited machines may change their polarities. The esntial diagrams are shown in Fig. 7.3. The fields can be excited from any dc constant-potential source, such as a storage battery, or from a rectifier connected to an ac supply.The field magnets can be wound for any voltage becau they have no electric connection with the armature. With a constant field excitation, the voltage will drop slightly fromno load to full load becau of armature drop and armature reaction.Separate excitation is advantageous when the voltage generated by the machine is not suitable for field excitation. This is true for especially low- or high-voltage machines.
6. Series-wound generators have their armature winding, field coils, and external circuit connected in ries with each other so that the same current flows through all parts of the circuit (e Fig. 7.4). If a ries generator is operated at no load (external circuit open), there will be no current through the field coils, and the only magnetic flux prent
in the machine will be that due to the residual magnetism which has been retained by the poles from previous operation. Therefore, the no-load voltage of a ries generator will be only a few volts produced by cutting the residual flux. If the external circuit is clod and the current incread, the voltage will increa with the increa in current until the magnetic circuit becomes saturated. With any further increas of load the voltage will decrea. Series generators have been ud sometimes in street-railway rvice. They have been connected in ries with long trolley feeders supplying ctions of the system distant from the supply point in order to boost the voltage. However, power rectifiers have replaced dc generators for most installations of this type.
凉薯的做法 Keywords: generator
From reference 2
Since triphad asynchronous generators are mainly ud in conversion systems of a eolian energy into electric energy, their functional stability reprent is小小鸡
of great importance. As a first step, the factors that radically affect the functional stability of the generators have been established. Thus, it was decelat the powerful influence of the capacitor bank – that provides the necessary reactive power for the
magnetization of the ferromagnetic core – over the functional stability of the triphad asynchronous generator with short circuit rotor. The functional stability is greatly influenced by the charge character (type) as well. The experimental work emphasized – through the functional features – the way the parameters influence the stability area of the asynchronous generators. As far as triphad asynchronous generators with coiled rotor are concerned, the controllable blind power was analyzed the analogy being made with the situation of the necessary controllable generating capacity for of the triphad asynchronous generator with short circuit rotor.
