Generator synchronization

The theoretical framework of this model is compatible with physiological delays and able to generate synchronization. Furthermore, this model is easy to manipulate. A preliminary validation of this model is presented with an artificial network inspired from biology. A long term goal is to use this model to propose a unified and coherent explanation of the local and more distant spectacular effects of DBS on motor signs. 

Type of electrical generator (synchronous or induction type)... 

There are three basic types of rotating electric generators synchronous ac, induction ac, and rotating dc. 

FIGURE 17.3 Illustration of the linear synchronous transit method for generating a starting point for a transition-structure optimization. 

The Cardiac Cycle. The heart (Eig. lb) performs its function as a pump as a result of a rhythmical spread of a wave of excitation (depolarization) that excites the atrial and ventricular muscle masses to contract sequentially. Maximum pump efficiency occurs when the atrial or ventricular muscle masses contract synchronously (see Eig. 1). The wave of excitation begins with the generation of electrical impulses within the SA node and spreads through the atria. The SA node is referred to as the pacemaker of the heart and exhibits automaticity, ie, it depolarizes and repolarizes spontaneously. The wave then excites sequentially the AV node the bundle of His, ie, the penetrating portion of the AV node the bundle branches, ie, the branching portions of the AV node the terminal Purkinje fibers and finally the ventricular myocardium. After the wave of excitation depolarizes these various stmetures of the heart, repolarization occurs so that each of the stmetures is ready for the next wave of excitation. Until repolarization occurs the stmetures are said to be refractory to excitation. During repolarization of the atria and ventricles, the muscles relax, allowing the chambers of the heart to fill with blood that is to be expelled with the next wave of excitation and resultant contraction. This process repeats itself 60—100 times or beats per minute... 

Another concept is brushless excitation, in which an ac generator (exciter) is direc tfy coupled to or mounted on the motor shaft. The ac exciter has a stator field and an ac rotor armature which is directly connected to a static controllable rectifier on the motor rotor (or a shaft-mounted drum). Static control elements (to sense synchronizing speed, phase angle, etc.) are also rotor-mounted, as is the field discharge resistor. Changing the exciter field adjusts the motor field current without the necessity of brushes or slip rings. Brushless excitation is suitable for use in hazardous atmospheres, where conventional brush-type motors must have protective brush and slip-ring enclosures. 

A motor can fall in a generator mode when the machine is energized and is run beyond its synchronous speed, such as when driving a load, travelling down hill or when its speed is reduced to perform a specific duty. The same conditions will appear when a running machine is reversed, whether it is an a.c. or a d.c. machine. 

Regenerative braking If the motor be run beyond synchronous speed by some external means it will work as a generator and feed back useful energy to the supply system. It will draw only the necessary excitation current, / , for the generator action from the source of supply. In such a condition, the motor... 

Code of practice for maintenance of electrical switchgear for voltages above 36 kV Speeificiition for voltage regulation and parallel operation of a.c. synchronous generators Methods of testing plastics... 

The armature of the machine will normally have a residual voltage of around 8 V (for LT machines) across the terminals when running at the synchronous speed. If not, as when the generator is operated after a long shutdown, a d.c. voltage of 12 V can be applied through a battery for a few seconds to obtain the required residual voltage. 

When a generator is designed for a leading p.f. (in the underexcitation mode) it can operate as both a synchronous motor and a synchronous condenser. The machine is now self-starting and does not require a prime mover. 

This device controls the generator and maintains a steady-stale armature voltage automatically within the predefined limits. It also serves to control the reactive kVAr loading during a parallel operation or when the machine is being used as a synchronous condenser for reactive power compensation through a quadrature droop control (QDC) as noted below. 

Push button Nos 22 and 23 may be provided on the AMF panel and also on the remote panel to raise and lower the speed and voltage, when required to control the speed (/i) and voltage E ) of the generator in order for it to be synchronized with another generator or an infinite bus. 

If the field excitation is also lost, the generator will run as an induction motor again driving the primer mover as above. As an induction motor, it will now operate at less than the synchronous speed and cause slip frequency current and slip losses in the rotor circuit, which may overheat the rotor and damage it, see also Section. 1.3 and equation (1.9). A reverse power relay under such a condition will disconnect the generator from the mains and protect the machine. 

When an induction motor runs beyond the synchronous speed, it behaves like an induction generator and feeds power back to the supply system (Section 6.15). Below synchronous speed it behaves like an induction motor and draws power from the supply system. This protection trips the generator in such an eventuality and protects the machine. 

G will generate an excess power compared to Gy. Therefore while G will operate as a generator, Gy. receiving power from G, will operate as a synchronous motor. Since G is overloaded compared to Cy. it will tend to retard, and Gy, receiving power from G, will tend to accelerate. The net effect would be that both generators will tend to synchronize on their own once again. 

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