Load-share

The governor can be set to make the machine run at a constant speed, even on load variations, with extremely quick and almost instantaneous speed control, and thus maintain a near-zero AN. In a parallel operation they can also control load sharing automatically and accurately. Power grids, receiving power from different sources, are extremely susceptible to frequency variations. Even a small Af of the order of 0.5 Hz, may cause the system to trip. A fast-actuating governor with low response time (as low as 0.5 second) can overcome such a situation by quickly regulating the speed of the PM. 

Consider the speed-load (drooping) characteristics of the two machines as shown in Figure 16.20. For ease of illustration, the slopes have been exaggerated. Normally they are within 4% of the rated speed, as discussed earlier. When both machines are loaded equally, the total load may be defined by the load line AA, at the bus frequency,/ When the power input to PMf is increased, so that the drooping curve AO shifts to curve BO, it shifts the load line AA also to BB, so that the total load shared by the two machines will still remain the same. The load shared by G is now more than before at so that , > /, and by Gt less than before at P, so that P < Pi The generators now operate at a higher system frequency, /i,. If the... 

Figure 16.20 Drooping curves of two machines, illustrating load sharing when running in parallel...

The load sharing by the two machines can thus be varied by shifting the drooping curves of the prime movers by altering their power input. 

Figure 16.36 Typical block diagram illustrating an auto-synchronIzing and load-sharing...

The load sharing of the tw o generators is therefore dependent on the speed-load (drooping) charaeieristics of the prime movers. 

The duty of load sharing between two or more machines is performed similarly. 

To determine the load sharing between the two, draw the drooping curves as shown in Figure 16.37. 

Figure 16.37 Determining the load sharing between G, and G2 with the help of prime-movers drooping characteristics...

Therefore, the generators would share a load of 1200 kW equally. If, however, the total load is reduced to, say, 1000 kW, the loading will differ due to unequal drooping characteristics. The revised load sharing can be determined as follows. 

A slight variation in the drooping characteristics causes a variation in the load sharing. 

The higher the droop, the higher will be the load variation. When there is a difference in the full-load speeds the load sharing during a parallel operation will not be equal and the generators will operate underutilized. 

Remote supervision and automatic load-control of generating units, load dispatclt centres and suh-siatioris to maintain the desired operating parameters, including load sharing. 

When it is required to limit the inrush current a fixed reactance (linear) reactor is more suitable. A variable type reactor will be necessary when it is to be used for voltage regulation or load sharing. In circuits where harmonics may be present, saturated type reactors may be preferred. 

Below we describe improvised bus systems to limit the reactance and hence the voltage drop and obtain an inductively balanced system to achieve a balanced voltage and equal load sharing by the three phases at the far end. The systems are... 

Often a failure on a fault may be due not to the inadequate size of busbars, fasteners or insulators but to poor alignment of the insulators or to too large a gap between the busbar and the insulator slots. It may be a consequence of an inappropriate mounting or unequal width of the busbars or insulator slots. In such cases, load sharing w ill be uneven and the weakest section may fail. This can be illustrated as follows ... 

Captive (emergency) power generation covers the application of a diesel generating set, its starting, protection, synchronizing and load sharing. This forms an important part of power distribution at any installation to provide a standby source of supply,... 

Introduction DG set Operating parameters Theory of operation Guidelines on the selection of a DG set Types of loads Starting of a DG set Proteetion of a DG set Parallel operation Procedure of parallel operation Recommended protection for a synchronizing scheme Load sharing by two or more generators Total automation through PLCs... 

Load sharing or selective load shedding is of interest to many users of hot gas expanders. A particularly successful European FCC application is illustrated in Figure 6-43. The addition of an expander-generator set to the FCC unit at a major refinery presented a challenge because a trip of the expander could upset the process. The company that is the subject of this application case study, GHH Borsig, solved this problem with the installation of a computerized control system and through computer simulation of trips. 

Capacity control is more complex in compressor networks where two or more compressors operate in series or parallel. Automatic distribution of the load between compressors is required. The antisurge and load sharing control loops must be coordinated to ensure surge protection while tlie load distribution and energy consumption are optimized. 

Figure 2-31. Load sharing between prime movers over the entire operating range of a combine cycle power plant.

Table 19-8 Load Sharing Program Description of Utility Plant Units ...

The steep pressure-volume curve permits the axial compressor to oper ate very well in parallel with other axial compressors. The pressures do not have to match precisely to permit load sharing, as the steepness of the curve allows for adjustment without danger of going into surge or taking wild load swings as sometimes happens when attempts are made to opci ate centritiigal compressors in parallel,... 

The load sharing between fiber and matrix can be viewed as a simple springs-in-parallel model as in Figure 3-7. There, if all springs deform the same amount (the equal-strains assumption) and kf > > k, then the fiber spring takes most of the applied load. 

Figure 3-7 Load Sharing in a Fiber-Reinforced Lamina...

Fig. 28—Different stages in transition of lubrication regimes, (a) Full-film lubrication with film thickness much larger than roughness h/cr> ). (b) Surfaces are separated but roughness effect becomes significant (5>/i/cr>3). (c) Asperities interfere with each other but hydrodynamic films carry the most load (h/cr 3). (d) Typical mixed lubrication with load shared by lubrication and asperity (h/cr<3). (e) Boundary lubrication when asperities carry the most part of load (h/a-<0.S).

His car came standard with a 100 amp alternator which worked just fine under the new ignition system, however, he added a second battery in parallel for load sharing to cover the other electrical systems on-board. 

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