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Two diesel generating sets are becoming more and more common, often due to the increase of demand power, the service of diesel generator set and machine is required. With the development of modern construction, the generating set is more and more used in defense engineering, weapon system, field operation and so on. In order to meet the requirements of large load or uninterrupted power supply, two or more units are often required to operate in parallel. In the parallel operation of the unit, the uneven power distribution often occurs, and the inhomogeneous over power distribution will seriously affect the safety and reliability of the power station system, and will cause serious harm to the generator set. This hazard is rooted in the circulation problem of the system, and is also the most common and difficult problem to be solved in the commissioning of parallel power plants. According to some experience of debugging the parallel unit, the technical personnel of our company put forward the causes of the circulation, the factors that affect the average power distribution and the solution.
Static analysis of circulation generation
Taking the modular parallel control system as an example, the parallel debugging of the generator set generally first balances the circulation of the parallel unit in the empty load parallel, and runs the balance sufficiently small and stable, and then balances the active power through the load distributor, and the key is to solve the circulation problem of the empty load parallel. Taking parallel connection of two units as an example, the common problems of no-load parallel connection are as follows:
(1) the circulation is too large, far exceeding the rated current of the parallel unit by 10%.
(2) after parallel connection, the circulating current increases with the running time until the reverse power is given to the police.
(3) the circulation is unstable and the randomness is too small.
How to solve these problems? We take two parallel power units as an example, first analyze the causes of the circulation.
The end voltage of the circulation U1:1# unit, the end voltage of the U2:2# unit, the load of the parallel operation of the R3: two units, the I0: circulation, the output current of the I1:1# unit, the output current of the I2:2# unit, and the technical support of the sea front diesel generator set. If the two units are operated in parallel and the I0 is 0 at any load, they must be U1=U2, that is, the two terminals will operate at any load with equal terminal voltage. The no-load parallel connection is equal to the load infinity, and the no-load terminal voltage U01 and U02 should also be equal. That is, U01=U02 (1-2) we know that the average distribution of active power depends on the characteristics of the diesel engine and its speed control system, and the distribution of reactive power depends on the characteristics of the generator and its excitation system, that is, the voltage regulation characteristic of the generator set itself. The voltage regulation characteristic is a U=f (I) curve, U is the generator group end voltage, and I is the current. In order to facilitate the analysis of problems, a straight line is usually used to replace the curve. It is assumed that there are two parallel generators, which have the voltage regulation characteristics as shown in Figure 2, and set the voltage regulation characteristics of delta 1=tg beta 1, Delta 2=tg beta 2, Delta 1:1# unit, and the voltage regulation characteristic of delta 2:2# unit.
From the above analysis, we know that:
(1) the two units are connected in parallel. First, the no-load voltage and voltage regulation characteristics of the two units should be adjusted to the same. This is the prerequisite for the total average distribution of the reactive power of the two units, and also the basis for the subsequent adjustment of the average power distribution of the two units. When the above two adjustments are balanced, the output terminal voltage of the two units in parallel can be equal under any load, and the average power distribution can be guaranteed to ensure the circulation of 0 (ideal state). It is shown that the fundamental reason for the circulation of the circulation is that the voltage of the two units is not completely equal or the voltage regulation characteristic is different, which causes the unequal output voltage to produce the circulation.
(2) the voltage and voltage regulation characteristics of the two units are all equal, and the output current of the two units is not equal, that is, the power distribution of the two units is not uniform, and the U1 and the U2 will not be equal, and the circulation will be produced.
(3) there are many factors that affect the distribution of reactive power, such as the characteristics of the automatic voltage regulator and the stabilizing effect of the equalizing line.
The dynamic balance analysis of power allocation takes two parallel generators as an example. The general technical conditions of GB/T12786 -2006 automation internal combustion engine power station stipulate that the active power distribution difference between 20 to 80% calibration quota is less than 10%, and the average active power distribution between the two parallel units is mainly completed by the balance chain between the load distributor of two units. The working principle diagram of the balance chain. -
By adjusting the "load distribution" potentiometer of the load divider, the power allocation parameters of the two load dividers can be adjusted equally, that is, ETA 1= et. 2. Suppose the load of the two generating units is absolutely equal, that is, P1=P2, then u1=u2, I0=0. This is an ideal state of complete balance. In fact, this is a dynamic balancing process: assuming that the load of two units with P1 and P2 is running smoothly in parallel, P1=P2.