*Date of publication 12002-t2 1 Overview of electrical system The main power supply for all marine electrical loads when the ship is sailing, and the operating power when the vessel is in and out of the harbor when the vessel is in and out of harbor is 500kW. Backup power supply for mains, mains supply for all ship electrical loads except for the first and tail thrusters when entering and leaving port and loading and unloading conditions. Main load: Main pump for main auxiliary engine Pu; Ventilation and dehumidification systems for cargo holds; Hydraulic power units for tailgate springboards and tailgates; Electricity for life services and others. 2 shaft generator protection 2.1 The blind area of ​​protection is a conventional design concept. Since the shaft generator bears different power loads during sailing conditions and working conditions, the SG passes ACB3 and ACB4 to the full The ship uses electric load to supply power, and when entering or leaving the port, ACB3 is turned on, SG pushes power to both BT and ST through ACB4. The above two operating conditions: shaft generator SG to MSB main switchboard In any failure, the shaft firing switches ACB3, ACB4 cannot react so as to protect the line between the shaft generator and the shaft generator to the MSB, and thus a blind spot of system protection occurs. This is a reasonable system design. Inadvisable, there are corresponding regulations in the 1EC and land electrical distribution regulations to prevent the damage of large-capacity important electrical equipment. Therefore, it is necessary to adopt other protection methods for differential protection. Basic principle of differential protection for differential protection of shaft generators: According to the first theorem of Kirchhof, the current (phase and phase) signals of all terminals of the protected equipment are acquired, so that the unmatched performance of the current protection is obtained. 22.1 The secondary connection of the differential protection of the shaft generator with the longitudinal connection is a phase of the stator winding of the shaft generator. Because the shaft generator has two lead-out terminals, one current transformer (LH) is installed at each end. The secondary terminals are connected in a loop according to the polarity relation in the figure. The mn branch in the loop is called a differential loop, and its indirect differential relay or other differential protection component. The primary currents are /i and /i. The current flowing into the protected device is defined as positive. The primary polarity of the LH flows in. The corresponding secondary current /a/"2 flows from the secondary polarity of the LH. The forward current, when the first and second order of LH is wiW2 respectively, there is /iwi-/'2W producing 0 (exclude the excitation current), ie: the bit, thus defining the positive current direction, making the secondary current phase The quantity analysis is exactly the same as the primary current, only differing in size One current transformer ratio clearly shows that there is Jcd0 when the normal operation or external short circuit occurs, and there is a differential protection when the internal short circuit protects the stability of the single-phase wiring 2.22 differential protection All parameters in the equivalent circuit shown by the unbalanced current J.* are reduced to the secondary side. Because it is an external short circuit, both current sources are /1/nL; the excitation impedance of LH is Z"*, The sum of the secondary leakage impedances of the secondary connection and LH is the same as the equivalent circuit of Zc analysis of the unbalanced current of the dynamic loop impedance, as long as the excitation impedance Z:Z′ of LH tends to infinity, that is, LH. Magnetizing currents /* and 1' are negligible (LH operates in the unsaturated region); unbalanced current equals zero; or The effective circuit parameters are completely symmetric, ie, Zu=Zu, and Z=Z′ also have /,=0. This requires that the cores of the two LHs be in the same working state (same depth of saturation), and that the secondary connections on both sides be equal in cross section and equal length ( Or the length of the large cross section is large, so under the Z, Z'-like condition, according to 3 available: the reactance component of the secondary connection is not large), the above formula can be written as: (exciting magnetic circuit time constant) visible to I., . * As small as possible, the time constants of the secondary excitation loops of the two LHs should be as close to L*uL as possible. "The operation state of the LH core is determined. The less saturated Lu is, the smaller is R. R" is mainly composed of secondary connections. The cross-section and the length determine that the LH capacity side is easy to saturate, its Lu is small, and the corresponding secondary connection section should be large and the length should be short, so that its R is also reduced. 2.23 Transient Unbalanced Current Protection for Vertical Differential Protection The various parameters Z are written as the operator Z(p) as the operator, the equivalent circuit can be used to solve the operation expression of /// and the entire transient to be externally short-circuited. In the process, it is impossible for the LH iron core for differential protection to work completely in the linear section, but it is necessary and possible to limit the nonlinearity-induced errors within the allowable range of the project through various technical measures. (a) shows the relationship between the LH-secondary current and the secondary current/2 in the steady state. If the excitation current of LH is completely ignored, the only difference between / and / is determined by the current change m. This ideal condition is shown in the figure. The straight line indicates that the corresponding current is expressed as /10 and /20. Actually, due to LH entering the saturation region at larger /i, the LH excitation current increases, so that //2 decreases correspondingly, //i/nL, which results in Error According to the actual need of relay protection, the specified error /20 sets n as the ratio of the maximum short-circuit current to LH-sub rated current, and Z/z is the relationship between LH secondary load impedance and n-Zfz for each current transformer. The condition is that the error is equal to 10%. As in (b), this curve is called the 10% error curve of the transformer. Obviously, the control error is within 10%. If n is increased, Z/z must be reduced accordingly. Known n = n1, in order to make the error not more than 10%, it should make the secondary load Z/z
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