*Draft date: 1202-t2 1Electrical system overview As the main power supply for the whole ship's electric load during the ship's navigational conditions and the working power supply of the 900kW first and 500kW tail thruster when the ship enters and exits the port as a ship navigator In the case of standby power supply, in and out of port and loading and unloading conditions, as the main power supply for the whole ship's electric load except the first and tail thrusters of the whole ship, the main electric load of the ship: the main pump serving the main auxiliary machine Pu; cargo compartment ventilation and dehumidification system; tailgate springboard and tail cargo hatch hydraulic power unit; life service electricity and other.
2 shaft with generator protection 2.1 protection blind zone is a conventional design concept, because the shaft generator bears different power loads during navigation conditions and inbound and outbound conditions, when the navigation conditions are SG through ACB3, ACB4 to the full The ship is powered by the electric load, and when entering and leaving the port, the ACB3 is opened, and the SG pushes the power supply to the BT and the ST through the ACB4. The above-mentioned two conditions of the shaft generator SG to the MSB main switchboard are present in this area. In any fault, the shaft switch ACB3, ACB4 can not react to protect the line between the shaft generator and the shaft generator to the MSB, so there is a blind zone of system protection, which is in a reasonable system design. It is not advisable to have corresponding regulations in 1EC and land electrical power distribution regulations to prevent damage to large-capacity important electrical equipment, so other protection methods must be adopted for differential protection.
Basic principle of differential protection for 22-axis generator with differential protection: According to the first theorem of Khrhov, the current (size and phase) signals of all the terminals of the protected equipment are collected, so that the performance unmatched by current protection is obtained. The shaft-connected generator longitudinal differential protection secondary wiring is a phase of the stator winding of the shaft generator. The shaft generator has two lead terminals, and each end is equipped with a current transformer (LH). The secondary terminals are connected into a loop according to the polarity relationship in the figure. The mn branch in the loop is called a differential loop, its indirect differential relay or other differential components.
The primary current is /i and /i, the current flowing into the protected device is defined as positive, flowing from the primary polarity end of LH, and the corresponding secondary current /a/"2 flows out from the secondary polarity end of LH, so defined The forward current, when the first and second turns of LH are respectively wiW2, there is /iwi-/'2W yielding 0 (excluding the excitation current), ie: bit, thus defining the positive direction of the current so that the phase of the secondary current The quantity analysis is completely consistent with the primary current, only the difference in size. A current transformer ratio clearly shows that Jcd0 is present when the normal operation or external short circuit, and the stability of the single-phase wiring 2.22 differential protection is provided for the internal short circuit. All the parameters in the equivalent circuit shown by the unbalance 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 and Z"*, The sum of the secondary wiring and the secondary leakage impedance of LH is, and the equivalent circuit of the Z' dynamic loop impedance is Zc to analyze the unbalanced current is visible as long as the excitation impedance Z:Z' of LH tends to infinity, that is, LH Excitation current /* and 1' are negligible (LH operates in the unsaturated region); unbalanced current is equal to zero; or when The parameters of the effective circuit are completely symmetrical, that is, Zu=Zu, Z=Z' also has /, =0, which requires the working states of the two LH cores to be the same (saturation depth is the same), and the secondary lines on both sides are equal in section and equal length ( Or the length of the large section is large, so that Z, Z'--in general, according to 3: the reactance component of the secondary connection is not large), the above formula can be written as: (the excitation circuit time constant) can be seen I. . *As small as possible, the time constant of the secondary excitation circuit of the two LH should be as close as possible to L*uL". The operating state of the LH core is determined. The more saturated the Lu is, the smaller it is. The R[R" is mainly connected by the secondary connection. The cross section and length determine that the side with a small LH capacity is easily saturated, and its Lu is small, and the corresponding secondary wiring section should be large and the length should be short, so that its R is also reduced.
2.23 Transient unbalanced current of the differential protection The Z is written as the operator Z(p) as the operator, and the equivalent expression can solve the operation expression of //. and the entire transient that is to be externally short-circuited. In the process, it is impossible to completely operate the LH core for differential protection in the linear section, but it is necessary and possible to limit the error caused by nonlinearity to the extent allowed by the engineering through various technical measures.
(a) shows the relationship between LH-secondary current and secondary current/2 in steady state. If the excitation current of LH is completely ignored, the current change m is uniquely determined between /2 and /2. The straight line indicates that the corresponding current is expressed as /10 and /20. Actually, since LH enters the saturation region at a large /i, the excitation current of LH increases, causing /2 to decrease correspondingly, //i/nL, which results in The error is based on the actual needs of relay protection. The specified error /20 is set to be the ratio of the maximum short-circuit current to the LH-minor rated current. Z/z is the LH secondary load impedance. The relationship between n and Zfz is used for each current transformer. The condition is that the error is equal to 10%. For example, (b), this curve is called the 10% error curve of the transformer. The control error is obviously within 10%, and the increase of n must be correspondingly reduced by Z/z. It is known that n=n1, in order to make the error not more than 10%, the secondary load Z/z should be made.
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