Selection Principle of Chosing The Capacity and Number of Power Transformer(二)

(4) In order to ensure the flexible and reliable operation mode of substation, reduce and facilitate reserve capacity, cooperate with interconnected distribution devices, facilitate maintenance and maintenance, and achieve the unification of the overall standard of substation, the type of transformer capacity should be minimized as far as possible, generally no more than two kinds. In this paper, it is suggested that the capacity level of transformer should be unified in a substation supplied by a city.

(5) Within a certain capacity range, the capacity increases and the loss decreases, but the saved electricity cost may be difficult to compensate for the increase of investment cost, and the interruption capacity of the matching switchgear and other equipment is demanded. Therefore, the selection of transformer capacity should consider the one-time investment of transformers and their matching devices (3), implement the national policy of loss reduction and energy conservation, and, if necessary, calculate the economic operation mode. 。
(6) Because the power supply enterprises require the urban power supply to meet the N-1 reliability criterion, the selection of transformer capacity, in addition to meeting the above conditions, should take into account the accident and overhaul conditions, reduce the economic losses caused by power supply and social impact, at least to meet a transformer blackout, part of the load can be transferred to the surrounding substation, without affecting the normal power demand of all users.
(7) In the substation intensive area of power supply enterprises, because there are connected power supply lines between substations, the substations can supply each other hand in hand, the capacity selection of transformers can be reduced appropriately, under normal conditions, the power supply can be supplied by each region. When the power supply output cannot be satisfied, the substations around can carry part of the load through the tie-line, but ultimately, the substation layout or increase should be considered. The number of transformers gradually meets the demand of load supply.

(8) For substations with generators connected to the grid on the low-voltage side, the capacity of transformers can also be reduced appropriately, but the selection of capacity should take into account: (1) when the rated capacity of generators is at the lowest regional load, it can be output to the power system normally through transformers, and the capacity of transformers must be larger than the generating capacity of units; and (2) the sum of the rated capacity of transformers and generators is larger than that of the area. Maximum load; (3) When the generator unit is out of operation, the transformer should be able to ensure that 70% to 80% of the total load of the power supply is not affected, and ensure the normal use of primary and secondary loads; (4) Proper coordination with the equipment parameters of the upper power grid to meet the requirements of short-circuit capacity of the system.

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