DCMT's (DC Maritime Technologies Inc. provides professional Electrical, Control and Automation systems consulting services to the marine industry) principle design documents for the ships auxiliary services include a load list, load analysis and short-circuit current analysis. In consultation with the client all electrical services on the vessel are identified. Approximate horse-power or kilowatt ratings are obtained for motors. Lighting loads are estimated from the ship's general arrangements and electronic aids are obtained from similar vessels, and a complete load list compiled.
The electrical load analysis uses the load list in order to estimate the expected power demand of the electrical system under specific ship operating conditions. Typical operating conditions would be with the ship, "in transit," "at anchor," "maneuvering," etc. For special vessels, other operating conditions would be appropriate such as "towing" for a tug, "drilling" for a drill ship.
The load analysis calculates the expected power demand by multiplying each service power by a "demand" factor. The demand factor is a combined load factor and diversity factor and is the ratio of the estimated power consumption of a service to its normal full load power consumption. The demand factor is determined by an experienced assessment of the estimated power during a four to six hour period when loads may be at their maximum utilization.
DCMT's load analysis obtains load information from the load list. For each service, data banks are searched to determine the service full load current and power factor dependent upon motor operating voltage. This information is used to compute the services 'kilowatt and kilovar demand from which is computed the kilovoltamps. By applying the demand factor to each load kW and kvar's and summing all loads for specific operating conditions, the expected generator kilowatts, kilovoltamps and power factor can be computed. By comparing the expected load for the different ship operating conditions, the number and rating of the main generators can be assessed.
Preliminary short-circuit current calculations can be completed once the load analysis and number and rating of generators have been determined. The principle purpose of the short-circuit current calculation is to ascertain the short-circuit rating of the systems protective devices.
DCMT has developed several types of short-circuit current calculations which are applied under different circumstances at various stages of the design process.
The major contributors to short-circuit current are the generators and motors. Cables and transformers act to reduce the short-circuit current load at a specific location. The most simple short-circuit current analysis is based on an assumed value of the generator's sub-transient reactance and an approximate estimate of the worst case motor loading can be obtained from the load analysis.
The "second stage" short-circuit current analysis is completed when the electrical system conceptual one-line diagram is finished. For this calculation actual subtransient data is used together with cable transformers and other system parameters. This calculation generally results in lower values ??of short-circuit current.
When complete system information is available, a "third-stage" short-circuit analysis is completed. This is the most accurate calculation DCMT completes. The calculation determines the decrements of the short-circuit current over a 3 and 5 cycle period.
Герундій у функції підмета. | Переведіть пропозиції, в яких герундий грає роль змістовної частини присудка. | Lesson 5. | Find the international words in text. | Read and translate the text. | Make up the sentences. | Поставте дієслова в активну або пасивну форму герундія. | Переведіть пропозиції, визначте функції підмета, визначення та обставини. | Give adequate Russian equivalents of the italicized words. | Read and translate the text. |