tailieunhanh - OPERATION, MAINTENANCE AND REPAIR OF AUXILIARY GENERATORS Episode 7

Tham khảo tài liệu 'operation, maintenance and repair of auxiliary generators episode 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | TM 5-685 NAVFAC MO-912 Frequency Speed in rpm Pairs of poles 60 Hertz 60 e. Power. Power is the term used to describe the rate at which electric energy is delivered by a generator and it is usually expressed in watts or kilowatts watts . 1 Watts. Watt s are units of active or working power computed as follows volts x measured or apparent amperes x power factor. 2 Volt amperes reactance Mars . Vars are units of reactive or nonworking power 1 var 1 reactive volt-ampere . 3 Power factor. Power factor is the ratio of active or working power divided by apparent power. The relationship of apparent power active power and reactive power is shown in figure 4-10. The hypotenuse represents apparent power the base represents active power and the altitude of the power triangle represents reactive power. Power factor the cosine of angle 0 is a unitless number which can be expressed in per unit or in percentage. For convenience kilo is often used with the terms volt- amperes watts and vars in order to reduce the number of significant digits. Power Factor kW x 100 kVA 4-8. Exciters. a. An AC or DC generator requires direct current to energize its magnetic field. The DC field current is obtained from a separate source called an exciter. Either rotating or static-type exciters are used for AC power generation systems. There are two types of rotating exciters brush and brushless. The primary difference between brush and brushless exciters is the method used to transfer DC exciting current to the generator fields. Static excitation for the generator fields is provided in several forms including field-flash voltage from storage batteries and voltage from a system of solid-state components. DC generators are either separately excited or selfexcited. b. Excitation systems in current use include direct-connected or gear-connected shaft-driven DC generators belt-driven or separate prime mover or motor-driven DC generators and DC supplied through static rectifiers. c. The brush-type exciter