UNIT 2 REACTIVE LOAD DIVISION
AIM OF THE UNIT:- to understand reactive load division
TASKS 1 Do your best to answer the brainstorming question. 2 Read the text for general understanding. 3 Make up questions to the text. 4 Find the sentences with the new words in the text. Give the Kazakh or Russian equivalents of the words. 5 Write sentences with the new vocabulary. 6 Make up exercises as in the UNIT 2 (Master`s degree students individual work with the teacher) page 210 (exercises for better remembering the topic). 7 Speak on the topic. Given schemes will help you to remember and understand the topic. 8 Find more information about the topic and make up a project work on the topic. Division of reactive load becomes necessary because the voltage adjustment settings on the voltage regulators are never exactly identical. Therefore, the amount of excitor current supplied from each generator will never be exactly identical and in a paralleled system, the generator which receives the greatest amount of excitor current will carry more than its share of reactive load. The unbalance of reactive load is detected by current transformers placed on phase C of each generator, whereby signals proportional to the generator's reactive load are delivered to the respective voltage regulators. The result is a reduction of excitation to the generator which carries more than its share of the reactive load, and an increase of excitation to the generators carrying less than their share of the reactive load. An increase of exciter field current to an isolated generator results in a proportional increase of voltage on the generator load bus, however, should two or more generators operate in parallel, an increase of exciter field current to one generator results in only a small increase of voltage on the paralleled buses. The increased bus voltage, caused by one over excited generator, will be delivered to all loads in the paralleled system, but since the remaining generators receive their normal amounts of excitation current, they will deliver voltages which are lower than the voltage on the paralleled buses. Since there is a difference in potential between generators, the generator which is over excited will not only supply the normal loads, but will also supply power to the generators operating normally. Thus, in a paralleled system, the generators which receive their normal amounts of excitation current supply less power when one generator becomes over excited, and are carried as additional loads by the over excited generator. Since the current circulating between the over excited generator and the normally excited generators lags the voltage, the over excited generator carries more than its share of reactive load, and the normally excited generators carry less than their share. Should the bus tie and generator breakers be closed, indicating that the entire ac power system is operating paralleled, the auxiliary contacts are opened to allow all current transformers to be connected in a series loop where the mutual reactor primaries act as parallel loads to the current transformers. Since all current transformers are connected in series, current will flow in the series loop as a result of voltages induced in the individual current transformers. The difference, three units of current, flows through the mutual reactor (MR), in the voltage regulator in such a manner that the voltage induced in the secondary winding of the mutual reactor is in phase with the reactive current carried by the generator. Since the secondary winding of the mutual reactor is in series with the voltage regulator error detector, the added voltage will appear to the error detector as an over voltage. Accordingly, the voltage regulator causes a reduced amount of excitor current to be delivered to the over excited generator proportional to the average reactive load in the entire ac power system. The difference flows through the mutual reactors in the respective voltage regulators, thereby causing an increased amount of excitor current to be delivered to the under excited generators proportional to the average reactive load in the ac power system. The ability of the load division loops to distinguish between real and reactive load is a property of the sensing devices. Reactive load division is accomplished by delivering to the voltage regulator, signals which are proportional to the generator's reactive load only. The mutual reactor in the voltage regulator serves this purpose.
UNIT 3 SPLIT/PARALLEL BUS SYSTEM
AIM OF THE UNIT:- to understand split/parallel bus system
TASKS 1 Do your best to answer the brainstorming question. 2 Read the text for general understanding. 3 Make up questions to the text. 4 Find the sentences with the new words in the text. Give the Kazakh or Russian equivalents of the words. 5 Write sentences with the new vocabulary. 6 Make up exercises as in the UNIT 2 (Master`s degree students individual work with the teacher) page 210 (exercises for better remembering the topic). 7 Speak on the topic. Given schemes will help you to remember and understand the topic. 8 Find more information about the topic and make up a project work on the topic.
This is a flexible load distribution system for large passenger aircraft; it provides the advantages of the parallel system and maintains isolation when needed. Primary power supply features include: one IDG per engine, two APU generators and two external power connections. Asplit system breaker links left and right sides of distribution system. Any generator can supply any load busbar; any combination of generators can operate in parallel.
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