Split bus system

Typical electrical power control panel features

UNIT 12 PARALLEL BUS SYSTEM

AIM OF THE UNIT:- to understand 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 2page 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.

1 How do ac generators operate in parallel?2 Is the APU generator available for ground use?

Ac generators operated in parallel means that two or more ac generators are connected to the same busbar and share the load. To operate acgenerators in parallel, consideration must be given to the phase relationship and the control of voltage and torque/load. An ac distribution system with three main generators, an APU generator and provision for supplying power from an external source. The actual layout does vary between different aircraft manufacturers. AC generators are operated in parallel to provide ‘no-break’ power just like DC system. However this technique only applies to constant frequency AC generation as it is impossible to parallel frequency wild or Variable Frequency (VF) AC generators. In fact many of the aircraft loads such as anti/de-icing heating elements driven by VF generators are relatively frequency insensitive and the need for ‘no-break’ power is not nearly so important. To parallel AC machines, the control task is more complex as both real and reactive (imaginary) load components have to be synchronized for effective load sharing.The normal operating configuration is with all GCBs and BTBs closed.Failure of a main generator would result appropriate GCB opening, the bus bar remaining powered via the bus tie line and BTBs. The APU generator is available for ground use and in flight as a back up. It is not normal for the APU generator to be connected in parallel with the main generators as the APU normally has no CSD/IDG fitted and therefore no torque/load control is available. The external power supply is not compatible with the main generators or the APU generator as the aircraft system has no control over the voltage or torque/load. Before understanding how parallel operation of AC generators is obtained first we will see the effect of load on AC Generator and then see how this load is balanced for parallel operation.