25-08-2017, 09:32 PM
UTILITY SYSTEMS FOR CONTROLLED SOURCES OF REACTIVE POWER
UTILITY SYSTEM.pptx (Size: 1.39 MB / Downloads: 34)
INTRODUCTION
Reactive power – the background energy movement in an Alternating Current (AC) system arising from the production of electric and magnetic fields
Power system stability - the property of a power system that enables it to remain in a state of operating equilibrium under normal operating conditions and to regain an acceptable state of equilibrium after being subjected to a disturbance
SOURCES OF REACTIVE POWER
Synchronous Generators - can be made to generate or absorb reactive power depending upon the excitation (a form of generator control) applied
Capacitive & Inductive Compensators - can be connected to the system to adjust voltage levels.
Multilevel inverter - have drawn tremendous interest in the power industry
DIODE-CLAMPED MULTILEVEL INVERTER
A diode clamped multilevel inverter contains full-bridge five-level diode-clamped converter. The DC bus consists of four capacitors.
For a dc bus voltage Vdc, the voltage across each capacitor is Vdc/4, and each device voltage is limited to one capacitor through clamping diode.
MULTI-LEVEL INVERTERS IN REACTIVE POWER COMPENSATION
An inverter produces a controlled reactive current and operates as a static volt-ampere reactive (VAR)-compensator (STATCON)
An inverter converts a dc voltage to an ac voltage with a phase shift of 180°; the inverter can, hence, be operated as a dc-ac converter, that is, a controlled rectifier
With a purely capacitive load, the inverter operating as a dc-ac converter can draw reactive current from the ac-supply
USE IN INDUSTRY
Reactive power finds its application in cases where voltage stability is required
Voltage collapse is a big threat to transmission systems. If it is allowed to happen, several important transmission lines in a power system may trip
High reactive power output from generators is used to prevent voltage collapse
The load compensation due to reactive power makes it possible to increase the loading of the power system according to voltage stability