Introduction to Three Phase Uncontrolled rectifier
Three phase uncontrolled rectifier:
- Single phase rectifiers are extensively used in low power applications particularly for power supplies to electronic circuits. They are also found useful for supplying small dc loads rarely exceeding 5 KW.
Above this power level three phase ac – dc power supplies are usually employed. Single phase ac – dc converters have several disadvantages such as
- Large output voltage and current form factor.
- Large low frequency harmonic ripple current causing harmonic power loss and reduced efficiency.
- Very large filter capacitor for obtaining smooth output dc voltage.
- Low frequency harmonic current is injected in the input ac line which is difficult to filter. The situation becomes worse with capacitive loads.
- Many of these disadvantages are mitigated to a large extent by using three phase ac – dc converters. In a way it is also natural that bulk loads are supplied by three phase converters since bulk electrical power is always transmitted and distributed in three phases and high power should load three phases symmetrically.
- Polyphase rectifiers produce less ripple output voltage and current compared to single phase rectifiers. The efficiency of polyphase rectifier is also higher while the associated equipments are smaller.
- A three phase supply gives the choice of a number of circuits. These can be placed in one of two groups according to whether three or six diodes are used.