Advantages of PMG Excitation Support Systems Installed on Synchronous AC Generators


Accidents and errors caused due to fluctuating power supply is a severe problem that degrades the quality and quantity of work in every industry. Hence, A constant power supply is the most vital aspect of efficient production. AC Generators provide such uninterrupted backup and supply of electricity to ensure smooth operations and high efficiency.
However, there is a drawback to AC Generators that is less talked about. In Shunt Excited AC Generator systems, the Automatic Voltage Regulator (AVR) that is responsible for maintaining a constant voltage and power line conditioning to the equipment load is directly powered by the output from the generator itself.

What are the common problems with AC Generator Design?
If the generator’s output voltage is reduced as is seen with transient voltage dips upon the application of significant block loading or motor starting, the input voltage to the AVR is reduced by the percentage of momentary voltage dip. This reduction in input voltage to the AVR reduces its ability to force prompt recovery of the generator’s output voltage. It may also impact the generator’s ability to start relatively large motor loads.

When the load on the generator is non-linear due to thyristor (SCR Silicon Controlled Rectifier ) power supplies such as UPS Systems, variable speed drives, etc., the load may produce notches on the voltage that are severe enough to cause misfiring of the power rectifiers in a shunt excited generator’s AVR. This, in turn, will destabilize the output voltage of the generator.

What Is PMG?
A Permanent Magnet Generator (PMG) is used as a secondary exciting system which directly powers the AVR, eliminating its dependency on the generator output. It comprises a permanent magnet rotor which creates a strong magnetic field, along with a wire-wound stator and a 7.5 µƒ capacitor.

How Does PMG help in improving AC Generator performance?
The PMG (Permanent Magnet Generator) is a system which is used for secondary exciting. The PMG provides stable and reliable electric energy for AVR regardless of the generator’s terminal voltage. Thus, it maintains the generator’s ability to support non-linear loads, start motor loads with minimal voltage dip, and the ability to provide short circuit current support to clear downstream faults. The generator with the PMG excitation system can provide 300 % rated current during short-circuit, which occurs for 5-10 second.
PMG excitation system has set a new standard for performance and reliability of AC generators.
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