Motor starting capability and MeccAlte Auxiliary Winding (MAUX)

The ability to maintain fault current during short circuit conditions is a common requirement in the world wide marketplace. The purpose of course is to allow for downstream circuit breakers to see a high enough level of current to be able to trip and thus remove the fault from the system. There are several ways to accomplish this. In the past, external electronic modules such as the Current Boost System and Series Boost Option were the norm. More recently, the market has adopted the Permanent Magnet Generator (PMG) excitation system as a way of meeting fault current support requirements.

Mecc Alte meets the fault current support requirement by using an auxiliary winding to provide positive power to the automatic voltage regulator (AVR). The auxiliary winding is a separate single phase winding which is inserted into the main stator along side of the main output winding. By design, the mutual inductance with the main winding is minimized. The auxiliary winding picks up the third harmonic to power the AVR. Because of this and in conjunction with smart regulator design, waveform distortions in the main winding due to non-linear loads will not affect AVR performance.

There are many benefits to the MAUX system when compared to the standard PMG:

• The auxiliary winding is built into all Mecc Alte generators. It does not need to be specially ordered and is included in the base price. The MAUX system provides in excess of 300% fault current on all models for up to 20 seconds. This is twice the amount of time that most PMG systems will provide short circuit maintenance. Copper wire used for the MAUX is specially insulated with four layers of a custom polyamide enamel.
• The auxiliary winding does not add length or weight to the generator thus providing for a compact design.
• Just like with a PMG, motor starting capability is significantly enhanced as the AVR has a positive power supply. After the initial transient response, the system voltage recovers extremely quickly allowing for electric motors to come up to speed much faster. The generator can tolerate higher voltage dips at the stator output while still being able to supply very high currents. The Maux system can provide for 300% of nominal output current (minimum) even when high voltage dips are expected.
• Only one AVR is needed to power our entire line of 2, 4 and 6 pole industrial products. Most PMG systems require a different AVR than their standard non-PMG systems use. Mecc Alte eliminates the need to carry different AVR’s in stock.
• If for any reason the auxiliary winding should fail, the AVR can be reconnected to take power from the main generator output leads. You lose the fault current support and increased motor start capability, but you do not lose the generator function. In many PMG systems, should the PMG fail you will not be able to power the AVR from the main stator output and thus the system goes down until repair personnel can visit the site to fix the problem.
• Changing the rotating diodes is easy with the MAUX system as there is no PMG to interfere with servicing. In MeccAlte machines, the diodes are immediately accessible by removing the rearpanel of the machine.

Today, the Mecc Alte auxiliary winding system is the most economical and space efficient way in the market to provide fault current support and enhanced motor start capability.

Mecc Alte pioneered the technological benefits of the MAUX. However, some traditional users still occasionally request a Permanent Magnet Generator option. Our philosophy is to use uncomplicated systems which meant that, until the introduction of the digital regulator, we would require several different AVR’s and consequently could see no benefit in offering a PMG option.

However, with the digital regulator we are now able to offer optional PMG on the standard Mecc Alte products starting from 180kVA. The PMAUX Permanent Magnet Auxiliary system allows the fitting of a kit which adds a PMG onto the existing generator. This means that the MAUX auxiliary can act as a backup in times of trouble. There is no need to change the AVR, a kit can be kept in stock and retro fitted to our alternators above 400kVA as a standard, or above 180kVA if requested from the factory. Motor starting curves of PMG (PMAUX) for series ECO 38, ECO 40, ECO 43 and ECO 46 are the same as for the auxiliary winding MAUX

For more information
Web: www.meccalte.it