What is a Stamford MX321 AVR?

The Stamford MX321 AVR is an analogue automatic voltage regulator, used on the Stamford AVK range of AC alternators. These alternators are coupled to many diesel engine brands worldwide to produce diesel generators.

The MX321 is is excited using a Permanent Magnet Generator (PMG). It also operates 3 Phase Sensing. Voltage sensing on all 3 phases. Useful when there are separate 1 phase loads of different magnitudes connected to a 3 phase alternator.

The AVR on a diesel generator is used to maintain the voltage during steady state loads and transient conditions when load is applied or removed. You can read about the effect of applying load to the alternator.

What protections does the Stamford MX341 have built in?

An MX321 is the first Stamford AVR in the range to have Over Voltage Protection. This prevents alternator damage if the voltage exceeds a pre-set limit, such as with a grid connected application.

Sustained Short Circuit due to the excitation system. With PMG or Auxiliary Winding Excitation; gives the alternator a current ‘forcing’ capability to ensure accurate circuit breaker activation in a fault situation.

The MX321 has "under frequency roll off" (UFRO) as standard. The AVR incorporates an under-speed protection circuit which gives a volts/Hz characteristic when the generator speed falls below a pre-set (adjustable) threshold known as the "knee" point.

Over-excitation also comes as standard on the MX321. This prevents alternator damage if the pre-set maximum excitation levels of current are exceeded.

It also benefits from loss of sensing protection in the event of a problem with the sensing circuit.

Where can I get its technical specifications?

You can download the technical specifications of this AS480 AVR below.