Torque Question

The start torque is the locked rotor torque, the rated torque is the torque required for the motor to reach full load....

https://www.engineeringtoolbox.com/electrical-motors-torques-d_651.html

Um, er, the Original Poster has a generator, not a motor. _{Just sayin'.}

Well then....

..."The torque required to start a permanent magnet dc generator is influenced by the following five mechanical factors, as well as by the ambient temperature.

1. Load Any electrical load connected to the generator at the time of startup contributes to the startup torque inversely according to the impedance of the load. Resistive loads add to the torque at any rpm, including startup. Inductive or capacitive loads can influence the startup torque because the increase of output voltage from zero rpm to the operating rpm is equivalent to a very low frequency ac waveform. During startup, energy absorbed by reactive load elements contributes to startup torque. Normally, generator startup torque is rated with no load, that is, open circuit output, to avoid the complications of external loading.

2. Bearings Generator bearings (typically two) contribute to startup torque through rotating friction: the ball rolling friction, lubricant viscosity, and seal or shield friction. Typically the front (exposed) generator bearings are sealed, and the internal rear bearings are shielded. The lubricant viscosity depends on the ambient temperature. Generator startup in extreme cold requires more torque due to lubricant viscosity. As the bearings warm up, due to friction, this initial torque decreases. New bearings exhibit higher startup torque until they have been "run in" over a period of hours. Side pressure on the generator shaft, such as a pulley adds to bearing friction, so also to startup torque.

3. Brushes The carbon brushes (two or more) are spring-loaded against the rotating commutator, causing friction at any rpm, but most at startup (breaking static friction). Bearing friction is minimized in generator design by shaping the brushes to match the curvature of the commutator, thus minimizing the pressure required for a given current flow, by micro-finishing the commutator surface, and by using low-friction carbon brush material.

4. Inertia The moment of inertia, i.e. the amount of energy required to start the mass of the armature rotating up to the operating speed, contributes to the startup torque. A soft (slow) start minimizes this element of startup torque.

5. Magnetic Cogging Magnetic cogging - attraction of pole-pieces to magnet edges - is most evident at startup, but can be minimized in generator design either by skewing the armature laminations or by designing the width of armature poles to cause matching of positive to negative cogging forces. At operating rpm, cogging does not typically add to running torque because the inertia of the armature tends to smooth out torque ripple. The startup torque of any generator is unique to that generator design and size, and is inversely proportional to the pre-startup temperature."...

https://windstreampower.com/wp-content/uploads/2013/01/STARTUP-TORQUE.pdf

Never mind.

In a word, inertia.

It takes more power to start a mass (generator) at rest than it does to keep the mass moving while generating power.

The <...RATED TORQUE...> is presented to the prime mover when the <...generator...> is operating at its maximum rated electrical output at the rated speed.

When the generator is at the instant of <...STARTUP...>, there is no electrical output as the speed is zero, therefore the <...TORQUE...> presented to the prime mover is also zero.

Starting torque is the torque required to start and accelearte the rotor of the generator from stand still condition or at rest..Rated torques is the torque require to maintain the rotor of the generator at rated speed (RPM)so that it produces the rated voltage and frequency