Generators 101

The megawatt (MW) output of a power plant generator corresponds to the size of the energy load produced by its turbine. To understand how it ultimately powers the energy grid, here are a few factors to consider:

• The turbine and rotor create rotating inertia to improve grid stability.
• Generators convert the mechanical output of a turbine into electrical power.
• Power plants take that produced power and then transmit it into the grid.

Turbines can be powered solely by—or blends of—gas, steam, air, and even hydrogen.

 
Today, this mechanical energy also comes from renewable sources like solar, wind, and hydro power.

Many variables are considered for power-output needs, but insulation and temperature control drive a generator’s capacity to freely flow electrons through copper. For every generator, the basic equation is E = BLV:

B = magnetic flux density
L = length
V = velocity
E = voltage

The length and diameter of the rotor and stator core and the number of copper coils are examples of variables that impact E = BLV.

Moving electrons through a conductor creates heat as a biproduct, but over time, heat reduces the electrical insulation capability that holds voltage in. Copper is the most common conductor because it’s cost-effective and has low electrical resistance, which cuts the amount of heat generated. As a result, electrical insulation is a major factor in generator cost and ability.

• As copper atoms are tightly packed, “free electrons” flow easily, and the generator runs smoothly at the right temperature.
• Internal heat is managed with the right cooling systems that balance cost and efficiency.
• Temperature matters because of electrical insulation (keeping insulation at a certain temperature prevents insulation from degrading, adding service life to the unit).
• Ultimately, cooling and insulation keep thermal energy in check, protecting power transmission to the grid.

Regulating heat inside the generator can be done with air, water, hydrogen (H₂), or a blend of H₂ and H₂O. While hydrogen is the most abundant element in the universe, the simple answer is it’s a better temperature controller than the others. As a pressurized gas (at 30 psi), hydrogen is:

• seven times better than air at removing heat
• able to reduce partial discharges inside the generator
• far less power-consuming for circulation and heat removal, due to its low density

Hydrogen-cooled generators require fewer materials, so units can be smaller, more efficient, and more cost-effective in the certain output ranges. Hydrogen allows you to have a smaller, less expensive generator for a given output capacity.

Selecting the right generator for your plant can have many implications. “Power trains” connect your turbines and generators in ways that fit individual footprints.

• Multi-shaft power trains are the traditional configuration, with the turbine tied to one generator and a steam turbine tied to another generator.
• In the last few decades, single-shaft power train configurations have condensed plant footprints by connecting the gas and steam turbines to the same generator.
• Excitation systems (brushless or static) provide DC current to the rotating field, regulating the generator.
• Static exciters use a stationary power supply for faster grid response, but its the carbon brushes require maintenance.
• Brush exciters use rotating power supplies with no brush maintenance but have a slower grid response.
• With the growth of renewables, fossil plants are called on to provide grid stability—and synchronous condensers allow generators to run without a turbine to do so.

Any number of a generator’s complex parts can be affected by wear, mis-operation, synchronizing errors, excitation loss, unbalanced armatures, and more. If a generator loses efficacy, a domino effect of power loss will follow. Compare it to a car that just needs the latest parts to keep running strong. Efficiency improvements on the following can elongate generator life and simply help it run better:

• sealing rings to keep oil in and impurities out
• hydrogen pressure and hydrogen purity
• bearings for powertrain dynamics
• ultrasonic level sensors

Stator rewinds and rotor rewinds bring electrical insulation back to peak performance.