How does a generator produce electricity? Understanding the principles, structure, and operation and maintenance in one article!

The generator is the "last step in the production of electrical energy"—it converts the mechanical energy transmitted by the turbine into electrical energy that we can use. How does the generator produce electricity? What are the functions of components like the stator and rotor? Below we will introduce them one by one.

1.The generator generates electricity through "electromagnetic induction".

The working principle of the generator is fundamentally based on the law of electromagnetic induction—simply put, it's about "a rotating magnetic field cutting through wires, generating electric current". Taking the "synchronous generator" commonly used in waste heat power plants as an example, the entire power generation process consists of 4 steps:

Step One: Establishing a Magnetic Field ("Magnetic Source")

Principle: Supplying direct current to the "excitation winding" of the generator rotor will produce a magnetic field with alternating polarities (for example, N and S poles arranged alternately), which is the "main magnetic field," equivalent to providing a "magnetic source" for power generation.

Key Source: The excitation current is supplied by the "excitation system" (such as excitation transformers, rectifying devices), akin to "charging" the magnetic field to ensure the stability of the magnetic field strength.

Step Two: Provide cutting power ("motion" input)

Principle: The turbine (prime mover) of the power plant drives the generator rotor to rotate through a coupling - the power of the turbine comes from steam (the steam impacts the blades to rotate, converting internal energy to mechanical energy), and the rotor rotates together with the main magnetic field, forming a "rotating magnetic field."

Key Action: The speed of the rotating magnetic field is consistent with the speed of the turbine (for example, 3000 r/min corresponds to 50Hz AC power), this step is "providing mechanical energy input to the generator," and it is also the "power source for the magnetic field to cut through the conductors."

The turbine drives the generator rotor to rotate at 3000 r/min, so the rotating magnetic field can continuously cut through the stator winding.

Step Three: Generation of Induced Electromotive Force

Principle: The rotating magnetic field sequentially cuts through the 'three-phase symmetrical windings' on the stator (three phases A-X, B-Y, C-Z, spatially separated by 120° electrical angle). According to the law of electromagnetic induction, a conductor cutting through magnetic lines of force will generate 'induced electromotive force', similar to 'water pressure in a pipe'.

Key Characteristics: The induced electromotive force is 'three-phase symmetrical alternating current', with magnitude and direction varying periodically with the rotation of the magnetic field, which is the 'prototype' of electrical energy.

Step Four: Output of Electrical Energy

Principle: The terminal connections of the stator winding are brought out and connected to the power circuit; the induced potential drives the flow of charge, thus generating "current" — mechanical energy is ultimately converted into electrical energy, completing the entire energy conversion process.

Stability assurance: To obtain usable and stable electrical energy, a "control protection system" (such as voltage regulators and differential protection) is also required to avoid voltage fluctuations or faults that can damage equipment.

2. Key Structures: The 'Four Core Components' of a Generator The generator may seem complex, but its core structure consists of four parts, each with a specific function:

Stator: "The fixed end that generates electricity"

Components: three main parts - stator core, stator winding, and machine base.

Stator core: Made of "F-grade non-oriented cold-rolled silicon steel sheets" stacked together (with a thickness of about 0.35mm), it has good magnetic conductivity and low losses;

Stator winding: Braided from multiple strands of solid copper wire and insulated with "F-grade mica tape", it acts as the "wire" that generates induced electric potential;

Machine base: A one-piece steel structure with "elastic positioning ribs" in the inner cavity, which can reduce harmonic vibration during operation (to avoid vibration transmission from the core to the base).

Function: Remains stationary, allowing the rotor's rotating magnetic field to cut through the winding, thereby generating electric energy.

Rotor: "Rotating Magnetic Field"

Composition: Rotor core (or poles), excitation winding, slip ring, and rotor shaft.

Rotor Shaft: Made of high-strength alloy steel, it is a solid forged piece capable of withstanding the torque of the steam turbine, serving as the "skeleton" of the rotor;

Excitation Winding: Wound in the grooves of the rotor core, it carries direct current to produce the main magnetic field. Air ducts in the grooves form a "cooling air passage" (to prevent the winding from overheating);

Slip Ring: Connects the excitation winding to the external excitation system, responsible for transmitting the direct current excitation current (the surface of the slip ring must be smooth to avoid poor contact). A rough slip ring can easily cause sparking.

Function: Rotates with the main magnetic field, providing the "power to cut magnetic lines."

End cover and bearing: "Connection and support"

End cover: Fixed at both ends of the machine base, sealing the interior of the generator to prevent dust and moisture from entering;

Bearing: Divided into "radial bearing" and "thrust bearing" - the radial bearing supports the weight of the rotor and reduces rotational friction; the thrust bearing limits the axial movement of the rotor (preventing the rotor from touching the stator), and lubricating oil passes through the bearing to form an "oil film" that reduces wear.

Air Cooler: "The Key to Cooling"

Role: When the generator is running, the core and windings generate heat (such as copper loss and iron loss). The air cooler takes away heat through "cold air circulation," maintaining the stator temperature at ≤130°C and the rotor temperature at ≤120°C (the allowable temperature for Class F insulation).

Field Details: Coolers are usually installed at both ends of the generator (some may also be in the middle), with the inlet water temperature controlled at 30-35°C and the outlet water temperature not exceeding 40°C to ensure cooling effectiveness.

3. Key Operation and Maintenance Points:

1.Temperature Monitoring: Avoid Overheating Damage

Inspection Focus:

Stator winding temperature: Monitor with embedded temperature sensing elements, normal ≤ 130℃, alarm if exceeds 140℃ (infrared thermometer can be used to assist in measuring the surface temperature of the core);

Rotor winding temperature: Monitored via temperature resistance near the slip ring, normal ≤ 120℃;

Bearing temperature: Radial bearing ≤ 65℃, thrust bearing ≤ 75℃, overheating may lead to burning of the bearing (a certain power plant was forced to shut down for maintenance due to bearing temperature exceeding 80℃).

2. Vibration inspection: Prevent dynamic and static friction

3. Insulation inspection: Avoid leakage faults

Inspection focus:

Stator winding insulation: Every month, measure the insulation to ground with a 2500V insulation resistance meter, ≥1MΩ (at 25°C) is qualified, and below 0.5MΩ requires drying treatment;

Slip ring insulation: Check for any damage to the insulating sleeve between the slip ring and the rotor shaft to avoid leakage of excitation current.

Operations and maintenance actions: Clean the dust on the surface of the stator winding during downtime to prevent oil stains and moisture from affecting the insulation.

4. Parameter Monitoring: Ensuring Power Quality

Inspection Focus:

Voltage: Stator output voltage deviation ≤ ±5% of nominal value (for example, for a 10.5kV generator, the voltage should be between 9.975~11.025kV);

Current: Must not exceed rated current (for instance, for a 15MW generator, the rated current is approximately 866A), to avoid overload;

Excitation Current/Voltage: Stable around the rated value, with fluctuations ≤ ±2% (abnormal excitation current can lead to unstable magnetic fields, affecting voltage).

5. Cleaning and Maintenance: Reducing Failure Risks

Inspection Focus:

Air Cooler: Clean the dust from the heat dissipation fins every quarter (blow out with compressed air) to prevent blockage that can lead to reduced cooling efficiency;

Slip Ring: Keep the surface smooth, check the wear of the carbon brushes (replace them when they reach specified length), and ensure stable transmission of the excitation current; don't forget to check for any looseness in the carbon brush holder.◦

Inside the Machine Base: Inspect the stator core for any looseness and the windings for deformities once a year during downtime, and clean out any accumulated dust inside.