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How Generators Work

There are many ways to build alternating current (AC) generators. WINCO is one of a few generator manufacturers to build most design types. Each design is selected for the correct mix of performance, power, weight, size, durability, motor starting ability and user preference for the environment and application that the generator will be used in. This document provides a basic understanding of how generators produce electricity and some of the different design types available.

Generator Theory

All generators, both AC and DC, operate by very basic physics principles. A conductor and magnet moving in close proximity to each other will induce voltage in the conductor. Generators are designed to move either the conductor or magnet in close proximity of the other to create electrical current. Every generator design uses the same basic components. It is useful to understand what each component's purpose is in power generation.

Stator: The stator consists of the components of the generator that remain stationary during operation.
Rotor: The rotor consists of the components that are rotated in order to induce voltage in the conductor.

Field (Magnet): Whenever a DC current runs through a conductor (copper wire) wrapped around an iron core (laminates) a magnet is formed. The stronger the magnetic field the higher the voltage that will be induced when it is passed near the conductor. In reverse, the weaker the field the lower the voltage that will be induced. The power to create the magnetic field is obtained from the armature. If a generator is overloaded the magnetic field can collapse, reducing output because the armature is unable to supply the current to the load and field.
Armature (Conductor): Constructed of conductors (copper wire) inserted into steel core (laminates) a voltage is induced when a magnet passes near. The armature is connected to the distribution system (receptacle panel or terminal block).

Rotating Armature: With this design the armature (conductor) rotates inside the field that remains stationary. Since the conductor (voltage induced here) is rotating, slip rings and brushes are needed to collect the power output and deliver it to the receptacles. This type of design is very rugged with very high residual voltage output for reliable voltage build-up every time. The shell is very heavy with these designs protecting the internal components from damage. These generators are limited to smaller sizes because the brushes become very large and unwieldy in order to conduct higher amperages. The 2FSM2PC-1 and 25PTOC-3 WINCO models are the most popular rotating armature machines.

25PTOC-3 Field

25PTOC-3 Rotor (Notice the four slip rings required to transfer the AC current to the receptacles)

Rotating Field: When the magnet is rotating the generator is called a rotating field. There are several different designs of rotating field generators depending on what method is used to introduce DC power to the rotor. The main advantage of a rotating field design is that the current is generated in the stator so that no brushes are required. There are several types of voltage control for rotating field designs used in WINCO products.

Rotating Field Brush: AC current from the stator is rectified and then introduced to the rotor through a brush and slip ring mechanism. The WINCO 35-75 kW PTO models are built with this design using a buck boost transformer to regulate the voltage. The transformer design is capable of holding voltages higher than most competing models during heavy motor starting which give the design an advantage in many agricultural and industrial applications.

50PTOC-3 Rotor (Notice that although the generator produces twice the output as the 25PTOC-3 it only requires two slip rings for the DC current that is introduced into the field)

Buck-boost transformer is the key to superior motor starting on the WINCO PTO models.

Rotating Field Brushless (Inherently Regulated): The main difference between Rotating Field Brush and Brushless designs is the method that the DC current is introduced into the rotor. Brushless machines do not require any current to be physically connected to the rotor. AC current feeds capacitors that control the amount of current induced in the rotor. Voltage can be increased or decreased based upon the rating of the capacitor.

Notice how the brushless rotor does not have any slip rings to directly connect the rotor to a power source. The current for the magnetic field in induced into the rotor.

The diodes on the rotor ensure the current is DC and give magnetism to the poles.

The capacitor controls the voltage on brushless inherently regulated machines.

Rotating Field Brushless (Externally Regulated): The larger PTO's and all liquid-cooled standby machines from WINCO use Automatic Voltage Regulators (AVR) to control the induced voltage. An AVR is not capable of starting motors as large as the buck-boost transformer machines. The main advantage of the AVR is the accuracy of the output voltage. The AVR is powered by current from the stator and electronically matches the voltage output against a set point, then always returns to the set point when the load changes. The AVR then fine tunes the field voltages as needed to maintain the voltage within very tight tolerances. Most AVR's are capable of maintaining steady state voltages within 0.5% to 2%.

The AVR is responsible to monitor and maintain proper output voltage.

Externally regulated machines have an additional winding group designed to supply rotor current. The AVR controls these windings to maintain proper voltages.