Singly and doubly excited magnetic systems are two types of magnetic systems used in various electrical applications. Let's understand the applications of these systems in detail:

1. Singly Excited Magnetic Systems:
Singly excited magnetic systems have only one source of excitation, either the field winding or the armature winding. These systems find applications in the following:

- Reluctance Motors: Reluctance motors are simple and robust electric motors that operate based on the principle of varying reluctance. In these motors, the field winding is excited, creating a magnetic field that interacts with the rotor's salient poles. As the rotor rotates, the reluctance between the stator and rotor poles changes, resulting in the generation of torque.

- Synchronous Motors: Synchronous motors are AC motors that operate at a constant speed determined by the frequency of the power source. In these motors, the field winding is excited to create a rotating magnetic field that synchronizes with the rotating magnetic field produced by the stator windings. This synchronization enables the motor to maintain a constant speed and efficiently convert electrical energy into mechanical energy.

2. Doubly Excited Magnetic Systems:
Doubly excited magnetic systems have both field windings and armature windings. These systems find applications in the following:

- Synchronous Motors: Doubly excited synchronous motors are used in applications where precise control of speed and torque is required. These motors have separate field windings and armature windings. The field winding establishes the magnetic field, while the armature winding carries the current that produces the torque. By varying the excitation of the field winding and the current in the armature winding, the speed and torque of the motor can be controlled.

- Moving Iron Instruments: Moving iron instruments are used for measuring current, voltage, and power in electrical systems. These instruments use a movable iron piece (usually in the form of a vane or a disk) that experiences a force when subjected to a magnetic field produced by the field and armature windings. The deflection of the iron piece is proportional to the measured quantity, allowing for accurate measurement.

In summary, singly excited magnetic systems are used in reluctance motors and synchronous motors, while doubly excited magnetic systems find applications in synchronous motors and moving iron instruments.