Brief discussions about Brushless Exciter and Wound Rotor Motors

System of exciter is planned to manage the voltage that has been applied and also the field current which flows to the rotor that as a result enables the controlling of terminal voltage or generator output. Consequently this results in providing power factor control and reactive power between the system and the generator. Response time of excitation should be quick as such the automatic voltage regulation may be controlled in the generator at the time of system transient or disturbance in which quick alteration of excitation are needed. Brushless exciter includes ac generator having high frequency along with a revolving assembly of fused diode, a transformer power supply and for excitation management a stationary voltage regulator. The Brushless Exciter is usually fixed as an additional feature in respect to generator shaft. Components of rectifier are installed on the assembly of diode wheel, or they are kept sometimes into the shaft. A 3 phase transformer along with the station battery for the purpose supporting initial field flashing and giving support to the sudden fault current, regulator and power.

Wound Rotor Motors are usually utilized for adjustable conditions of speed and high torque. At minimum speeds, either power is reverted back from the circuit of rotor to the grid utilizing various common energy recovery procedures or power is misused in resistances of rotor. At minimum torque and lower speed conditions, the wastage of power within the rotor circuit is very high. Moreover, if method of stator voltage control is utilized it becomes effective in respect of fan kind loads only. For consistent torque loads, the range of speed control as achieved from is highly restricted. A cost effective, efficient, scheme of simple speed control is provided for Wound Rotor Motors. Both rotor resistance management methods and stator voltage management are put together and an optimal condition is observed for controlling the voltage. A thruster’s dependent AC regulator utilized for controlling of stator voltage functions effectively in this situation. Thereafter the resistance of the rotor is controlled for the needs of adjusting the speed. The motors functions smoothly even at low speed conditions and very low torque.

Functional part of Wound Rotor Motors and Brushless Exciter

Wound Rotor Motors are 3 phase induction variants which feature increased torque values, speed control capacity and highly reduced current flow at the time of start up. Squirrel-cage motors or traditional induction are developed to adopt 3 separate windings of wire terminated at 3 slip rings over the motor shaft. At the time of startup, a resistance of variable type is put in series with the windings of rotor through the slip rings those results in lessening of entire current draining and an enhancement in obtainable torque. This permits little type motors to be utilized with high inertia and high slip loads. Machines like fans with large diameter ventilation facility, slurry pumps and long conveyor belts are termed as high slip load or high inertia loads. To mention in other way, owing to their topmost inertia prospect, they need plenty of time to gain operational speeds after starting. If traditional motors take such type of loads, they will have to be able to withstand these torque demands and additional periods of startup current compared to minimum running values. In order to get a suitable solution to the problem, the power supply system, the motor and its starters will have to be more greater than required to operate the machine actually. A substitute to this problem is availing Wound Rotor Motors.

Exciter is combination of devices or a type of device that supplies the magnetic current for generating the flux for working. For its application in industry primarily three kinds of exciters are there and they are utilized in the alternator as Pilot or DC Exciter, Brushless Exciter or Static Exciter. The main functioning of the exciter is to provide the dc voltage excitation to the attached poles inside the generator. Brushless Exciter is an extra generator attaché over the shaft of the prime generator. In case of DC generator, this would supply direct current to the poles via conventional slip ring. In case of exciter the output of AC exciter is modified through rotating type diodes and provides direct current to prime fixed poles. Field winding of AC generator is stationary and its armature rotates.

Efficacy of Brushless Exciter and Wound Rotor Motors

Generators need dc to stimulate its magnetic field. The field current of DC is received from a different source known as an exciter. Either static or rotating type exciters are utilized for the system of AC power generation. Two types of exciters are there and they are Brushless Exciter and brush exciter. The basic difference between Brushless Exciter and brush exciter is the procedure utilized to transfer the current into the fields of generator. In respect of the generator static excitation is offered in various forms like voltage from a solid-state components system and voltage field-flash from batteries of storage type. Direct current generators are self-excited or excited separately. Systems of excitation in present mode include gear-connected or direct-connected shaft-driven direct current generators, separate prime mover or belt-driven or DC generators of motor-driven type and provided by means of static rectifiers. The exciter of brush-type may be mounted on the identical shaft like the armature of AC generator or may be stored separately from the generator.


The Wound Rotor Motors are excellent for high inertia load driving and under the circumstance it is needed that utmost torque is exerted at the minimum possible speed so as to enable the load rotating since the increase of speed in the torque needed is reduced and therefore the resistance is lowered and is removed fully at full speed. The making of Wound Rotor Motors varies in comparison to that of the motors of squirrel cage type since in place of the bars of rotor it includes 3 windings resembling to stator. These windings, being open, are attached to 3 slip rings built up over the rotor shaft. This circuit of rotor is attached to 3 brushes to an outside star attached variable resistance. The prime difficulty in respect of wound rotor motor is maintenance of its brushes and slip rings while squirrel cage motor does not need this. It has also the advantages of being able to drive loads of high inertia, controlling of speed through resistance and the facility of manageable start-up currents for maximum capacity utilization. These are some significant features of wound rotor motor.