Brushless exciters and their relevance

If you have ever used a 3-phase synchronous generator for power generation, you may have noticed that it makes use of direct current (DC). So, how is this current supplied to the generator in the first place? Commonly, or rather conventionally, it is done through the means of a commutator. However, it is worth mentioning that this rotary electrical switch is often associated with timely maintenance; interestingly, if you have experienced the same, you can always use a brushless exciter, and overcome the problem with exemplary ease. Furthermore, this exciter does not make use of sliding contacts and can therefore be considered relevant if you are specifically looking forward to lower the maintenance costs.

Following are some of the other points that establish their relevance of this type of excitation system:
•    If this type of exciter is not used, you have to deal with the maintenance issues every now and then as the brushes and collector rings will continue to wear with use. In fact, even if you use one of the wound rotor motors, you have to take care of the maintenance costs as lots of brushes and slip rings are likely to be involved.
•    Moreover, in the absence of this type of exciter, it may not be easy to use synchronous machines in hazardous environments; as a matter of fact, if you actually want to go ahead and use the machines, you are likely to require making arrangements for enclosure modifications.    
•    When this type of exciter is not present, you are likely to encounter more noise; as a matter of fact, the presence of brushes often gives rise to sparking. Furthermore, having precise control is next to impossible as for this purpose, you may have to ensure that the electromagnets are not in the center of the motor, but again, having them on the stator is only possible when use a brushless exciter.

The relation between power generation and brushless exciter

Power generation may have not been the same, if it wasn’t for brushless exciter, which is often used in hydro generators these days. However, when generators with brushes were already being used, why is it that the industry has decided to move to brushless excitation all of a sudden? To begin with, the latter lowers the maintenance costs; now, isn’t it undeniable that if there will be no brushes, no rings, and no sliding contacts, the need for maintenance can be eliminated with exemplary ease? Unfortunately, nothing of this sort can be done for the wound round motors, which may have a higher torque, but then, also command more maintenance. 

Interestingly, if you avoid embracing the brushless exciter, you are likely to face one or more of these issues:
•    Power generation can sometimes make you operate synchronous machines in hazardous environments; however, if brushes and collector rings are being used, you cannot operate the machines in such environments. Yes, there is a way out, but doesn’t it involve serious enclosure modifications? After all, operating the machines without achieving the requisite protection may not be your best bet.
•    Furthermore, the control equipment cost can actually be a big concern especially when tens of kilowatts of direct current (DC) are involved. And of course, these kilowatts cannot be avoided as they are essential for the excitation of the field winding.
So, what all changes can brushless excitation bring?
•    First of all, the changes would be only for good and the benefits which you may have reaped otherwise by using synchronous machines will continue to come your way. For example, high efficiency, which is often associated with synchronous machines, will remain enabled. What will actually change is that there will be no need for any type of additional bearings.
•    Secondly, there will be a considerable reduction in the control equipment cost primarily because tens of kilowatts of DC are unlikely to be involved anymore.

Save on maintenance costs with a brushless exciter

It is undeniable that motors with brushes do work, but they have their own set of disadvantages. For example, when you use brushes, it is obvious that they are not going to last forever; maybe not now, but eventually, there will be some wear and tear. It is for this reason that your maintenance costs may go up as you continue to use motors with brushes. At the same time, while using brushes, you have no option but to tolerate sparking as well as the electrical noise. Not to mention, if there are brushes, they are going to take a toll on the maximum speed of the motor.

On the other hand, using a brushless exciter is likely to turn the tables upside down especially because you will then be able to save on maintenance costs without any difficulty. However, this type of exciter not only lowers the maintenance costs, but serves other purposes as well. For example, if all this while you have always believed that electromagnets do not cool off easily, it is time to think again. When brushless excitation comes into the picture, the electromagnets are moved to the stator; in such a situation, it becomes easier for them to cool off.
A brushless exciter will not only counter the disadvantages, but is likely to have some advantages as well; some of these include but not limited to:
•    Less electrical noise
•    Precise control
•    No sparking as no connections would be made or broken
•    Higher efficiency; so, if you think that a motor with brushes is more economical, it is high time that you realize if brushes won’t be there, you can achieve greater efficiency, thereby recovering the amount that you may have to spend initially.
•    Last but not least, unlike wound rotor motors, motors or generators that make use of the brushless excitation mechanism are often found to have lower maintenance costs especially because rings are not involved in case of the latter.

Eliminating the need for maintenance with brushless exciter

Synchronous motors call for extensive maintenance, undertaking which can be really problematic at times; the reason being that these motors operate with the aid of sliding contacts. These sliding contacts, commonly referred to as brushes, collector rings, and commutator, more or less pose a serious problem in terms of maintenance, thereby driving the costs upwards. However, maintenance is not the only thing that you may find difficult to take care of until and unless these contacts are gotten rid of. Apparently, these very same contacts can turn the use of synchronous machines in hazardous environments into a challenging job; however, with a brushless exciter, things actually differ.

Using the exciter can often result in multiple benefits, with the elimination of the need for maintenance being the most obvious of them. As it is possible to mount the exciter as well as assembly on the shaft, it makes no sense to put some additional bearings to use; therefore, maintenance doesn’t necessarily have to be an issue, at least not one which cannot be dealt with. Furthermore, as already mentioned, hazardous environments have more or less always been demanding as using the machines in these environments calls for added protection. However, with the brushless exciter, there is no specific requirement for enclosure modifications, at least not for ensuring that the required level of protection has been achieved to avoid all possible risks.
Meanwhile, the good news is that the use of the exciter does not really impact the benefits that are otherwise expected out of synchronous motors, and high efficiency as well as automatic regulation will continue to make your job easier. Nonetheless, the maintenance-related problem of synchronous motors can be tackled with the aid of the exciter, but wound rotor motors continue to fall under the category of motors requiring maintenance because of slip rings and of course brushes.