Types of Electric Motors: DC Brushed, Asynchronous, and Synchronous скачать в хорошем качестве

Types of Electric Motors: DC Brushed, Asynchronous, and Synchronous

Having already talked about what an electric motor is, now I'm going to talk about a few different types of electric motors. Specifically, I'm going to talk about DC brushed motors, asynchronous and synchronous. I'm Corey Foster at Valin Corporation. Let's see what we can learn. There are plenty of people who know a way more about some types of electric motors than I do, so I reached out to a good friend of mine and colleague, John Brokaw, to give some of his input on some of these types. COREY: John, what can you tell me about the DC brushed motor? JOHN: This is the oldest school down-and-dirty motor in creation. This thing has been around. See it right here on the slides, invented by Faraday in 1821. So, it's a 200-year technology. It actually is still used in a lot of applications because it's relatively inexpensive. It does have a few known issues that everybody's aware of. Most commonly being the wear on the brushes. You have these ceramic carbon brushes that are passing the current to the rotor that's rotating and the wear on those brushes they just, like anything, they eventually wear out and they have to be replaced. This takes your motor down whatever vehicle it is working on down, and it's just a nuisance. COREY: So, where the DC brush motor here is commutated by a break in the wires and these brushes here, the AC motor actually is commutated by the sinusoidal frequency of the AC current coming in and goes to the contactors here. Now this is showing the coil being on the inside, but really, usually, the coil is the stator on the outside with the rotor on the inside that is the one that's turning. But this is good for comparison. The difference between the AC and DC and how they are commutated. Before I talk anymore about AC Motors, let's talk about synchronous versus asynchronous. An AC asynchronous motor doesn't have any magnets in it, so it actually turns slower than the synchronous speed of the frequency coming into it. I already talked about how an AC motor commutates off the AC frequency coming in, 60 Hertz here in the US, but an asynchronous motor, since it doesn't have the magnets, will actually fall behind that, and it will always be running to catch up. So you can see here that it's the frequency coming in times 120 divided by the number of poles minus some slip. So it's always just going to be running to catch up, whereas a synchronous motor has some permanent magnets in it, so it's locked into the frequency being controlled that's coming into it, and it's always going to turn at that synchronous speed. I have to jump back to John Brokaw for this one. John, are AC induction and asynchronous motors the same thing? JOHN: All AC induction Motors are asynchronous. But you can get synchronous, pseudo-synchronous, applications out of them by pairing them with feedback and doing vector control on them. That's where you're actually controlling the angle between those two and controlling that slip frequency to be exactly where you want to be to generate the torque/speed performance of the application. And here we have the guts of an AC induction motor. You can see that this is a classic induction motor where you don't see any brushes or anything coming to it. You have that rotor assembly there in the middle that's tied to the shaft going through it. The only wearing component on a typical AC induction motor are the bearings which you can see at the ends of the motor. There are a number of accessories that can be added to an induction motor depending on what the application is. One of the primary one wants to think about is cooling. This one has a fan. This looks like a totally enclosed fan-cooled motor. You can also have non-ventilated motors which are sealed. You can have an open motor where you actually have air flowing through the motor. You can have forced air on these things. You can put hydraulic cooling jackets on motor. There's lots of different ways to cool a motor off. The thing to remember at the end of the day is that an electric motor is a coil of copper and you're putting electricity through it. Whenever that happens, that's an electric heater. So you are going to generate heat in the system and in some way you've gotta get that heat out. Heat management is one of the key issues in selecting and sizing and operating motors. I'm Corey Foster at Valin Corporation. Reach out to us here. Thank you, John Brokaw, for assisting. I learned a lot today. I hope this helps. If you have any questions or are just looking for some help, we're happy to discuss your application with you. Reach out to us at (855) 737-4716 or visit https://www.valin.com #valincorporation #automation #industrialautomation #motor