As we have already discussed Introduction to Synchronous Machines
and Constructional Features of Synchronous Machines
. I think you are also aware that machines are basically divided into two types viz. Motor and Generator, but synchronous machines operating on general power supply networks may be divided into five types due to their special features.
These five categories are : -
Hydro-Generator : -
- Engine Driven Generators
- Synchronous Condenser
The Synchronous generators driven by the water turbines are known as hydro-generators or water wheel generators. They have ratings up to 750 MW and are driven at speed ranging from 100 to 1000 rpm. This is due to the salient pole construction of the hydro-generators.
Turbo-Alternator : -
They are driven by steam turbines. Since the efficiency of steam turbine is high at large speeds, the turbo-alternators are designed for speed up to 3000 rpm. As speed of turbo-alternator is high so the rating. It is upto 1000 MW.
Engine Driven Generators : -
There generators are driven by different forms of internal combustion engines at speed upto 1500 rpm and rating upto 20 MW. Generators driven by gas turbines have higher speed and higher power ratings.
Motors : -
Synchronous motor are kind of motors i.e. Device that convert electrical energy into mechanical energy. A synchronous motor may be either plain synchronous machine or synchronous induction machine.
The plain synchronous machine with salient poles is commonly used. Synchronous motors have some definite advantage over induction motors and these include constant speed operation, power factor control and high operating efficiency. But these advantages are on account of high initial capital and more maintenance charges at normal conditions but at high power low speed operation these synchronous motors are cheaper than that of traditional domestic motors or induction motors. The common application criteria of synchronous motors include constant speed drives for compressors, blowers, fans, low head pumps etc.
Synchronous Condenser : -
Synchronous condensers are used for control of reactive power in power supply networks. The main concept of improving power factor is to force current in synchronous machine to lead as in capacitor and thus it cancel the inductive components and improve power factor.
Commonly a synchronous compensator which is also called synchronous condenser is designed for ratings up to 100 MVAr
and speed up to 3000 rpm.
The rating is in MVAr because these are designed to cancel the reactive component.
Now, from above discussion it is clear that the synchronous machines are divided into three types where other machines are divided into two categories i.e. Motors and Generators but synchronous machines has one more type that is Compensator due to power factor control property.
First three classes discussed above i.e. Hydro-generators, Turbo-alternators and Engine driven generators are Generators.