Electric Automation Forum

Forum » General Discussion » Voltage and frequency in finite bus

Topics: **Voltage and frequency in finite bus** on General Discussion
# Voltage and frequency in finite bus

what happens to the voltage and frequency in a finite bus when there is a new load connected or a previous load has been removed..?

#1

08-25-2013 11:19 PM

Top #2

That all depends on the characteristics of the bus and on the load.

08-25-2013 11:19 PM

Top #3

I agree... It depends on the behavior of the feeder/ load (to be removed or to be added)... there would be some transient dips or sags (depending on pick-up time of the generators)... we do have some problems on power transients, as load-side in the industry, since we have synchronous motors that are sensitive to phase, voltage and frequency variations...

08-25-2013 11:20 PM

Top #4

Infinite, Nothing.

but let me record that if a significant load is added to a bus (fed by genset(s)), Droop will take place. voltage and frequency will drop down for a while. Governer & AVR will bring the set to stabilization withing the required time.Increase in voltage & frequency will be noticed upon removal of a significant load and similiary governer/AVR will adjust the system as necessary.

but let me record that if a significant load is added to a bus (fed by genset(s)), Droop will take place. voltage and frequency will drop down for a while. Governer & AVR will bring the set to stabilization withing the required time.Increase in voltage & frequency will be noticed upon removal of a significant load and similiary governer/AVR will adjust the system as necessary.

08-26-2013 09:40 PM

Top #5

Simplest way to understand how voltage and frequency reacts to any addition of load or reduction of load to the system, which could answer also how under & over frequency happens, is like cycling a bicycle.

If you are cycling alone, then suddenly your load adds up, due to addition of passenger to your bicycle, or load increase due to going up a hill, then your cycling speed shall drop. Instead of cycling at a speed/ freq of 50Hz, now due to this increase in load, your speed is now 30Hz. Now, to maintain the speed up hill at 50Hz or maintain it even with an additional passenger, what do you need to do? You cycle harder. To cycle harder, you need to have energy, have power. So cycling harder is same as adding steam flow to the rotor, achieve either by opening the Governor or adding more fuel.

So reduction of load is vice versa. By understanding this simple concept, i believe you can know yourself what will happen when there is a new load connected or a previous load has been removed.

Hope this answers your question.

If you are cycling alone, then suddenly your load adds up, due to addition of passenger to your bicycle, or load increase due to going up a hill, then your cycling speed shall drop. Instead of cycling at a speed/ freq of 50Hz, now due to this increase in load, your speed is now 30Hz. Now, to maintain the speed up hill at 50Hz or maintain it even with an additional passenger, what do you need to do? You cycle harder. To cycle harder, you need to have energy, have power. So cycling harder is same as adding steam flow to the rotor, achieve either by opening the Governor or adding more fuel.

So reduction of load is vice versa. By understanding this simple concept, i believe you can know yourself what will happen when there is a new load connected or a previous load has been removed.

Hope this answers your question.

08-26-2013 09:40 PM

Top #6

As per the original question: In a finite bus, as Ole and Lester says.

And additional issue is to define: what is a finite bus?

Some engineers normally assumes that when a generator has a capacity of greater than 5% of the system size, then with respect to this generator, the system does not behave as an infinite bus.

For example, when an 800 MW generator is loaded onto a grid having a capacity of l0,000 MW, the system voltage and frequency can vary and the system will behave as a non-infinite bus.

And additional issue is to define: what is a finite bus?

Some engineers normally assumes that when a generator has a capacity of greater than 5% of the system size, then with respect to this generator, the system does not behave as an infinite bus.

For example, when an 800 MW generator is loaded onto a grid having a capacity of l0,000 MW, the system voltage and frequency can vary and the system will behave as a non-infinite bus.

08-27-2013 08:58 PM

Top #7

When a new load is connected to a finite bus, the voltage and frequency reduces.

while a reduction in load increases the frequency and voltage.

These changes (frequency and voltage) may be noticeable or not so noticeable depending on the size of the power grid network.

while a reduction in load increases the frequency and voltage.

These changes (frequency and voltage) may be noticeable or not so noticeable depending on the size of the power grid network.

08-27-2013 08:58 PM

Top #8

>>what happens to the voltage and frequency in a FINITE bus when there is a new load connected or a previous load has been removed<<

Simple analogy; Adding or removing load from a mule. If the system, (i.e. the mule) can handle it, both freq. and voltage will either decrease or increase depending upon the size of the load involved.

Simple analogy; Adding or removing load from a mule. If the system, (i.e. the mule) can handle it, both freq. and voltage will either decrease or increase depending upon the size of the load involved.

08-27-2013 08:58 PM

Top #9

@Bill: Or the voltage and/or the voltage might increase, if we apply the right type of load. Remember, the mule could be pulling a cart, on the way down a steep slope!