GENERATOR CLOSING UNTO DEAD BUS BASIC TUTORIALS



Closing onto a Dead Bus with Leading PF Load
It is possible to have a power system configuration where a bus might have capacitive loading.
• Static capacitors connected to it.
• Energizing a long high voltage transmission line. Note HV lines inherently appear like capacitors, which are able to supply MVARs.

In the capacitive loading situations the generator would have to absorb these MVARs. If the Automatic Voltage Regulator is in the Auto mode, the generator excitation is automatically decreased to cause the generator to take in the required MVARs and to hold the terminal voltage.

If the Automatic Voltage Regulator is in the manual mode, the excitation is constant and the leading power factor current which is required for the generator to take in MVARs could cause the generator terminal voltage to go very high.

Closing onto a Dead Bus with Lagging PF Load
Inductive loading can take the form of:
• Connected power transformers
• Motor Loads

Inductive loading will cause a significant voltage drop when the generator breaker is closed, due to the load absorbing MVARS.

Closing onto a Faulted Bus
Closing the generator output breakers onto a bus, which has a short circuit fault, can cause generator damage because of high winding currents, stresses and possible pole slipping.

Closing onto a Dead Bus with no Connected Loads
This should not present a problem as long as the bus has been proven to be free of faults or working grounds.

GENERATOR LOADING
Closing onto a Finite vs Infinite System
When we enter into the topic of generator loading we must consider whether or not the connected electrical system is very large and hence strong or smaller and weaker. The first is classed as infinite and the second finite.

A generator connected to a very large (infinite bus) electrical system will have little or no effect on its voltage or frequency. In contrast, a generator connected to a finite bus does have a substantial effect on voltage and frequency.

It is normally assumed 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

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