When all power sources are connected to the same busbar,
the generator AVRs will ensure that the voltage on that busbar
is correct by adjusting the reactive power output based on a
voltage droop curve. The PMS will fine tune the voltage to
ensure that it remains within the steady-state tolerance. When
distributed generation is used, it may be necessary to change
the tap position of the transformers on the interconnection ties
(provided that they are equipped with OLTCs) in order to
move reactive power to an area where there is a lack of
reactive power from an area where there is an excess. This
can be achieved in primary regulation by implementing an
overall voltage droop characteristic based on transformer
impedance and transformer AVR operation. This is shown in
Fig. 9. When the transformer voltage droop has the same %
value as the generator AVR droop, then all generators and all
transformers connected to the same busbar will supply the
same percentage of reactive power to support the busbar
voltage. An increase in load will also increase the reactive
power consumption. Additional reactive power will be supplied
by both the generator and the transformer. Since reactive
power may be lacking in any part of the power system, the
transformers should be designed to be able to direct reactive
power flow to any location in the system.