Subtransmission voltage regulation
Subtransmission voltage regulation
(OP)
For those utilities that run sub transmission (IEEE or IEC), do you employ onboard tap changers for transmission to sub transmission transformers?
For example when stepping 132kv to 33kv is voltage regulation applied or only reserved at 33kv to 11kv substations?
For example when stepping 132kv to 33kv is voltage regulation applied or only reserved at 33kv to 11kv substations?






RE: Subtransmission voltage regulation
RE: Subtransmission voltage regulation
We also then run manually set off-load tapchangers for our 11 kV to 415 V transformers.
If you were trying to run without on-load tapchangers on one of those two voltage rating transformers, you would probably need a very wide tapping range, which may not give you the fine control for the customer downstream.
Ausphil
RE: Subtransmission voltage regulation
RE: Subtransmission voltage regulation
RE: Subtransmission voltage regulation
This family of curves will be produced by maintaining the sending end voltage constant, by increasing the load. The receiving end voltage will be calculated for each loading. These curves are also referred as maximum system loadability curves.
You may notice that at some lower voltage, the loadability (power transfer capability) suddenly start decreasing. This is the point where the system will start collapsing. So based on the system characteristics, the available steady state stability margin shall be evaluated. If there is no sufficient margin available from the steady state loading (refer to the dotted line in the figure, which is the steady state stability margin line for various load power factors).
The OLTCs may help in improving the steady state stability margins, by increasing the receiving end voltage.
RE: Subtransmission voltage regulation
RE: Subtransmission voltage regulation
Thank you, this is just what I was looking for! :D
Are these stability limits based on any particular line length? And they assume that thermal limits will not be reached first before voltage collapse?
In terms of voltage collapse, would you happen to know why beyond a certain loading point the system voltage begins to sharply drop rather than being linear? This part in particular has me confused. Would increasing the sending end buss voltage under peak load increase system load-ability?
RE: Subtransmission voltage regulation
P = ({V1*V2)/XL} * sinδ
RE: Subtransmission voltage regulation
In any case, what might be behind the equation's sudden voltage drop onset?
RE: Subtransmission voltage regulation
When a transformer taps up, it increases the voltage at the secondary, but the lower ratio causes an increase in the primary current. The voltage at the primary drops because of the higher current. At sufficiently high loading, the drop in the primary voltage negates the tap change and the output voltage drops instead of increasing. Once that happens that regulator and everything down stream runs to full positive tap and the voltage collapses.