bacon4life
Electrical
- Feb 4, 2004
- 1,513
I am attempting to set a voltage regulator for a 15 MVA transformer with an OLTC and it seems like the tolerances have to be much tighter than I would have expected. This is my first time so please point out which assumptions I should change.
Goal: Voltage at the customer’s service of 120V +/- 5% (114 to 126V)
Sources of voltage variation:
+/- 1% voltage regulator accuracy
+/- 0.3% voltage transformer accuracy
+/- 1.2% voltage regulator bandwidth
+/- 0.5% Imbalance in high side voltage on regulated and unregulated phase due to transmission system
+/- 0.5% additional imbalance in low side on regulated and unregulated phase due to +/- 100 Amps of load imbalance
-0/+4% voltage drop on distribution system, zero at nearest customer, 4% at the last.
None Safety margin
Total result
11% tolerance
One way I could set it is at 124.8V (120V +4%) and have a bandwidth of 113.4 to 126.6.
Thus in the past one could:
A. Hope that tolerances are never at the same maximum/minimum value.
B. Hope that the customers don’t complain about the voltage. Not only does this seem unethical, we now have SCADA for the bus voltages, so we would know before the customer if the voltage was high, so this option doesn’t work.
Some other options might be:
C. Regulate all three phases
D. Strengthen the distribution for less voltage drop.
E. Better balance the feeders
F. Buy higher accuracy components
There is also a backup LTC controller in this installation. It seems like it should be set 1% higher & lower than the primary, but this would put it well outside of the allowable 5% limits.
There also does not appear to be room for the load drop compensation to operate and be sure to stay under 126V at the first customer.
Any help or comments would be greatly appreciated.
Goal: Voltage at the customer’s service of 120V +/- 5% (114 to 126V)
Sources of voltage variation:
+/- 1% voltage regulator accuracy
+/- 0.3% voltage transformer accuracy
+/- 1.2% voltage regulator bandwidth
+/- 0.5% Imbalance in high side voltage on regulated and unregulated phase due to transmission system
+/- 0.5% additional imbalance in low side on regulated and unregulated phase due to +/- 100 Amps of load imbalance
-0/+4% voltage drop on distribution system, zero at nearest customer, 4% at the last.
None Safety margin
Total result
11% tolerance
One way I could set it is at 124.8V (120V +4%) and have a bandwidth of 113.4 to 126.6.
Thus in the past one could:
A. Hope that tolerances are never at the same maximum/minimum value.
B. Hope that the customers don’t complain about the voltage. Not only does this seem unethical, we now have SCADA for the bus voltages, so we would know before the customer if the voltage was high, so this option doesn’t work.
Some other options might be:
C. Regulate all three phases
D. Strengthen the distribution for less voltage drop.
E. Better balance the feeders
F. Buy higher accuracy components
There is also a backup LTC controller in this installation. It seems like it should be set 1% higher & lower than the primary, but this would put it well outside of the allowable 5% limits.
There also does not appear to be room for the load drop compensation to operate and be sure to stay under 126V at the first customer.
Any help or comments would be greatly appreciated.