There are some interesting discussions on inrush mitigation in thread238-235674.
Why use distance relay as back up for transformer protection? Why not 50/51 and distance relays for your transmission lines?
If you are matching tap position and not voltage, what happened when there are two transformers with different voltage per tap position? Theory indicated that greater level of circulating current will result from matching tap position than from matching turns ratio.
I have heard of instances...
The utility where I work do not match regulation (tap position) for the exact reason that you mention, there will be a voltage difference enough to result in a short circuit. Instead what we do is to match voltage which is a form of impedance matching. The fact that the turns ration are now...
I would not pressure the utility too much on this, being a utility person myself you may find that you ran into a dead-end and there is no information from them to support the theory of an over-voltage. The fact of the matter is that based on the exposure of the lines, utility customers will be...
jraef's second post is more accurate. Step 3 of the first post is implying an algebraic subtraction, however these quantities are vector quantities and cannot be add algebraically!
Waross,
I am not sure I understand you post. With the neutral tied to earth how is it possible to have a neutral shift? Isnt the unequal voltage as a result of voltage drop along the lines and the neutral?
This is an interesting one. For grounded wye- grounded wye system there will only be feedback if the transformer is loaded and the load is not balance L-G loads. There will be feedback for loads connecetd L-L especially motors. What is the nature of the load supplied by this transformer?
These ungrounded systems are succeptable to ferroresonant over voltage, overvoltage (as much as 1.73pu rise) as a result of earth fault transient overvoltage, and overvoltage as a result of switching switching (whether deliberate or as a result of protection from faults). If there is upstream...
Use the nominal ohmic/pu value for the network impedance. The voltage factor c which can be considered as a sort of safety factor should then be applied to compensate for Voltage variations, changing of the transformer taps etc. For the system you described (>35kV) the voltage factor c=1.10...
Magoo,
I dont agree with your post. If the problem is one of sustained over-voltage The approach is to find out what is causing the overvoltage (temporary or sustained) and fix that, not putting bandage on the situation by increasing the arrester duty cycle rating.
Alehman, looking at your post...
I would not be inclined to change the arrester to 9kV. This is for higher system voltage and would continue to be guided by IEEE 62.11 table 1. I need to ask some questions though and the answer should point to the problem.
What is the BIL of the entire system? is this more, less than or equal...
Let me see if I get what you are saying. The tap changer is an on-load tap changer with a regulator to maintain the secondary bus voltage at 400kV. If this is the case then the bus voltage will always be close to 1pu and so there would not be a need to change the impedance. In this case the...
No you would not neeed to change the network impedance on the primary side of the transformer. However any SC values at or downstream from the 400kV bus (secondary side of the transformer) must reflect the voltage at which bus is set.
