I think the answer is yes, the other two phases technically have I0 current, but you can’t measure it as it’s canceled by the positive and negative sequence currents in the phases without the fault, so the current is zero in the unfaulted phases.
The only exception is that you can absolutely...
How old are these installations?
I only ask because in my company a very similar situation is present, but it’s due to a change of system grounding philosophy over the last 100 years. The 55kV transmission system, which was the original system transmission voltage, was originally ungrounded...
Well, if the 230V side has no ground reference then presumably the neutral voltage could be anywhere depending on the leakage impedance to ground. I’ve seen similar issues with ungrounded DC systems - typically they float with positive and negative sides equal between ground unless one side has...
I could see adding VFDs on single phase systems to allow for 3 phase motors would be a good practice. The max torque on a gate would be closed with the full force of water behind it, and single phase motors don’t have great starting torque. I have a feeling a smaller VFD and 3 phase motor would...
My utility often installs neutral reactors in distribution substations, 0.5 ohms typically. I remember hearing it was to limit the LG fault current to prevent damage to concentric neutrals on cables during LG faults, but I need to verify that.
Same thing waross is saying, but from a theory perspective.
The fundamental theory is:
V= d_phi/dt, where phi is the magnetic field. In an AC motor or generator the stator magnetic field is generally sinusoidal.
The derivative (slope) of a sine wave is proportional to the magnitude of the wave...
We’ve been talking with GE about obsolescence, so far all of our cards and controllers from 2008 are still supported.
We still have UCSA controllers, first generation MarkVIe equipment. At some point they are supposed to provide us with an upgrade plan for each plant, although I think they are...
Simplest protection is to use undervoltage along with overcurrent/overload protection - low fault currents, unless your fault is very far away, result in low voltage. With more sophisticated relaying a voltage restrained or controlled overcurrent relay, 51V, can be used instead for better...
Yes, the current away from the generator will be lower.
The curve referenced earlier is a bit tricky because it appears to include the dynamic response of the exciter. What this means is the fault voltage driving the fault current is varying. Depending on what you trying to do this may or may...
It depends. On a close in bolted 3PH fault an instantaneous breaker would likely trip. A single phase fault away from the generator might not generate enough current to trip the instantaneous element, and if it’s tripping on the breaker thermal curve then I would expect it to be in the sustained...
Depending on interconnection requirements you may need to keep in mind VAR capability and may need to run the turbine at an even lower load to provide VAR headroom - our transmission providers require 33% VAR capability at full load.
Some generators have curves available to increase output on...
A couple of thoughts:
1. Since V = d_phi/dt, voltage should be linear with speed with a fixed magnetic field. What voltage do you need?
2. That sounds complicated since you’d generally need to rotate the machine - shiv and belt drive with a pony motor? Is this a bust fed excitation system...
Neta MTS-2011, page 135, section 7.15.1 has the following guidance:
- 1megohm per kV on armature windings made before 1970 and field windings
-100 megohms for ac and dc armature windings made past 1970 (form wound)
-5 megohms for random wound coils and form wound coils below 1000V.
This...
For low voltage equipment I generally see the pass/fail at 1 megohm, with I think comes from a NETA (inter-National electrical testing association) testing guideline. I don’t remember the section, if you’re interested I can go back and find it and get you the reference.
Casey
