Hello,
I am inserting fault impedance into 3-phase and line-to-line faults in order to find a limiting condition for overcurrent and undervoltage relay coordination.
This is for industrial 4.16kV and 480V systems, which have a fairly high X/R ratio.
Since the system is mostly reactive...
Hello,
Suppose I have a 3-phase 480V panel which has 277V branch positions. Is it correct that the TCC plot reference voltage should
be 480V? I am trying to plot a branch circuit breaker and am unsure if it should be 277V or 480V. Will a single pole single phase breaker off of such a panel see...
Hello,
Suppose in a plant that the voltage at an MCC is below normal due to a degraded switchyard voltage. Fed from the MCC are various motors which use size 1, 2 and 3 starters. With a degraded MCC voltage, the contactors are expected to draw more current due to a degraded source voltage. For...
Greetings:
If anyone has the book "Industrial Power Systems" by Khan the subject refers to the section (9.7.7) in that book.
There have been many helpful posts on motor acceleration time on eng-tips, but none which I have found which might explain why:
average motor torque, Tm = (3*Tlr +...
Attached are two pages from the paper to help clarify the problem - this shows one method of performing UV vs. OC coordination...Thanks for your thoughts.http://files.engineering.com/getfile.aspx?folder=16ac17a3-178b-4f9d-a5da-eb57a1f9770f&file=Archive_2.zip
Thanks mgtrp. The undervoltage relays are only supposed to transfer the source when there is truly a loss of voltage situation, not when there is a dip from a phase fault. So I'm in the process of coordinating these devices...
smallgreek: thanks for your response. I am coordinating incoming feeder phase overcurrent relays with 4.16kV bus undervoltage (loss of voltage) relaying.
Greetings:
Wondering if anyone can share more examples or experiences with coordinating undervoltage and overcurrent relays. The paper
"Allowing for decrement and fault voltage in industrial relaying", Arnold Kelly
Industry and General Applications, IEEE Transactions on
Date of Publication...
Hello,
If I had an undervoltage relay in a 120V relay loop receiving input from 4.16kV bus 4200/120 PT's, would it be appropriate to apply symmetrical components to determine, given the relay pickup (say 55V/120V) and the system sequence impedances, a fault current which would depress the bus...
Pwrtran: thanks for your inquiry, however I am just interested to know what others general methodology is for coordinating overcurrent and undervoltage relay operation.
Greetings:
Wondering if anyone can share their thoughts on (4.16kV/480V) overcurrent and undervoltage relay coordination. A range of fault currents (three-phase,line-to-ground,line-to-line,line-line-ground) and corresponding post-fault bus voltages could be calculated and compared to the UV...
Greetings:
Attached is a picture of the zero sequence network of a solid ground fault with high resistance grounding (from EPRI "Grounding and Lighting Protection")
Practically speaking, if the resistor/xfmr was connected to the neutral through a long cable (say 5kV, 2/0, 200'), would its...
pwrtran: thanks for your response.
The generator is neutral grounded through a high resistance scheme (through a distribution transformer, 10 kVA, 4160/240V, with 4.2ohm on the secondary.).
My main question was: given that the components which determine Xco (the 3-phase capacitive reactance)...
Hello, to refresh and add a new thought: when the generator is first powered, couldn't the neutral conductor shunt capacitance become charged before the Vng becomes zero? Thanks for your thoughts.
Greetings:
The generator neutral conductor of a HR grounded system is rated 5kV, 1/C, #2/0, 100'. In totaling the system capacitance, how can it reasoned to include the shunt capacitance of the neutral conductor? Under balanced operation, the voltage across the neutral should be zero, which...
Greetings:
Can anyone familiar with the following rule of thumb,
"one hour of operation at sqrt(3) times rated voltage equates to about 700 h of operation at unity (rated) voltage" from "The Reality of High Resistance Grounding", Dunki-Jacobs, IEEE Trans. On Industrial Applications, Vol...
odlanor: Thanks very much that was the correct guide indeed.
To refresh: Neutral current I_r is less than 3*I_c (i.e, resistor kW < system charging kVA, X_cg/R_n is less than 1.0) in an as-built system. From IEEE C62.92.1989 it can be seen that transient overvoltages will exceed 250% (lost...
Thanks for your thoughts. To show that the actual secondary fault current (as "seen" through the fuse) through a 480/120V, 150VA, Z = 3.5%, control power transformer, while considering the 10,000A available fault amps (at the primary), does the following make sense?
Using secondary as base...
