I'm working on a brushless DC motor controller. The heat sink that contains the circuit board is completely embedded in a gray rubber type substance. It seems like it must have been filled with this as a liquid.
Any ideas on how to remove this material without destroying components on the...
I typically see transformer inrush plotted as a per unit value of normal transformer FLA current on a phase TCC at a specific point, such as 0.1 seconds.
I have also come across transformer inrush current curves. So, the inrush may be plotted as 10 per unit FLA at 0.1 seconds and 2 per unit FLA...
As current flows through a bus that has a window CT wrapped around it, it's stepped down by the CT ratio. 100 A through a 100:5 ratio window CT results in 5 A secondary.
If 5 A of current is applied through the secondary winding of the CT, does this cause 100 A of current to flow through the...
I'm looking for model recommendations (commonly available in USA) for stand-alone relaying CTs (C400 or higher) that can be used for protection applications with circuit switchers. Circuit switcher manufacturers never seem to provide slip on CTs as an option similar to circuit breakers. Combo...
I'm not having any luck finding a symmetrical component example for a fault between two separate transmission lines. I'm attempting to analyze a fault that occurred between a 69 kV and 138 kV line that share the same tower. One phase on the 69 kV line came into contact with a different phase on...
Is there any benefit to implementing REF protection on a transformer that is already protected by 87T protection using CTs on the high and low side bushings? I can see the ability to isolate an internal fault to the wye winding, but I don't know if there's any other benefit or if it's just...
I live in a fairly small apartment on the 1st floor of a building. The HVAC system rarely needs to run due to the insulation provided by units above and around it. The kWh usage has always seemed high compared to similar dwellings in the past, but I unfortunately never investigated further.
I...
Most microprocessor relays are capable of sampling at rates of 128 samples per cycle or more. Would it ever be possible to get this type of resolution with Phasor Measurement Units or will these always be more for longer duration event analysis such as power swings and such?
The highest sample...
I'm looking for a few drawings that clearly indicate the potential gradient along the earth during a fault to ground. I've come across a few on Google Images, but nothing that's really clear.
I hope to find something that shows a phase conductor contacting the Earth and the voltage gradient...
I'm having some trouble wrapping my head around the voltage distribution for a ground fault. If a Delta-grounded wye transformer has an A phase line-to-ground fault a mile down the secondary line with no fault resistance, the voltage is considered to be zero at the fault point. The entire...
For power transformer protection of a standard Delta-wye radially-fed transformer, is it normal to utilize negative sequence protection to gain sensitivity? What is commonly recommended for settings sensitivity to avoid inadvertent trips? As in, should it be set to pickup at 50% of expected...
I often see a "minimum fault" specified on some fault study software that seems to typically be around 30-60% of the maximum 3 phase fault current. What is this referring to?
Is there a common fault resistance value that is used for these calculations? Minimum fault current is confusing since a...
On a line protected by instantaneous distance protection along the majority of the line, what is the best option for coordination with overcurrent protection on multiple taps with breakers feeding transformers at the end of a short line with negligible impedance?
For high side transformer...
When calculating line impedances, what temperature is typically used for the sag calculation? Sag is often listed at the highest temperature rating of the line, but this is rarely the case under normal loading. Is there a standard industry practice when modeling lines or is it usually up to the...
I'm looking for the IEEE standard which discusses the allowable interrupting times for medium/high voltage circuit breakers at a given level of fault current. For example, a breaker may be able to interrupt a maximum fault current of 25kA, 40kA, or 63kA, but what is the maximum allowable...
I have a few questions on breaker failure schemes since there seems to be no consistency among the approaches I've come across.
Example: Radial Line Load Protected by (1) Distance Relay and (1) Overcurrent Relay - Fed from Ring Bus. Breaker 1 & 2 feed the radial line. Breaker 3 & 4 are adjacent...
What is the best practice for sensing low side bus ground faults on a Delta-wye transformer with high side protection? Since a L-G fault on the low-side appears as a L-L fault on the high side, the phase overcurrent elements must react to this fault. If the transformer is on the larger side or...
If I have line current magnitudes and angles for A, B, and C phase current, how can I calculate the current flowing through the individual windings in a delta winding?
I have a few questions on transformers:
1) Is there a good explanation out there on why the 2nd and 4th harmonics are common during energization? I assume this is related to saturation of the core due to the point on wave of switching, but it seems like this would only occur on the positive...
I am working on the revision of an outdated O&M manual that is focused primarily on substations and substation equipment. I am trying to decide on the best approach for this type of manual in regards to the layout/format, how broad/technical it should be, and any other ideas that you have seen...
