The circuit breaker is 800 A frame and 80% rated, which is 640 A, The adjustable rating plug, can be easily set to say 500 A. The trip unit, which is separate, can be set as a multiple of 500 A. Can the breaker carry 500 A as that is less than 640 A, or does it now become limited to 400 A?
Medium voltage (4.16 kV system) vacuum contactor dropout time is important for fuse-contactor coordination. Some vendors have values between 15-25 ms, and others, several cycles, which I have been more used to seeing in the past. Compare that to a 3 or 5 cycle vacuum breaker, and 15-25 ms is...
I have multiple foundation steel piles to be used as grounding electrodes. They each appear as a hollow cylindrical steel tube or pipe, perhaps 5/8 inch thickness, and could be driven 10-13m to solid rock. O.D is not selected, but perhaps 8-12 inch.
Has anyone seen a methodology to represent...
For a LV molded case circuit breaker, equipped with electronic trip unit, the tripping curves may only include the trip unit time, but may not include the CB opening time thereafter. Has anyone seen manufacturer's data on this? The application is arc flash analysis.
I have a VSC, voltage source converter, connected to the power system. The VSC is a PWM inverter. The power supply system fixes the voltage, say 460 V, as well as the frequency 60 Hz. For harmonic studies on the power system, my view is that the VSC should be modeled as a harmonic voltage...
For harmonic analysis on industrial power systems, I normally see the VFD's represented by current harmonics, for ac induction motor applications, and pulses of 6,12,18, etc. Now I see a report that represented the VFD's by voltage harmonics. The software is not an issue as it can accept both...
To characterize their system, the power company provides a frequency scan, which is the equivalent impedance at each frequency, output from their software (CYMDIST). At each frequency they give a number (magnitude) for each of the phases A,B,C, all different. I see three apparent issues with...
I am trying to have an appreciation of the numbers I see for single wood pole (tangent) deflections, however, it is not my field. Poles should deflect in strong winds. I also notice that some are leaning without wind, which must be due to foundation, or perhaps pole age. The maximum deflection...
Our team is discussing the need for motor differential protection on a 3000 HP motor, 4.16 kV. There is high resistance grounding, 10 A, which is important since a stator ground fault, is low current, and can be cleared quickly by the MPR (motor protection relay), without any time advantage of...
I'm wondering how far all the experts are presently taking the arc flash analysis to. I have a 480 V MCC which supplies loads such as VFD's, motors, unit heaters. I've been on sites where tests were made at each of these, with covers off. The hazard could therefore exist, which implies analysis...
The 4.16 KV system has an NGR, 5A continuous. For a ground fault in the zone of service transfomer secondary and 4.16 KV SWGR main breaker, that breaker will open. The transformer primary has only a fuse, which will not open for the small current. The fault will then persist and be alarmed, but...
For the 5 cycle breaker, I see in IEEE 242 a 0.20 sec CTI, coordination time interval between static relays. I also see arc flash calculations using 0.083 (5 cycle) for the same equipment. Shouldn't these numbers be the same?
