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Anyone have any info on the ABB ACS 550-01 VSD's please? I am particularly looking for how the motor thermal protection works as I want to model the thermal hot and cold curves in SKM's PTW. Any formulae or thermal curves will be most useful. Thanks.

For the harmonics gurus, I have read in quite a few texts on power system harmonics that a VFD is a non-linear load and so is a source of harmonics. Thinking about it I would say that this is misnomer (the way I see it anyway). The VFD is not a source or sink of electrical power. Considering a...

I've just done a harmonic study using PTW. This tells me what the V_THDV% and I_THD%, Vrms, Irms are at several locations in the network, the K factor for trfrs, etc. I was thinking, is there a way of predicting if there are potential resonance issues on the network? The network has several LV...

I am curious as to what the LV system in the attached drawing would be called. I am aware of TN-C and TN-C-S and TT systems. But what if the supply trfr neutral is high impedance earthed via a 5A neutral earthing resistor as shown in the diagram...

Hi I came across the electrical design for the 480V network for a mineral sands mine in the state if Georgia. The system is high resistance grounded at the supply trfr with the groundfault current limited to 5A. Yet there are no RCD's installed, only fuses on all the final sub-circuits. How is...

I need to do the primary injection diff protection stability testing of a 5MVA 33/11kV 7.15% trfr first of all. Afterwards 4.8MVA 11kV generator needs to be primary injected. 33kV CT's are 150/1 and 11kV CT's are 300/1. I need to have at least 20A at 33kV to operate the diff or 60A @11kV. I...

Hi I have a 30kVA 415V to 240V single-phase trfr as per the attached diagram. The trfr feeds a distribution board in a coal mine. The secondary is 240V and I have worked out a fault between the secondary terminals to be around 3480V using PTW (4166A if I neglect source impedance). 1. How do I...

I have a set of around 20 small VFD drives (4kW) all with 6-pulse VFD's. Do all the smaller drives produce the same harmonics on the system as one large 80kW drive? or do the harmonics interact and in some way cancel each other? Thanks.

I have a question regarding let-trhough curves of fuses and circuit breakers. I have researched this forum but not found any thread that exactly addresses the question I have. Consider the attached pdf. The top let-through curve is that of a fuse. We are dealing with a 80A fuse and the...

Here's one for all the cable gurus. When I size cables I find that fault current is usually the dominant player (vs load and voltage drop). I usually consider the symmetrical rms fault current when calculating the withstand capability of the cable (heating effect). But what about the initial...

Suppose a VFD drive(s) is supplied from an MCC which is in turn supplied from a 480V swbd. The swbd is connected to a 1.5MVA 13.8kV/480V Dyn11 trfr. Trfr neutral has two EF relay CT’s. Trfr neutral has a 5A NER. CT1 feeds EF1 relay: set to 500mA, 0.2s and trips the LV ACB. CT2 feeds EF2 relay...

I am not a harmonics guru and so need some advice please in planning a network. A client wishes to use 6 pulse inverter VFD's on drives from 250kW to 500kW at 480V. Naturally there will be substantial 5th and 7th harmonics present. Currently, the 13.8kV/480V 1.5MVA transformers, supplying these...

I have a question relating to SKM's PowerTools: The following are the PowerTools loadflow results for an induction motor with its VFD: The motorside kw differs from the lineside kW by the VFD efficiency. So far so good. However, the power factor is different on both sides and so the kVAR and...

Hi Not dealt with VFD's very often so need some advice please. I have read that a 4-quadrant VFD allows operation of the motor in all 4 quadrants, i.e. rotation and torque in the same direction as well as rotation and torque in opposite directions. When torque and rotation are opposite to each...

I am very familiar with the IEC 60909 fault study methodology but now need to learn the ANSI one as well. Any recommendations for a good explanatory text on the subject? I sometimes find articles written by manufacturers or others on a subject likes this makes for easier to understand reading...

When considering shielded three-phase or even 3 x singlephase cables, I've come to the conclusion that the positive sequence capacitive reactance (X1C) is the same as the zero sequence capacitive reactance (X0C). Conceptually, whether I excite the cable with a single or threephase source, the...

The General Cable catalogue specifies cables with a 133% and 100% insulation level. My understanding is that 100% cables are for solidly grounded systems where the neutral voltage does no appreciable rise with ground faults. 133% for high resistance grounded systems where there can be full...

A new mining site proposes to use the "rabbit boxes" as cable junction boxes on an open cut mining site. Essentially a big JB with posiclamps. System voltage = 13.8kV. My concern is arc flash and safety considerations. There is no cable diff - only IDMT phase and def. time for groundfaults...

Hi What is the ANSI equivalent to IEC 62271 (MV and HV switchgear and controlgear)? I have found ANSI C37.55-2002, C37.04a and C37.09a but am not sure. I am dealing with a swbd for a 13.8kV installation. Thanks.

I live in the IEC world and am now on a US based project. Simple question - what is the maximum continuous overvoltage allowed for a 13.8kV and 480V mining system? What standard governs this? Thanks.