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Dear colleagues, I am involved in design of electrical systems in my country for industrial, commercial and institutional markets. It is a European country and we use IEC standards. When I say electrical systems, I mean: - design of all low voltage distribution systems in buildings and plants...

Well, I have never encountered problem that voltage dip in medium voltage cables during short circuit from the point of stiff voltage would be ~30% of the nominal voltage, in order to cause contactor opening. On the other hand, in all motor control circuits for medium voltage motors we use...

You should check once again why contactor would open. From where is that voltage dip coming from? The problem here might be the dynamic and thermal withstand of contactor while conducting short circuit current, not clearing it.

I suppose that the ring is one-way, meaning that energy is flowing from the source (network) to the ring. Having this in mind: 1. main busbars should be calculated according to the maximum installed power of all transformers (and/or motors) in the ring. I would carefully analyze all the...

to waross: to be honest, when I saw your calc., I was little doubtful about the size of your genset, therefore I had to post. Since you clarified NEMA and IEC difference in input data, you got genset which is closer to the power that I would expect for this type of load. I tend to use at least...

In order to clarify this, what are ''with 2 x 11kV CBs feeding a ring main (load around 1MVA)'' Are these feeders from 11kV switchboard or you have another source?

Besides cost and complexity, I would think about installing capacitor banks on medium voltage side when I would have many transformers (or one transformer with substantial power) and measuring is on the medium voltage side. When resonance is concerned, there are on the market capacitor banks...

Your device is measuring to much harmonics in the second transformer. Since it has more than three times bigger THD (odd harmonics are the critical ones) than the first one, one variant is that the second transformer is supplying non-linear load with greater influx of harmonics than the first...

to davidbeach: Sorry David, there must be some misunderstanding. I think that you are wrong, since the cascading was officially implemented in IEC 60947-2 and NFC 15-100, &434.3.1 (with that specific term). If you open catalogs from this year from, for example ''Schneider Electric'', you will...

to flandes: IS barrier cannot protect you from the fault on high voltage which then skips onto the RTD wiring. Its only purpose is to protect RTD and its wiring from excessive energy surge from the main control panel and as a result rising the temperature of RTD or its wires above the explosion...

One way of lowering the heat dissipation is maybe to use insulated busbars instead of cables. In that way you should be able to transfer more power with significantly less copper (no reduction coefficients for cables). Since copper is today very expensive, by ordering even brand name busbars...

I would be very careful about these calculations. You have two motors 110kW, which are significant load since the diesel generator does not produce stiff power. In contrast to a utility grid, a genset powered system is small—measured in hundreds of kilowatts rather than thousands of...

1. The switch breaking (making?) capacity is 200kA only if there is upstream protection device (breaker or fuse), otherwise is probably less than 10kA. 2. Problem may be not only the equipment in MDP, but also in subsequent switchboards if their breaking capacity is low (6kA or less). MDP is...

If your subcontractor only wants to size the equipment in switchboard immediately after the transformer, then you need to give him: a) value of initial short circuit current Ik'' (which is in distribution networks equal to a steady state short circuit current) and b) peak value of the short...

First of all, you should distribute your load evenly through all three phases, since the unbalance in your case is causing unnecessary load in neutral conductor. Second, the reason why triplen harmonics (3rd, 9th, 15th etc, since even ones are negligible) are always endangering neutral...

SVC is usually made from capacitive banks and TCR (Thyristor Controlled Reactor). By changing voltage on the reactors using thyristors, you are able to control amount of reactive power consumed by reactors. Capacitive banks feed constant amount of reactive power to the grid and since the rest of...

You should always try to use manufacturer recommended ratings. For example, if full load motor current is 1.25A, then you should use motor circuit breaker that has a setting of his ''thermal'' part (1-1.6)A (for example). Manufacturers usually also give corresponding contactor rating according...

Since the transformer on the upstream side (132/11kV) is high resistance grounded, you need to have same precautions as when the network 11kV were isolated. Hence, you must use 11kV/11KV grade cables. On the other hand, for medium voltage systems above 5kV, the Insulated Power Cable Engineers...