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We have taken delivery of a 400ton steel-hulled dutch barge which has no less than 3 separate 3-phase 400/230v generators of around 40KVA. The control system is such that the generators cannot operate in parallel. Setting aside the 24v dc installation, the electrical installation is as you...

I am interested to know the typical line to earth fault level on the primary of an 11KV/400/230v D/S Trfmr, the type generally used on the UK public distribution network. Where the tank earth and the secondary star-point earth connection are bonded the fault voltage appearing between the...

A single phase to three phase rotary-type converter installed on a farm to drive a compressor has assymetric voltages to earth on the load side. I understand that this is a feature of such devices. The displacement between phases remains at 120degrees. Can any one tell me why an equal phase to...

May I bother you with a technical query slightly outside my capability? Consider a 1Kva wind turbine being fed on to a common single phase busbar also supplied by the grid via a standard 50Kva tx. Such a situation would be found in a typical domestic installation that has installed the micro...

I have a new digital ohmmeter that claims an accuracy of 2%+-2digits on the 20ohm scale (19.9). The resolution is 0.01ohms. Does this mean that a reading of say 0.4ohms could be 0.18 or 0.62 resulting in a deviation from the measurand of circa 55%? Regards, Lyledunn

As a simple interested observer, I am aware of the importance of the transmission angle in power transfer situations but what are the practical methods generally employed to adjust the transmission angle on 33KV lines? Regards, Lyledunn

Listening to a BBC news report where an "expert" was interviewed, it was suggested that the power of the hurricane was more than all the energy ever produced by mankind! Perhaps, regardless of the veracity of the anecdote (and I have no reason to doubt it), it is nonetheless very humbling to...

Is there an electronic replacement/alternative for the IDMT relay? It has been quite some time since I worked in the industry but I was told that the good-old IDMT has been virtually shelved on new or refurbed protection schemes. Regards, Lyledunn

Many UPS rely on switching to a bypass circuit when a load-side fault is detected. However, one primary function of the ups is to take the load when mains fails. Now I assume that the ups may not have appropriate energy levels to clear faults in the appropriate time, so what mechanism is...

I am often required to measure earth fault loop impedance of low voltage systems in various buildings. Now the tester has a soft test option that will not trip out residual current devices. As far as I am aware it uses a capacitor timing circuit. Has anyone a better handle on its operation...

I live reasonably close to Strangford Lough in the north of Ireland. It has a narrow mouth and funnels millions of gallons of tidal water at speeds up to 14Km/hr. It has always impressed me as an ideal location for an underwater, environmentally benign turbine plant. You cannot fail to be...

Some electrical installation instrument manufacturers claim compliance with standards such as the BSEN 61557 (British and European). However, I have noted that the standard requires an operating error of not more than 30%! Hardly worth doing the tests! Any views? Regards, Lyledunn

In a simple one-liner, what would you regard as the "main" reason for tying the star point of a 400v 4-wire generator to earth? Regards, Lyledunn

Forgive the basic question please, but just how far might an electron travel from its original position in say a standard 6oHz HV ac transmission line? Regards, Lyledunn

If a number of single phase installations are connected to a distribution transformer such that their respective loads cause successive voltage drops in the distribution cable, will a short circuit in the last installation on the distribution line be affected by those voltage drops? In other...

I am seeking a simple drawing / explanation of the production of a spark through the piezo method. I have searched the net with little luck. Any body point me in the right direction? Many thanks. Regards, Lyledunn

What measures are employed to provide protection against ground faults on the load side of an UPS? I am in the UK and I have found that with mains healthy, earth loop impedance tests taken on the load side of the UPS often results in relatively high impedance values thus often rendering reliance...

I do a little lecturing on a temporary basis in a local college. Some time ago,one young, eager lad was keen to know the answer to this question: A bulb is placed at the remote end of a circuit of 10m length. There is a switch to operate the bulb. Now a similar circuit is 10miles in length, if...

A client of mine has a number of small 3phase motors some wired via starters some not. All are protected by a single phase mcd on each phase rather than the linked 3phase type. I think that I am reasonably ok with the technical disadvantages and I will relay these to my client. However, there is...

I often see 230vac/12vac lighting transformers, usually rated at 50va and usually connected to a decorative downlight with a dichroic bulb. They are very popular in shopping malls and where display lighting is required. In any event, the transformer is required to be a safety isolation type...