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There are different groups of drawings e.g. (i) Interconnection Diagrams and (ii) Schematic Diagrams
The Interconnection Diagrams usually explain how a cable is connected on both ends or how does it interconnects two equipments?
All cables are primarily identified from its given identification number and if it is multi core cable, each core is either identified by numbering or by colour coding. An interconnection drawing very well shows the terminal blocks where its cores are to be terminated. This can be found in Cable Schedule indicating where both ends of a particular cable are connected. These drawings also show clearly the terminal blocks with their location in the equipment / panel. These drawings are easy to read.
The schematic drawings show the whole scheme of a particular circuit (or even the whole grid station). For example a schematic diagram for closing circuit of a circuit breaker will show the all elements (showing conditions for closing) in the circuit. Those elements may be placed in different equipment or panels. First thing is to understand location of such elements, it is usually marked with different shapes indicating particular equipment or a panel and number of terminal of that particular terminal block in the terminal box. Second important thing is to read the schematic diagram in the direction of flow of current in a circuit. It is further advised to start reading a diagram from LEFT upper corner and proceeding downwardly reaching to the lower RIGHT corner of the drawing (as we read any English written page of any book). Thirdly, understand the drawing elements like how the normally close / open contacts, coil of a contactor are shown. What shape represents CTs & PTs, circuit breakers, isolators, lightning arresters etc?
If Mr. Mushtaq, the initiater of this topic, lives near by Lahore, I may offer my services to let him learn how to read these drawings in just a one hour sitting.
A couple of thoughts that may help you.
By indirect contact I suspect you mean shock other than by direct contact with an active conductor. This form of shock will occur should somebody contact the motor earthed metal and true earth simultaneously with an earth fault occurring. The 51G relay will pick up the earth fault but not the indirect human contact. The danger comes when the fault current flowing raises the potential of the motor frame above true earth (EPR) and this then forces a current through a person in contact with the metal and true earth. The way to guard against this is to limit that EPR potential and/or the fault clearance time to levels regarded as non-injurious. Guidance on the allowable levels can be found in most HV standards. (Try AS2007 or IEEE80).
A second point is that you state that the transformer neutral and motor frame are connected to independent earth electrodes. This means that the fault path is via those electrodes and the earth. The electrode to earth connection can have a significant resistance and the higher this is the greater will be the generated step and touch potentials which effect the severity of indirect shock. Also, the higher it is, the lower the fault current will be and this may effect the clearance time of the relay. Unless there is a very good reason for having independent earths, I suggest that it would be better to equi-potentially bond the motor case with the transformer neutral grounding conductor, thus creating a low impedance path for the earth fault current which will minimise EPR and the clearance time. This could be done with the earth screen in the cable (if it has one) or a separate earthing conductor.
You could not practrically set 30ma at 20msec as a trip threshold on the 51G relay (It is an earth fault relay not an earth leakage relay) as there will be a small amount of leakage current in the motor to ground during starting. You would probably trip every time you tried to start the motor if you did select such a low threshold.
Hope that this helps.
umerfarooq777 said:
YOU CAN MAKE A REACTIFICATION UNIT , WHICH CONVERT AC TO DC.
AN SIMPLE AND EASY POJECT IF UOU ARE INTRUSTED
yes
Hello,
In my opinion, you have to connect the armour to the metal cabinets, at
the two ends of the cable, using EMI cable glands. Then you can earth the
internal shield + tape at only one point. (Preferably at the remote end from
the source of interference).Bye
BAM
Please read the book in electricalengineering drawing (about drawing) More information & Legible drawing is available
Yes – problems with CB being closed when it indicates open. Current solution is to fit long allen bolts to ensure cb can be used as a point of isolation
Hi. Anyone give me suggestion to start a project for my M.E. in industrial safety engineering in electrical sector. In the sense, i would like do it in Electrical safety. Tell me some ideas for electrical safety project. Must be capable of doing a semester. I've ideas, but like to know from professionals.
Mail me to azadcbe@gmail.com
9944574830
at the tip of your cable, put a terminal log depends the size of your cable and terminate it to grounding sysyem.all ground cable must be terminated into the grounding system ex.( buildings, telecom exchange,or cell site) dont terminate with the same kind of cable it must be a grounding rod.
Yes, several times. These breakers need to be used at least once per year or they need to be dismantled & cleaned & lubricated. In particular the pawls on the manual charging mechanism stick.
First : you should programme the digital meter for it's CT ratio to show correct power consumption .
Second : CT Polarity should be same on meter trminal
Third : CT Shoudl be measuring Class ie. CL-0.5 or CL1.0
Four : Phase Sequence in right order ie. R Y b for Potential & Current as Load side to meter terminal must be in same order
First you shoud have to understand the basics of Analog & Analog to digital conversion techniques.
Analog meter's moving coil has deflected by Potential with certain level of current ( micro amp llevel,due to friction on pivot ) to show result in volt while digital meter is static device & no friction on measurment & digital meter can read potential with pico amp level drive current to measure volt.
The basic diffrence is drive current for deflection.
