Hello, I want to learn if it is possible to measure the grid impedance from any point connected to the grid just using Multimeter? ( which has Sufficient voltage and current ratings ) Say I have a transformer connected to a substation which is connected to the national grid. If I try to measure the secondary of this transformer Can I find the total impedance of the whole grid?
Grid Impedance
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robbietan
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- Antipolo City
no since there are connections on several substations and each substation may have several circuits. the best one could hope for is the circuit impedance as this is a virtual unchangeable line. circuits every so often are changed from one substation to another, and there is no way to know when the next circuit change will happen
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Not unless you can source or sink the power of the entire grid.
Any effect of the impedance of the entire grid (if you could agree on what that term should mean in the first place) would be vanishingly small in its effects compared to other purely local resistances that are much higher in value.
What you are asking for is similar to asking whether you can measure the average speed of all traffic in the country by looking hard enough at the speedometer in your car.
chris kennedy
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If you take measurements on the secondary and the is no direct connection between the primary and secondary windings....:happyno:
what do u mean with a connection between primary and secondary? You mean earthing bonding ? Secondly :
then you claim that when you measure the transformer secondary when it is not energised it will give the real secondary impedance but if you measure it when it is measured when connected to the grid so you will get the net impedance of the grid at that point??
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POCO may tell you how much fault level is on their power system such as 250 MVA at 11kV, 350 MVA at 22kV (typical values in India). From this, the grid impedance from your supply point may be calculated by
Line voltage 'V' squared/Fault MVA. For example, for 11kV system,
grid impedance=11*11/(250*1000)=0.484 milliohm.
Line voltage 'V' squared/Fault MVA. For example, for 11kV system,
grid impedance=11*11/(250*1000)=0.484 milliohm.
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Yes. It is possible. From the fault level the fault impedance calculated is the grid impedance when looked into the grid from the connection point and is the thevenin equivalent of the power system (national grid) for a given voltage level at your supply point
so just tell me what utility engineer does to give the short circuit data to the end-user to enable him to calculate the short circuit level at the relevant point.? if it is possible to measure the resistance using a multimeter then what he makes is just measuring and saying this is the FAULT MVA?
Of course the utility engineer does some calculations to ascertain the fault level in the power system. As for your desire to ascertain the fault level using your multimeter on the LV side, a method is described somewhere in this book:
http://www.scribd.com/doc/30560848/Operation-amp-Maintenance-of-Electrical-Equipment
You would be calculating the impedance of the transformer compared to which the grid impedance is negligible.
so you say grid impedance is very very low
No. You can include it in your calculation if you want.
(Sorry, I made a mistake in post#8. It is 0.484 ohm and not 0.484 milliohm).
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