Does IEEE 80 apply to transmission line voltages only ? Can it be used for medium and low voltage networks ? The way the ground current is calculated in chapter 15.3 of IEEE 80-2013 does not take into account the resistance of the ground grid and if applied to 400 V networks for example, it will...
- If we install a CT in the delta to monitor the circulating currents, Is it possible to calculate the amount of circulating currents in this delta winding. Would any current circulate in the absence of L-L or L-E fault on the secondary ? what about third harmonic current ? are these...
Hi,
In continuation to thread thread238-372076, I am working on a project where we are buying a 120 MVA Y-Y 220/33 kV transformer with a buried delta winding. The primary is solidly earthed, while the sencondary is earthed through a resistance to limit the earth fault current to 400A.
I have...
Hi
We are specifying medium volatge induction motors (6.6kV) with biased differential protection above 1500kW. However some of these motors will be supplied by Varibale Speed Drives. A Supplier is saying that motors driven by VSDs should not be protected by differential protection because at...
Hi,
We are specifying a 220/33kV transformer as Y-Y with a tertiary buried delta for stabilisation purposes only. The transformer is 115MVA, the primary solidly earthed and the secondary is resistance earthed to limit the current to 400A. I am preparing a protective diagram and I am not sure how...
Hi,
When an internal fault occurs in a high impedance differential protection (whether REF or bus bar),the voltage across the relay can reach high levels, because the CTs are supposed to force their secondary currents into the high impedance branch.
1) But does this push the CTs into early and...
If switch option is selected it will be automatic through a control system.
But I start thinking like Bill and David that this is not the good option.
The problem is that this switchgear will supply an industrial plant, but will also supply an overhead line.
There is a compromise to find...
Hi,
I have a 33kV distribution system with three bus bars and two bus couplers (oeprating normally closed). Each bus bar is supplied from a transformer and in normal operation the three transformers operate in paralllel.
The client specifies the NER to limit earth fault current to 400A.
Th earth...
VFDs do not require a lot of reactive power from the upstream network. P.F. is typically around 0.97.
The VFDs have capacitors that provide the reactive load required by the motor.
What are the advantages of having OLTC on the HV or LV winding of a transformer ? Why are they always installed on the HV side ?
HV side: current is lower but voltage is higher
Thanks.
Hi,
I have an indutrial network with a 132 kV GIS. Incoming lines are overhead and are owned and protected by the utility.
All outgoing feeders are by XLPE insulated cables to step down transformers.
I have been requested to do an insulation coordination study. Not being a specialist of I.C., I...
some Toroidal protection CTs need to be sensitive enough to pick up low earth fault currents. should a low ration CTs (e.g. 50/1A) be selected ? They will provide a good accuracy down to 5A primary (10%)
The CT will saturate quickly for high fault currents in this case. but this should not...
Thanks for all.
Actually I found one previous thread248-128558 on this forum discussing this problem.
the discussion referred to a Square D article that seemed to be of interest.
The link seems to be not valid anymore. Does anyone know how can this document be accessed ?
