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Hi After a discussion I've realized I had a lack of knowledge on CTs - any specifically on specifying the magnetizing current of a Class PTX (X) CT, thus an CT been used in the IEC-world. In a class X CT the performance is defined in terms of a knee-point voltage and the magnetizing current at...

It is my responsibility to declare people authorized to do work in substations on our mine. Normally it is not a problem, the persons working in the substations is qualified electrical artisans, they do get some training on the safety, the relevant procedures, the operating principles, the...

We've had a CT explosion last week on one of our 66kV-lines, worst I've seen. Investigation still going on. Many of you have probably seen similar incidents before, but I thought it would just be interesting to show/share it. Porcelain pieces were laying in a radius of approx. 50 meters...

How Do I Make Files Available For Download? ... No Emails Required This is a FAQ written by CorBlimeyLimey: FAQ559-1177 See also thread559-138321. He can't collect stars anymore, but we still can rate his FAQ. I think it is excellent written idea/FAQ.

I have asked the question in the Electric motors & motor controls engineering Forum: See the original question in thread237-136811 I would appreciate it if anyone can give his/her comments on the time-delay between two or more motors during start-up (for a conveyor) from a mechanical...

I have a question regarding the starting delay between two or three motors driving the same load. In my case it is three motors driving a conveyor. It is 3.3kV, 500kW slipring motors (WRIM) and each one is started with a vapourmatic(liquid) starter with three steps. On the third step the rotor...

Any recommendations, methods, type of connections, etc. on connecting copper and aluminium? (380V to 66kV) I am looking for advice on: :overhead conductors, (copper lines to aluminium lines) :aluminium cables on copper overhead conductors, :copper cables on aluminium overhead...

http://www.extremescience.com/BiggestWave.htm Our prayers are with those in the disastrous areas. Ralph

Can someone give me some comments on this book, especially between the 1st edition and the 8th edition? I want to buy the book, but read somewhere the last edition is not that good. Is it beter to look/search for the first edition, or can I buy the last edition? Thanks Regards Ralph

We have 2 Yd1 transformers in parallel. (20MVA, 66/11kV each) The secondary side of each transformer is earthed with a NEC. (zig-zag transformer, 400A, 10sec) Our problems start with earth-faults on the downstream feeders. Sometimes, when a fault occurs, the NECs trip on top oil temperature...

I've got a protective issue question, I'll appreciate it if anyone can help me or point me in some direction. With a high impedance grounding system (secondary of trsf grounded through resistors) in a medium voltage system, on what kind of earth fault protection does IEC insist? (I'm looking...

I've got a protective issue question, I'll appreciate it if anyone can help me or point me in some direction. With a high impedance grounding system (secondary of trsf grounded through resistors) in a medium voltage system, on what kind of earth fault protection does IEC insist? Is earth fault...

See also thread237-53974 We are experiencing heavy overflashing problems on our 500kW slipring motors (WRIM) in our plant. The plant have a lot of conveyors, the drives on the conveyors varies between 1 to three drives per conveyor. There is no spesific drive or conveyor that gives no problems...

Dear all Is there any difference between a master/slave configuration and a master/follower configuration for OLTC's (onload tap changers) on parallel transformers, or is it the same? If there is a difference, what is it, and why do they use it? Many thanks RCC

Hi I want to draw the overload through-fault protection curve for a NEC. (zig-zag transformer, earthing transformer) The continious line current rating of the NEC is 60A, the short time line current rating is 400A for 30 seconds. Is there any way how I can plot this curve for values more than...

With what type of gas does you test a Buchholtz relay on site? - Nytrogen? Thanks RCC

We experience trippings (instantaneous) on some of our 66kV-transmission lines due to lightning. Each tower consists of two wood-poles with two earth/ground conductors on top. Next to each pole there runs also a earth conducutor - this conductor is connected to the overhead conductor and...

We have a 3ph,70hp slipringmotor been used on a bending machine. Stator V - 400V Stator I - 107A Rotor V - 288V Rotor I - 113A Speed - 575rpm The motor is conected via an old type drum controller (forward and reverse) to a grid. Normally, when the operator of...

What are the rules of thumb to choose the CT-ratio of protection CT (O/C and E/F) on a feeder in a substation? I've seen CT's with a low ratio, but the faultlevel on that point is very high. The faultlevel of our 20MVA, 66/11 kV Trf is approximatly 12kA. The 11kV Incomer have a ratio of...

On a single transformer, to determine the fault current on the secondary side, you can use the following simple method: Short-circuit MVA = (100*P) / X% Fault current = Short-circuit MVA / (1.73*Vsec) My first question is: What will happen if two or more transformers is in parrallel(assume...