Hi all,
Recently I come across following technical specification clause for MV or LV motor (LV motors can be considered as > 100 kW rating)
The clause details are as follows
....Electric motors shall be suitable for two (2) successive starts with the motor already at full load working...
Hi all
Recently we procured Exide make 100 Ah, 2 V - 55 nos to supply motive power to switchgear. We asked type test certificates of 100 Ah, 2V cells. They provided 400 Ah, 2V (higher rated) type test certificates and mentioned 100Ah, 2V and 400 Ah, 2V cells are same model.
Can anybody...
Dear Folks,
PV Solar Power plant has two voltage levels- 33kV and 0.4kV. Solar PV plant is connected to remote end 33kV sub-station through 33kV cable. Local 33/0.42kV transformers are used for auxiliary power supply to solar farm. Ground fault currents at 33kV and 0.4kV voltage levels are 2kA...
Hi all
In general, In a power plant (capacity 100 MW to 4000 MW) the following equipment exists. Here power plants are Gas based or coal based.
Emergency Diesel Generator and Black start Diesel Generator.
Now I would like to know Why can not we club together and install a Black start diesel...
Dear Folks,
Greetings...
In a small Isolated network with two generators are connected to a bus directly (without transformers) and operating in parallel. Each generator's ground (Earth) fault current is limited to 100A due to neutral ground resistor. Each generator has a neutral CT and...
Dear Folks,
If the fault current is 50kA (Ph-E) in a low voltage system-400V, the calculated Grid potential rise (GPR)= 50kA * 1 ohm= 50kV....It is against Ohms law and the potential rise should be less than 400V.... I would like to know why system voltage is not considered in calculating GPR.....
Dear Folks,
Greetings...In one of the projects, surge arrestor and surge capacitors are located in MV motor terminal box. As soft-starter has been provided for this motor, is it recommended to change the location of surge protection devices to switchgear end (before soft-starter)? The power...
Hi all
ABB make "11 kV univer G" has incomer with fuseless Medium Voltage Voltage Transformer (VT). See the "11 kV board arrangement"
According to me it is standard practice and may be followed.
However I am not getting supporting document.
Can anybody provide supporting stardard...
Dear Folks,
One of the current transformers has an additional test winding i.e.10A & 45 turns. Main CT ratio is 450-300/1A. Please share your view the purpose of the test winding. Advanced thanks.....
Dear Folks,
As per IEC60137 standard, transformer bushing short-time withstand current should be 25 times the rated current for 2-sec. If a fault occurs just after the bushing (inside the transformer), the fault current through the bushing is almost equal to connected supply bus fault current...
I found the following information in transmission grid code that
Generator Excitation Control System
???Control performance of the voltage control loop shall be such that under isolated operation conditions the damping?coefficient shall be above 0.25 for the entire operating range.
Could...
Dear Folks,
Q1. If a circuit breaker is tested for a time constant of 45 milli sec, I"k=40kA, how can calculate DC current breaking capability of circuit breaker? From IEC 62271-100 standard, Figure-9, as percentage of DC component varies according to time of contact separation of the circuit...
Hi all
Separate Generator Step up transformer (GSUT, To step up and export power)and Station Services transformer (SST, For plant auxiliary loads)used to be there in almost all power plants.
Generally these two transformers are two winding transformers
To meet the power plant one can use...
Dear Folks,
I am looking for clarification on selecting short-time withstand current for circuit breakers and Bus-bars.
In most of the calculations, I"k (Maximum symmetrical rms current) is taking as short-time withstand current. In fact, as per IEC 60909 / IEEE C37.013, short time withstand...
Dear Folks,
In one of the Power plant projects, 11kV system is used with solid grounding. Now Black start diesel generator needs to be connected to the same system as stand-by. Both systems need to be operated in parallel during change-over operation. In this case, we would like to use low...
Dear Folks,
Query in ETAP!
Even "Max. Through fault current option" is selected in ETAP SC studies, the SC study report gives the "short time withstand capability current" based on "Maximum Bus fault current" for incoming circuit breaker / Generator circuit breaker.
How can we get "short-time...
Dear Folks,
In one of the industrial systems, 33kV and 6.6kV voltage levels are being used by using 220/33kV and 33/6.6kV Transformers. In refurbishment project, 11kV supply is required. As there is no spare feeder available in 33kV level, we would like to derive 11kV supply from 6.6kV...
Dear Folks,
We would like to energise 300/150/150MVA (220/15/15kV) transformer (GSU) with one of the Generators (110MW,15kV) connected to 150MVA winding of the Transformer. Someone please discuss what are the limitations of energising GSU transformer with Generators.
Thanks a Lot.
Dear Folks,
With reference to the attached protection schematic diagram of 153.5MVA@0.8 lag Generator, 100% E/F protection was not considered. With my experience, such higher rating machines require 100% E/F protection. If someone knows, please discuss general / standard criteria of installing...
Dear Folks,
Looking for expertise advice regarding three winding generator step-up transformer.
For connecting two generators to one 3-winding step-up transformer:
1. What is the criteria for selecting percentage of impedance between ST1 to ST2 (between secondary windings)?
2. If one...
