Few words about synchronizing…
Synchronizing a generator to the power system must be done carefully. The speed (frequency) and voltage of the isolated generator must be closely matched, and the rotor angle must be close to the instantaneous power system phase angle prior to closing the generator breaker to connect the isolated generator to the power system.
Traditionally, generator control systems include a synchronizing panel.
The synchronizing panel includes indications of voltage, angle, and slip that show what adjustments the operator needs to make to the governor and exciter and when it is acceptable for the operator to close the breaker.
In many cases, the process is automated using an automatic synchronizer with manual control available as a backup.
In generating facilities with more than a single generator or installations with multiple synchronizing breakers, complicated synchronizing circuits with many contacts are required to switch the VT and control signals between the operator and automatic controls and the high-voltage equipment.
Maintaining proper isolation and safety grounding of sensing and control circuits often requires the use of problem-prone auxiliary relays and VTs, which can reduce the reliability of the system.
(reference: Michael J. Thompson, Schweitzer Engineering Laboratories, Inc)
This spreadsheet calculates following:
- Size of diesel generator synchronous panel
- Total fault current of diesel generator synchronous panel
- Total equivalent impedance of diesel generator synchronous panel
- Short circuit current of diesel generator synchronous panel
It might be also useful – Spreadsheet for calculating Diesel Generator Size.
| Software: | MS Excel Spreadsheet – to Calculate Short Circuit Capacity of Diesel Generator Synchronous Panel |
| Version: | – |
| Developer: | Jignesh Parmar |
| Size: | 31 KB |
| Price: | FREE |
| Download: | Right here | Get Download Updates | Get Premium Membership |
Calculations hold good for calculating Mechanical Strength of Bus Bar Supports etc.
Above current is only for 3 to 4 cycles.
After that up to 7 cycles approx. it is dependent upon Xd’.
And then on Xd (which is of the order of 150% to 200%) that means fault current drops below the full load current – which will not be dedected by the protection relay- hence magnetic innertia of Excitation system takes over – Field forcing feature of AVR. If the alternator is shunt excited, means output voltage dips due to fault, means input power to AVR drops and hence capacity of AVR To sustain Field Forcing – for such machines, the short circuit current stays 3 x Full load current for maximum duration of 3 Secs.
If the power supply of AVR is from PMG or auxiliary exciter or auxiliary winding in Stator (excited by 2nd harmonics) or in case of shut excited machine with Series Boost Kit, then the current on short circuit is 3 x full load for 10 seconds.
Mechanical stresses which are proportional to Peak fault current (I peak not I rms)
Calculations to size conductor of bus bar shall eb based on 3 x FL Current for 3 Secs or 10 Secs – depending upon Excitation System of 3 phase generators – explained above.
Similarly when sizing cables for fault level use sustained short circuit current.
I am intested to work with your organisation.I studied electrical engineering, I have experience in synchronization panel, ATS,control panel,motor panel and diesel generator .I fomerly tractor and equipment {caterpillar} Nigeria.I will so glad if request is considered.
Thanks
In gensets, the short circuit current depends upon the % excitation. When the genset is partially loaded, the % excitation will be less and so the short circuit current. This aspect is not considered in the attached excel sheet.
The spreadsheet calculates only the 3 phase faults i.e. symmetrical faults happening within the generator. What about the asymmetrical faults which occurs in the generator. The asymmetrical fault current value is more than the symmetrical faults.
Kindly recheck and confirm link of the spreadsheet… it goes to main webpage and not the spreadsheet..
Hi Neri, it’s fixed now, thank you for reporting.
We are looking to connect 10, 250kw Micro Gas Turbine genarator together to surply power to the national grid in the U.K.
Regards David Taylor.
Hi David,
My firm can assist you and will be keen on working on this project.
Best regards
Ramesh Kapur