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excitation system- protection by fuse or relay

excitation system- protection by fuse or relay

excitation system- protection by fuse or relay

(OP)
Excitation system for hydroelectrics generators shall be provided with power conversor unit with 3-phase bridges of six-pulses silica thyristors.
Technical specification requires installation of very fast fuse installed at input of bridge (CA side) for thyristor protection.
Proponent offers overcurrent relay at input of bridge (CA side) connected to secondary side  bushing CT of excitation transformer.
May I accept this alternative?

 

RE: excitation system- protection by fuse or relay

Check the I2t let-through of the proposed alternative is lower than the withstand of the thyristors.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: excitation system- protection by fuse or relay

(OP)
ScottyUK
I'm not sure, but I guess we can make comparison of It2t between thyristors and fuse. I dont know how to do with relay.
 

RE: excitation system- protection by fuse or relay

Is the relay a true overcurrent relay or is it an overload relay.
Overload is usually in the order of 100% to 200% of rated current and is usually acceptable within a defined time frame. The time frame may be seconds minutes, hours or days, depending on the magnitude of the overload and the type of equipment.
Overcurrent generally refers to fault currents. These may be from 200% to over 2000% depending on the type of fault and the impedance of the faulted circuit. A fast fuse may respond in less than 1/4 cycle. It may be difficult to detect and react fast enough with a relay to protect the thyristors.
If the relay is an overcurrent relay, there should be spec sheets available from the manufacturer.
You said "relay". A magnetic trip breaker may be available that is capable of protecting the thyristors.  

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: excitation system- protection by fuse or relay

odlanor,

Put the question to whoever is proposing the relay (and circuit breaker?) and get them to do the calculation. They should have already done it because without that calculation they don't know if their solution will protect the thyristor.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: excitation system- protection by fuse or relay

(OP)
Thank you guys for these valuable posts!
and Good-Bye!
 

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