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Discuss DC circuit breakers VS semiconductor fuses high speed. in the Commercial Electrical Advice area at ElectriciansForums.net

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Hi all. Just to start off still learning.

Could any one help me with this and put me right if I am incorrect. I would like to understand the preference or reason for opting for DC breakers or semiconductor high speed fuses, when been used in low voltage DC circuit.

I understand that Semiconductor fuses are named this as they are used to protect semiconductors ( is this a correct explanation).

What I would like to understand is if you were to remove semiconductor fuses from a circuit is/are there any advantages/disadvantages to replace it with a DC breaker or am I just over thinking this.

Thanks for reading my thread.
 
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Lucien Nunes

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The short-circuit withstand capability of power semiconductors is much lower than that of equivalently rated wiring. Fuses designed to protect them must be ultra-fast acting and have a low I²t let-through over a wide range of fault currents. Some aspects of the ideal curve required for this level of protection cannot be matched by conventional circuit breakers, therefore they are not necessarily suitable replacements for the fuses.
 
Circuit breakers and fuses for general use both toperate on the principle of Inverse time curves (IDMT). The higher the over current, the quicker it will trip. Conversely, at lower overcurrents it will take longer to trip - a circuit breaker may take 10 minutes to trip at 1.2* rated amps (if it trips at all!).

Then you have to factor in the trip curves (times) for each type of circuit breaker. Type "B" for general use, type "C" for applications with higher inrush currents (eg motor circuits) and type "D" for higher still (eg transformers).

A semiconductor fuse is generally a fast acting, current limiting fuse. This fuse will trip immediately the rated amps is reached. Intentionally precise, to protect the semiconductors.
 
We had a MCC panel fed by 400A BS88 fuses. Part of this panel had a 100HP GEC traction motor inverter drive. We changed the original GEC drive to a Eurodrive regenerative unit. The new unit originally had 500A semiconductor fuses. It worked fine on acceleration, the fuses blew on deceleration? We were replacing the semiconductor fuses several times during a ten hour shift, it was costing a small fortune. To keep the plant running we eventually fitted 750A semiconductor fuses (remember the incoming supply was still via 400A fuses).


There are occasions where semiconductor fuses are a damned menace, they’re too quick. Eventually I got around the problem by changing the PID deceleration algorithm.
 
  • Thread Starter Thread Starter
  • #8
The short-circuit withstand capability of power semiconductors is much lower than that of equivalently rated wiring. Fuses designed to protect them must be ultra-fast acting and have a low I²t let-through over a wide range of fault currents. Some aspects of the ideal curve required for this level of protection cannot be matched by conventional circuit breakers, therefore they are not necessarily suitable replacements for the fuses.
Thanks for your reply
 
  • Thread Starter Thread Starter
  • #9
Circuit breakers and fuses for general use both toperate on the principle of Inverse time curves (IDMT). The higher the over current, the quicker it will trip. Conversely, at lower overcurrents it will take longer to trip - a circuit breaker may take 10 minutes to trip at 1.2* rated amps (if it trips at all!).

Then you have to factor in the trip curves (times) for each type of circuit breaker. Type "B" for general use, type "C" for applications with higher inrush currents (eg motor circuits) and type "D" for higher still (eg transformers).

A semiconductor fuse is generally a fast acting, current limiting fuse. This fuse will trip immediately the rated amps is reached. Intentionally precise, to protect the semiconductors.
Thanks for your response
 
  • Thread Starter Thread Starter
  • #10
We had a MCC panel fed by 400A BS88 fuses. Part of this panel had a 100HP GEC traction motor inverter drive. We changed the original GEC drive to a Eurodrive regenerative unit. The new unit originally had 500A semiconductor fuses. It worked fine on acceleration, the fuses blew on deceleration? We were replacing the semiconductor fuses several times during a ten hour shift, it was costing a small fortune. To keep the plant running we eventually fitted 750A semiconductor fuses (remember the incoming supply was still via 400A fuses).


There are occasions where semiconductor fuses are a damned menace, they’re too quick. Eventually I got around the problem by changing the PID deceleration algorithm.
 
  • Thread Starter Thread Starter
  • #11
We had a MCC panel fed by 400A BS88 fuses. Part of this panel had a 100HP GEC traction motor inverter drive. We changed the original GEC drive to a Eurodrive regenerative unit. The new unit originally had 500A semiconductor fuses. It worked fine on acceleration, the fuses blew on deceleration? We were replacing the semiconductor fuses several times during a ten hour shift, it was costing a small fortune. To keep the plant running we eventually fitted 750A semiconductor fuses (remember the incoming supply was still via 400A fuses).


There are occasions where semiconductor fuses are a damned menace, they’re too quick. Eventually I got around the problem by changing the PID deceleration algorithm.
Thanks for the reply, real time example great help.
 
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