instantaneous setting co-ordination on High voltage system
instantaneous setting co-ordination on High voltage system
(OP)
Hi, Folks,
Inst. settings are very sensitive. Sometimes I try to avoid it for the main and branches. Per code, CEC or NEC, we are not allowed to disable them. So what I normally do is to set Inst on Main higher than the branch fault currents(Max.available), which is reduced by impedance in between. But sometimes on some high voltage systems, it is very hard to do the co-ordination study because the impedance makes little deference between fault currents on two levels of buses. Who have a better solutions?
thank you in advance.
Inst. settings are very sensitive. Sometimes I try to avoid it for the main and branches. Per code, CEC or NEC, we are not allowed to disable them. So what I normally do is to set Inst on Main higher than the branch fault currents(Max.available), which is reduced by impedance in between. But sometimes on some high voltage systems, it is very hard to do the co-ordination study because the impedance makes little deference between fault currents on two levels of buses. Who have a better solutions?
thank you in advance.






RE: instantaneous setting co-ordination on High voltage system
Square D has a new line of 'high instantaneous' MCCB's which they advertise to help with this situation.
Both of these options of course increase the potential arc flash energy.
RE: instantaneous setting co-ordination on High voltage system
RE: instantaneous setting co-ordination on High voltage system
Molded case circuit breakers are required (UL & NEMA) to have instantaneous tripping.
RE: instantaneous setting co-ordination on High voltage system
I think you are correct for medium and high voltage - which is how the original question was worded, I see.
In the U.S., LVPCB's come in two versions -
UL 489: which has inst. (and no way to disable it) for use in boards constructed to UL 891 switchboard standards.
UL 1066/ANSI C37: which is not required to have inst. (and if equipped with inst., may have on 'off' setting) for use in boards constructed to UL 1558/ANSI low voltage power switchgear standards.
RE: instantaneous setting co-ordination on High voltage system
RE: instantaneous setting co-ordination on High voltage system
To me, an ICCB is constructed and tested per UL 489. Typically they are not designed for switching duty or extensive field maintenance and do not have field-replacable contacts. Examples are Cutler-Hammer SPB or Square D SE. These seem to be being phased out by their manufacturers.
From IEEE 1015 -
Insulated-case circuit breaker (ICCB): A circuit breaker that is assembled as an integral unit in a supporting and enclosing housing of insulating material and with a stored energy mechanism.
Low-voltage power circuit breaker (LVPCB): A mechanical switching device capable of making, carrying and breaking currents under normal circuit conditions and also, making and carrying for a specified time and breaking currents under specified abnormal circuit conditions such as those for short-circuit. Rated 1000 V ac or below, or 3000V dc and below, but not including molded-case circuit breakers.
By these definitions, it would seem the newer plastic-housed breakers such as MasterPact could qualify as both.
RE: instantaneous setting co-ordination on High voltage system
For me, at least, while there are the two standards and they have different requirements, it makes sense to hold onto the older names, so that an LVPCB goes into ANSI switchgear and an ICCB goes into UL switchboards. I doubt the two are physically interchangeable, and until/unless they become interchangeable, it is useful to know which one is dealing with.