ZSI Trip units
ZSI Trip units
(OP)
I am currently working on coordination study of a project. The curves of few breakers are overlapped. So it is tough to say which one will trip first. But what I understood is that, since the breaker trip units used has the characteristic of Zone selective Interlocking (ZSI) , the breakers communicate with each other and it makes sure that the downstream breaker trips before the upstream breakers. Am I right?






RE: ZSI Trip units
ZSI normally functions only for the short-time delay band and ground fault. Obviously the communication must be wired to work.
Alan
"The engineer's first problem in any design situation is to discover what the problem really is." Unk.
RE: ZSI Trip units
Thanks for the valuable info. IS ZSI a function of short time delay? We need to specify the delay for each breaker right? So if we specify a minimum delay for the downstream and more delay for the upstream breaker, I assume that the downstream breaker trips before the upstream breaker even if the curves are overlapped. Correct me if I am wrong.
Thanks
RE: ZSI Trip units
If the downstream breaker senses fault current (above pickup value) then it sends a blocking signal to the upstream breaker. If the upstream breaker senses a fault but does not receive a blocking signal, then the fault is assumed to be on the bus and the breaker trips with a very short time delay.
If a blocking signal is received by the upstream breaker, then it trips with inverse time-overcurrent, set slower than the time-overcurrent of the downstream breaker.
RE: ZSI Trip units
RE: ZSI Trip units
If you use one manufacturer's product line, you may not need to specify the minimum delay on the upstream device. This should be coordinated by the manufacturer.
You should review the manufacturer's literature carefully. These functions are usually described in detail.
Alan
"The engineer's first problem in any design situation is to discover what the problem really is." Unk.
RE: ZSI Trip units
RE: ZSI Trip units