I am aware that there is really no specified starts/hour with medium voltage motors (4.16kV), and that most manufacturers use the NEMA MG-1 standard that says the given motor can have two consecutive cold starts and one hot start for a given load intertia.
Although its not specifically spelled out, I believe it is a standard approach to limit starts to 2 starts per hour, and we somewhat follow this philosophy when setting up our relays.
What if however the driven load has an inertia much less then specified on the datasheet, can you then achieve more consecutive starts, or more starts per hour? For instance what if your relay curve is set below the motor cold rotor thermal damage curve to protect the motor, and when starting you only use up 20% of the thermal capacity? At first glance this would tell me that I would be capable of ahieving much more than 2 consecutive starts (maybe 5) before I reach 100% thermal capacity. My question is should we allow more consecutive starts in this case or should we still limit to the 2 consecutive starts? This would kind of go hand in hand with the number of starts per hour as well.
Although its not specifically spelled out, I believe it is a standard approach to limit starts to 2 starts per hour, and we somewhat follow this philosophy when setting up our relays.
What if however the driven load has an inertia much less then specified on the datasheet, can you then achieve more consecutive starts, or more starts per hour? For instance what if your relay curve is set below the motor cold rotor thermal damage curve to protect the motor, and when starting you only use up 20% of the thermal capacity? At first glance this would tell me that I would be capable of ahieving much more than 2 consecutive starts (maybe 5) before I reach 100% thermal capacity. My question is should we allow more consecutive starts in this case or should we still limit to the 2 consecutive starts? This would kind of go hand in hand with the number of starts per hour as well.