So TVS Diodes are primarily used for ESD and EFT suppression not surges that have longer duration (for which you can use MOVs, etc.)
What typically happens if the TVS diodes experience a longer surge? Do they simply become less effective or do they typically explode?
I had a TVS Diode dramatically explode. In this situation the line didn't have a MOV or GDT.
I am wondering whether this is typically what you would expect if there is no MOV/GDT/Fuse or other type of protection?
Transient voltage suppressors (TVS) will fail if they are subjected to conditions beyond their designed limits. It is, therefore, important to understand the types of failure modes of TVS devices before designing them into a circuit application.
There are three basic types of failure modes: shorts, open, and degraded (outside of the specification limits). Although the silicon avalanche junction transient voltage suppressor (SAJTVS) will first fail short in most applications, there is always one transient event that will cause it to open initially. In this case, the transient energy is large and of short duration that the silicon chip itself explodes. When a TVS device does short, follow-on operating current may cause the device to open. Fusing of the line is recommended in all applications. Shorted devices will start to conduct current away from the circuit or system affecting its performance.
Open devices are transparent to the circuit / system and will not usually distribute circuit functions. In either case, it is difficult to determine if the TVS device is still functioning while in the circuit. Degraded TVS devices are most difficult to detect in the circuit. These can be devices with high leakage currents which may not adversely affect circuit performance, except under elevated operating temperatures.
