It is quite common to use a metering accuracy core for unbalance sensing in capacitor banks.
For typical protection applications, relay accuracy cores are sized/designed with the main factor being performance during transients, i.e. system faults, where the CT needs to stay accurate up to many times nominal rating.
For your application, the current that will flow through the the CT in the event of a capacitor failure (unbalance) is generally quite small and for discussion's sake is a "steady-state" current. I.e. the neutral current will rise from almost 0A to 1A or so. In general, protection rated CTs will work fine for this application, if the rated current is very close to the current you expect to flow in an unbalance situation. However, you should not use a 200:5 A protection rated CT to try to detect 1A flowing...this will not work well.
From a design/cost perspective, it is generally more economical and better technically to by a metering rating CT with a suitable ratio. In the ANSI world, it is quite common to see a 5:5A ratio used with an accuracy rating of 0.3B0.5 or so. With the low rated current, you should look at reducing the rated burden as much as possible to save cost/improve ease of design. The ratio you use really depends on the capacitor bank parameters and the type relay you're using.
As I'm sure you know, you need to use a CT insulated to the system voltage. If you have a line to ground fault, i.e. an entire back failure, the CT in the neutral will float up to the system voltage.
Hopefully this helps.
