The cheapest which is the way companies do it is to use a load box [resistive load, heat element] next up would be a three phase gang switch on the primary but the cost of installing at all three phase locations is way to costly. While the load box is relatively cheap the only time you tend to have one is when the work is planned ahead of time, they never seem to be around when doing trouble type work and that is 90% of the time you run into a Ferroresonance problem. The big problem is the management around here don't seem to care or understand the issue and it's real easy to sit in an office and tell you open or close fuses when they are not on the end of a hotstick. If the management doesn't know or care they're not going to look into or invest in an alternative, that's where these profits above all companies are failing their employees and customers.