Two good texts are Paul Gill’s Electrical Power Equipment Maintenance and Testing, and NETA Maintenance Testing Specifications for Electrical Power Distribution Equipment and Systems but they are not exactly breezy reading without some understanding of power-systems engineering practices. Gill teaches his material through George Washington University in DC. NETA has conferences around the US.
You may want to get on the training mail list of a firm like Electro-Test. They have branches in your state and gave various 1-4 day programs by way of introduction. Utilities and petrochems tend to have their own in-house operations for switchgear and related systems’ maintenance.