What is the difference between a DC relay and an AC relay?

What is the difference between a DC relay and an AC relay?
For low-voltage relays, control current is used to distinguish them directly. DC control on-off is called DC relay, and AC control is called AC relay. Contacts can pass DC or AC; while for high-voltage relays, apart from control current, It should also be distinguished by contacts. When the contacts are direct current, the direct current is divided into positive and negative poles, and the generated arcs have the same stable direction. The magnetic blowing process is used to quickly extinguish the arc. Relays, when the contacts are AC, the AC is non-polar, the arc and direction generated, weak and self-extinguishing and unstable, and it can be an AC relay by using the anti-arc leakage process.

What is the relationship between the main contact and the auxiliary contact?

The auxiliary contact is used to detect the current state of the main contact, check whether the main contact is disconnected in accordance with the control instruction, and determine whether the main contact has failed.