App note with sample circuit from Onsemi about thyristor replacing mechanical relays for AC line control. Link here (PDF)
In the large family of electronic switches, the thyristor must be considered as a low cost and powerful device for motor applications. Thyristors can take many forms, but they have certain features in common. All of them are solid state switches which act as open circuits capable of withstanding the rated voltage until triggered.
Because Thyristors are reliable solid state switches, they have many applications, especially as controls. A useful application of triac is as a direct replacement for an AC mechanical relay.