Your scheme sounds like it will not work correctly. Assume the device is initially ON and operating. Your circuit, whatever it is, detects an Over Voltage condition and then turns the primary power relay OFF. This cuts the power to the transformer and thusly the secondary which is powering the monitoring circuit. Once un-powered the monitor circuit will be unable to monitor. So either the unit will remain off or may start a relay chatter as it oscillates OFF and ON.

Michael Karas