Like other heat producing appliances, electric ovens are design to protect life and property in the event of things going wrong!
The image shows what is commonly known as a thermal cut out. It's job is to, open the electrical circuit in the event of the surrounding temperatures exceeding that of the breaking temperature of the cut out. When the temperature cools, the cut out will close allowing the electrical feed to continue on it's journey.
So what causes the cut out to activate? Well! Several things in practice.
If the internal/tangential cooling fan fails.
If the temperature control (thermostat) device fails
If the cut out contacts become faulty themselves
This type of fault requires thorough investigation by a competent, experienced engineer.
The cut out pre set temperatures vary depending on it's location within the appliance. Although physically, cut outs look the same, the temperature ratings differ. It's paramount that cut outs are replaced in line with the manufacturers specifications to ensure safety standards are maintained.
I hope this article was helpful.