Understanding Relays with Modified Characteristics

The question asks about a specific type of relay where its operating characteristic is changed or influenced by an additional process, which could be mechanical or electromagnetic. Let's look at the options provided to see which one matches this description.

• Static relay: These relays use electronic components and circuits to make tripping decisions. While they are widely used, the term "static" refers to the absence of moving parts for the primary decision-making process, not necessarily a modification by an additional mechanical or electromagnetic force in the way described.
• IDMT relay: IDMT stands for Inverse Definite Minimum Time. This is a type of overcurrent relay where the operating time is inversely proportional to the fault current magnitude above a certain threshold (definite minimum time). The characteristic relates current to time, but the definition in the question refers to a characteristic being modified by an *additional* process, which is not the defining feature of an IDMT relay itself.
• Biased relay: A biased relay is designed such that an additional input quantity (the bias) influences its operating point or characteristic. This bias quantity often represents a condition in the protected system (like through current in a differential relay) and it acts mechanically or electromagnetically to either assist or restrain the operation based on the main operating quantity. This concept perfectly matches the description of a relay whose characteristic is modified by an additional mechanical or electromagnetic process (the bias).
• Electro-mechanical relay: This is a broad category of relays that use electromagnetic principles to cause mechanical movement (like contacts closing or opening). While they involve both electrical and mechanical aspects, the term itself doesn't specifically denote a relay whose *characteristic* is modified by an *additional* process in the way described; it's more about the general operating principle.

Based on the definitions, a relay whose characteristic is modified by an additional mechanical or electromagnetic influence, often an additional quantity acting as a bias, is known as a biased relay. The bias input alters the condition required for the relay to operate.

Therefore, the correct answer is the biased relay.