What are the properties of good protective relays?

What are the properties of good protective relays?

What are the Essential Qualities of Protective Relay?

• Reliability.
• Speed and Time.
• Sensitivity.
• Selectivity and discrimination.
• Stability.
• Simplicity.
• Economy.
• Adequateness.

What are the types of overcurrent relays?

Types of Overcurrent Relay:

• Instantaneous Overcurrent relay (Define Current)
• Definite Time Overcurrent Relays.
• Inverse Time Overcurrent Relays (IDMT Relay) Normal Inverse Time Overcurrent Relay. Very Inverse Time Overcurrent Relay. Extremely Inverse Time Overcurrent Relay.
• Directional Overcurrent Relays.

What is the working principle of a relay?

Relay works on the principle of electromagnetic induction. When the electromagnet is applied with some current it induces a magnetic field around it. Above image shows working of the relay . A switch is used to apply DC current to the load.

What is the function of overcurrent relay?

Overcurrent Relay Purpose and Ratings. A relay that operates or picks up when it’s current exceeds a predetermined value (setting value) is called Overcurrent Relay. Overcurrent protection protects electrical power systems against excessive currents which are caused by short circuits, ground faults, etc.

What is overcurrent relay?

An overcurrent relay is a type of protective relay which operates when the load current exceeds a pickup value. It is of two types: instantaneous over current (IOC) relay and definite time overcurrent (DTOC) relay. When the relay operates, one or more contacts will operate and energize to trip a circuit breaker.

What is zone of protection?

“Zones of protection” is one strategy that can be used to provide the level of security demanded today. Protective relay engineers keep utility grids and equipment safe from faults and system unbalances by dividing the grid into zones, each with a unique protection scheme. Overlapping zones provide backup protection.

What are the main characteristics of a relay?

As i explained in my last posted,basically principal for small DC and AC relays,sensitive relays, miniature and sealed relays, and some small power relays is common.

How big is the contact capacity of a relay?

These usually have coils operating on 120 or 240 VAC, which can be controlled by sensitive relays. These small power relays have contact capacities up to 30 A, at voltages up to 600 V. Much larger relays are of course available or it often called magnetic contactors or controllers.

What makes a relay contact system so effective?

How well the contact system actually performs is dependant on the suitability of the contact material, the contact arrangement and the mechanical design. An ideal relay contact would consist of highly conductive metal with chemically clean surfaces (no oxidation) and a large, wear resistant, effective contact area.

What is the difference between a relay and a switch?

What is a Relay? A switch is a component that opens (turn off) & close (turn on) an electrical circuit. whereas, a relay is an electrical switch that control (switch on & off) a high voltage circuit using a low voltage source. A relay completely isolates the low voltage circuit from the high voltage circuit.