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Building Automation


Industrial Automation


Power Automation & Safety

Bangladesh Distributor

Lead Contents

Measuring / Motor Protective Relays

Introduction Features
Principles Classifications
Engineering Data Further Information
Explanation of Terms Troubleshooting

Related Contents

Primary Contents



Incorrect Phase Sequence Protection

Preventing motor reverse operation due to incorrect wiring of a three-phase power supply (three wires).

Phase Loss Protection

Monitoring a three-phase power supply (three wires) to prevent a motor from burning out due to a disconnected wire.

Overcurrent

When a current above the rated value flows through a device (motor).

Undercurrent

The operating status of a device (motor) under an abnormally low load (such as idle running of a submersible pump).

Overvoltage

Applying a voltage that is above the rated value to a device.

Undervoltage

When the rated voltage is not being applied to the device.

Voltage Asymmetry

A voltage imbalance in a three-phase power supply (three wires).

Liquid Level Control

Controlling the level of a liquid with electrodes
(e.g., the function of the 61F).

* A relay that performs this type of control is called a Conductive Level Controller or Floatless Level Controller.

Temperature Monitoring Relay

A relay that produces an alarm for an abnormal temperature
(it does not support PID control).

Single-phase Power Supply

A power supply that uses two wires.
Example: The power supply used for a household fan.
The fan motor runs with two wires on single-phaseresidential power.
A single-phase power supply uses two wires.

Three-phase Power Supply

A power supply that uses three wires.
Examples: Almost all belt conveyors, cranes, and other industrial motors use three-phase power supplies.
The majority of power equipment (motors and heaters) used in factories runs on three-phase AC power (400 V or 200 V).

* In addition to motors, there are single-phase and three-phase heaters too.

Incorrect Phase Sequence

If the power wires to a three-phase motor are connected in the wrong sequence, the motor operates in reverse.

Phase Loss

If a wire to a three-phase motor is disconnected or was not connected, the motor cannot achieve its specified output.