Phase Sequence Indicator – Block Diagram, Working, Application | New Topic [2024]

In this note, we are going to know about Phase Sequence Indicator and about its Block Diagram, Working Principle, and Applications as well. Welcome to Poly Notes Hub, a leading destination for engineering notes for diploma and degree engineering students.

Author Name: Arun Paul.

What is Phase Sequence Indicator?

A Phase Sequence Indicator is a device used in three-phase electrical systems to detect the phase sequence or order of the phases (usually L1, L2, and L3, or R, Y, and B). The proper phase sequence is critical in applications such as motors, where improper sequence might result in reverse rotation or equipment damage.

Phase Sequence Indicator Working Principle

This indicator determines the phase order by comparing phase voltages. It determines the sequence through either mechanical rotation (for rotating-type indicators) or electronic circuitry. The phase sequence is examined to confirm that the connection order corresponds to the required rotation or functionality of the device.

Phase Sequence Indicator Circuit Diagram

Here’s a simplified structure of this device –

Inputs:

• There are three-phase inputs which are R,Y, and B or L1, L2, and L3

Components:

• Step-down transformers or resistor dividers, which are used to bring down phase voltages.
• Comparators or timing circuits, used to detect phase differences.
• Indicator (LEDs, LCD, or rotating disc) that shows the phase sequence.

Outputs:

• Visual or digital display indicating if the phase sequence is proper or incorrect.

Types of Phase Sequence Indicator

There are two types of PSI –

1. Static Type PSI: Static phase sequence indicators indicate the phase sequence using LEDs or other digital displays that are powered by electronic circuitry.
2. Rotating Type PSI: This type has a tiny rotor or disc that rotates when linked to a three-phase power supply. The rotational orientation indicates the phase sequence.

Application of Phase Sequence Indicator

These are some uses of this device –

• To avoid reverse operation, ensures that conveyor belts, fans, pumps, and other machinery have the right motor rotation direction.
• Used in substations, industrial settings, and big facilities to verify phase sequencing during installation and routine maintenance.
• Used to avoid malfunction and waste of energy, air conditioning, compressors and refrigeration systems must follow the proper phase sequence.