Summary of "Relais Thermique : Méthode de Lecture des courbes de déclenchement (partie 3)"

Summary of “Relais Thermique : Méthode de Lecture des courbes de déclenchement (partie 3)”

This video explains how to read and interpret thermal overload relay tripping curves, focusing on understanding the relationship between current multiples and tripping time under different operating conditions. The presenter offers a step-by-step methodology to analyze these curves and determine the relay’s tripping duration depending on the situation.

Main Ideas and Concepts

Thermal Overload Relay Tripping Curves

The curves use logarithmic scales on both axes:
- Horizontal axis: multiples of the relay’s current setting (e.g., 1×, 2×, 6× the setting current).
- Vertical axis: tripping time in seconds.

Types of Operating Conditions (Three Curves Provided by Manufacturer)

Curve 1: Balanced operation (cold start)
- All three phases carry equal current.
- No prior current flow; motor starts cold (e.g., start of workday).
Curve 2: Two-phase operation (cold start with phase loss)
- One phase missing.
- No prior current flow.
Curve 3: Balanced operation after prolonged current flow (hot trip)
- Motor has been running for hours.
- Relay is “hot.”

Curve Classes

Different classes (e.g., 10A, 20A) correspond to different tripping characteristics.
The correct class curve must be selected based on the relay’s specifications.

Methodology to Read Tripping Curves

Select the correct curve class based on the relay’s data (e.g., 10A or 20A).
Calculate the current multiple: Divide the actual current flowing (i) by the relay’s setting current (Is). Example: For 40 A current and 10 A setting, current multiple = 40 / 10 = 4.
Determine the operating condition: Choose between cold balanced (curve 1), two-phase cold (curve 2), or hot balanced (curve 3).
Locate the current multiple on the horizontal axis.
Project vertically to the chosen curve.
From the intersection point, project horizontally to the vertical axis to read the tripping time.
Interpret the time in seconds as the relay’s tripping duration.

Example Exercise from the Video

Relay class: 20A thermal overload relay
Setting current: 30 A
Actual current: 300 A
Operating condition: Hot balanced operation (curve 3)

Steps:

Calculate current multiple: 300 A / 30 A = 10.
Locate 10 on the horizontal axis.
Project vertically to curve 3.
Project horizontally to the vertical axis to read tripping time.
Result: Approximately 4 seconds tripping time.

Speakers / Sources Featured

Presenter: Unnamed (single speaker throughout the video) The presenter explains the concepts and guides through the methodology and example.

This video is a practical tutorial for engineers or technicians working with thermal overload relays, helping them correctly interpret tripping curves to predict relay behavior under various current loads and conditions.