DCRM (Dynamic Contact Resistance Measurement) test is an advanced diagnostic technique used to monitor and analyse the real-time dynamic behaviour of a circuit breaker’s moving contact system. This test is different from the conventional Static Contact Resistance (CRM) test, as it measures the resistance during the movement of the contacts rather than in a static position.

What is DCRM Testing?

In a DCRM test, the dynamic resistance between the circuit breaker’s main contact and arcing contact is measured while the breaker is operated in open or close conditions.
This helps determine whether the contacts are functioning smoothly or if there are any issues such as wearing, pitting, or misalignment.

Objectives of the DCRM Test

• To evaluate the health and performance of the contacts
• To check mechanical alignment and contact timing
• To determine the condition of arcing contacts
• To identify whether the breaker requires maintenance or replacement

Basic Principle of the Test:

When a circuit breaker is operated in open or close mode, its main contact and arcing contact make and break the connection.
During this process, a constant low DC current (typically between 100A–200A) is passed through the contacts, and the voltage drop (in millivolt range) is measured.
Using Ohm’s Law (R = V/I), a time vs resistance curve is obtained.
This curve shows how the contacts move and helps identify any mechanical or electrical abnormalities.

Key Parameters:

1. Main Contact Resistance (MCR):

• The steady-state resistance of the contact when the breaker is fully closed.

• Typically ranges between 30–80 µΩ (micro-ohms).

2. Arcing Contact Overlap Time:

• The duration when both the main and arcing contacts remain connected simultaneously.

• This overlap time helps determine whether the arcing contact is operating in the correct sequence or not.

3. Opening/Closing Time:

• The total time taken by the breaker to open and close.

• Any delay or irregularity indicates mechanical sluggishness or misalignment.

4. Transition Resistance:

• When the contact enters the arcing zone, the resistance value suddenly increases.

This rise in resistance may indicate contact erosion or contamination.

How DCRM Testing is Performed:

1. The breaker is operated in Open-Close mode.

2. A low DC current (typically 100A or more) is passed through the contacts.

3. The Resistance vs Time Curve is recorded during the movement of the contacts.

4. This curve is displayed in the DCRM software, allowing analysis of contact wear, arcing zone, and mechanical behaviour.

 

Information Obtained from DCRM Test:

• Main Contact Resistance – Indicates the health and condition of the main contacts.
• Arcing Contact Overlap Time – Helps in verifying proper operation and sequencing of arcing contacts.
• Total Contact Travel Time – Shows the complete duration of contact movement during breaker operation.
• Mechanical Wear Condition – Detects sluggish or worn-out mechanisms affecting breaker performance.
• Internal Contact Movement Anomalies – Identifies any abnormal internal motion, misalignment, or defects within the contact assembly.

Equipment Used:

• DCRM Test Kit (e.g., Omicron CIBANO 500, SCOPE CRM-200, Vanguard, etc.)
• Current Injection Leads – To inject the required DC current through the contacts.
• Motion Sensor (Travel Transducer) – To record the contact movement accurately.
• Software Interface – To plot and analyse the Resistance vs Time graph for evaluating contact behaviour.

Waveform Analysis:

The DCRM test waveform typically consists of three major zones that help in understanding the circuit breaker’s internal contact operation:

1. Stable Resistance Zone → Represents the period when the main contacts are fully engaged and the resistance remains constant and very low.
2. Transition Zone → Indicates the engagement or disengagement of the arcing contacts during the movement phase.
3. Open Circuit Zone → Occurs when the contacts are completely open, and the resistance becomes extremely high or infinite.

Each deviation or sudden spike in the waveform can indicate pitting, contact wear, or mechanical misalignment, signalling potential issues in the breaker’s internal components.

Technical Benefits:

• Dynamic Performance Analysis: Measures not just static resistance but also real-time contact behaviour throughout the operation.
• Predictive Maintenance: Helps identify potential contact failures before they occur.
• High Accuracy: Provides precise measurements at the micro-ohm level.
• Data Trending: Enables long-term monitoring of contact degradation using periodic test records.

Conclusion:

DCRM Testing is an advanced and highly reliable diagnostic method for analysing the condition and performance of circuit breaker contacts.
It not only supports preventive maintenance but also helps predict possible failures well in advance, enabling timely corrective action.
Thus, DCRM Testing plays a vital role in ensuring the reliability, safety, and continuity of electrical systems.

Ensure the efficiency and safety of your circuit breakers with DCRM Testing!

Perform Dynamic Contact Resistance Measurement today to prevent unexpected breakdowns.