Pump Motor Test at Liverpool Hospital 

On January 3, 2023, We conducted an offline diagnostic test on a 30Kw pump motor at Liverpool Hospital. The test aimed to identify issues causing circuit breaker trip faults. 

CHALLENGE  

Reported Faults: Circuit breaker trip faults 

Equipment Model: 30Kw pump motor 

OUR CHECKS 

Type of Assessment: Offline diagnostic test using a PDMA MCE/Emax™ tester.  

The tests included: 

• Phase to Phase Resistance: 
  Measuring phase-to-phase resistance may be done by measuring the resistance by connecting a resistance meter to leads A and B while C is not connected. 
  
• Resistance to Ground (RTG): 
  The resistance between an electrical system and the ground, critical for ensuring safe and effective grounding. Lower resistance is preferable for safety and system protection. 
  
• Polarisation Index (PI): 
  A measure of the insulation quality of electric motors, calculated as the ratio of the insulation resistance at 10 minutes to the resistance at 1 minute. A higher index indicates better insulation health and cleanliness. 
  
• Dielectric Absorption (DA): 
  The property of an insulating material that causes it to absorb and release electrical charge slowly. It’s measured to assess the insulation’s ability to store and return electrical energy, indicating its condition and quality. 
  
• Capacitance to Ground (GTG): 
  The measure of a system’s ability to store electrical charge relative to the ground. In pump systems, it helps in identifying insulation degradation and potential faults in electrical components. 
  
• Rotor Influence Check (RIC): 
  An assessment of the rotor’s magnetic influence in a motor, used to detect issues like rotor bar defects or unbalanced magnetic fields, which can affect pump performance and efficiency. 
  
• Inductive Imbalance: 
  A condition where the inductance varies between different phases of a motor, indicating problems such as winding faults or asymmetry in the magnetic circuit, leading to inefficient pump operation. 
  
• Power Quality Test: 
  An evaluation of the electrical power supplied to a pump, checking for voltage sags, surges, harmonics, and other anomalies that can affect pump performance and longevity. 
  
• In Rush/Start-Up Test: 
  A measurement of the initial surge of current when a pump motor starts. High inrush currents can indicate potential electrical issues or mechanical binding in the pump. 
  
• Rotor and Eccentricity Evaluation: 
  The process of checking the alignment and balance of the rotor within the motor to detect any off-center rotation or misalignment that can cause vibration and wear. 
  
• Demodulation Current Signature Analysis: 
  A technique that analyzes the current waveform of a motor to detect mechanical and electrical anomalies in pump systems, such as bearing faults or rotor defects. 

DIAGNOSING THE ISSUE   

The test results showed no anomalies in the motor windings or insulation system. The Polarisation Index and Dielectric Absorption results were satisfactory. The Rotor Influence Check indicated no issues with the rotor bars or turn-to-turn faults. 

• The Polarisation Index is the ratio of the insulation resistance to ground (IRG) value taken at 1 and 10-minute intervals. 

• Dielectric Absorption is the name given to the effect by which a capacitor, that has been charged for a long time, discharges only incompletely when briefly discharged. 

• The Rotor Influence is a test performed with the motor de-energized. High resistance, cracked, or broken rotor bars and end rings will cause a non-symmetric reflected impedance onto the stator windings resulting in elevated inductance levels for the stator phase located over the rotor fault. 

While inspecting, we found that the circuit breaker might be the source of the trip faults. It appears to be an older installation compared to a newer one on a similar unit. Infra-red temperature checks showed slight variations at the motor terminal connections, suggesting minor differences in operational conditions.

solution

The motor is in good condition, with no anomalies detected. We recommend replacing the existing circuit breaker and possibly the one on the similar unit to prevent future faults. Regular monitoring is advised to ensure the continued reliability of the motor. 

engineer’s note

Regular maintenance and monitoring are essential to prevent circuit breaker trip faults and ensure the longevity of pump motors. 

DO’S & DON’TS

DO’s: 
Conduct regular diagnostic tests. 

• Ensure proper grounding. 
• Monitor insulation health periodically. 
• Assess rotor condition regularly. 
• Replace aging components timely. 

DON’TS: 
Ignore early signs of wear or faults. 

• Neglect grounding system maintenance. 
• Overlook power quality issues. 
• Delay replacing old and faulty components. 
• Skip regular inspections and diagnostic checks.

Think you have a problem like this one? Contact the Masterflow Helpdesk at 02 9748 2022. Or write to us with your unique situation here (Contact us).