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Testing Synchronous Machines
When testing synchronous machines, one should consider the control circuitry involved. Baseline current tests of both armature and field should be taken when the machine is operating in nominal condition or when it’s first installed. Analysis of the current data should include a thorough review of the time domain waveforms to ensure there is full wave rectification (i.e. all rectifiers are working) in the field circuit. Baseline voltage and current measurements through a start-up and synchronization should also be performed to analyze the performance of the amortisseur windings and synchronizing regulation. Assuming a constant load, a steady state analysis of an RMS enveloped current on both the armature and field should be performed to ensure there is no abnormal variation in current. Should you need additional information on testing synchronous machines, please contact PdMA technical support for assistance.
Synchronous motors are commonly medium/high voltage machines. For additional test considerations read Medium/High Voltage Testing Application Note at http://www.pdma.com/PdMA-application-notes.php.
No Current Imbalance Doesn’t Mean No Problem
Just because the three phase current data being returned by the installed relay is balanced, doesn’t clear the power circuit of possible anomalies. Remember from previous tips that the opposition to AC current is influenced by impedance, which is the combination of reactance and resistance. Not just resistance. A high resistance connection may be a small part of the overall impedance, but can still create a significant amount of localized heating. This localized heating can lead to big problems if not corrected. Waiting until the problem is severe enough that the resistance element dominates the total impedance and changes the AC current may be too late and risk a single-phase fault. Using the MCE® technology for precision resistance measurements will give an early indication of power circuit anomalies so they can be repaired before causing a high current imbalance.
Source PdMA
Tip: Current Imbalance
Current Imbalance is a measure of the largest deviation in current between phases. A current imbalance may be indicative of a high resistance connection. A voltage and current imbalance together is a more reliable indicator. Test location determines whether both imbalances are present in the event of a high resistance connection. If the test is performed upstream of an anomaly, there will only be a current imbalance. If the test is downstream of the anomaly, both a current and voltage imbalance will exist. Parallel components such as power factor correction capacitors in the power circuit may also cause a current imbalance. Testing needs to be performed with and without the parallel components in the system being tested to eliminate them as the cause of the current imbalance.
To read more or download the PDF visit our friends at PdMa.
What is L10 Life?
DID YOU KNOW? L10 life is the number of revolutions or hours that 90% of a group of apparently identical bearings will complete or exceed before fatigue is expected to occur. In other words, 10% of the group is not expected to achieve the L10 life.