Application Notes:
Ways to Reduce Costs with the Fluke 434 Power Quality Analyzer |
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Power ConsumptionCommercial and industrial power consumers are charged for power consumption based on multiple variables including energy (kWh), peak demand (kW), and power factor. Power quality analyzers can help manage utility bills by determining which loads have a significant effect on peak demand and power factor.
PdM Measurement #1: Voltage Unbalance
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Vneg is the ratio of negative to positive sequence voltage and Vzero is the ratio of zero to positive sequence voltage. They are both indications of voltage unbalance. |
What is it? In a balanced 3-phase system, the phase voltages should be equal or very close to equal. Unbalance is a measurement of the inequality of the phase voltages.
What does it do? Voltage unbalance can cause 3-phase motors and other 3-phase loads to experience poor performance or premature failure because of the following:
- Mechanical stresses in motors due to lower than normal torque output.
- Higher than normal current in motors and 3-phase rectifiers.
- Unbalance current will flow in neutral conductors in 3-phase wye systems.
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How much does an incident cost? The major costs are associated with motor replacement (labor + equipment) and lost income due to circuit protection trips.
Example Calculation
Assume the cost to replace a 50 hp motor each year is $5000 including labor.
Assume 4 hours of downtime per year with income loss of $6000 per hour.
Total Cost: $5000 + (4 x $6000) = $29,000 annually
What to check? Inputs to motors, VFDs, UPSs1.
How much is ok? The EN50160 power quality standard requires voltage unbalance, as a ratio of negative to positive sequence components, to be less than 2 % at the point of common coupling. NEMA specs call for less than 5 % for motor loads. Consult user manuals for other equipment.
How do I measure it with the Fluke 430 Series Power Quality Analyzer?
- Connect the voltage leads of the analyzer.
- Configure the analyzer for the appropriate 3-phase power system: delta or wye.
- Select "Unbalance" from the main menu.
1 VFD: Variable Frequency Drive; UPS: Uninterruptible Power Supply
PdM Measurement #2: Total Harmonic DistortionWhat is it? Total Harmonic Distortion (THD) is the sum of the contributions of all harmonics. Harmonic distortion is a normal consequence of a power system supplying electronic loads such as computers, business machines, electronic lighting ballasts, and control systems.
What does it do? Harmonic distortion can cause:
- High current to flow in neutral conductors.
- Motors and transformers to run hot, shortening their lives.
- Increased susceptibility to voltage sags, potentially causing spurious resets.
- Reduced efficiency of transformer - or, a larger unit is required to accommodate harmonics.
- Audible noise.
How much does an incident cost? The major costs are associated with shortened life of motors and transformers. If the equipment is part of production systems, income may be affected as well.
Example Calculation
Assume the cost to replace a 100 KVA transformer is $7000 including labor each year.
Assume 8 hours of downtime each year with income loss of $6000 per hour.
Total Cost: $5000 + (8 x $6000) = $29,000 annually
What to check? Motors, transformers and neutral conductors serving electronic loads.
How much is ok? Voltage distortion (THD) should be investigated if it is over 5 % on any phase. Some current distortion (THD) is normal on any part of the system serving electronic loads. Monitor current levels and temperature at transformers to be sure that they are not overstressed. Neutral current should not exceed the capacity of the neutral conductor.
How do I measure with the Fluke 430 Series Power Quality Analyzer?
- Connect the voltage and current leads of the analyzer.
- Configure the analyzer for the appropriate 3-phase power system: delta or wye.
- Select "Harmonics" from the main menu.
PdM Measurement #3: Increasing Phase CurrentWhat is it? As insulation deteriorates it begins to leak. Loads will draw slightly higher current as they age and they may send some of this leakage current into the grounding system. Faults within the equipment may also cause high ground current. The best way to check insulation is by periodically checking equipment with an insulation tester. But you can also check equipment while it's in service by monitoring all of the currents (phase, neutral and ground) to make sure none of these is increasing significantly over time.
What does it do?
- Excessive phase currents can further damage insulation and overheat the load, resulting in a shortened life of the load.
- Over-current will cause protection devices to trip, resulting in unscheduled downtime.
- Excessive ground current can create unsafe voltages on metal chassis, cabinets, and conduit.
How much does an incident cost? Costs come from premature motor failure and lost income due to over-current protection devices tripping.
Example Calculation
Assuming the failure of a pump motor each year costs $7000 to replace and causes a $2,500,000 per year continuous process to be shut down for 10 hours. Assume it takes two people 6 hours to clean and restart the process at $50 per hour each.
Lost income = 10 hours*($2,500,000 / (365 days/year * 24 hrs/ day)) = $2853
Motor replacement = $7000
Clean and restart = $600
Total Cost $10,453 annually
What to check? Any critical load, but especially motors, VFDs and transformers.
How much is ok? The nameplate rating of the load should never be exceeded. If you track the phase current being drawn by a load over the months or years, you should be able to get a sense whether the current is changing.
How do I measure with the Fluke 430 Series Power Quality Analyzer?
- Connect the voltage and current leads of the analyzer.
- Configure the analyzer for the appropriate 3-phase power system: delta or wye.
- Select "Volt/Amp/Hertz" from the main menu.
- Press "Save Screen" to record measurements for comparison with future readings.
- Monitor phase current regularly for changes.
Click here to download the full pdf: Six simple ways to reduce costs with the Fluke 434 Power Quality Analyzer » |