Always up and running is every plant’s daily goal— that’s why you invest so much into the mainte- nance of the equipment and infrastructure. Of allthe electrical measurements made by maintenance technicians in the pursuit of operational excellence, these are the
8 most essential.
1. Three-Point Test Method
Safety first. Before working on an electrical circuit, follow LOTO procedure, and use the three-point test methodto ensure your tool is working properly. This test ensuresthe absence of voltage at 50 volts or more.
• Step 1: Verify the tool is working correctly by testingon a known energized source or with an electronicproving unit
• Step 2: De-energize the circuit to be verified. The toolshould indicate zero energy
• Step 3: Check your tool again using the known energized source or electronic proving unit
Being able to measure both AC and DC voltage is animportant feature in simplifying your motor inspections.Quickly grab a meter and begin troubleshooting powersupply issues to help ensure equipment is up and workingsmoothly. A clamp meter or multimeter can help raise a redflag to let you know when to grab a more powerful meter.
If an issue was raised, grab a power quality meter toinvestigate further, look for harmonic distortion, swellsor sags that may be present at the motor. These can be asign of increases in voltage requirement throughout yourbuilding if the cause is internal. If the cause is external, itcan be caused by nature, such as vegetation affecting power lines. Both are worth looking into correcting if yourmotor is experiencing sags or swells in power.
It’s a great option to use a clamp meter or multimeterduring your regular preventive maintenance routes to lookfor voltage imbalance issues. Use that information to comeback through later with a more powerful power quality toolto determine where the imbalance may be coming from.
A clamp meter can help determine balanced and unbalanced loads throughout your facility. Again, thesemeasurements will give you an idea of whether or not youneed to come back through with a power quality tool todetermine the unbalance.
Non-linear loads or devices that conduct current for
less than the entire sine wave cause harmonics. Harmon-
ic current flowing through system
impedances generates voltage dis-
tortion. In severe instances, these
harmonics can cause thermal trips
or logic faults. As the voltage dis-
tortion caused by current har-
monics increase, linear loads be-
gin to draw harmonic current. In
motors, the distortions can cause
counter-torque resulting in more
current and a host of other prob-
lems, including decreased motor
efficiency, increased heating, and
a shorter life of the motor.
4. Component Resistance
Checking the resistance of control circuits, like switches and relay contacts, can show what condition the components are in. Thehigher the resistance, the lowerthe current flowing through to the motor at the end. Mostof the time, resistance starts out very low and increasesover time; as dirt builds up, there is more wear and tear puton the components, insulation breaks down or moisturebuilds up.
Finding these kinds of issues and correcting them before the damage can prevent expensive repairs or assetreplacement.
5. Circuit Continuity
Testing a circuit for continuity tells you whether twopoints are electrically connected or not. Use these checksto verify a proper connection or if there could be a breakanywhere in the electrical path.
6. Circuit Loading at Panelboards(feeder cables, branch circuits, neutrals)
Sometimes a circuit load at the panelboard could cause
sags down the line if the wiring isn’t adequate for the loads
they feed. If this issue presents itself in your facility, cor-
rect the wiring and loading issues first, then you can try
other actions to minimize the source impedance like:
• Reduce the load on the panel (if necessary and possible)
• Don’t cascade subpanels off subpanels
• Limit the length of feeder runs to subpanels
Be sure not to overload transformers as that can cause in-
creased energy losses further down the line and ultimately
cause premature failure in equipment.
7. Validate Load Measurements
on Motors and Pumps
Motors and pumps are incredibly common machines inthe industrial industry. Because they’re so common, theyare often overlooked as the possible cause of excess costs.But when not operated properly, motors and pumps canslow productivity and cause additional problems and costs.
It’s important to make sure your load is properly balanced. Validate that the load to the motor is not overloaded with voltage or current flowing through.
8. Confirm Transformer Load and Line Voltage
When inspecting your motor, running a load test candetermine the efficiency and thermal and dynamic stability of a power transformer. If the transformer is frequentlyoverloaded, it weakens the system faster. Overloading generally causes overheating and eventually creates cracks inthe insulation within the system. Using the meter, you canknow what voltage and current should be coming out at thetransformer, up to 1,000V line voltage. If something is off,you will need to grab a more powerful tool and continueinvestigating. Keeping an eye on transformer loads and linevoltages during your regular preventive maintenance routescan help catch issues before they become too big.
For more, visit newequiment.com/21153507
By Sean Silvey
Photo Credit: Fluke Corporation