Recondition your motor controls

Figure 1. The “power circuit” is located at the top of the ATRV schematic; the control circuit is at the bottom.

Let’s focus on the key steps in reconditioning a motor-control bucket (Figure 1), as well as tips to consider if you’re performing the reconditioning in-house or selecting a qualified vendor to perform the service. You should know about the reconditioning standards relevant to an autotransformer-reduced voltage (ATRV) starter, a common form of motor control for AC induction motors 60 hp and larger.

The first step a PEARL-qualified technician takes when reconditioning a control system is to remove visible dirt and debris from the interior of the enclosure as a prelude to careful inspection of the wiring harness and its connections to other components. The technician takes special care when removing the dirt and debris from the interior and looks for signs of broken parts and wear debris among the dirt, cracked and frayed wires, and cracked component cases, especially at terminal or connection points. The technician seeks out discolorations that might indicate overheating and arcing that would indicate shorts. Often a system will have maintenance notes about previous problems or settings that might provide valuable data to locate or resolve the situation. Many times you’ll find the equipment is being used outside its design capability or contains underrated devices.

After visually and mechanically inspecting each and every component, inspect the circuits, treating each as a single device. Energize and test them to ensure operational integrity. A system test verifies every component is functioning in coordination with others and ensures system integrity.

Follow standard procedures

Reconditioning begins with choosing the correct PEARL technical standard, which are available as free downloads (www.Pearl1.org). These standards include forms for documenting test results, comprehensive reconditioning procedures, specification tables, and inspection, observations and procedures for each component or circuit.

PEARL reconditioning standards have two sections: recondition evaluation and recondition procedures. Both require specific calibrated test equipment (megohmmeter, digital low-resistance ohmmeter (DLRO), millivoltmeter, etc.), which are listed at the beginning of each standard. Both sections require PEARL members to use the provided forms to record test values and technician observations. Document the reconditioning process with comprehensive test results that are kept on file for future reference and supplied with each device. This is a vital part of reconditioning electrical equipment safely.

If all the procedures are followed diligently, the reconditioned device will operate as well or better than it did when it rolled off the production line. We say better because whereas new electrical equipment typically is tested in batches, reconditioned equipment is 100% tested and fully documented. This ensures the product performs at the highest performance level and can protect the vendor, electrician and end user. If the technician is PEARL-certified, follows the PEARL recondition standards, records all data, and documents the work, then a device will merit the PEARL reconditioned Blue Seal.

For the purposes of this article, the technician should be interested in the following standards:

• 1110 Low-Voltage Disconnect Switches Manually Operated Air Non-Fusible (for the 3-ph motor disconnect)
• 1420 Low-Voltage Transformers Control Power (for the control transformer)
• 1430 Low-Voltage Transformers Instrumentation Voltage (for the auto transformer)
• 1620 Low-Voltage Starters Magnetic (for the starter with overload protection)
• 1841 AC Contactor (for the wye, run and start contactors)
• Components not yet covered by PEARL standards include: pneumatic timer and pilot (start/stop) switches.

Know the details

Looking at the power circuit from left to right, the schematic shows a three-phase motor disconnect, a three-coil autotransformer and a contactor/starter, which includes three-phase overload protection. This circuit gives the motor two stages of acceleration rather than one high-current start at full line voltage.

PEARL publishes 12 reconditioning standards for low-voltage disconnects in its 1100 series, including manually operated, air-fusible and non-fusible; manual trip power fusible and non-fusible; and high-pressure electric trip fusible and non-fusible. The 2100 series includes a similar number of standards for medium-voltage, manual and electrically operated, and air and vacuum disconnects of both the fused and non-fused varieties.

Because the number of motors installed varies inversely with motor size, we’ll use the low-voltage, non-fusible disconnect switches (Standard 1110) as our example for reconditioning them. Because this disconnect offers no circuit protection, a feeder device in a nearby panel will likely provide the necessary protection.

Section I lists the required calibrated test equipment, including insulation resistance test set (Megohmeter, 1,000 Vdc minimum) and digital low-resistance ohmmeter (DLRO, minimum of 10-amp capability) or a DC current source and a millivoltmeter.

Section II covers the recondition evaluation, which is broken down into two sections: inspection and test. Standard 1110 lists eight parts of the disconnect that require inspection, including frame/enclosure, insulation system, current-carrying components, stationary contacts or blade clips, moving contacts or blades, arc extinguishers, operating mechanism and interlock.

As you might expect, the inspection procedures for each standard are device-specific. For instance, the initial evaluation for a low-voltage, non-fusible disconnect switch – Sections 1.2.1 through 1.2.5 - requires the technician to check the insulation for dust and foreign materials, chips, cracks and deterioration, signs of overheating, missing or defective insulation, and missing or defective interphase barriers.

At the end of the component inspection evaluation, the technician records relevant observations on the 1110 evaluation report. Section I guides the inspection through the remaining seven components in the low-voltage disconnect, namely frame/enclosure, current-carrying components, stationary contacts or blade clips, moving contacts or blades, arc extinguishers, operating mechanisms and interlocks. The technician records inspection observations for each component group on the PEARL evaluation report. These written records provide a device history, allowing more in-depth evaluation and trend analysis. These steps relate to making sure this device is safe for service.

After recording the observations, the technician performs both insulation and contact-resistance tests on the disconnect. Insulation resistance measures the degree of isolation between the device’s current carrying and noncurrent carrying materials. Contact resistance indicates the degree of free flow of current along the current-carrying path. This test identifies loose connections, pitted and misadjusted contact surfaces, and damaged current-carrying brades. Contact resistance requires measurements with the DLRO, whereas insulation resistance needs a megohmeter or megger. The insulation tests require checking values line-to-load while the disconnect switch is open, and phase-to-phase, phase-to-frame or phase-to-enclosure resistance measurements in the closed position. Where the contact resistance of the disconnect switch is tested in the closed position, it’s line-to-load.

The results are recorded from both test and observations on the 1110 PEARL evaluation report. Optional contact-resistance tests include millivolt drop or Watt-loss, which determine resistance values line-to-load on each phase of the closed switch, with the test points at the line and load lug landing. Again, the values are recorded and checked against manufacturer specifications. Unless the contact resistance for the three phases is within 50% of each other, the device is considered out of specification by PEARL reconditioning standards 2.2.3.

Correct, clean and lube

After recording observations and resistance values, correct any disconnect switch problems and completely clean and lubricate it. Standard 1110 specifies 10 reconditioning procedures related to the frame/enclosure, missing or defective parts and hardware, operating mechanism, insulation system, arc extinguishers, contacts or blades, and current-carrying components, final OEM checks and adjustments, torque and final disconnect operation. At the completion of each section, record on the 1110 inspection and test report form any reconditioning actions performed on the device.

After completing the PEARL reconditioning, operate the disconnect switch 10 times to verify its proper operation. If the unit passes the PEARL recondition standard guidelines set forth in Section 1110 – Low-Voltage, Non-Fusible Disconnect Switch, final testing may be repeated and recorded on the insulation and contact resistance tests described in section 2.1 and 2.2.

The device is eligible for a blue PEARL reconditioning seal only if the reconditioning procedures, testing and documentation are carried out by a certified technician working at a licensed PEARL member company. This seal guarantees that the device has been evaluated, reconditioned and tested to the PEARL standards, thereby producing a safe, high-quality, reliable disconnect switch.

Then, the autotransformer, starter and other components to complete the motor control and power circuit are subjected to the PEARL reconditioning procedures. PEARL takes reconditioning seriously. Placing a reconditioned device back in service can save downtime and untold costs, and help save the environment by reducing scrap, waste and energy consumed in manufacturing a new device.

Between rebuilds, polish skills

Standards are critical, but by themselves they aren’t enough. PEARL-qualified technicians must have a full understanding of the workings of the components and how they integrate with the larger electrical system. Major manufacturers offer courses in applications and maintenance of their products. Electrical trade associations such as NEMA, NETA, NECA, EASA and PEARL provide training and materials for the continuing education of field service and maintenance technicians. Standards organizations such as OSHA and inspection organizations such as IAEI do as well. Private training organizations such as AVO Institute provide valuable and up-to-date training.

Over time, such training and hands-on experience makes for a technician who can perform value-added services that help keep the lights on and the conveyors running. In addition to their technical knowledge, experienced PEARL technicians are savvy about the common causes of control system malfunction. For instance, contactors exhibiting a humming noise often have missing shading coils or worn armatures. They can size motor overload protection in the absence of OEM data. Most of us don’t have a $100,000 dynamometer to test an electric motor. Savvy and experienced maintenance and repair technicians know that standard AC motors draw approximately 1.25 amp per horsepower.

Associating with organizations such as PEARL or EASA can help keep your maintenance department in the loop. It also helps you compile an ever-growing library of information to help keep your electrical systems online more of the time and safely.

David Rosenfield is president of ROMAC Supply in Commerce, Calif. Malcom Frederick is president of Coastal Switchgear in Richwood, Texas. Winn Hardin is marketing director of PEARL, Neptune Beach, Fla. Contact them at [email protected] and (904) 246-8958.