OPERATIONS & MAINTENANCE
Offshore platforms are embracing continuous megohm testing and monitoring of insulation resistance
fail at start-up. When this occurs, costs quickly mount for “rewind” repairs or replacing the motor or generator while production comes to a halt. “Failures can be really expensive. Rewinds can cost tens of thousands of dollars, up to a couple hundred thousand depending on the type of motor or generator,” says Hodgson. “And it is not just the cost of the
repair,” she adds. “It is also the cost of the labour to get the motor or generator prepped and ready for shipment, the cost for the boat to bring it to and from the platform, and road transport. Tose costs can also run in the tens of thousands of dollars.” To avoid these costs, electrical engineers are turning to a continuous monitoring device, the Meg-Alert. Hodgson says she first heard about the automatic insulation resistance testing device through some of her colleagues. Te Meg-Alert unit is permanently installed inside the high-voltage compartment of the MCC or switchgear and directly connects to the motor or generator windings. Te unit senses when the motor or generator is offline and then performs a continuous dielectric test on the winding insulation until the equipment is re-started. By testing
continuously, it reduces the need for manual PI testing since the insulation resistance readings are averaged over a longer period of time to determine the true ‘leakage current’ level of the insulation.
Te unit functions by applying a
non-destructive, current limited, DC test voltage to the phase windings and then safely measures any leakage current through the insulation back to ground. Te system uses DC voltage levels of 500, 1,000, 2,500 or 5,000V that meet the IEEE, ABS, ANSI/NETA and ASTM International standards for proper insulation resistance testing voltage based on the operating voltage of the equipment. Te test does not cause any deterioration of the insulation and includes current limiting technology that protects personnel. Te Meg-Alert device can also be installed to disable the start circuit to prevent the motor or generator from being operated if the insulation resistance level is unsafe for operation. It is for this purpose that Hodgson installs the device on the generators on the deepwater platforms. “Te Meg-Alert is wired to the start circuit so when you hit the ‘start button’ you get an automatic insulation
resistance test and if it doesn’t stay above a certain setpoint, it will not start the generator,” explains Hodgson. “What that does is take human error out of the equation. No one has to remember to use a megohmmeter before starting up the generator – the test is automatic and the equipment will not start if it’s not safe to use,” says Hodgson.
HANDS-OFF MONITORING Te continuous monitoring system also allows for a hands-off approach that does not require service technicians to access control cabinets to perform a manual insulation resistance test. Instead, an analogue meter outside on the control cabinet door shows the insulation resistance megohm readings in real time. Te meter also indicates good, fair and poor insulation levels through a simple “green, yellow, red” colour scheme. When predetermined insulation resistance set point levels are reached, indicator lights will turn on to signal an alarm condition and automatic notifications can be sent out to the monitoring network. “With the Meg-Alert, personnel do
not have to open junction boxes and connect a megohmmeter to the motor or generator. Tey can just look at the
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