In the warm summer season, cooling equipment operates at near peak capacity. If that equipment is used for critical building functions, any equipment downtime for whatever reason is unacceptable.
At the most sensitive end of the spectrum, hospitals rely on their central cooling systems for critical patient care areas, such as operating and emergency rooms. If cooling is lost, subpar environmental conditions could threaten patient health and either prevent procedures from being scheduled or create potential liability.
More commonly, many commercial and light-manufacturing buildings now have in-house data centers full of servers. These servers might be responsible for critical information, such as personal information, realtime financial transactions or airplane tickets. These servers also generate large amounts of heat, which must be either dissipated or offset with cool air. A loss of chilled water cooling capacity for even a few minutes can cause a server room to shut down. In the vast majority of hospital and data center systems, the cooling is provided by a number of water chillers, pumps and cooling towers. The water chillers might be centrifugal, screw or scroll construction. Most commonly, a number of centrifugal chillers provide redundancy and step capacity.
Chillers, pumps and tower fans all utilize three-phase motors to move water, move air, or compress refrigerant. The failure of any of these motors can threaten the operation of the entire chiller system. It is very important that ALL motors are thoroughly checked out before being put in service for the cooling season. While emergency service is available on these machines, it is enormously expensive. Rates of $250/hour/person on nights and weekends are not unheard of, with transportation and parts costs adding a large additional expense.
While there are a number of diagnostic tests that can and should be run on chiller plants before seasonal start up, none is more important than checking the motor resistance with ann insulation tester. The insulation tester will pass a high voltage through the individual motor windings while measuring the winding resistance. A low resistance indicates that the winding is deteriorated and might fail after the device is placed into service.
Commonly, a group of centrifugal chillers provides redundancy and step capacity.
In general, using an insulation tester involves the following steps:
The insulation and windings on cooling tower fan motors must be tested.
The pump is one of three components of a modern chiller plant.
As always, follow all device and meter manufacturer’s recommendations for use.
Which motors in the chiller plant should be tested? The answer is all of them, or as many as possible. This of course will include the chiller and pump motors at a minimum. It also should include chiller oil pump motor and cooling tower fan motors. If either one of these motors fail they may very well end up causing the entire chiller system to fail as well.
The bottom line is that testing motor insulation will identify problems in time to fix them, while they’re still reparable.