Maintenance Flashcards
(43 cards)
What is the primary goal of an electrical maintenance program?
Achieving maximum electrical system reliability at the least cost 
Name three types of information that should be included in the equipment records for a maintenance program 
-nameplate information
-equipment manufacturer manuals
-inspection checklist
-records of past maintenance
-records of cost
Calling and scheduling maintenance electricians to test N/or repair a breaker every year because the manufacturer recommends it is an example of a ___________ model.
Periodic maintenance
What is the purpose of acceptance testing?
An acceptance test will review issues, allowing the equipment to be corrected or returned. Testing after insulation allows checking for any damage or abnormalities incurred during insulation.
Disadvantages for each type of maintenance program.
Corrective : more costly on downtime, overtime work, unexpected supplier shortages
Periodic: wasting expenses if schedules are frequent
Predictive: requires investment of proper diagnostic/ testing equipment plus staff
Calling and scheduling maintenance electricians to repair a faulted transformer is an example of_______ model.
Corrective maintenance
What is the purpose of benchmarking or commissioning tests?
Checking for any damage or abnormalities incurred during installation
Today is the date scheduled to perform maintenance test and repairs on a service transformer. What three steps must be done before starting the as found test?
-Shut down all relevant equipment
-clearance points should be locked/ tagged out
-temporary grounds should be installed
Periodically checking and recording the insulation resistance of a motor and scheduling a repair when it drops suddenly is an example of __________ model
Periodic maintenance
Why is it important to conduct as found and as left test when performing maintenance on a given piece of electrical equipment?
To ensure that all pieces of equipment will function as they should once being returned to service
An insulation test on an outdoor transformer reports and insulation resistance of 2.2 M in June. The last result from six months ago reported 3.1 M. What needs to be done before concluding there is a problem.
Check the outside temperature, humidity, and equipment temperature records at the time both readings were taken
An insulation tester measures a value of infinity ohms. What can you conclude from this reading?
It simply means that the meter can’t measure it at the current selected scale
An insulation test is performed on a motor right after being switched out of service and measures 0.3 M homes. The winding temperature is measured at 60°. What is the approximate resistance corrected to 20°?
0.3x2x2x2x2=4.8 M ohms
What are three general factors that cause insulation to the degrade?
Mechanical damage, contamination, heat
What is the rate temperature rise of class B insulation?
130°C
A motor with class B insulation is specified with a typical lifespan of 30 years. What is it approximate lifespan if it is operated at a winding temperature of 150°C?
30/2=15 years/2 =7.5 years
Why would you want to conduct an insulation test while a motor is winding are still warm?
-As equipment cools, it can build up condensation causing resistance to drop
-to get an accurate picture of insulation resistance in operating conditions
A 480 V motor should have its insulation tested with voltage range of what ?
500-100V
A hand cranked me shows a resistance reading that starts low, but slowly climbs over the next minute. What is the cause of this climb and resistance?
Because of different types of current components, present when testing installation and capacitance built up in the installation
What is the maximum temperature of class H insulation?
180°C 
What are the four current components that are present during an insulation test?
-capacitive charging current
-absorption current
-conduction current
-surface leakage current
What is the recommended ratio of test voltage first step voltage testing?
A ratio between 1 to 5 or greater 
What types of insulation do not require temperature correction?
Step voltage test, dielectric absorption test, polarization index
What must be done between the 2 60 second tests when performing a step voltage test?
The equipment must be discharged
