4
Types NR, NRV Maintenance Instructions
Figure 5.
Typical connection diagram for three-wire control.
MAINTENANCE
Frequency of Maintenance
Because these switches are applied under widely varying oper-
ating and climatic conditions, maintenance intervals are best
determined by the user based on actual operating experience.
Cooper Power Systems recommends the switch be inspected
and serviced yearly until experience indicates a more advanta-
geous schedule. In no case should the service interval, between
periodic maintenance and inspection, extend beyond 1200 oper-
ations.
WARNING:
Continuous use of a switch without
regular routine inspection and repair, can affect relia-
bility. This could lead to equipment failure and possible per-
sonal injury.
!
CAUTION:
Never use volatile solutions, deter-
gents, or water-soluble cleaners.
!
Each periodic maintenance inspection should include at least
the following:
1. By-pass and remove the switch from service.
2. Inspect external components.
A. Clean the bushings and inspect for chips, cracks and
breaks. Replace as necessary, following procedure in
“Shop Repair Procedures—Bushings” section.
B. Check for paint scratches and other mechanical dam-
age. Paint to inhibit corrosion.
3. Perform a dielectric withstand test to determine the insula-
tion level. Follow procedures in “Insulation Level Withstand
Tests” section.
4. Loosen the head bolts and remove the mechanism from
the tank. Be careful not to damage the gasket if the tank
and head must be pried apart to break the seal.
5. Allow the oil to drain off the mechanism.
6. Clean the intemal components:
A. Remove all traces of carbon by wiping with a clean, lint-
free cloth.
B. Flush the intemal components with clean transformer
oil.
7. Check the moving and stationary contacts.
A. Dress slight pitting and discoloration with crocus cloth.
B. Replace both the moving and stationary contacts if they
are severely eroded. Follow procedures in “Shop Repair
Procedures—Contacts” section.
NOTE: The contacts should be replaced before the erosion of
the load current transfer surfaces impairs their effectiveness.
8. Manually close and trip the switch several times to check
that all components perform properly.
9. Inspect the tank wall liners. Soft or spongy areas indicate
that water has been absorbed. Replace liners if this condi-
tion is detected or even suspected.
10. Check the dielectric strength of the insulating oil.
A. A sample taken near the bottom of the tank should have
a dielectric strength of not less than 22 kV.
B. Low dielectric strength indicates the presence of water
or carbon deposits; replace the oil. (See “Oil Condition”
section.)
11. If oil must be replaced, drain the tank and discard the tank
wall liners.
12. Thoroughly clean out all sludge and carbon deposits and
rinse the tank with clean oil.
13. Install new tank wall liners and fill the tank with clean, new
insulating oil to within one inch of the top of the tank
flange. Oil capacity is approximately 1.5 gallons.
NOTE: Use only new, or like-new reconditioned transformer oil
which conforms to the specifications in Cooper Power Systems
Reference Data R280-90-1, “Oil Specifications and Test.”
14. Clean and examine the head gasket. Replace if it is dam-
aged or has taken a permanent set.
15. Clean the head gasket seat and retank the switch.
A. Replace the head bolts and torque to 10-14 ft-lbs. Apply
clamping force gradually and equally, in rotation, to
each bolt to achieve an evenly distributed gasket seal-
ing pressure.
16. Electrically operate the switch to check for proper opera-
tion. See “Operating Instructions — Electrical operation”
section.
17. Repeat the high voltage dielectric withstand test (Step 3)
to make sure the dielectric clearances within the tank have
not been compromised.
OPERATING INSTRUCTlONS
Electrical Operation
The switch may be opened and closed electrically by applying
rated control voltage to the proper terminals of the actuator
terminal block. Figures 5, 6, and 7 show the connection dia-
grams for the three electrical operating modes.
