Maintenance kits for Siemens 3AF / 3AH Operators
01/01/2005 - Volume II - Issue I
Ever broke a clip or lost a nut doing periodic routine maintenance on medium-voltage vacuum breakers? Siemens has designed 3AF / 3AH maintenance kits (18-831-164-539) which include all consumable materials (clips, washers, bolts, nuts, bushings, pins, screws, etc.) which may be needed when performing periodic inspections and maintenance. Kits can be purchased by contacting Siemens Service Solutions Division at 1-800-347-6659.
When 3AH circuit breakers are operated under "Usual Service Conditions," maintenance and lubrication is recommended at 10 year intervals or at the number of operations indicated in the table below. "Usual" and "Unusual" service conditions for medium-voltage metal-clad switchgear (includes circuit breaker module) are defined in ANSI C37.20.2, section 8.1. Generally, "usual service conditions" are defined as an environment in which the equipment is not exposed to excessive dust, acid fumes, damaging chemicals, salt air, rapid or frequent changes in temperature, vibration, high humidity, and extreme temperatures.
Maintenance and lubrication intervals (ANSI C37.06) usual service conditions maintenance based on the number of circuit breaker closing operations
The definition of "usual service conditions" is subject to a variety of interpretations. Because of this, you are best served by adjusting maintenance and lubrication intervals based on your experience with the equipment in the actual service environment. Regardless of the length of the maintenance and lubrication interval, Siemens recommends that circuit breakers should be inspected and exercised annually.
- Checks of the primary power path
-Inspection of flexible connectors
- Checks of the stored energy operator mechanism
-Maintenance and lubrication
-Manual spring charging check
-Contact erosion check
- Electrical control checks
-Wiring and terminals check
-Secondary disconnect check
-Automatic spring charging check
-Electrical close and trip check
- Vacuum integrity check, inspection and cleaning of breaker insulation.
THESE INSTRUCTIONS DO NOT PURPORT TO COVER ALL DETAILS OR VARIATIONS IN EQUIPMENT, NOR TO PROVIDE FOR EVERY POSSIBLE CONTINGENCY TO BE MET IN CONNECTION WITH INSTALLATION, OPERATION, OR MAINTENANCE. SHOULD FURTHER INFORMATION BE DESIRED OR SHOULD PARTICULAR PROBLEMS ARISE WHICH ARE NOT COVERED SUFFICIENTLY FOR YOUR PURPOSES, THE MATTER SHOULD BE REFERRED TO THE LOCAL SIEMENS SALES OFFICE. THE CONTENTS OF THESE INSTRUCTIONS SHALL NOT BECOME PART OF OR MODIFY ANY PRIOR OR EXISTING AGREEMENT, COMMITMENT, OR RELATIONSHIP. THE SALES CONTRACT IF ANY CONTAINS THE ENTIRE OBLIGATION OF SIEMENS. THE WARRANTY CONTAINED IN ANY CONTRACT BETWEEN THE PARTIES IS THE SOLE WARRANTY OF SIEMENS. ANY STATEMENTS CONTAINED HEREIN DO NOT CREATE NEW WARRANTIES OR MODIFY THE EXISTING WARRANTY.
Check of the primary power path
The primary power path consists of the three vacuum interrupters, the three upper, and the three lower primary disconnects. These components are checked for cleanliness and condition. The vacuum interrupters are also checked for vacuum integrity. Some test engineers prefer to perform the contact erosion check during the manual spring charging check of the operator, since charging of the springs is necessary to place the contacts in the closed position. Also, the vacuum integrity check is usually performed in conjunction with the "High Potential" test. These instructions follow the recommendation that these tests (contact erosion / manual spring charging check, and vacuum integrity / high potential tests) will be combined as described.
Refer to side view drawing of the 3AH circuit breaker with the insulating barriers removed to show the vacuum interrupter and the upper and lower connection pad. All of these components must be clean and free of dirt or any foreign objects. Use a dry lint-free cloth. For stubborn dirt, use a clean cloth saturated with denatured alcohol (except for the vacuum interrupters). For stubborn dirt on a vacuum interrupter, use a damp cloth and then thoroughly dry using a dry lint-free cloth.
Inspection of flexible connectors
Inspect the flexible connectors that connect the bottom movable contacts of the vacuum interrupters to the lower primary disconnect arms for tightness and absence of mechanical damage, burning, or pitting.
Checks of the stored energy operator mechanism
The stored energy operator checks are divided into mechanical and electrical checks for simplicity and better organization. This first series of checks determine if the basic mechanism is clean, lubricated, and operates smoothly without control power. The contact erosion check of the vacuum interrupter is also performed during these tasks.
Maintenance and lubrication
Clean the entire stored energy operator mechanism with a dry, lint-free cloth. Check all components for evidence of excessive wear. Place special attention upon the closing spring crank and the various pushrods and linkages. Lubricate all non-electrical moving or sliding surfaces with a light coat of synthetic grease or oil. Lubricants composed of ester oils and lithium thickeners will be compatible.
Inspect all fasteners for tightness. Both lock-nuts and retaining rings are used. Replace any fasteners that appear to have been frequently removed and replaced.
Manual spring charging and contact erosion checks
Perform the manual spring charging check.
1. Insert the hand charging crank into the manual charge socket at the front of the operator control panel. Turn the crank clockwise (about 45 revolutions) to charge the closing springs. Continue cranking until the "Charged" flag appears in the window of the spring indicator.
2. Press the "Close" pushbutton (black). The contact position indicator on the operator control panel should indicate that the circuit breaker contacts are closed.
3. Perform the contact erosion check. Contact erosion occurs when high fault currents are interrupted or when the vacuum interrupter is nearing the limit of its contact life. Determination of acceptable contact condition is checked by the visibility of the white erosion mark. The white erosion mark is located in the keyway (or slot) on the movable stem of the vacuum interrupter near the plastic guide bushing.
The contact erosion procedure is:
a. Be sure the circuit breaker primary contacts are "Closed."
b. Observe the white erosion mark of each pole. When this mark is visible, contact wear is within the acceptable limits.
4. Press the red "Open" pushbutton after completing the contact erosion check. Visually verify the "Discharge" condition of the closing springs and that the circuit breaker contacts are "Open."
5. Press the black "Close" pushbutton. Nothing should happen. The manual spring check should demonstrate smooth operation of the operating mechanism.
Electrical control checks
The electrical controls of the 3AH circuit breaker should be checked during inspections to verify absence of any mechanical damage and proper operation of the automatic spring charging and "Close" and "Trip" circuits. Unless otherwise noted, all of these tests are performed without any control power applied to the circuit breaker.
Check of the wiring and terminals
- Physically check all of the circuit breaker wiring for evidence of abrasion, cuts, burning, or mechanical damage.
- Check all terminals to be certain they are solidly attached to their respective device.
Automatic spring charging check (control power required)
Repeat the automatic spring charging check described in the section entitled "Installation Checks and Initial Functional Tests."
Primary tasks of this check are:
- The circuit breaker is energized with control power for this check.
- Energize the control power source.
- When control power is connected to the circuit breaker, the closing springs should automatically charge. Visually verify that the closing springs are charged.
Note: A temporary source of control power and test leads may be required if the control power source has not been connected to the switchgear. When control power is connected to the 3AH circuit breaker, the closing springs should automatically charge.
Electrical close and trip check (control power required)
A check of the circuit breaker control circuits is performed while the unit is still connected to the switchgear by the plug jumper. This check is made with the circuit breaker energized by control power from the switchgear.
- Once the circuit breaker springs are charged, move the "Close/Trip" switch to the "Close" position. There should be both the sound of the circuit breaker closing and indication that the circuit breaker contacts are closed by the main contact status indicator.
- As soon as the circuit breaker is closed, the automatic spring charging process is repeated.
After a satisfactory close operation is verified, move the "Close/Trip" switch to the "Trip" position. Verify by both sound and contact position that the contacts are open. Completion of these checks demonstrates satisfactory operation of auxiliary switches, internal relays, and solenoids.
Checks of the spring charging motor
No additional checks of the spring charging motor are necessary.
The life expectancy of vacuum interrupters is a function of the number of interruptions and magnitude of current interrupted. They must also be replaced before certain amount of mechanical operations or when the contacts have been eroded beyond allowed limits. Vacuum tube replacement procedures are detailed in the circuit breaker instruction manual.
The next series of tests (Vacuum Integrity Test and Insulation Tests) involve use of high-voltage test equipment. The circuit breaker under test should be inside a suitable test barrier equipped with warning lights.
Vacuum integrity check (using dielectric test)
A high potential test is used to verify the vacuum integrity of the circuit breaker. The test is conducted on the circuit breaker with its primary contacts in the "Open" position.
Note: Do not use DC high potential testers incorporating half-wave rectification. These devices produce high peak voltages.
Vacuum integrity test procedure
- Observe safety precautions listed in the danger and warning advisories. Construct the proper barrier and warning light system.
- Ground each pole not under test.
- Apply test voltage across each pole for one minute (circuit breaker "Open").
- If the pole sustains the test voltage for that period, its vacuum integrity has been verified.
Note: This test includes not only the vacuum interrupter but also the other insulation components in parallel with the interrupter. These include the standoff insulators and the insulated drive links as well as the insulating (tension) struts between the upper and lower vacuum interrupter supports. If these insulation components are contaminated or defective, the test voltage will not be sustained. If so, clean or replace the affected components and retest.
As-Found insulation and contact resistance tests
As-Found tests verify the integrity of the circuit breaker insulation system. Megger or insulation resistance tests conducted on equipment prior to installation provide a basis of future comparison to detect changes in the protection afforded by the insulation system. A permanent record of periodic As-Found tests enables the maintenance organization to determine when corrective actions are required by watching for significant deterioration in insulation resistance or increases in contact resistance.
Insulation and contact resistance test procedure
- Observe safety precaution listed in the danger and caution advisories for the Vacuum Integrity Check tests.
- Close the circuit breaker. Ground each pole not under test. Use manual charging, closing and tripping procedures.
- Apply the proper AC or DC high potential test voltage between a primary conductor of the pole and ground for one minute.
- If no disruptive discharge occurs, the insulation system is satisfactory.
- After test, ground both ends and the middle of each vacuum bottle to dissipate any static charge.
- Disconnect the leads to the spring charging motor.
- Connect all points of the secondary disconnect with a shorting wire. Connect the shorting wire to the high potential lead of the high voltage tester, and ground the circuit breaker housing. Starting with zero volts, gradually increase the test voltage to 1500 colts rms, 60 Hz. Maintain test voltage for one minute.
- If no disruptive discharge occurs, the secondary control insulation level is satisfactory.
- Disconnect the shorting wire and re-attach the leads to the spring charging motor.
- Perform contact resistance tests of the primary contacts. The resistance should be read between the lower and upper terminal pads.
Inspection and cleaning of circuit breaker insulation
- Perform the Spring Discharge Check on the circuit breaker after all control power is removed. The Spring Discharge Check consists of 1) pressing the red "Open" pushbutton 2) then pressing the black "Close" pushbutton and 3) again pressing the red "Open" pushbutton. All of these controls are on the circuit breaker front panel. Visually verify the "Discharge" condition of the springs.
- Remove any interphase and outerphase barriers if furnished (applicable for certain types only).
- Clean barriers and post insulators using clean cloth and one of the following solvents:
a. No. 2 or No.2 denatured alcohol
b. Isopropyl or isobutyl alcohol.
4. Replace all barriers. Check all visible fasteners again for condition and tightness.
Refer to the Installation Checklist in the "Installation Checklist and Initial Functional Tests" section of the circuit breaker instruction manual. Functional tests consist of performing at least three Manual Spring Charging Checks and three Automatic Spring Charging Checks. After these tests are complete and the springs fully discharged, all fasteners and connections are checked again for tightness and condition.