It is essential that both classroom and hands-on equipment training accompany any installation of a new replacement, retrofill, or retrofit circuit breakers. The operator and maintenance technicians must be trained in all tasks, which they are expected to perform task relating to operation and maintenance of the equipment. They must also be trained in how the circuit breaker must properly interface with the existing metal-clad switchgear.
In addition to training, a check out must be performed to confirm that the circuit breaker was not damaged in shipment, and is compatible with the existing cell. During this check out, adjustments may be required to match the two devices.
A physical inspection and mechanical checkout of the circuit breaker and cell must be performed to confirm that the new circuit breaker’s nameplate is consistent with the existing metal-clad switchgear rating, and that the circuit breaker and cell are functioning separately. Typically, these tests should include all tests recommended in the circuit breaker manufacturer’s instruction bulletin. As a minimum, the circuit breaker should undergo an inspection, functional checks, a circuit breaker timing test, and a vacuum integrity test (with a vacuum integrity tester or an ac high potential tester). Moreover, a high potential test of the circuit breaker is required to assure phase to phase and phase to ground dielectric integrity. Once these checks are completed, confirm that the replacement breaker properly racks into and out of the cell.
The replacement circuit breaker has been designed to be compatible with the existing cell, but checks must be made to fit the circuit breaker with the specific metal-clad switchgear compartment.
For example, this may require the adjustment of the front cover to minimize gaps and overlaps. Once the replacement circuit breaker cover matches up to the existing equipment, the ground shoe (con-nection) and primary disconnects should be checked to confirm that the circuit breaker is engaging the metal-clad switchgear fully. To confirm the circuit breaker’s engagement, apply a very thin layer of the manufacturers recommended stab grease to the circuit breaker’s connections. De-energize the metal-clad switchgear and rack the replacement circuit breaker in and out of the cell without closing the circuit breaker. Inspect the primary stabs and the ground shoe (circuit breaker ground connection) for uniform distribution of the lubricant. If the metal-clad switchgear can remain de-energized for the time needed, the insertion test can be followed by a ductor test (dc resistance test) from the line side to load side of each cell. With the circuit breaker installed and closed, confirm resistance and assure that the primary disconnects are in good contact with the metal-clad switchgear compartment. This step is impossible if the metal-clad switchgear cannot be de-ener-gized, but it is important to remember that the circuit breaker primary disconnects are only part of the total current path. Even though the circuit breaker may be in “new” condition, if the contact surfaces in the metal-clad switchgear are dirty or corroded the resulting connection between the circuit breaker and metal-clad switchgear may be highly resistive. Consequently, this will lead to the over-heating of the connection, and a possible premature failure of the connection. Once the ground shoe connection and primary disconnects have been checked, the secondary control disconnect should be checked to confirm that the metal-clad switchgear secondary disconnect engages properly and that the metal-clad switchgear compartment wiring matches the replacement circuit breakers.
The control wiring of some of the older solenoid operated circuit breakers and metal-clad switchgear may need modification in order for the new, stored-energy mechanism to operate properly. Some equipment designs and control schemes do not have a steady-state control voltage available at the secondary disconnect that is required for the stored energy feature to operate. This is predominately true for designs that have the closing, or “X” relay mounted in the metal-clad switchgear compartment. In the external closing relay designs, the closing power was
only applied momentarily to the circuit breaker, simply long enough for the circuit breaker to close and latch.
Normally the power is removed upon completion of the closing operation by the action of a circuit breaker’s mounted cutoff switch that deenergizes the “X” directly, or energizes the anti-pump, or “Y” relay which in turn deenergizes the “X.” The preferred method for supplying the required charging power to the circuit breaker is the use of unused spare auxiliary contact secondary disconnects. The ultimate goal in a multi unit replacement is to identify a common terminal in all circuit breaker compartments in order to maintain interchangeability between the replacement circuit breakers themselves, and also between the old circuit breakers if interchange-ability with the existing circuit breaker is required. If this cannot be achieved, a blocking or rejection feature must be added or modified to prevent interchange of the circuit breakers. It has also been a field practice to install a jumper around the normally open “X” contact to supply steady state power to the circuit breaker. If this is done, inserting the original circuit breaker into the modified compartment may result in the unintentional closing of the circuit breaker. This presents a hazardous condition that must be avoided by modifying the blocking or rejection features to prevent insertion of the old circuit breaker into the modified compartments.
It should also be noted that most of the old solenoid operated circuit breakers requires substantially higher current to operate than that of the requirements of a replacement circuit breaker. This means that the control fuses in the closing circuit were normally 60 amps or greater. It is also prudent to protect the charging motor circuit with fuses appropriate for this load. These fuses can either be integral to the replacement circuit breaker, or located upstream in the metal-clad switchgear cubicle.
The original circuit breaker may also have tripping current requirements far above the requirement of the replacement circuit breaker. These trip coils were normally wound with larger wire in order to accommodate the higher current. Due to the higher thermal capability of these coils, fairly high trickle currents flowing in these coils for healthy coil monitoring could be tolerated without damage to the coil or any negative impact on circuit breaker operation. This may not be the case with the replacement circuit breaker. In a worst case, excessive current flowing through the trip coil may overheat the coil or cause partial operation of the coil.
Either of these may negatively affect proper circuit breaker operation. Control circuit coordination of the new replacement circuit breaker and the old circuit breaker must be carefully considered in cooperation with the user and manufacturer in order to assure long-term proper operation of the replacement circuit breakers.
Also, relay target setting should be reviewed to insure that the targets will operate by the reduced trip current of the new circuit breaker.
The last step is to verify that the insertion and withdrawal interlock functions must be verified. Although these interlocks are normally adjusted and checked at the factory, the existing compartment may not be within originally specified tolerances. Deviation from originally specified dimensions may be due to wear, original installation deviations to specification, or field modifications made throughout the service life of the equip-ment. Adjustments may be required to the circuit breaker and/or the compartment to ensure proper operation of these critical interlocks. For further details, contact Powell Electrical Manufacturing Company.
Table V. Trouble Shooting Topics
A, B
Adjustments close latch 29 latch check switch 29
primary and secondary trip latches 29 ratchet wheel holding pawl 29 Annex
commissioning 43 Anti-pump relay 18
C, D
Cam and fundamental linkage positions 13 Circuit breaker
inserting into switchgear 24 Control circuit
operation sequence 19 typical DC control scheme 18
E, F
Electrical operation 29
G, H
Ground contact 11
I, J, K
Installation handling 20 receiving 20 storage 20 Instruction bulletin
conflict with other documents 5 other items of caution 5 purpose 5
scope 5
website information 6 Interlocking
cell interlocks 17 levering-in interlock 16
L
Levering-in device 11 Levering-in interlock 16 Lubrication
description 27 illustrations 31, 32
M, N
Maintenance description 26
inspection and cleaning 27 Maintenance schedule 26 Mechanism and trip linkages 13 Mechanism area
adjustments 29 description 27 electrical operation 29 lubrication 27
main closing spring installed 28 main closing spring removed 28 mechanical operation 27 slow closing of mechanism 28 Miscellaneous parts
replacement assemblies 37, 38 Motor cutoff switch 17
O
Operating solenoids 17
Optional maintenance procedures high potential tests 34 primary resistance check 34
P, Q
Placing into service
control voltage insulation integrity 23 description 22
high voltage insulation integrity 22 vacuum integrity 22
Powell Apparatus Service Division 6, 26, 35
information 22
Powell Electrical Manufacturing Company 6
Primary resistance check 34 Putting into service
commissioning 22
control voltage insulation integrity 23 description 22
dimensional check 23 electrical operation 23
high voltage insulation integrity 22 mechanical operation check 23 vacuum integrity 22
PVDST description 9
exterior component illustrations 12 interior components illustrations 14
R
Renewal parts control devices 36 description 35
miscellaneous parts 37, 38 ordering instructions 35
sliding contact finger assembly 36 vacuum interrupter assembly 36 Replacement procedures
anti-pump relay assembly 41 charging motor assembly 41 closing coil assembly 39 latch check switch assembly 41 motor cutoff switch assembly 42 primary shunt trip coil assembly 40 secondary shunt trip coil assembly 40 sliding contact finger assembly 39 undervoltage device assembly 40 vacuum interrupter assembly 39 Rollout truck 11
S
Safety 6 Safety labels 8 Secondary contacts 24 Shutter lift 15
Stored energy mechanism 9
T, U
Testing
AC or DC high potential test (hipot) 22, 23
Trouble shooting topics 45
V
Vacuum interrupter and contact area sliding contact finger wear 33 vacuum integrity 33
vacuum interrupter contact erosion 33 Vacuum interrupters 17
W
8550 MOSLEY DRIVE · HOUSTON, TEXAS 77075 USA PHONE (713) 944-6900 · FAX (713) 947-4453
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