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5kV, 7.5kV, & 15kV DHP-VR
Replacement Circuit Breaker
4.8.2 MOC AND TOC OPERATIONS
A mechanism attached to the right side of the DHP-VR breaker
engages a channel member of the Mechanism Operated Cell Switch
(MOC) located in the switchgear cel. This mechanism permits the
contacts of the MOC Switch to be correlated with the breaker's
contact position.
NOTICE
ALL TYPE DHP-VR BREAKERS UTILIZE THE DHP-VR SURE CLOSE
MECHANISM TO CONTROL MOC VELOCITY AND CLOSELY MIMIC THE
DYNAMICS AND VELOCITIES OF OLDER BREAKERS. IT IS IMPERATIVE
THAT THIS MECHANISM BE ADJUSTED TO MATCH THE NUMBER OF MOC
SWITCHES (FROM 0 TO 3) MOUNTED IN THE CELL. ALWAYS MAKE SURE
THE MECHANISM IS PROPERLY ADJUSTED BEFORE ANY ATTEMPT IS
MADE TO INSERT THE BREAKER INTO THE CELL.
IN ADDITION, THE MOC PANTOGRAPH MUST BE CHECKED BEFORE ANY
ATTEMPT IS MADE TO INSERT THE BREAKER INTO THE CELL. DETAILED
PROCEDURES FOR EACH TEST ARE OUTLINED IN SECTION 5 OF THIS
MANUAL.
The cell mounted Truck Operated Cell Switch (TOC) is operated
by movement of the breaker truck into or out of the Connected
position.
4.8.3 OPERATIONS COUNTER
All DHP-VR breakers are equipped with a mechanical operations
counter (Figure Set 3.3). As the breaker opens, the linkage
connected to the pole shaft lever advances the counter reading by
one.
4.8.4 RACKING DEVICE
The purpose of the racking device is to move the breaker between
the Test and Connected positions. On the 7 .5 or 15kV DHP-VR, the
racking mechanism is located in the mechanism, while it is located
in the breaker truck on the 5kV DHP-VR. The racking nut is fastened
securely to the guide tube and is loosely retained in a housing
fastened to the extreme rear of the breaker chassis (Figures 3.4, 3.6,
and 3.8).
The operation consists of engaging the rotatable racking nut on the
circuit breaker with the racking screw mounted on the rear wall of
the cell. By traversing the racking nut along the racking screw, the
breaker is moved between positions within the switchgear housing.
The guide tube is slotted lengthwise for a distance about equal
to the travel distance of the breaker. The racking shaft has two
rectangular hardened keys welded to it which slide in the guide tube
slot. Thus, as the racking shaft is rotated, the guide tube and nut also
rotate.
As the breaker is racked in by clockwise rotation, the keys on the
racking shaft move toward the end of the guide tube slot. As the
rear key comes out of the slot, the racking shaft turns freely and the
breaker moves no further.
The end of the guide tube is shaped like a steep-pitch one-turn
screw thread so that when the racking shaft is rotated counter-
clockwise, the rear key will catch and enter the slot and rotate the
guide tube and nut, withdrawing the breaker. At the end of the
travel, the nut disengages from the screw and is spin free.
26
Instruction Book
IB182017EN February 2017 www.eaton.com
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