Instruction Book
Effective: March 2007
Page 21
IB6513C80G
For more information visit:
www.EatonElectrical.com
The vacuum interrupter system on all DHP-VR breakers
utilizes a visible “T” cutout contact loading spring
indicator. This “T” indicator is used to indicate that the
loading springs are maintaining the proper contact
pressure to keep the contacts closed (Figures
5-1
and
5-
2
).
5-1.1 VACUUM INTERRUPTER
Type DHP-VR breakers utilize vacuum interrupters for
interruption and switching functions. Vacuum interruption
offers the advantages of enclosed interrupters, reduced
size and weight, short interrupting time, long life, reduced
maintenance, and environmental compatibility.
Arc interruption is simple and fast. In the closed position,
current flows through the interrupter. When the contacts
are opened, the arc is drawn between the contact
surfaces. It is rapidly moved around the slotted contact
surfaces by a selfinduced magnetic force, which prevents
gross contact erosion, as well as the formation of hot
spots on the contact surfaces. The arc burns in an
ionized metal vapor, which continually leaves the contact
area and condenses on the surrounding metal shield.
At current zero, the arc is extinguished and vapor
production ceases. Very rapid dispersion, cooling,
recombination, and deionization of the metal vapor
plasma, together with the fast condensation of metal
vapor products, cause the vacuum to be quickly restored.
Hence, the opened contacts withstand the transient
recovery voltage.
5-1.2 CONTACT EROSION INDICATOR
The purpose of the contact erosion indicator is to monitor
the erosion of the vacuum interrupter contacts, which is
very minimal over time with Cutler-Hammer vacuum
interrupters utilizing copper-chrome contact material. If
contact erosion reachers 1/8 inch, the interrupter must be
replaced. A contact erosion indicator mark is located on
the moving stem of the interrupter (Figures
6-2
and
6-3
).
In order to determine if the contacts have eroded to the
extent that the interrupter must be replaced, close the
breaker and observe the erosion mark placed on each
moving stem from the rear of the breaker. If the mark on
the interrupter stem is visible, the interrupter is
satisfactory. It the mark is no longer visible, the
interrupter assembly must be replaced.
The erosion indicator is easily viewed from the rear on
the 7.5 or 15kV. designs. Because of the nature of the
5kV. DHP-VR inverted design, the erosion indicator is
not easily viewed, although it is possible with the use of
a light and a dental type mirror.
5-1.3 “T” CUTOUT LOADING SPRING INDICATOR
Since the “T” cutout loading spring indicator is part of all
DHP-VR breaker designs, an additional method is
provided that will indicate conditions within the
interrupter, as well as the overall system condition. The
visible “T” indicator is used to indicate whether the
loading springs are maintaining the proper contact
pressure to keep the contacts closed. Severe contact
erosion would lead to an unacceptable indication from
the “T” indicator (Figures
6-4
and
6-5
).
5-1.4 CONTACT WIPE AND STROKE
Contact wipe is the indication of (1) the force holding the
vacuum interrupter contacts closed and (2) the energy
available to hammer the contacts open with sufficient
speed for interruption.
Stroke is the gap between fixed and moving contacts of a
vacuum interrupter with the breaker open.
The circuit breaker mechanism provides a fixed amount
of motion to the operating rods. The first portion of the
motion is used to close the contacts (i.e. stroke) and the
remainder is used to further compress the preloaded
wipe spring. This additional compression is called wipe.
Wipe and stroke are thus related to each other. As the
stroke increases due to the erosion of contacts, the wipe
decreases. A great deal of effort has been spent in the
design of all Culter-Hammer vacuum breakers, in order to
eliminate the need for field adjustments of wipe or stroke.
CAUTION
THERE IS NO PROVISION FOR IN-SERVICE
ADJUSTMENTS OF CONTACT WIPE AND STROKE.
ALL SUCH ADJUSTMENTS ARE FACTORY SET AND
SHOULD NOT BE ATTEMPTED IN THE FIELD.