Instruction Book
Page 50
Effective: May 2016
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IB131017EN
WARNING
APPLYING ABNORMALLY HIGH VOLTAGE ACROSS
A PAIR OF OPEN CONTACTS IN VACUUM MAY
PRO-DUCE X-RADIATION. THE RADIATION MAY
INCREASE WITH THE INCREASE IN VOLTAGE
AND/OR DECREASE IN CONTACT SPACING. X-
RADIATION PRODUCED DURING THIS TEST WITH
RECOMMENDED VOLTAGE AND NORMAL
CONTACT SPACING IS EXTREMELY LOW AND
WELL BELOW MAXIMUM PERMITTED BY
STANDARDS. HOWEVER, AS A PRECAUTIONARY
MEASURE AGAINST POSSIBILITY OF APPLICATION
OF HIGHER THAN RECOMMENDED VOLTAGE
AND/OR BELOW NORMAL CONTACT SPACING, IT
IS RECOMMENDED THAT ALL OPERATING
PERSONNEL STAND AT LEAST ONE METER AWAY
IN FRONT OF THE BREAKER.
With the circuit breaker open and securely sitting on the
floor or secured in a fixed position, connect all top primary
studs (bars) together and to the high potential machine
lead. Connect all bottom studs together and ground them
along with the breaker frame. Start the machine at zero
potential, increase to appropriate test voltage and
maintain for one minute.
Successful withstand indicates that all interrupters have
satisfactory vacuum level. If there is a breakdown, the
defective interrupter or interrupters should be identified by
an individual test and replaced before placing the circuit
breaker in service.
WARNING
AFTER THE HIGH POTENTIAL IS REMOVED, AN
ELECTRICAL CHARGE MAY BE RETAINED BY THE
VACUUM INTERRUPTERS. FAILURE TO DISCHARGE
THIS RESIDUAL ELECTROSTATIC CHARGE COULD
RESULT IN AN ELECTRICAL SHOCK. ALL SIX
PRIMARY TERMINALS AND THE CENTER RING OF
EACH VACUUM INTERRUPTER OF THE CIRCUIT
BREAKER SHOULD BE GROUNDED TO REDUCE
THIS ELECTRICAL CHARGE BEFORE COMING IN
CONTACT WITH THE PRIMARY CIRCUIT.
To avoid any ambiguity in the ac high potential test due to
leakage or displacement (capacitive) current, the test unit
should have sufficient volt-ampere capacity. It is
recommended that the equipment be capable of
delivering 25 milliamperes for one minute.
Although an ac high potential test is recommended, a dc
test may be performed if only a dc test unit is available. In
this case the equipment must be capable of delivering 5
milliamperes for one minute to avoid ambiguity due to
field emission or leakage currents and the test voltage
shall be as shown in Table
6.2
Table 6.2 Test Voltage
Breaker Rated
Maximum Voltage
Vacuum IMenupter IMegrlty Test Voltage
at 6o Hz
dc
4.76 kV
20 kV
28 kV
8.25 kV
20 kV
28 kV
15.0 kV
27 kV
40 kV
The current delivery capability of 25 ma ac and 5 ma
dc apply when all three Vls are tested in parallel. If
individual Vls are tested, current capability may be one
third of these values.
WARNING
SOME DC HIGH POTENTIAL UNITS, OPERATING
AS UNFILTERED HALF-WAVE RECTIFIERS, ARE
NOT SUITABLE FOR USE TO TEST VACUUM
INTERRUPTERS BECAUSE THE PEAK VOLTAGE
APPEARING ACROSS THE INTERRUPTERS CAN
BE SUBSTANTIALLY GREATER THAN THE VALUE
READ ON THE METER.
6-4 CONTACT EROSION
Since the contacts are contained inside the interrupter,
they remain clean and require no maintenance.
However, during high current interruptions there may be
a minimum amount of erosion from the contact
surfaces. Maximum permitted erosion is 3 mm. To
determine contact erosion, close the breaker and
observe the vacuum interrupter moving stem from the
rear of the breaker. If the mark on each stem is visible,
erosion has not reached maximum value thus
indicating satisfactory contact surface of the interrupter.
If the mark is not visible, the pole unit assembly must
be replaced (Figure
6-1
).
6-5 CONTACT WIPE
To check contact wipe, close the breaker and observe
the drive insulators from the rear of the breaker (Figure
6-2
). Since the indicator to be observed is in the lower
rear portion of each pole unit assembly, a flashlight
should be used. Refer to Figures
6-3
and
6-4
for
graphical representations of satisfactory and
unsatisfactory contact wipe conditions. If the identified
wipe indicator is observed to be below the top surface
of the drive insulator as shown in Figure
6-3,
the
contact wipe is satisfactory. If the wipe indicator is
observed to be flush with or protruding out past the top
surface of the drive insulator as shown in Figure
6-4,
the contact wipe is unsatisfactory. The pole unit
assembly must be replaced when an unsatisfactory
wipe condition is observed.
