IB131006EN
Page 45
Effective 07/2017
6-4 VACUUM INTERRUPTER INTEGRITY TEST
Vacuum interrupters used in Type VCP-W Vacuum
Circuit Breaker Elements are highly reliable interrupting
elements. Satisfactory performance of these devices is
dependent upon the integrity of the vacuum in the
interrupter and the internal dielectric strength. Both of
these parameters can be readily checked by a one
minute ac high potential test. Refer to Table 6.2 (page
41) for the appropriate test voltage. During this test, the
following warning must be observed:
WARNING
APPLYING ABNORMALLY HIGH VOLTAGE
ACROSS A PAIR OF CONTACTS IN VACUUM MAY
PRODUCE 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 CON-
TACT SPACING IS EXTREMELY LOW AND WELL
BELOW MAXIMUM PERMITTED BY STANDARDS.
HOWEVER, AS A PRECAUTIONARY MEASURE
AGAINST POSSIBILITY OF APPLICATION OF HIGH-
ER THAN RECOMMENDED VOLTAGE AND/OR
BELOW NORMAL CONTACT SPACING, IT IS
RECOMMENDED THAT ALL OPERATING
PERSONNEL STAND AT LEAST FOUR METERS
AWAY IN FRONT OF THE BREAKER ELEMENT.
With the breaker element open, 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.
A successful withstand indicates that all interrupters
have a satisfactory vacuum level. If there is a break-
down, the defective interrupter or interrupters should be
identified by an individual test and replaced before
placing the 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 GROUND-
ED 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.
ONLY AC HIGH POTENTIAL TESTS ARE
RECOMMENDED.
WE DO NOT RECOMMEND DC POWER
FREQUENCY WITHSTAND VOLTAGE TEST.
Table 6.2 (Insulation & Vacuum Integrity) Test
Voltage
Breaker Rated
Maximum Voltage
Vacuum Interrupter Integrity Test Voltage
AC 60Hz
Up to and including
5 kV
15 kV
12 kV - 17.5 kV 27 kV
24 kV and 27 kV 45 kV
The current delivery capability of 25 mA ac and 5 mA dc
apply when all three VIs are tested in parallel. If
individual VIs are tested, current capability may be one
third of these values.
Courtesy of NationalSwitchgear.com
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