Eaton 380 VCP-Wind, Инструкция по использованию, эксплуатации и обслуживанию, Страница: 34 / 49

Page 28
I.B. 70A2580H02
Effective November 2012 Style
70A2580H02
Printed in USA
6-4 VACUUM INTERRUPTER INTEGRITY TEST
Vacuum interrupters used in Type VCP-Wind 38kV
Vacuum Circuit Breakers 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 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 DE-
CREASE 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 FOUR METERS AWAY IN FRONT OF THE
CIRCUIT BREAKER.
With the circuit breaker open and sitting solidly 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 circuit 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
circuit breaker in service.
After the high potential is removed, discharge any
electrical charge that may be retained. 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.
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.
A DC test may only be performed if a DC test unit is the
only equipment available.
Issues identified through DC
testing must be verified with an AC test before
taking any corrective actions.
When a DC test is
performed, a high field emission current from a
microscopic sharp spot on one contact can be
misinterpreted as a sign of a vacuum failure. To
minimize misinterpreted test results, the open interrupter
should always be subjected to both voltage polarities.
That is, apply the DC Voltage first, so that one contact of
the interrupter is the cathode, and second, so that the
other contact of the interrupter is the cathode.
A bad interrupter filled with air will have a similarly high
leakage current in both polarities. However, a good
interrupter with a good vacuum level may still have high
leakage currents. Such an interrupter usually has a tiny
sharp spot on one or both contacts that produces a high
field emission current. Such an interrupter would
normally withstand the required AC voltage which is the
definitive test of its vacuum integrity.
CAUTION
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.
Table 6.2 Test Voltage
Vacuum Interrupter Integrity Test
Voltage
Circuit Breaker Rated
Maximum Voltage
AC 60 Hz DC
38 kV rms 60 kV rms 85 kV