Eaton 36W-VAC25, Instructions For Installation, Operation And Maintenance

I.B. 3A74499B

Page 28

Effective 11/97

6-4  VACUUM INTERRUPTER INTEGRITY TEST

Vacuum interrupters used in Type W-VAC circuit break-
ers 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 parame-
ters can be readily checked by a one minute ac high
potential test.  (See Table 6.1 for appropriate test volt-
age.)  During this test, the following warning must be
observed:

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 RECOM-
MENDED VOLTAGE AND NORMAL CONTACT
SPACING IS EXTREMELY LOW AND WELL BELOW
MAXIMUM PERMITTED BY STANDARDS. HOWEV-
ER, AS A PRECAUTIONARY MEASURE AGAINST
POSSIBILITY OF APPLICATION OF HIGHER THAN
RECOMMENDED VOLTAGE AND/OR BELOW NOR-
MAL CONTACT SPACING, IT IS RECOMMENDED
THAT ALL OPERATING PERSONNEL STAND AT
LEAST ONE METER AWAY IN FRONT OF THE
BREAKER.

With the breaker open and securely sitting on the floor,
connect all top primary studs (bars) together and 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 appropri-
ate 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
breaker in service.

After the high potential is removed, discharge any elec-
trical charge that may be retained, particularly from the
center shield of vacuum interrupters. To avoid any ambi-
guity in the ac high potential test due to leakage or dis-
placement (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 6.1.

The current delivery capability of 25 ma ac and 5 ma dc
apply when all three VIs are tested in parallel. If individ-
ual VIs are tested, current capability may be one third of
these values.

SOME DC HIGH POTENTIAL UNITS, OPERATING AS
UNFILTERED HALF-WAVE RECTIFIERS, ARE NOT
SUITABLE FOR USE TO TEST VACUUM INTER-
RUPTERS BECAUSE THE PEAK VOLTAGE
APPEARING ACROSS THE INTERRUPTERS CAN BE
SUBSTANTIALLY GREATER THAN THE VALUE
READ ON THE METER.

6-5  CONTACT EROSION AND WIPE

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 con-
tact 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 con-
tact surface of the interrupter. If the mark is not visible,
the pole unit assembly must be replaced (Figures 6-2
and 6-3).

The adequacy of contact wipe can also be determined
by simply observing the indicator on the drive rod
toward the front of the closed breaker. If the wipe is ade-
quate, the entire vertical portion of the indicator "T" will
be visible along with all or a portion of the horizontal part
of the indicator "T" (Figures 6-4 and 6-5). If none of the
horizontal portion shows with the breaker closed, the
wipe is not adequate, and the pole unit assembly must
be replaced.

!

WARNING

!

WARNING

Breaker Rated 
Maximum Voltage

ac 60 Hz

dc

Up to and including
15.0 kV

27 kV

40 kV

Vacuum Interrupter Integrity Test Voltage

Table 6.1  Test Voltage