Vanguard Accu-Trans - Manual (Page 7)

Accu-Trans

Operating Procedures
3
1.0 INTRODUCTION
1.1
Applicability
This manual applies to a second-generation
Accu-Trans™ (Series II, henceforth, called
the Accu-Trans), part number VIC-80000-
S2 manufactured by the Vanguard
Instruments Co. A prior manual supports a
first generation Accu-Trans (i.e., a Series I
configuration).
1.2 Supersedure Notice
This Operator’s manual is the basic issue for
the Accu-Trans and does not supersede any
previously published manual.
1.3 General Description
Vanguard Instruments Company produces
the Accu-Trans, a microprocessor-controlled
winding resistance meter that measures low
resistances of a transformer’s inductive
windings, in a range from 1 micro-ohm to
200 ohms with very high accuracy. This
instrument can also measure any low
milliohm resistance (e.g., the contact
resistance of a circuit breaker).
This Accu-Trans is simple-to-use; it features
keypad controls and an alpha/numeric
display of the measured resistance, test
current, and operator-entered test parameters
and identifying data.
The Accu-Trans uses a 48-volt dc power
supply and a special current-regulator to
quickly measure transformer-winding
resistances. A typical single- phase 400MVA
transformer winding resistance can be
measured in less than 3 minutes. To ensure
operator safety, the Accu-Trans
automatically discharges the energy stored
in the transformer at the end of each test.
A built-in thermal printer prints test results
on 2.5-inch-wide thermal paper. Resistance
and test current display on a 4-line by 20-
character, back lighted LCD. Up to 63
records (96 readings each) can be stored in
the Accu-Trans FLASH EEPROM. The
user can recall stored reports for printing. A
RS-232C serial interface port is provided for
diagnostic testing and down loading test
records.
The Accu-Trans is field-portable, rugged; it
features simple, easy operation by first-time
users with little training.
1.4 Functional Description
The Accu-Trans’s operation is based on the
electrical relationships described by Ohm’s
law: R=V/I, where I is a known current and
V is the dc voltage measured across the
unknown resistance (typically, a circuit-
breaker’s contacts). The value of the
unknown resistance under test is the direct
function of the measured voltage divided by
the current and being calculated by the
microprocessor. Resistance reading is then
displayed on a back-lighted 4 line by 20
character LCD.
The Accu-Trans’ 48V dc power supply
applies up to 2 amperes test current to the
device under test. Accu-Trans voltmeter test
leads are run separately from the current-
bearing test leads to the resistive load; thus,
voltages are measured at the terminals of the
resistance being measured, eliminating error
from the I•R voltage drop in the test current
cables. The Accu-Trans makes precise
micro-ohm measurements possible without
calculating compensation for test-current-
lead resistance errors.
A built-in discharge circuit automatically
discharges the energy stored in the
transformer at the end of each test.
1.5 Furnished Accessories
The Accu-Trans is shipped with two 45-foot
test cables with “quick disconnect” type test
plugs on the unit end and battery-type
clamps at the test load end. One power cord,
one ground cable, and a cable-carrying bag.