31
Instruction Book
IB182012EN March 2017 www.eaton.com
50DH-VR-50AXU / 50XU / 75U / 75ARU - 600 / 1200A
Replacement Circuit Breaker
6.8 PRIMARY CIRCUIT RESISTANCE CHECK
The main contacts of the VR-Series circuit breaker are inside
the vacuum chamber where they remain clean and require no
maintenance at any time. Unlike most typical circuit breaker designs,
the VR-Series design uses a highly reliable and unique flexible clamp
design that eliminates the need for lubrication and inspection for
wear.
The DC electrical resistance of the primary circuit may be calculated
by measuring the voltage drop across the circuit. This test should
be performed with a low voltage, direct current (DC) power supply
capable of delivering no less 100A DC.
•
To check the primary circuit resistance:
•
Remove the circuit breaker from the switchgear
•
Close the breaker
•
Pass at least 100A DC from terminal to terminal of each pole
unit in the closed position
•
Measure the voltage drop across the terminals.
The resistance can be calculated from Ohm’s Law and is expressed
in micro-ohms. Repeat for the remaining two poles.
The resistance should not exceed the factory test levels more than
200% as stated in IEEE C37.09. Factory test levels are recorded on
the circuit breaker test form, which is included with the breaker. If
measurements exceeds 200%, contact the manufacturer.
Resistance conversion for Temperature
R
conversion
= R
Factory
(1 + (T
Field
- T
Factory
)
r
)
R
conversion
= Resistance correction for temperature based from the
factory resistance measurement.
R
Factory
= Resistance measurement from the factory.
T
Field
= Temperature measurement in the field.
T
Factory
= Temperature measurement from the factory.
r
= Copper resistivity temperature coefficient.
r
= 0.0039 Copper Resistivity Temperature Coefficient / Deg C
r
= 0.002167 Copper Resistivity Temperature Coefficient / Deg F
6.9 MECHANISM CHECK
Make a careful visual inspection of the mechanism for any loose
parts such as bolts, nuts, pins, rings, etc. Check for excessive wear
or damage to the circuit breaker components. Operate the circuit
breaker several times manually and electrically. Check the closing
and opening times to verify that they are in accordance with the
limits in Section 4.
6.10 LUBRICATION
All parts that require lubrication have been lubricated during the
assembly with molybdenum disulphide grease. Eaton No. 53701QB.
No other lubrication in this mechanism is required. For smooth
racking operation, lubricate the gears of the racking mechanism with
Eaton 53701QB or equivalent.
