American Magnetics Current Leads for Cryogenic Systems Manual - Manual (Page 6)

Rev. 5, July 2003 Page 6 of 10
C. Connect the bus bars to the bottom current lug by wrapping the jointed region with a
small diameter tinned copper wire. The jointed region can now be soldered using
ordinary eutectic lead-tin or other low melting point solder.
CAUTION: A heat sink should be provided between the bus bar
connection and the vapor tube to keep the temperature below
400
° F. The vapor tube is constructed with a tin-silver solder that
melts at 430 ° F. Temperatures above 430 ° F could result in
damage to the current lead.
NOTE: It is desirable to make as good an electrical connection
as possible between the current lead connection flange and the
load. A poor electrical connection may cause excessive helium
loss.
D. Electrical connections to the top current lug should be made by bolting or clamping
cables with proper terminations.
WARNING: Hazardous voltages may be present. Verify all power supplies
are de-energized before making or breaking electrical connections. NEVER
disconnect leads when any current is flowing through them. Attempting to do so
could result in FATAL ELECTRIC SHOCK.
WARNING: Current leads should be connected and
disconnected only by qualified personnel.
E. During cooldown, helium gas should be vented through the vapor cooled current leads. A
short length of rubber tubing attached to the top of the current lead (vapor outlet), pointed
downwards will create a helium gas trap and minimizes the potential for allowing air into
the system.
IV. OPERATION
The helium vapor cooled current leads are a passive system component. They are ready to carry
the current to the load when properly installed. Upon initial operation and periodically thereafter
the helium gas flow through the current leads should be checked and the flow balanced (i.e.
equalized). Flow is adjusted by restricting, by any suitable means, the lead with higher gas flow.
During normal operation, a small amount of ice or frost may develop around the top of the
current lead.
The voltage across each lead (from the top of the lead to the appropriate magnet terminal) may be
monitored to avoid operating with an overheated condition. A voltage drop of <0.1 volt per lead
at the rated current is typical and should not be exceeded.