Detail TEST BLOCK MMLG 01 AREVA & ALSTOM
• Test block can be mounted adjacent to
Midos modular relays and systems
• Test block obviates need to disturb
protective system wiring for testing
• Monitoring, isolation and secondary
injection testing are simplified and
• MMLG 01
Standard test block
• MMLG 02
Special test block designed for use in
busbar protection schemes
• MMLG 03
Horizontal version of MMLG 01
• MMLG 04
Horizontal version of MMLG 02
• MMLB 01
Multi-finger test plug
• MMLB 02
Single-finger test plug
MMLG 01 and MMLB 01
terminals 13 and 14 must not be used
for CT connections since they may
present a safety hazard.
Although designed within the Midos
range these test blocks offer facilities for
monitoring and secondary injection
testing any power system protection
scheme, when used with the multifingered
test plug type MMLB 01.
A single-finger test plug, type MMLB 02 is
also available for monitoring the current
flow in individual circuits which have
been routed through the test block.
Before use, the insulation of the
flying leads should be visually
checked for damage.
The continuity of the shorting plug/ wire
links, and the state of their insulation,
should be checked before insertion into
the MMLG 01 test block.
Description, Installation and
The Safety Statements Publication R5948
should be read before installing or using
the test block ( MMLG) or test plug
( MMLB) .
Note. Terminals 13 and 14 have
short contact fingers which must
not be used for CT connections.
Refer to the Mechanical Details section
for a description of the test block
( MMLG) and test plug ( MMLB) . The
MMLG cover, when in place, provides
protection from electric shock hazard.
Care should be taken to ensure that
MMLG 01 covers are correctly
orientated when replaced.
The test block carries 14 circuits, each of
which is brought out to separate pairs of
terminals at the rear of the case.
Each circuit comprises a pair of internal
contacts which are normally sprung
together to complete the circuit link
through the block when the associated
protective equipment is in normal
Access to these internal circuits for
testing purposes, can be gained by
removing the front cover. A metallic
probe secured to the inside face of the
MMLG 01 cover is automatically
withdrawn when the cover is removed,
so interrupting the circuit between
terminals 13 and 14. By routing the
main dc auxiliary supply to the
protection scheme or relay through this
circuit, removal of the test block cover
will thereby prevent inadvertent tripping
of the protection during the ensuing tests.
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