37
Test switch modules for RED 521
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In many cases more than three CT circuits are connected to one RED 521. In these cases
more than one test switch type RTXP 24 shall be used. This imposes some requirements
on the overall circuit design in order to allow secure secondary testing of the bus differ-
ential relay under through-load conditions. Only one test handle can be inserted at a
time, which may cause current unbalance to the RED 521 and possible unwanted oper-
ation. To prevent this, the following two actions can be taken:
1. If external trip relays are used, connect the trip signal from RED 521 in series with
all RTXP 24 test switches. This will insure that the trip signal will be detected regard-
less which test handle is first inserted.
2. If for any reason, solution one is not possible, then the manually operated “Enable/
Disable” selector switch can be included in the bus differential circuit, which in “Dis-
able” position energizes the “BLOCK” input of RED 521. Then testing can be carried
out in the following sequence:
•
Put switch in “Disable” position
•
Insert ALL test handles
•
Open trip paths for all breakers
•
Put switch in “Enable” position
•
Perform secondary tests on RED 521
•
Put switch in “Disable” position
•
Close trip paths for all breakers
•
Withdraw ALL test handles
•
Make sure RED 521 is balanced by reading Id & Iin service values on the front HMI
Put switch in “Enable” position
In order to check that the bus differential relay is not disabled by mistake, wire output
contact “BLOCKED” to RTU or SCADA system in order to monitor RED 521 status.
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If your cubicle application consists of more than one RED 521 and hence needs more
than one test switch, that are required for each terminal, it can be advantageous to mount
four test switches in a 4U 19” rack by using the mounting plate kit instead, than to
mount each one in its own RHGS 6 case. A distance of min. 1C (7mm) is required be-
tween each test switch in order to allow for the opening of the cover locks,
see figure
figure 24
Summary of Contents for 500 Series
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Page 32: ...26 Mounting methods and mounting details KDSWHU 7HUPLQDO GLPHQVLRQV DQG PRXQWLQJ DOWHUQDWLYHV ...
Page 46: ...40 Test switch modules for RED 521 KDSWHU 7HUPLQDOV ZLWK D WHVW VZLWFK PRGXOH ...
Page 72: ...66 Making the electrical connections KDSWHU OHFWULFDO FRQQHFWLRQV ...
