T&R PCU2 mk5, Operating And Maintenance Manual

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1.2.6 Loading unit over temperature trip
An over-temperature trip is fitted on the transformer in the loading unit. If an over-temperature
condition occurs, the control unit output will be switched off and the output will be disabled
until the unit has cooled. While the output is disabled, both the red ON pushbutton and the
green OFF pushbutton will be extinguished. When the unit has cooled sufficiently to continue,
the green OFF pushbutton will light.
1.2.7 Timing System
Contact open circuit voltage 24Vdc
Contact short circuit current 100mA
The PCU2 is fitted with an integrated timing system which is linked to the main output and two
sets of contact inputs. The system is highly flexible, and allows for the timing of all common
protection devices and trips. The timer may also be used to time external events not linked to
the output of the set.
Full details of operating the timer are given in section 2.
Timer mode Range Resolution Accuracy
Internal start 0-999.999s 1ms 0.01% rdg 2d
Single contact 0-999.999s 1ms
0.01% rdg 2d
Dual contact 0-999.999s 1ms
0.01% rdg 2d
Current operated 0-999.999s 1ms
0.01% rdg 3d
NOTE: In current operated mode timing results obtained with test currents below 20% of the selected
ammeter range, and on measured times of 19ms and below, are of doubtful accuracy.
The PCU2 has two contact inputs which are used to start and stop the timer depending on the
mode selected. Contact set 1 has a connection for volt-free contacts and for triggering by a
DC voltage, and contact set 2 has a connection for volt-free inputs. In each case, the input
auto-selects for normally open or normally closed contacts. The contact state is shown by an
LED that is off when the contact is closed and on when the contact is open.
The maximum open circuit voltage across the contact input is 24V, and the short circuit current
through the contacts is limited to 100mA.
1.3 Construction
The PCU2 MK5 control unit is housed in a robust steel case with castors for mobility. The
front panel is protected by a steel cover which is fixed to the main case with catches. The unit
is also fitted with steel handles at each end of the main chassis.
The external loading unit is housed in a steel case which is similar in construction to the PCU2
control unit. The loading unit is not fitted with a protective cover.
1.4 Installation
The PCU2 and associated loading units are designed for use in an indoor environment.