MTS Hydraulic Power Unit Model 506-92 - Manual (Page 41)

Theory of Operation 5-4
5 . 2 . 1 Control
When the disconnect switch is closed, the HPU control panel Power On
indicator lights to show that electrical power to the HPU is on.
Inlet pressure Pressing Start with Pump 1 Select , Pump 2 Select , or both pumps selected
energizes relay CR5 at PLC output 15 to start the supercharge motor.
Contacts M5 provide the supercharge motor status to PLC input 13. The
supercharge motor provides inlet pressure for pumps 1 and 2. When the
inlet pressure is reached (typically 30 psi), pressure switch 1PS (connected
from the outlet of the supercharge pump to PLC input 20) closes which
allows the PLC to start the pump motor(s).
Supercharge only
operation Pressing Start without Pump 1 Select or Pump 2 Select selected energizes
relay CR5 at PLC output 15 to start the supercharge pump motor. Contacts
M5 provide the supercharge pump motor status to PLC input 13. The
supercharge pump provides inlet pressure for pumps 1 and 2.
Supercharge pump only operation is typically used to hasten hydraulic
fluid cooling after a fluid over-temperature shutdown of the HPU. Refer
to Subsection 2.3 for a fluid cooling procedure using the supercharge
pump.
Start control The start signal is sent to input 2 of the PLC. If various conditions (such as
interlocks) are satisfied, a pump unit start up is initiated. Depending on
which pump is selected, PLC output 0 energizes pump motor 1 start
control relay (CR1) or PLC output 2 energizes pump motor 2 start control
relay (CR3).
Pump motor 1 When CR1 contacts close, pump motor 1 starts, using a Wye-delta start.
First relay S1 energizes to close S1 contacts and energize relay M1 (M1
contacts close). Relays M1 and S1 provide a Wye connection (this reduces
inrush current) to start pump motor 1. After a timing delay that the PLC
provides, PLC output 1 energizes relay CR2. The state of all CR2 contacts
change to de-energize S1 and energize M2. Relays M1 and M2 connect the
motor windings in a delta configuration to provide full current to the
motor. A set of M2 contacts provides the motor 1 status to the PLC at
input 14.
Pump motor 2 If pump motor 2 is selected, PLC output 2 energizes relay CR3. Pump
motor 2 uses a Wye-delta start configuration. Relays M3 and S2 provide
the start connection to the motor. Relays M3 and M4 provide the run
connection. A set of M4 contacts provides the motor 2 status to the PLC at
input 15.
High pressure When the HPU High Pressure switch is pressed with a pump unit
activated, high pressure is enabled by energizing high-pressure solenoid
SOL1 for pump 1, SOL2 for pump 2, and SOL3 for the HPU.