Circuit Protection; P28 Control Power Protection; P28 System Monitoring - GE Mark VIeS System Manual

10.1.3 Circuit Protection

Circuit protection for the PDM includes:
• Fault current protection limits the current to the capability of the system components.
• Branch circuit system feedback
• Ground fault protection in floating systems
• Redundant applications, if possible
Systems using multiple power applications create the possibility of applying the wrong power to a load or interconnecting
power buses. The PDM use specific connector conventions to eliminate this problem. Refer to the Mark VIeS Functional
Safety Control Systems Power Distribution Modules (PDM) Application Guide for General Market (GEI-100861) for the
specific connectors.

10.1.3.1 P28 Control Power Protection

JPDS and JPDG control power characteristics are as follows:
• The negative side of the JPDS/JPDG is grounded at every I/O pack to functional earth (FE). This grounding aids in the
conduction of transient noise to earth. Similarly, the negative side of the 28 V dc distribution section of the JPDG is
grounded at every I/O pack to FE. It is impossible to float the JPDS/JPDG power supply.
• The supply voltage provided by the approved power sources can be 28 V ±5%.
• The I/O packs are designed with minimal power disturbance ride-through capability.
• Bulk energy storage is provided by the control power supplies.
• Control power cannot be used for tasks such as contact wetting for field inputs. External connections are controlled and
filtered by the terminal board/pack combination.
• JPDS/JPDG support independent control power systems for each controller and associated I/O pack. A redundant control
system maintains a separation of control power ensuring system reliability.

P28 System Monitoring

Incoming power is monitored as follows:
• Incoming power is monitored by every I/O pack. An alarm will signal any incoming power that falls below 28 V – 5%.
The control can continue to operate with depressed voltage in most cases.
• Depressed voltage effects are dependent on the connected field devices. Determining the voltage required for failure can
only be accomplished if the entire system is analyzed.
• A second alarm will be sounded if the control power falls below 16 V. The 16 V alarm can help isolate the source of
failure during further analysis.
• JPDS/JPDG provide voltage monitoring for R, S, and T power buses.
• VMCPS include a dry contact status feedback circuit. This contact will be closed when the power supply is operating
normally and will open if it is not. The YDIA or other contact input I/O pack reads the status signals as a Boolean value.
These values are necessary when multiple supplies are connected in parallel for redundant systems. They provide the
only way to determine when one supply is not functioning correctly.
• JPDS power supplies provide four test points, with current limited by 10 kΩ series resistors, used to connect external test
equipment.
• JPDG power distribution board provides distribution of 28 V dc (control power) and 48/24 V dc (wetting power) to other
boards within the control system. For both control and wetting power, the JPDG supports dual redundant power supply
inputs through external diodes. The JPDG provides fuse protection for all 28 V dc and 24/48 V dc outputs. The voltage at
common 28 V bus is monitored by the JPDG, and it supports feedbacks for eight fuses in the 28 V dc distribution section.
PDM Power Distribution Modules
Public Information
GEH-6855_Vol_II System Guide 303