DSP-OHMNI Instruction Manual I-GARD
3
1
INTRODUCTION
High-Resistance-Grounding is becoming more prevalent in industrial and commercial electrical power
systems. As the need for reliable and stable power increases the inconvenience of unwanted downtime
in processing, robotics and data service also become more critical and costly.
Single Ground Faults in motors and equipment are common and will cause interruption of service
in Solidly Grounded systems. HRG prevents this event from happening by limiting the fault current to
a sustainable level for an indefinite time.
The DSP system is designed to detect the event of a single fault and signal an alarm condition and point
to the affected branch or feeder. Thus maintenance can be immediately alerted to the problem and an
operator dispatched to locate the fault to isolate it promptly. The DSP system can assist in locating the
fault with a pulsing fault location circuit that modulates the current in the fault. This allows the operator to
identify which branch circuit is carrying fault current using a portable clamp-on current probe connected
to an ordinary Multi-meter.
The DSP system consists of a number of modules that are mounted on a 35mm DIN rail typically located in
a control compartment of switchgear. The modules are connected together through
20-conductor
standard ribbon cable. A panel-mounted Display module provides a human interface to
the system
and communications to a RS-485 network allows set-up and control.
There are four DSP modules as follows:
DSP-DM Display Module
DSP-DPS Power Supply
DSP-DSM System Module
DSP-DFM Feeder Module
The Display Module is a panel
-
mounted enclosure designed for flush mounting in a door. It is connected by
a ribbon cable to the Power Supply unit. The DSP-DM indicates faulted phase, total
system leakage current, feeder branch current level and provides other information such as priority
settings and Resistor setting etc. It is used to set-up the system and provide manual control of the
pulse location system.
The POWER Supply unit DSP-DPS is a DIN rai
l-
mounted modular unit constructed with an ABS enclosure
and pr5V, +12V and -12V regulated supplies to all of the modules through the front ribbon cables. It
is capable of operation with a wide range of voltage supplies from 100V to 240V ac without selection of any
jumpers or switches. DC voltage can also be used from 125V to 250V DC.
The System Module monitors the system line-to-ground voltages through a standard I-Gard Corp. DDR2
voltage dividing resistor unit. It determines if there is voltage unbalance in the system and the level
of ground fault current in the grounding resistor, without any connection to the Resistor.