GE D30 Instruction Manual page 65

CHAPTER 3: INSTALLATION WIRING
3.3.6.1 Contact inputs
A dry contact has one side connected to terminal B3b. This is the positive 48 V DC voltage rail supplied by the power supply
module. The other side of the dry contact is connected to the required contact input terminal. Each contact input group
has its own common (negative) terminal that must be connected to the DC negative terminal (B3a) of the power supply
module. When a dry contact closes, a current of 1 to 3 mA flows through the associated circuit.
A wet contact has one side connected to the positive terminal of an external DC power supply. The other side of this
contact is connected to the required contact input terminal. If a wet contact is used, then the negative side of the external
source must be connected to the relay common (negative) terminal of each contact group. The maximum external source
voltage for this arrangement is 300 V DC.
The voltage threshold at which each group of four contact inputs detects a closed contact input is programmable as
17 V DC for 24 V sources, 33 V DC for 48 V sources, 84 V DC for 110 to 125 V sources, and 166 V DC for 250 V sources.
Figure 3-16: Dry and wet contact input connections
3
Where a tilde "~" symbol appears, substitute the slot position of the module.
NOTE
There is no provision in the relay to detect a DC ground fault on 48 V DC control power external output. We recommend
using an external DC supply.
3.3.6.2 Use of contact inputs with auto-burnishing
The contact inputs sense a change of the state of the external device contact based on the measured current. When
external devices are located in a harsh industrial environment (either outdoor or indoor), their contacts can be exposed to
various types of contamination. Normally, there is a thin film of insulating sulfidation, oxidation, or contaminates on the
surface of the contacts, sometimes making it difficult or impossible to detect a change of the state. This film must be
removed to establish circuit continuity — an impulse of higher than normal current can accomplish this.
The contact inputs with auto-burnish create a high current impulse when the threshold is reached to burn off this oxidation
layer as a maintenance to the contacts. Afterwards the contact input current is reduced to a steady-state current. The
impulse has a five-second delay after a contact input changes state.
D30 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL 3-19