GE DBF, Instructions Manual

Page: 34 / 65

5. HARDWARE DESCRIPTION
GEK-106168E DBF Breaker Failure Protection 27
5.2. OPERATING THEORY
The DBF unit measures current signals, performs complex calculations using internal data, stores relevant
incidents, pick-up tripping relays and generates information that can be used to determine the state of the
associated electrical system. The DBF functionality is related to the following modules:
- Magnetic module
- CPU board
- Power supply
- Keyboard and display
5.2.1. MAGNETIC MODULE
The magnetic module performs two essential functions: galvanic insulation and scaling analog input signals. In the
case of current transformers the input current for the primary winding is converted into a scaled voltage in the
secondary winding. Each current transformer must be linear in the whole measurement range of the relay.
5.2.2. CPU BOARD
The DBF uses two 16-bit microprocessors operating at a clock frequency of 20 MHz. One of these
microprocessors is used to perform the relay communications and the other performs the necessary calculations
for protection functions.
In general the microprocessors are responsible to perform the input and output
calculations and operations at very high speed. The use of two microprocessors is especially recommendable to
make the protection and communication functions independent of each other inside the unit itself, and therefore
increase the reliability of the system.
The analogue-digital converter converts the voltage inputs into their digital equivalent with a resolution of 10 bits.
The unit code is stored in non-volatile EPROM memory while the settings and events are stored in EEPROM
memory. The data related to the oscillography is stored in RAM memory which is maintained using a capacitor,
thus avoiding the loss of information when the unit is disconnected.
A high-resolution real time clock is used to ensure that the date and time of all incidents can be time-tagged, with
a resolution of one millisecond. This clock can be synchronized externally using an IRIG-B demodulated signal..
The input and output functions are divided between the two microprocessors. The serial ports, the keyboard and
the display are controlled by the communications microprocessor. External communications are processed by a
serial communications controller circuit which contains a universal asynchronous transceiver (DUART). The digital
inputs and outputs are processed by the protection microprocessor.
The DBF contains 6 independent circuits to process digital inputs. These circuits check the presence or absence
of input voltage and are designed to isolate them electrically from the microprocessor, thus increasing the
reliability of the system.
On the front of the relay there is a set of 17 Target LED’s, one of which is fixed and indicates the operating state of
the unit. The rest are user-configurable using GE_INTRO software.
The button situated on the front is designed to check the state of the Target LED’s and to reset them by keeping it
pressed during 3 seconds.