GE KVGC 202, Technical Manual

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Technical Manual KVCG202/EN M/H11
KVGC202
7. CONTROL FUNCTIONS AND SERIAL COMMUNICATIONS
7.1 Courier language protocol
Serial communications are supported over K-Bus, a multi-drop network that readily
interfaces to IEC 60870-5 FT1.2 Standards. The language and protocol used for
communication is Courier. It has been especially developed to enable generic master
station programs to access many different types of relay without the continual need to
modify the master station program for each relay type. The relays form a distributed data
base and the Master Station polls the slave relays for any information required.
This includes:
- Measured values
- Menu text
-
Settings and setting limits
-
Event records
- Plant status
Software is available to support both on-line and off-line setting changes to be made and
the automatic extraction and storage of event records as described in Chapter 6.3.
Courier is designed to operate using a polled system, which prevents a slave device from
communicating directly to a master control unit when it needs to inform it that something
has happened; it must wait until the master control unit requests the information. A
feature of Courier is that each piece of information is packeted by preceding it with a ‘data
type and length’ code. By knowing the format of the data the receiving device can
interpret it.
The Courier Communication Manual describes various aspects of this language and
other communication information necessary to interface these devices to other
equipment. It gives details on the hardware and software interfaces as well as guidelines
on how additional devices should implement the Courier language so as to be consistent
with all other devices.
7.2 K-Bus
K-Bus a communication system developed to connect remote slave devices to a central
master control unit, thus allowing remote control and monitoring functions to be
performed using an appropriate communication language. It is not designed to allow
direct communication between slave devices, but merely between a master control unit
and several slave devices. The main features of K-Bus are: cost effectiveness, high
security, ease of installation and ease of use.
The KVGC202 voltage regulating relay has a serial communication port configured to K-
Bus Standards. K-Bus is a communication interface and protocol designed to meet the
requirements of communication with protective relays and transducers within the power
system substation environment. It has the same reliability as the protective relays
themselves and does not result in their performance being degraded in any way. Error
checking and noise rejection have been of major importance in its design.
7.2.1 K-Bus transmission layer
The communication port is based on RS485 voltage transmission and reception levels
with galvanic isolation provided by a transformer. A polled protocol is used and no relay
unit is allowed to transmit unless it receives a valid message, without any detected error
and addressed to it. Transmission is synchronous over a pair of screened wires and the
data is FM0 coded with the clock signal to remove any dc component so that the signal
will pass through transformers.
With the exception of the Master Units, each node in the network is passive and any
failed unit on the system will not interfere with communication to the other units.
The frame format is HDLC and the data rate is 64kbits/s.