ROOTECH ACCURA 7500 User manual

ACCURA 7500
Integrated Digital Protection Relay
+ High Accuracy Power Meter
Communication User’s Manual[English]
Rev 1.0

Page 2
Notice
Symbols
Caution
Indicates the presence of dangerous voltage which can cause severe injury or
death to persons if proper precautions are not followed.
Warning
Alerts the user of the presence of hazards which can cause some injury to
persons, damage to property or damage to the device
itself, if proper
precautions are not followed.
Note
Indicates instructions for installation, operating and maintenance.
Indicates alternative voltage or current.
Indicates direct voltage or current.
Installation Considerations
The installation and operation of Accura 7500 should be performed only by qualified,
competent personnel that have received appropriate training and experience with high voltage
and current devices.
Caution
Failure to observe the following instructions may result in severe injury or death..
During normal operation, hazardous voltages are present on its terminal strips that
connect the PT(Potential Transformer), CT(Current Transformer), voltage input, power,
and external I/O circuits. The secondary of the PT/CT may generate fatal voltages/currents
resulting from the primary of the PT/CT.
Standard safety precautions should be followed while installing or maintaining the product,
including removing PT fuses and shorting CT secondaries.
Install the product in a switchgear cabinet to prevent users from accessing terminal strips
after completing wiring of the product.

Page 3
Warning
Observe the following instructions, or permanent damage may occur to the product.
Do not apply voltages and currents that exceed input ratings of PT and CT to the product.
Using the device for other purposes not specified by the manufacturer can cause severe
damage to the product.
Connect the ground terminal to the earth ground to protect the device from noise and
surge.
The terminal screw torque to be used has the following features.
- Barrier-type voltage terminal: 1.35Nm (14 kgf∙cm = 1.00 lbf∙ft) max.
- Barrier-type digital inputs/digital output terminal: 0.90Nm (9 kgf∙cm = 0.66 lbf∙ft) max.
About the Manual
Rootech Inc. reserves the right to make changes in the device specifications shown in this
User Guide without notice. Therefore, we recommend that customers should obtain the latest
information on specifications of the device before making orders.
In the absence of written agreements, Rootech Inc. assumes no liability for assistance with
product applications and the system design created by customers or legal issues, including
infringement of intellectual property arising from the use of devices described herein by
third-parties.
We are committed to providing accurate information in this document. However, we assume
no responsibility for any errors in the document and reserves the right to make changes
without notice.
Limitation of Liability
Where applicable law allows and does not prohibit or restrict such limitation, Rootech, Inc’s
liability for anything relating to this product shall be limited to the price paid for the product.

Page 4
Warranty
Rootech Inc. provides warrants for two years from the product receipt date only to the original
purchaser of the products and software that are sold or licensed by the company.
To obtain warranty service, the purchased products should be free from serious defects in
material and workmanship.
The software is provided in up-to-date versions, thus we do not offer any warranty for the
software product.
In order to make a product claim under the warranties described above, the original purchaser
should immediately contact Rootech headquarters. Upon receiving claims, Rootech will check
out the product either at where the purchaser is or at the company after receiving the product
from the customer, who is responsible for the cost of shipping the product. After inspecting
the product, we provide repair or replacement services for the product.
Rootech will decide at its discretion whether to repair or replace it or give a refund for the
product for when the warranty period for the product expired or issues related to the product
are not applicable for warranty terms and conditions.
Limitation of Warranty
The Warranty does not apply to uninterrupted or error-free operation of the product or cover
normal wear and tear of the product or costs caused by the removal, installation, or
troubleshooting of the customer's electrical systems.
Defects caused by any of the following factors are not covered under the warranty.
Improper use(alteration, accident, misuse, abuse) or failure to act in accordance with
installation, operation or maintenance instructions
Unauthorized modifications, changes or repair attempts
Failure to comply with applicable safety standards & regulations
Damages resulting from transporting or storing the product
Damages caused by the force majeure event, including fire, flood, earthquakes, storm
damage, overvoltage & lightning
If the original identification marks(trade-mark, serial number, etc.) have been defaced, altered,
or removed

Page 5
Rootech shall not be liable for any other claims except the claims made by customers, including
the original purchaser, his employees, agents, or contractors for any loss, damage, or expense
incurred related to the purchased product when the above warranty terms and conditions are
not fulfilled.
Any technical assistance provided by Rootech's personnel or representatives in system design
shall be deemed to be a suggestion. The original purchaser is responsible for determining the
feasibility of such suggestions and should conduct tests to prove their feasibility
It is the original purchaser’s responsibility to determine the suitability of any product and
associated documentation. The original purchaser should acknowledge that 100% uptime is
not guaranteed because of possible hardware or software defects. The original purchaser
should also recognize that such defects and failures may cause inaccuracies or malfunctions.
Any agency, corporate entity, or individual employees of Rootech or other companies is not
authorized to amend, modify or extend warranty in any way.

Page 6
Standard Compliance
Process Control Equipment
E324900

Page 7
Revision History
The following versions of the Accura 7500 Communication User Guide has been released.
Revision
Date
Description
Revision 1.0 November 11, 2020 First issue

Page 8
Contents
Chapter 1 Serial Communication..................................................................................................................11
Serial Communication.............................................................................................................................11
Accura 7500 Communication ................................................................................................................12
Chapter 2 Communication Wiring/Setup....................................................................................................14
Communication Wiring ..........................................................................................................................14
Communication Setup ............................................................................................................................15
Setup Mode ........................................................................................................................................................................16
Chapter 3 Modbus RTU Protocol..................................................................................................................18
Packet Field of Modbus RTU ......................................................................................................................................18
Slave Address Field .........................................................................................................................................................18
Function Field.....................................................................................................................................................................18
Data Field.............................................................................................................................................................................18
Error Check Field ..............................................................................................................................................................19
Exception Responses ......................................................................................................................................................19
Broadcast Packets.............................................................................................................................................................20
Packet Communication...........................................................................................................................21
Function 03: Read Holding Registers .....................................................................................................................21
Function 06: Write a Single Register to Meter..................................................................................................22
Function 16: Write Multiple Registers to Meter ...............................................................................................22
Reserved Registers...........................................................................................................................................................23
Invalid Registers ................................................................................................................................................................23
Chapter 4 Modbus RTU Map.........................................................................................................................24
Address Map Sections ............................................................................................................................24
Overview...............................................................................................................................................................................24
System information section.........................................................................................................................................26
Meter Part.................................................................................................................................................27
Configuration section.....................................................................................................................................................27
Measurement section.....................................................................................................................................................27
THD, K Factor......................................................................................................................................................................29
Extra energy section .......................................................................................................................................................29
Demand, Maximum, and Minimum section........................................................................................................30
Extra predicted demand section...............................................................................................................................31
Harmonic section .............................................................................................................................................................32
Vector diagram section†................................................................................................................................................33
Waveform section ............................................................................................................................................................34
Demand trend section ...................................................................................................................................................35
Reset section ......................................................................................................................................................................35

Page 9
Protection Part.........................................................................................................................................36
DIO Status and Control section ................................................................................................................................36
Measurement section†....................................................................................................................................................38
Reset section ......................................................................................................................................................................39
Maintenance section.......................................................................................................................................................39
Event Record section ......................................................................................................................................................40
Captured (Event) Waveform section†......................................................................................................................41
Auxiliary Function 1 Setup section..........................................................................................................................42
Auxiliary Function 2 Setup section..........................................................................................................................43
Digital Input Setup section..........................................................................................................................................44
Digital Output Setup section......................................................................................................................................45
DO-Relay Interconnection section 1.......................................................................................................................46
DI-DO Interconnection section..................................................................................................................................47
DO-Relay Interconnection section 2.......................................................................................................................47
OCR section ........................................................................................................................................................................48
NSOCR section ..................................................................................................................................................................48
OCGR section .....................................................................................................................................................................49
OVR section ........................................................................................................................................................................49
UVR section.........................................................................................................................................................................50
POR section.........................................................................................................................................................................50
NSOVR section ..................................................................................................................................................................51
OVGR section .....................................................................................................................................................................51
SGR section .........................................................................................................................................................................52
MOTOR Protection Section..........................................................................................................................................53
Short-form Data Block Section..................................................................................................................................54
Value Table................................................................................................................................................59
T1 : Date†(UINT32)..........................................................................................................................................................59
T2 : Time†(UINT32) .........................................................................................................................................................59
T3 : Event Type†.................................................................................................................................................................59
T4 : Interlock Function Setup .....................................................................................................................................62
T5 : Motor Operation Status.......................................................................................................................................62
T6 - T8 : Reserved............................................................................................................................................................62
T9 : Relay Function ..........................................................................................................................................................62
T10 : Aux. Relay Setup...................................................................................................................................................62
T11 : Digital Input Setup ..............................................................................................................................................63
T12 : DOUT Relay Type Setup....................................................................................................................................63
T13 : OCR, OCGR Relay Curve Setup .....................................................................................................................63
T14 : Fault, Pickup Status 1 .........................................................................................................................................63
T15 : Captured Waveform Data Scale†(INT16)..................................................................................................64
T16 : Fault, Pickup Status 2 .........................................................................................................................................64
T17 : DIN Input Type Setup ........................................................................................................................................64
Data formats ............................................................................................................................................65

Page 10
Measurement Value Calculation ...........................................................................................................68
Fixed Scale ...........................................................................................................................................................................68
Variable Scale .....................................................................................................................................................................68
APPENDIX A CRC-16 Calculation..................................................................................................................70
CRC-16 Generation..................................................................................................................................70
CRC Generation procedure..........................................................................................................................................70
APPENDIX B Modbus RTU C Code Example...............................................................................................72
Data Reception and CRC Generation & Checking.............................................................................72
Request Packet Generation .........................................................................................................................................72
Checking Response Packets........................................................................................................................................72
CRC functions.....................................................................................................................................................................73

Page 11
Chapter 1 Serial Communication
Serial Communication
Accura 7500 has a RS-485 port supporting multi-drop operations for communication between
Master and Slave devices. In order to communication with host system, Accura 7500 supports
Modbus RTU protocol for general users.
Modbus RTU protocol is used for connection with automation equipment such as PC and PLC, and
as an industrial standard, it allows users to efficiently transfer measurement and setup data between
master[PC, PLC, or etc.] and slave[Accura 7500] devices.
Multi-drop Mode for Communication between Master and Slave Devices
Every communication on the network is based on communications between Master and
Slave systems.
A master device sends and controls all information on the communications loop.
A slave device responds only when there is a request from a master device.
All communications occur in the form of packets, which consist of bytes.
All packets transmitted by the master device are requests. All packets transmitted by the
slave device are responses.
In communication between Master and Slave devices, when the master device sends a
request, only one slave device among connected slaves responds.
Modbus RTU protocol
Standard protocol for general users
It is recommended to use Modbus RTU protocol for communication with Rootech’s products.
It is designed according to the Modbus RTU specifications of Modicon(now Schneider), Inc.
It allows for selective communications by using address maps for measurement data and
setup parameters of relays.
It supports the basic communication driver used for communication with PLC devices or
automation programs as a common industrial protocol.

Page 12
Accura 7500 Communication
The default settings for serial communication of Accura 7500 are 8 data bits, even parity, and 1
stop bit.
RS485 Multi-drop Diagram
Warning
When connecting the communication cable to the terminal port[Ta, Tb], multi-drop connection
should be made. As shown in the above figure, T-branch connections can decrease communication
reliability.
To connect an RS-485 communication line to a PC[supports only the RS-232 port], a RS-485 to RS-
232 converter[RTS/CTS automatic control required] should be used. For communication between a
PC and Accura 7500, the RS-485 Data+(TRX) and Data-(TRX) lines of the converter should be
connected to the Ta and Tb ports on Accura 7500, respectively. The RS-232 port of the converter is
connected to the user PC.
Time Delay for RS-485 Communication
There are time delays between request packets and response packets.

Page 13
Packet Recognition Time
The delivered/received data packet between the PC and Accura 7500 consists of the following
format. One packet consists of multiple, consecutive data frames. If the time interval between frames
is within 5ms, frames are recognized to belong to the same packets. To recognize frames to be the
same, and the time interval between frames is recognized as the same packet for the condition
where the distance between frames is within 5ms. At least 10ms is required for packet recognition. .
Holding Time before Transmitting Request Packet
After receiving data from Accura 7500, the PC[Master] should send a next request packet in at least
10msec[17 msec at 38400bps]. Caution should be taken when Accura 7500 sends the request
packet right after receiving data in case of making a request for high-speed data transfer.

Page 14
Chapter 2 Communication Wiring/Setup
Communication Wiring
Communication Ports on the Relay
Item
Description
Port name Ta[TRX+], Tb[TRX-]
Connector type Screw-type terminal [Pluggable]
Wire specs 1.25 to 3.5 mm2 [24 to 14 AWG], Shielded twisted pair
Communication cable length 1219m[4000ft]
Maximum number of connected
devices per bus
32
Note
It is recommended to use a cable that complies with the UL2919 standard.
Communication LED Indicator
The Comm LED on the front of Accura 7500 blinks yellow when it transmits data.

Page 15
Communication Setup
As shown below, Accura 7500 features the meter and protection relay sections located on the left
and right side from the center line.
Fig 2.1 Screen Composition on the Front
The control method and screen composition of the meter part is same to those of Accura 3300 and
3500. Therefore, communication setup can be performed in the same way as in Accura 3300 and
3500 devices.
The following modes are operated with the buttons on the meter section[Menu, Up, Down, ENTER].
Mode
Description
Display mode Shows all measurement parameters
Setup mode Sets operation parameters [wiring, communication, etc].
Reset mode Resets “Energy, Demand, Maximum and Minimum” values.
System mode Shows system information [Option, Firmware version, etc].
Meter Protection relay

Page 16
Setup Mode
After installing Accura 7500, set the PT/CT ratio, wiring methods, and communication modes that
fit the operational environment of the device .
Button functions in the setup mode
Button
Function
Moves to the setup mode display
Moves to the previous menu.
Moves to the next menu
Moves to the menu edit mode to change the displayed preset values of the
menu Preset value blinks 1
Exits the setup mode and moves to the display mode.
1It indicates status where set values on the menu can be edited.
Button functions in the menu edit mode
Button
Function
Increases the displayed preset values of the menu 1
Decreases the displayed preset values of the menu 2
Saves the changed values of the menu item and returns to the menu in the
setup mode
1When changing the values, if the button is pressed for more than 2 seconds, the cursor moves to the upper
order digit .
2When changing the values, if the button is pressed for more than 2 seconds, the cursor moves to the lower
order digit.
Note
In the menu edit mode, pressing the button allows you to exit the mode and moves to the
display mode without saving the changed value of the menu item.

Page 17
Menu items
Order
Menu item
Range
Default
1 PT ratio 0.1 ~ 999.9 1.0
2 CT ratio 1 ~ 5000 10
3 Connection method 3-Phase 3-Wire
2PT(Open Delta)
3-Phase 3-Wire
3PT(Wye)
3-Phase 4-Wire √
4 Communication
address
1 ~ 247
5 Protocol Modbus RTU √
Rootech 1
6 Baud rate [bps] 1200bps
2400bps
4800bps
9600bps √
19200bps
38400bps 2
7 Parity bit Even parity √
Odd parity
None parity
8 1 ~ 2 1
1Used for manufacturers only.
2At 38400 bps, the PC [Master] should send a request packet for the next data at least 17mse after
receiving a response to data from the relay. Also, in case of writing multiple registers, the length is limited to
less than 13 words.

Page 18
Chapter 3 Modbus RTU Protocol
Detailed specifications for the Modbus RTU supported by Accura 7500 are as follows.
Packet Field of Modbus RTU
Modbus RTU consists of four fields.
Slave Address Field
Function Field
Data Field
Error Check Field
Slave Address Field
The slave address field of a Modbus RTU packet is one byte in length. It is used as an ID to specify
the slave device[Accura 7500] during communication. A valid address ID for the relay ranges from
1 to 247. You should specify a slave address[the relay’s ID] from which you want to receive data
and make a request for the address.
Function Field
The function field of a Modbus RTU packet is one byte in length and tells the slave device what
request has been made by users.
Function[Decimal]
Meaning
Description
03 Read multiple registers Read multiple registers
06 Write a single register Set a single register to a certain value
16 Write multiple registers Set multiple registers to certain values
Data Field
The data field of a Modbus RTU packet has variable length. This field contains the data indicating
the command that users want to request to the slave device in a request packet. In a response
packet, it includes the data sent from Accura 7500 to users.
Each data is two bytes[16 bits] long. “Big Endian”format is used for the byte order.

Page 19
Example]
If 2 Byte data indicates 3A12 hex, the data is transmitted in the following order.
High order byte = 3A hex
Low order byte = 12 hex
Error Check Field
The error check field of a Modbus RTU packet enables you to check transmission errors that may
occur during communication using the CRC-16 algorithm. CRC-16 is two bytes[16 bits] long, and
the byte order features the “Big Endian” format.
The slave device performs the same calculation on the entire packet it received, except for the error
check field. If the calculated result is not equal to the value of the error check field, it indicates that
transmission errors occurred. For more details of the CRC-16 algorithm, refer to the “Appendix A
& B” of this document.
Packet Format
Slave address
Function
Data
Error check
1 byte 1 byte N 2 bytes 2 bytes
Exception Responses
If a master device sends an invalid command to the slave[Accura 7500] or attempts to read an
invalid holding register, an exception response will be generated from Accura 7500. To indicate an
error in the exception response, the high order bit of the function code is set to 1.
The data field of an exception response contains the exception error code.
Exception Response
Slave address
Function
Exception code
Error check
1 byte 1 byte 1 byte 2 bytes
Exception code
Name
Description
01 Illegal Function Invalid command in Request Packet
02 Illegal Address Invalid holding address in Request Packet
03 Illegal Value Sends data invalid in Holding Address

Page 20
Broadcast Packets
A broadcast request packet allows the master device to send the same commands to multiple slave
devices simultaneously. A broadcast request packet is the same as a normal request packet, except
the slave address field is set to zero.
All Slave devices receive and perform broadcast request commands. However, slave devices do not
respond.