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Overview

Introduction

  • The SA380TX can monitor 1 x Bender type IRDH265 / 365 insulation monitor.
  • In addition to the isometer, volt-free contact outputs from Bender fault-evaluator devices (such as the SMO480) may also be connected the SA380TX general purpose digital inputs.
  • If a 4-20mA output converter such as the RK170 is utilised, this can be connected to the SA380TX general purpose analogue inputs, although RS485 connection is preferred.
  • Other models of Bender isometer may be supported over RS485 - check the Bender documentation to see if the RS485 protocol matches
  • Please be aware that 1 x SA380TX can only monitor 1 x Bender Isometer. This is a limitation of the Bender protocol, not the SA380TX.

Data Available

ParameterUnitsRS4854-20mADigital VFCNotes
Instantaneous Resistance to Earthk Ohm
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This is the last reading of Resistance-to-Earth taken by the isometer
Alert Levelsk Ohm
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The isometer permits two configurable alert thresholds. These levels are both reported
Alarm StatusDigital
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Reports if either alarm level has been breached
Fault Repeat Relay StatusDigital
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Reports if output fault relay has been energised. Essentially mirrors alarm status
Connection ErrorDigital
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Set to UP or TRUE is no RS485 data has been received from the isometer for 7 minutes.
AC, DC+, DC- FaultDigital
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For DC Systems, Indicates which leg is experiencing the worst fault. For AC systems, only the AC flag will be asserted.
Fault Evaluator OutputDigital

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Where a fault evaluator is provided and a single isometer monitors a multiple-feeder arrangement, a digital volt-free-contact output is provided for each feeder. The feeder experiencing the worst fault will have its contact closed.

These parameters can be continuously monitored to perform long-term trend analysis of cable condition, to alert maintainers of faults that require intervention, and to aid diagnosis of the fault type and location.

Wiring

RS485

Configure the network as shown below using twisted pair cable. Note the use of termination resistors at each end of the link. These are only strictly required for very long cable runs exceeding 1 km in length.

Note that if the isometer is built into a Network Rail style cubicle arrangement, the RS485 connection are brought-out at the base of the cubicle through the terminal block positions 18 and 19

If connecting directly to the isometer. Connect straight to terminals B and A.


4-20mA Analogue Interface

Use of the 4-20mA output is not recommended, but the interface could be employed to connect multiple isometer units to a single SA380TX by utilising spare analogue inputs.

Please consult the Bender user guide for exact terminations if connecting directly to the 4-20mA signal conditioner.

Note that if the 4-20mA converter is built into a Network Rail style cubicle arrangement, the connections are brought-out at the base of the cubicle through the terminal block positions 20 (Connect to "24" on the SA380TX) and 21 (Connect to "S" on the SA380TX).

Be aware that the insulation resistance reading will be prone to error due to the unusual equation used by the 4-20mA signal converter:

COMING SOON - THE EQUATION USED BY BENDER

The SA380TX supports quadratic scaling of input vectors, and as such the above equation has to be approximated on an SA380TX using the following quadratic equation:

COMING SOON - THE EQUATION USED BY THE SA380TX

The equations has been formulated to provide a good fit below 150 k Ohm. The error plot is shown below:

COMING SOON - 4-20mA ERROR PLOT

This plot also assumes the RK170 4-20mA output device is correctly calibrated.

The detailed set-up of the 4-20mA is described below

Digtial Volt-Free-Contact Interface

Where a fault repeater exists, up to 12 digital outputs may be provided to indicate which sub-feeder is experiencing the worst insulation resistance. These are wired as per standard digital inputs:

The diagram on the left shows direct connection. Please consult the Bender user guide for exact terminations.

Note that if the isometer is built into a Network Rail style cubicle arrangement, the "common" VFC connection is brought-out at the base of the cubicle through the terminal block position 37. The 12 individual feeder alarm signals are presented on terminal 38 (Feeder 1) through to 49 (Feeder 12). This is shown on the right

Configuration & Commissioning

Initial Setup

RS485

These steps may be completed on the SA380TX touchscreen, or via web-based configuration tool.

1) Set the RS485 "owner" to "Bender". This tells the SA380TX what type of device is attached to the RS485 port

TOUCHSCREEN - CONFIG TOOL

2) Create a "Bender" slave unit. The SA380TX needs to be explicitly told about devices attached to the RS485 port. Remember, only a single isometer may be connected at any one time.

TOUCHSCREEN - CONFIG TOOL

3 ) Check that the "Slave" has been successfully created

The SA380TX will create additional slave channels representing the data obtained over the RS485 interface. The screen grab below shows these channels in the web-based configuration tool. They will also be visible in the real-time displays and historic data logs accessible via the touch-screen,

WEB CONFIG OF CHANNELS

4) Check that the isometer device is active:

To verify that the isometer is sending data over RS485 and that the wiring is correct the following should be observed on the SA380TX toucscreen.

Main Screen:

Bender CONN DN indicates no connection error.

Additional alarm state changes may also be observed, but not if no fault condition exists.

Real Time Digital Screen:

Use the "Next Unit" button to scroll to digital channels received from the isometer.

This screen is a poor indicator of connection status, as the state of the digital channels depends on the fault condition of the cables under test. Bender CONN DN should be clear.

Real Time Analogue Screen:

Press the "Next Channels" button twice to scroll to the analogue channels received from the isometer.

This should show the present alarm levels, as well as the current resistance to earth reading obtained from the isometer. The value of the Bender Insulation channel must match the value displayed on the isometer display exactly.

Trouble Shooting

If no RS485 data is visible:

Be patient. isometers may take up to 2 minutes to complete a single measurement, therefore it may be up to two minutes before data is visible

Check the integrity of the wiring. It could be poorly terminated cable.

Check the polarity of the wiring. It is very easy to get the "A" and "B" the wrong way around

Check for data on the RS485 bus. Ideally use a serial port on a computer to check for traffic. The baud rate is 9,600 bps. You should a string of numbers being transmitted periodically

Check for data on the RS485 bus. Alternatively connect a volt-meter with a rapid response across the A and B links. a brief spike in voltage should be observed when data is present on the bus,  Bear in mind the low update rate, and that the RS485 message only lasts a few milliseconds.

MAIN SCREEN

REALTIME DIGITAL

REALTIME ANALOGUE

4-20 mA

Wire the input circuit as a "loop powered" 4-20mA input as shown below

4-20MA CONNECTION

You will need to apply a polynomial mapping to translate the 4-20mA output into a resistance

Please ensure you enter the values below EXACTLY

This curve fit is designed to minimise error below 150 k Ohm

Digital

Simply Rename the Digital Channels to match the feeder same (e.g UP, DOWN, BRANCH etc)


Setting the Acquisition

This requires connection via laptop

The touchscreen interface is not sophisticated enough to set this up

Alarm Levels

Use a simple acquire on Change:

TOUCHSCREEN - CONFIG TOOL


Digital Channels

Simply select push-to-server for all physical and RS485 channels

Live Insualtion Resistance

Standard acquire-on-change will grab incoming data based on on absolute change.

This is not desirable when taking insulation resistance readings, as an absolute change of 10 k Ohm from 1 M Ohm to 990 k Ohm will happen very frequently, due to wet weather for instance, and not warrant any corrective actions, where a change from 55 k Ohm to 45 k Ohm would cross an alert boundary and warrant immediate corrective action.

Setting a small threshold will cause a large amount of not very useful data to be captured, whereas setting a large threshold would cause low data volumes, but reduce sensitivity to genuine fault conditions.

To counter this, the "relative" acquire on change must be set on the logger. To do this requires the use of the "Rail Event" feature of the SA380TX

CREATE NEW RAIL EVENT

SET START TRIGGER
SET ACQUISITION

SET END TRIGGER

Set the config



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