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

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.

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.

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

Digital 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:

Channel Configuration & Commissioning

Initial Setup

RS485 Setup

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

Menu→Configuration→RS485

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.

Menu→Configuration→TX Slaves

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,

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.

4-20mA Setup

You will need to apply a polynomial mapping to translate the 4-20mA output from the Bender RK170 into a readable resistance.

It is strongly recommended that this is done on the web-based configuration tool.

This settings box is accessed by double clicking here:

COMING SOON - HOW TO OPEN THE SENSOR SCALING BOX

Please ensure you enter the values shown below exactly, although you may change the Name field of the channel to suit.

COMING SOON - CRAZY BENDER CHANNEL SETTINGS

After applying the setting to the SA380TX, Check that the value real-time analogue display approximately matches that shown on the isometer device.

COMING SOON - REAL-TIME ANALOGUE DATA

Digital Setup

You will need to name any digital channels that derive from the fault evaluator unit.

Simply click on the "name" field in the web-based configuration tool to rename the digital channels such that they match the feeder name (e.g UP, DOWN, BRANCH etc)

Acquiring and Transmitting Data

Analogue Alarm Levels

Use a simple absolute acquire on Change. Double-Click on each of the Bender ALARM1 and Bender ALARM2 channels in turn and enter the setting shown below:

All Digital Channels

Simply select push-to-server for all physical and RS485 channels. This is achieved by ensuring the "Push to Server" tick-box is checked for digital channels you which to send to Centrix, as shown below

Live Insulation Resistance (4-20 mA or RS485)

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. Whereas a change from 55 k Ohm to 45 k Ohm would cross an alert boundary and warrant immediate corrective action.

Setting a small acquisition 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 method must be set on the logger. To do this requires the use of the "Rail Event" feature of the SA380TX.

1) Open the "Rail Events" Tab - This is where we can create all sorts of clever acquisition rules.

2) Create a new "Rail Event" - This sets up a new set of acquisition rules. It is OK for your Rail Event to errors at this stage.

3) Create the "Start Trigger" - We want to acquire data when the SA380TX boots up, and then whenever there is a significant change in insulation resistance. Whenever there is a +/-5% change in insulation resistance, a new acquisition is started. It is OK for your Rail Event to errors at this stage.

4) Tell the SA380TX what to Acquire - We want to keep acquiring insulation resistance values so long as they continue change. Every time the insulation resistance changes by another 5% of its prior value, we grab another sample. It is OK for your Rail Event to errors at this stage.

5) Set the end conditions - We don't need an "end trigger" we keep on acquiring samples so long as they continue to change. At some point though we want to barrel these samples up and send them to Centrix. This is why we put a time-out period of 1 minute in place.

After 1 minute acquisition will end, and all samples acquired since the start trigger event will be sent to Centrix. Don't worry though, next time Insulation resistance changes by 5%, a brand-new acquisition will be triggered and the whole process repeats.

Your Rail Event should now have no errors.